On the mechanical fatigue study of second-level interconnects using the E-N curve approach

The authors presented, in an earlier paper, an unified component-level approach for characterizing fatigue behavior of BGA package solder joints under Vibration, Cyclic Bend and Cyclic Shock loading conditions [1,2]. The approach involves creating a board strain versus number of cycles-to-failure curve, also known as E-N curve, using data collected from the three tests. For BGA packages used in mobile notebooks, the authors showed that all of the data points, for a given failure mode, fall along a straight line - similar to the classical metal fatigue (S-N) curves. In this paper, that effort is extended to other market segments, with varying board thickness, and component types. Specifically, applicability of the E-N curve approach to CPU sockets and small-form-factor (SFF) packages used in mobile internet devices and the effect of board thickness on the mechanical fatigue performance are explored. The study was limited to lead-free solders, but the learnings can be applied to leaded solder systems.