Modification of solder alloy compositions to suppress interfacial void formation in solder joints
View Patent ↗A solder joint comprising a solder capture pad on a substrate having a circuit; and a lead containing or a lead free solder selected from the group comprising Sn—Ag—Cu solder, Sn—Cu solder and Sn—Ag solder adhered to the solder capture pad; the solder selected from the group comprising between 0.1 and 6.0 per cent by weight Zn. A solder joint, comprising a solder capture pad on a substrate having a circuit; and a Sn—Cu lead free solder adhered to the solder capture pad, the solder comprising between 0.1 and 6.0% by weight Zn. Formation of voids at an interface between the solder and the solder capture pad is suppressed. A method for forming solder joints using the solders.
1. A method for forming a solder joint on a solder capture pad of a substrate having a circuit, comprising:
applying to said capture pad a lead free solder, the lead free solder being selected from the group consisting of Sn—Ag—Cu solder, Sn—Cu solder and Sn—Ag solder; and
adhering said solder to said solder capture pad by melting and cooling said solder;
said solder containing between 0.1 and 6.0 percent by weight Zn, so that formation of voids at an interface between said solder and said solder capture pad is suppressed; Zn content of said solder being determined in accordance with a ratio of volume of said solder to surface area of said solder capture pad;
wherein the solder capture pad is comprised of plated Cu, further comprising annealing of the plated Cu pad at a temperature of approximately 550° C., prior to forming the solder joint.
2. The method of claim 1 , wherein said selected solder is Sn—Cu solder.
3. The method of claim 2 , wherein the solder further comprises 0.5% by weight Bi.
4. The method of claim 3 , wherein copper content of said solder is between 0.7 and 2.0% by weight Cu.
5. The method of claim 4 , wherein said solder is heated to a temperature of less than 280° C. to melt said solder.
6. The method of claim 4 , wherein said solder is heated to a temperature of between 217 and 280 degrees C. to melt said solder.
7. The method of claim 1 , wherein said selected solder is Sn—Ag solder.
8. The method of claim 1 , further comprising placing an organic solderability preservative on said solder capture pad prior to applying said solder to said pad.
9. The method of claim 1 , wherein at least substantially 4×10 −12 grams of Zn are present in said solder per square micron of solder capture pad surface area.
10. The method of claim 1 , wherein solder is Sn—Ag—Cu solder containing 0.7 percent by weight Zn and wherein the formation of Cu 3 Sn is retarded in its development on the solder capture pad.
11. The method of claim 1 , wherein the solder capture pad is comprised of Ni.
12. The method of claim 1 , wherein the Zn content of the solder is less than 0.6 percent by weight.