US20150328722A1 - Lead-free solder alloy - Google Patents

Lead-free solder alloy Download PDF

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Publication number
US20150328722A1
US20150328722A1 US14/653,502 US201214653502A US2015328722A1 US 20150328722 A1 US20150328722 A1 US 20150328722A1 US 201214653502 A US201214653502 A US 201214653502A US 2015328722 A1 US2015328722 A1 US 2015328722A1
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United States
Prior art keywords
solder
solder alloy
content
alloy
lead
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US14/653,502
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English (en)
Inventor
Masayuki Suzuki
Naoko Hirai
Shunsaku Yoshikawa
Ken Tachibana
Rei Fujimaki
Hikaru Nomura
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Senju Metal Industry Co Ltd
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Senju Metal Industry Co Ltd
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Publication of US20150328722A1 publication Critical patent/US20150328722A1/en
Assigned to SENJU METAL INDUSTRY CO., LTD. reassignment SENJU METAL INDUSTRY CO., LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: HIRAI, NAOKO, NOMURA, HIKARU, SUZUKI, MASAYUKI, TACHIBANA, KEN, YOSHIKAWA, SHUNSAKU
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
    • B23K35/02—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape
    • B23K35/0222—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape for use in soldering, brazing
    • B23K35/0244—Powders, particles or spheres; Preforms made therefrom
    • B23K35/025—Pastes, creams, slurries
    • 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
    • B23K35/02—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape
    • B23K35/0222—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape for use in soldering, brazing
    • 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
    • B23K35/02—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape
    • B23K35/0222—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape for use in soldering, brazing
    • B23K35/0244—Powders, particles or spheres; Preforms made therefrom
    • 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
    • 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
    • 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
    • B23K35/36—Selection of non-metallic compositions, e.g. coatings, fluxes; Selection of soldering or welding materials, conjoint with selection of non-metallic compositions, both selections being of interest
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C13/00—Alloys based on tin
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C13/00—Alloys based on tin
    • C22C13/02—Alloys based on tin with antimony or bismuth as the next major constituent
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/30—Assembling printed circuits with electric components, e.g. with resistor
    • H05K3/32—Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits
    • H05K3/34—Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits by soldering
    • H05K3/3457—Solder materials or compositions; Methods of application thereof
    • H05K3/3463—Solder compositions in relation to features of the printed circuit board or the mounting process
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K2201/00—Indexing scheme relating to printed circuits covered by H05K1/00
    • H05K2201/10—Details of components or other objects attached to or integrated in a printed circuit board
    • H05K2201/10613—Details of electrical connections of non-printed components, e.g. special leads
    • H05K2201/10621—Components characterised by their electrical contacts
    • H05K2201/10636—Leadless chip, e.g. chip capacitor or resistor
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present invention relates to a lead-free solder alloy.
  • in-vehicle electronic circuits Electronic circuits (hereinafter referred to as “in-vehicle electronic circuits”) obtained by soldering electronic parts to printed circuit boards are mounted on a vehicle.
  • Such in-vehicle electronic circuits are used in units for electrically controlling components such as engine, power steering and brake, and are safety parts which are very important for the vehicle travel. Therefore, the in-vehicle electronic circuits must be operable in a stable state over a prolonged period of time without causing any failure.
  • an in-vehicle electronic circuit for engine control is often disposed in the vicinity of the engine and is in a rather severe operating environment.
  • the in-vehicle electronic circuit is exposed to heat cycles in a range from ⁇ 30° C. or less to +100° C. or more by repeatedly operating and stopping the engine.
  • solder alloy joining the electronic parts to the printed circuit board is required to be expandable and contractible, in other words, to have ductility so as to prevent fracture of the solder joints.
  • the solder alloy having excellent ductility reduces the stress caused by the thermal displacement as described above.
