JP2012250240A - Metal filler, solder paste, and connected structure - Google Patents

Abstract

Even when the Cu surface of the substrate is treated with an organic film, it can be melt-bonded under normal lead-free solder reflow heat treatment conditions, and after bonding, it has excellent heat resistance and good bonding strength at room temperature. Providing a metal filler.
A metal filler including a mixture of first metal particles and second metal particles as a main component, wherein the mixture includes second metal particles with respect to 100 parts by mass of the first metal particles. 55 to 400 parts by mass, the first metal particles are Cu particles or Cu alloy particles, the second metal particles contain Ag and Sn, and the Ag content is 0.3 to Metal filler which is 4 mass% Sn alloy particle.
[Selection figure] None

Description

  The present invention relates to a metal filler, a solder paste, a connection structure, and the like.

The trend toward miniaturization, weight reduction, and high functionality of electronic devices typified by mobile phones is remarkable, and following this trend, high-density packaging technology continues to make rapid progress.
Various mounting techniques have been developed in order to incorporate components in a substrate, package a plurality of LSIs in one package, and effectively use a limited volume. On the other hand, as the density increases, the solder joints of components built into the board or package are more frequently subjected to heat treatment in the subsequent process, and the solder re-use that occurs in the gap between the component and the sealing resin occurs. The short problem due to melting has become apparent.
Therefore, there is a demand for the development of a lead-free solder material that does not melt even if it is subjected to multiple heat treatments in the subsequent process for connecting components incorporated in the substrate or package.

The present inventors have proposed a lead-free solder material that can be melt-bonded under reflow heat treatment conditions for lead-free solder and that does not melt under the same heat-treatment conditions after bonding (see Patent Document 1 below).
The reflow heat treatment conditions for lead-free solder are typical Sn-3.0Ag-0.5Cu (melting point: 217 ° C), and are general reflow heat treatment conditions for solder connection, and have a peak temperature of 240-260 ° C. It is a range.

The conductive filler of the solder material is composed of a mixture of first metal particles mainly composed of Cu and second metal particles that melt in the reflow heat treatment, and forms a new stable alloy phase in the reflow heat treatment. In the reflow heat treatment again, it has a feature that it does not melt.
The solder material has been proposed for use as a solder paste in a solder connection portion of a component built-in a component built-in wiring board in which a component is incorporated in a substrate or a package.

On the other hand, a solder material having a conductive filler as a mixture of Cu particles and Sn particles having an average particle diameter of 30 μm has been proposed (refer to Patent Document 2 below).
The solder material is characterized in that it is connected by a heat treatment to a CuSn compound containing Cu6Sn5 and a connecting portion having Cu particles, and the Cu particles are connected by the CuSn compound.

  By the way, in recent years, with the development of the component-embedded substrate, the substrate-embedded technology has been improved. In the component built-in wiring board, when an inner layer substrate having a copper foil circuit pattern on the surface is laminated and pressed with another inner layer substrate or copper foil with the prepreg in between, the adhesion between the copper foil surface of the inner layer substrate and the prepreg is improved. In order to improve the surface, a surface treatment called an organic film treatment for roughening the surface of the copper foil and further improving the adhesion to the resin on the roughened surface has been proposed (refer to Patent Document 3 below).

  According to this technique, even a resin used in a prepreg having a high glass transition temperature improves adhesion to the copper foil surface. For example, a base material having a thickness of 0.1 mm or less per layer called a thin multilayer printed wiring board Even if a rigorous test such as heating after humidifying a printed wiring board in which four or more layers are laminated, a printed wiring board such as a substrate for a semiconductor package, a component built-in board, etc. by a pressure cooker test, The resin can be prevented from being separated from the copper foil, which contributes to improving the reliability of the component-embedded substrate and the like.

International Publication No. 2006/109573 Pamphlet Japanese Patent No. 3414388 Japanese Patent No. 3909920

However, in the technique described in Patent Document 1, the solder material is characterized by not melting again (hereinafter, not remelted) even in reflow heat treatment by using fine particles having an average particle diameter of 6 μm or less. However, when used together with the technique described in Patent Document 3, there may be a case where bonding failure occurs at the metal bonding portion between the copper foil surface treated with the organic film and the solder material. There was room for improvement in later connection reliability.
In the technique described in Patent Document 2, there is still room for improvement in connection reliability after joining parts to a copper foil surface that has been similarly treated with an organic film.

