Characterizing the interfacial fracture toughness for microelectronic packaging

Abstract

In a microelectronic package there are many interfaces where the adhesion between different materials plays an important role in its reliability issue. Take an example in a flipchip package: delamination at the interfaces between underfill/passivation, underfill/substrate, etc. will lead to the speeded breakdown of the interconnection. Proper characterization of interfacial adhesion strength is very important for process control as well as reliability prediction.

From a fracture mechanics point of view, a strained body with defects will break when the rate of change in its potential energy G reaches a critical value Gc (toughness). In this paper both analytical and experimental descriptions are given on the determination of Gc using single cantilever beam (SCB) specimens. A composite beam on an elastic foundation model is employed to interpret the testing results once the modulus of the foundation is known. The modulus of the foundation can be estimated by analytical approach or deduced from the experimental record. The approach described in our paper is generically suitable for many more interfacial toughness determinations.