Impact of thermal cycles during the packaging assembly process on RF-MEMS switch performance

The RF-MEMS (microelectromechanical systems) switch shows a potential market growth for high frequency wireless handset applications and as a replacement for costly relays in the instrumentation industry. This switch is attractive because of its smaller size, lower insertion loss, higher isolation, higher reliability and lower power requirements. According to many product research surveys, this switch can potentially replace 4-6 conventional switches in current handsets. The projected revenues could be in the $2-3 billion range with an optimum growth for 3G wireless systems. Prototype switches and integrated packaged systems have already been introduced into the market place. The RF-MEMS switch is a sub-millimeter sized mechanical structure that actuates with applied voltage. One of the most common mechanical designs is an anchored cantilever consisting of metal contacts that open or close the RF circuit by electrostatic voltage actuation. The cantilever is a bi-layer structure with different CTE materials and layer thicknesses in several micrometers. The thermal cycles in the assembly and post-assembly processes greatly influence the material properties and induce thermo-mechanical stresses that can deform the cantilever structure. The effect of the packaging assembly processes on the mechanical design, and hence, the electrical performance of the switch has been investigated. This study revealed that the thermo-mechanical stresses, caused by the assembly processes, deformed the mechanical structure. The actuation voltage of switches in wafer form was typically 20-40 V that increased to 60-90 V after packaging. This was attributed to structural deformations. This paper reviews the various switch designs and the selection of a design that has minimum impact in the package assembly process.