JP4728755B2 - Method for forming conductive joint - Google Patents

Description

  The present invention relates to a method for forming a conductive bond, and more particularly, to a method for forming a conductive bond via a conductive bonding layer composed of metal nanoparticles when two metal layers are surface bonded.

  As a conductive adhesive using metal nanoparticles, a conductive metal paste using an organic binder component, which uses metal nanoparticles as a conductive medium has been proposed. On the metal surface of the metal nanoparticle, the movement of metal atoms occurs even near room temperature. Therefore, when this feature is utilized, it is possible to cause fusion of the nanoparticles at the contact point by bringing the metal surfaces of the metal nanoparticles into contact with each other.

  When blending metal nanoparticles in a conductive adhesive, a technique of coating the surface of metal nanoparticles with coating molecules is used to prevent aggregation due to fusion between metal nanoparticles. Moreover, this coating agent molecule has a function of improving the dispersibility of the metal nanoparticles themselves. In addition, after heating the metal nanoparticles in the conductive adhesive, removing the coating molecules covering the surface and exposing the active metal surface of the metal nanoparticles, It can be used to form a conductive layer. Specifically, in the form in which the organic binder component is used for adhesion, a thermosetting resin or a thermoplastic resin is blended as the organic binder component, and in parallel with the heat treatment, the coating agent molecule is thermally removed. It has been removed (see Patent Document 1). Thereafter, the metal nanoparticles are fused together to form a sintered conductive layer, and at the same time, the sintered conductive layer is bonded to the two metal layers using the adhesive force of the organic binder component. Are in close contact.

In addition, by coating the surface of the metal nanoparticles with coating agent molecules and using a dispersion liquid dispersed in an organic solvent, a sintered body layer composed of the metal nanoparticles is formed on the surface of the metal layer. A technique has also been proposed (see Patent Document 2). In this method, in order to accelerate the removal of the coating molecule, a compound capable of reacting with the coating molecule in a heated state is added to the dispersion and subjected to a heat treatment to quickly remove the coating molecule. It is carried out. Since the sintered body layer comprised of the metal nanoparticles to be produced does not contain an organic binder component, it is possible to apply solder bonding, and it can be used as an alternative to a plating film.
International Publication No. 2002/35554 Pamphlet JP 2002-334618 A

  As a conductive medium to be blended in a conductive metal paste using an organic binder component, a conductive adhesive using metal nanoparticles is more conductive than a conventional conductive adhesive using metal powder. Performance has improved significantly. However, since the adhesion with the metal layer to be joined uses the adhesive force of the organic binder component, the overall coefficient of thermal expansion has a large difference. Moreover, the subject that the adhesive force of an organic binder component falls under low temperature conditions is inherent.

  In addition, the conductive bonding method in which solder bonding is applied using a sintered body layer composed of metal nanoparticles that can substitute for a plating film is a useful technique in which the application target is greatly expanded. However, the problem that solder bonding has, for example, the solder alloy itself is susceptible to oxidation, and when the oxide film is formed at the bonding interface, the point of causing peeling at that portion is not essentially overcome.

  In the wire bonding process used in the assembly of many semiconductor devices, a metal-to-metal bonding is used for bonding between a bonding wire and a bonding pad. In other words, a welding technique is used in which metal surfaces are brought into contact with each other, pressed and heated, thereby causing interdiffusion and rearrangement of metal atoms at the metal interface to form an intermetallic bond. Has been. In this welding method, if the metal surfaces to be joined are clean, the interface is integrated with the interdiffusion and rearrangement of metal atoms, so that the interface substantially disappears. In addition, strong bonding can be achieved.

  Also in the die bonding process, it is desired to form a conductive bond between metal layers by applying a technique of welding.

  The present invention solves the above-mentioned problems, and the object of the present invention is to provide two metals via a conductive bonding layer composed of metal nanoparticles when conducting conductive bonding between metal layers. Conductivity that can be achieved by metal-to-metal bonding formed by applying a welding technique when the metal surfaces of the metal layers and the conductive bonding layer are bonded together by conductive bonding of the surfaces of the layers. It is to provide a method for forming a sexual bond.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive research and obtained the following knowledge. When a dispersion liquid in which metal nanoparticles are dispersed in an organic solvent is applied to the metal film surface of the metal layer, the organic solvent is evaporated, a drying treatment is performed, and a high-frequency plasma treatment is performed at a heating temperature of 150 ° C. or less. The inventors have found that a sintered body type conductive layer made of metal nanoparticles is formed. It was also found that this sintered body type conductive layer was fixed to the metal film surface of the metal layer by forming a dense intermetallic bond. In addition, the sintered body type conductive layer On the upper surface, the metal nanoparticles are exposed so as to form a substantially flat surface. When the metal film surface of the other metal layer is superimposed on the upper surface and heated while applying pressure and pressing between the metal nanoparticles exposed on the upper surface and the metal film surface of the other metal layer, It was found that an intermetallic bond was formed. In order to use metal nanoparticles, a welding process for forming an intermetallic bond by interdiffusion and rearrangement of metal atoms by applying pressure to the contact interface and applying heat is less than 200 ° C. It can be carried out at a low heating temperature. Based on these findings, the present inventors have completed the present invention.

That is, the first aspect of the method for forming a conductive bond according to the first aspect of the present invention is:
A method for conductively bonding the surfaces of two metal layers,
The conductive bonding is one in which the surfaces of two metal layers are bonded to each other through a conductive bonding layer composed of metal nanoparticles.
The process of forming the conductive bond is as follows:
Using a metal nanoparticle dispersion liquid in which metal nanoparticles having a coating agent molecular layer on the surface of the nanoparticles are dispersed in an organic solvent on the metal surface constituting one metal layer, the metal nanoparticles are used. Forming a coating layer of the dispersion;
A step of evaporating an organic solvent contained in the coating layer of the metal nanoparticle dispersion to form a dried coating layer;
A coating molecular layer provided on the surface of the nanoparticle is obtained by treating the dried coating layer formed on the metal surface constituting one metal layer at a heating temperature of 150 ° C. or less in a high-frequency plasma atmosphere. Removing and then fusing the metal nanoparticles together to form a conductive bonding layer composed of the metal nanoparticles on the metal surface constituting one metal layer;
The surface of the conductive bonding layer composed of the metal nanoparticles is overlapped with the surface of the metal constituting the other metal layer, and the pressure is applied to press the surfaces of each other while maintaining the temperature within a range of 100 ° C to 200 ° C. Forming a metal-to-metal bond between the surface of the conductive bonding layer and the metal surface constituting the other metal layer at a selected temperature by performing a heat treatment;
Metal nanoparticles having a coating molecular layer on the surface of the nanoparticles,
For metal nanoparticles with an average particle size selected in the range of 1-100 nm,
The group capable of coordinative bonding with the metal element contained in the metal nanoparticle includes a nitrogen, oxygen, or sulfur atom, and has a group capable of coordinative bonding by a lone electron pair possessed by these atoms. It is a method for forming a conductive bond, characterized in that it is nanoparticles formed by coating one or more organic compounds as coating molecules on the surface of the metal nanoparticles.

In the first aspect of the method for forming a conductive bond according to the first aspect of the present invention,
The metal species constituting the metal nanoparticles are preferably a metal selected from the group consisting of gold, silver, copper, platinum, palladium, and nickel.

In the step of performing the treatment at a heating temperature of 150 ° C. or less in the high-frequency plasma atmosphere,
The high-frequency plasma atmosphere is preferably a plasma atmosphere generated using an inert gas. In that case, argon, helium, or a mixture thereof can be used as the inert gas.

The second aspect of the method for forming a conductive bond according to the first aspect of the present invention is:
A method for conductively bonding the surfaces of two metal layers,
The conductive bonding is one in which the surfaces of two metal layers are bonded to each other through a conductive bonding layer composed of metal nanoparticles.
The process of forming the conductive bond is as follows:
Using a metal oxide nanoparticle dispersion liquid in which metal oxide nanoparticles having a coating agent molecular layer on the surface of the nanoparticle are dispersed in an organic solvent on the metal surface constituting one metal layer, Forming a coating layer of the metal oxide nanoparticle dispersion;
A step of evaporating an organic solvent contained in the coating layer of the metal oxide nanoparticle dispersion to form a dried coating layer;
The dried coating layer formed on the metal surface constituting one metal layer is treated at a heating temperature of 150 ° C. or less in a high-frequency plasma atmosphere in the presence of a reducing gas, and the surface of the nanoparticle And the metal oxide nanoparticles are reduced to produce metal nanoparticles, and then the metal nanoparticles are fused together to form the metal nanoparticles. Forming a conductive bonding layer on a metal surface constituting one metal layer;
The surface of the conductive bonding layer composed of the metal nanoparticles is overlapped with the surface of the metal constituting the other metal layer, and the pressure is applied to press the surfaces of each other while maintaining the temperature within a range of 100 ° C to 200 ° C. Forming a metal-to-metal bond between the surface of the conductive bonding layer and the metal surface constituting the other metal layer at a selected temperature by performing a heat treatment;
Metal oxide nanoparticles having a coating molecular layer on the surface of the nanoparticles,
For metal oxide nanoparticles with an average particle size selected in the range of 1-100 nm,
A group capable of coordinative bonding with a metal element contained in the metal oxide nanoparticles includes a nitrogen, oxygen, or sulfur atom, and a group capable of coordinative bonding by a lone pair of electrons of these atoms It is a nanoparticle formed by coating the surface of the metal oxide nanoparticles with one or more organic compounds having a coating agent molecule.

In the second aspect of the method for forming a conductive bond according to the first aspect of the present invention,
The metal oxide constituting the metal oxide nanoparticles is preferably a metal oxide selected from the group consisting of silver, copper, and nickel.

In the step of performing the treatment at a heating temperature of 150 ° C. or lower in the high-frequency plasma atmosphere in the presence of a reducing gas,
The high-frequency plasma atmosphere is preferably a plasma atmosphere generated using a mixed gas of a reducing gas and an inert gas. that time,
In the mixed gas of reducing gas and inert gas,
Argon, helium or a mixture thereof can be used as the inert gas, and hydrogen, ammonia or a mixture thereof can be used as the reducing gas.

Furthermore, the 1st aspect of the formation method of the electroconductive joining concerning the 2nd form of the present invention,
A method for conductively bonding the surfaces of two metal layers,
The conductive bonding is one in which the surfaces of two metal layers are bonded to each other through a conductive bonding layer composed of metal nanoparticles.
The process of forming the conductive bond is as follows:
Using a metal nanoparticle dispersion liquid in which metal nanoparticles each having a coating molecule layer on the surface of the nanoparticles are dispersed in an organic solvent on the metal surfaces constituting the two metal layers. Forming a coating layer of the nanoparticle dispersion;
A step of evaporating an organic solvent contained in the coating layer of the metal nanoparticle dispersion to form a dried coating layer;
A coating agent provided on the surface of the nanoparticles by treating the dried coating layers formed on the metal surfaces constituting the two metal layers at a heating temperature of 150 ° C. or less in a high-frequency plasma atmosphere, respectively. Removing the molecular layer and then performing fusion bonding between the metal nanoparticles to form a conductive bonding layer composed of the metal nanoparticles on the metal surface constituting each metal layer;
Heat treatment is performed at a temperature selected from the range of 100 ° C. to 200 ° C. while superimposing the surfaces of the conductive bonding layer composed of the metal nanoparticles on each other, applying pressure, and pressing the surfaces of both together. Applying and forming an intermetallic bond between the surfaces of the two conductive bonding layers,
Metal nanoparticles having a coating molecular layer on the surface of the nanoparticles,
For metal nanoparticles with an average particle size selected in the range of 1-100 nm,
The group capable of coordinative bonding with the metal element contained in the metal nanoparticle includes a nitrogen, oxygen, or sulfur atom, and has a group capable of coordinative bonding by a lone electron pair possessed by these atoms. It is a method for forming a conductive bond, characterized in that it is nanoparticles formed by coating one or more organic compounds as coating molecules on the surface of the metal nanoparticles.