  The present invention has been made in view of the above problems, and can be melt-bonded under reflow heat treatment conditions of lead-free solder to improve the adhesion between the copper surface of the inner substrate and the prepreg in a component built-in wiring board or the like. An object of the present invention is to provide a metal filler that is excellent in heat resistance after bonding and can provide good bonding strength at room temperature even on a copper surface that has been subjected to an organic film treatment. Another object of the present invention is to provide a lead-free solder or conductive adhesive containing the metal filler, a connection structure obtained using the lead-free solder or conductive adhesive, a substrate, and the connection structure. It is another object of the present invention to provide a component mounting board.

  As a result of intensive studies to solve the above-mentioned problems and repeated experiments, the present inventors have reached the present invention.

That is, the present invention is as follows.
[1] A metal filler containing, as a main component, a mixture of first metal particles and second metal particles, the mixture containing 55 parts of second metal particles with respect to 100 parts by mass of the first metal particles. -400 parts by mass, the first metal particles are Cu particles or Cu alloy particles, the second metal particles contain Ag and Sn, and the Ag content is 0.3 to 4 Metal filler which is Sn alloy particles of mass%.
[2] The Cu alloy particles are Sn 13.5 to 16.5% by mass, Ag 9 to 11% by mass, Bi 4.5 to 5.5% by mass, In 0.1 to 5% by mass, and the balance is Cu as a main component. Metal filler as described in said [1] which is Cu alloy particle | grains to contain, or Cu alloy particle | grains which contain Cu as a main component in 15-15 mass% of Ag and remainder.
[3] The metal filler according to [1] or [2], wherein the second metal particles are Sn alloy particles containing 96 to 99% by mass of Sn.
[4] A solder paste containing the metal filler according to any one of [1] to [3].
[5] A conductive adhesive containing the metal filler according to any one of [1] to [3].
[6] A first electronic component, a second electronic component, and a solder joint that joins the first electronic component and the second electronic component, wherein the solder joint is the [4] Or the connection structure formed by carrying out reflow heat processing of the solder paste or conductive adhesive as described in [5].
[7] A component mounting board having a board and the connection structure according to [6] mounted on the board.
[8] A component-embedded substrate comprising a substrate and the connection structure according to [6] mounted on the substrate.

  Even if the metal filler of the present invention is a copper surface that has been subjected to an organic film treatment to improve the adhesion between the copper surface of the inner layer substrate and the prepreg in a component built-in wiring board or the like, the normal reflow heat treatment conditions Can be melt-bonded, and after bonding, has excellent heat resistance and gives good bonding strength at room temperature.

2 is a DSC chart obtained by differential scanning calorimetry of the metal filler produced in Example 1. FIG. 2 is a DSC chart obtained by differential scanning calorimetry of a sample after heating created in Example 1. FIG.

  Hereinafter, modes for carrying out the present invention (hereinafter abbreviated as actual modes) will be described in detail. In addition, this invention is not limited to the following embodiment, It can deform | transform and implement within the range of the summary.

<Metal filler>
The metal filler according to the present embodiment is a metal filler containing a mixture of first metal particles and second metal particles as a main component, and the mixture is the first with respect to 100 parts by mass of the first metal particles. The second metal particles are 55 to 400 parts by mass, the first metal particles are Cu particles or Cu alloy particles, the second metal particles contain Ag and Sn, and the content of the Ag Is 0.3 to 4% by mass of Sn alloy particles.

  To illustrate the preferred composition of the metal filler, the mixing ratio of the first metal particles and the second metal particles is 400 parts by mass of the second metal particles with respect to 100 parts by mass of the first metal particles from the viewpoint of heat resistance. On the other hand, from the viewpoint of improving the initial bonded state, the lower limit is 55 parts by mass or more of the second metal particles with respect to 100 parts by mass of the first metal particles.

  The component of the first metal particles may be Cu, but a Cu alloy is more preferable from the viewpoint of alloying by thermal diffusion with the second metal particles. As a preferable embodiment, Sn 13.5 to 16.5% by mass, Ag 9 to 11% by mass, Bi 4.5 to 5.5% by mass, In 0.1 to 5% by mass, and Cu containing Cu as a main component in the balance An alloy is mentioned. Another preferred embodiment is a Cu alloy containing 15 to 25% by mass of Ag and Cu as the main component in the balance. In the present embodiment, the main component means that the proportion of the specific component in the matrix component containing the specific component is preferably 50% by mass, more preferably 80% by mass, and 100% by mass. Indicates that it may be.

  The shape and size of the first metal particles can be determined according to the application. For example, in solder paste applications, it is preferable to use particles having a relatively high sphericity with an average particle diameter of 2 to 40 μm in consideration of printability. For conductive adhesive applications, it is preferable to use irregularly shaped particles in order to increase the contact area of the particles.

