There is no validated way to create a reliability prediction for interaction with the housing in thermo-mechanical loads. There is currently no reliability model for solder joint reliability based on PCB or component strain. Large deformations due to board-housing interactions are a mistake in the design. There should be only one connection point on the board with a rigid attach in the X-Y (in plane) direction. The rest of the bolts should have a shoulder bolt with a smaller diameter than the hole. This attach method prevents the bending that can occur from the CTE mismatch between the housing and the board.
The current method to determine solder joint reliability due to thermo-mechanical loads is to create a full FEA model of the component and board with the solder joints and track the strain energy density(SED) in the joint. The model is subjected to two temperature cycles and the SED at the end of the second cycle is compared to the SED at the end of the first cycle. This difference has a correlation to number of cycles to failure but only in a relative way. More SED equals more damage. There are several models that attempt to relate the SED to number of cycles to failure but each of them has issues.
The over constrained boards problem was solved years ago with specific design rules. These rules seem to have been forgotten in the past couple of years and we are seeing this preventable problem rearing its head again.Please do not hesitate to contact me with more information regarding this preventable phenomenon.
Copyright Gil Sharon December 4, 2014. All rights reserved.