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Reliability characterization of UV-curable adhesives used in optical devices

UV (ultra-violet)-curable adhesives were identified as the underlying cause for failure of devices subjected to accelerated aging conditions. These adhesives must be resistant to degradation and dimensional/mechanical instabilities such as creep. We examined two UV-curable adhesives and found that thermal post-curing caused some shrinkage and degradation. However, post-curing also raised the adhesive glass transition temperature, thereby reducing the reliability risk associated with mechanical instability. We investigated the dimensional/mechanical stability of UV adhesives by measuring thermal expansion/contraction and creep compliance. We found that the adhesive thermal expansion and creep compliance are large enough to pose device reliability risk. Raising the glass transition temperature of UV-curable adhesives by thermal post-cure can improve optical device reliability by lowering the creep compliance.