Accurate, stable, high-speed interconnections using 20- to 30-μm-diameter microsolder bumps

A microalignment, high-speed electrical interconnection technique that uses 20- to 30-μm diameter microsolder bumps is described and evaluated. Test chips are self-aligned by the surface tension of the molten solder. The alignment accuracy increased as the number of bumps increased. An average misalignment of less than 0.2 μm was obtained for more than 20 bumps with a diameter of 26 μm. The shear strength increased as the number of bumps and the Pb content of the In-Pb solder increased; the average shear strength per bump for 50% In-Pb was about 1 gf, which is about three times the shear strength for 100% In. The decrease in shear strength after 1000 heat cycles was very small and the bump connections were very stable. Also described is a dc-to-60 GHz coplanar waveguide interconnection technique using microsolder bumps. Three-dimensional (3-D) electromagnetic field analysis showed that this technique can potentially achieve dc to 90-GHz frequency response. This interconnection technique using 20- to 30-μm diameter microsolder bumps will thus be very effective for future opto-electronic circuit boards mounting opto-electrical chips and optical waveguides/fibers in high-speed optical-interconnection communication systems