JP2008221290A - Bonded body and bonding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a joined body and a semiconductor device which use a joining material substantially not containing Pb and can maintain a good mechanical strength even under a high temperature condition.
SOLUTION: The present invention comprises Sn and a metal having a higher melting point than Sn, and uses two bonding agents having a solidus temperature of 400 ° C. or higher, which are composed of intermetallic compounds or heat-resistant alloys of these components. It is the joined body which joined the member.
[Selection figure] None

Description

The present invention particularly relates to a joined body suitably used for joining parts of an electronic device and a joining method.

  Conventionally, solder bonding has been carried out in a very wide range as a method for electrical connection in electrical and electronic equipment, and since it is extremely suitable for practical use in this solder joint, Sn-Pb-based materials are used. Crystalline solder has been frequently used. However, since Pb contained in Sn—Pb eutectic solder is harmful to the human body, development of so-called non-Pn solder that does not contain Pb is urgently required.

  On the other hand, among the current semiconductor devices, for example, power device bonding materials are mainly low-temperature solder (Sn—Pb eutectic solder) having a melting point of 183 ° C. and high-temperature solder (Pb—) having a melting point of about 300 ° C. 5Sn solder) is widely used, and is used properly according to the process.

  Among these, for low-temperature solders, those centered on Sn-Ag-Cu alloys have reached the stage of practical application, and in the next few years, many set manufacturers will replace non-Pb eutectic solders. It is scheduled to be completed.

  However, for high-temperature solder, that is, a bonding material that forms a joint that maintains good mechanical strength even at a high temperature of, for example, 260 ° C., an Au-based alloy containing Au as a main component other than a high Pb-containing material is used. Although it is mentioned, since the noble metal Au is used, the material price is significantly increased, so that it is difficult to use for general purposes. In addition, metal alloys mainly composed of metal materials other than Pb and Au have not yet been put into practical use as high-temperature solders.

  Up to now, Zn-based alloys have been cited as candidates as one of the bonding materials that form a bonding portion that has a metal material other than Pb and Au as a main component and maintains good mechanical strength even at a high temperature of 260 ° C. (See Patent Documents 1 and 2). Since this bonding material is a metal material made of Zn element, it is inexpensive and is a bonding material that is environmentally friendly. However, since it has poor wettability with Cu and is hard as a bonding material, it has not been put into practical use.

Further, an attempt has been made to apply a high temperature solder to a Sn-based alloy containing Sn as a main component (see Patent Documents 3 and 4), but in the case of a Sn-based alloy, the bondability and hardness with a material to be bonded such as Cu. However, it is difficult to satisfy the heat resistance as a high-temperature solder because liquefaction starts at a low melting point.

JP 2004-237357 A JP 2001-121285 A JP 2003-364363 A JP 2001-284792 A

An object of the present invention is to provide a bonding method and a bonded body that can form a bonded portion that uses a material that does not substantially contain Pb and Au and that still maintains good mechanical strength even under high temperature conditions. Is.

1st this invention is the joined body which consists of a 1st to-be-joined member, a 2nd to-be-joined member, and the joining layer interposed between these to-be-joined members,
The bonding layer includes Sn and a metal material having a melting point higher than Sn;
In the bonded layer, the bonded layer has a first layer in which the amount of Sn is 20% by mass or more and 50% by mass or less.

  The bonding layer of the first aspect of the present invention preferably includes an intermetallic compound composed of a plurality of layers having different mass ratios and Sn and a metal material having a melting point higher than Sn. The bonding layer is preferably made of a material having a solidus temperature of 400 ° C. or higher. Moreover, it is preferable that a 1st to-be-joined member is Cu. The bonding layer is preferably an intermetallic compound of Cu and Sn. The first layer is an intermetallic compound of Cu and Sn having a mass ratio of Sn of 20% to 50%, and a metal of Ag and Sn having a mass ratio of Sn of 10% to 35%. It is preferable to further include a second layer that is an intermetallic compound.

The second aspect of the present invention is a step of providing an Sn film on the surface of the first member to be joined including a metal material having a melting point higher than Sn;
The bonding method is characterized in that the second member to be bonded is brought into close contact with the surface of the Sn film and heated at a temperature of 300 ° C. or higher and 450 ° C. or lower while being pressurized.

The third aspect of the present invention is a process of providing at least one layer each of an Sn film and a metal material film having a melting point higher than Sn on the surface of the first bonded member;
The bonding method is characterized in that the second member to be bonded is brought into close contact with the surface of the film of the metal material applied in the step and heated at a temperature of 300 ° C. or higher and 450 ° C. or lower while being pressurized.

