Practical assessment methodologies for circuit cards under mechanical shock loading

Problem description. Currently many military contractors do not specifically evaluate circuit cards in a shock environment. They rely on either past experience, or the attenuation of shock pulses from shock mounts without actually evaluating the effect of shock on the electronic equipment. A practical assessment methodology for assessing and evaluating circuit cards in shock environment is needed, because the development of electronics for military equipment is constrained by schedule requirements. If shock assessment is actually to be performed in design, an approach that uses little or no testing and relatively simplistic finite-element analysis is needed.; Methods used. The objective for this dissertation was to develop a practical assessment approach for examining circuit card reliability under mechanical shock loading. To develop this approach, a combination of experimentation and modeling was used to characterize failure mechanisms and sites. Because of electrodynamic shaker-table limitations, a drop-impact tester was developed that provided dynamic three- or four-point bend tests on circuit cards. The tester produced repeatable strain responses in the circuit card, which resembled half-sine wave pulses. To characterize circuit board fracture, circuit cards were tested using a shaker table, the drop-impact tester and a static three-point bend tester. Test results and finite-element analysis were used to develop failure models based on failure risk due to strain in the outer layer of the board. To characterize component failure, the drop-impact tester was used to fracture components and leads. Failure models were developed for specific component types in terms of failure risk based on inertial loading or stress from the circuit board bending.; Results/conclusions. Using results of the circuit board and component research, a practical assessment approach for circuit cards subjected to shock loading was developed. This approach recommends specific finite-element analyses and testing to determine or validate board response. The practical assessment approach was successfully demonstrated on two US Army circuit cards. This practical assessment approach will allow electronic circuit card designers to quickly evaluate circuit cards with minimal testing and finite-element analysis. It also provides information necessary for circuit card redesign to improve failure risk for shock loading.