Mechanical shock testing and modeling of PC motherboards

Due to a variety of manufacturing, environmental, shipping, and end-use conditions, personal computer (PC) motherboards and other circuit boards may be subjected to potentially damaging mechanical shock loads. As these loads can lead to product failure, an understanding of the response of circuit boards subjected to suddenly applied loads is necessary. A first step in this direction is to develop and validate modeling approaches for the simulation of shock load response on PC motherboards. Since building a detailed model of the motherboard would be difficult due to the wide variation in length scales and localized concentrations of mass/stiffness due to components, two simplified modeling approaches were investigated: global property smearing and simple block modeling. Both of these methods approximate the influence of regions with widely differing stiffness and mass properties resulting from the placement of components, connectors and other items on the circuit board while simultaneously avoiding problems associated with developing large, expensive, detailed models. Both the shock response spectrum (SRS) method and an implicit direct integration (i.e., time-marching) scheme were used to simulate the shock response. In addition to modeling, programmed shock pulse and drop table measurements were carried out on the motherboard to validate and understand the limits of the finite element simulations. The results show that the predicted peak response at a number of locations on the motherboard correlated well with measurements made during the shock loading; however, improvements in the simple models are still required to strengthen their correlation. Surprisingly, the simple global smear approach produced good results with significantly less solution time than the block model. Finally, it was found that the SRS method significantly under predicted the response of the motherboard. This may be due to large displacements induced in the motherboard by the high-g shock loads.