Designing Adhesives for Cooled Infrared Detectors

摘要

Many microelectronic devices require bonding dissimilar materials to operate under extreme operating conditions. Furthermore, certain applications, such as cooled infrared (IR) detection, require large temperature cycles between ambient and cryogenic temperatures under ultra-high vacuum (UHV) conditions. The complex expansion and contraction of the various materials within the detector package structure during temperature cycles introduces significant internal stresses that may ultimately result in the failure of the sensor and/or the package. Added to this complexity is the process sensitivity of the fabricated device to elevated temperatures and adhesive application. With orders-of-magnitude difference between gap sizes, adhesive properties such as viscosity, cure kinetics, and process temperatures become paramount for successful sensor integration. In addition, stringent outgassing requirements associated with ultra-high vacuum application further complicates the selection process for cryogenic adhesives. Under these constraints, a myriad of commercial epoxy adhesives were evaluated. We devised a characterization methodology using a combination of various analytical techniques which elucidated the complex flow properties, and cure kinetics while highlighting critical characteristics necessary for a successful material for this application with a focus on rapid cycles of learning. As the application space matures, we see the need for a next generation of adhesives for demanding and ubiquitous infrared sensing applications.