US20060067853A1 - Lead free solder - Google Patents

Lead free solder Download PDF

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Publication number
US20060067853A1
US20060067853A1 US11/222,808 US22280805A US2006067853A1 US 20060067853 A1 US20060067853 A1 US 20060067853A1 US 22280805 A US22280805 A US 22280805A US 2006067853 A1 US2006067853 A1 US 2006067853A1
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Prior art keywords
tin
solder
lead
zinc
free solder
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US11/222,808
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Inventor
Toshihide Takahashi
Kazutaka Matsumoto
Izuru Komatsu
Masahiro Tadauchi
Yoshiyuki Fukuda
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Toshiba Corp
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Toshiba Corp
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Assigned to KABUSHKI KAISHA TOSHIBA reassignment KABUSHKI KAISHA TOSHIBA ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: FUKUDA, YOSHIYUKI, KOMATSU, IZURU, MATSUMOTO, KAZUTAKA, TADAUCHI, MASAHIRO, TAKAHASHI, TOSHIHIDE
Publication of US20060067853A1 publication Critical patent/US20060067853A1/en
Abandoned legal-status Critical Current

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
    • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
    • B23K35/24—Selection of soldering or welding materials proper
    • B23K35/26—Selection of soldering or welding materials proper with the principal constituent melting at less than 400 degrees C
    • B23K35/262—Sn as the principal constituent

Definitions

  • the present invention relates to lead-free solder and, in particular, to lead-free solder including tin as a base material and having an excellent creep property. Moreover, the present invention relates to lead-free solder having enough tensile strength and excellent rupture elongation.
  • lead-free solder mainly a tin-silver-copper based alloy is at a practical stage and the substitution of lead-free solder for lead solder is scheduled to be completed.
  • lead-free solder technologies are used for bonding materials used when electronic parts are mounted on a printed wiring board.
  • a lead-free solder technology used for lead included in the plating of electrodes or the internal bonding material of electronic parts is not at a mature stage. For this reason, there is a further required to advance the technology for completely eliminating all lead from electronic device products including lead in the electronic parts.
  • a heat radiating function is indispensable and hence a heat sink is used in the device.
  • a ceramic material which is a body having high thermal conductivity and insulation, is used for a substrate with a power semiconductor element thereon. Tin-lead eutectic solder was conventionally used for a bonding material in a power device for bonding this ceramic substrate to a heat sink including copper as a main component.
  • the ceramic substrate is greatly different in the coefficient of thermal expansion from copper used for the heat sink, when the tin-lead eutectic solder is cooled from the solidification point of tin-lead eutectic solder, that is, 183° C. to room temperature, thermal stress is developed in the solder for bonding the ceramic substrate to the copper plate.
  • the conventional tin-lead eutectic solder can decrease the developed thermal stress because of its characteristic that the tin-lead eutectic solder creeps easily.
  • the present invention provides a lead-free solder comprising tin and zinc at a weight ratio between tin and zinc ranging from about 88:12 to about 80:20.
  • FIG. 1 shows a schematic sectional side view of a power semiconductor device.
  • FIG. 2 shows a graphic diagram illustrating the dependency upon the Zn content for strain rate.
  • FIG. 3 shows a graphic diagram illustrating the dependency upon the Ag content for strain rate.
  • FIG. 4 shows a graphic diagram illustrating the dependency upon the Cu content for strain rate.
  • solder in accordance with the first embodiment, have characteristics including a high stain rate even under low stress and have excellent in creep properties. Hence, the lead-free solders can relax the thermal stress developed when substrates having different thermal coefficients of expansion, for example, a ceramic substrate, and a copper plate are bonded to each other and can relax warping of the substrates.
  • these solders will be described.
  • Tin-zinc solder with an eutectic composition is lower in melting point than tin and zinc and is also lower in surface tension than tin and zinc. Moreover, the tin-zinc eutectic composition solder is lower in melting point than the other lead-free solders and is close in the melting point to tin-lead eutectic composition solder. Hence, soldering by the tin-zinc solder can be conducted at the same bonding temperature as the conventional tin-lead solder. Moreover, the tin-zinc based solder is higher in electric conductivity than the conventional tin-lead based solder and, hence, is lower in heat generation developed by the passage of current. Therefore, the tin-zinc based solder is advantageous also in terms of energy consumption and thermal measures at the time of conductive bonding.
