Flip chip soldering on printed wining boards using vapor phase reflow

The interconnection of lead-tin bumped chips soldered on organic substrate was investigated. Chips having a Ni-Au UBM were mechanically bumped with PbSn2 and PbSn61. The PbSn2 bumped chips were soldered on FR4 substrate with PbSn60 bumped pads. For comparison, chips with Cu UBM and electroplated PbSn60 bumps were also used. Soldering was performed in vapor phase using flux. To enhance the reliability of the assemblies during thermal cycling underfiller was applied. Underfilled and non underfilled packages were subjected to thermal cycling tests between -55 deg C and 125 deg C. The interconnections using PbSn2 bumped chips showed a slight increase of contact resistance from 4mOhm to 6mOhm after 1000 thermal cycles. The interconnections of the PbSn60 bumped chips failed after 1000 thermal cycles.