Feasibility and reliability study on the electroless nickel bumping and stencil solder printing for low-cost flip chip electronic packaging

摘要

We present a study on the feasibility and reliability of a low-cost flip chip technology using a combination of electroless nickel bumping and stencil solder printing. Circular aluminum bump pads of diameter 250 /spl mu/m and pitch 400 /spl mu/m with 200 /spl mu/m openings in the passivation layer were patterned for the study. Since it has been suggested that phosphorus from the electroless nickel solution will degrade the adhesion of solder, three types of electroless nickel deposits were prepared as the under bump metallurgy (UBM) consisting of electroless nickel-high phosphorous (EN-HP), electroless nickel-low phosphorous (EN-LP) and electroless nickel-boron (EN-B). Eutectic lead-tin solder paste of composition 63Sn-37Pb was screen-printed on the electroless nickel UBM followed by reflow at a peak temperature of 230/spl deg/C. The final solder bump height achieved was 155/spl plusmn/8 /spl mu/m. The shearing strength was found to decrease in the order of EN-B (1857.5 g/bump)