The second aspect of the method for forming a conductive bond according to the second aspect of the present invention is:
A method for conductively bonding the surfaces of two metal layers,
The conductive bonding is one in which the surfaces of two metal layers are bonded to each other through a conductive bonding layer composed of metal nanoparticles.
The process of forming the conductive bond is as follows:
Using a metal oxide nanoparticle dispersion liquid in which metal oxide nanoparticles each having a coating molecule layer on the surface of the nanoparticles are dispersed in an organic solvent on the surfaces of the two metal layers. And forming a coating layer of the metal oxide nanoparticle dispersion liquid;
A step of evaporating an organic solvent contained in the coating layer of the metal oxide nanoparticle dispersion to form a dried coating layer;
The dried coating layers formed on the metal surfaces constituting the two metal layers are each subjected to treatment at a heating temperature of 150 ° C. or less in a high-frequency plasma atmosphere in the presence of a reducing gas, and The coating material molecular layer provided on the surface of the particles is removed, and the metal oxide nanoparticles are reduced to produce metal nanoparticles, and then the metal nanoparticles are fused together to form the metal nanoparticles. Forming a conductive bonding layer comprising: a metal surface constituting each metal layer;
Heat treatment is performed at a temperature selected from the range of 100 ° C. to 200 ° C. while superimposing the surfaces of the conductive bonding layer composed of the metal nanoparticles on each other, applying pressure, and pressing the surfaces of both together. Applying and forming an intermetallic bond between the surfaces of the two conductive bonding layers,
Metal oxide nanoparticles having a coating molecular layer on the surface of the nanoparticles,
For metal oxide nanoparticles with an average particle size selected in the range of 1-100 nm,
The group capable of coordinative bonding with the metal element contained in the metal nanoparticle includes a nitrogen, oxygen, or sulfur atom, and has a group capable of coordinative bonding by a lone electron pair possessed by these atoms. It is a method for forming a conductive bond, characterized in that it is nanoparticles formed by coating one or more organic compounds as coating molecules on the surface of the metal nanoparticles.

The method for forming a conductive bond according to the present invention described above is as follows.
The two metal layers are
The present invention can be suitably used in the case of a combination of a metal wiring layer formed on the surface of the wiring board and a metal electrode layer of an electronic component bonded on the metal wiring layer of the wiring board.

  That is, the method for forming a conductive bond according to the present invention can be suitably used for a process of fixing an electronic component on a wiring board by conductive bonding.

  Using the method for forming a conductive bond according to the present invention, conventionally, using a conductive adhesive containing a binder resin component, instead of the step of conductively bonding the surfaces of two metal layers, essentially, Without using the binder resin component, the surfaces of the two metal layers can be conductively bonded to each other by metal-to-metal bonding through the conductive bonding layer composed of metal nanoparticles. In particular, when forming this conductive bond, in the process of producing a conductive bonding layer composed of metal nanoparticles, as a means to remove the coating molecule layer covering the surface of the metal nanoparticles in advance In this case, a welding process for forming a conductive bond through a conductive bonding layer composed of metal nanoparticles is performed at a low heating temperature of less than 200 ° C. It is possible to implement. In addition, high-frequency plasma treatment is performed on metal nanoparticles (metal oxide nanoparticles) having a surface oxide film in the presence of a reducing gas to reduce the surface oxide film and restore the metal nanoparticles. In addition, it is possible to form a conductive bond through a conductive bonding layer composed of such metal nanoparticles.

  Hereinafter, the present invention will be described in more detail.

  In the method for forming a conductive bond of the present invention, the conductive bonding layer is formed using metal nanoparticles. In the conductive bonding layer, the metal nanoparticles are fused to each other to form a sintered-type conductor layer by low-temperature heating. On the other hand, at the bonding interface with the metal layer to be bonded by the conductive bonding layer, metal nanoparticles exposed on the surface of the sintered conductive bonding layer are forged against the metal surface constituting the metal layer. (Welding), the metal-to-metal bonding is made. Accordingly, the surfaces of the two metal layers can be conductively bonded to each other by metal-to-metal bonding through the conductive bonding layer composed of metal nanoparticles. Specifically, when metal nanoparticles are fused together to form a sintered-type conductor layer by low-temperature heating, the coating molecules covering the surface of the metal nanoparticles are preliminarily subjected to plasma treatment. Has been removed. Therefore, as a result of the metal nanoparticles laminated contacting the metal surfaces with each other, the movement of metal atoms on the surface of the metal nanoparticles proceeds even at a low temperature, so that mutual fusion is performed quickly. At that time, in the metal nanoparticles in contact with the surface of the metal layer, metal atoms moving on the surface of the nanoparticle are gradually accumulated in narrow gaps existing at the contact sites with the surface of the metal layer. That is, between the surface of the metal layer and the surface of the metal nanoparticle, the metal atoms constituting the metal nanoparticle are closely embedded in the narrow gap, and the contact area of the contact site is greatly expanded. In order to promote the formation of this metal-to-metal bond, by applying a uniform pressure to the contact surface between the sintered-type conductive bonding layer and the metal layer, the metal nanoparticles that adhere to the surface of the metal layer The surface density is increased. By heating in this state, the movement of the metal atoms on the surface of the metal nanoparticles is promoted, and as a result, the total area of the bonding site between the surface of the metal layer and the metal nanoparticles can be increased.

  On the other hand, when using a metal oxide nanoparticle dispersion instead of a metal nanoparticle dispersion, the metal oxide nanoparticle dispersion is once applied to the surface of the metal layer, and then applied to the coating layer. A dried treatment is performed to form a dried metal oxide nanoparticle coating layer. Next, the metal oxide nanoparticles used are metal nanoparticles having a surface oxide film, and the surface thereof is coated with coating agent molecules in the same manner as the metal nanoparticles. By applying high-frequency plasma treatment to the dried metal oxide nanoparticle coating layer in the presence of a reducing gas, first, the release of coating molecules covering the surface of the metal oxide nanoparticles proceeds, The surface oxide film is exposed. Next, when the high-frequency plasma treatment is continued, the reduction of the surface oxide film proceeds using the coexisting reducing gas, and the outermost surface is covered with metal atoms. In that state, using the energy supplied from the high-frequency plasma, an exchange reaction of oxygen atoms proceeds between the metal oxide layer remaining inside and the metal atomic layer generated on the outermost surface, Metal atoms accumulate in the inner core portion, and the outermost surface is again covered with the metal oxide layer. The metal oxide layer regenerated on the outermost surface undergoes a reduction reaction due to the coexisting reducing gas during the high-frequency plasma treatment. As a result of repeating this reduction reaction and the exchange reaction between the metal atomic layer and the metal oxide layer, finally, the surface oxide film layer existing on the surface portion from the metal nanoparticles having the surface oxide film. Are all reduced and restored to metal nanoparticles.

  After the metal nanoparticles with surface oxide film are restored to metal nanoparticles, the mechanism is exactly the same as the formation process of the sintered conductor layer by low-temperature heating in the stacked metal nanoparticles. Through this, a conductive bonding layer composed of metal nanoparticles is generated. Once the conductive bonding layer composed of the metal nanoparticles is generated, the metal nanoparticles exposed to the surface of the sintered conductive bonding layer are then exposed to the metal surface constituting the metal layer. By being forged, metal-to-metal bonding is made. This latter process is essentially the same when using a dispersion of metal nanoparticles and when using a dispersion of metal oxide nanoparticles.

  In the conductive bonding forming method of the present invention, in the conductive bonding layer, the metal nanoparticles are fused to each other in the process of performing the high-frequency plasma treatment, and a sintered-type conductive layer is formed by low-temperature heating. There is a need. Therefore, the average particle diameter of the metal nanoparticles used is selected at least in the range of 1 to 100 nm. Preferably, the average particle size of the metal nanoparticles used is selected in the range of 1-20 nm.

  In the process of performing high-frequency plasma treatment, the coating molecules that coat the surface of the metal nanoparticles are supplied with the excitation energy of the charged particles from the charged particles (ionic species) present in the plasma, Excited by the intramolecular vibration. This vibrational excitation promotes the detachment of the coating molecule forming a coordinate bond with the metal atom, similarly to the vibrational excitation due to thermal energy. In addition, when the high frequency plasma treatment is performed, since it is usually in a reduced pressure state, once this coating agent molecule is detached from the metal surface, it is exhausted out of the system again without being bound to the metal surface. Since it is in a reduced pressure state, the detached coating agent molecules can move out of the metal nanoparticle coating layer through a narrow gap even inside the dried metal nanoparticle coating layer. Yes. Accordingly, the metal nanoparticles existing inside the dried metal nanoparticle coating layer, for example, at the interface with the metal layer, are also released from the coating molecules that have covered the surface, and the metal nanoparticles are in contact with each other. The surfaces are in direct contact with each other, and the fusion of the metal nanoparticles proceeds. The metal nanoparticles in contact with the surface of the metal layer are brought into a state in which the metal nanoparticles are fused to the surface of the metal film by contacting the metal surface with the surface of the metal film of the metal layer.

  In addition, when the metal layer surface is covered with the oxide film layer, the contact between the metal surface of the metal nanoparticles and the metal film surface of the metal layer is not achieved. When the surface of the metal layer is covered with the oxide film layer, it is necessary to simultaneously reduce the oxide film layer on the surface of the metal layer by coexisting a reducing gas in the process of performing the high-frequency plasma treatment.

  In addition, when performing high-frequency plasma treatment, the temperature of the plasma itself has risen to some extent, and the fusion of the metal nanoparticles from which the surface coating molecules are desorbed, and the metal nanoparticles on the metal film surface of the metal layer Fusion is also accelerated by this temperature rise. At the time of this high-frequency plasma treatment, the temperature rises at the point of contact between the metal nanoparticles present at the interface between the dried metal nanoparticle coating layer and the metal layer and the metal film surface of the metal layer. The metal atoms that move on the surface of the metal nanoparticles gather. Due to the contribution of the metal atoms gathered at the contact point, a bonding site having a certain contact area is formed. Of course, the laminated metal nanoparticles that make up the dried metal nanoparticle coating layer are fused together at the contact point to form a network-like sintered conductive conductive bonding layer. The sintered body type conductive bonding layer is fixed to the surface of the metal film of the metal layer.

  At that time, on the lower surface side of the sintered-type conductive bonding layer, at the stage of applying a dispersion of metal nanoparticles on the metal film surface of the metal layer and performing a drying treatment, first, metal nanoparticles on the metal film surface. Are in contact with each other to form a lowermost covering layer with high density. Thereafter, the metal nanoparticles from the next layer are stacked on top of each other to form the entire laminated structure. Therefore, the surface density of the contact point between the metal nanoparticles and the metal film surface of the metal layer is sufficiently high, and the sintered type conductive bonding layer is firmly fixed to the metal film surface of the metal layer. It becomes a state.

  The entire sintered-type conductive bonding layer has a network-like structure formed by fusion of metal nanoparticles, and the metal nanoparticles are exposed at a high surface density on the upper surface. However, although the metal nanoparticles exposed on the upper surface are arranged on a substantially flat surface, they are microscopically in a state of showing irregularities. Therefore, when another metal layer is superimposed on this upper surface, some of the metal nanoparticles present on the upper surface come into contact with the metal film surface of the metal layer. When the upper surface of the sintered type conductive bonding layer and the metal film surface of another metal layer are pressed under pressure, the entire sintered type conductive bonding layer is crushed, resulting in metal nanoparticles present on the upper surface. Almost all of them are in contact with the metal film surface of the other metal layer.

