Pressure Contact Micro-Springs in Small Pitch Flip-Chip Packages

This work investigates electrical pressure contacts based on a micro-spring with orders of magnitude smaller pitch and force than conventional pressure contacts. The springs are beams which curl out of the surface and can be used for wafer-scale testing and packaging. They are fabricated with standard wafer-scale thin film techniques and have been previously demonstrated on active silicon integrated circuits. Single springs and their electrical contacts are characterized with force versus compression and compression versus resistance measurements. Flip-chip packages with hundreds of micro-springs were assembled with 20-mum pad pitch and 40-mum spring pitch. Each spring operates with a force of approximately 0.01 g and contacts a gold pad. These packages are shown to have stable resistance values during both in-situ thermocycle (0degC to 125degC) and humidity testing (60degC at 95%RH). Spring electrical contacts inside the package are shown not to degrade during environmental testing through measurements of four-wire resistance and electrical isolation structures. High-speed glitch measurements are performed to confirm that the pressure contact does not have intermittent opens during thermocycling. These results suggest that a low-force solder-free pressure spring contact is a viable technology for next generation flip-chip packaging