ADVANTAGE OF THE INVENTION According to this invention, the joining method and joined body which can form the junction part which uses the material which does not contain Pb and Au substantially, and hold | maintains favorable mechanical strength also in high temperature conditions can be provided. .

[First embodiment: joined body]
In the joined body of this embodiment, Sn having a melting point of 232 ° C. and a metal element having a higher melting point are reacted or alloyed to form a high melting point intermetallic compound or a high melting point alloy. This is made by paying attention to the fact that a bonded body having excellent heat resistance can be obtained by bonding.
That is, as shown in FIG. 1 which is a schematic cross-sectional view of a joined body, the joined body 10 of the present embodiment includes a first and a second two members to be joined 11, 12 and a joint interposed therebetween. It is a joined body composed of the layer 13.
The bonding layer 13 includes three layers 13a, 13b, and 13c, and each is made of an intermetallic compound. An intermetallic compound comprising a metal component in the member to be bonded 11 and a metal component of a bonding layer material (hereinafter referred to as a bonding layer material) disposed between the first and second bonded members at the time of bonding; Is a metal compound composed of a metal component in the member to be bonded 12 and a metal component of the material for the bonding layer. 13b indicates an intermetallic compound composed of the metal component of the member to be bonded 11 and the member 12 to be bonded and the metal component of the bonding layer material.
In the bonding layer according to the present embodiment, at least one of the three layers 13a, 13b, and 13c in the drawing may be made of an intermetallic compound, and the metal components in the members to be bonded 11 and 12 and the bonding layer are used. An alloy composed of a metal component of the material may be included.
In the joined body of the present embodiment, the joining layer 13 is made of Sn and a metal material having a melting point higher than Sn, and the amount of Sn in the joining layer is in the range of 20 mass% or more and 50 mass% or less. It has a certain first layer.

Specifically, the joined body of the present embodiment is a joined body formed by joining a circuit board and an electronic component mounted thereon, or a lead frame and a semiconductor element mounted thereon. is there. The joined body may be incorporated into a part of the mounting board of the electronic device. In addition, since this bonded body has excellent heat resistance, it is particularly suitable in the field of electronic equipment products used in high-temperature environments, or in the field of products that employ a process for performing reflow solder bonding after the bonding is formed. Demonstrate the effect.
The bonded body of the present embodiment has sufficient bonding strength without substantially using harmful Pb and expensive Au, and can maintain mechanical strength even under high temperature conditions, and has high heat resistance. .

(Members to be joined)
As a material of a to-be-joined member, if it is a material which has heat resistance, it will not be restrict | limited at all and can be used. A material having an affinity for Sn is preferable, but even a material having no affinity can be used by forming a metallized layer on the surface thereof as described later.

Specifically, the material of the member to be joined is preferably Cu, Au, Ni, Ag, Pd, Pt, Al, Ge, Be, Nb, Mn, or an alloy thereof.
Furthermore, materials having a low affinity with Sn but suitable for use by forming a metallized layer include, but are not limited to, Si, Fe—Ni alloys, and the like.

The metallized layer refers to a metal film formed on the surface of a material to be bonded to improve the affinity with the material for the bonding layer. For example, Si of a semiconductor element is inferior in affinity with Sn, and it is difficult to perform bonding, but the surface of Si is covered with a material having affinity with Sn, such as Cu, Ti, Ni, Au, etc. By doing so, it becomes possible to perform bonding. Such a thin film material is well known in the semiconductor technical field as a metallization technique, and such a technique can also be employed in this embodiment.
For the formation of this metallized layer, means well known as a thin film forming technique such as sputtering, vacuum deposition, chemical plating, ion plating, etc. can be employed.

  In addition, although different from the metallized layer for improving the affinity with Sn, a layer of Au or the like may be formed on the surface of Cu or the like in order to improve electrical characteristics. Even in such a case, if the Au layer is about 10 μm or less, it can be used without any problem.

(Bonding layer)
The bonding layer of the present embodiment is composed of Sn (first metal component) and a metal material (second metal component) having a melting point higher than Sn, and these metal components are refractory metals. It is preferable to form an intermetallic compound or a high melting point alloy, and the bonding layer 13 material is preferably made of a material having a solidus temperature of 400 ° C. or higher. When the solidus temperature is lower than 400 ° C., when this joined body is applied to a heat treatment process such as a solder reflow process, there is a disadvantage that the high-temperature strength of the joint is not maintained. In addition, there is a disadvantage that it is inappropriate to apply to a device used in a high temperature environment.

