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AssigneeInternational Business Machines Corporation
InventorsMukta G. Farooq, Mario Interrante, William Sablinski
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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.
A method for creating a lead free solder melting hierarchy for first level assembly comprising the steps of;
Dependencies are inferred from the claim text.