Gold-tin-indium solder for processing compatibility with lead-free tin-based solder
View Patent ↗Disclosed in this specification is a lead-free soldering alloy made of gold, tin and indium. The tin is present in a concentration of 17.5% to 20.5%, the indium is present in a concentration of 2.0% to 6.0% and the balance is gold and the alloy has a melting point between 290° C. and 340° C. and preferably between 300° C. and 340° C. The soldering alloy is particularly useful for hermetically sealing semiconductor devices since the melting temperature is sufficiently high to permit post-seal heating and sufficiently low to allow sealing of the semiconductor without causing damage.
1. A lead-free soldering material consisting essentially of an alloy of gold, tin and indium wherein the tin is present in a concentration of 17.5% to 20.5%, the indium is present in a concentration of 2.0% to 6.0% and the balance is gold and the alloy has a melting point greater than 290° C.
2. The soldering material as recited in claim 1 , wherein the alloy has a melting point in the range of 290° C. to 340° C.
3. The soldering material as recited in claim 1 , wherein the alloy has a melting point in the range of 290° C. to 320° C.
4. The soldering material as recited in claim 1 , wherein the alloy has a melting point in the range of 305° C. to 315° C.
5. The soldering material as recited in claim 3 , wherein the tin is present in a concentration of 18.3% to 20.3% and the indium is present in a concentration of 3.5% to 5.5%.
6. The soldering material as recited in claim 3 , wherein the tin is present in a concentration of about 19.3% and the indium is present in a concentration of about 4.5%.
7. A method of hermetically sealing a semiconductor package with a lead-free soldering material including the steps of:
applying a soldering material to a surface of a semiconductor package, wherein the soldering material consists essentially of an alloy of gold, tin and indium wherein the tin is present in a concentration of 17.5% to 20.5%, the indium is present in a concentration of 2.0% to 6.0% and the balance is gold and the alloy has a melting point in the range of 290° C. to 320° C.;
heating the soldering material to a temperature sufficient to cause the soldering material to reflow such that the semiconductor package is hermetically sealed.
8. The method as recited in claim 7 , further comprising the step of heating a portion of the hermetically sealed semiconductor package to a temperature greater than 270° C. during a post-sealing operation without reflowing the soldering material.
9. A method of mounting a semiconductor device to a surface with a lead-free soldering material including the steps of:
applying a soldering material to a semiconductor device, wherein the soldering material consists essentially of an alloy of gold, tin and indium wherein the tin is present in a concentration of 17.5% to 20.5%, the indium is present in a concentration of 2.0% to 6.0% and the balance is gold and the alloy has a melting point in the range of 290° C. to 320° C.;
disposing the semiconductor device on a surface such that the soldering material contacts both the semiconductor device and the surface;
heating the soldering material to a temperature sufficient to cause the soldering material to reflow;
cooling the soldering material thus mounting the semiconductor device to the surface.
10. The method as recited in claim 9 , further comprising the step of heating a portion of the semiconductor device to a temperature greater than 270° C. during a post-mounting operation without reflowing the soldering material.
11. A hermetically sealed semiconductor assembly that includes a semiconductor device hermetically sealed with a soldering material wherein the soldering material consists essentially of an alloy of gold, tin and indium, the tin having a concentration of 17.5% to 20.5%, the indium having a concentration of 2.0% to 6.0% and the balance is gold and the alloy has a melting point in the range of 290° C. to 320° C.
12. A lead-free soldering material consisting essentially of an alloy of gold, tin and indium, the tin having a concentration of 17.5% to 20.5%, the indium having a concentration of 2.0% to 6.0% and the balance is gold and the alloy has a melting point in the range of 290° C. to 320° C.
13. The soldering material as recited in claim 12 , wherein the tin is present in a concentration of 18.3% to 20.3% and the indium is present in a concentration of 3.5% to 5.5%.
14. The soldering material as recited in claim 12 , wherein the tin is present in a concentration of about 19.3% and the indium is present in a concentration of about 4.5%.