Microspring Characterization and Flip-Chip Assembly Reliability

Electronics packaging based on stress-engineered spring interconnects has 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
$({<}{\rm 100}~{\rm m}\Omega)$
and high compliance
$({>}{\rm 30}~\mu{\rm m})$
in dense 2-D arrays (180–180-
$\mu{\rm m}$
pitch). Mechanical characterization shows that individual springs operate at approximately 150-
$\mu{\rm N}$
force. Electrical measurements and simulations imply that the interface contact resistance contribution to a single contact resistance is
${<}{\rm 40}~{\rm m}\Omega$
. A daisy-chain test die consisting of 2844 contacts is assembled into flip-chip packages with 100% yield. Thermocycle and humidity testing suggest that packages with or without underfill can have stable resistance values and no glitches through over 1000 thermocycles or 6000 h of humidity. This paper suggests that integrated testing and packaging can be performed with the springs, enabling new capabilities for markets such as multichip modules.