Flip-Chip Bonding on 6-um Pitch using Thin-Film Microspring Technology

Bonding-pad densities on high-performance integratedcircuit chips are beginning to exceed the limits of available interconnect technologies. Also, stresses due to thermal mismatch in flip-chipped packages are reducing time to contact failure. We have addressed both of these problems by microlithographically fabricating highly elastic cantilever springs in linear arrays on pitches down to 6 μm. We have soldered test arrays of 52 springs on this pitch to Si chips with 100% contact yield and good solder wetting to every spring. The fine-pitch capability also facilitates off-chip routing; the very high compliance of the springs should avoid thermal fatigue; and the low thermal conductance along the springs should allow fast-cycle soldering of chips to multi-chip modules as well as replacement of chips subsequently testing faulty.