Assessment of thermally-aged conformally-coated printed circuit boards
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Date
2019-09-16
Authors
Zeynali, Ehsan
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Abstract
Printed circuit boards (PCBs) are key components of electrical and electronic systems. The electrical performance of PCBs under harsh operating conditions is a decisive factor to ensure the reliability of the system. As a result of increased demand for electric power, the operating voltage of many systems is increased. The increased operational voltage level, imposes a higher level of electrical stress on the insulation system and, therefore, discharges and failure are more likely to happen. To provide a better insulation level, PCBs are coated with a film of conformal coating polymer. The protective layer provides a barrier against environmental factors including moisture, contamination, temperature changes, and mechanical abrasion. However, in exposure to humidity and temperature, some levels of aging happen in the coated PCBs. Degradation of the conformal coating layer decreases the performance of the coated assembly.
In this thesis, a series of experiments were conducted to evaluate the electrical performance of conformally-coated PCBs under accelerated aging conditions. Test samples were designed and fabricated based on industry standards. Test boards were coated with silicone conformal coating using dipping application technique. Partial discharge tests were conducted on coated samples under pollution and conductive particles. The impact of conductive particles and location of the pollution on PD activity were observed. A group of test samples were aged using an automatic thermal and humidity chamber. Specimens were exposed to temperature and humidity. The level of degradation was evaluated by visual inspection. Capacitance and loss tangent of the test samples were measured using a dielectric spectrometer after cycles of aging. The level of change in the capacitance and loss tangent due to aging was investigated. Further, the breakdown voltage of both aged and new test samples was measured. Electrical performance of the different samples were discussed based on the partial discharge activity and breakdown voltage.
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Keywords
Printed circuit boards, Conformal coating, PCB