Analyses of printed circuit boards subjected to vibration loadings under various clamping types and reinforced ribs

Electronic systems installed under the dynamic environment such as those on the transportation vehicles, military and aerospace equipment, and handheld mobile devices, are often subjected to harsh vibrations. How to improve the life of these electronic devices is an important issue other than their functional design. In this study, these electronic systems with different installation conditions and vibration loadings, are analyzed for their deformation at each vibration mode. The locations where key electronic components mounted were examined for the resulting stresses. Finally, either the ribs or the special fixtures are designed in reducing the resulting dynamic stresses and thus enhance the system's life. In the experimental study, the Scanning Laser Doppler Vibrometer(SLDV) was used for measuring the dynamic characteristics such as the natural frequencies and the mode shapes of the printed circuit boards (PCB) under various clamping conditions. The resulted displacement can be input to the finite element analysis software or the simplified mathematical model for calculating the stresses in estimating the life. It is quite often that due to circuit design constraints, some electronic components are inevitably mounted on those locations with severe deformation. Thus, it has to use the reinforced ribs to improve the local stiffness of the mounting locations. Furthermore, the wedge lock which is commonly used in avionics was also studied for its effect on the PCB deformation and the solder ball stresses. Through the study, it was found that the vibration resistance of the board equipped the ribs is better than that without the ribs. The stress act on the solder balls of former is less than the latter relatively. Meanwhile, those PCB's with long ribs were better than those of short ribs in vibration resistance. However, the effects of short ribs varies depend on its using conditions. For the clamping with wedge lock, it is much better than other clamping methods in the study since it can reduce the stresses on the solder balls dramatically. The effects can even compete with the boards equipped the long ribs. This might explain why wedge lock is usually used on those important and precise avionic electronic equipments.