The component of the second metal particles includes Ag and Sn from the viewpoint of alloying by thermal diffusion with the first metal particles and from the viewpoint of improving the bondability with the substrate surface subjected to the organic film treatment, and An Sn alloy having an Ag content of 0.3 to 4% by mass is preferred. Specifically, the second metal particles are Sn—Ag eutectic solder particles, Sn—Ag—Cu eutectic solder particles, or solder obtained by adding any one or more of In, Zn, Bi, etc. thereto. Particles can be used. By adding In, the melting point can be lowered without significantly reducing the metal properties of the alloy. Zn and Bi, as well as In, have the effect of lowering the melting point when added. Examples of the composition of the Sn alloy include Sn0.3Ag0.7Cu, Sn1.0Ag0.5Cu, Sn2.0Ag0.5Cu, Sn3.0Ag0.5Cu, Sn3.5Ag, Sn4.0Ag0.5Cu, Sn57Bi1Ag, etc., particularly Sn3 .5Ag is preferred. Moreover, you may use these individually by 1 type or in mixture of 2 or more types.

As the second metal particles, it is preferable to use a powder containing no particles of 4.3 μm or less. The inclusion of particles of 4.3 μm or less is preferable because the alloying reaction by thermal diffusion with the first metal particles proceeds at an appropriate rate and the joint strength with the component can be increased.
In the present embodiment, the powder containing no particles of 4.3 μm or less means that particles of 4.3 μm or less are included in the cumulative distribution obtained when the powder is measured with a laser diffraction particle size distribution measuring device. It means that it is not detected.
The average particle diameter of the second metal particles is preferably 10 to 40 μm, and more preferably 10 to 30 μm.

  As will be described later, the metal filler according to the present embodiment can form a paste-like lead-free solder, for example, by being combined with a flux. When component mounting is performed using this solder paste, a thin flux layer may be formed on the surface of a solder joint portion (particularly a fillet portion) formed by reflow heat treatment. Since the average particle size of the second metal particles is 10 μm or more, the fine particles of the second metal particles are less likely to be entrained in the flux layer at the time of component mounting, and generation of suspended particles in the flux layer can be suppressed. This is preferable because the number of particles flowing out into the cleaning liquid can be reduced. On the other hand, when the average particle size is 40 μm or less, the adhesive strength of the solder paste is hardly impaired, which is preferable.

  The particle size distribution of the first metal particles and the second metal particles can be determined according to the paste application. For example, in screen printing applications, it is preferable to make the particle size distribution broader with an emphasis on plate slippage, and in dispensing applications, it is preferable to focus on ejection fluidity and make the particle size distribution sharper.

  Can be used as the first metal particles, Sn 13.5 to 16.5% by mass, Ag 9 to 11% by mass, Bi 4.5 to 5.5% by mass, In 0.1 to 5% by mass, Cu in the balance The Cu alloy particles contained as the main component have at least one metastable alloy phase observed as an exothermic peak in differential scanning calorimetry (DSC) at 230 to 300 ° C. and a melting point observed as an endothermic peak at 480 to 530 ° C. It is preferable to have at least one. Heat generation in differential scanning calorimetry (DSC) is detection of latent heat generated when a new alloy phase is formed, and indicates that a metastable alloy phase is present in the alloy particles.

  As a manufacturing method of the first metal particles and the second metal particles, a rapid solidification method is preferable. Examples of the method for producing fine powder by the rapid solidification method include a water spray method, a gas spray method, and a centrifugal spray method. From the viewpoint of suppressing the oxygen content of particles, the gas spray method and the centrifugal spray method are more preferable. preferable. In the gas spraying method, inert gas such as nitrogen gas, argon gas, helium gas, etc. can usually be used, but helium gas with a low specific gravity is used to increase the linear velocity during gas spraying and increase the cooling rate. Is preferably used. The cooling rate is preferably in the range of 500 to 5000 ° C./second. In the centrifugal spray method, from the viewpoint of forming a uniform molten film on the upper surface of the rotating disk, the material is preferably sialon, and the disk rotation speed is preferably in the range of 60,000 to 120,000 rpm.