  When the surface density of the metal nanoparticles in contact with the metal film surface of another metal layer is sufficiently high, metal atoms that move on the metal nanoparticle surface of the metal nanoparticles gather at each contact point by performing heat treatment . Due to the contribution of the metal atoms gathered at the contact point, a bonding site having a certain contact area is formed. In addition, heating is also performed at the interface between the lower surface side of the sintered-type conductive bonding layer and the metal film surface of the metal layer, and at the fusion site between the metal nanoparticles in the network-shaped sintered-type conductive bonding layer. The fusion proceeds further during processing. Finally, at the interface between the metal film surface of the upper and lower metal layers and the sintered body type conductive bonding layer, a dense intermetallic bond is formed, and through the conductive bonding layer composed of metal nanoparticles, By the intermetal bonding, the surfaces of the two metal layers are conductively bonded to each other.

  In the method for forming a conductive bond according to the present invention, instead of using metal nanoparticles, metal oxide nanoparticles, specifically, metal nanoparticles having a surface oxide film are used to reduce the surface oxide film. It is also possible to use regenerated metal nanoparticles. In that case, after apply | coating the dispersion liquid of a metal oxide nanoparticle on the metal film surface of a metal layer, the drying process is given to the application layer, and the dried metal oxide nanoparticle application layer is once formed. In this state, in order to make the surface density of the metal oxide nanoparticles in contact with the metal film surface of the metal layer to be the same as that of the dried metal nanoparticle coating layer, the average of the metal oxide nanoparticles to be used The particle size is selected in the range of at least 1 to 100 nm. Preferably, the average particle diameter of the metal oxide nanoparticles used is selected in the range of 1-20 nm.

  Compared to the specific gravity of the metal itself, the specific gravity of the metal oxide is small, and when comparing metal oxide nanoparticles with the same particle size and metal nanoparticles, the metal content in the metal oxide nanoparticles is relative Less. Therefore, when metal oxide nanoparticles are converted into metal nanoparticles by performing high-frequency plasma treatment in the presence of a reducing gas, the particle diameter is slightly reduced. The degree depends on the content ratio of the metal oxide in the metal oxide nanoparticles, and the whole is composed of a metal oxide and a thin surface oxide film is formed on the surface of the metal nanoparticle. There is a clear difference from case to case.

  Considering this point, it is usually preferable that the metal oxide nanoparticles to be used have a form in which a thin surface oxide film is formed on the surface of the metal nanoparticles. In particular, the process of reducing the surface oxide film and converting it into metal nanoparticles by applying high-frequency plasma treatment in the presence of a reducing gas is a form in which a thin surface oxide film is formed on the surface of the metal nanoparticles. It is more preferable that it is completed in a shorter time.

  Regarding the method for forming a conductive joint of the present invention, a sintered-type conductive joint layer is formed in advance on one surface of two metal layers to be joined, and then the sintered-type conductive joint layer is formed. The first embodiment has been described above in which the metal film surface of another metal layer is pressed onto the upper surface, and the heat treatment is performed in a state where the metal film is pressed by applying pressure. In addition to this first form, both of the two metal layers to be joined are preliminarily formed with a sintered body type conductive joint layer on their surfaces, and then the sintered body type conductive joint layers are pressed together, It is also possible to select the second mode in which the heat treatment is performed in a state where the pressure is applied and pressed. In this second mode, the metal-to-metal bonding at the interface between the metal film surface of each metal layer and the sintered body type conductive bonding layer is the same as that of the first mode described above. It is formed in the same process as metal-to-metal bonding at the interface where the bonding layer is formed in advance. On the other hand, the intermetallic bonding at the interface where the sintered body type conductive bonding layers are in contact with each other is formed by the following mechanism.

  The metal nanoparticles exposed on the upper surface of the sintered-type conductive bonding layer are arranged on a substantially flat surface, but are microscopically in a state of showing irregularities. Therefore, if the sintered type conductive bonding layers are simply overlapped, only a part of the contact between the metal nanoparticles exposed on the two upper surfaces is made. When this sintered body type conductive bonding layer is pressed against each other and pressure is applied, the microscopic unevenness is flattened, and the metal nanoparticles exposed on the two upper surfaces are contacted at a high surface density. It becomes a state. When heat treatment is performed with this pressure applied and pressed, fusion occurs at the point where the metal nanoparticles are in contact with each other, and the sintered-type conductive bonding layers are fused together between the metal nanoparticles, It will be in the state where it was connected closely. In other words, the two sintered body type conductive bonding layers are integrated. Finally, at the interface between the metal film surfaces of the upper and lower metal layers and the integrated sintered body type conductive bonding layer, a dense intermetallic bond is formed, and the conductivity composed of metal nanoparticles. Through the bonding layer, the surfaces of the two metal layers are conductively bonded to each other by metal-to-metal bonding.

  In the method of forming a conductive bond of the present invention, the interface between the upper surface of the conductive bond layer composed of metal nanoparticles and the metal film surface of another metal layer, or between the sintered-type conductive bond layers At the interface, a metal-metal bond is formed by performing a heat treatment in a state where pressure is applied and pressed. Therefore, the sintered-type conductive bonding layers that perform this bonding are easily melted even at a heating temperature of 200 ° C. or lower when the metal nanoparticles constituting each layer are brought into contact with each other. It is necessary to cause wearing. In addition, when the metal surface of the metal nanoparticle is brought into contact with the metal film surface of another metal layer, it is necessary to easily cause fusion even at a heating temperature of 200 ° C. or less.

  When the metal surfaces are brought into contact with each other, in order for fusion to proceed at the contact interface, it is necessary that both metal atoms locally diffuse to form a continuous metal structure. is there. When both are the same type of metal, naturally, the interdiffusion of metal atoms proceeds at the interface, so that it is most suitable for fusion at the contact interface. When both are different types of metals, mutual diffusion between the two types of metal atoms can easily proceed even at a heating temperature of 200 ° C. or less, so that the two types of metals can form a complete solid solution type alloy. It is desirable that it can be formed. Or the combination which can achieve high adhesiveness between two types of metals is also suitable for forming a good intermetallic bond.

  From the above viewpoint, the metal species forming the metal film constituting the metal layer to be joined and the metal species of the metal nanoparticles constituting the sintered body type conductive joining layer are gold, silver, It is preferable to select from the group consisting of copper, platinum, palladium and nickel. In particular, when the metal nanoparticles constituting the sintered body type conductive bonding layer are pressed against the surface to be bonded by applying pressure, the network-shaped sintered body type conductive bonding layer itself is crushed, It is necessary that the metal nanoparticles exposed to the surface be in close contact with the surface to be joined. From this point of view, the metal species constituting the metal nanoparticles are preferably excellent in ductility and malleability, and gold, silver, copper, platinum, palladium, and nickel are preferable options also in this point of view. Further, the metal film constituting the metal layer to be bonded is also preferably excellent in ductility and malleability in close contact with the metal nanoparticles, and from this viewpoint, gold, silver, copper, platinum, Palladium and nickel are preferred options.

  On the other hand, in place of metal nanoparticles, metal oxide nanoparticles, in particular, when using metal nanoparticles having a surface oxide film, the metal species of the metal nanoparticles obtained by reduction are gold, It is preferable to select from the group consisting of silver, copper, platinum, palladium and nickel. In other words, a surface oxide film obtained by converting the surface of a metal nanoparticle of a metal species selected from the group consisting of gold, silver, copper, platinum, palladium, and nickel into a surface oxide film Metal nanoparticles having are preferred. In particular, in order to coat the surface of the metal oxide nanoparticles with the same kind of coating molecules as the coating molecules used for coating the corresponding metal nanoparticles, the metal nanoparticles are prepared in advance, and then the surface What oxidized more and made the metal oxide nanoparticle is preferable. Of metal oxide nanoparticles composed of metal oxides selected from the group consisting of gold, silver, copper, platinum, palladium and nickel, consisting of metal oxides selected from the group consisting of silver, copper and nickel The metal oxide nanoparticles can be easily produced by applying the above technique. Therefore, in the method for forming a conductive bond according to the present invention, when a dispersion of metal oxide nanoparticles is used, metal oxide nanoparticles made of a metal oxide selected from the group consisting of silver, copper, and nickel are used. A dispersion can be used more suitably.

  As the metal oxide nanoparticles, it is preferable to use metal nanoparticles having a surface oxide film. However, if the nanoparticles are spherical particles having a target average particle diameter, the entire nanoparticles are metal oxides. It is also possible to use what consists of In general, metal oxides have various crystal systems, and it is often difficult to directly form nano-sized spherical nanoparticles. In the present invention, when the metal oxide nanoparticles are used, the outer shape is substantially spherical because the metal oxide nanoparticles are once converted into metal nanoparticles by performing high-frequency plasma treatment in the presence of a reducing gas. It is desirable to be. That is, if it is a substantially spherical shape, the outer shape of the metal nanoparticles obtained when the reduction is carried out from the surface and finally converted into the metal nanoparticles can also be a substantially spherical shape. On the other hand, when utilizing metal nanoparticles having a surface oxide film, the outer shape is generally spherical, and the film thickness of the surface oxide film preferably has a uniform distribution.

When reducing the surface oxide film, for example, it is estimated that the metal atoms generated by the reduction reaction are accumulated in the center of the nanoparticle on the nanoparticle surface through the following process. . For example, when the surface oxide film is assumed to be an oxide (M (II) O) represented by M (II) O and containing a divalent metal cation species, the surface oxide film is in contact with a hydrogen molecule (H ₂ ) that is a reducing gas. The reaction is partially reduced to an oxide (M (I) O) containing a monovalent metal cation species.

2M (II) O + H ₂ → M (I) ₂ O + H ₂ O
In the heated state, from an oxide containing a monovalent metal cation species (M (I) O) to an oxide containing a divalent metal cation species (M (II) O) and a metal atom (M (0)). Then, non-uniformization proceeds.

M (I) ₂ O → M (0) + M (II) O
As a result, an oxide (M (II) O) containing a divalent metal cation species is regenerated on the outermost surface of the nanoparticle, and a metal atom (M (0)) is gradually added to the center of the nanoparticle. accumulate. Eventually, the entire metal oxide nanoparticles are converted into nanoparticles composed of metal atoms.

  On the other hand, when the metal nanoparticles are oxidized from the surface, an oxide (M (II) O) containing a divalent metal cation species is formed on the surface, and then an internal metal atom (M (0)) is formed. ) To form an oxide (M (I) O) containing a monovalent metal cation species. The oxide (M (I) O) containing the monovalent metal cation species causes non-uniformity, the metal atoms (M (0)) are regenerated on the outermost surface, and the metal oxide layer is accumulated inside. The As a result, the surface has a surface oxide film layer, and the inside has a metal core particle. Eventually, when the metal oxide layer reaches the center of the nanoparticle, the metal oxide nanoparticle is completely converted into the metal oxide.

2M (0) + 1 / 2O ₂ → M (I) ₂ O
M (I) ₂ O + 1 / 2O ₂ → 2M (II) O
M (0) + 1 / 2O ₂ → M (II) O
M (0) + M (II) O → 2M (I) ₂ O
In any process, the presence of metal oxides containing metal cation species having different valences is essential for the progress of the mechanism, and metal oxides selected from the group consisting of silver, copper, and nickel are: This condition is also satisfied.

