Post-curing influence on electrostatic charges deposited on epoxy/silica composites used for microelectronic packaging

In this work, we present the potentialities of the surface potential method to investigate electrostatics charges deposited on epoxy resins used in packaging. Curing and post-mould-curing (PMC), with various durations have been performed on epoxy resins. Negative ions are deposited by corona discharge on the surface of these epoxy resins. Then the flowing of charges as a function of time, namely the surface potential decay (SPD), is measured by a non-contacting electrostatic probe. These measurements were performed in a climatic chamber at different temperatures (30degC, 50degC, 70degC) and a 50% relative humidity rate. Our results have shown a strong influence of the curing and the post-mould-curing on the SPD. Practically the fastest SPD is obtained for the sample having the longest curing. The SPD is strongly slowed down when the samples were subjected to a PMC. We suggest that dipoles in the bulk and traps near the surface influence the surface potential decay. For a longer time of curing, traps appear near the surface and trap ions. Thus induces a fast decrease of SPD. We suggest that the PMC reduces dipoles and is favorable to the filling of the traps. Thus, less traps and dipoles after a PMC explain why the SPD is slower