JOINING A CHIP TO A SUBSTRATE WITH SOLDER ALLOYS HAVING DIFFERENT REFLOW TEMPERATURES
A method including forming a first solder bump on a chip, the first solder bump made of a first alloy, and forming a second solder bump on a chip, the second solder bump made of a second alloy, where the first alloy has a different alloy concentration and is different from the second alloy.
1 . A method comprising:
forming a first solder bump on a chip, the first solder bump made of a first alloy; and
forming a second solder bump on a chip, the second solder bump made of a second alloy,
wherein the first alloy has a different alloy concentration and is different from the second alloy.
2 . The method of claim 1 , wherein the first and second alloys comprise at least one common element.
3 . The method of claim 1 , wherein the first solder bump will be used to subsequently form a solder first connection for high current density power transfer, and wherein the second solder bump will be used to subsequently form a second solder connection for low current density signal transfer.
4 . The method of claim 1 , wherein the first and second alloys comprise copper, silver, tin, or some combination thereof.
5 . The method of claim 1 , wherein the first and second alloys are lead-free.
6 . The method of claim 1 , wherein the first and second alloys comprises silver, the first alloy having a different silver concentration than the second alloy.
7 . The method of claim 1 , wherein the first and second alloys comprise silver, and the first solder alloy having a higher silver content than the second solder alloy.
8 . The method of claim 1 , wherein the first and second alloys both comprise a first element and a second element, the first element having a higher concentration than the second element, and the first solder alloy having a higher concentration of the first element than the second solder alloy.
9 . A structure comprising:
a first solder connection between a substrate and a chip, the first solder connection made of a first alloy;
a second solder connection between the substrate and the chip, the second solder connection made of a second alloy,
wherein the first alloy has a different alloy concentration than the second alloy.
10 . The structure of claim 9 , wherein the first solder connection is intended for high current density, and the second solder connection is intended for low current density.
11 . The structure of claim 9 , wherein the first alloy has better electromigration resistance than the second alloy.
12 . The structure of claim 9 , wherein the first alloy forms a stiffer solder connection than the second alloy.