Adhesion of poly(arylene ether benzimidazole) to copper and polyimides

Poly(arylene ether benzimidazole) (PAEBI) is a high-performance thermoplastic polymer with imidazole functional groups which form the polymer backbone structure. It is proposed that upon coating PAEBI onto a copper substrate, the imidazole groups of PAEBI form a bond with or chelate to the copper surface, resulting in strong adhesion between the polymer and copper. The adhesion of PAEBI to other polymers such as poly(biphenyl dianhydride-p-phenylene diamine) (BPDA-PDA) and 6F photosensitive polyimide was also quite good and stable. The resulting locus of failure as studied by X-ray photoelectron and external reflectance infrared spectroscopy indicates that the failure is in the polyimide layer for the case of polyimide/PAEBI/Cu adhesion. Owing to its good adhesion and mechanical properties, PAEBI can be used in the fabrication of thin film semiconductor packages such as multichip module dielectric (MCM-D) structures. In these applications, a thin PAEBI coating is applied directly to the wiring layer for enhancing adhesion to both the copper wiring and the polymer dielectric layer. In addition, a thin layer of PAEBI can also function as a protection layer for the copper wiring, eliminating the need for Cr or Ni barrier metals, and thus significantly reducing the number of process steps. Once the PAEBI layer was spin applied onto the Cu and/or polyimide film, it was overcoated with a thick layer (similar or equal to 7 mu m) of BPDA-PDA polyimide. TEM analysis of the BPDA-PDA/PAEBI/Cu interface indicated that BPDA-PDA poly(amic acid) solution did not penetrate through a thin PAEBI layer. Applications of PAEBI to MCM packaging technologies, as well as the properties of PAEBI, are discussed.