Breakdown voltages phenomena at molding compound-chip interface

The effects of molding compound chemical formulations on some electrical failures of plastic encapsulated power MOSFETs under high temperature reverse bias testing (HTRB) have been studied. For this purpose, various molding compounds with different chemical formulations were prepared. The chemical formulations were modified in order to study the influence of volume resistivity, ion content, glass transition temperature and the segregation of organic additives at the molding compound-die interfaces. X-ray photoelectron spectroscopy (XPS) was used to characterize the die-molding compound interfacial chemical composition in these devices. Volume resistivity, ion content and the glass transition temperature characteristics are not enough to explain the power MOS failures. The segregation of polar components like polyoxyalkylene ethers and, to a lesser extent, the presence of polar chemical bonds coming from the matrix resin at the relevant interfaces were found to be the main cause of the observed failures