Can be used as the first metal particles, Sn 13.5 to 16.5% by mass, Ag 9 to 11% by mass, Bi 4.5 to 5.5% by mass, In 0.1 to 5% by mass, Cu in the balance The Cu alloy particles contained as the main component preferably include crystal grains of a Cu—Sn alloy phase or a Cu—In alloy phase, and Ag or Bi is preferably present at the interface of the alloy phase. By having a metastable alloy phase with high reactivity such as Cu—Sn alloy phase and Cu—In alloy phase inside, it is possible to rapidly alloy with molten Sn particles or Sn alloy particles in reflow heat treatment. This tends to be possible and is preferable.
Note that the elemental composition of the first metal particles and the second metal particles defined in this specification can be confirmed by, for example, inductively coupled plasma (ICP) emission analysis. The elemental composition of the particle cross section can be analyzed by using SEM-EDX (characteristic X-ray analyzer).

<Solder paste>
The present embodiment also provides a solder paste including the metal filler of the present embodiment described above. The solder paste can be lead-free. In the present embodiment, lead-free means that the lead content is 0.1% by mass or less in accordance with EU environmental regulations. The solder paste preferably includes a metal filler component and a flux component, and typically includes a metal filler component and a flux component. The metal filler component is the metal filler described above, but may contain a small amount of other metal filler as long as the effect is not impaired.

  The content of the metal filler component in the solder paste is preferably in the range of 84 to 94% by mass based on the total mass of the solder paste (that is, 100% by mass) from the viewpoint of paste characteristics. A more preferable range of the content of the metal filler component in the solder paste can be determined according to the use of the paste. For example, in screen printing applications, the ability to remove the plate is important, so the content of the metal filler component in the solder paste is preferably in the range of 87 to 92% by mass, based on the total mass of the solder paste, More preferably, it is the range of 88-91 mass%. For example, in dispensing applications, discharge fluidity is important, so the content of the metal filler component in the solder paste is preferably in the range of 85 to 89% by mass based on the total mass of the solder paste, and more Preferably, it is the range of 86-88 mass%.

  In general, flux refers to a material that melts faster than solder and cleans the metal surface. The flux component used in the present embodiment preferably contains rosin, a solvent, an activator and a thixotropic agent. Such a flux component is suitable for the surface treatment of the metal filler. That is, the flux component promotes alloying due to metal melting and thermal diffusion by removing the oxide film of the metal filler component in the solder paste during reflow heat treatment and suppressing reoxidation. As the flux component, a known material can be used.

<Conductive adhesive>
The present embodiment also provides a conductive adhesive containing the metal filler of the present embodiment described above. In general, the conductive adhesive refers to an adhesive containing a material having good conductivity such as silver, copper, or carbon fiber. The content of the metal filler component in the conductive adhesive is preferably in the range of 70 to 90% by mass based on the total mass of the conductive adhesive (that is, 100% by mass) from the viewpoint of characteristics. More preferably, it is in the range of 75 to 85% by mass.

  In general, the conductive adhesive has features such as lead-free, volatile organic compound (VOC) -free, fluxless, easy low-temperature packaging, etc., so the conductive adhesive of this embodiment is intended to be electrically connected but soldered. Suitable for parts that cannot be attached (for example, devices related to semiconductor chips, liquid crystals, organic EL, LEDs, etc.). Further, the conductive adhesive of the present embodiment can have the same composition as the lead-free solder. However, the conductive adhesive of the present embodiment may or may not include a flux component.

<Connection structure>
The present embodiment includes a first electronic component, a second electronic component, and a solder joint that joins the first electronic component and the second electronic component, or the first electronic component and the first electronic component. There is also provided a connection structure including an adhesive portion for adhering two electronic components. In the solder paste, when a mounting component electrode such as an electronic device is connected to a substrate electrode, a heat history equal to or higher than the melting point of the second metal particle is given under reflow heat treatment conditions of lead-free solder. The metal particles are melted, and the mounting component electrode and the substrate electrode are joined via the first metal particles. As a result, the thermal diffusion reaction between the metals proceeds at an accelerated rate, and a new stable alloy phase having a melting point higher than the melting point of the second metal particles is formed, and the mounting component electrode and the substrate are interposed via the first metal particles. A connection structure that connects the electrodes is formed.

  The melting point of this new stable alloy phase is higher than the reflow heat treatment temperature of lead-free solder, and since it does not melt even when subjected to a plurality of heat treatments in the subsequent process, it is possible to suppress a short circuit due to solder remelting.

  Examples of the combination of the first electronic component and the second electronic component include a combination of a substrate electrode and a mounted component electrode. As a method of joining the first electronic component and the second electronic component for forming the connection structure according to the present embodiment, a solder paste is applied to the substrate electrode, and then the mounting component electrode is placed and joined by reflow heat treatment. And a method in which a solder paste is applied to the mounting component electrode or the substrate electrode, bumps are formed by reflow heat treatment, the mounting component electrode and the substrate electrode are overlapped, and then reflow heat treatment is performed again. In the above case, the electrodes can be connected by solder bonding between the electrodes.

