JP2010167465A - Metal filler and solder paste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lead-free solder material which can be melted and joined at lower temperature conditions (peak temperature:≥150°C) than the mounting temperature (reflow heat treatment temperature)of Sn-37Pb eutectic solder, and can be repaired under the temperature conditions same as those of Sn-37Pb eutectic solder after the mounting. <P>SOLUTION: The metal filler includes: first metal grains composed of an alloy having a composition containing, by mass, 5 to 15% Ag, 15 to 25% Bi, 10 to 20% Cu, 15 to 25% In and 15 to 55% Sn; and second metal grains composed of an alloy having a composition containing 25 to 40% Ag, 2 to 8% Bi, 5 to 15% Cu, 2 to 8% In and 29 to 66% Sn, and in which regarding the mixing ratio between the first metal grains and the second metal grains to the first metal grains 100 pts.mass, the ratio of the second metal grains is 90 to 110 pts.mass. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a metal filler used for connecting electronic devices. The present invention particularly relates to a lead-free solder paste and a conductive adhesive.

  Sn-37Pb eutectic solder containing Pb (melting point: 183 ° C) is generally used as the solder material used for electronics mounting, but environmental pollution caused by Pb and harmfulness to the human body have become a problem. In July 2006, the RoHS Directive was enforced in the European Community (EU), and the movement to strengthen Pb regulations worldwide increased, and the development of solder materials that do not contain Pb is being promoted.

As a lead-free solder material replacing Sn-37Pb eutectic solder, Sn-3.0Ag-0.5Cu (melting point: 217 ° C.) solder (hereinafter referred to as Patent Document 1) is mainly used. Low melting point lead that can be mounted at low temperatures because it has a higher melting point and higher mounting temperature, ie, reflow heat treatment temperature, and is not applicable to electronic devices with high thermal load and low heat resistance. Development of free solder is required.
In general, the reflow heat treatment temperature is set within 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 composed mainly of Sn, In, Bi, Sn-58Bi (melting point: 139 ° C.) solder (hereinafter, Patent Documents 2, 3) See). 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. On the other hand, in 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, There is a problem in connection reliability.

  The present inventors have previously proposed lead-free solder that can be connected at a lower mounting temperature than Sn-37Pb eutectic solder as one of means for solving the above problems (see Patent Documents 4 and 5 below). However, these solder materials are characterized by maintaining the bonding strength even at 260 ° C. after mounting, and have no repairability.

Japanese Patent Laid-Open No. 05-050286 Japanese Patent Application Laid-Open No. 08-252688 JP-A-11-221694 JP 2006-281292 A JP 2008-183582 A

  The present invention has been made in view of the above problems, and can be melt-bonded at a temperature lower than the mounting temperature (reflow heat treatment temperature) of Sn-37Pb eutectic solder (peak temperature of 150 ° C. or higher). It is an object to provide a lead-free solder material that can be repaired under a temperature condition equivalent to that of Sn-37Pb eutectic solder.

As a result of studies to solve the above problems, the present inventors have completed the present invention.
Specifically, the present invention is the following [1] to [3]:
[1] First metal particles made of an alloy having a composition of Ag 5 to 15 mass%, Bi 15 to 25 mass%, Cu 10 to 20 mass%, In 15 to 25 mass%, and Sn 15 to 55 mass%, and Ag 25 to 40 mass %, Bi 2-8 mass%, Cu 5-15 mass%, In 2-8 mass%, and second metal particles made of an alloy having a composition of Sn 29-66 mass%, the first metal particles and the second A metal filler, wherein a mixing ratio of metal particles is 90 to 110 parts by mass of the second metal particles with respect to 100 parts by mass of the first metal particles.

  [2] Third 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, and Sn 4 metal particles, and the mixing ratio of the first to fourth metal particles is 90 to 110 parts by mass of the second metal particles and 4 to 3 parts of the third metal particles with respect to 100 parts by mass of the first metal particles. The metal filler according to the above [1], which is 2120 parts by mass and 5 to 2505 parts by mass of the fourth metal particles.

  [3] A solder paste containing the metal filler according to [1] or [2].

  The metal filler of the present invention can be melt-bonded at a temperature lower than the mounting temperature (reflow heat treatment temperature) of Sn-37Pb eutectic solder (peak temperature 150 ° C. or higher), and after mounting, it is equivalent to Sn-37Pb eutectic solder. Since repair can be performed under temperature conditions, there is an advantage that the thermal burden during mounting is small, and it can be applied to an electronic device with low heat resistance, and the manufacturing cost and environmental load can be reduced.