  • a vehicle not only runs on a flat road but may also run on a rugged road. Therefore, the vehicle is subject to vibration and impact from the road surface and in-vehicle electronic circuits mounted on the vehicle are also subject to such vibration and impact. Then, since solder joints of the in-vehicle electronic circuits need to have a sufficient strength to withstand such vibration and impact, the solder alloy itself also needs to have a higher tensile strength.
  • Patent Literature 1 discloses an Sn—Ag—In—Bi solder alloy for use in a general electronic device to which Sb and Ni are added, the solder alloy comprising: 0.5 to 5% of Ag; 0.5 to 20% of In; 0.1 to 3% of Bi; in total up to 3% of at least one of Sb, Zn, Ni, Ga and Cu; and a balance of Sn.
  • a solder alloy whose composition is closest to that in the invention to be described later and is specifically disclosed is an Sn-3.5Ag-12In-0.5Bi-0.2Sb-0.3Ni solder alloy described in Example 22 of Patent Literature 1.
  • Patent Literature 1 only shows the results of whether or not the solder alloy becomes deformed after heat cycling, and does not study at all as to whether or not it is possible to obtain mechanical characteristics (e.g., tensile strength and ductility) sufficient for the solder alloy to be durably used as an in-vehicle electronic circuit.
  • mechanical characteristics e.g., tensile strength and ductility
  • the solder alloy studied in the foregoing literature contains no less than 8 to 24% of In but contains only 0.5% of Bi. Therefore, the solder alloy is considered to be inferior in tensile strength in spite of a high In content.
  • a high Bi content enlarges the solid-liquid coexisting region to make the solder alloy brittle due to precipitation of Bi, thus deteriorating the mechanical strength properties such as tensile strength and ductility.
  • the Bi content of only 0.5% is considered to avoid these problems.
  • composition described in Patent Literature 1 contains Sb and Ni in a total amount of no less than 0.5% in order to suppress allotropic transformation of Sn while also making the alloy structure uniform and compact to suppress ⁇ transformation of Sn.
  • solder alloy described in Patent Literature 1 thus needs to have a higher mechanical strength in an environment where vibration and impact are to be taken into account as in in-vehicle electronic circuits.
  • solder alloy for use in vehicles needs not only to suppress deformation in a heat cycle environment but also to suppress crack growth in solder joints in order to enhance the connection reliability.
  • An object of the present invention is to provide a solder alloy which has excellent tensile strength and ductility and which is capable of reducing costs while suppressing solder bump deformation and crack growth in solder joints after heat cycling.
  • the present invention aims at providing a lead-free solder alloy in which there is no deformation even after the passage of 800 cycles in a heat cycle test which involves keeping at temperatures of ⁇ 40° C. and +125° C. for 10 minutes, respectively, as one reference assuming an actual use, in which occurrence and growth of cracks are suppressed even after the passage of 3,000 cycles in a heat cycle test which involves keeping at temperatures of ⁇ 40° C. and +125° C. for 30 minutes, respectively, as one reference assuming an actual use, and which exhibits high tensile strength and ductility even at a reduced In content and can achieve a low cost.
  • the inventors of the present invention have made an intensive study on an alloy composition having a high tensile strength even at a reduced In content in the Sn-3.5Ag-12In-0.5Bi-0.2Sb-0.3Ni solder alloy specifically disclosed in Example 22 of Patent Literature 1.
  • the inventors of the invention have focused attention on how much Bi which is considered to deteriorate the tensile strength and the ductility because of its brittleness is contained and precisely adjusted the In and Bi contents.
  • the inventors of the invention obtained the finding that, by increasing the Bi content to 1.5 to 5.5% while suppressing the In content in a range of 1.0 to 7.0%, the tensile strength and the ductility are enhanced to such an extent that the solder alloy is usable under severe conditions as in a vehicle, thus suppressing deformation of the solder alloy after heat cycling.
  • the inventors of the invention confirmed refinement of crystal grains at joint interfaces when the Ni content is in a range of 0.01 to 0.2% and the Sb content is in a range of 0.01 to 0.15% as compared to Patent Literature 1.
