Adhesion and interface investigation of polyimide on metals

Abstract

The interface and adhesion of PMDA-ODA and PAA-ethyl ester polyimides to several metals including Cr, Ni, Cu, and Au have been studied by transmission electron microscopy (TEM) and a 90° peel test. The adhesion strength of polyimide on metals is generally very high compared with that of metals on polyimide. The trend in both cases is the same, i.e., Cr has the highest adhesion strength followed by Ni, Cu, and Au. Cross-sectional TEM studies showed that very fine particles were precipitated in the polyimide near the interface in the case of polyimide on Cu (or Ni). The precipitates were not found closer than 80-200 nm from the polyimide/Cu (or Ni) interface. Some large particles were identified as Cu2O (NiO in the case of polyimide/Ni) by scanning transmission electron microscopy and microdiffraction analyses. The formation of these particles was ascribed to a process involving first the reaction of polyamic acid with Cu (or Ni) to form a polyamic acid complex. During subsequent thermal curing, the complex decomposes, resulting in Cu2O (or NiO) and aggregates to form particles during imidization. The precipitation-free zone is due either to heterogeneous nucleation of the oxide particles or to a temperature gradient during curing which causes the interfacial product to migrate from the vitrifying polyimide into still plasticized polyamic acid. © 1988 VSP.