Accurate, stable, high-speed interconnections using 20- to 30-/spl mu/m-diameter microsolder bumps

A microalignment, high-speed electrical interconnection technique that uses 20- to 30-/spl mu/m 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 /spl mu/m was obtained for more than 20 bumps with a diameter of 26 /spl mu/m. 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-/spl mu/m 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.