Influence of temperature, humidity and defect location on delamination in plastic IC packages

The J-integral and the stress intensity factor based on linear elastic fracture mechanics can be applied to predict the growth of interfacial delamination in IC packages. One of the key parameters required is the interfacial fracture toughness. This paper describes the measurement of the interfacial fracture toughness as a function of temperature and relative humidity using a three-point bending test. The interfacial fracture toughness was found to decrease with temperature and relative humidity. It is proposed that delaminations propagate from very small voids or defects present at the interface. The effect of the location of these interfacial defects on delamination is studied. The IC package evaluated in this paper is an 80-pin quad flat package with a defect at the edge or the center of the interface. It was found that as the package temperature was increased, the stress intensity factor of the edge delamination was higher than that of the centre delamination. However, whether the edge delamination propagates first as temperature is increased depends on the ratio of mode II interface toughness to that of the mode I interface toughness. For the package under investigation, it was established that when this ratio is less than 2.7, the edge delamination is first to propagate; otherwise, the centre delamination is first. For small defects, it was found that the water vapor pressure developed at the interface did not have a significant effect on the value of J and hence the crack-tip stress intensity factor