Gideon Analytical Labs received three partial boards with four coupling Vishay MKT 1817 63V ERO 0225 film capacitor failures. After electrical measurements and considerable testing, the ESR was found to be the cause of the failure, however, what caused the ESR to elevate?
It was determined the packaging on the capacitor was not adequately protecting the terminal end from the outside environment. Moisture ingress elevated the ESR and with higher ESR, the higher the heat produced in the circuit. This capacitor was a replacement for another capacitor once used in the circuit. This capacitor had higher ESR than its predecessor. Thus, with the higher ESR to begin with, the moisture and ionic ingress through the package and the ripple current being used in the application this lead to thermal failures.
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