Microstructure, adhesion strength and failure path at a polymer/roughened metal interface

Metals and polymers are extensively used in microelectronics packaging where they are joined together. Since both the yield and reliability of packages are strongly affected by the interfacial adhesion between polymers and metals, extensive studies have been performed in order to improve the resistance to debonding of many resulting interfaces. In the present work, the interfacial fracture energy of representative polymer/metal interfaces commonly encountered in micoroelectronics packaging was characterized. A copper-based alloy leadframe was used as the metal and an epoxy molding compound (EMC) was used as the polymer. The leadframe surfaces were roughened by chemical oxidation in a hot alkaline solution and molded with the EMC. In general, roughening of metal surfaces enhances their adhesion to polymers by mechanical interlocking, yet often produces a cohesive failure in the polymer. Sandwiched double-cantilever beam (SDCB) specimens were employed to measure the adhesion strength in terms of interfacial fracture energy. After the adhesion test, the microstructures of metal surfaces before molding with the EMC were correlated to the adhesion strength, and the fracture surfaces were analyzed using various techniques to determine the failure path.