ANALYSIS OF COATINGS WHICH INHIBIT EPOXY BLEEDING IN ELECTRONIC PACKAGING

The bleeding of epoxy resin around surfaces, undergoing bonding in ele ctronic packaging assembly, has for long caused sporadic yield-loss. T his loss is more severe in advanced and dense packages. Previously it has been supposed that the loss results from surface contaminants whic h are reduced by vacuum bakeout. In fact, that procedure generates coa tings of hydrocarbons as we show by surface analysis. The coatings ver y strongly affect the wettabilities and measured surface energies of s ubstrates. In particular, the comparatively low surface energy of hydr ocarbon films on gold surfaces shows how the surfaces can be engineere d, with coatings of ''appropriate cleanliness'', to systematically inh ibit epoxy bleeding.