JP2008183582A - Electrically conductive filler, and solder paste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly heat resistant, electrically conductive filler which can be melted and joined under a temperature condition (peak temperature of ≥149°C) lower than the reflow heat treatment condition of Sn-37Pb eutectic solder. <P>SOLUTION: The electrically conductive filler comprises metal grains having a metastable alloy phase observed as a heat generation peak by differential scanning calorimetry (DSC) by at least one between 250°C and 285°C, and having melting points observed as heat absorption peaks in the two parts of 50 to 95°C and 400 to 475°C at least one by one, respectively. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a conductive filler used for a bonding material of an electronic device, and particularly relates to a lead-free solder paste and a conductive adhesive.

Conventionally, Sn-37Pb eutectic solder (melting point: 183 ° C.) has been generally used in solder mounting of electronic devices and the like, but environmental pollution due to Pb and harmfulness to the human body are regarded as problems. In July 2006, the European Union (EU) enforced the RoHS directive, and global movements to strengthen Pb regulations have increased, and the development of alternative solder materials and joining technologies that do not contain Pb is being promoted.
Under such circumstances, Sn-3.0Ag-0.5Cu (melting point: 220 ° C.) solder (see Patent Document 1) is widely known as a joining material that replaces Sn-37Pb eutectic solder and lead-free solder. However, the melting point is higher than that of Sn-37Pb eutectic solder, and the mounting temperature, i.e., reflow heat treatment temperature, is increased, which increases the thermal load on electronic devices and base materials and cannot be used for materials with low heat resistance. Therefore, development of a low melting point lead-free solder that can be mounted at low temperature is required.
In general, the reflow heat treatment temperature is set in the range of the melting point of the solder alloy +10 to 50 ° C.

On the other hand, as a low melting point lead-free solder, Sn-52In (melting point: 117 ° C.) solder mainly composed of Sn, In, Bi, Sn-58Bi (melting point: 139 ° C.) solder (see Patent Documents 2 and 3) Etc. These have the advantage that the melting point is lower than that of Sn-37Pb eutectic solder and the mounting temperature can be used at a low temperature in the range of 150 to 180 ° C. However, in Sn-52In solder, In is a scarce resource. Since it is an expensive metal, there are problems in terms of stable supply and cost. With Sn-58Bi solder, in addition to mechanical properties such as the material itself being hard and brittle and having low ductility, thermal fatigue strength is low, and connectivity There is a problem.
In addition, the assembly process requires multiple solder mountings, and the soldering temperature is gradually lowered using solder with a low melting point so that the parts mounted in the previous process are not remelted and removed. Although the above-described low melting point lead-free solder has a low melting point and a low heat-resistant temperature, there is a problem that it can be used only for solder mounting at the final stage.
In addition, the present inventors previously used a lead-free conductive material that can be connected at a mounting temperature lower than that of Sn-37Pb eutectic solder as one of the means for solving the above-mentioned problems. A conductive filler made of a mixture of three types of metal particles that can maintain strength and can be used for multiple solder mountings has been proposed (see Patent Document 4).

Japanese Patent Laid-Open No. 05-050286 Japanese Patent Application Laid-Open No. 08-252688 JP-A-11-221694 JP 2006-281292 A

  The present invention has been made in view of the above circumstances, and can be melt-bonded at a temperature lower than the mounting temperature (reflow heat treatment temperature) condition of Sn-37Pb eutectic solder (peak temperature of 149 ° C. or higher). Another object is to provide a conductive filler that can be used as a bonding material having a heat resistance of 260 ° C. Another object of the present invention is to provide a solder paste using the conductive filler.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have made the present invention.
That is, in the first aspect of the present invention, at least one metastable alloy phase observed as an exothermic peak in differential scanning calorimetry (DSC) is in the range of 250 to 285 ° C., and a melting point observed as an endothermic peak is 50 to 95. It is an electroconductive filler which consists of a metal particle which has at least 1 each in two places of the range of 400 degreeC and the range of 400-475 degreeC.
The metal particles include first metal particles made of an alloy having a composition of Ag 5 to 15% by mass, Bi 15 to 25% by mass, Cu 10 to 20% by mass, In 15 to 25% by mass, and Sn 15 to 55% by mass; -15 mass%, Bi2-8 mass%, Cu49-81 mass%, In2-8 mass%, and a mixture with second metal particles made of an alloy having a composition of Sn10-20 mass%, and its mixing The ratio is preferably 50 to 150 parts by mass of the second metal particles with respect to 100 parts by mass of the first metal particles.