  • the inventors of the invention also obtained the finding that the refinement of crystal grains suppresses occurrence and growth of cracks due to a heat cycle test and thus completed the invention.
  • the ductility as used in the specification refers to a value calculated from the ratio of the cross-sectional area of a fractured portion of a solder specimen to the cross-sectional area of the solder specimen before testing in a case where the solder specimen was broken in a tensile test.
  • the present invention is as follows:
  • a lead-free solder alloy having an alloy composition comprising: 1.0 to 7.0 wt % of In, 1.5 to 5.5 wt % of Bi, 1.0 to 4.0 wt % of Ag, 0.01 to 0.2 wt % of Ni, 0.01 to 0.15 wt % of Sb, and a balance of Sn.
  • solder paste comprising the lead-free solder alloy according to (1) or (2) above.
  • a solder joint comprising the lead-free solder alloy according to (1) or (2) above.
  • FIG. 1 is a cross-sectional schematic view for illustrating the crack growth rate.
  • FIG. 2( a ) is a cross-sectional scanning electron micrograph of a solder bump having a composition of Sn-3Ag-3Bi-3In-0.07Sb-0.05Ni according to the invention before heat cycling;
  • FIG. 2( b ) is a cross-sectional scanning electron micrograph of the solder bump after 200 heat cycles;
  • FIG. 2( c ) is a cross-sectional scanning electron micrograph of the solder bump after 800 heat cycles.
  • FIG. 3( a ) is a cross-sectional scanning electron micrograph of a solder bump having a composition of Sn-3Ag-3Bi-6In-0.07Sb-0.05Ni according to the invention before heat cycling;
  • FIG. 3( b ) is a cross-sectional scanning electron micrograph of the solder bump after 200 heat cycles;
  • FIG. 3( c ) is a cross-sectional scanning electron micrograph of the solder bump after 800 heat cycles.
  • FIG. 4( a ) is a cross-sectional scanning electron micrograph of a solder bump having a composition of Sn-3Ag-3Bi-9In-0.07Sb-0.05Ni in a comparative example before heat cycling
  • FIG. 4( b ) is a cross-sectional scanning electron micrograph of the solder bump after 200 heat cycles
  • FIG. 4( c ) is a cross-sectional scanning electron micrograph of the solder bump after 800 heat cycles.
  • FIG. 5( a ) is a joint surface scanning electron micrograph of a solder bump after reflow soldering which has a composition of Sn-3Ag-3Bi-3In in a comparative example
  • FIG. 5( b ) is a joint surface scanning electron micrograph of a solder bump after reflow soldering which has a composition of Sn-3Ag-3Bi-3In-0.02Sb-0.01Ni according to the invention
  • FIG. 5( c ) is a joint surface scanning electron micrograph of a solder bump after reflow soldering which has a composition of Sn-3Ag-3Bi-3In-0.06Sb-0.03Ni according to the invention.
  • FIG. 6( a ) is a joint surface scanning electron micrograph of a solder bump after reflow soldering which has a composition of Sn-3Ag-3Bi-3In-0.07Sb-0.05Ni according to the invention
  • FIG. 6( b ) is a joint surface scanning electron micrograph of a solder bump after reflow soldering which has a composition of Sn-3Ag-3Bi-3In-0.10Sb-0.07Ni according to the invention
  • FIG. 6( c ) is a joint surface scanning electron micrograph of a solder bump after reflow soldering which has a composition of Sn-3.0Ag-3.0Bi-3In-0.22Sb-0.29Ni in Comparative Example 8.
  • FIG. 7 is a diagram showing the distribution of the crack growth rate in solder joints of chip resistors joined using solder paste having a composition of Sn-3Ag-3Bi-3In in a comparative example and solder paste having a composition of Sn-3AG-3Bi-3In-0.07Sb-0.05Ni according to the invention.
  • a lead-free solder alloy according to the invention has the alloy composition as described below.
