Evaluation of flip-chip bonding electrical connectivity for ultra-large array infrared detector

Abstract

Flip-chip bonding is a key technology for infrared focal plane array (IRFPA) detectors. Due to the high cost of device preparation, the ultra-large array infrared detector cannot be directly used for the flip-chip bonding experiment, and the connectivity rate cannot be measured. To evaluate the flip-chip bonding process, a test device which has the same interconnecting structure as current IRFPA detectors is proposed. Indium bumps are electrically extracted to test electrodes. Electrical measurements were performed to characterize the connection and adhesion of the indium bumps and to calculate the connectivity rate. The electrical connectivity characteristics of the test devices correspond to the observation results of the indium bump extrusion, effectively detecting the interconnecting anomalies such as disconnection, adhesion, overall misalignment, etc., and verifying the feasibility of the test method. The test device has similar multi-layer components and thermal properties as HgCdTe infrared detector for process evaluation and post-processing experiment. The connectivity rate of the test device is up to 100%, and remains above 99% after thermal recycle experiment. The contact resistance of the interconnecting structure is calculated to be about 31.84 Ω based on the test results.