In addition, the metal particles include first metal particles made of an alloy having a composition of Ag 5 to 15% by mass, Bi 15 to 25% by mass, Cu 10 to 20% by mass, In 15 to 25% by mass, and Sn 15 to 55% by mass. Second metal particles made of an alloy having a composition of 5-15% by mass of Ag, 2-8% by mass of Bi, 49-81% by mass of Cu, 2-8% by mass of In, and 10-20% by mass of Sn, and 25-25% by mass of Ag. , Bi 2-8 mass%, Cu 5-15 mass%, In 2-8 mass%, and a mixture with third metal particles made of an alloy having a composition of Sn 29-66 mass%, the mixing ratio of which is The second metal particles are preferably 50 to 150 parts by mass and the third metal particles 1 to 150 parts by mass with respect to 100 parts by mass of the first metal particles.
The second of the present invention is a solder paste characterized by containing the first conductive filler of the present invention.

  The conductive filler of the present invention can be melt-bonded at a lower temperature condition (peak temperature of 149 ° C. or higher) than the mounting temperature (reflow heat treatment temperature) condition of Sn-37Pb eutectic solder. Since it can be used as a bonding material at 0 ° C., it has the advantage that thermal damage to components, base materials, and peripheral devices during mounting can be reduced, and manufacturing costs and environmental loads can be reduced.

The conductive filler of the present invention has at least one metastable alloy phase observed as an exothermic peak by differential scanning calorimetry (DSC) in the range of 250 to 285 ° C., and a melting point observed as an endothermic peak of 50 to 95 ° C. And a metal particle having at least one each in two places in the range of 400 to 475 ° C.
In addition, the measurement temperature range in the differential scanning calorimetry (DSC) in the present invention is 30 to 600 ° C., and a calorific value or an endothermic amount of ± 1.5 J / g or more is determined as a peak derived from the measurement object. However, peaks less than that are excluded from the viewpoint of analysis accuracy.
The “melting point” in the present invention is a melting start temperature, and indicates a solidus temperature in differential scanning calorimetry (DSC).

Examples of metal particles that are preferable as the conductive filler of the present invention include metal particles having at least one melting point observed as an endothermic peak in differential scanning calorimetry (DSC) (hereinafter referred to as “first embodiment”). ) And at least one metastable alloy phase observed as an exothermic peak in the range of 240 to 290 ° C., and at least one melting point observed in the endothermic peak in the range of 480 to 520 ° C. And a mixture of metal particles (hereinafter also referred to as “metal particles of the second embodiment”).
In addition, at least one of the metal particles of the first embodiment, the metal particles of the second embodiment, and the metastable alloy phase observed as an exothermic peak is in the range of 110 to 130 ° C., and the melting point observed at the endothermic peak is 165. Examples include a mixture of metal particles (hereinafter also referred to as “metal particles of the third aspect”) at least one each in two places in a range of ˜200 ° C. and a range of 320 to 380 ° C.

If the heat treatment gives a thermal history equal to or higher than the minimum melting point of the metal particles, the metal particles are melted and joined. Thereby, the thermal diffusion reaction between the metal particles proceeds at an accelerated rate, the metastable alloy phase decreases, and a new stable alloy phase is formed on the higher temperature side than the lowest melting point. That is, the presence of a metastable alloy phase observed as an exothermic peak by DSC has an effect of promoting the thermal diffusion reaction.
As the metal particles of the first aspect, metal particles made of an alloy having a composition of Ag 5 to 15% by mass, Bi 15 to 25% by mass, Cu 10 to 20% by mass, In 15 to 25% by mass, and Sn 15 to 55% by mass ( Hereinafter, it is also referred to as “first metal particle”). More preferably, it is a metal particle which consists of an alloy which has composition of Ag8-12 mass%, Bi17-23 mass%, Cu12-18 mass%, In17-23 mass%, and remainder Sn.