2 is a DSC chart obtained by differential scanning calorimetry of the first metal particles granulated and classified in Example 1. FIG. 2 is a DSC chart obtained by differential scanning calorimetry of second metal particles granulated and classified in Example 1. FIG. 2 is a DSC chart obtained by differential scanning calorimetry of third metal particles granulated and classified in Example 1. FIG.

  The metal filler of the present invention is composed of 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 Ag 25 to 40% by mass, Bi 2 to 8% by mass, Cu 5 to 15% by mass, In 2 to 8% by mass, and Sn 29 to 66% by mass, the first metal particles The mixing ratio of the second metal particles is 90 to 110 parts by mass of the second metal particles with respect to 100 parts by mass of the first metal particles.

  Further, the metal filler of the present invention is composed 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. In addition to the second metal particles made of an alloy having a composition of Ag25-40 mass%, Bi2-8 mass%, Cu5-15 mass%, In2-8 mass%, and Sn29-66 mass%, Ag5-15 mass% %, Bi2-8% by mass, Cu49-81% by mass, In2-8% by mass, and third metal particles made of an alloy having a composition of Sn10-20% by mass, and fourth metal particles made of Sn. The mixing ratio of the first to fourth metal particles is 90 to 110 parts by mass of the second metal particles, 4 to 2120 parts by mass of the third metal particles, and 100 parts by mass of the first metal particles. 4 metal grains Is preferably 5 to 2,505 parts by weight.

  When a heat history having a peak temperature of 150 ° C. or higher is given, the first metal particles are melted and joined to surrounding metal particles. As a result, the thermal diffusion reaction between the metal particles proceeds at an accelerated rate, and a new alloy phase is formed. At this time, it is preferable that metal particles having a metastable alloy phase exist. Since the metastable alloy phase is easy to form a new alloy phase, it has the effect of promoting the thermal diffusion reaction.

The first metal particles preferably have at least one melting point observed as an endothermic peak in the range of 50 to 95 ° C. in differential scanning calorimetry (DSC).
Moreover, as a metal particle which expresses such a thermal characteristic, the alloy which has composition of Ag8-12 mass%, Bi17-23 mass%, Cu12-18 mass%, In17-23 mass%, and remainder Sn is more preferable. .

In the differential scanning calorimetry (DSC), the second metal particles have at least one metastable alloy phase observed as an exothermic peak in a range of 110 to 140 ° C. and a melting point observed as an endothermic peak of 165 to 200 ° C. It is preferable to have at least one each at two locations in the range of 320 to 380 ° C. Heat generation in differential scanning calorimetry (DSC) is detection of latent heat generated when a new alloy phase is formed, indicating that a metastable alloy phase is present in the metal particles.
Moreover, as a metal particle which expresses such a thermal characteristic, the alloy which has composition of Ag30-35 mass%, Bi3-7 mass%, Cu8-12 mass%, In3-7 mass%, and remainder Sn is more preferable. .

  As a method for producing metal particles having a metastable alloy phase, 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 be usually used. Is preferably used. The cooling rate is preferably in the range of 500 to 5,000 ° 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.

  The mixing ratio of the first metal particles and the second metal particles is preferably 90 to 110 parts by mass of the second metal particles with respect to 100 parts by mass of the first metal particles, and further, 100 parts by mass of the first metal particles. On the other hand, it is more preferable that it is 100-105 mass parts of 2nd metal particles.

  The particle size of the metal filler is preferably in the range of 2 to 30 μm as an average particle size, and more preferably in the range of 5 to 30 μm. When the average particle size is 2 μm or more, the specific surface area of the particles becomes small, so there is little reaction with the flux, the life of the paste is lengthened, and reflow heat treatment occurs due to reduction by flux (particle oxide film removal). Since the amount of gas is reduced, it is preferable from the viewpoint that voids hardly occur inside the connection, and more preferably 5 μm or more. The upper limit of the average particle diameter is preferably 30 μm or less from the viewpoint of paste characteristics. When the particle size is increased, the gap between the particles is increased, so that the adhesive force is easily impaired.

  The particle size distribution of the metal filler can be determined according to the paste application. For example, for screen printing applications, emphasis is placed on the plate slippage and the particle size distribution is preferably broad.For dispensing applications, emphasis is placed on discharge fluidity. The distribution is preferably sharp.

