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 will present the studies conducted in order to achieve high adhes ion between the flip chip pads and the insulation layer on the organic subs trate. Simulation studies on the stress at both SMD (Solder Mask Defined) a nd NSMD (Non Solder Mask Defined) flip chip pads were performed (Figure 1 s hows the x-section of these two pad structures). 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 sample s. Most of the solder joints on the SMD samples showed breakage at the sold er joints after the test (taffy mode) and the pull strength was above the r equirement standard. As for NSMD, the Cu pads were lifted from the resin du ring the test and the pull strength was much lower than SMD samples.