  • the weight ratio between tin and zinc is from about 88:12 to about 80:20. This is because when the ratio of zinc in the weight ratio between tin and zinc is higher than about 80:20, although a solidus line temperature is constant at 199° C., a liquidus line temperature increases. Hence, the solder of this composition is hard to melt sufficiently at a soldering temperature. On the other hand, when the ratio of zinc in the weight ratio between tin and zinc is lower than about 88:12, the composition of the solder is close to a eutectic composition and the difference between a solidus line temperature and a liquidus line temperature is smaller.
  • the weight ratio between tin and zinc (Sn:Zn) is from about 86:14 to about 83:17.
  • the upper limit value of Zn content is determined from a liquidus line temperature, which is measured at a temperature increasing rate of 10° C./min by the use of a differential scanning calorimeter (DSC) and is shown in Tables 1, 2.
  • the coefficient of linear expansion of the tin-zinc based solder having a weight ratio between tin and zinc (Sn:Zn) ranging from about 88:12 to about 80:20 is smaller than those of simple substances of tin and zinc, and currently used lead-containing solder (Sn-37Pb) and is close to the coefficient of linear expansion of copper (1.62 ⁇ 10 ⁇ 5 [1/K]).
  • this tin-zinc based solder is particularly useful as the bonding material of devices and apparatuses including power semiconductor elements. Moreover, this tin-zinc based solder is similarly useful also for bonding parts formed of metal, except copper, having a small coefficient of linear expansion, for example, iron, nickel and the like.
  • strain rate is a steady strain rate when stress is 10 MPa.
  • a test sample 10 having a weight ratio between tin and zinc of about 88:12 was higher in strain rate when stress was 10 MPa than a test sample 9 of eutectic composition. Moreover, the test sample 10 with a weight ratio between tin and zinc of about 88:12 was the lowest in a 0.2% proof stress. It could be said from these facts that the solder having a weight ratio between tin and zinc of about 88:12 was more easily deformed and was more excellent in creep characteristic under low stress than the eutectic composition solder. In other words, in the case of relaxing thermal stress developed in a power device, the use of solders excellent with a creep characteristic is preferable.
  • tin-silver-copper based solder is the most suitable solder for practical use as a lead-free solder.
  • Sn-3.0Ag-0.5Cu which is used for a wide variety of applications as described in the Background of the Invention, as it is, as the bonding material for a power device.
  • Ag 3 Sn of a metallic compound crystallizes out in the structure of solder or the eutectic composition of tin, silver, and copper is hard, the solder increases in mechanical strength and, hence, does not have enough ductility and, hence, does not permit stress relaxation.
  • the tin-silver based binary solder it is preferable to prepare the tin-silver based binary solder.
  • a weight ratio between tin and silver (Sn Ag) is from about 99.9:0.1 to about 98.0:2.0, more preferably, about 99.7:0.3 to about 99.0:1.0. It is possible to increase the creep characteristic of the tin-silver based solder by decreasing the weight ratio of silver less than eutectic composition.
  • the difference between a liquidus line temperature and a solidus line temperature can be increased, which in turn can make the solidification process progress gradually and, hence, can reduce residual stress.
  • a weight ratio between the total weight of tin and silver and copper ((Sn+Ag):Cu) is from about 99.9:0.1 to about 99.5:0.5, in the case a weight ratio between tin and silver (Sn:Ag) is from about 99.9:0.1 to about 98.0:2.0.
  • a weight ratio between tin and copper (Sn:Cu) is about 99.3:0.7 and, hence, the longest part of the solder comprises tin. For this reason, when comparison is made on the creep characteristic among tin-silver based solder, tin-zinc based solder, and tin-copper based solder, each of which has a eutectic composition, the tin-copper based solder having a eutectic composition shows the most excellent creep characteristic.
  • the 11 phase (Cu 6 Sn 5 ) of a metallic compound, which is hard and brittle, is crystallized in the solder by supercooling.
  • solder having this composition ratio When solder having this composition ratio is cooled at a cooling rate conducted in a wide variety of applications, a metallic structure of a tin-copper eutectic structure and a ⁇ -Sn phase is observed and the crystallization of a metallic compound can be prevented.