  In the method for forming a conductive bond according to the present invention, the metal nanoparticle dispersion or the metal oxide nanoparticle dispersion is used to form a predetermined film thickness on the metal film surface of the metal layer to be bonded. The coating film is formed. The metal nanoparticles are uniformly dispersed in the dispersion solvent, and the surface of the metal nanoparticles is coated in the dispersion to prevent the metal nanoparticles from coming into contact with each other and causing fusion. It is set as the state coat | covered with the agent molecule | numerator. As the coating agent molecule, an organic compound having a group capable of coordinative bonding with the metal element constituting the metal nanoparticle is used. Specifically, an organic compound having a group capable of coordinative bonding to a metal element using a lone electron pair (unshared electron pair) of a nitrogen atom, an oxygen atom, or a sulfur atom is used. Is done.

That is, in the present invention, a compound that forms a stable bond similar to a covalent bond such as MSR type metal thiolate, MOR type metal alcoholate or metal phenolate to metal (M). Instead, an organic compound having a group capable of coordinative bonding with a metal element is used. Examples of the group capable of coordinative bonding with the metal element include an amino group (—NH ₂ ), a hydroxy group (—OH), and a sulfanyl group (—SH). In some cases, a lone electron pair (unshared electron pair) present in an imino group (—NH—), an ether (—O—), or a sulfide (—S—) is used for a metal element, An organic compound capable of coordinative bonding can also be used. When the metal nanoparticles whose surface is coated with the coating molecules are uniformly dispersed in the dispersion solvent, the coating molecules that function also as a dispersing agent are selected. In other words, a hydrocarbon skeleton that has a group capable of coordinative bonding with a metal element and has an affinity for a dispersion solvent is preferably used as the hydrocarbon skeleton constituting the organic compound.

When the dispersion solvent to be used is, for example, a nonpolar solvent such as a chain hydrocarbon or a solvent having a low polarity such as an aromatic hydrocarbon, the chain hydrocarbon skeleton is coordinated with a metal element. An organic compound having an amino group (—NH ₂ ), a hydroxy group (—OH), or a sulfanyl group (—SH) can be used as a group capable of forming a group.

As a representative example of an organic compound having an amino group that can be used, a primary amine compound having an amino group (—NH ₂ ) at the end of a chain hydrocarbon skeleton, particularly an alkylamine can be given. Such an alkylamine is preferably one that does not desorb in a normal storage environment, specifically in a range not reaching 40 ° C., in a state in which a coordinate bond is formed with the metal element, and has a boiling point. A range of 60 ° C. or higher, preferably 100 ° C. or higher is preferred. For example, those having a boiling point in the range of 150 ° C. or higher can be suitably used. On the other hand, detachment of the alkylamine covering the metal nanoparticles is performed by applying a high frequency plasma treatment. In the process of performing high-frequency plasma treatment, the alkylamine molecules covering the surface of the metal nanoparticles are given excitation energy of the charged particles from charged particles (ionic species) present in the plasma, Excited by the intramolecular vibration. Specifically, when a vibration unique to the terminal amino group (—NH ₂ ) is excited, a coordination mechanism for a metal element using a lone electron pair (unshared electron pair) of a nitrogen atom is used. Bonding is greatly weakened. At that time, when the high-frequency plasma treatment is performed under a reduced pressure condition, the vibrationally excited alkylamine molecules are rapidly detached. It is desirable that after detachment from the surface of the metal nanoparticle, it is possible to evaporate under a reduced pressure condition, and at least the boiling point is in the range not exceeding 300 ° C., usually in the range of 250 ° C. or less. For example, as the alkylamine, those having an alkyl group selected in the range of C8 to C18 and having an amino group at the end of the alkyl chain are used. For example, alkylamines in the range of C8 to C18 have thermal stability, and the vapor pressure near room temperature is not so high. When stored at room temperature or the like, the content is maintained within a desired range. It is preferably used in terms of handling properties, such as being easy to control.

  Moreover, as a typical example of a compound having a sulfanyl group (—SH) that can be used, a primary thiol compound having a sulfanyl group (—SH) at the terminal of a chain hydrocarbon skeleton, particularly an alkanethiol can be given. . In addition, such alkanethiol is preferably in a state in which a coordinate bond is formed with a metal element and does not desorb in a normal storage environment, specifically, in a range not reaching 40 ° C., and has a boiling point. A range of 60 ° C. or higher, preferably 100 ° C. or higher is preferred. For example, those having a boiling point in the range of 150 ° C. or higher can be suitably used. On the other hand, the alkanethiol coating the metal nanoparticles is detached by applying a high-frequency plasma treatment. In the process of performing high-frequency plasma treatment, the alkanethiol molecule that coats the surface of the metal nanoparticles is supplied with excitation energy of the charged particles from charged particles (ionic species) present in the plasma, Excited by the intramolecular vibration. Specifically, when a vibration inherent to the terminal sulfanyl group (—SH) is excited, a coordinated bond to a metal element utilizing a lone pair (unshared electron pair) of a sulfur atom Is greatly weakened. At this time, if the high-frequency plasma treatment is performed under a reduced pressure condition, the vibrationally excited alkanethiol molecules are quickly detached. It is desirable that after detachment from the surface of the metal nanoparticle, it is possible to evaporate under a reduced pressure condition, and at least the boiling point is in the range not exceeding 300 ° C., usually in the range of 250 ° C. or less. For example, as an alkanethiol, the alkyl group is selected in the range of C8 to C18, and one having a sulfanyl group at the terminal of the alkyl chain is used. For example, the alkanethiol in the range of C8 to C18 has thermal stability and the vapor pressure near room temperature is not so high, and the content rate is maintained in a desired range when stored at room temperature. It is preferably used in terms of handling properties, such as being easy to control.

  Moreover, alkanediol can be mentioned as a representative of the compound which has a hydroxyl group which can be utilized. Examples include glycols such as ethylene glycol, diethylene glycol, and polyethylene glycol. In addition, such alkanediols are preferably those that do not desorb in a normal storage environment, specifically in a range that does not reach 40 ° C., in a state in which a coordinate bond is formed with the metal element. Those in the range of 60 ° C. or higher, usually in the range of 100 ° C. or higher are preferred. For example, those having a boiling point in the range of 150 ° C. or higher can be suitably used. On the other hand, the alkanediol covering the metal nanoparticles is detached by applying a high-frequency plasma treatment. In the process of applying the high-frequency plasma treatment, the alkanediol molecules covering the surface of the metal nanoparticles are given excitation energy of the charged particles from the charged particles (ionic species) present in the plasma, Excited by the intramolecular vibration. Specifically, when an intrinsic vibration is excited in the terminal hydroxy group (—OH), a coordinated bond to a metal element utilizing a lone electron pair (unshared electron pair) possessed by an oxygen atom. Is greatly weakened. At that time, if the high-frequency plasma treatment is performed under a reduced pressure condition, the vibrationally excited alkanediol molecules are rapidly detached. It is desirable that after detachment from the surface of the metal nanoparticle, it is possible to evaporate under a reduced pressure condition, and at least the boiling point is in the range not exceeding 300 ° C., usually in the range of 250 ° C. or less. For example, those involving two or more hydroxy groups such as 1,2-diol type can be suitably used.

  On the other hand, the metal oxide nanoparticles do not cause fusion even if the nanoparticles come into contact with each other in the dispersion. However, in order to uniformly disperse the metal oxide nanoparticles in the dispersion solvent, the surface of the metal oxide nanoparticles is kept in a state of being coated with a coating agent molecule. As the coating agent molecule, an organic compound having a group capable of coordinative bonding with the metal element constituting the metal oxide nanoparticles is used. Specifically, an organic compound having a group capable of coordinative bonding to a metal element using a lone electron pair (unshared electron pair) of a nitrogen atom, an oxygen atom, or a sulfur atom is used. Is done.

  Utilizing lone electron pairs (unshared electron pairs) of nitrogen atoms, oxygen atoms, and sulfur atoms that can be used as coating molecules for the metal nanoparticles described above, they are coordinated with metal elements. An organic compound having a group capable of bonding can be similarly used for metal oxide nanoparticles.

At that time, the dispersion solvent shows affinity for the hydrocarbon skeleton portion constituting the coating agent molecule, but does not show polarity, such as an aromatic hydrocarbon solvent such as toluene, a chain hydrocarbon solvent such as hexane, or the like. It is preferable to use a solvent having a small polarity. The coating agent molecule itself is an organic compound having an amino group (—NH ₂ ), a hydroxy group (—OH), and a sulfanyl group (—SH). Has low solubility. After applying the dispersion, the contained dispersion solvent is evaporated and the coating layer is dried. The dried metal nanoparticle coating layer includes metal nanoparticles whose surface is covered with coating molecules and coating molecules dissolved in the dispersion. That is, since the coating agent molecules dissolved in the dispersion liquid do not evaporate at room temperature and atmospheric pressure, the coating molecules are held in the gap between the metal nanoparticle laminate structures whose surfaces are covered with the coating agent molecules. Therefore, surplus coating agent molecules deposited by the drying treatment function as a binder component, and are partly involved in maintaining the laminated structure of metal nanoparticles whose surfaces are covered with the coating agent molecules. Also, in the coating layer of metal oxide nanoparticles whose surface is covered with coating agent molecules, when the drying treatment is performed, surplus coating molecules precipitated by the drying treatment function as a binder component.

  In the dispersion, the coating molecules are almost saturated in the dispersion solvent in addition to the amount required to coat the entire surface of the metal nanoparticles or metal oxide nanoparticles to be dispersed. It is preferable to mix | blend the quantity to do. In addition, the quantity which coat | covers the whole surface of a metal nanoparticle or a metal oxide nanoparticle is suitably determined according to the average particle diameter of a metal nanoparticle or a metal oxide nanoparticle. On the other hand, the amount of saturation in the dispersion solvent depends, of course, on the solubility of the coating agent molecule and the amount of the dispersion solvent.

  For example, it is desirable to select the coating agent molecule in the range of 5 to 35 parts by mass per 100 parts by mass of the metal nanoparticles contained in the dispersion. Moreover, it is desirable to select the coating agent molecules in the range of 5 to 25 parts by mass per 100 parts by mass of the metal oxide nanoparticles contained in the dispersion. More specifically, the coating material molecular layer is at least 0.5 nm or more on the surface of the metal nanoparticles having an average particle diameter of 1 to 100 nm. In the case of metal nanoparticles having an average particle size of 1 nm, the coating agent molecular layer should be in the range of 0.5 nm to 1 nm, while in the case of metal nanoparticles having an average particle size of 100 nm, the coating agent molecular layer should be within 10 nm. Is desirable. For example, when the average particle diameter of the metal nanoparticles is selected in the range of 1 to 20 nm, the thickness of the coating agent molecular layer is at least 0.5 nm or more, and the average particle diameter of the metal nanoparticles is used as a reference. It is preferable to select in the range of 2/10 to 5/10. In addition, it is desirable to select the coating agent molecular layer provided on the surface of the metal oxide nanoparticles within the above range.

  In the method for forming a conductive bond according to the present invention, first, a dispersion containing metal nanoparticles or a metal nanoparticle or metal oxide having a surface oxide film layer is formed on the surface of the metal layer forming the conductive bond. The dispersion liquid containing the product nanoparticles is applied in a predetermined planar shape to produce a coating film layer having a desired film thickness. For example, in a circuit pattern formed on the surface of the wiring board, a coating film layer having a predetermined planar shape is formed on a surface of a metal layer used as the wiring layer in a predetermined portion. In preparing the coating film layer, a suitable method is selected from various drawing methods in consideration of the planar shape pattern of the coating film layer, its minimum line width, and the layer thickness of the target coating film layer. . From the drawing method of screen printing, ink jet printing, or transfer printing, which has been conventionally used for coating and drawing of dispersions containing metal fine particles, the minimum line width and the layer thickness of the target coating film layer are determined. It is preferable to select a suitable method after consideration.

