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Chapter 10 analyses the dynamic response of the printed circuit board (PCB) assembly due to a board-level drop-shock, with the ultimate intention of establishing the maximum magnitude of PCB strain. The PCB was first modelled as a spring-mass system, then as a beam supported at its two ends and subjected to a half-sine shock. The analytical solutions provide many insights into the shock response of the PCB assembly, such as that specified in the JEDEC standard JESD22-B111, which specifies a perfect half-sine acceleration shock. It is shown that the magnitude of response of the test board in the JEDEC standard JESD22-B111 increases linearly with the shock impulse – the area under the acceleration–time curve, independent of the shape of the shock pulse. This highlights the inadequacy of the JEDEC standard JESD22-B111: it is impossible in practice to produce a perfect half-sine pulse. Distorted pulses that have the same magnitude and duration could have different shock impulses, hence inducing different responses from the same PCB assembly. The numerical algorithms for transient dynamics used in commercial finite element software are also introduced. |
