RELIABILITY OF SPACE FLIGHT CRYSTAL CONTROLLED OSCILLATOR USING LEAD-FREE SURFACE MOUNT TECHNOLOGY

摘要

Space satellites and probes both use quartz crystal oscillators in their respective designs for operation. Such devices have been launched beyond the Earth’s atmosphere to orbit the earth or travel into deep space. Environmental conditions in space are considered severe in comparison to most terrestrial applications. High vacuum, intense solar radiation and extreme temperatures all impact the reliability of a given space system. Companies throughout the electronics industry are now in compliance with Restriction of Hazardous Substances (RoHS) regulations written by the European Commission (EC). Compliance to this legislation requires that products be free of any applicable banned substances. The most prevalent of these banned substances is lead (Pb), which is found in solder. Due to the high reliability requirements of military and aerospace products, the use of Pb-free solder is under much skepticism and the use of such solder is discouraged or banned completely. As new technologies evolve, a greater dependency on commercial off the shelf (COTS) electronic parts and assemblies is becoming more prevalent. The aerospace industry will have a very small share of the overall market and thus have little influence on Pb-free material avoidance. The intent of this research is to investigate possible usage of Pb-free solder and associated Pb-free materials for space flight applications. Serious reliability risks have been associated with the use of pure-tin (Sn) and thus a tin, silver, and copper (96.5Sn/3.0Ag/0.5Cu) alloy was examined for space flight feasibility. Quartz crystal controlled clock oscillators were constructed using only Pb-free materials and subjected to harsh environmental testing. The test plan was designed to address the many stresses of launch, flight, altitude, radiation, and the risk of tin-whisker growth resulting from the use of tin in solders. Under the conditions of this analysis, Pb-free clock oscillator technology tested herein showed no change in performance or degradation and proved to be reliable for some of the harsh environments encountered in space flight applications.