  • the In content is 1.0 to 7.0%. In enters into solid solution in ⁇ Sn to enhance the mechanical characteristics. Therefore, In enhances the tensile strength of the solder alloy. When the In content is less than 1.0%, the tensile strength of the solder alloy cannot be improved and crack growth cannot be suppressed after heat cycling. When the In content is 7.0 to 10.0%, ⁇ Sn is transformed into ⁇ Sn to deform the solder alloy itself after the heat cycle test independently of the external stress, thereby causing short circuit between adjacent electrodes. An In content of more than 7.0% not only increases costs but also excessively lowers the solidus temperature to cause the solder alloy to melt through the heat cycle test. An In content of more than 10% deteriorates the tensile strength.
  • the In content is preferably 1.0 to 6.5% and more preferably 1.0 to 6.0%.
  • the Bi content is 1.5 to 5.5%. Bi enters into solid solution in ⁇ Sn to enhance the mechanical characteristics. Therefore, Bi enhances the tensile strength of the solder alloy. Bi also improves the heat cycle characteristics and lowers the liquidus temperature. When the Bi content is less than 1.5%, addition of Bi does not produce any effect. When the Bi content is more than 5.5%, Bi enters into solid solution in a supersaturated state to make the solder alloy brittle. The Bi content is more preferably 2.5 to 4.0%.
  • the Bi and In ranges are thus optimized so as to obtain excellent joint reliability in terms of tensile strength, ductility and the like.
  • the reason why the joint reliability is obtained in terms of tensile strength, ductility and the like is presumed as follows: According to an Sn—Bi binary phase diagram, when the Bi content is more than 0.6% but less than 5.5%, Bi is in a supersaturated solid solution state with respect to Sn at room temperature. It is generally known that a Bi-rich phase appears when free energy for allowing the Bi-rich layer (enriched phase) to appear exceeds activation energy in the above state. When the Bi-rich phase appears, the solder joint portions get brittle.
  • the activation energy depends on energy stored by crystal grain boundaries and lattice defects such as point defects in a solder structure. In other words, the smaller the energy stored by lattice defects is, the higher the activation energy is.
  • the solder alloy according to the invention contains In. In has the effect of suppressing Sn lattice defects while increasing the activation energy necessary for allowing the Bi-rich phase to appear. For this reason, the Bi-rich phase (enriched phase) is considered to be prevented from appearing, thus stabilizing the solid solution state of Bi.
  • the alloy composition was precisely investigated from this point of view and as a result it was revealed that, in a case where the Bi content is 1.5 to 5.5%, an In content ranging from 1.0 to 7.0% suppresses appearance of the Bi-rich phase (enriched phase), reduces supersaturated solid solution of Bi and achieves high tensile strength and excellent ductility.
  • the solder alloy according to the invention can exhibit a high tensile strength and maintain excellent ductility because the Bi content is in a proper range although the In content is decreased compared to the alloy composition disclosed in Patent Literature 1.
  • the Ag content is 1.0 to 4.0%.
  • Ag precipitates intermetallic compounds such as Ag3Sn and hence enhances the tensile strength of the solder alloy. Ag also contributes to improving the heat cycle characteristics and improves the wettability on soldered portions at the time of soldering.
  • addition of Ag cannot produce any effect. Addition of Ag in an amount of more than 4.0% does not considerably improve the tensile strength.
  • the liquidus temperature is also increased to reduce the solderability. In addition, it is not economically preferable to add expensive Ag in a large amount.
  • the Ag content is preferably 1.0 to 3.0% and more preferably 2.0 to 3.0%.
  • the Ni content is 0.01 to 0.2% and the Sb content is 0.01 to 0.15%.
  • Ni and Sb promote refinement of intermetallic compound crystal grains formed at a solder joint interface to suppress occurrence and growth of cracks resulting from a heat cycle test and to maintain the joint strength and the ductility of the solder joint.
  • the foregoing effects cannot be obtained when these contents are each less than 0.01.
  • the ductility deteriorates when the Ni content is more than 0.2% or/and the Sb content is more than 0.15%.
