Metal fusion bonding – Process – Plural joints
Reexamination Certificate
2005-02-15
2005-02-15
Stoner, Kiley (Department: 1725)
Metal fusion bonding
Process
Plural joints
C228S246000
Reexamination Certificate
active
06854636
ABSTRACT:
An electronic package having a solder interconnect liquidus temperature hierarchy to limit the extent of the melting of the C4 solder interconnect during subsequent second level join/assembly and rework operations. The solder hierarchy employs the use of off-eutectic solder alloys of Sn/Ag and Sn/Cu with a higher liquidus temperature for the C4 first level solder interconnections, and a lower liquidus temperature alloy for the second level interconnections. When the second level chip carrier to PCB join/assembly operations occur, the chip to chip carrier C4 interconnections do not melt completely. They continue to have a certain fraction of solids, and a lower fraction of liquids, than a fully molten alloy. This provides reduced expansion of the solder join and consequently lower stresses on the C4 interconnect.
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Farooq Mukta G.
Interrante Mario
Sablinski William
Cioffi James J.
International Business Machines - Corporation
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