  The heat treatment peak temperature during reflow is preferably in the range of 240-270 ° C, more preferably in the range of 250-260 ° C. The peak temperature during this heat treatment is typically set to be equal to or higher than the melting point of the second metal particles. When the lead-free solder according to the present embodiment is used to connect a mounting component electrode such as an electronic device and a substrate electrode, the second metal particle is given a thermal history equal to or higher than the melting point of the second metal particle. It melts and an alloying reaction by thermal diffusion proceeds between the first metal particles and the second metal particles, and a stable alloy phase having a melting point higher than the melting point of the second metal particles is formed. The melting point of this new stable alloy phase is higher than the reflow heat treatment temperature (for example, about 260 ° C.) of the lead-free solder made of Sn-3.0Ag-0.5Cu, Does not melt. Therefore, according to the present embodiment, it is possible to prevent a short circuit occurring between the component electrodes due to remelting of the solder.

<Component mounting board>
The present embodiment also provides a component mounting board including the connection structure of the present embodiment mounted on the board. The component mounting board is preferably a board on which electronic components are mounted, and can be used for manufacturing various electronic devices.

<Component built-in board>
The present embodiment also provides a component built-in substrate including the connection structure of the present embodiment built in the substrate. The component-embedded substrate is preferably a substrate in which an electronic component is embedded, and can be used for manufacturing various electronic devices.

  The various parameters described above are measured according to the measurement method in the examples described later unless otherwise specified.

Next, the present embodiment will be described more specifically by way of examples and comparative examples. However, the present embodiment is not limited to the following examples as long as it does not exceed the gist thereof.
The physical properties of each metal particle, metal filler, and solder paste were evaluated by the methods shown below.
(A) Average particle diameter The volume integrated average value was measured by a laser diffraction particle size distribution measuring apparatus “HELOS & RODOS” manufactured by Sympatec (Germany), and the average particle diameter value was obtained.
(B) Particle size distribution The particle size distribution was measured using a laser diffraction particle size distribution measuring apparatus “HELOS & RODOS” manufactured by Sympatec (Germany). The measurement range can measure the cumulative distribution in the range of 0.9 μm to 175 μm [R3: 0.5 / 0.9. . . 175 μm] was selected, the trigger condition was set to dry standard, the disperser was set to RODOS, and the dispersion pressure was 3.0 bar. The calculation mode was LD, and the shape factor was 1.0. It was confirmed that the element of the HELOS detector was 10% or more, and the measurement concentration was 5 to 10%.
(C) Differential scanning calorimetry (DSC)
Using “DSC-60” manufactured by Shimadzu Corporation, the temperature was increased within a temperature range of 30 to 600 ° C. under a nitrogen atmosphere under a temperature rising temperature of 10 ° C./min. Those having an exotherm or endotherm of ± 1.5 J / g or more were quantified as peaks derived from the measurement object, and peaks below that were excluded from the viewpoint of analysis accuracy.
(D) Elemental composition The elemental composition of the metal particles was confirmed by inductively coupled plasma (ICP) emission analysis. The elemental composition of the particle cross section was analyzed by using SEM-EDX (characteristic X-ray analyzer).

<Example 1>
(1) Production of Cu alloy particles as first metal particles Cu 32.5 kg (purity 99% by mass or more), Sn 7.5 kg (purity 99% by mass or more), Ag 5.0 kg (purity 99% by mass or more), Bi2. 5 kg (purity 99% by mass or more) and In2.5 kg (purity 99% by mass or more) were placed in a graphite crucible and heated and melted to 1442 ° C. with a high-frequency induction heating apparatus in a 99% by volume or more helium atmosphere.
Next, this molten metal was introduced from the tip of the crucible into a spray tank in a helium gas atmosphere, and then helium gas (purity 99 vol% or more, oxygen concentration 0.185 vol%) was supplied from a gas nozzle provided near the crucible tip. , Pressure 2.61 MPa) and atomizing to produce Cu alloy particles. The cooling rate at this time was 2600 ° C./second.

When the obtained Cu alloy particles were observed with a scanning electron microscope “S-3400N” manufactured by Hitachi, Ltd., they were spherical.
The Cu alloy particles are classified at 1.6 μm setting using an airflow classifier “TC-15N” manufactured by Nissin Engineering Co., Ltd. After collecting the large particle side, it is classified again at 10 μm setting, and the small particle side is classified. It was collected. The average particle size of the collected alloy particles was measured and found to be 2.69 μm.