As the metal particles of the second aspect, metal particles made of an alloy having a composition of Ag 5 to 15% by mass, Bi 2 to 8% by mass, Cu 49 to 81% by mass, In 2 to 8% by mass, and Sn 10 to 20% by mass ( Hereinafter, it is also referred to as “second metal particle”). More preferably, it is a metal particle which consists of an alloy which has composition of Ag8-12 mass%, Bi3-7 mass%, In3-7 mass%, Sn12-18 mass%, and remainder Cu.
Moreover, as a metal particle of 3rd aspect, it consists of an alloy which has composition of Ag25-40 mass%, Bi2-8 mass%, Cu5-15 mass%, In2-8 mass%, and Sn29-66 mass%. Particles (hereinafter also referred to as “third metal particles”) are exemplified. More preferably, it is a metal particle which consists of an alloy which has composition of Ag30-35 mass%, Bi3-7 mass%, Cu8-12 mass%, In3-7 mass%, and remainder Sn.

The mixing ratio of the metal particles of the first embodiment and the metal particles of the second embodiment in the mixture of the metal particles of the first embodiment and the metal particles of the second embodiment is 100 parts by mass of the metal particles of the first embodiment. On the other hand, 50 to 150 parts by mass of the metal particles of the second aspect are preferable, and further, 80 to 120 parts by mass of the metal particles of the second aspect are more than 100 parts by mass of the metal particles of the first aspect. preferable.
The metal particles of the first embodiment, the metal particles of the second embodiment, and the third embodiment of the mixture of the metal particles of the first embodiment, the metal particles of the second embodiment, and the metal particles of the third embodiment. The mixing ratio of the metal particles is preferably 50 to 150 parts by mass of the metal particles of the second aspect and 1 to 150 parts by mass of the metal particles of the third aspect with respect to 100 parts by mass of the metal particles of the first aspect. Furthermore, 80 to 120 parts by mass of the metal particles of the second aspect and 80 to 120 parts by mass of the metal particles of the third aspect are more preferable with respect to 100 parts by mass of the metal particles of the first aspect.

The particle size and shape of the 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. In addition, as a conductive adhesive application, in filling vias, it is preferable to use particles with relatively high sphericity with emphasis on hole filling properties, and in surface mounting of components and the like, in order to increase the contact area, It is preferable to use irregularly shaped particles.
Usually, fine metal particles are often surface oxidized. Therefore, in order to promote melting and thermal diffusion by the heat treatment in the above-mentioned application, it is preferable to mix at least one of an activator for removing the oxide film or pressurize, and to perform both. Further preferred. Further, as the reflow heat treatment atmosphere, nitrogen is more preferable than air because oxidation during heating can be suppressed.

As the method for producing the metal particles of the second and third aspects which are the conductive fillers of the present invention, in order to form a metastable alloy phase or a stable alloy phase in the metal particles, the inert solidification method is a rapid solidification method. It is desirable to adopt a gas atomizing method. In the inert gas atomization method, an inert gas such as nitrogen gas, argon gas, or helium gas is usually used. However, in the present invention, it is preferable to use helium gas having a low specific gravity, and the cooling rate is 500 to 5000. It is preferably in the range of ° C / second.
The solder paste of the present invention is composed of the conductive filler of the present invention and a flux composed of components such as rosin, a solvent, an activator, and a thixotropic agent. The content of the conductive filler in the solder paste is preferably 85 to 95% by mass. The flux is optimal for the surface treatment of the conductive filler made of metal particles, removes the oxide film of the metal particles during heat treatment, and promotes melting of the particles and alloying by thermal diffusion. A known material can be used as the flux, but it is preferable to add an organic amine as an oxide film remover because it is more effective. If necessary, a solvent may be added to a known flux to adjust the viscosity.