  On the other hand, a dispersion liquid containing metal nanoparticles used for coating, or a dispersion liquid containing metal nanoparticles or metal oxide nanoparticles having a surface oxide film layer is a suitable liquid according to the drawing technique employed. It is desirable to prepare it to have a viscosity. For example, when screen printing is used for drawing a target coating film layer, the dispersion viscosity of the metal nanoparticles is selected within the range of 30 to 300 Pa · s (25 ° C.). It is desirable to do. Moreover, when using transfer printing, it is desirable to select the liquid viscosity of the dispersion in the range of 3 to 300 Pa · s (25 ° C.). On the other hand, when using inkjet printing, it is desirable to select the liquid viscosity of the dispersion in the range of 1 to 100 mPa · s (25 ° C.). The liquid viscosity of the dispersion containing the metal nanoparticles is determined depending on the average particle diameter of the metal nanoparticles to be used, the dispersion concentration, and the type of the dispersion solvent being used. The target liquid viscosity can be adjusted. In addition, regarding the dispersion containing the metal oxide nanoparticles, the viscosity of the liquid is determined depending on the average particle diameter of the metal oxide nanoparticles used, the dispersion concentration, and the type of the dispersion solvent used. These factors can be appropriately selected to adjust to the target liquid viscosity.

  The coating film layer is dried by evaporating the dispersion solvent being used, and by densely laminating metal nanoparticles whose surface is covered with coating molecules on the metal film surface of the metal layer to be bonded. The finished coating layer. In this state, the surface of the metal nanoparticles is covered with at least one molecular layer of coating molecules, and excess coating molecules dissolved in the dispersion solvent are simultaneously deposited in the dried coating layer. ing. Even when metal oxide nanoparticles are used, the surface is covered with at least one molecular layer of coating molecules, and excess coating molecules dissolved in the dispersion solvent are also present in the dried coating layer. Precipitated in

Next, the coating agent molecules contained in the dried coating layer are removed by performing high-frequency plasma treatment. The coating molecule covering the surface of the metal nanoparticle forms a coordinate bond to the metal element. This coordinate bond is, for example, higher than the boiling point of the coating molecule. It is also dissociated by heating to temperature. That is, when a thermal energy is supplied and vibration excitation of the entire coating agent molecule is performed, an amino group (—NH ₂ ), a hydroxy group (—OH), a sulfanyl involved in a coordinate bond to a metal element. Vibrations inherent to the group (-SH) are also excited. At that time, the coordinate bond to the metal element, for example, the distance between the metal atom, nitrogen atom, sulfur atom, and oxygen atom in —NH ₂ : M, —SH: M, —OH: M is extended, and the coating agent Molecular detachment is facilitated.

  In the method of the present invention, instead of thermal energy, the charged particles (ion species) present in the high-frequency plasma are supplied with excitation energy of the charged particles to be fixed on the surface of the metal nanoparticles. The excitation of the intramolecular vibration of the coating molecules. Specifically, the charged particles (ion species) generated in the high-frequency plasma fly to the dried coating layer surface while maintaining high excitation energy. At that time, when the charged particles (ion species) directly bombard the coating molecules that coat the surface of the metal nanoparticles, excitation energy is provided in the process, and various vibrations of the coating molecules themselves occur. The mode is excited.

  In addition, when performing high-frequency plasma treatment, the system is usually in a reduced pressure state, and the coating molecules are not originally present in the gas phase. On the other hand, when further thermal energy is applied, it is detached from the surface of the metal nanoparticles. Once this coating agent molecule is detached from the metal surface, it is exhausted out of the system again without binding to the metal surface.

  The supply of excitation energy from the charged particles (ion species) generated in the high-frequency plasma first occurs on the surface of the dried coating layer, and then the supplied excitation energy is transmitted to the inside of the coating layer. . Specifically, the vibration energy is resonantly transferred from the vibrationally excited coating molecules to other coating molecules, and the coating molecules existing inside the coating layer are also excited by vibration. It will be in the applied state. Thereafter, the coating molecules released by applying further thermal energy maintain a desired reduced pressure state, so that a narrow gap is formed from the inside of the coating layer under the condition that the exhaust in the system is continued. It is possible to move to the outside of the coating layer via.

  The process of detaching the coating molecules promoted by this high-frequency plasma treatment is performed by placing a coating layer that has been dried in a high-frequency plasma generator and exposing the coating layer to the generated high-frequency plasma atmosphere. . In addition, since it also heats simultaneously when exposed to a high frequency plasma atmosphere, the part which arrange | positions an application layer is made into the state which can be heated to the temperature which does not exceed 150 degreeC. On the other hand, after the release of the coating agent molecules, the metal nanoparticles are fused to each other in a state of being maintained in a high-frequency plasma atmosphere.

  Therefore, the high-frequency plasma atmosphere to be used does not include charged particles (ionic species) that are reactive with metal nanoparticles, and can simultaneously cause vibration excitation of the coating molecule. Specifically, the charged particles (ion species) generated in the high-frequency plasma use high-frequency plasma generated using an inert gas that does not show reactivity with metal atoms. In particular, high-frequency plasma generated using an inert rare gas such as argon or helium is used. In order to avoid oxygen molecules and nitrogen molecules derived from air from remaining in the high-frequency plasma generator, the inside of the apparatus is evacuated in advance until the internal pressure reaches 150 Pa or less. Next, the exhaust flow rate of the exhaust system is controlled, and the rare gas is supplied from the gas inlet at a predetermined flow rate so that the system is filled with the rare gas adjusted to a predetermined pressure.

  That is, the flow rate and partial pressure of the gas for plasma generation introduced into the high-frequency plasma generator are selected within a range in which proper high-frequency plasma generation can be maintained according to the frequency and power amount of the high-frequency power used. . The flow rate of the gas introduced into the apparatus uses, for example, a flow rate adjusting mechanism that can be adjusted within a range of 1 to 1000 ml / min (normal state converted flow rate). The exhaust flow rate adjustment function provided in the exhaust system constituting the apparatus controls the valve opening of the exhaust system in a state where gas is introduced at a constant flow rate, and the internal pressure in the apparatus is, for example, 1 to 20,000 Pa. A material that can be adjusted within a range, preferably 1 to 1,000 Pa, is selected. For example, when generating high-frequency plasma, the argon gas flow rate (regular state equivalent flow rate) is selected in the range of 10 to 500 ml / min, and at the same time, the argon gas partial pressure in the apparatus is selected in the range of 1 Pa to 1000 Pa. The high frequency power is supplied while maintaining the reduced pressure state. For example, as the high frequency power, a high frequency power source having a frequency of 13.56 MHz can be used, and the amount of supplied power can be set in a range of 100 to 5000 W.

  When using metal oxide nanoparticles, it is necessary to perform reduction treatment of the metal oxide nanoparticles in high-frequency plasma in addition to removal of the coating agent molecules. In the reduction treatment of metal oxide nanoparticles in this high-frequency plasma, a reducing gas used to reduce the metal oxide was added to the inert gas used to remove the coating agent molecules during the generation of the high-frequency plasma. A mixed gas of an inert gas and a reducing gas is used. The mixed gas of the inert gas and the reducing gas is prepared using nitrogen, helium, argon or the like as the inert gas and hydrogen, ammonia or the like as the reducing gas. In addition, the composition of the mixed gas has an inert gas: reducing gas ratio (volume ratio) in the range of 50:50 to 99.9: 0.1, preferably in the range of 80:20 to 99: 1. More preferably, it is preferable to select in the range of 90:10 to 98: 2. That is, an inert gas is mainly used for generation and maintenance of the high-frequency plasma, and excitation energy is supplied by using charged particles (ion species) derived from the inert gas for removing the coating agent molecules. When the metal oxide nanoparticles are advanced after removal of the coating agent molecules, the charged energy (ionic species) derived from the inert gas is used to supply excitation energy and the coexisting reducing gas. The reduction reaction of metal oxide is promoted using as a hydrogen atom supply source.

  When the reduction reaction is completed, the metal oxide has become metal nanoparticles, and the coating molecules that coat the surface have also been removed, so that the metal nanoparticles are in direct contact with the metal surface, and the metal nanoparticles are in contact. Fusion of particles progresses. The metal nanoparticles in contact with the surface of the metal layer are brought into a state in which the metal nanoparticles are fused to the surface of the metal film by contacting the metal surface with the surface of the metal film of the metal layer.

  Even when metal nanoparticles are used, a mixed gas of an inert gas and a reducing gas may be used when performing high-frequency plasma treatment.

In a high-frequency plasma atmosphere, there is a temperature rise due to the occurrence of plasma. For example, when the metal layer to be bonded is an electrode layer of an electronic component, it is often necessary to handle the electronic component itself within a range of 150 ° C. or less. Alternatively, when the metal layer to be bonded is an electrode layer on a wiring board, it is often desirable to handle the substrate material itself in a range of 200 ° C. or lower. Considering these, a temperature adjusting mechanism is provided so that the temperature of the coating layer exposed to the high-frequency plasma atmosphere can be maintained at 150 ° C. or lower, for example, in the range of 50 ° C. to 150 ° C.

  When the metal oxide nanoparticles are used, the time for performing the high-frequency plasma treatment is added to the time required for the metal oxide reduction reaction to the time required for using the metal nanoparticles. The time required for the reduction reaction of the metal oxide depends on the thickness of the surface oxide layer to be reduced and the generation conditions of the high-frequency plasma containing the reducing gas used. On the other hand, the time required for using metal nanoparticles is the total time required for removing the coating agent molecules covering the surface and fusing the metal nanoparticles together. It is necessary to select the plasma treatment time depending on the thickness of the coating molecular layer covering the nanoparticle surface, the setting of the heating temperature when performing the high-frequency plasma treatment, and the generation conditions of the high-frequency plasma. The time required for using the metal nanoparticles can be selected in the range of 1 second to 1 hour, preferably in the range of 15 seconds to 20 minutes.

  When high-frequency plasma treatment is performed, first, the coating molecule on the surface of the metal nanoparticle is detached, so that the metal surface of the metal layer and the metal surface of the metal nanoparticle arranged at a high surface density on the surface are in direct contact with each other. It becomes a state. At that stage, since metal atoms easily move on the surface of the metal nanoparticles by heating, the metal atoms that have moved to the contact point between the metal surface of the metal layer and the metal nanoparticles gradually accumulate. That is, the contact between the metal surface of the metal layer and the metal nanoparticles is initially a point contact, but metal atoms that have moved through a narrow gap around the metal layer are buried, and the contact area is expanded. In addition, at this contact site, thermal interdiffusion and rearrangement occur between the metal atoms exposed on the surface of the metal film of the metal layer and the metal atoms derived from the metal nanoparticles. A combination is formed. At the same time, the laminated metal nanoparticles are also fused at the contact point, and the metal nanoparticles constituting the dried coating layer form a sintered-type conductive bonding layer.

  In the first embodiment of the present invention, a sintered body type conductive bonding layer is formed in advance on one surface of two metal layers to be bonded, and then the upper surface of the sintered body type conductive bonding layer is formed. A metal film surface of another metal layer is pressed, and heat treatment is performed in a pressed state by applying pressure. On the other hand, in the second embodiment, both of the two metal layers to be bonded are previously formed with a sintered body type conductive bonding layer on the surface thereof, and then the sintered body type conductive bonding layers are pressed against each other, pressure Heat treatment is performed in a state where the pressure is applied and pressed.

