Die attach interface property characterization as function of temperature using cohesive zone modeling method

Interface delamination is one of the most important issues in the microelectronic packaging industry. Silver filled die attach is a typical adhesive used between the die and copper die pad for its improved heat dissipation capacity. Delamination between die attach and die pad will severely impact the heat conduction and result in product failure. In order to predict this delamination, interface properties should be characterized. Tri-material, copper-die attach-EMC, samples are made according to the 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. This will provide the delamination geometry information needed for determining the interface properties. Four point bending tests have been performed at room temperature, 40, 60, 85, and 150?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 no effects on the ?critical delamination load? compared with the dry samples tested at the same temperatures. This means that moisture has no effects on the interface toughness between copper and die attach. 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 26.5J/m2 at room temperature to 1.9J/m2 at 150?C as calculated from the cohesive zone element model. These results show that temperature has a large effect on the interface toughness. By means of an extensive model parameter sensitivity study, combined with the measured delamination length in horizontal direction along the copper-die attach interface at room temperature critical opening value has been determined.