Further, more preferable metal fillers are, for example, 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 Sn10 to 10% in addition to the first metal particles and the second metal particles. It is a mixture in which third metal particles made of an alloy having a composition of 20% by mass and fourth metal particles made of Sn are further mixed.
In the differential scanning calorimetry (DSC), the third metal particles have at least one metastable alloy phase observed as an exothermic peak in the range of 240 to 300 ° C. and a melting point observed as an endothermic peak of 475 to 525 ° C. It is preferable to have at least one each in the range.

  Further, as the third metal particles that exhibit such thermal characteristics, an alloy having a composition of Ag 8 to 12% by mass, Bi 3 to 7% by mass, Cu 60 to 70% by mass, In 3 to 7% by mass, and the remaining Sn is more. preferable. The main component of the third metal particles is Cu. On the other hand, the main component of the first metal particles, the second metal particles, and the fourth metal particles is Sn. Cu and Sn have good reactivity and easily form an intermetallic compound by thermal diffusion.

  The mixing ratio of the first metal particles, the second metal particles, the third metal particles, and the fourth metal particles is 90 to 110 parts by mass of the second metal particles and 100 parts by mass of the third metal particles with respect to 100 parts by mass of the first metal particles. 4 to 2120 parts by mass, and 5 to 2505 parts by mass of the fourth metal particles are preferable, and further, 100 to 105 parts by mass of the second metal particles and 4 to 446 of the third metal particles with respect to 100 parts by mass of the first metal particles. Mass parts and 5 to 527 parts by mass of the fourth metal particles are more preferable.

  The solder paste of the present invention preferably contains a metal filler and a flux component, and the content of the metal filler is preferably in the range of 84 to 94% by mass with respect to 100% by mass of the solder paste from the viewpoint of paste characteristics. More preferably, it can be determined according to the paste application.

For example, in screen printing applications, emphasizing plate slipping out, the metal filler content is preferably in the range of 87 to 91 mass%, more preferably in the range of 88 to 90 mass%.
In dispensing applications, the metal filler content is preferably in the range of 85 to 89% by mass, more preferably in the range of 86 to 88% by mass, with emphasis on ejection fluidity.

The flux component preferably contains a modified rosin, a solvent, an activator, and a thixotropic agent. The flux is optimal for the surface treatment of the metal filler, removes the oxide film of the metal filler during the reflow heat treatment, and promotes melting of the metal and alloying by thermal diffusion. A known material can be used as the flux.
In addition, as a connection method using a solder paste, a paste is applied to the substrate electrode, and then a mounting component is mounted and connected by reflow heat treatment, or a paste is applied to the mounted component electrode or the substrate electrode and bumps are formed by reflow heat treatment. Thereafter, a method of connecting the component and the substrate and connecting them again by reflow heat treatment may be used.

Hereinafter, the present invention will be specifically described by way of examples.
[Example 1]
(1) Production of first metal particles Ag 1.0 kg (purity 99 mass% or more), Bi 2.0 kg (purity 99 mass% or more), Cu 1.5 kg (purity 99 mass% or more), In 2.0 kg (purity 99 mass%) Above), and 3.5 kg of Sn (purity 99% by mass or more) were placed in a graphite crucible and heated and melted to 1400 ° C. with a high-frequency induction heating apparatus in a helium atmosphere of 99% by volume or more.
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. (Pressure less than 2.5 MPa) was atomized to produce metal particles. The cooling rate at this time was 2600 ° C./second.

When the obtained metal particles were observed with a scanning electron microscope (Hitachi, Ltd .: S-3400N), they were spherical.
The metal particles were classified with an airflow classifier (Nisshin Engineering: TC-15N) at a setting of 5 μm, the large particle side was collected, and then again classified at a setting of 20 μm, and the small particle side was collected. When the recovered metal particles were measured with a laser diffraction particle size distribution analyzer (HELOS & RODOS), the average particle size was 6.3 μm.
Next, the metal particles were measured with a differential scanning calorimeter (Shimadzu Corporation: DSC-50) in the range of 40 to 580 ° C. under a nitrogen atmosphere under a temperature rising rate of 10 ° C./min. The obtained DSC chart is shown in FIG.
As shown in FIG. 1, endothermic peaks were detected at 65 ° C., 88 ° C., and 383 ° C., and the presence of a plurality of alloy phases was confirmed from the presence of a plurality of melting points.