The second metal component can be used as long as it is a metal material having a melting point higher than that of Sn. Preferably, a material that reacts with Sn by heating to form a high melting point intermetallic compound or a high melting point alloy is used. It is preferable to do. More preferably, it is a metal material that forms a high melting point intermetallic compound with Sn.
Specific examples of the refractory metal element as the second metal component include Cu, Ag, Ni, Pd, Au, and Co, and at least one of them can be used.

When reacting with Sn using Cu as the second metal component, intermetallic such as η phase (Cu ₆ Sn ₅ ), ε phase (Cu ₃ Sn) or δ phase (Cu _40.5 Sn ₁₁ ) A compound is formed. The η phase has a melting point of 415 ° C., and the ε phase has a melting point of 676 ° C., and the heat resistance after bonding is preferably within a sufficient temperature range.
In such an intermetallic compound, the Sn mass ratio is in the range of 20% by mass to 70% by mass. If Sn is less than 20% by mass or exceeds 70% by mass, an intermetallic compound may not be formed, which is not preferable.
In addition, when the Sn mass ratio is low, diffusion of the refractory metal element used as the second metal component is promoted, resulting in a bonding layer with higher strength. Therefore, the mass ratio of Sn is more preferably 50% by mass or less.

In addition, when Ag is used as the second metal component, an intermetallic compound such as Ag ₃ Sn is formed. In order to form such an intermetallic compound, the Sn mass ratio is preferably 10% to 35%.

Further, when Ag and Cu are used as the second metal component, an intermetallic compound having a composition such as Ag ₃ Sn, η phase (Cu ₆ Sn ₅ ), ε phase (Cu ₃ Sn) or δ An intermetallic compound having a composition such as a phase (Cu _40.5 Sn ₁₁ ) is formed to provide a heat-resistant bonding material.

In the intermetallic compound, a part of the constituent elements may be substituted with other elements. For example, when Ag is substituted for Ag ₃ Sn, Ag is substituted for (Ag, Cu) ₃ Sn, and when Ag is substituted for Cu ₃ Sn, Ag is substituted for (Cu, Ag) ₃ Sn, Cu _40.5 Sn ₁₁ In this case, a crystal structure such as (Cu, Ag) _40.5 Sn ₁₁ is obtained.

  The bonding layer is preferably sandwiched between the first and second members to be bonded and is divided into a plurality of layers having different mass ratios.

That is, when one kind of metal element is used as the second metal component, a layer formed by reaction or alloying of the first and second metal components exists in the central portion of the bonding layer, It is preferable that the layer in the surface layer direction includes a layer containing a large amount of a metal component that permeates through the member to be bonded by diffusion in addition to the composition constituting the central portion.
For example, when a Sn layer is laminated between two Cu layers and reacted, the reaction starts at the interface between the Cu layer and the Sn layer, and Cu diffuses from the Cu layer to the Sn layer and reacts to form an intermetallic compound. In the central part, an intermetallic compound having a composition richer in Sn is formed, and in the surface layer part, an intermetallic compound having a composition rich in Cu is formed.

  In addition, when the reaction is performed using a plurality of metal elements as the second metal component, for example, when Ag and Cu are used, the Ag component is rich in the (Ag, Cu) Sn layer, and the Cu is rich. A (Cu, Ag) Sn layer can be formed.

By forming the bonding layer as a layer composed of a plurality of layers, the time required for complete formation of an intermetallic compound in the plurality of layers is reduced as compared with the case of forming a single layer. Is advantageous in that it is unlikely to remain.
This reaction form forms an intermetallic compound having a high melting point and contributes to an improvement in heat resistance.

  The bonding layer is preferably a thin film, and the thickness is preferably in the range of 1 to 20 μm. If this thickness exceeds 20 μm, it takes a long time to form an intermetallic compound, resulting in a problem that the bonding efficiency is deteriorated. If this thickness is less than 1 μm, the wettability with the object to be bonded decreases. This is not preferable.

  In the present embodiment, by adopting the above configuration, the bonding layer is composed of a metal intermetallic compound or a high melting point alloy having a high melting point, and when soldering is further performed by reflow after the bonding is formed. Since it has a melting point higher than the reflow temperature (usually around 250 ° C.), it exhibits the effect that no thermal deterioration after reflow is observed. In addition, in the electronic device adopting this bonding, a device having high temperature reliability can be realized without causing deterioration of the bonding even when used in a high temperature environment.