  • the tin-zinc based solder is a solder having an excellent creep characteristic as described above and is suitable for use as the internal bonding material of a power device and also in terms of the bonding temperature and the coefficient of linear expansion. Moreover, by adding silver to the tin-zinc based solder, solder wettability can be improved.
  • the weight ratio between tin and zinc ranges from about 88:12 to about 80:20
  • This tin-zinc-copper based solder has small surface tension and excellent solder wettability when it is melted.
  • the weight ratio of silver is outside the above range, the weight ratio of silver in an eutectic phase is increased to make the eutectic phase stronger or to crystallize Ag 3 Sn of a metallic compound thereby to losing the conventional characteristic of an excellent creep characteristic, which is not preferable.
  • the weight ratio between the total of tin and zinc and silver preferably ranges from about 99.99:0.01 to about 95:5, more preferably, from about 99:1 to about 97:3.
  • the solidus line temperature of the tin-zinc based solder is approximately 199° C. and, hence, soldering by the tin-zinc based solder can be conducted at a bonding temperature that is the same as using the tin-lead eutectic solder currently used.
  • the addition of copper to the tin-zinc based solder like the addition of zinc, decreases the melting point.
  • the weight ratio between tin and zinc ranges from about 88:12 to about 80:20 and that the weight ratio between the total of tin and zinc and copper ((Sn+Zn):Cu) ranges from about 99.9:0.1 to about 99.5:0.5.
  • the solidus line temperature of tin-zinc based solder of this composition is approximately 194° C.
  • the addition of copper is conducive to the enhancement of mechanical strength, in particular, tensile strength, and, hence, is not preferable in terms of losing the creep characteristic intrinsic to the tin-zinc based solder.
  • the weight ratio between the total of tin and zinc and copper ((Sn+Zn):Cu) preferably ranges from about 99.9:0.1 to about 99.5:0.5, more preferably, from about 99.9:0.1 to about 99.7:0.3.
  • the second embodiment relates to a semiconductor including: a first body to be bonded; a second body to be bonded which is different in the coefficient of thermal expansion from about the first body; and lead-free solder that is interposed between the first body to be bonded and the second body to be bonded.
  • the solder contains tin and zinc and the zinc content in a surface in contact with the first body to be bonded is larger than the zinc content in a surface in contact with the second body to be bonded.
  • the second embodiment relates to solder for bonding the first body to the second body which is different in the coefficient of thermal expansion from the first body to be bonded and to lead-free solder which contains tin and zinc.
  • the zinc content in a surface in contact with the first body is larger the a zinc content in a surface in contact with the second body to be bonded.
  • Such lead-free solder has the function and effect of having excellent tensile strength and rupture elongation.
  • the second body 8 to be bonded is arranged on the first body 2 to be bonded with lead-free solder 4 and a metal circuit board 6 sandwiched there between.
  • a power semiconductor element 20 a including a metal circuit board 10 a , a solder resistor 12 a arranged on the metal circuit board 10 a and having high-temperature solder 14 a embedded therein, a power semiconductor pellet 16 a arranged on the high-temperature solder 14 a ; and a power semiconductor element 20 b having the same construction as the power semiconductor element 20 a.
  • the power semiconductor pellets 16 a , 16 b such as power transistors generate a large amount of heat when high voltage and high current are applied thereto. For this reason, when the power semiconductor device mounted with the power semiconductor pellets 16 a , 16 b is repeatedly activated and deactivated to repeat the cycles of increasing and decreasing temperature, a thermal stress is developed by the difference in the coefficient of linear expansion between materials to cause strain in the bonded portions of parts in the power semiconductor device. When the temperature is rapidly increased, the high-temperature solders 14 a , 14 b , comprising the bonded portions, are melted. When physical damage, such as crack and rupture, is caused by the melting, the performance of the power semiconductor device is changed. In short, thermal fatigue has a large effect.
  • the second body 8 on which the power semiconductor pellets 16 a , 16 b are directly mounted, is made of aluminum, silicon oxide, or silicon nitride to ensure the strength of the whole power semiconductor device.
