Establishing mixed mode fracture properties of EMC-copper (-oxide) interfaces at various temperatures

Interfacial delamination is known as one of the root causes of failure in microelectronic industry. In order to explore the risk of interface damage, FE simulations for the fabrication steps as well as for the testing conditions are generally made in the design stage. In order to be able to judge the risk for interface fracture, the critical fracture properties of the interfaces being applied should be available, for the occurring combinations of temperature and moisture preconditioning. As a consequence there is an urgent need to establish these critical interface fracture parameters. For brittle interfaces such as between epoxy molding compound (EMC) and metal (-oxide) substrates the critical energy release rate (or delamination toughness, Gc) can be considered as the suitable material parameter. This material parameter is strongly dependent on the temperature, the moisture content of the materials involved and on the so-called mode mixity of the stress state near the crack tip. The present study deals with experimental investigation of the delamination toughness of EMC-Copper lead-frame interfaces as can directly be obtained from the production line. The experimental set-up as designed for this purpose was previously reported, together with some measurement results and toughness evaluations for room temperature fracture tests. This study deals with the experimental and simulation procedures to establish the interfacial fracture toughness from fracture test results at different temperatures, especially in the glass transition temperature region of epoxy molding compound. In order to calculate accurate fracture toughness, the viscoelastic material properties of molding compound are measured and considered. A special test procedure used to investigate the fracture properties in the glass transition temperature region of EMC will be introduced. The FE model used to simulate the viscoelastic material behavior will be discussed. The delamination toughness as a function of mode mixity at different temperatures will be given in the result section