(2) Production of second metal particles Ag 3.2 kg (purity 99 mass% or more), Bi 0.5 kg (purity 99 mass% or more), Cu 1.0 kg (purity 99 mass% or more), In 0.5 kg (purity 99 mass%) Above) and Sn 4.8 kg (purity 99 mass% or more) were put in a graphite crucible and heated and melted to 1400 ° C. with a high-frequency induction heating apparatus in a helium atmosphere of 99 volume% or more.
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. (Pressure less than 2.5 MPa) was atomized to produce metal particles. The cooling rate at this time was 2600 ° C./second.

When the obtained metal particles were observed with a scanning electron microscope (Hitachi, Ltd .: S-3400N), they were spherical.
The metal particles were classified with an airflow classifier (Nisshin Engineering: TC-15N) at a setting of 5 μm, the large particles were collected, and then classified again at a setting of 30 μm, and the small particles were collected. The recovered metal particles were measured with a laser diffraction particle size distribution analyzer (HELOS & RODOS), and the average particle size was 6.6 μm.
Next, the metal particles were measured with a differential scanning calorimeter (Shimadzu Corporation: DSC-50) in the range of 40 to 580 ° C. under a nitrogen atmosphere under a temperature rising rate of 10 ° C./min. The obtained DSC chart is shown in FIG.

  As shown in FIG. 2, endothermic peaks were detected at 197 ° C., 363 ° C., and 416 ° C., and the presence of multiple alloy phases was confirmed from the presence of multiple melting points. In addition, since an exothermic peak was detected at 131 ° C., the presence of a metastable alloy phase could be confirmed.

(3) Production of third metal particles Ag 1.0 kg (purity 99 mass% or more), Bi 0.5 kg (purity 99 mass% or more), Cu 6.5 kg (purity 99 mass% or more), In 0.5 kg (purity 99 mass%) Above) and 1.5 kg of Sn (purity 99% by mass or more) were placed in a graphite crucible and heated and melted to 1400 ° C. with a high-frequency induction heating device in a helium atmosphere of 99% by volume or more.
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. (Pressure less than 2.5 MPa) was atomized to produce metal particles. The cooling rate at this time was 2600 ° C./second.
When the obtained metal particles were observed with a scanning electron microscope (Hitachi, Ltd .: S-3400N), they were spherical.

The metal particles were classified with an airflow classifier (Nisshin Engineering: TC-15N) at a setting of 1.6 μm, the large particle side was collected, and then again classified at a setting of 10 μm, and the small particle side was collected. The recovered metal particles were measured with a laser diffraction particle size distribution analyzer (HELOS & RODOS), and the average particle size was 2.7 μm.
Next, the metal particles were measured with a differential scanning calorimeter (Shimadzu Corporation: DSC-50) in the range of 40 to 580 ° C. under a nitrogen atmosphere under a temperature rising rate of 10 ° C./min. The obtained DSC chart is shown in FIG.

  As shown in FIG. 3, endothermic peaks were detected at 499 ° C. and 519 ° C., and the presence of a plurality of alloy phases was confirmed from the presence of a plurality of melting points. Further, an exothermic peak was detected at 255 ° C., and the presence of a metastable alloy phase could be confirmed.

(4) Manufacture of 4th metal particle Sn 10.0kg (purity 99 mass% or more) was put into the graphite crucible, and it heated and melted to 1400 degreeC with the high frequency induction heating apparatus in 99 volume% or more helium atmosphere.
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) was atomized to produce Sn particles. The cooling rate at this time was 2600 ° C./second.
When the obtained Sn particles were observed with a scanning electron microscope (Hitachi, Ltd .: S-3400N), they were spherical.

The Sn particles were classified with an airflow classifier (Nisshin Engineering: TC-15N) at a setting of 5 μm, the large particles were collected, and then classified again at a setting of 40 μm, and the small particles were collected. The collected Sn particles were measured with a laser diffraction particle size distribution analyzer (HELOS & RODOS), and the average particle size was 6.9 μm.
Next, the metal particles were measured with a differential scanning calorimeter (Shimadzu Corporation: DSC-50) in the range of 40 to 580 ° C. under a nitrogen atmosphere under a temperature rising rate of 10 ° C./min. As a result, an endothermic peak was detected at 242 ° C., and it was confirmed that it had a melting point of 232 ° C. (melting start temperature: solidus temperature). A characteristic exothermic peak was not detected.

(5) Production of solder paste The first to fourth metal particles were mixed at a weight ratio of 100: 103: 112: 91 to obtain a metal filler. Next, 89.5% by mass of the metal filler and 10.5% by mass of the rosin flux are mixed and solder paste is sequentially applied to a solder softener (Malcom: SPS-1) and a defoaming kneader (Matsuo Sangyo: SNB-350). Was made.