  • the coefficient of linear expansion of the second body 8 is greatly different from that of the first body 2 and the difference in the coefficient of linear expansion is approximately 2 to 10 times (for example, the coefficient of linear expansion of aluminum nitride (AIN) is 4 ⁇ 10 ⁇ 6 /K, whereas that of copper (Cu) is 17.7 ⁇ 10 ⁇ 6 /K).
  • AIN aluminum nitride
  • Cu copper
  • the conventionally used tin-lead (Sn—Pb) eutectic solder has an excellent ductility property in a range from room temperatures to 125° C.
  • the solder can follow the contraction due to its deformability.
  • the solder does not cause substantial cracking at the bonding portions and, hence, is useful for ensuring the reliability of the power semiconductor device.
  • solder containing lead cannot be used.
  • tin (Sn)-zinc (Zn) based solder in which the zinc content is changed in a functionally gradient manner from one bonding surface to the other bonding surface in one pair of portions to be bonded, is useful as a deformable solder.
  • the inventors have found it useful: to change the zinc content of tin-zinc based solder in a functionally gradient manner to increase deformability to the tin-zinc based solder; and to insert the tin-zinc based solder between one pair of surfaces to be bonded, in which the surfaces are different in the coefficient of linear expansion, to use the tin-zinc based solder as a bonding material.
  • This can be achieved by arranging an alloy layer having low deformability characteristic and a composition high in zinc content on the second body 8 having a small coefficient of linear expansion of the power semiconductor device and by arranging an alloy layer having high deformability and a composition relatively low in zinc content on the first body 2 having a large coefficient of linear expansion.
  • equation (1) shows that when the second body 8 and the first body 2 are arranged on the upper side and on the lower side in the structure of the power semiconductor device, the zinc content of the uppermost layer of lead-free solder 4 in contact with the second body 8 on the upper side of the power semiconductor device is X (mass %).
  • equation (2) shows that the zinc content Y (mass %) of the lowermost layer of lead-free solder 4 in contact with the first body 2 on the lower side of the device varies as a dependent variable of X.
  • the tin-zinc based alloys are worked in a low-oxygen atmosphere with an oxygen concentration of 100 ppm or less, the tin-zinc based alloys can be worked into the shape of a sheet while they are put into press-contact with each other. For this reason, not only by arranging two sheets of different compositions in layers as the solder construction but also arranging multiple layers, such as three and four layers of different compositions in a functionally gradient manner, deformability can be enhanced within a range satisfying equations (1) and (2).
  • the process temperature of an apparatus in a melting process can be set within a range from 240° C. to 270° C., which is within the range of process temperature control of a currently used soldering apparatus.
  • the process temperature of the layers of sheet-shaped solder can be easily controlled.
  • solder containing zinc When solder containing zinc is oxidized, a melting temperature is rapidly increased and wettability and strength are extremely decreased.
  • a process of preparing solder in particular, a process of melting and mixing solder is performed in such a way that the oxygen content of obtained solder is 100 ppm (by weight) or less while the solder is prevented from being oxidized by the use of a non-oxidizing atmosphere such as nitrogen or argon.
  • a non-oxidizing atmosphere such as nitrogen or argon.
  • phosphorus, magnesium or the like which has a low melting point and easily reacts with oxygen, as a deoxidizer for these melted raw materials.
  • the deoxidizer reacts with oxygen in the melted raw materials and floats up as a slug to the surface of the melted raw materials, so that the oxygen contained in tin and zinc as raw materials can be easily removed. It is preferable that the amount of deoxidizer is approximately 0.01 to 0.1 weight % of the raw materials. When raw materials deoxidized by this method are used, sheet-shaped solder with an oxygen content is decreased to 30 ppm or less can be prepared.
  • the prepared solder has flux added thereto, if necessary, after it is worked into the sheet-shaped solder, so that bonding can be completed.
  • the flux is prepared by mixing various substances as required to achieve efficient chemical and physical action.
  • the amount of oxygen on the surface of the bonded body is decreased by a reducing treatment.
  • the reducing treatment may use alcohol vapor such as methanol vapor, ethanol vapor, or propanol vapor; acid vapor such as formic acid, acetic acid, or the like; and a reducing gas such as ammonia, hydrogen, or the like, whereby soldering can be performed.
