A new flip-chip technology for high-density packaging

We have used sputter-deposition and standard lithography to fabricate arrays of cantilevered metal micro-springs on 80 /spl mu/m pitch, and we have obtained 100% electrical contact to 200-pad chips bonded face-down against them. Four-point resistance is 0.38 /spl Omega/ for Mo-Cr springs on Al pads. Since the contacts themselves are not bonded and since the springs have high elastic compliance, this technology is very resistant to mechanical shock and stress, can accommodate large nonplanarity in mating surfaces, facilitates replacement of bad chips, and could be used for wafer-scale probing.