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Low Cost Cu Column fcPoP Technology
Keywords: Low Cost Fine Pitch Cu Column , PoP (Package On Package) , Assembly & Reliability
Adoption of Cu column in place of flip chip solder bumps enables bump pitch reduction and in some cases it will allow for substrate design rule relaxation by using wider Line and Space for signal routing in a given design. In this paper a 65nm Si originally designed with wire bond pads is converted to Flip Chip design by plating 60um diameter Cu bumps on 100um bump pitch and with solder cap for bonding to substrate that has incorporated the trace design. Cu column height and solder cap volume are optimized to allow for uniform wetting of bump to substrate trace while also providing the required gap height needed for proper Capillary Underfill (CUF) process, which otherwise would have not been possible by using the solder bumps at such a given tight bump pitch. Dummy center grid bump array at 250um bump pitch were added to the original design in order to provide mechanical support for the Flip Chip attached die and also promote the CUF process. Polyimide re-passivation was used prior to bumping process in order to enable the Cu bump plating with suitable design rules for assembly with the additional benefit of providing Low-K dielectric protection against crack. CUF process was successfully developed to meet the void-free process requirement for 100um back-grinded thin die. Package is a 520 Ball, 12x12mm bare-die fcPoP configuration with 6 layer Pre-Preg Laminate Build Up, 250um core thickness, and top and bottom ball pitch of 0.5mm. All functional tests and package level reliability including Moisture Sensitivity Level-3 (MSL3), Temperature Cycle-B (TC-B) 500 cycles, High Temperature Storage (HTS) 500 hours, and unbiased HAST 96 hours were successfully passed. Board Level Reliability (BLR) tests including Drop Shock and Temperature Cycle are in progress to complete the package qualification. Rozalia/Ron ok move from 2.5/3D to FC/WLP 12-21-11.
Hamid Eslampour , Deputy Director - Technology Marketing
Fremont , CA

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