  Next, when differential scanning calorimetry of the Cu alloy particles was performed, endothermic peaks were detected at 499 ° C. and 519 ° C., and the presence of a plurality of alloy phases could be confirmed from a plurality of melting points. Further, an exothermic peak was detected at 255 ° C., and the presence of a metastable alloy phase was confirmed.

(2) 2nd metal particle Yamaishi Metal Co., Ltd. Sn particle "Y-SnAg3.5-Q2510" (henceforth, Sn3.5Ag) was used as a 2nd metal particle. The average particle size of the particles was measured and found to be 22.0 μm. Moreover, when the particle size distribution was measured and the cumulative distribution of particles of 4.3 μm or less was obtained, it was 0%. Moreover, when the elemental composition of this particle | grain was analyzed, the content rate of Ag was 3.5 mass%. Next, differential scanning calorimetry of the particles was performed. As a result, it was confirmed that the particles had an endothermic peak at 223 ° C. by differential scanning calorimetry and had a melting point of 221 ° C. There was no characteristic exothermic peak.

(3) Production of metal filler The Cu alloy particles and Sn3.5Ag particles were mixed at a weight ratio of 100: 83 to obtain a metal filler. Differential scanning calorimetry was performed using this metal filler as a sample. The DSC chart obtained by this measurement is shown in FIG. As shown in this figure, it was confirmed that an endothermic peak was present at 225 ° C. The endothermic peak at 225 ° C. had a melting point of 217 ° C., and the endothermic amount was 23.1 J / g. In addition, characteristically, exothermic peaks existed at 253 ° C. and 340 ° C.

(4) Preparation of lead-free solder paste Next, 91.4% by mass of a metal filler and 8.6% by mass of a rosin flux were mixed, and solder softener “SPS-1” manufactured by Malcolm Co., Ltd., defoamed by Matsuo Sangyo Co., Ltd. A solder paste was prepared by sequentially applying to a kneader “SNB-350”. The solder paste thus obtained was measured with a spiral viscometer “PCU-205” manufactured by Malcolm Corporation. The viscosity was 197 Pa · s and the thixo index was 0.40.

(5) DSC measurement of sample after heating The obtained solder paste was placed on an alumina substrate, and reflow heat treatment was performed at a peak temperature of 260 ° C. in a nitrogen atmosphere. As the heat treatment apparatus, Malcolm Reflow Simulator (SRS-1C) was used. The temperature profile increased from 1.5 ° C / second to 140 ° C from the start of heat treatment (room temperature), gradually increased from 140 ° C to 170 ° C over 110 seconds, and then increased at 2.0 ° C / second. The conditions of heating and holding at a peak temperature of 250 ° C. for 15 seconds were employed.

  When this heat-treated solder paste was used as a sample and differential scanning calorimetry was performed, it was confirmed that an endothermic peak was present at 350 ° C. and the endothermic peak at 225 ° C. was lost (the endothermic amount was 0 J / g). To do). The DSC chart obtained by this measurement is shown in FIG. As shown in this figure, in the DSC endotherm, if the ratio of the endotherm in the metal filler state (before heat treatment) and the endotherm of the sample after heating (after heat treatment) is the endothermic residual rate after heat treatment, the heat treatment of this sample The subsequent endothermic residual rate was 0.0%.

(6) Preparation of organic film-treated substrate Glass cloth epoxy resin impregnated copper clad laminate (FR-4 grade) with both sides laminated with 18 μm thick copper foil 1005 size (1.0 mm × 0.5 mm) on one side of 100 mm × 100 mm ) A Cu electrode portion was prepared by photolithography so that a resistance component could be mounted.

  A microetching agent “CZ-8101” manufactured by MEC Co., Ltd. was sprayed on the produced substrate at 30 ° C. for 1 minute, and the copper surface was etched by 1.5 μm. Subsequently, an organic film treatment agent “CL-8301” manufactured by MEC Co., Ltd. was used. Was soaked at room temperature for 30 seconds to prepare an organic film-treated substrate (with organic film treatment). In accordance with this, a substrate not subjected to the treatments of CZ-8101 and CL-8301 (without organic coating treatment) was also prepared.

