Structure and method for lead free solder electronic package interconnections
US6854636B2 · kind B2 · utility
Assignee
Inventors
Key dates
| Filing date | Dec 6, 2002 |
| Grant date | Feb 15, 2005 |
| Priority date | — |
| Expiry date | Feb 28, 2023 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH01L2924/181
- WIPO fieldSemiconductors
- WIPO sectorElectrical engineering
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.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.