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 vs. compression and compression vs. resistance measurements. Flip-chip packages with hundreds of micro-springs were assembled with 20 um pad pitch and 40 um spring pitch. Each spring operates with a force of approximately 0.01 grams and contacts a gold pad. These packages are shown to have stable resistance values during both in-situ thermocycle (0˚C to 125˚C) and humidity testing (60˚C at 95% RH). Spring electrical contacts inside the package are shown not to degrade during environmental testing through meas-urements of four-wire resistance and electrical isolation structures. High-speed glitch measurements are performed to confirm 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.
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Chow, E. M. ; Chua, C. L. ; Hantschel, T. ; Van Schuylenbergh, K. ; Fork, D. K. Pressure contact micro-springs in small pitch flip-chip packages. IEEE Transactions on Components and Packaging Technologies. 2006 December; 29 (4): 796-803.
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