Improvement of adhesion and long-term adhesive reliability of liquid crystalline polyester film by plasma treatment

Abstract

Surface modification of thermotropic liquid crystalline aromatic polyester (LCP) films was examined by low-pressure plasma treatment to improve initial adhesion and long-term adhesive reliability between the LCP film and an epoxy bonding sheet for printed circuit boards. Plasma irradiation was carried out in various plasma gases with different plasma modes as reactive-ion-etching (RIE), direct-plasma (DP) with pressures ranging from 4.0 to 26.6 Pa. Although the initial adhesion of the DP-treated film increased, the long-term adhesive reliability estimated by pressure cooker test (PCT) decreased with decreasing the plasma gas pressure in every gas. The higher concentration of the generated polar groups such as phenolic hydroxyl group and carboxyl group enhanced the initial adhesion by the increase in the chemical interaction; however, it damaged the long-term adhesive reliability due to the acceleration of the penetration of water molecules into the interface. The large surface roughness was effective to enhance the initial adhesion and the long-term adhesive reliability. The RIE-treatment generated the polar groups and the larger surface roughness than the DP-treatment. The RIE-treatment in the O2 atmosphere at the gas pressure of 13.3 Pa was the best plasma condition for both the initial adhesion and the long-term adhesive reliability. ©2007 Wiley Periodicals, Inc.