Investigation of temperature and moisture effect on interface toughness of EMC and copper using cohesive zone modeling method

Abstract

Interface delamination is one of the most important issues in the microelectronic packaging industry. Epoxy molding compound (EMC) and copper interfaces are the most important interface mostly concerned by the industry and researchers. Delamination between EMC and copper will severely result in product failure. In order to predict this delamination, interface properties should be characterized. Bi-material, copper-EMC, samples are made according to the industrial package processes. A four point bending test system is established in order to perform delamination tests at different temperatures using a universal tester Zwick/Roell Z005. In addition, a Keyence optical system is mounted to capture a series of pictures during the delamination processes. Four point bending tests have been performed at room temperature, 85°C respectively. In addition pre conditioning sample are also tested at room temperature and 85°C respectively after 48 hours pre conditioned at 85°C/85%RH. Experiments show that the “critical delamination load” decreases steadily with temperature increasing. Experiments also show moisture has effect on the “critical delamination load” compared with the dry samples tested at the same temperatures. This means that moisture has effects on the interface toughness between copper and EMC. To quantify the interface properties, numerical simulations of the four point bending test have been performed by using a finite element model comprising cohesive zone elements which will describe the transient delamination process during the four point bending tests. Correspondently, the interface toughness decreases from 21.2 J/m2 at room temperature to 3.7 J/m2 at 85°C as calculated from the cohesive zone element model. These results show that temperature has a large effect on the interface toughness. Saturated moisture, at 85°C/85%RH, decrease about 20% interface toughness between EMC-copper.