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Wafer-Level Packaging With Soldered Stress-Engineered Micro-Springs

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5 Author(s)
Chow, E.M. ; Palo Alto Res. Center, Palo Alto, CA ; Fork, D.K. ; Chua, C.L. ; Van Schuylenbergh, K.
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Micro-springs for integrated circuit test and packaging are demonstrated as soldered flip chip interconnects in a direct die to printed circuit board package. The spring interconnects are fabricated with thin film metallization as the last step in a wafer-scale process. The z-compliance of the interconnects can be used to test and/or burn-in parts in wafer form. After the parts are diced from the wafer, the springs then become the first-level (and often the last-level) interconnect between the chip and the board. The xy-compliance of the interconnect enables considerably large die to be soldered to an organic printed circuit board without underfill using a surface mount compatible process. To demonstrate this concept, daisy chain test vehicles were fabricated on die measuring 11.5 mm times 6.5 mm with 48 spring contacts on a 0.8 mm times 0.65 mm grid array, each spring measuring 400 mum times 100 mum. The parts were placed onto organic boards with screen printed solder paste using a pick and place machine. The parts were reflowed to complete the solder connection to each spring using eutectic and lead-free solder. Assembled parts have undergone >20 000 hot plate thermal cycles and >1000 oven thermal cycles without failure.

Published in:

Advanced Packaging, IEEE Transactions on  (Volume:32 ,  Issue: 2 )

Date of Publication:

May 2009

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