Evaluation of Cu capping alternatives for polyimide-Cu MCM-D

Among the 3 types of polyimide (PI) systems, pre-imidized, polyamic ester and polyamic acid, the latter has been shown to react with Cu surfaces when it is spun coated. This paper reviews Cu-polyimide adhesion and diffusion data and present various wet process alternatives to minimize Cu diffusion into poly(biphenyl dianhydride-p-phenylene diamine) (BPDA-PDA) polyamic acid precursor. Two different process options were investigated: a precoat or adhesion promoters (A1100, AP420 and benzotriazole) prior to the polyamic acid apply, and an additive (Tetrazole or BTA) formulated in the PAA solution. The 5 processes were compared with respect to adhesion, capacitance, dielectric constant and reliability. Only the BTA formulation had adhesion problems which were attributed to the A1100 precoat used. A1100 as a precoat was further evaluated on various copper surfaces and curing environments. All proposed solutions performed well when used on a MCM-D/C module which was used to extract electrical parametrics and was further subjected to reliability testing.