[Second Embodiment: Joining Method]
In the bonding method of the present embodiment, a bonding layer material is disposed between two members to be bonded, and the bonding layer material is reacted or alloyed by heating to form a heat-resistant bonding layer. Bonding is performed, and Sn (first metal component) and a metal material having a higher melting point (second metal component) are used as the bonding layer material.
In this joining method, the metal element contained in the member to be joined can be used as the second metal component. That is, a first metal component is interposed between two members to be bonded, and a bonding layer is formed by reacting or alloying between the metal element constituting the member to be bonded and the first metal component. It is.
According to this method, the film | membrane only of a 1st metal component can be provided to a to-be-joined member, and the film | membrane provision process of a 2nd metal component can be skipped. Further, it is expected that the bonding between the member to be bonded and the bonding layer becomes strong.

Hereinafter, the bonding method according to the present embodiment will be described in more detail.
In the bonding method of the present embodiment, the step of applying the Sn film to the surface of the first member to be bonded, the second member to be bonded is brought into close contact with the surface of the Sn film, and heated at 250 ° C. or higher and 450 ° C. or lower. It is the joining method which has the process of making it closely_contact | adhere, and joining. The bonding temperature is more preferably 300 ° C. or higher and 400 ° C. or lower. When the bonding temperature is lower than this, the bonding layer material does not sufficiently react or alloy, and the heat resistance is not improved sufficiently. On the other hand, when the bonding temperature exceeds the above range, there is a large possibility that the member to be bonded is thermally damaged, which is not preferable.

In the bonding step in this bonding method, the bonding layer material formed on the surface of the first member to be bonded may be placed with a first metal component foil, or the first metal component may be sputtered. Alternatively, it may be applied using a physical thin film forming technique such as vacuum deposition, ion plating, or electron beam deposition. Furthermore, a chemical plating method can also be employed.
In this method, the amount of the second metal component that reacts or alloys with Sn contained in the first and second members to be bonded needs to be larger than the amount of Sn. When the amount of Sn is smaller than the amount of the second metal component, unreacted Sn remains, and heat resistance may be lowered, which is not preferable.

In the joining step, it is more preferable that the heating time is 1 second to 5 minutes. If the heating time is shorter than this, the intermetallic compound or alloy is not sufficiently formed, and the heat resistance is not sufficient. On the other hand, even if heating exceeds the above range, the effect of improving heat resistance commensurate with the increase in heating time cannot be expected, which is uneconomical.
The bonding step may be performed in an air atmosphere, but when a bonding material including a metal that is easily oxidized is used, it is preferable to perform heating in a non-oxidizing atmosphere such as nitrogen. Furthermore, it is more preferable to perform heating in a reducing atmosphere containing hydrogen.

  The thickness of the bonding layer is preferably in the range of 1 μm or more and 50 μm or less. In the case of stratification over a plurality of layers, the total film thickness is preferably in the above range. When the bonding layer is thinner than 1 μm, it is difficult to ensure good bonding properties. When the bonding layer is 50 μm or more, manufacturing efficiency may be hindered when the bonding layer is formed by a physical film formation method. This is not preferable.

  According to the bonding method of the present embodiment, since a bonding layer having a heat resistance of 270 ° C. or higher is formed, the heat resistance of the bonding layer can be maintained even under a high temperature condition of 270 ° C. It can fully meet the demand for heat resistance at 250 ° C., which is required as a material. In addition, in the bonding layer material, the constituent elements of the first member to be bonded or the second member to be bonded are dissolved in the bonding layer, or the bonding material constituting elements in the bonding layer and each bonded portion. An intermetallic compound phase or the like composed of the layer material constituent elements may be generated. As a result, a bonded body with good mechanical strength can be obtained in a short time even under high temperature conditions.

  The joined body and joining method according to the present embodiment may be used in any field where solder joining can be performed. In particular, an electronic equipment component and a semiconductor device that are placed under high-temperature conditions during a manufacturing process or product use. In particular, it is suitably used for joining parts in power semiconductor devices. In particular, it is particularly preferably used for joining a semiconductor element and a lead frame.