  The upper surface of the produced sintered-type conductive bonding layer is macroscopically flat, but microscopically, the metal nanoparticles exposed on the upper surface are not located on the same plane. , Showing nanoscale extremely fine irregularities. When the upper surface of the conductive bonding layer and the metal film surface of the other metal layer are superposed, the surface density at the contact point between the two is low due to the fine unevenness. When the metal film surface of another metal layer is pressed against the upper surface of this sintered body type conductive bonding layer, it is in a pressed state by applying pressure, thereby forming a network shape constituting the sintered body type conductive bonding layer itself. Deform the soft structure of the. As a result, almost all of the metal nanoparticles exposed on the upper surface of the sintered body type conductive bonding layer are brought into contact with the metal film surface of the other metal layer. When heating is performed in a state where pressure is applied, thermal interdiffusion of metal atoms and rearrangement occur on the surface of the metal film of another metal layer at the contact site, and intermetallic bonding is performed. It is formed.

  In the first embodiment, it is preferable to select the thickness of the sintered body type conductive bonding layer in a range of 0.5 μm to 40 μm in order to cause a desired deformation by applying pressure and pressing. That is, by crushing and deforming about 1/10 of the thickness of the sintered-type conductive bonding layer, it is possible to make intimate contact with the metal film surface of another metal layer. Further, when the pressure is applied and pressed, the applied pressure is appropriately selected according to the average particle size of the metal nanoparticles constituting the sintered body type conductive bonding layer and the metal type. . That is, taking into consideration the average surface density of the metal nanoparticles present on the upper surface of the sintered-type conductive bonding layer and the force required to press each metal nanoparticle and partially deform the contact portion thereof flatly The pressure to be applied is appropriately selected.

When using metal nanoparticles made of gold, silver, copper, platinum, palladium, and nickel that are excellent in ductility and malleability, the applied pressure is usually 0.2 × 10 ⁶ Pa to 10 × 10 ^6. It is preferable to select in the range of Pa. Moreover, when aiming at this metal-metal joining, it is preferable to select heating temperature in the range of 100 to 200 degreeC.

  In the second form, since the upper surfaces of the sintered-type conductive bonding layers are overlapped with each other, both of them exhibit nanoscale extremely fine irregularities, so that the metal nanoparticles exposed on the upper surfaces are in contact with each other as they are. The frequency of doing is low. Therefore, the network-like flexible structure that constitutes the sintered body type conductive bonding layer itself is deformed by applying pressure and pressing. As a result, almost all of the metal nanoparticles exposed on the upper surfaces of the two sintered body type conductive bonding layers are in contact with each other. When heating is performed in a state where the pressure is applied and the metal nanoparticle is pressed, thermal interdiffusion of metal atoms and rearrangement occur at the contact sites between the metal nanoparticles, and fusion proceeds. That is, at the interface between the two sintered body type conductive bonding layers, the metal nanoparticles are formed with high surface density between the metal nanoparticles, and as a result, the two sintered body type conductive bonding layers are integrated. At the interface between the metal film surface of each metal layer and the sintered-type conductive bonding layer, a dense intermetallic bond is formed in advance. In other words, finally, a conductive bond is formed between the two metal layers via the integrated sintered body type conductive bond layer.

  In the second mode, since the desired deformation is caused by applying pressure and pressing, it is preferable to select the thickness of each sintered body type conductive bonding layer in the range of 0.25 μm to 20 μm. In other words, by crushing and deforming about 1/10 of the thickness of the sintered-type conductive bonding layer, close contact can be achieved at the mutual interface. Further, when the pressure is applied and pressed, the applied pressure is appropriately selected according to the average particle size of the metal nanoparticles constituting the sintered body type conductive bonding layer and the metal type. . That is, taking into consideration the average surface density of the metal nanoparticles present on the upper surface of the sintered-type conductive bonding layer and the force required to press each metal nanoparticle and partially deform the contact portion thereof flatly The pressure to be applied is appropriately selected.

When using metal nanoparticles made of gold, silver, copper, platinum, palladium, and nickel that are excellent in ductility and malleability, the applied pressure is usually 0.2 × 10 ⁶ Pa to 10 × 10 ^6. It is preferable to select in the range of Pa. Moreover, when aiming at this metal-metal joining, it is preferable to select heating temperature in the range of 100 to 200 degreeC.

  In the method for forming a conductive bond according to the present invention, a sintered-type conductive bonding layer to be formed is bonded to the metal film surface of the metal layer by metal-to-metal bonding in the process of performing high-frequency plasma treatment. ing. Therefore, it is not necessary to add a resin component that functions as an organic binder to the dispersion of metal nanoparticles or the dispersion of metal oxide nanoparticles. However, a resin component that functions as an organic binder is added as long as it does not hinder the removal of coating agent molecules by high-frequency plasma treatment, the fusion of metal nanoparticles, and the bonding of metal nanoparticles to the metal film surface of the metal layer. It is also possible. As the resin component that functions as the organic binder, a thermosetting resin such as a thermosetting epoxy resin can be used. The amount of the resin component added is selected within a range in which a desired deformation can be made in order to bring the upper surface into close contact with the object to be joined when pressure is applied to press the formed sintered body type conductive bonding layer. Specifically, a small amount of a resin component that functions as an organic binder may be used for the purpose of helping to fix the sintered type conductive bonding layer on the metal film surface of the metal layer. When the drying process is performed after the dispersion of the metal nanoparticles is applied, the resin component remains in a range close to the interface between the metal layer and the metal film surface in the dried coating layer. In addition, it is also possible to add a small amount of an organic acid anhydride or organic acid having an action of removing coating agent molecules in a heated state to the dispersion.

  This method for forming a conductive bond of the present invention can be suitably applied to a process of conductively bonding an electrode part of an electronic component to the surface of a metal layer on a printed wiring board.

  Hereinafter, the present invention will be described more specifically with reference to examples. These examples are examples of the best mode of the present invention, but the present invention is not limited by these examples.

(First form)
In the following Examples 1 to 4, a commercially available silver nanoparticle dispersion (trade name: Nanopaste NPS, Harima Kasei Co., Ltd.) is used as the silver nanoparticle dispersion. This nanopaste NPS is a dispersion in which silver nanoparticles having an average particle diameter of 5 nm are uniformly dispersed in calcoal 1098 (1-decanol, boiling point 232 ° C .: manufactured by Kao) as a dispersion solvent. At this time, the surface of the silver nanoparticles is coated with a coating molecule dibutylaminopropylamine (boiling point 205 ° C., manufactured by Guangei Chemical Industry Co., Ltd.). In the silver nanoparticle dispersion liquid, 14.9 parts by mass of the coating agent molecule dibutylaminopropylamine and 13.7 parts by mass of the dispersion solvent 1-decanol are contained per 100 parts by mass of silver nanoparticles having an average particle diameter of 5 nm. ing.

  The liquid viscosity of this silver nanoparticle dispersion (nano paste NPS) is adjusted to 150 Pa · s (25 ° C.).

(Example 1)
Conductive bonding between the two substrates was performed by the following procedure.

  The substrate to be bonded is a copper clad laminate, and a metal layer having an average thickness of 18 μm formed of copper (electrolytic copper foil) is provided as a conductive layer on the surface to be bonded. . In the bonding between the two substrates, a conductive bond is formed between the two conductive layers through a layer made of silver nanoparticles.

  First, the silver nanoparticle dispersion (nanopaste NPS) is applied to one substrate surface with a thickness of 10 μm. In order to evaporate and remove the dispersion solvent contained in the coating layer, a drying treatment is performed at 100 ° C. for 20 minutes. The average film thickness of the dried silver nanoparticle coating layer is 8 μm.

  After finishing the drying process, the substrate is put into a plasma processing apparatus, and the dried silver nanoparticle coating layer is subjected to plasma processing under the following conditions. The pressure inside the plasma processing apparatus is once reduced to 10 Pa, and then the internal pressure of the apparatus is about 30 to 40 Pa in the heating state (50 ° C.) while introducing argon gas from the gas inlet at a flow rate of 100 ml / min (normal state converted flow rate). Adjust to reduced pressure. A high frequency power of 500 W is supplied from a high frequency power source (frequency 13.56 MHz) to generate high frequency plasma in the argon gas. In this argon plasma, at 50 ° C., the dried silver nanoparticle coating layer on the substrate surface is subjected to plasma treatment for 5 minutes. After the plasma treatment, the average film thickness of the silver nanoparticle coating layer is 6 μm.

After the plasma treatment, the substrate is taken out from the apparatus, and the surface having the conductive layer of another substrate is adhered to the surface on which the silver nanoparticle coating layer is formed. A heat treatment at 150 ° C. for 1 minute is performed while applying a pressure of 3.6 × 10 ⁶ Pa to the entire surfaces of both substrates in close contact. As a result of performing the heat treatment under this pressure, the conductive layers provided on the surfaces of the two substrates are bonded via the conductive bonding layer formed of the silver nanoparticle coating layer.

  After bonding, the average film thickness of the conductive bonding layer made of the silver nanoparticle coating layer is 5 μm. Moreover, when the peel strength at the joint interface was evaluated, it was at least inferior to the peel strength when using a conductive paste using a thermosetting epoxy resin at the corresponding site. Note that peeling at the bonding interface mainly occurs at the interface between the surface of the other substrate having the conductive layer and the conductive bonding layer formed of the silver nanoparticle coating layer.

(Example 2)
Conductive bonding between the two substrates was performed by the following procedure.

  The substrate to be bonded is a copper-clad laminate, and a metal layer having an average thickness of 18 μm formed of copper is provided as a conductive layer on the bonded surface. In the bonding between the two substrates, a conductive bond is formed between the two conductive layers through a layer made of silver nanoparticles.

  First, the silver nanoparticle dispersion (nanopaste NPS) is applied to each of the two substrate surfaces to a thickness of 5 μm. In order to evaporate and remove the dispersion solvent contained in the coating layer, a drying treatment is performed at 100 ° C. for 20 minutes. The average film thickness of the dried silver nanoparticle coating layer is 4 μm.

  After finishing the drying process, the two substrates are put into a plasma processing apparatus, and the dried silver nanoparticle coating layer is subjected to plasma processing under the following conditions. The pressure inside the plasma processing apparatus is once reduced to 10 Pa, and then the internal pressure of the apparatus is about 30 to 40 Pa in the heating state (50 ° C.) while introducing argon gas from the gas inlet at a flow rate of 100 ml / min (normal state converted flow rate). Adjust to reduced pressure. A high frequency power of 500 W is supplied from a high frequency power source (frequency 13.56 MHz) to generate high frequency plasma in the argon gas. In this argon plasma, at 50 ° C., the dried silver nanoparticle coating layer on the substrate surface is subjected to plasma treatment for 5 minutes. In addition, after the plasma treatment, the average film thickness of the silver nanoparticle coating layer is 3 μm.

After the plasma treatment, the two substrates are taken out from the apparatus, and the surfaces on which the silver nanoparticle coating layers are formed are brought into close contact with each other. In this tight contact state, heat treatment is performed at 150 ° C. for 1 minute while applying pressure of 3.6 × 10 ⁶ Pa on both substrate surfaces and pressing them. As a result of heat treatment under this pressure, fusion proceeds at the interface between the silver nanoparticle coating layers formed on the conductive layers provided on the surfaces of the two substrates, and the two silver nanoparticle coating layers fused together Bonding is made through a conductive bonding layer made of

  After bonding, the average film thickness of the conductive bonding layer composed of two fused silver nanoparticle coating layers is 5 μm. Moreover, when the peel strength at the joint interface was evaluated, it was at least inferior to the peel strength when using a conductive paste using a thermosetting epoxy resin at the corresponding site. Note that the peeling at the bonding interface mainly occurs at the interface between the conductive bonding layers formed of the two silver nanoparticle coating layers.

(Example 3)
Conductive bonding of the electronic device onto the surface of the substrate was performed according to the following procedure.

  The board | substrate with which an electronic device is joined is a copper clad laminated board, and the average thickness 18micrometer metal layer formed with copper is provided as a conductive layer on the surface to be joined. The electrode part of the electronic device is conductively bonded onto the conductive layer on the substrate surface via a layer made of silver nanoparticles.