  Further, a thermosetting resin may be included as a binder for enhancing the bonding property. There is no restriction | limiting in particular in the kind of thermosetting resin, A well-known thing can be used. For example, resol type phenol resin, novolac type phenol resin, bisphenol type epoxy resin, novolac type epoxy resin, liquid epoxy compound having one or more glycidyl groups in one molecule, melamine resin, urea resin, xylene resin, alkyd Examples thereof include resins, unsaturated polyester resins, acrylic resins, polyimide resins, furan resins, urethane resins, bismaleimide-triazine resins, and silicone resins. Of these resins, epoxy resins are most preferred. Further, the thermosetting resin may be contained in the form of a monomer. The binder may contain a curing agent, and examples thereof include an amine epoxy curing agent, an acid anhydride epoxy curing agent, an isocyanate curing agent, and an imidazole curing agent. These thermosetting resins and curing agents may be used alone or in combination of two or more. Furthermore, you may make a binder contain a thermoplastic resin as needed.

EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example etc., this invention is not limited at all by these Examples.
The differential scanning calorimetry was performed in a range of 30 to 600 ° C. using a “DSC-50” manufactured by Shimadzu Corporation under a nitrogen atmosphere under a temperature rising rate of 10 ° C./min.
[Example 1]
(1) Production of first metal particles 1.0 kg of Ag particles (purity 99% by mass or more), 2.0 kg of Bi particles (purity 99% by mass or more), 1.5 kg of Cu particles (purity 99% by mass or more), In 2.0 kg of particles (purity 99% by mass or more) and 3.5 kg of Sn particles (purity 99% by mass or more) are placed 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. Less than the pressure of 2.5 MPa), atomization was performed to produce first metal particles. The cooling rate at this time was 2600 ° C./second.
When the obtained 1st metal particle was observed with the scanning electron microscope (Hitachi, Ltd. product: S-2700), it was spherical. The metal particles were classified using an airflow classifier (Nisshin Engineering Co., Ltd .: TC-15N) at a setting of 5 μm, and then the overcut powder was classified again at a setting of 15 μm. Undercut powder was collected. The collected first metal particles had a volume average particle size of 5.5 μm.
Differential scanning calorimetry was performed using the first metal particles thus obtained as a sample. As a result, it was confirmed that endothermic peaks of 66 ° C., 87 ° C., and 380 ° C. exist and have a plurality of melting points.

(2) Production of second metal particles Ag particles 1.0 kg (purity 99% by mass or more), Bi particles 0.5 kg (purity 99% by mass or more), Cu particles 6.5 kg (purity 99% by mass or more), In 0.5 kg of particles (purity 99% by mass or more) and 1.5 kg of Sn particles (purity 99% by mass or more) are placed 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), atomization was performed, and second metal particles were produced. The cooling rate at this time was 2600 ° C./second.
When the obtained 2nd metal particle was observed with the scanning electron microscope (Hitachi Ltd. make: S-2700), it was spherical. After classifying these metal particles with an airflow classifier (manufactured by Nisshin Engineering Co., Ltd .: TC-15N) at a setting of 1.6 μm, the overcut powder is classified again at a setting of 10 μm. The resulting undercut powder was recovered. The volume average particle size of the recovered second metal particles was 2.9 μm.
Differential scanning calorimetry was performed using the second metal particles thus obtained as a sample. As a result, it was confirmed that an endothermic peak at 496 ° C. was present and had a melting point. Moreover, the exothermic peak existed at 254 degreeC and it has confirmed having a metastable alloy phase.

(3) Production of third metal particles 3.2 kg of Ag particles (purity 99% by mass or more), 0.5 kg of Bi particles (purity 99% by mass or more), 1.0 kg of Cu particles (purity 99% by mass or more), In 0.5 kg of particles (purity 99% by mass or more) and 4.8 kg of Sn particles (purity 99% by mass or more) are placed 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. Less than the pressure of 2.5 MPa) and atomization was performed to produce third metal particles. The cooling rate at this time was 2600 ° C./second.
The obtained third metal particles were spherical when observed with a scanning electron microscope (manufactured by Hitachi, Ltd .: S-2700). The metal particles were classified using an airflow classifier (Nisshin Engineering Co., Ltd .: TC-15N) at a setting of 5 μm, and then the overcut powder was classified again at a setting of 15 μm. Undercut powder was collected. The volume average particle size of the recovered third metal particles was 4.9 μm.
Differential scanning calorimetry was performed using the third metal particles thus obtained as a sample. As a result, it was confirmed that endothermic peaks of 196 ° C., 359 ° C., and 415 ° C. exist and have a plurality of melting points. Moreover, the exothermic peak existed at 120 degreeC and it has confirmed having a metastable alloy phase.

