Evaluation of interfacial fracture toughness of a flip-chip package and a bimaterial system by a combined experimental and numerical method

In this paper, the interfacial fracture toughness of a flip-chip package subjected to a constant concentrated line load and a bimaterial system under thermal loading condition were evaluated using a unique six-axis submicron tester, a thermal vacuum chamber and FEM modeling coupled with a high density laser moire interferometry. The six-axis submicron tester was used to provide a constant concentrated line load, whereas the moire interferometry technique was used to monitor the crack length during the test. In addition, a finite element technique was simultaneously used to determine the near crack tip displacement fields of the specimens. The interfacial fracture toughness and phase angle were computed by using these near tip displacement variables through the analytical energy release rate and phase angle expressions derived by authors. The interfacial fracture toughness and the phase angle of the flip-chip package considered at the interface where the passivated silicon chip meets the underfill are 35 J/m(2) and -65 degrees, respectively, while the interfacial fracture toughness and the phase angle of the tested bimaterial specimen at the interface of the molding compound/silicon with the crack length of 3.3 mm under the temperature rise thermal load from room temperature (20 degrees C) to 138 degrees C are 20.02 J/m(2) and -54.8 degrees, respectively. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.