(7) Measurement of bonding strength of 1005 size resistance component 1005 size 0Ω resistance component (1005R) was mounted using the above solder paste, and then subjected to heat treatment under reflow conditions at a peak temperature of 250 ° C. in an N2 atmosphere. 1005R, 45 daisy chains were made.
The heat treatment apparatus used was a reflow simulator “SRS-1C” manufactured by Malcolm Corporation. The temperature profile increased from 1.5 ° C / second to 140 ° C from the start of heat treatment (room temperature), gradually increased from 140 ° C to 170 ° C over 110 seconds, and then increased at 2.0 ° C / second. The conditions of heating and holding at a peak temperature of 250 ° C. for 15 seconds were employed.

For the printing pattern formation, a substrate subjected to organic film treatment (with organic film treatment) and a substrate not subjected to organic film treatment (without organic film treatment) were used. For printing pattern formation, a screen printer “MT-320TV” manufactured by Micro Tech Co., Ltd. was used. The printing mask is made of metal, and the squeegee is made of urethane. The mask has a printing opening size of 400 μm × 500 μm and a thickness of 0.08 mm in accordance with the 1005R electrode portion. The printing conditions were a speed of 50 mm / second, a printing pressure of 0.1 MPa, a squeegee pressure of 0.2 MPa, a back pressure of 0.1 MPa, an attack angle of 20 °, a clearance of 0 mm, and a printing frequency of once.
Thereafter, a load was applied from the longitudinal direction of the component to measure the bonding strength of 15 components and the average value was calculated. The average value of the component bonding strength on the substrate without organic coating was 7.1 N, and the organic coating The average value of the component bonding strength on the treated substrate was 7.0N. The evaluation results are shown in Table 1.

<Examples 2 to 6, Comparative Examples 1 and 2>
The mixing mass ratio of the first metal particles and the second metal particles is fixed to the mixing ratio shown in Table 1, the alloy composition of the second metal particles is changed, and other conditions are the same as in Example 1. Each evaluation was performed. The Sn0.3Ag0.7Cu particles shown in Table 1 were those having a particle size of 20 μm to 38 μm and an average particle size of 29.8 μm. Sn1Ag0.5Cu particles having a particle size of 10 to 25 μm and an average particle size of 21.3 μm were used. Sn2Ag0.5Cu particles having a particle size of 10 to 25 μm and an average particle size of 21.7 μm were used. Sn3Ag0.5Cu particles having a particle size of 10 to 25 μm and an average particle size of 22 μm were used. Sn4Ag0.5Cu particles having a particle size of 10 to 25 μm and an average particle size of 21.8 μm were used. As the Sn particles, Sn particles “Y-Sn100-Q2510” (average particle diameter 21.2 μm) manufactured by Yamaishi Metal Co., Ltd. were used. Sn0.7Cu particles having a particle size of 10 to 25 μm and an average particle size of 22.9 μm were used. Any metal particle was measured for particle size distribution, and the cumulative distribution of particles of 4.3 μm or less was found to be 0%.

<Joint strength of 1005 size resistor parts>
From Examples 1 to 6 and Comparative Examples 1 and 2 in Table 1, when 100 parts by mass of the first metal particles are fixed to 83 parts by mass of the second metal particles, Ag is added to the second metal particles. When the metal particles contained were used, the bonding strength of the substrate with the organic coating treatment was almost the same as that of the substrate without the organic coating treatment, and a high bonding strength was obtained. In particular, in the case of particles having an Ag content of 3.5% by mass, a bonding strength exceeding 7 N was obtained both with and without the organic film treatment. On the other hand, with Sn particles not containing Ag and Sn0.7Cu particles, the bonding strength of the substrate with the organic film treatment was lower than the bonding strength of the substrate without the organic film treatment.

  From this fact, in addition to improving the bondability with the Cu substrate by including Ag in the second metal particles, it is possible to suppress a decrease in bondability even when the Cu substrate is subjected to an organic film treatment. It was confirmed that there was an effect. The reason for the effect that the bonding strength does not significantly decrease is not necessarily clear, but the inclusion of Ag in the second metal particles improves the wettability with the organic film layer on the substrate surface, effectively making the organic film layer effective. It is considered that it can be removed and bonded to the Cu substrate surface satisfactorily.

<Change in DSC endotherm by heat treatment>
From Examples 1 to 6 and Comparative Examples 1 and 2 in Table 1, when fixed to 83 parts by mass of second metal particles with respect to 100 parts by mass of first metal particles, heat treatment for DSC endotherm before heat treatment The subsequent DSC endothermic ratio was 0%, and it was confirmed that the same resistance to remelting, that is, high heat resistance was maintained.

