Oxygen induced adhesion degradation at metal/polyimide interface

Abstract

The role of oxygen in affecting the adhesive bonding at the metal/polyimide (polyimide-on-metal) interface has been studied. Both pyromellitic dianhydride (PMDA) -oxydianiline (ODA) and biphenyl-tetracarboxylic dianhydride(BPDA) -p-phenylene diamine (PDA) based poly(amic acid) precursors were cast and fully imidized on metal surfaces of Cr, Cu, Ni, Co, Cu/Ni, and Cu/Co in a nitrogen atmosphere. The peel strengths at the polyimide-on-metal interface were measured, using a 90° peel test, immediately after curing, and then remeasured after annealing in either nitrogen (N2−≤100 ppm O2 ) or air (N2 –21% O2 ) at 350 °C for 1 h. Very little or no change in peel strength was measured after these samples were annealed in nitrogen, while significant adhesion degradations were measured on all metals after annealing in air. The loss of polyimide (PI) adhesion to the Cu or Co surface is attributed to metal catalyzed thermal–oxidative degradation of the PI at the metal/PI interface, as characterized by polyimide thickness reduction, Fourier transform infrared and x-ray photoelectron spectrometries. The rate of degradation of the PMDA-ODA films on Cu or Co is several times faster than that of the BPDA-PDA films. The degradation products were characterized as CO2, CO, Cu carboxylate salts and a nitrile moiety entrapped in partially degraded PI films. The extent of degradation was found to increase with increasing oxygen content in the annealing ambient or with decreasing PI thickness, indicating that oxygen diffusion through the PI overcoating to the metal/PI interface plays a critical role in promoting degradation. On the Cr and Ni surfaces, such metal catalyzed degradation was not detected with our techniques, while some adhesion strength was still retained, a significant loss in adhesion strength was observed. This is probably due to oxidation of the metal underlayer causing debonding at the originally well adhered metal/PI interface. When all testing variables were held constant, the peel strength of a well adhered metal/PI joint is shown to increase with increasing peeling rate (crosshead speed). An increase of up to ∼40% in peel strength was measured when the crosshead speed was increased from a low speed of 0.05 mm/min to 10 mm/min. The locus of fracture of the as-cured films was cohesive, i.e., the fractured surface was located within PI, while for the thermal–oxidative degraded joint the failure mode was changed to adhesive.

Nanoparticles fabricated by selective reaction of Fe100−xPtx alloy films during imidization of polyamic acid

“…At 600 • C, it appears that the thermal degradation of the PI matrix expedited the vertical migration of materials from the metal film and led to eventual coarsening of the particles in the vertical dimension. It was previously shown that using FT-IR, the PI film did quickly deteriorate above 500 • C in the presence of a metal film [10]. We also confirmed that the PI structure was in fact thermally damaged above 500 • C, using FT-IR measurements.…”

Effect of Ni-Cr Layer on Adhesion Strength of Flexible Copper Clad Laminate

“…17 Shin et al reported that the loss of adhesion of polyimide to Cu is due to the metal-catalyzed thermal oxidative degradation of the polyimide at the metal/ polyimide interface, while that for Cr and Ni it is due to oxidation-induced debonding at the metal/polyimide interfaces. 18 As a result, in this study, the XPS and AFM results identified that the FCCL with the higher Cr ratio experienced a smaller change of the chemical functions and fracture surface roughness than did the FCCL with the lower Cr ratio.…”

Effect of Cr Thickness on Adhesion Strength of Cu/Cr/Polyimide Flexible Copper Clad Laminate Fabricated by Roll-to-Roll Process

“…Cu may also act as a catalyst to decompose polymeric bonds under oxygen or a moisture containing environment at elevated temperatures. 8) In order to improve the interface adhesion strength, an additional metal layer is generally deposited at the Cu/PI interface. Chromium (Cr) has been used as an interface metal layer because of the formation of strong Cr-C bonds.…”