Adhesion of polymer/metal bonds for molded interconnect devices (MID)

The market constantly demands an extension of the functional features of electronic devices and this leads to the application of new materials. Polymers represent an innovative potential due to their favorable properties for packing. The MID technology represents a new growing potential in packaging. Basis of this technology are polymer/metal bonds. For the quality and reliability of a polymer/metal bond the adhesive strength is a critical factor. For the adhesion improvement the plasma treatment of polymer surface wins a key position. Reactions between plasma species and polymer surface make it possible to form polar groups on the polymer surface. Polar chemical groups like C-OH, C=O, CHO, COOH are chemically reactive and cause an increase of the surface energy and wetting qualities. The adhesive strength of a polymer/metal bond can be positively affected by exposing to plasma treatment before metallization. Starting from the definition of adhesion investigations were undertaken to characterize the energetic and topological behavior of the polymer surfaces. Methods used were the contact angle method, atomic force microscopy (AFM), scanning electron microscopy (SEM) and auto focus laser scanning. The verification of the chemical surface change reached by the plasma treatment was accomplished with x-ray photoelectron spectroscopy (XPS). There are well known a large number of destructive testing methods to determine adhesive strength. In this work the examination of the bond strength of the vapor deposited metal layer on the polymer surface was carried out by tape tests on the basis of cross hatch cut procedure