(4) Manufacture of metal particle mixture Differential scanning is performed using a conductive filler prepared by mixing the first metal particles, the second metal particles, and the third metal particles at a weight ratio of 100: 105: 103. Calorimetry was performed. The DSC chart obtained by this measurement is shown in FIG. As shown in FIG. 1, endothermic peaks exist at 66 ° C., 86 ° C., 194 ° C., 330 ° C., and 433 ° C., and it was confirmed that they have a plurality of melting points. Moreover, the exothermic peak exists in 262 degreeC and 283 degreeC, and it has confirmed having a metastable alloy phase.

(5) Manufacture of solder paste 90.0% by mass of the above conductive filler and 10.0% by mass of rosin-based flux are mixed, solder softener (manufactured by Malcolm Co., Ltd .: SPS-1), defoaming kneader (Matsuo Sangyo) Solder paste was produced by sequentially applying to SNB-350.
(6) Confirmation of melting point and bonding strength The solder paste was placed on an alumina substrate and subjected to reflow heat treatment at a peak temperature of 149 ° C. in an air atmosphere. As the heat treatment apparatus, a mesh belt type far-infrared reflow apparatus “RQ-TC235” manufactured by Nihon Solder Co., Ltd. was used. The temperature profile is 5 minutes and 15 seconds for all the steps, reaching 69 ° C. in 1 minute from the start of the heat treatment, and then gradually increasing the temperature, reaching 114 ° C. in 3 minutes, reaching the peak temperature of 149 ° C. in 4 minutes, and gradually When the temperature dropped and the heat treatment was completed, a condition of 108 ° C. was adopted (hereinafter also referred to as “peak 149 ° C. heat treatment”).

  Next, differential scanning calorimetry was performed using the solder paste after the heat treatment as a sample. The DSC chart obtained by this measurement is shown in FIG. As shown in FIG. 2, it was confirmed that there are endothermic peaks at 105 ° C., 323 ° C., 356 ° C., and 434 ° C., and a plurality of melting points. It can be seen that the endothermic amount at 260 ° C. or lower is decreased and the endothermic amount at 260 ° C. or higher is increased when the amount ratio of the endothermic amount is compared with that before the heat treatment at 260 ° C. This indicates that the low melting point alloy phase diffused and shifted to the high temperature side by the heat treatment. Moreover, the exothermic peak existed at 244 degreeC, and it has confirmed having a metastable alloy phase. It can be seen that the calorific value is reduced by about 22% compared to before the heat treatment.

Next, the solder paste was printed on a Cu substrate with a size of 2 mm × 3.5 mm, and after mounting the chip, a sample was prepared by heat treatment at a peak of 149 ° C. in the air atmosphere by the heat treatment method described above. For the printing pattern formation, a printing machine “MT-320TV” manufactured by Microtech Co., Ltd. was used, the mask was a metal mask, and the squeegee was made of urethane. The opening of the mask is 2 mm × 3.5 mm, and the thickness is 100 μm. The printing conditions were a printing speed of 10 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. In addition, a Cu chip having a thickness of 2 mm × 2 mm and a thickness of 0.5 mm was used.
Next, at normal temperature (25 ° C.), the chip bonding strength in the shear direction of the prepared sample was measured with a push-pull gauge at a pushing speed of 10 mm / min, and converted to unit area, which was 7.1 MPa. Furthermore, when the fabricated sample was heated to 260 ° C. on a hot plate and held at 260 ° C. for 1 minute, the chip bond strength in the shear direction was measured by the same method as described above, and it was 3.2 MPa. The heat resistance capable of maintaining the bonding strength could be confirmed.

