Time dependent singular behaviours at interface edges of chip

Abstract

It is well known that the stress and strain become singular near the interface edges, therefore, the failure of an electronic package usually initiates from the edge of solder joints. Since the solder materials are viscoelastic or viscoplastic, the edge singular fields are intrinsically time dependent. Moreover, the singular field varies with the cycles of temperature or power on/off. A numerical method to determine the time dependent singular fields is demonstrated. Based on the thermal and structure analyses of the whole package, the stress and strain singular fields near the interface edges are obtained by a zooming up method. It is found that both the singular order and intensity coefficient are time dependent. The stress and strain ranges described by the maximum and minimum states are then computed. The thermal fatigue life of electronic package can be evaluated quantitatively, through the fatigue model obtained by the experiment and numerical results.

Keywords:

• Electronic package
• Interface edge
• Viscoelasticity/viscoplasticity
• Singular field
• Zooming up method

The research work was supported by the National Natural Science Foundation of China (grant nos. 10772116, 10772115 and 10932007).