  First, the silver nanoparticle dispersion (nanopaste NPS) is applied to the substrate surface to a thickness of 10 μm. In order to evaporate and remove the dispersion solvent contained in the coating layer, a drying treatment is performed at 100 ° C. for 20 minutes. The average film thickness of the dried silver nanoparticle coating layer is 8 μm.

  After finishing the drying process, the substrate is put into a plasma processing apparatus, and the dried silver nanoparticle coating layer is subjected to plasma processing under the following conditions. The pressure inside the plasma processing apparatus is once reduced to 10 Pa, and then the internal pressure of the apparatus is about 30 to 40 Pa in the heating state (50 ° C.) while introducing argon gas from the gas inlet at a flow rate of 100 ml / min (normal state converted flow rate). Adjust to reduced pressure. A high frequency power of 500 W is supplied from a high frequency power source (frequency 13.56 MHz) to generate high frequency plasma in the argon gas. In this argon plasma, at 50 ° C., the dried silver nanoparticle coating layer on the substrate surface is subjected to plasma treatment for 5 minutes. After the plasma treatment, the average film thickness of the silver nanoparticle coating layer is 6 μm.

After the plasma treatment, the substrate is taken out from the apparatus, and the electrode part of the electronic device is aligned with a predetermined position on the surface on which the silver nanoparticle coating layer is formed, and then brought into close contact. In this close contact state, a heat treatment is performed at 150 ° C. for 1 minute while applying a pressure of 3.0 × 10 ⁶ Pa and pressing the entire surface of the electronic device electrode portion. As a result of performing the heat treatment under this pressure, the electrode part of the electronic device is bonded to the conductive layer provided on the surface of the substrate via the conductive bonding layer made of the silver nanoparticle coating layer.

  After bonding, the average film thickness of the conductive bonding layer made of the silver nanoparticle coating layer is 5 μm. Moreover, when the peel strength at the joint interface was evaluated, it was at least inferior to the peel strength when using a conductive paste using a thermosetting epoxy resin at the corresponding site. Note that peeling at the bonding interface mainly occurs at the interface between the electrode portion of the electronic device and the conductive bonding layer formed of the silver nanoparticle coating layer.

Example 4
Conductive bonding of the electronic device onto the surface of the substrate was performed according to the following procedure.

  The board | substrate with which an electronic device is joined is a copper clad laminated board, and the average thickness 18micrometer metal layer formed with copper is provided as a conductive layer on the surface to be joined. The electrode part of the electronic device is conductively bonded onto the conductive layer on the substrate surface via a layer made of silver nanoparticles.

  First, the silver nanoparticle dispersion (nano paste NPS) is applied to the surface of the substrate with a thickness of 5 μm. The silver nanoparticle dispersion (nanopaste NPS) is also applied to the surface of the electrode part of the electronic device with a thickness of 5 μm. In order to evaporate and remove the dispersion solvent contained in the coating layer, a drying treatment is performed at 100 ° C. for 20 minutes. Note that the average film thickness of the dried silver nanoparticle coating layer is 4 μm.

  After finishing the drying process, the substrate and the electronic device are put into a plasma processing apparatus, and the dried silver nanoparticle coating layer is subjected to plasma processing under the following conditions. The pressure inside the plasma processing apparatus is once reduced to 10 Pa, and then the internal pressure of the apparatus is about 30 to 40 Pa in the heating state (50 ° C.) while introducing argon gas from the gas inlet at a flow rate of 100 ml / min (normal state converted flow rate). Adjust to reduced pressure. A high frequency power of 500 W is supplied from a high frequency power source (frequency 13.56 MHz) to generate high frequency plasma in the argon gas. In this argon plasma, at 50 ° C., the dried silver nanoparticle coating layer on the electrode part surface of the electronic device and the dried silver nanoparticle coating layer on the substrate surface are simultaneously subjected to plasma treatment for 5 minutes. In addition, after the plasma treatment, the average film thickness of the silver nanoparticle coating layer is 3 μm.

After the plasma treatment, the electronic device and the substrate are taken out from the apparatus, and after aligning the dried silver nanoparticle coating layer on the surface of the electrode part of the electronic device with a predetermined position on the surface on which the silver nanoparticle coating layer is formed on the substrate surface, The silver nanoparticle coating layers are combined and brought into close contact with each other. In this close contact state, a heat treatment is performed at 150 ° C. for 1 minute while applying a pressure of 3.0 × 10 ⁶ Pa and pressing the entire surface of the electronic device electrode portion. As a result of heat treatment under this pressure, fusion proceeds at the interface between the silver nanoparticle coating layers, and two silver nanoparticle coatings in which the electrode part of the electronic device is fused on the conductive layer provided on the surface of the substrate It joins through the conductive joining layer which consists of a layer.

  After bonding, the average film thickness (total film thickness) of the conductive bonding layer composed of the two silver nanoparticle coating layers fused is 5 μm. Moreover, when the peel strength at the joint interface was evaluated, it was at least inferior to the peel strength when using a conductive paste using a thermosetting epoxy resin at the corresponding site. Note that the peeling at the bonding interface mainly occurs at the interface between the conductive bonding layers formed of the two silver nanoparticle coating layers.

(Second form)
In Examples 5 and 6 below, a commercially available copper nanoparticle dispersion (trade name: Nanopaste NPC, Harima Kasei Co., Ltd.) is used as a copper nanoparticle dispersion having a surface oxide film layer. Yes. This nano paste NPC is a dispersion in which copper nanoparticles having an average particle diameter of 5 nm are uniformly dispersed in N14 (tetradecane, boiling point 254 ° C .: manufactured by Nikko Petrochemical Co., Ltd.) as a dispersion solvent. That is, the copper nanoparticle is a copper nanoparticle (copper oxide nanoparticle) having a surface oxide film layer in which a surface oxide film is present on the surface and the core is composed of copper. On the other hand, the surface of the copper nanoparticles is coated with a coating molecule dodecylamine (boiling point 248 ° C.). In the copper nanoparticle dispersion liquid, 15.0 parts by mass of the coating molecule dodecylamine and 25.0 parts by mass of the dispersion solvent tetradecane are contained per 100 parts by mass of copper nanoparticles having an average particle diameter of 5 nm.

  The liquid viscosity of this copper nanoparticle dispersion (nano paste NPC) is adjusted to 100 Pa · s (25 ° C.).

(Example 5)
Conductive bonding of the electronic device onto the surface of the substrate was performed according to the following procedure.

  The board | substrate with which an electronic device is joined is a copper clad laminated board, and the average thickness 18micrometer metal layer formed with copper is provided as a conductive layer on the surface to be joined. The electrode part of the electronic device is conductively bonded onto the conductive layer on the substrate surface via a layer made of copper nanoparticles.

  First, the copper nanoparticle dispersion (nanopaste NPC) is applied to the substrate surface with a thickness of 12 μm. In order to evaporate and remove the dispersion solvent contained in the coating layer, a drying treatment is performed at 100 ° C. for 20 minutes. In addition, the average film thickness of the dried copper nanoparticle application layer is 9 μm.

After finishing the drying process, the substrate is put into a plasma processing apparatus, and the dried copper nanoparticle coating layer is subjected to plasma processing under the following conditions. In this plasma treatment, copper oxide is reduced to metallic copper in high-frequency plasma using a mixed gas obtained by mixing hydrogen (H ₂ ) in argon (Ar) at a volume ratio Ar: H ₂ = 95: 5. Select possible conditions. The pressure inside the plasma processing apparatus is once reduced to 10 Pa, and then the argon (Ar) / hydrogen (H ₂ ) mixed gas is introduced from the gas inlet at a flow rate of 100 ml / min (normal state equivalent flow rate) while being heated (50 C), the internal pressure of the apparatus is adjusted to a reduced pressure of about 30 to 40 Pa. A high frequency power of 500 W is supplied from a high frequency power source (frequency 13.56 MHz) to generate high frequency plasma in the mixed gas. In this plasma, at 50 ° C., the dried copper nanoparticle coating layer on the substrate surface is subjected to plasma treatment for 5 minutes. In addition, after said plasma processing, the average film thickness of a copper nanoparticle application layer is 7 micrometers.

  In addition, in the above plasma treatment, the surface oxide film present on the surface of the copper nanoparticles is supplied with energy from the argon ion species present in the plasma, and from the copper oxide by coexisting hydrogen. Reduction to metallic copper has been made. As a result, when the plasma treatment is finished, the copper nanoparticle coating layer is composed of copper nanoparticles having no surface oxide film.

After the plasma treatment, the substrate is taken out from the apparatus, and the electrode part of the electronic device is aligned with a predetermined position on the surface on which the copper nanoparticle coating layer is formed, and then brought into close contact. In this close contact state, heat treatment is performed at 150 ° C. for 1 minute while applying pressure of 4.0 × 10 ⁶ Pa on the entire surface of the electronic device electrode portion and pressing it. As a result of performing the heat treatment under this pressure, the electrode portion of the electronic device is bonded to the conductive layer provided on the surface of the substrate via the conductive bonding layer formed of the copper nanoparticle coating layer.

  After bonding, the average film thickness of the conductive bonding layer made of the copper nanoparticle coating layer is 5 μm. Moreover, when the peel strength at the joint interface was evaluated, it was at least inferior to the peel strength when using a conductive paste using a thermosetting epoxy resin at the corresponding site. Note that peeling at the bonding interface mainly occurs at the interface between the electrode portion of the electronic device and the conductive bonding layer formed of the copper nanoparticle coating layer.

(Example 6)
Conductive bonding of the electronic device onto the surface of the substrate was performed according to the following procedure.

  The board | substrate with which an electronic device is joined is a copper clad laminated board, and the average thickness 18micrometer metal layer formed with copper is provided as a conductive layer on the surface to be joined. The electrode part of the electronic device is conductively bonded onto the conductive layer on the substrate surface via a layer made of copper nanoparticles.

  First, the copper nanoparticle dispersion (nanopaste NPC) is applied to the substrate surface in a thickness of 6 μm. The said copper nanoparticle dispersion liquid (nano paste NPC) is apply | coated by the thickness of 6 micrometers also to the electrode part surface of an electronic device. In order to evaporate and remove the dispersion solvent contained in the coating layer, a drying treatment is performed at 100 ° C. for 20 minutes. The average film thickness of the dried copper nanoparticle coating layer is 5 μm.

After finishing the drying process, the electronic device and the substrate are put in a plasma processing apparatus, and the dried copper nanoparticle coating layer is subjected to plasma processing under the following conditions. In this plasma treatment, copper oxide is reduced to metallic copper in high-frequency plasma using a mixed gas obtained by mixing hydrogen (H ₂ ) in argon (Ar) at a volume ratio Ar: H ₂ = 95: 5. Select possible conditions. The pressure inside the plasma processing apparatus is once reduced to 10 Pa, and then the argon (Ar) / hydrogen (H ₂ ) mixed gas is introduced from the gas inlet at a flow rate of 100 ml / min (normal state equivalent flow rate) while being heated (50 C), the internal pressure of the apparatus is adjusted to a reduced pressure of about 30 to 40 Pa. A high frequency power of 500 W is supplied from a high frequency power source (frequency 13.56 MHz) to generate high frequency plasma in the mixed gas. In this plasma, at 50 ° C., the dried copper nanoparticle coating layer on the surface of the electrode part of the electronic device and the dried copper nanoparticle coating layer on the substrate surface are simultaneously subjected to plasma treatment for 5 minutes. In addition, after said plasma processing, the average film thickness of a copper nanoparticle application layer is all 3 micrometers.

