Surface modification of thermoplastics by low-pressure microwave O2 plasma treatment for enhancement of the adhesion of the interface box/encapsulating resin and the influence on film capacitors operating under extreme humidity conditions

Abstract

A low-pressure microwave O2 plasma is applied on the plastic boxes of the metallized film capacitors to strengthen the interfacial adhesion of thermoplastic box/encapsulating resin. The effectiveness of the plasma is reported by analyzing Scanning Electron Microscopy (SEM) micrographs, X-Ray Photoelectron Spectroscopy (XPS) spectra, and contact angle and roughness measurements. An enhancement of the polar character and total free surface energy in both thermoplastics (polybutylene terephthalate (PBT) and polycarbonate (PC)) are determined. Hence, a better wettability of the plastic boxes with the encapsulating epoxy resin is achieved after the plasma application. During the Temperature-Humidity Bias Test (THB), the metallized film capacitors with PC box improves the performance after being plasma treated. Additional capacitor interfaces seem to play a key role in the performance of the device according to the loss of capacitance determined during the THB Test.