Flip chip pad structure for high density organic build up substrate

There has been a growing demand for high-density organic flip chip packages for high performance IC due to lower cost and lower electrical noise. The paper presents studies conducted in order to achieve high adhesion between the flip chip pads and the insulation layer on the organic substrate. Simulation studies on the stress at both SMD (solder mask defined) and NSMD (nonsolder mask defined) flip chip pads were performed. The SMD structure was found to have lower stress at the edges between the Cu pad and insulation layer. The simulation result was confirmed by chip pull tests on the actual samples. Most of the solder joints on the SMD samples showed breakage at the solder joints after the test (taffy mode) and the pull strength was above the required standard. As for NSMD, the Cu pads were lifted from the resin during the test and the pull strength was much lower than SMD samples