<Examples 7 to 10, Comparative Example 3>
The mixing mass ratio of the first metal particles and the second metal particles was changed to the mixing ratio shown in Table 2, and the other conditions were evaluated under the same conditions as in Example 1. It can be seen that the component bonding strength of the 1005 size resistance component increases as the mixing ratio of the second metal particles increases. Further, if the endothermic residual rate after heat treatment is in the range of 400 to 55 with respect to 100 parts by mass of the first metal particles, the endothermic residual rate after heat treatment is 90% or less, and shows resistance to remelting. That is, it was confirmed that high heat resistance was exhibited.

<Example 11>
Instead of Cu alloy particles composed of 65 mass% Cu, 10 mass% Ag, 5 mass% Bi, 5 mass% In, and 15 mass% Sn in Example 1, Cu alloy composed of 80 mass% Cu and 20 mass% Ag as the first metal particles. Particles were used.
The production of Cu alloy particles composed of Cu 80% by mass and Ag 20% by mass as the first metal particles was carried out by the following method. Cu 8.0 kg (purity 99% by mass or more) and Ag 2.0 kg (purity 99% by mass or more) were put in a graphite crucible and heated to 1400 ° C. with a high-frequency induction heating apparatus in a helium atmosphere of 99% by volume or more and melted. .

  Next, after this molten metal is introduced from the tip of the crucible into a spray tank in a helium gas atmosphere, helium gas (purity 99 vol% or more, oxygen concentration 0.1 vol%) is supplied from a gas nozzle provided near the crucible tip. And pressure was reduced to 2.5 MPa), and atomization was performed to prepare Cu alloy particles. The cooling rate at this time was 2600 ° C./second.

When the obtained Cu alloy particles were observed with a scanning electron microscope “S-3400N” manufactured by Hitachi, Ltd., they were spherical.
The Cu alloy particles are classified at 1.6 μm setting using an airflow classifier “TC-15N” manufactured by Nissin Engineering Co., Ltd. After collecting the large particle side, it is classified again at 10 μm setting, and the small particle side is classified. It was collected. The average particle size of the recovered Cu alloy particles was measured and found to be 3.47 μm.
Table 3 shows the results of the same evaluation as in Example 1 using these particles. Values close to those of Example 1 were obtained for the component bonding strength of the 1005 size resistance component and the endothermic residual rate after heat treatment.

<Example 12>
Fukuda Metal Foil Powder Co., Ltd., which is Cu particles as the first metal particles instead of the Cu alloy particles consisting of Cu 65% by mass, Ag 10% by mass, Bi 5% by mass, In 5% by mass, and Sn 15% by mass in Example 1. Cu particles “Cu-HWQ 3 μm” were used. The average particle diameter of the Cu particles was measured and found to be 2.53 μm. Table 3 shows the results of the same evaluation as in Example 1 using these particles. Values close to those of Example 1 were obtained for the component bonding strength of the 1005 size resistance component and the endothermic residual rate after heat treatment.

  The metal filler of the present invention and the lead-free solder containing the metal filler are used for a plurality of heat treatments in a subsequent process (for example, a solder material used for an electronic device such as a component-embedded substrate and a package, and further, for example, a conductive adhesive). In addition, high-density mounting with high reliability can be realized by improving connectivity.

Claims (8)

  A metal filler containing a mixture of first metal particles and second metal particles as a main component, wherein the mixture is 55 to 400 masses of second metal particles with respect to 100 mass parts of first metal particles. The first metal particles are Cu particles or Cu alloy particles, and the second metal particles contain Ag and Sn, and the Ag content is 0.3 to 4% by mass. Metal filler which is Sn alloy particles.   Cu alloy particles containing Sn 13.5 to 16.5% by mass, Ag 9 to 11% by mass, Bi 4.5 to 5.5% by mass, In 0.1 to 5% by mass, and the balance containing Cu as a main component 2. The metal filler according to claim 1, which is a particle or a Cu alloy particle containing 15 to 25 mass% of Ag and Cu as a main component in the balance.   The metal filler according to claim 1 or 2, wherein the second metal particles are Sn alloy particles containing 96 to 99 mass% of Sn.   The solder paste containing the metal filler in any one of Claims 1-3.   The electroconductive adhesive agent containing the metal filler in any one of Claims 1-3.   A first electronic component, a second electronic component, and a solder joint that joins the first electronic component and the second electronic component, wherein the solder joint is claim 4 or claim 5. A connection structure formed by reflow heat-treating the solder paste or conductive adhesive described in 1.   The component mounting board which has a board | substrate and the connection structure of Claim 6 mounted on the said board | substrate.   A component-embedded substrate comprising: a substrate; and the connection structure according to claim 6 mounted on the substrate.

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