A new under bump metallurgy for solder bump flip chip applications

A new under bump metallurgy (UBM) solution consisting of the TiW‐, Au‐ and Ni‐layers for solder flip chip applications has been developed. The metallurgy, being based on the well‐known TAB metallisation procedure, was modified by producing the galvanic nickel layer on the top of the Au‐TiW metallisation. Nickel is needed between high Sn liquid solder bumps and the Au layer to prevent fast and extensive dissolution of thin Cu or Au layers and consequently excessive intermetallic formation. The flip chip joints were manufactured, employing both the 60Sn40Pb‐ and pure Sn‐bumped chips together with the new UBM, which is relatively easy to implement into volume production. The different ageing tests demonstrated that reliable joints can be produced by using the UBM. On the basis of the results obtained the new UBM was found to be a significant improvement in the production of reliable flip chip joints.