Micro-alignment technique using 26-μm diameter microsolder bumps and its shear strength

This paper reviews the bonding performance (alignment accuracy and shear strength) of the 26-μm-diameter microsolder bump connection. The feature of this technique is self-alignment of the optical chips due to the surface tension of the molten solder. The alignment accuracy increases as the number of bumps increases. An average misalignment of less than 0.2 μm was obtained for more than 20 bumps. The shear strength increases as the number of bumps and the percentage of Pb in the In-Pb solder increase, and the average shear strength for 50% In-Pb was about 1 gf/bump-about three times as large as the shear strength of 100% In. Furthermore, the decrease of shear strength for 50% In-Pb after 1000 heat cycles was very small-less than 10%. Therefore, this micro-alignment technique using 26-μm-diameter microsolder bumps will be very effective for future opto-electronic circuit boards and mounting photonic devices and optical waveguides/fibers