  In addition, in the above plasma treatment, the surface oxide film present on the surface of the copper nanoparticles is supplied with energy from the argon ion species present in the plasma, and from the copper oxide by coexisting hydrogen. Reduction to metallic copper has been made. As a result, when the plasma treatment is finished, the copper nanoparticle coating layer is composed of copper nanoparticles having no surface oxide film.

After the plasma treatment, the electronic device and the substrate are taken out of the apparatus, and after aligning the dried copper nanoparticle coating layer on the surface of the electrode part of the electronic device with a predetermined position on the surface on which the copper nanoparticle coating layer is formed on the substrate surface, The copper nanoparticle coating layers are combined and brought into close contact with each other. In this close contact state, heat treatment is performed at 150 ° C. for 1 minute while applying pressure of 4.0 × 10 ⁶ Pa on the entire surface of the electronic device electrode portion and pressing it. As a result of applying heat treatment under this pressure, fusion proceeds at the interface between the copper nanoparticle coating layers, and the two copper nanoparticle coatings in which the electrode part of the electronic device is fused on the conductive layer provided on the surface of the substrate It joins through the conductive joining layer which consists of a layer.

  After bonding, the average film thickness (total film thickness) of the conductive bonding layer composed of two fused copper nanoparticle coating layers is 5 μm. Moreover, when the peel strength at the joint interface was evaluated, it was at least inferior to the peel strength when using a conductive paste using a thermosetting epoxy resin at the corresponding site. Note that peeling at the bonding interface mainly occurs at the interface between the conductive bonding layers formed of the two copper nanoparticle coating layers.

  When the conductive bonding forming method according to the present invention is used, a conductive adhesive containing a conventional binder resin component is used to bond the electrode portion provided on the back surface of the electronic device to the surface of the metal layer on the substrate. Instead of using the binder resin component essentially, the back surface of the electronic device is provided on the surface of the metal layer on the substrate by metal-to-metal bonding through the conductive bonding layer composed of metal nanoparticles. It becomes possible to join an electrode part. In particular, when forming this conductive bond, in the process of producing a conductive bonding layer composed of metal nanoparticles, as a means to remove the coating molecule layer covering the surface of the metal nanoparticles in advance The high-frequency plasma treatment is employed, and then the forging process for forming the conductive joint can be performed at a low heating temperature of less than 200 ° C. In addition, high-frequency plasma treatment is performed on metal nanoparticles (metal oxide nanoparticles) having a surface oxide film in the presence of a reducing gas to reduce the surface oxide film and restore the metal nanoparticles. In addition, it is possible to form a conductive bond through a conductive bonding layer composed of such metal nanoparticles.

Claims (11)

A method for conductively bonding the surfaces of two metal layers,
The conductive bonding is one in which the surfaces of two metal layers are bonded to each other through a conductive bonding layer composed of metal nanoparticles.
The process of forming the conductive bond is as follows:
Using a metal nanoparticle dispersion liquid in which metal nanoparticles having a coating agent molecular layer on the surface of the nanoparticles are dispersed in an organic solvent on the metal surface constituting one metal layer, the metal nanoparticles are used. Forming a coating layer of the dispersion;
A step of evaporating an organic solvent contained in the coating layer of the metal nanoparticle dispersion to form a dried coating layer;
A coating molecular layer provided on the surface of the nanoparticle is obtained by treating the dried coating layer formed on the metal surface constituting one metal layer at a heating temperature of 150 ° C. or less in a high-frequency plasma atmosphere. Removing and then fusing the metal nanoparticles together to form a conductive bonding layer composed of the metal nanoparticles on the metal surface constituting one metal layer;
The surface of the conductive bonding layer composed of the metal nanoparticles is overlapped with the surface of the metal constituting the other metal layer, and the pressure is applied to press the surfaces of each other while maintaining the temperature within a range of 100 ° C to 200 ° C. Forming a metal-to-metal bond between the surface of the conductive bonding layer and the metal surface constituting the other metal layer at a selected temperature by performing a heat treatment;
The pressure is selected in the range of ^{0.2 × 10 6 Pa~10 × 10 6} Pa,
Metal nanoparticles having a coating molecular layer on the surface of the nanoparticles,
For metal nanoparticles with an average particle size selected in the range of 1-100 nm,
The group capable of coordinative bonding with the metal element contained in the metal nanoparticle includes a nitrogen, oxygen, or sulfur atom, and has a group capable of coordinative bonding by a lone electron pair possessed by these atoms. A method for forming a conductive bond, which is a nanoparticle formed by coating one or more organic compounds as a coating agent molecule on the surface of the metal nanoparticle. A method for conductively bonding the surfaces of two metal layers,
The conductive bonding is one in which the surfaces of two metal layers are bonded to each other through a conductive bonding layer composed of metal nanoparticles.
The process of forming the conductive bond is as follows:
Using a metal oxide nanoparticle dispersion liquid in which metal oxide nanoparticles having a coating agent molecular layer on the surface of the nanoparticle are dispersed in an organic solvent on the metal surface constituting one metal layer, Forming a coating layer of the metal oxide nanoparticle dispersion;
A step of evaporating an organic solvent contained in the coating layer of the metal oxide nanoparticle dispersion to form a dried coating layer;
The dried coating layer formed on the metal surface constituting one metal layer is treated at a heating temperature of 150 ° C. or less in a high-frequency plasma atmosphere in the presence of a reducing gas, and the surface of the nanoparticle And the metal oxide nanoparticles are reduced to produce metal nanoparticles, and then the metal nanoparticles are fused together to form the metal nanoparticles. Forming a conductive bonding layer on a metal surface constituting one metal layer;
The surface of the conductive bonding layer composed of the metal nanoparticles is overlapped with the surface of the metal constituting the other metal layer, and the pressure is applied to press the surfaces of each other while maintaining the temperature within a range of 100 ° C to 200 ° C. Forming a metal-to-metal bond between the surface of the conductive bonding layer and the metal surface constituting the other metal layer at a selected temperature by performing a heat treatment;
The pressure is selected in the range of ^{0.2 × 10 6 Pa~10 × 10 6} Pa,
Metal oxide nanoparticles having a coating molecular layer on the surface of the nanoparticles,
For metal oxide nanoparticles with an average particle size selected in the range of 1-100 nm,
A group capable of coordinative bonding with a metal element contained in the metal oxide nanoparticles includes a nitrogen, oxygen, or sulfur atom, and a group capable of coordinative bonding by a lone pair of electrons of these atoms A method for forming a conductive bond, which is a nanoparticle formed by coating one or more organic compounds having a coating agent molecule on the surface of the metal oxide nanoparticle. The method for forming a conductive junction according to claim 1, wherein the metal species constituting the metal nanoparticles is a metal selected from the group consisting of gold, silver, copper, platinum, palladium, and nickel. . The method for forming a conductive junction according to claim 2, wherein the metal oxide constituting the metal oxide nanoparticles is an oxide of a metal selected from the group consisting of silver, copper, and nickel. In the step of performing the treatment at a heating temperature of 150 ° C. or less in the high-frequency plasma atmosphere,
The method for forming a conductive junction according to claim 1, wherein the high-frequency plasma atmosphere is a plasma atmosphere generated using an inert gas. In the step of performing the treatment at a heating temperature of 150 ° C. or less in the high-frequency plasma atmosphere in the presence of a reducing gas,
3. The method of forming a conductive junction according to claim 2, wherein the high-frequency plasma atmosphere is a plasma atmosphere generated by using a mixed gas of a reducing gas and an inert gas. The method for forming a conductive junction according to claim 5, wherein argon, helium, or a mixture thereof is used as the inert gas. In the mixed gas of reducing gas and inert gas,
The method for forming a conductive junction according to claim 6, wherein argon, helium or a mixture thereof is used as the inert gas, and hydrogen, ammonia or a mixture thereof is used as the reducing gas. A method for conductively bonding the surfaces of two metal layers,
The conductive bonding is one in which the surfaces of two metal layers are bonded to each other through a conductive bonding layer composed of metal nanoparticles.
The process of forming the conductive bond is as follows:
Using a metal nanoparticle dispersion liquid in which metal nanoparticles each having a coating molecule layer on the surface of the nanoparticles are dispersed in an organic solvent on the metal surfaces constituting the two metal layers. Forming a coating layer of the nanoparticle dispersion;
A step of evaporating an organic solvent contained in the coating layer of the metal nanoparticle dispersion to form a dried coating layer;
A coating agent provided on the surface of the nanoparticles by treating the dried coating layers formed on the metal surfaces constituting the two metal layers at a heating temperature of 150 ° C. or less in a high-frequency plasma atmosphere, respectively. Removing the molecular layer and then performing fusion bonding between the metal nanoparticles to form a conductive bonding layer composed of the metal nanoparticles on the metal surface constituting each metal layer;
Heat treatment is performed at a temperature selected from the range of 100 ° C. to 200 ° C. while superimposing the surfaces of the conductive bonding layer composed of the metal nanoparticles on each other, applying pressure, and pressing the surfaces of both together. Applying and forming an intermetallic bond between the surfaces of the two conductive bonding layers,
The pressure is selected in the range of ^{0.2 × 10 6 Pa~10 × 10 6} Pa,
Metal nanoparticles having a coating molecular layer on the surface of the nanoparticles,
For metal nanoparticles with an average particle size selected in the range of 1-100 nm,
The group capable of coordinative bonding with the metal element contained in the metal nanoparticle includes a nitrogen, oxygen, or sulfur atom, and has a group capable of coordinative bonding by a lone electron pair possessed by these atoms. A method for forming a conductive bond, which is a nanoparticle formed by coating one or more organic compounds as a coating agent molecule on the surface of the metal nanoparticle. A method for conductively bonding the surfaces of two metal layers,
The conductive bonding is one in which the surfaces of two metal layers are bonded to each other through a conductive bonding layer composed of metal nanoparticles.
The process of forming the conductive bond is as follows:
Using a metal oxide nanoparticle dispersion liquid in which metal oxide nanoparticles each having a coating molecule layer on the surface of the nanoparticles are dispersed in an organic solvent on the surfaces of the two metal layers. And forming a coating layer of the metal oxide nanoparticle dispersion liquid;
A step of evaporating an organic solvent contained in the coating layer of the metal oxide nanoparticle dispersion to form a dried coating layer;
The dried coating layers formed on the metal surfaces constituting the two metal layers are each subjected to treatment at a heating temperature of 150 ° C. or less in a high-frequency plasma atmosphere in the presence of a reducing gas, and The coating material molecular layer provided on the surface of the particles is removed, and the metal oxide nanoparticles are reduced to produce metal nanoparticles, and then the metal nanoparticles are fused together to form the metal nanoparticles. Forming a conductive bonding layer comprising: a metal surface constituting each metal layer;
Heat treatment is performed at a temperature selected from the range of 100 ° C. to 200 ° C. while superimposing the surfaces of the conductive bonding layer composed of the metal nanoparticles on each other, applying pressure, and pressing the surfaces of both together. Applying and forming an intermetallic bond between the surfaces of the two conductive bonding layers,
The pressure is selected in the range of ^{0.2 × 10 6 Pa~10 × 10 6} Pa,
Metal oxide nanoparticles having a coating molecular layer on the surface of the nanoparticles,
For metal oxide nanoparticles with an average particle size selected in the range of 1-100 nm,
The group capable of coordinative bonding with the metal element contained in the metal nanoparticle includes a nitrogen, oxygen, or sulfur atom, and has a group capable of coordinative bonding by a lone electron pair possessed by these atoms. A method for forming a conductive bond, which is a nanoparticle formed by coating one or more organic compounds as a coating agent molecule on the surface of the metal nanoparticle. The two metal layers are
11. A combination of a metal wiring layer formed on the surface of a wiring board and a metal electrode layer of an electronic component bonded on the metal wiring layer of the wiring board. A method for forming a conductive joint according to claim 1.