  • the Ni content is preferably 0.02 to 0.08% and more preferably 0.03 to 0.07%.
  • the Sb content is preferably 0.03 to 0.09% and more preferably 0.05 to 0.08%.
  • the crystal grains have an average particle size of about 1 to 3 ⁇ m. Such a particle size allows occurrence of cracks to be suppressed after a heat cycle test.
  • the average particle size in the invention is a value determined by image analysis software Scandium (Seika Corporation).
  • solder alloy according to the invention can be suitably used in the form of a preform material, solder balls or solder paste.
  • a preform material is in the shape of a washer, a ring, a pellet, a disk, a ribbon, a wire, or the like.
  • the solder alloy according to the invention can be used in the form of solder paste.
  • the solder paste is in a paste form and is obtained by mixing solder alloy powder with a small amount of flux.
  • the solder alloy according to the invention may be used in the form of solder paste when mounting electronic parts on a printed circuit board by a reflow soldering method.
  • the flux for use in the solder paste may be a water-soluble flux or a water-insoluble flux. Typically, a rosin flux which is a rosin-based water-insoluble flux is used.
  • the solder joint according to the invention uses the solder alloy according to the invention to join and connect terminals in a package (PKG) of an IC chip or the like to terminals of a board such as a printed circuit board (PCB).
  • the solder joint according to the invention refers to a portion where the terminals as described above are joined to the solder.
  • the solder joint according to the invention can be thus formed using common soldering conditions.
  • the in-vehicle electronic circuit according to the invention is an electronic circuit that may be incorporated in a central computer of a so-called automotive electronic control unit for electrical control such as engine output control and brake control, and specific examples of the electronic circuit that may be illustrated include a power module and a hybrid semiconductor electronic circuit.
  • the solder alloy according to the invention can reduce a dose by using a low a material.
  • the solder paste, the preform material and the solder joint according to the invention can reduce a dose in the same manner as the solder alloy according to the invention by using a low a material.
  • the in-vehicle electronic circuit according to the invention uses a low a solder joint and can hence suppress memory errors.
  • solder bumps using each solder alloy were subjected to a heat cycle test and deformation of the solder bumps after the heat cycle test was examined.
  • a solder joint of a chip resistor joined using solder paste was subjected to a heat cycle test to examine the crack growth rate of the solder joint of the chip resistor.
  • Each solder alloy was subjected to a tensile test to examine the tensile strength and the ductility.
  • Each examination content is as follows:
  • solder alloy was formed into solder pellets with a size of 2.5 ⁇ 2.5 ⁇ 0.5 mm.
  • the solder pellets were mounted on a Cu pad and were then subjected to reflow soldering at 245° C. to prepare solder bumps.
  • These solder bumps were charged into a heat cycle tank which was set to conditions of keeping at ⁇ 40° C. and +125° C. for 10 minutes, respectively, and exposed to a heat cycle environment where the foregoing conditions were repeated for 200 cycles or 800 cycles. Then, whether or not there was deformation of the solder bumps was visually observed in cross-sectional scanning electron micrographs.
  • a chip resistor was mounted on each of 20 electrodes in a glass epoxy substrate (MCL-E-67, FR-4 manufactured by Hitachi Chemical Co., Ltd.) with a size of 110 mm ⁇ 110 mm ⁇ 1.6 mm (thickness) using each of the solder alloys.
  • This substrate was subjected to reflow soldering at 245° C. to join the chip resistor to the substrate thereby forming a solder joint.
  • This substrate was charged into a heat cycle tank which was set to conditions of keeping at ⁇ 40° C. and +125° C. for 30 minutes, respectively.
  • a heat cycle test was carried out in which the foregoing conditions corresponding to one cycle were repeated for 1,000 cycles, 2,000 cycles and 3,000 cycles.
  • FIG. 1 is a cross-sectional schematic view for illustrating the crack growth rate.
