Microspring characterization and flip chip assembly reliability (Best Paper Award)

Abstract

Electronics packaging based on stress-engineered spring interconnects have the potential to enable integrated IC testing, fine-pitch, and compliance not readily available with other technologies. We describe new spring contacts which simultaneously achieve low resistance (<100 mohm) and high compliance (>30 micron) in dense two-dimensional arrays (180 x 180 micron pitch). Mechanical characterization show individual springs operate at ~0.01 gm force. Electrical measurements and simulations imply the interface contact resistance contribution to a single contact resistance is < 40 mohms. Daisy chain test die consisting of 2844 contacts are assembled into flip chip packages with 100% yield. Thermocycle and humidity testing suggest packages with or without underfill can have stable resistance values and no glitches through over 1000 thermocycles or 7000 hrs of humidity. This work suggests that integrated testing and packaging can be performed the springs, enabling new capabilities for markets such as multi-chip modules