[Examples 2 to 7]
After making the mixture which changed the mixing ratio of the 1st metal particle of Example 1, the 2nd metal particle, and the 3rd metal particle into a conductive filler, and pasting by the same method as Example 1, and heat-treating, Table 1 shows the results of measuring the chip bonding strength as Examples 2 to 7.
[Comparative Examples 1 to 9]
In Table 1, as a comparative example, when the second metal particle is less than the lower limit (Comparative Example 1), when the second metal particle is not included (Comparative Example 2), the second metal particle is the lower limit. Less than (Comparative Example 3), when the first metal particles are alone (Comparative Example 4), when the third metal particles are not included, and when the second metal particles exceed the upper limit (Comparative Example 5), 3 is not included, the second metal particle is less than the lower limit (Comparative Example 6), the third metal particle exceeds the upper limit (Comparative Example 7), and the results of measuring the conventional solder material Show. Comparative Example 8 is an example of Sn-37Pb eutectic solder, and Comparative Example 9 is an example of Sn-58Bi eutectic solder.

As is clear from the results in Table 1, in the state heated to 260 ° C., the eutectic solders of Comparative Examples 8 and 9 remelt, whereas in Examples 1 to 7, there is a bonding strength of 2 MPa or more. It can be seen that there is heat resistance that can maintain the bonded state. Moreover, in Example 1, In ratio is reduced to 9.9 mass%.
As described above, by using the conductive filler of the present invention, it can be melt-bonded at a temperature lower than the mounting temperature (reflow heat treatment temperature) condition of Sn-37Pb eutectic solder, that is, at a peak temperature of 149 ° C. or higher. Thermal damage to parts, base materials, and peripheral equipment can be reduced, and after mounting, it can be used as a heat-resistant 260 ° C bonding material, so heat resistance is high, and solder mounting multiple times with a kind of paste Therefore, it is possible to provide a bonding material that can reduce the manufacturing cost.

  The conductive filler of the present invention can be melt-bonded at a lower temperature (peak temperature of 149 ° C. or higher) than the mounting temperature (reflow heat treatment) condition of Sn-37Pb eutectic solder, and after mounting, as a highly heat-resistant bonding material Can be expected.

Obtained by differential scanning calorimetry using as a sample a conductive filler produced by mixing the first metal particles, the second metal particles, and the third metal particles prepared in Example 1 at a weight ratio of 100: 105: 103. It is the obtained DSC chart. It is the DSC chart obtained by the differential scanning calorimetry which used what reflow-heat-treated the solder paste produced in Example 1 at the peak temperature of 149 degreeC in air | atmosphere atmosphere.

Claims (4)

  At least one metastable alloy phase observed as an exothermic peak in differential scanning calorimetry (DSC) in the range of 250 to 285 ° C., and melting point observed as an endothermic peak in the range of 50 to 95 ° C. and 400 to 475 ° C. A conductive filler comprising metal particles having at least one each at two locations in the range.   First metal particles made of an alloy having a composition of 5 to 15% by mass of Ag, 15 to 25% by mass of Bi, 10 to 20% by mass of Cu, 15 to 25% by mass of In, and 15 to 55% by mass of Sn; 15% by mass, Bi 2-8% by mass, Cu 49-81% by mass, In 2-8% by mass, and a mixture with second metal particles made of an alloy having a composition of Sn 10-20% by mass. The conductive filler according to claim 1, wherein the second metal particles are 50 to 150 parts by mass with respect to 100 parts by mass of the first metal particles.   First metal particles made of an alloy having a composition of 5 to 15% by mass of Ag, 15 to 25% by mass of Bi, 10 to 20% by mass of Cu, 15 to 25% by mass of In, and 15 to 55% by mass of Sn; Second metal particles made of an alloy having a composition of 15% by mass, Bi2-8% by mass, Cu49-81% by mass, In2-8% by mass, and Sn10-20% by mass, Ag25-40% by mass, Bi2− 8 mass%, Cu 5-15 mass%, In 2-8 mass%, and a mixture with third metal particles made of an alloy having a composition of Sn 29-66 mass%, the mixing ratio of the first 2. The conductive filler according to claim 1, wherein the second metal particles are 50 to 150 parts by mass and the third metal particles are 1 to 150 parts by mass with respect to 100 parts by mass of the metal particles.   A solder paste comprising the conductive filler according to claim 1.

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