Military applications often push technologies to their limits. Applications such as electronic warfare (EW), radar, communications, and surveillance have made demands on RF/microwave technologies over the years. Levels of integration have increased with growing demands for greater packaging densities and reduced weight, and increased reliability over a wider range of operational parameters (such as wider temperature ranges, increased thermal rates of change, greater ranges of vibration and longer storage in field conditions at the point of deployment).
One of the challenges most unique to military and aerospace electronics is the high value of and length of service expected of these assemblies, often being 20-30 years. During the program life, the electronics are likely to be periodically repaired, refurbished and upgraded. Therefore, the degree of reworkability of the coating material needs to be thoroughly evaluated and the reliability of repair solutions thoroughly evaluated.
These electronic assemblies continue to become an increasingly sophisticated and important aspect of both the functionality and reliability of modern military and aerospace systems. The costs of failure, both in direct fiscal cost and especially the loss of highly trained personnel and civilian casualties are extremely high, and so it is extremely important that these systems function exactly as required, when required, for the entire duration of the program. Conformal coating is one of the main mitigation solutions, preventing degradation to the assembly from the external environment.
Although not subjected to Pb-Free production, the reality is that many commercial components are supplied with a pure tin finish (Lead-free compliant) to preserve solderability. There has recently been much concern about the potential for tin whisker growth, as a potential failure mechanism, due to the long service lifetimes and extreme operating environments encountered in military/aerospace electronics (http://nepp.nasa.gov/whisker/background/). The use of the correct conformal coating has been shown to be an effective mitigation strategy against the formation of these whiskers