Interfacial adhesion in metal/polymer systems for electronics

The effects of the different surface modification methods on the adhesion of electroless and sputter-deposited metals to dielectric polymers were investigated. The adhesion of Cu and Cr/Cu metallizations to the epoxies, liquid crystalline polymer and inorganic-organic hybrid polymer was measured with the newly developed pull test method. The microstructure and chemical state of the surfaces were characterized with the help of X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and contact angle measurements. The adhesion not only depends on the surface pretreatments but also the metallization techniques. The investigation revealed that plasma, reactive ion etching (RIE) and wet-chemical treatments induced clearly different physico-chemical changes on the polymer surfaces that strongly affected the adhesion of the metals to the polymers. The wet-chemical treatment produced large numbers of microcavities to anchor deposited electroless copper. The dependence of the adhesion on the surface roughness in the electroless copper/polymer systems confirmed the dominant role of the mechanical interlocking. The plasma and RIE treatments were very effective in improving the wettability of the polymer by increasing the surface polarity. It led to considerably better adhesion of sputter-deposited copper to the polymer than the chemical treatment. The enhancement of the surface polarity of the polymer and the enlarged surface contact area due to the increased roughness were the most important factors in the adhesion. SEM of the fracture surfaces showed that the failure modes of the copper/polymer systems were predominantly cohesive in nature within the polymer. By performing the theoretical and experimental investigations into controlling adhesion mechanisms in the metal/polymer systems, a better fundamental understanding of the adhesion between metals and polymers in the high-density built-up modules has been achieved.reviewe