Absorption and interaction of methylene chloride with metallized polyimide films

Abstract

Metallized polyimide films are commonly used for the fabrication of flexible circuits for tape automated bonding (TAB) applications. Although there has been an extensive effort to understand the formation of the metal/polyimide interface, little information exists on the effects of humidity and temperature on adhesion. Further, since circuit fabrication processes involve a variety of chemicals, these materials can potentially induce adhesion degradation. Methylene chloride (MC), used for photoresist stripping, absorbs readily into Kapton-H. Residual MC levels in the polymer undergo decomposition upon heating above 100 °C to yield HCl. Optical microscopy, Rutherford backscattering spectroscopy and Auger electron spectroscopy are used to characterize the resulting interfaces on actual TAB circuit lines before and after exposures to humid and thermal environments. Thin metallized Kapton-H films were exposed to MC followed by a thermal cycle to determine the role of chloride on adhesion degradation. After a thermal cycle or additional temperature/humidity exposure, the fracture mode shifts from cohesive in the polyimide to the chromium/copper interface. This results in adhesion loss with concentration of chloride at the weaker interface.