  • the cross-sectional schematic view shown in FIG. 1 is a schematic view of a cross-section obtained by cutting a chip resistor mounted on a substrate along the center plane in its width direction so as to include electrodes. In Examples, this cross-section was observed to evaluate the crack growth rate.
  • a chip resistor 11 is connected to an electrode land 12 with solder 13 .
  • FIG. 1 is a chip resistor 11 in FIG.
  • the crack growth rate was calculated according to expression 1 shown below by the ratio between the sum (S 1 +S 2 ) of lengths (S 1 and S 2 indicated by solid lines in the drawing) of actually occurring cracks and the total length (S 0 indicated by a broken line in the drawing) of a presumed crack line estimated from the actually occurring cracks.
  • the higher of the crack growth rate values in the left and right electrodes shown in FIG. 1 was taken as the crack growth rate of the part.
  • the void was deemed to be a crack.
  • the tensile strength was measured according to JIS Z 3198-2. Each solder alloy described in Table 1 was cast into a mold to prepare a specimen with a gauge length of 30 mm and a diameter of 8 mm. The thus prepared specimen was pulled by Type 5966 (Instron) at room temperature at a stroke of 6 mm/min to measure the strength upon fracture of the specimen. The ductility (reduction of area) was measured from the ratio of the cross-sectional area S 1 of a fractured portion of the specimen to the cross-sectional area S 0 before testing. According to the invention, a case where the tensile strength was 73 MPa or more and the ductility was 18% or more was deemed to be at a level at which there was no problem in practical use.
  • Example 1 Tensile Crack Alloy composition [%] strength Ductility growth Sn In Bi Ag Ni Sb Deformation [MPa] [%] rate Refinement
  • Example 2 bal. 5.0 3.0 3.0 0.05 0.07 No 81.82 22.59 Good Yes
  • Example 3 bal. 6.0 3.0 3.0 0.05 0.07 No 87.98 19.72 Good Yes
  • Example 4 bal. 3.0 2.5 3.0 0.05 0.07 No 73.01 33.95 Good Yes
  • Example 5 3.0 4.0 3.0 0.05 0.07 No 87.17 18.06 Good Yes
  • Example 6 bal. 3.0 3.0 3.0 0.01 0.02 No 78.86 28.90 Good Yes
  • Examples 1 to 10 each showing an alloy composition within the scope of the invention did not cause deformation after heat cycle testing and showed a tensile strength of 73 MPa or more and a reduction of area of 18% or more. Moreover, refinement of intermetallic compounds at the joint interfaces owing to the addition of Ni and Sb was confirmed, and crack growth was suppressed.
  • FIGS. 2 to 4 are scanning electron micrographs for observing the relation between the In content and the solder bump deformation. The micrographs are taken at a magnification of 25 ⁇ .
  • FIG. 2( a ) is a cross-sectional scanning electron micrograph of a solder bump having a composition of Sn-3Ag-3Bi-3In-0.07Sb-0.05Ni according to the invention before heat cycling
  • FIG. 2( b ) is a cross-sectional scanning electron micrograph of the solder bump after 200 heat cycles
  • FIG. 2( c ) is a cross-sectional scanning electron micrograph of the solder bump after 800 heat cycles.
  • FIG. 3( a ) is a cross-sectional scanning electron micrograph of a solder bump having a composition of Sn-3Ag-3Bi-6In-0.07Sb-0.05Ni according to the invention before heat cycling;
  • FIG. 3( b ) is a cross-sectional scanning electron micrograph of the solder bump after 200 heat cycles; and FIG. 3( c ) is a cross-sectional scanning electron micrograph of the solder bump after 800 heat cycles.
  • FIG. 4( a ) is a cross-sectional scanning electron micrograph of a solder bump having a composition of Sn-3Ag-3Bi-9In-0.07Sb-0.05Ni in a comparative example before heat cycling;
  • FIG. 4( b ) is a cross-sectional scanning electron micrograph of the solder bump after 200 heat cycles; and
  • FIG. 4( c ) is a cross-sectional scanning electron micrograph of the solder bump after 800 heat cycles.
