A novel, maskless, low‐volume bumping material, called solder bump maker, which is composed of a resin and low‐melting‐point solder powder, has been developed. The resin features no distinct chemical reactions preventing the rheological coalescence of the solder, a deoxidation of the oxide layer on the solder powder for wetting on the pad at the solder melting point, and no major weight loss caused by out‐gassing. With these characteristics, the solder was successfully wetted onto a metal pad and formed a uniform solder bump array with pitches of 120 µm and 150 µm.

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The recent advancement in high performance semiconductor packages has been driven by the need for higher pin count and superior heat dissipation. A one-piece cavity lid flip chip BGA package with high pin count and targeted reliability has recently been developed by UTAC. The flip chip technology can accommodate VO count of more than five hundreds, and the die junction temperature can be reduced to a minimum level by a metal heat spreader attachment. Nonetheless, greater expectations on these high performance packages arose such as better substrate land estate utilization for multiple chips, ease in handling for thinner core substrates and improved board level solder joint reliability. A new design ofthe flip chip BGA package (patent pending) has been looked into for meeting such requirements.By encapsulating the flip chip with molding compound leaving the die top expo:jed, a planer top surface can he formed. And a flat lid can then be mounted on the planer moldldie top surface. In this manner the direct interaction of the metal lid with the substrate can be removed. The new package is thus less rigid under thermal loading and solder joint reliability enhancement is expected. This paper discusses the process developmenl. of the new package and its advantages for improved solder joint fatigue life,, and being a multi-chip package and thin core substrate options. Finite element simulations have been employed for the study of its structural integrity, ~themoal and electrical performances. Detailed package and hoard level reliability test results will also be reported.