The influence of leadframe on passivation cracks growth

Passivation layer in the IC interconnect has a very small feature size comparing with the global package size. When using, Finite Element Modelling (FEM) to analyse the passivation cracks, the effect of leadframes are usually neglected. In this paper, the influence of leadframes on the passivation crack growth is studied by J-integral theory using a certain leadframe thickness model with different crack lengths, different crack starting positions and different crack directions. For different critical process steps, here the final process temperature is acted as a representative parameter to analyse its impact. Yielding stress and thickness of leadframe are the design variables, wherein J-integral values of crack with certain crack lengths and different crack directions were gained Furthermore, Response Surface Model (RSM) of J-integral is established using the two leadframe design parameters. Since the yielding stresses of leadframes are strongly process dependent and probabilistic in nature, a histogram is derived to understand the probability of the J-integral under the given distribution of yielding stresses. Results show that the leadframe will make the passivation crack grow much more easily.