Solder alloy, solder ball, solder paste, and solder joint

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%, and
• at least one selected from the group consisting of,
• at least one of P, Ge, Ga, and As:
• 0.1% or less in total,
• at least one of Fe and Co:
• 0.1% or less in total,
• Pd:
• 0.1% or less,
• Zr:
• 0.1% or less,
• Zn:
• 0.1% or less, and
• Pb:
• 0.02% or less,
• 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.

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%, and
• at least one selected from the group consisting of,
• P:
• less than 0.01%,
• Ge:
• 0.01% or less,
• Ga:
• less than 0.01%,
• As:
• more than 0.001% and 0.01% or less,
• Co:
• less than 0.01%,
• Pd:
• 0.01% or less, and
• Pb:
• less than 0.004%,
• 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.