Abstract:

Silicones are commonly used as encapsulation materials, given that theyprovide excellent properties like high thermal stability, chemical resistance, protection against handling, and dielectric isolation. Furthermore, they impose minimal mechanical stress on the encapsulated devices and interconnections. However, silicones are highly susceptible to moisture ingress. To address this issue, this study primarily focuses on reducing moisture ingress into silicone encapsulations with a simple and cost-effective design. This design approach explores the fabrication of bi-layered encapsulation material, which includes the addition of a polyurethane moisture barrier layer over silicone, as it is a highly moisture-resistant and economical encapsulation material. In contrast to silicone, it can impose considerable mechanical stress on the encapsulated devices. Hence, combining polyurethane with silicone permits a reduction in moisture penetration and absorption while reducing mechanical stress. Four sets of four samples, consisting of silicone, polyurethane, and two composite architectures, were tested at two different environmental conditions. The samples were initially baked at 125°C for 24 hours to remove moisture. Then, the samples were tested at 85°C-85 % RH, using the JEDEC standard, and later, the samples were tested at 50°C-60 % RH. The samples remained in the test environment until they reached an equilibrium with the surroundings. Based on the results, itwas evident that polyurethane outperformed all other samples, but the composites were better than silicone in both testing conditions without placing undue stress on the devices. Hence, the barrier layer significantly improves the moisture ingression performance of the silicone encapsulation.

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