Utilizing the Novel Laser Spallation Technique to Measure Interfacial Strength in Microelectronic Packages

Abstract

Laser spallation is a high strain rate adhesion measurement technique. Based on the principle of pulsed laser ablation, strain rates of the order of 105–106s−1 are achieved with laser spallation. At these strain rates, low strain rate losses such as due to plasticity or viscoelasticity get minimized and so the strength measurement from laser spallation will be close to the intrinsic strength of the interface. In addition, the high strain rates also enable an understanding of “shock” stress conditions. This work focuses on the application of laser spallation to understand two types of interfaces in flip chip microelectronic packages — BGA solder joints and copper-epoxy based dielectrics. The ability of laser spallation to differentiate samples on the basis of their adhesive strength is understood.