| CPC B23K 35/262 (2013.01) [B23K 35/0244 (2013.01); B23K 35/025 (2013.01); C22C 13/02 (2013.01)] | 11 Claims |
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1. A solder alloy having an alloy composition consisting of, by mass %,
Bi: 30 to 60%,
Ag: 0.7 to 2.0%,
Cu: more than 0% and 1.00% or less,
Ni: 0.01 to 1.00%,
Sb: 0.2 to 1.5%, with the balance being Sn,
wherein the solder alloy exhibits the following properties:
a melting rate in which 99.9% has melted before reaching 200° C., wherein the melting rate is judged based on an area ratio of a DSC curve and is a value obtained by dividing reaction calories necessary for complete melting by reaction calories completed before reaching 200° C., and multiplying the result of dividing by 100;
an average surface hardness of 7.0 Hv or more, wherein the average surface hardness is determined by measuring surface hardness of 5 bumps that are subjected to a load of 1.96N for 60 seconds at 110° C.;
an average number of heat cycles until rupture of at least 3,000, wherein the heat cycles include a low temperature of −40° C., a high temperature of +100° C., and a holding time of 10 minutes, wherein determining the average number of cycles until rupture includes subjecting test substrates to the heat cycles, monitoring resistance values using a daisy chain circuit, and judging that rupture has occurred when a resistance value increase of over 200% is reached from the start of the test, wherein the test substrates are prepared by placing solder balls with a diameter of 0.24 mm on electrodes of a substrate on which a soldering flux comprising a solvent, an activator, a thixotropic agent, and an organic acid was applied, mounting BGA components, and performing reflow soldering under conditions of a maximum temperature of 190° C. and a holding time of 90 seconds; and
an electromigration resistance in which at least 300 hours elapses until the electrical resistance increases by 150% compared with an initial electrical resistance value, wherein the electrical resistance is determined by connecting a test substrate to a variable switching power supply and applying a current in a silicon oil bath held at 110° C. and continuously measuring the electrical resistance, wherein the test substrate is prepared by fabricating a package using solder balls with a diameter of 0.24 mm made of the solder alloy by performing reflow soldering on a package substrate with a size of 12 mm×12 mm including Cu electrodes with a diameter of 0.24 mm by using a water-soluble flux, printing solder paste on a glass epoxy substrate with a size of 29 mm×19 mm and a thickness of 0.8 mm, and mounting the fabricated package to the glass epoxy substrate using reflow soldering under conditions of a maximum temperature of 190° C. and a holding time of 90 seconds to fabricate the test substrate.
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