Analysis of coatings which inhibit epoxy bleeding in electronic packaging

The bleeding of epoxy resin around surfaces, undergoing bonding in electronic packaging assembly, has for long caused sporadic yield-loss. This loss is more severe in advanced and dense packages. Previously it has been supposed that the loss results from surface contaminants which are reduced by vacuum bakeout. In fact, that procedure generates coatings of hydrocarbons as we show by surface analysis. The coatings very strongly affect the wettabilities and measured surface energies of substrates. In particular, the comparatively low surface energy of hydrocarbon films on gold surfaces shows how the surfaces can be engineered, with coatings of “appropriate cleanliness”, to systematically inhibit epoxy bleeding. This revised version was published online in July 2006 with corrections to the Cover Date.