Miscibility behavior of polyimide (PI)/poly(arylene ether benzimidazole) (PAEBI) blends and its effects on the adhesion of PI/PAEBI/copper joints

Abstract

Poly(amic acid) (PAA) and poly(amic diethyl ester) (PAE) precursors of poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA), which is a representative polyimide (PI) being used widely in the microelectronic industry as an interdielectric material, were synthesized. The miscibility behavior of these precursors with poly(arylene ether benzimidazole) (PAEBI), which is known to exhibit strong cohesive adhesion to copper metal conductor, were studied in N-methyl-2-pyrrolidone (NMP) as well as the condensed state and the imidized state using light scattering technique. And, the miscibility effect on the adhesion strength of PI/PAEBI/copper joint, in which the locus of failure is known to be within the PI layer, was investigated by 90°peel test. The PAA precursor was miscible completely with PAEBI in the NMP solution as well as in the condensed state via the strong interaction between carboxylic acid groups of the precursor and imidazole groups of PAEBI. However, imidization-induced phase-separation took place during thermal imidization of the PAA precursor, leading to domains of 0.7-1.4 μm for the imidized blends containing 30-70 wt % PI. The other blend compositions still were optically transparent. In contrast, the PAE precursor was miscible with PAEBI in the NMP solution with a limited concentration of <11.3-14.5 wt %, but immiscible almost completely in the condensed state, causing phase-separation. The phase-separation occurred further during thermal imidization, producing domains of 0.8-3.0 μm. In particular, the 50/50 (=PAEBI/PAE, wt/wt) blend had domains of >3.6 μm. Only the 90/10 blend film was optically transparent. The difference in the miscibilities of PAEBI with the polyimide precursors was reflected on the adhesion strength of PI/PAEBI/copper joint. The PAA precursor gave a relatively high peel strength, compared to the PAE precursor. In addition, the PAEBI having a relatively low intrinsic viscosity provided a high peel strength in the adhesion joint.