Development of WLCSP for Accelerometer Packaging with Vertical CuPd Wire as Through Mold Interconnection (TMI)

A Wafer Level Chip Scale Packaging (WLCSP) solution with CuPd wire in epoxy mold compound (EMC) as through mold interconnection (TMI) was proposed for the capacitive MEMS such as accelerometer packaging. The size of fabricated WLCSP is 2 mm × 2 mm × 0.83 mm. Silicon cap was designed as 1 mm × 2 mm × 0.1 mm. Device wafer and cap wafer was bonded with wafer level Al/Ge eutectic bonding process. Vertical CuPd wire with diameter of 2 mils embedded in the EMC was used as the TMI. Dummy ASIC die with the size of 1 mm × 1 mm × 0.15 mm can be mounted on the UBM above the RDL of the WLCSP with micro-bumps. MSL1, -40
^o
C to 125
^o
C thermal cycling (TC), unbiased highly accelerated stress test (HAST) and 150
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C high temperature storage (HST) testing was conducted on the fabricated dummy test vehicle samples. Testing results show that the fabricated test vehicle can pass the tests without electrical failure. The WLCSP with CuPd wire in EMC as TMI has been successfully demonstrated, which provides the confidence for the next step fabrication of WLCSP with functional accelerometer.