Power Allocation Towards Hermetic Solder Joint Health of High Powered MEMS Chip for Harsh Environment Applications

Solders have been utilized extensively in the MEMS packaging industry to create vacuum or hermetic seals in a variety of applications. MEMS technology is finding applications in wide range of products like pressure sensors, actuators, flow control devices etc. For many harsh low temperature environment applications, like commercial refrigeration systems, MEMS based pressure sensors and flow actuators are directly mounted on to metal substrates using solders to create hermetic sealing. Solders attaching silicon devices directly to metal substrates may be subjected to very high thermal stresses due to significant difference in thermal expansion coefficients during chip operation or environment temperatures. In this paper, case study of a high powered MEMS chip (referred in the paper as die) operating in a commercial refrigeration system is presented. Accelerated test method for qualifying solder joint for high pressure applications is briefly discussed. Lab experiments showing typical refrigeration cycle thermal load on solder joint are presented. Based on the study, concepts of die power toggling and power allocation towards enhancing hermetic solder joint reliability are discussed. Detailed numerical case studies are presented to quantify the improvement in solder joint reliability due to the proposed concept.