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Vibrational fatigue of surface mount solder joints

The most common reliability problem of surface mount solder interconnects in advanced electronic packages is solder cracking due to thermal cycling. However, it is believed that the vibration loading can increase the crack growth rate. In this study, an advanced global/local finite element modeling (FEM) technique combined with the fracture mechanics approach was used to study the crack propagation event along the interface of surface mount solder joint and leadframe. Several detailed 3D local models of the interconnect (leadframe and solder joint) with different interfacial crack lengths were built. The effective stiffness and mass properties of the local model were used in the global model which consists of PWB, component, and interconnect to determine the overall dynamic response of the system subjected to random base excitation at the PWB supports. Then, the absolute displacement power spectrum density (PSD) of the top and bottom of the critical corner pin were applied to the local model to establish the interfacial J-integral PSD for different crack lengths. A example of a 160-pin gull-wing lead quad-flat-pack (QFP) on PWB was illustrated in this study.