Improved Sensitivity for Hot Spot Detection using Liquid Crystals

Liquid crystals have been used for various purposes in failure analysis for several years. Hiatt, using cholesteric liquid crystals, demonstrated that hot spots could be detected and readily photographed under polarized light [1]. West omitted the polarized light for simplicity, but applied a 5-20 Hz square wave pulse to the failing device to make initial detection of the defect easier [2]. Fleuren achieved great sensitivity by adding temperature control, but the steps required to routinely reproduce his success were not clear [3]. This paper introduces a new heating method and detailed observations for use of a particular nematic liquid crystal. The resulting technique is both sensitive and convenient.