Synthesis and manufacture of polyamide-imide/copper foil laminates without adhesive

Three kinds of polyamide-imide (PAI) were synthesized. The polyimide prepolymer was synthesized from 4,4'-diphenylmethane diisocyanate (MDI) and 3,3'-4,4'-benzophenone tetracarboxylic dianhydride (BTDA), after which the prepolymer was reacted respectively with terephthalic acid (TPA), isophthalic acid (IPA), and 4,4'-oxybisbenzonic acid (OBBA) to form PAI-1, PAI-2, and PAI-3. Their chemical structures were characterized using elemental analyses (EA), Fourier transform infrared spectrometry (FTIR), and nuclear magnetic resonance (NMR). The thermal properties, electrical properties, solubility, and mechanical properties of these PAIs, and the peel strength retention and electrical properties of PAI/Cu laminates were measured. The dielectric constants of PAI laminates were lower than 5.5 and the dissipation factors were lower than 0.035, and were in the order of PAI-3 < PAI-1 < PAI-2. These PAI/Cu laminates exhibited peel strength higher than 2.30 kN/m under normal circumstances and higher than 2.15 kN/m after heating. The order of peel strength was PAI-1 > PAI-3 > PAI-2.