(6) Confirmation of bonding strength (shear strength (MPa))
Next, the solder paste is printed and applied onto a Cu substrate having a size of 25 mm × 25 mm and a thickness of 0.25 mm, and after mounting a Cu chip having a size of 2 mm × 2 mm and a thickness of 0.5 mm, under a nitrogen atmosphere at a peak temperature of 150 ° C. A sample was prepared by reflow heat treatment.
A reflow simulator (Malcom: SRS-1C) was used as the heat treatment apparatus. The temperature profile is as follows: from the start of heat treatment (normal temperature) to 65 ° C. at a rate of 1.0 ° C./second, gradually increasing from 65 ° C. to 115 ° C. over 120 seconds, then from 115 ° C. to 150 ° C. The temperature was raised at a rate of 5 ° C./second, and a condition of holding at a peak temperature of 150 ° C. for 20 seconds was adopted. For the printing pattern formation, a screen printer (Microtech: MT-320TV) was used, the plate was made of metal, and the squeegee was made of urethane. The mask opening size is 2 mm × 3.5 mm, and the thickness is 0.1 mm. 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.
Next, the chip bonding (shearing) strength in the shearing direction of the produced sample was measured at a pressing speed of 10 mm / min with a push-pull gauge at room temperature (25 ° C.), and the unit area was 4.8 MPa.

(7) Confirmation of repairability (180 ° C repair)
The prepared sample was placed on a hot plate heated to 180 ° C. After a few seconds, partial melting of the solder was confirmed. The Cu chip could be removed by simply pressing it with tweezers.

[Examples 2 to 7]
A mixture in which the mixing ratio of the first to fourth metal particles described in Example 1 was changed to a metal filler, and after pasting and reflow heat treatment in the same manner as in Example 1, chip bonding strength was measured. Table 1 below shows as Examples 2-7.

[Comparative Examples 1-3]
Also, in Table 1, as Comparative Examples 1 and 2, the case where the metal filler is a mixture of only the third metal particles and the fourth metal particles, and as Comparative Example 3 is the result in the case of Sn-37Pb eutectic solder. Indicates.
As apparent from the results in Table 1, when the metal filler of the present invention is used, solder connection can be performed at a peak temperature of 150 ° C., and after connection, repair can be performed at 180 ° C.

[Examples 8 and 9]
The third metal particles before classification produced by gas atomization in Example 1 were classified using an airflow classifier (Nisshin Engineering: TC-15N) at a setting of 20 μm, and after collecting the large particles, classification was performed again at a setting of 30 μm. Then, using the metal particles having an average particle diameter of 13.9 μm obtained by collecting the small particle side, similarly to Example 1, mixed with the first metal particles, the second metal particles, and the fourth metal particles, After pasting and reflow heat treatment, the chip bonding strength (shear strength) in the shear direction and 180 ° C. repair were confirmed. The results are shown in Table 2 below.
As is clear from the results in Table 2, it was confirmed that even with the third metal particles having the same composition, the bonding strength was improved when the particle size was large.

  The present invention can be melt-bonded at a temperature lower than the mounting temperature (reflow heat treatment temperature) of Sn-37Pb eutectic solder (peak temperature of 150 ° C. or higher), and after mounting, at a temperature condition equivalent to Sn-37Pb eutectic solder. It can be applied as a repairable lead-free solder material.

Claims (3)

  1st metal particle which consists of an alloy which has composition of Ag5-15 mass%, Bi15-25 mass%, Cu10-20 mass%, In15-25 mass%, and Sn15-55 mass%, Ag25-40 mass%, Bi2 Second metal particles made of an alloy having a composition of ˜8 mass%, Cu 5-15 mass%, In 2-8 mass%, and Sn 29-66 mass%, the first metal particles and the second metal particles The metal filler, wherein the mixing ratio is 90 to 110 parts by mass of the second metal particles with respect to 100 parts by mass of the first metal particles.   3rd metal particle which consists of an alloy which has composition of Ag5-15 mass%, Bi2-8 mass%, Cu49-81 mass%, In2-8 mass%, and Sn10-20 mass%, and 4th metal particle which consists of Sn The mixing ratio of the first to fourth metal particles is 90 to 110 parts by mass of the second metal particles and 4 to 2120 parts by mass of the third metal particles with respect to 100 parts by mass of the first metal particles. And the metal filler of Claim 1 which is 5-2505 mass parts of this 4th metal particle.   A solder paste containing the metal filler according to claim 1.

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