[Third Embodiment: Modification of Joining Method]
In the joining method of the second embodiment, the example in which the metal itself constituting the member to be joined is used as the second metal component is shown. However, in the present embodiment, the first metal component and the second metal component are used. This is an example in which each metal component is applied as a film to a member to be joined.
That is, in the bonding method of the present embodiment, a step of applying at least one layer each of an Sn film and a metal material film having a melting point higher than Sn to the surface of the first member to be bonded is applied in the above step. The bonding method is characterized in that the second member to be bonded is brought into close contact with the surface of the metal material film and heated at a temperature of 250 ° C. to 450 ° C. while pressing.

  In the joining step in this joining method, the joining layer material formed on the surface of the first member to be joined may be mounted with a foil of the first metal component and the second metal component, respectively. The layer material film may be applied using a physical thin film forming technique such as sputtering, vacuum vapor deposition, ion plating, or electron beam vapor deposition. Furthermore, a chemical plating method may be employed to provide the film.

In addition, the first metal component and the second metal component, which are the bonding layer materials of the present embodiment, may be formed into a thin film at the same time, or each may be sequentially laminated one by one or a plurality of layers. In the case of sequentially depositing each component, a single element layer may be divided into a plurality of layers. Specifically, in the case where the A metal and the B metal are formed, the film can be divided into a plurality of layers, such as the A layer, the B layer, the A layer, and the B layer. Such a film forming method is preferable because the reaction or alloying of the A metal and the B metal proceeds promptly.
In the case where a plurality of metal elements are used as the second metal component, the respective elements and the first metal component may be formed individually or simultaneously. Alternatively, a single element layer may be formed in a plurality of times.

  The thickness of the thin film bonding material is preferably in the range of 1 μm or more and 50 μm or less. When thinning over a plurality of layers, the total film thickness is preferably in the above range. When the metal layer is thinner than 1 μm, it is difficult to ensure good bonding properties. When the metal layer is 50 μm or more, when the bonding layer is formed by a physical film forming method, the production efficiency may be hindered. This is not preferable.

In the bonding step, the heating time may be 1 second to 5 minutes.
The bonding step may be performed in an air atmosphere, but when a bonding material containing a metal that is easily oxidized is used, it is preferable to perform heating in a non-oxidizing atmosphere such as nitrogen. Furthermore, it is more preferable to perform heating in a reducing atmosphere containing hydrogen.

In the above-described embodiment, the example in which the bonding layer material is formed on one surface of the two members to be bonded has been described. However, the bonding layer material is used as the surface of both the first bonded member and the second bonded member. You may form in.
In this case, the two bonding layer materials may be layers having the same composition, or layers having different compositions. The solder joint of this embodiment can be formed by adjusting the composition of each layer so that the joint layer material after the final solder joint has the composition of the joint layer of the present embodiment. it can.
Moreover, the thickness of the thin film formed on each substrate surface can be set so that the total amount thereof is in the range of 1 μm or more and 50 μm or less.

[Fourth Embodiment: Another Modification of Joining Method]
In the bonding method of this embodiment, at least one of the first member to be bonded and the second member to be bonded is formed by forming a metallized layer on the surface of a base material made of metal, ceramics, or semiconductor. is there. This method is suitable when a material that is not suitable for soldering is used as a member to be joined.

  As described above, the first member or the second member is composed of a base material made of a material such as metal, ceramics, or semiconductor, and a metallized layer formed on the surface thereof. The metallized layer is preferably a material selected from the group consisting of Cu, Au, Ag, Ni, Pd, Co, Ti, Pt, Al or a metal alloy using these metal materials, depending on the application. And can be selected without any particular limitation. This metallized layer may be a single material layer, or may be composed of a plurality of metallized layers made of different materials. As means for metallizing on the surface of the base material, physical or chemical film formation methods such as vapor deposition, sputtering, plating treatment, and electron beam treatment can be employed.

  The thickness (average thickness) of the metallized layer is not particularly limited, but is preferably in the range of 0.1 μm or more and 500 μm or less. If this thickness is 0.1 μm or less, sufficient solder joint strength cannot be obtained. In addition, forming a metallized layer of 500 μm or more requires a long time to form a thin film and is not practical.

  In the present embodiment, a bonding layer can be formed on the metallized layer surface by applying the film forming method, and bonding can be performed in the same manner as in the method in the first embodiment. Further, a bonding material layer can be formed on the surface of the bonding member not provided with the metallized layer, and bonded to the base material provided with the metallized layer.

[Fifth Embodiment: Semiconductor Device Applying the Joining Technique]
The solder joining technique can be applied to the manufacture of semiconductor devices.