  • a method of integrating a device with a heat sink includes reflow heating and VPS.
  • a non-oxidizing atmosphere such as nitrogen gas, argon gas, or the like, or in a low-oxygen atmosphere having an oxygen concentration of 1000 weight ppm or less, the reliability of bonded surfaces can be improved.
  • Lead-free solder in accordance with the first and second embodiments can be used as a substitute for the internal bonding material of the conventional power semiconductor device.
  • the lead-free solder in accordance with the first and second embodiments is a material suitable for forming a junction and a film in a power semiconductor pellet and a device using the same.
  • the power semiconductor device is constructed in the form of a power module, such as power transistor module, a power IC, or the like, which uses a power bipolar transistor, a thyristor, a GTO thyristor, a power diode, a power MOS field effect transistor (power MOSFET), or the like as the power semiconductor pellet.
  • the lead-free solder in accordance with the first and second embodiments can be applied to the bonding of not only parts of one kind of metal such as copper, silver, gold, nickel, aluminum, SUS stainless steel, or the like, but also parts of alloy materials, composite metallic materials, or the like.
  • a metallic pre-coating may be previously applied to the parts by plating, press-contacting, or the like according to the materials of the parts to be bonded, and the composition of the pre-coating and a method of pre-coating can be suitably selected.
  • the thickness of a sheet-shaped lead-free bonding material is within a range from about 0.05 mm to about 0.5 mm and, to secure appropriate thermal conductivity, it is more preferable that the thickness is within a range from about 0.1 mm to about 0.3 mm.
  • An ingot of tin having a purity of 99.99% or higher was put into a rectangular solder melting tank. Then, the tin ingot was heated to the melting point by a heater attached to the outside of the solder melting tank. At the start of melting, nitrogen was introduced into the upper portion of the solder melting tank to bring the concentration of oxygen in a nitrogen atmosphere to 50 ppm or less. After the tin ingot was melted, the temperature of tin melt was kept at 450° C. by a feedback control.
  • a zinc ingot, a silver ingot, and a copper ingot were added to the tin melt to be melted so as to make composition ratios shown in Table 3.
  • the temperature of the melt was maintained at 450° C. by the feedback control. Parts of the melts were taken out of the solder melting tank and were cooled to room temperature to produce uniform materials of solder.
  • the materials of solder produced in the above manner were cut into tensile test samples, each having a cross section of 4.0 mm ⁇ 5.0 mm and a gage length of 25.0 mm.
  • the dependency upon Zn, Ag, Cu concentrations for strain rate are shown in FIG. 2 to FIG. 4 .
  • a clear characteristic of the Sn—Zn based alloy of binary elements is that it does not form a metallic compound, and when the zinc content is from about 9 to about 20 mass %, as shown by the results of rupture elongation, a reduction in ductility was not observed.
  • the Sn—Zn based solder showed more remarkably excellent characteristics than Sn-9Zn eutectic solder, the peak of which was shown by the Sn—Zn based solder containing about 15 mass % zinc.
  • the samples of Sn—Zn based solder were excellent on the whole.
  • a sheet-shaped solder of 1 mm length ⁇ 1 mm width ⁇ 0.1 mm thick was placed on a copper plate (oxygen-free copper having its surface previously cleaned by acid) of 15 mm length ⁇ 30 mm width ⁇ 0.3 mm thick. Then, the solder was heated by a hot plate to 250° C. to check the wettability of the solder. At that time, experiments were conducted in the case of using flux (RA) and in the case of not using flux.
  • RA flux
  • A A case where the sheet-shaped solder was wetted and kept its initial area was assumed to be A
  • B a case where the sheet-shaped solder wetted, though the area decreased, was assumed to be B
  • C a case where the sheet-shaped solder was not wet was assumed to be C.
  • a three-point bending test (load capacity: ⁇ 1 kN, displacement accuracy: 0.5 ⁇ m) was conducted to check the bending elastic characteristic of bonded portion of the sheet-shaped solder.
  • a sheet-shaped solder of 1 mm length ⁇ 1 mm width ⁇ 0.1 mm thick was bonded to the center of a copper plate (oxygen-free copper having its surface previously cleaned by acid) of 15 mm length ⁇ 30 mm width ⁇ 0.3 mm thick. The center was made a reference point and a measurement was conducted at a jig displacement speed of 0.1 mm/sec.