  • the solder bump using the solder alloy in Example 1 in which the In content was 3% and the solder bump using the solder alloy in Example 3 in which the In content was 6% did not have solder bump deformation even after 800 heat cycles.
  • the solder bump using the solder alloy in Comparative Example 3 in which the In content was 9% began to get distorted after 200 cycles as shown in FIG. 4( b ) and became clearly deformed after 800 cycles as shown in FIG. 4( c ).
  • ⁇ transformation of the Sn phase was confirmed by DSC (Differential Scanning Calorimetry).
  • the solder alloy in Comparative Example 1 was low in In content and was hence inferior in tensile strength.
  • the solder alloy in Comparative Example 2 showed a tensile strength of 75 MPa because the In content was higher than in Comparative Example 1. However, the solder alloy in Comparative Example 2 has an In content of less than 1.0%. Therefore, in the solder joint using the solder alloy in Comparative Example 2, there was no refinement of intermetallic compounds at the joint interface and the crack growth rate was poor.
  • solder alloys in Comparative Examples 4 and 5 were low in Bi content and were hence inferior in tensile strength.
  • the solder alloy in Comparative Example 6 was high in Bi content and was hence inferior in ductility due to precipitation of Bi.
  • FIGS. 5 to 6 are scanning electron micrographs for observing the relation between the Sb and Ni contents and the solder alloy structure. The micrographs are taken at a magnification of 3,000 ⁇ . These micrographs are surface micrographs after reflow soldering at a maximum temperature of 245° C.
  • FIG. 5( a ) is a joint surface scanning electron micrograph of a solder bump after reflow soldering which has a composition of Sn-3Ag-3Bi-3In in a comparative example
  • FIG. 5( b ) is a joint surface scanning electron micrograph of a solder bump after reflow soldering which has a composition of Sn-3Ag-3Bi-3In-0.02Sb-0.01Ni according to the invention
  • FIG. 5( c ) is a joint surface scanning electron micrograph of a solder bump after reflow soldering which has a composition of Sn-3Ag-3Bi-3In-0.06Sb-0.03Ni according to the invention.
  • FIG. 5( a ) is a joint surface scanning electron micrograph of a solder bump after reflow soldering which has a composition of Sn-3Ag-3Bi-3In-0.06Sb-0.03Ni according to the invention.
  • FIG. 6( a ) is a joint surface scanning electron micrograph of a solder bump after reflow soldering which has a composition of Sn-3Ag-3Bi-3In-0.07Sb-0.05Ni according to the invention
  • FIG. 6( b ) is a joint surface scanning electron micrograph of a solder bump after reflow soldering which has a composition of Sn-3Ag-3Bi-3In-0.10Sb-0.07Ni according to the invention
  • FIG. 6( c ) is a joint surface scanning electron micrograph of a solder bump after reflow soldering which has a composition of Sn-3.0Ag-3.0Bi-3In-0.22Sb-0.29Ni in Comparative Example 8.
  • Comparative Example 9 specifically disclosed in Patent Literature 1 was inferior in tensile strength because of a low Bi content although the In content was 12%.
  • FIG. 7 is a diagram showing the distribution of the crack growth rate in solder joints of chip resistors joined using solder paste having a composition of Sn-3Ag-3Bi-3In in Comparative Example 7 and solder paste having a composition of Sn-3Ag-3Bi-3In-0.07Sb-0.05Ni in Example 2 according to the invention.
  • the crack growth rate exceeded 50% in a lot of samples in Comparative Example 7 after the passage of 3,000 hours.
  • the crack growth rate did not exceed 50% after the passage of 3,000 hours in Example 2 in which crystal grain refinement at the joint interface was confirmed, as compared to Comparative Example 6.
  • the lead-free solder alloy according to the invention suppresses solder bump deformation and solder joint cracking after heat cycle testing and is hence particularly useful as a solder alloy for in-vehicle electronic circuits.
  • the lead-free solder alloy according to the invention can be used without any problem in electronic circuits in cold regions and tropical regions.