Hereinafter, a semiconductor device to which this embodiment mode can be applied will be described with reference to the drawings.
FIG. 6 is a cross-sectional view showing an example of a semiconductor device to which the bonding technique of this embodiment is applied. The semiconductor device of this embodiment includes a lead frame 62 having a lead portion 65 serving as an external terminal, a semiconductor element 64 disposed on the surface of the lead frame 62, and both between the lead frame 62 and the semiconductor element 64. It has the joining layer 63 which has joined, and the sealing resin 61 which surrounds these.
The lead frame 62 may be subjected to, for example, Ag plating or Cu plating on the surface of a low thermal expansion material such as 42 alloy or a high thermal expansion material such as Cu. Examples of the semiconductor device of this embodiment include a diode, a transistor, a capacitor, and a thyristor.

  In the semiconductor device of the present embodiment, the surface of the semiconductor element is made of a material selected from the group consisting of Au, Ni, Ag, Cu, Pd, Pt and Al, or a metal alloy using these metal materials. The surface of the semiconductor element metallized with the metal thin film and the metal lead frame on which the semiconductor element is placed are composed of Sn and a metal element having a higher melting point. It joins by.

  In the semiconductor device, the metal frame may be made of Au, Ni, Ag, Cu, Pd, Pt, and Al, or a material selected from the group consisting of metal alloys using these metal materials. The surface of any metal matrix is metallized with a metal thin film using a material selected from the group consisting of Au, Ni, Ag, Cu, Pd, Pt and Al, or a metal alloy using these metal materials. May be.

  In the present embodiment, the metal material having a melting point equal to or higher than Sn constituting the bonding layer material includes Ag, Cu, Ni, Pd, Pt, and Al, or a group of metal alloys using these metal materials. It is preferred to use the material selected. Even if a trace amount of other metal elements is added, the effect of the present invention does not change.

According to the method of manufacturing a semiconductor device and the semiconductor device of the present embodiment, the semiconductor element and the lead can be used even when exposed to high temperature conditions without using a high Pb-containing bonding layer material that is harmful in the manufacturing process of the semiconductor device. The bonding strength between the frames is maintained, and a highly reliable semiconductor device can be provided in a short time.

  Hereinafter, the present invention will be described in detail by way of examples.

(Example 1)
A pure Sn foil of 10 mm × 10 mm thickness 0.1 mm is placed on the surface of a 20 mm × 20 mm, 0.3 mm thick Cu plate, rosin activation flux is applied, and a Cu plate of the above size is applied thereon. Placed. This was heated at 300 ° C. for 5 minutes for bonding.
As a result, a plurality of intermetallic compound layers made of SnCu were formed between the Cu plates. As a result of elemental analysis, it was found that the central layer was composed of η phase, and the surface layer side layers located on both sides of the central layer were composed of ε phase.
This bonding layer had heat resistance that withstands heating at 400 ° C.

(Example 2)
Ti, Ni, and Au thin films were formed in this order on the surface of a 600 μm thick silicon wafer by sputtering. Thereafter, Sn, Ag, Sn, Cu, and Sn were vapor-deposited in this order on the surface to form a thin film. These film thicknesses are as shown in Table 1 below.

The formed silicon wafer was cut into a size of 2.5 × 3.0 mm, and was closely adhered to a Cu plate treated with rosin activation flux, and was heated and bonded at 300 ° C. for 30 seconds.
FIG. 4A shows a cross-sectional SEM photograph of the joined body thus obtained and an elemental analysis result of the joining layer by EDX. The elemental analysis results are shown in mass%. Moreover, the die-joint test was done by the following method on 25 degreeC, 250 degreeC, and 270 degreeC temperature conditions for the obtained joined body. The result is shown in FIG. As is clear from the results of FIG. 2, it was found that for each sample, a shear strength exceeding 10 MPa was obtained, sufficient shear strength was obtained even under high temperature conditions, and heat resistance was obtained.

(Die share test)
A test piece in which the semiconductor element 33 is bonded to the surface of the lead frame 31 via the bonding layer 32 in the high-temperature shear test performed using the test apparatus shown in FIG. Apply a force in the direction of the arrow using and measure the strength at break.