  • a ceramic substrate of 70 mm length ⁇ 35 mm width ⁇ 1 mm thick was bonded to a copper plate of 100 mm length ⁇ 50 mm width ⁇ 10 mm thick by a sheet-shaped solder of 65 mm length ⁇ 30 mm width ⁇ 0.1 mm thick, and the amount of warp developed at that time was measured at a bonding temperature of 25° C. and in the case of using flux (RA).
  • lead-free bonding materials could be provided, which could be prepared at low cost and with ease, by the use of raw materials, with a wide variety of applications, and can relax the thermal stress caused by the coefficient of thermal expansion of a substrate.
  • Respective alloys were prepared by heating and melting tin having a purity of 99.98% and zinc having a purity of 99.99% in a nitrogen atmosphere of an oxygen concentration of 100 ppm or less, so as to make the compositions of examples 30 to 45 and comparative examples 13 to 16 shown in Table 6. Then, the melts were cooled to room temperature and were rolled into sheets by a rolling machine to produce sheet-shaped materials of solder.
  • Flux containing 12 mass % rosin, 0.1 mass % halogen in terms of chlorine, and isopropyl alcohol as a solvent was dropped at a rate of 0.01 cc/cm 2 over the surface of the produced solder and then was sandwiched between a ceramic substrate (size: 35 mm ⁇ 70 mm ⁇ 1 mm t) as the second body to be bonded and a copper plate (heat sink plate: 40 mm ⁇ 75 mm ⁇ 3 mm t) as the first body to be bonded. Further, the sandwiched product was heated and melted within a reflow peak temperature ranging from about 230° C. to about 270° C. for a maximum of 20 seconds to melt the solder to produce a bonded body.
  • the degree of warp developed at this time was measured and evaluated as follows: when compared with the warp (mean warp: 100 ⁇ m) of a bonded body produced by the same method except for overlaying two sheets made of tin-lead eutectic solder and having a thickness of 100 ⁇ m, a case where the degree of warp is +30 or less was determined to be A; a case where the degree of warp was from +30% to +70% was determined to be B; and a case where the degree of warp was +70% or more or a case where cracks developed was determined to be C.
  • the evaluation results are shown in Table 6.
  • Example 30 100 0 100 silicon nitride copper 230 A
  • Example 31 25 100 1 100 silicon nitride copper 230 A
  • Example 32 25 100 2 100 silicon nitride copper 230 B
  • Example 33 30 100 0 100 silicon nitride copper 240 A
  • Example 34 30 100 5 100 silicon nitride copper 240 A
  • Example 35 30 100 5 70 silicon nitride copper 240 A
  • Example 36 30 130 5 70 silicon nitride copper 240 A
  • Example 37 30 100 7 100 silicon nitride copper 240 B
  • Example 38 30 100 5 100 aluminum nitride copper 240 A
  • Example 39 30 100 5 100 aluminum nitride copper 240 A
  • Example 40 30 100 5 100 aluminum nitride nickel/gold 240 A plating
  • Example 41 30 100 5 100 silicon nitride without 240 A (subjected to asperity producing treatment)
  • Example 42 30 100 5 100 silicon nitride tungsten 240 A
  • Example 43
  • the bonding layer having a large deformability was formed by arranging the alloy with a small ductility on the side of the ceramic substrate having a small coefficient of thermal expansion and by arranging the alloy having a large ductility on the side of metal with a large coefficient of thermal expansion, even if the solder was lead-free, it was possible to prevent the occurrence of crack in the bonded portion of the power ceramic device.
  • lead-free solder that has an excellent creep characteristic and effective in stress relaxation.
  • the present invention can include various examples which have not described above. Therefore, the technical scope of the present invention should be determined only by the following claims appropriately derived from the above descriptions.

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US9308603B2 (en) 2012-11-15 2016-04-12 Industrial Technology Research Institute Solder, solder joint structure and method of forming solder joint structure
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CN105190869A (zh) * 2013-03-18 2015-12-23 三菱综合材料株式会社 接合体的制造方法、及功率模块用基板的制造方法
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