Single Stitch Low Loop Capability and Optimization on Al 500um Wire for Top Side Cooling Package

Abstract

The introduction of new package to accommodate Power silicon technologies with die sizes ranging from a minimum A mm2 to the maximum B mm2 with gullwing feature introduced new challenge to Al 500um wire size as the clearance between the highest looping wire to the top package becomes narrower and critical. The downset dimension of the new package reduced by 41% (from 760 µm to 350um with reference to existing package) leaving the looping clearance now only 1000um from previously 1400um for Al 500um wire to have an ample space for looping formation (measure from the lead post). This will cause a new challenge to be proven for looping formation as it becomes critical. Initial feasibility study shows an evidence of expose wire from the molding compound on new package and package stack analysis also revealed potential of having exposed wire in ppm level. Looping optimization for single stitch has been conducted and able to perform a stable looping formation within the 1000um clearance for Al 500um wire. A new specification for the maximum looping has been implemented to ensure all the readings for maximum wire loop heights are under production control. This paper describes in details the looping optimization and the actual capability demonstrated for Al 500um wire to enable the project to be released for production without any issue in the project qualifications and production released in Dec 2017. The new looing capability for stable production has been demonstrated for such a low loop (< 800um) with critical looping clearance (within 1000um) for Al 500um wire and passed the Automotive requirements. This performance will enhance to enable another new package platform to be introduced in the semiconductor industry with Top Side Cooling capability which currently under feasibility stage.