(Example 3)
The semiconductor element and the lead frame in the power semiconductor device were joined. A semiconductor element having a size of 2.5 × 3.0 × 0.6 mm was used. In this power semiconductor module, a metallized layer made of 0.1 μm thick Au was formed by vapor-depositing Au as a first member to be bonded on a 10 mm square Si semiconductor element. Further, a 5 μm-thick bonding layer material containing substantially 25% Sn and 22% Cu in terms of the mass composition ratio and the balance being made of Ag was formed on the metallized layer surface by vapor deposition.
A lead frame made of Cu was used as the second member to be joined.
Furthermore, it laminated | stacked so that the said material for joining layers and Cu might contact | connect, and then it heated and joined. The heating was performed on a hot plate in a forming gas (nitrogen + hydrogen) atmosphere having an oxygen concentration of 100 ppm or less. The heating conditions were 350 ° C. and 5 seconds.

  FIG. 4B shows a cross-sectional SEM photograph of the joined body thus obtained and an elemental analysis result of the joining layer by EDX. The elemental analysis results are shown in mass%. When the cross section of the bonded interface after bonding was observed with an SEM, no voids were observed and good bonding properties were exhibited.

  Finally, the joined lead frame and the semiconductor element were sealed with a resin to obtain a power semiconductor device having heat resistance of 260 ° C.

Example 4
The semiconductor element and the lead frame in the power semiconductor device were joined. A semiconductor element having a size of 2.5 × 3.0 × 0.6 mm was used. In this power semiconductor module, a metallized layer made of 0.1 μm thick Au was formed by vapor-depositing Au as a first member to be bonded on a 10 mm square Si semiconductor element. Further, a 10 μm-thick bonding layer material containing substantially 25% Sn and 22% Cu in terms of mass composition ratio and the balance being made of Ag was formed on the metallized layer surface by vapor deposition.
Further, as the second member to be joined, a 10 μm metallized layer made of Cu was formed by electroless plating on the surface of a lead frame made of 42 alloy.
Further, the bonding layer material and the metallized layer were laminated so as to be in contact with each other, and then heated to perform bonding. The heating was performed on a hot plate in a forming gas (nitrogen + hydrogen) atmosphere having an oxygen concentration of 100 ppm or less. The heating conditions were 400 ° C. and 5 seconds.

  FIG. 4C shows a cross-sectional SEM photograph of the joined body thus obtained and an elemental analysis result of the joining layer by EDX. The elemental analysis results are shown in mass%. When the cross section of the bonded interface after bonding was observed with an SEM, no voids were observed and good bonding properties were exhibited.

  Finally, the joined lead frame and the semiconductor element were sealed with resin to obtain a power semiconductor device having heat resistance of 270 ° C.

(Example 5)
As the bonding layer material, substantially the same as in Example 3 except that a 5 μm-thick bonding layer material containing 35% Sn and 13% Cu with the balance being made of Ag was used. Then, the power semiconductor and the lead frame were joined.
When the cross section of the bonded interface after bonding was observed with an SEM, the generation of voids was not observed, indicating good bondability.

(Example 6)
As the bonding layer material, substantially the same mass composition ratio as that of Example 3 except that a 5 μm thick bonding layer material containing 40% Sn and 13% Cu and the balance being Ag is used. Then, the power semiconductor and the lead frame were joined.
When the cross section of the bonded interface after bonding was observed with an SEM, the generation of voids was not observed, indicating good bondability.

(Example 7)
In this example, a power semiconductor device was obtained in the same manner as in Example 3 except that a metallized layer made of Ag was formed on a lead frame made of 42 alloy as the second member to be joined.

  From the SEM observation of the cross section of the bonded interface after bonding, no void was generated and good bonding property was exhibited, and the bonding property at high temperature was also good.

  Finally, the joined lead frame and the semiconductor element were sealed with resin to obtain a power semiconductor device having heat resistance of 270 ° C.

(Reference example)
In this example, further vacuum deposition was performed on the surface of the 0.1 μm thick Au layer and the 10 μm thick Sn layer formed by vacuum deposition on the semiconductor element 13 of 2.5 × 3.0 × 0.6 mm size. Thus, a power semiconductor device was obtained in the same manner as in Example 3 except that a 10 μm thick Zn—Sn bonding layer was formed. The Zn—Sn bonding layer formed by vapor deposition uses a Zn—Sn based alloy in which Sn is 50.0% by mass and the remainder is Zn. This bonding layer was mounted on a Sn layer formed on a lead frame made of Cu, and heated on a hot plate in a forming gas (nitrogen + hydrogen) atmosphere having an oxygen concentration of 100 ppm. The heating conditions were 400 ° C. and 5 seconds.

  When the cross section of the bonded interface after bonding was observed by SEM, no voids were generated and good bonding properties were exhibited, and bonding properties at high temperatures were also good.

