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Analysis of PCB subassembly dynamic responses using integrated analytical, numerical and experimental techniques

The mechanical shock causes multiple PCB bending or vibration which induces the solder joint fatigue failure. The solder joint failures are strongly dependent on many factors. In particular, PCB design and mounting method is one of the key factors. It determines the dynamic responses, and the degree of PCB flexing which is the root cause of solder joint failure. In this paper, dynamic strains of PCB are measured and analyzed in detail with a real-time electrical monitoring system. The effects of test variables, such as drop height, number of PCB mounting screws, and tightness of screws, are studied by comparing and analyzing the dynamic responses. Frequency domain analysis is introduced to perform advanced spectrum analysis on the dynamic responses of PCB during drop impact. Spectrums of impact pulse and dynamic strains are obtained by using fast Fourier transform (FFT) technique. Bending mode shapes and frequencies of PCB extracted from strain spectrums are consistent with the results of modal analysis by finite element modeling. Knowledge of spectrums of PCB dynamic responses is very important to understand the PCB bending characteristics which affect the solder joint reliability. Most of the fundamental modes of PCB with frequencies lower than 2.5kHz are excited during drop impact. The first mode is the dominant one. From the spectrum analysis, it is clear that the bending mode shapes and frequencies are unique for different PCB mounting configurations.