Extending Reliability in Encapsulated Fine Wire Arrays

Consumer and automotive electronics increasingly contain high functionality components with arrays of fine pitch thin wire interconnections. Protecting these wire arrays from environmental conditions can be a challenge for both design and materials. One method involves encapsulating the wire loops to maintain electrical isolation from debris and wire movement induced by vibration and thermal or mechanical shock. Encapsulants can range from hard and rigid epoxies to soft and flexible silicones. If the part experiences very large thermal swings, CTE mismatches between the encapsulating material and system components can over-stress wires and especially wirebonds to cause breakage. A study was undertaken to evaluate several encapsulants, showing a strong correlation between thermal shock induced wirebond breakage and encapsulant hardness, with the softest silicone gel providing far superior protection.