Helical Wiring Type Stress Relaxation Structures for LSI Packages

Thermal stress, which is caused by the difference in thermal expansion coefficients of different materials, is a serious problem for large scale integrated (LSI) circuit packaging. The stress causes damage to LSI devices, especially those that have low-
k
materials in their LSI layer, and packaging substrates. We have developed a helical-micro-spring (HMS) to reduce damage due to thermal stress. The spring has a helical wiring structure that relieves any thermal stress. We have fabricated the HMS using a negative-type photopolymers or a positive-type photopolymer as dielectric layers. We have also simulated the spring's mechanical and electrical properties and compared the properties with other stress relaxation structure.