MEMS For Rolling-Element Bearings

摘要

Improvement of the operating characteristics of rolling-element bearings was sought through development and implementation of MEMS (Micro Electro-Mechanical System) based strain sensors. The strain sensors developed in this program employ a piezoresistive transducer to convert changes in applied strains to output voltages with an on-chip temperature detector compensating for thermal effects in the strain measurement. Bonding of MEMS strain sensors to application substrates was accomplished with induction heating using a wafer-level deposition process to pre-coat Au/Sn eutectic alloy on the MEMS chips and a process to pre-coat steel substrates with a Ni/Au layer. A flexible-circuit board and a back-fill process were also developed for connecting MEMS strain sensors to signal-conditioning electronics. A wafer- level gold bumping process was used to place gold bumps on the MEMS chip solder pads and a thermo-ultrasonic bonding flip-chip technique was developed to bond the MEMS strain sensors to the flexible-circuit board. Performance evaluation of MEMS strain sensors was accomplished with the development of several high- precision test systems. For quick installation of MEMS strain sensors on application structures, a low-cost bolt-on displacement sensor and associated electronics were developed. Their usefulness was demonstrated on a public bridge structure using Timken's StatusCheck 2.4 wireless data collection system.