  • the lead-free solder alloy according to the invention has both of high tensile strength and high ductility and is hence extremely promising as a solder alloy capable of also withstanding impact applied while a vehicle is running.

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  • Electric Connection Of Electric Components To Printed Circuits (AREA)
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US20180001426A1 (en) * 2012-12-18 2018-01-04 Senju Metal Industry Co., Ltd. Lead-free solder alloy
US10322471B2 (en) * 2014-07-21 2019-06-18 Alpha Assembly Solutions Inc. Low temperature high reliability alloy for solder hierarchy
US10773345B2 (en) 2016-03-08 2020-09-15 Senju Metal Industry Co., Ltd. Solder alloy, solder ball, chip solder, solder paste, and solder joint

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JP5638174B1 (ja) 2014-06-24 2014-12-10 ハリマ化成株式会社 はんだ合金、はんだ組成物、ソルダペーストおよび電子回路基板
CA2892420C (fr) * 2014-06-24 2016-08-09 Harima Chemicals, Incorporated Alliage de soudure, pate de soudure et plaquette de circuit electronique
WO2017164194A1 (fr) 2016-03-22 2017-09-28 株式会社タムラ製作所 Alliage de brasage sans plomb, composition de flux, composition de pâte à braser, carte à circuits imprimés électronique et dispositif de commande électronique
US10456872B2 (en) 2017-09-08 2019-10-29 Tamura Corporation Lead-free solder alloy, electronic circuit substrate, and electronic device
JP6439893B1 (ja) * 2018-05-25 2018-12-19 千住金属工業株式会社 ハンダボール、ハンダ継手および接合方法
JP6708942B1 (ja) * 2019-05-27 2020-06-10 千住金属工業株式会社 はんだ合金、はんだペースト、プリフォームはんだ、はんだボール、線はんだ、脂入りはんだ、はんだ継手、電子回路基板および多層電子回路基板
JP2021027178A (ja) * 2019-08-05 2021-02-22 日立オートモティブシステムズ株式会社 電子制御装置
CN113674260A (zh) * 2021-08-26 2021-11-19 万安裕高电子科技有限公司 一种smt焊点缺陷检测方法
JP7161140B1 (ja) * 2022-07-22 2022-10-26 千住金属工業株式会社 はんだ合金、はんだボール、はんだペーストおよびはんだ継手

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US20180001426A1 (en) * 2012-12-18 2018-01-04 Senju Metal Industry Co., Ltd. Lead-free solder alloy
US10343238B2 (en) * 2012-12-18 2019-07-09 Senju Metal Industry Co., Ltd. Lead-free solder alloy
US10322471B2 (en) * 2014-07-21 2019-06-18 Alpha Assembly Solutions Inc. Low temperature high reliability alloy for solder hierarchy
US20160226466A1 (en) * 2015-02-04 2016-08-04 Nihon Dempa Kogyo Co., Ltd. Solder material and electronic component
US10507552B2 (en) * 2015-02-04 2019-12-17 Nihon Dempa Kogyo Co., Ltd. Solder material and electronic component
US10773345B2 (en) 2016-03-08 2020-09-15 Senju Metal Industry Co., Ltd. Solder alloy, solder ball, chip solder, solder paste, and solder joint

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TW201437385A (zh) 2014-10-01
JPWO2014097390A1 (ja) 2017-01-12
US20180001426A1 (en) 2018-01-04
CN104870673A (zh) 2015-08-26
KR20150068505A (ko) 2015-06-19
CN104870673B (zh) 2016-07-06
TWI502073B (zh) 2015-10-01
EP2937432A4 (fr) 2016-10-05
EP2937432A1 (fr) 2015-10-28
US10343238B2 (en) 2019-07-09
WO2014097390A1 (fr) 2014-06-26
ES2658593T3 (es) 2018-03-12
EP2937432B1 (fr) 2017-11-22
KR101639220B1 (ko) 2016-07-13

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