  Finally, the joined lead frame and the semiconductor element were sealed with resin to obtain a power semiconductor device.

(Examples 8-13 and Comparative Examples 1-3)
In Example 8, as a first member to be bonded, a member to be bonded which is Cu-plated to 42 alloy is used. In Examples 9 to 13, Cu is used as a member to be bonded, and a material for an AgCuSn-based bonding layer is shown in Table 2. Each element was formed into a film by vapor deposition so as to have a ratio. The heating was evaluated at 450 ° C. in the case of Example 7, 400 ° C. in the case of Examples 9 to 13, and the bondability was evaluated under an N ₂ atmosphere.
On the other hand, Comparative Examples 1 and 2 used 42 alloy as the material to be joined, and deposited each element by vapor deposition in the same manner as in Example 8 so that the ratios shown in Table 2 were obtained. Each element was formed by vapor deposition and evaluated so as to contain 75% Sn and 13% Cu substantially by mass composition ratio using Cu, and the balance being Ag.
Table 2 shows the results. The evaluation was performed based on the bondability of each bonding layer and the bonding strength at 265 ° C. As in the case of Example 3, the bonding interface was observed with an SEM, and “Good” indicates that the bonding is good, “V” indicates that a void is generated on the bonding interface, and “X” indicates that bonding is not performed. Moreover, the measurement of joining strength produced the test body to which the semiconductor element was joined similarly to Example 2, and measured the shear strength in 260 degreeC of each test body.
This measurement was performed on each test piece for 10 samples each at room temperature and at 275 ° C. heating.
FIG. 5 is an example of the shear strength test result for the sample provided by the embodiment of the present application, and the shear strength at room temperature and 275 ° C. is measured. In each example, 3 to 5 samples were prepared, the shear strength of each sample was measured, and the average value was calculated.
As can be seen from FIG. 5, in each result, even when heated at 275 ° C., the shear strength was comparable to that at room temperature, indicating that it had heat resistance.
The specimens that were not joined and for which the shear strength could not be measured were “-”, and the specimens that could be measured showed the strength at break (MPa).
While Examples 8 to 13 of the present invention were all sufficiently joined, Comparative Example 1 was not joined. In addition, Examples 8 to 13 all had a bonding strength greater than 13.0 MPa and showed a sufficient bonding strength, whereas Comparative Examples 2 and 3 had a bonding strength at 265 ° C. of 13 MPa or less (in Table 2, “×”). It was not practically sufficient.

It is a schematic sectional drawing of the conjugate | zygote of embodiment of this invention. It is sectional drawing of the graph which shows the shear strength of the Example of this invention. It is a conceptual diagram of the apparatus which measures the shear strength of a joined body. It is a figure which shows the effect of the Example of this invention. It is a graph which shows the result of the Example of this invention. It is a schematic sectional drawing which shows the example of the semiconductor device using the conjugate | zygote of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Bonded body 11 ... 1st to-be-joined member 12 ... 2nd to-be-joined member 13 ... Joining layer

Claims (8)

A joined body comprising a first joined member, a second joined member, and a joining layer interposed between these joined members,
The bonding layer includes Sn and a metal material having a melting point higher than Sn;
A joined body comprising a first layer having an amount of Sn of 20% by mass or more and 70% by mass or less in the joining layer.   The joined body according to claim 1, wherein the joining layer includes a second layer having a mass ratio different from that of the first layer.   The joined body according to claim 1, wherein the joining layer is made of a material having a solidus temperature of 400 ° C. or more.   4. The joined body according to claim 1, wherein the joining layer is an intermetallic compound of Cu and Sn. The first layer in the bonding layer includes an intermetallic compound of Cu and Sn having a Sn mass ratio of 20% to 50%,
The joined body according to any one of claims 1 to 5, wherein the second layer includes an intermetallic compound of Ag and Sn having a mass ratio of Sn of 10% to 35%.   The joined body according to claim 1, wherein the first member to be joined is Cu. A step of providing a Sn film on the surface of the first member to be bonded containing a metal material having a melting point higher than Sn;
A bonding method characterized in that a second member to be bonded is brought into close contact with the surface of the Sn film and heated at a temperature of 250 ° C. or higher and 450 ° C. or lower while being pressurized. A step of providing at least one layer each of an Sn film and a metal material film having a melting point higher than Sn on the surface of the first bonded member;
A bonding method, wherein the second member to be bonded is brought into close contact with the surface of the film of the metal material applied in the step and heated at a temperature of 250 ° C. to 450 ° C. while being pressurized.