Accelerated tests to determine the reliability of the cable-encapsulant interface

Encapsulants are mainly used with the cable in various outdoor products, to act as barriers against the operating environment. In some applications, the encapsulants can also be used to provide strain relief for the cable. The reliability of the cable-encapsulant interface is critical for product functionality as well as its long-term reliability. The reliability of this interface depends on the cable and encapsulant chemistry, their interaction, process conditions and other properties like the glass transition temperature (T_g), hardness, coefficient of thermal expansion (CTE) etc. This reliability is usually determined as part of the final product tests. This is very time-consuming and can lead to appreciable loss of design time, especially when failures are discovered at the end. This study has developed quick screening tests which can optimize the process conditions and reasonably determine the reliability of the cable-encapsulant interface, without testing the entire product. The failure at this interface is mainly due to cracking of the cable. The failure mechanism is influenced by the exothermic reaction, cure temperature, hardness and adhesive properties of the encapsulant. The results of these tests have also been correlated to conventional accelerated product tests like ALT, 85/85 to determine their product applicability. Thereby, these tests could be used as a screening tool for the various cable-potting combinations at the start of the design, thus reducing the design time and achieving the required reliability and optimum process conditions.