The Use of Potting Materials for Electronic-Packaging Survivability in Smart Munitions

Abstract

Potted electronics are becoming more common in precision-guided artillery due to demands for increased structural-robustness. In field artillery applications, the potted electronics are inactive for most of their lifetime. Projectiles may be stored in a bunker without environmental (temperature and humidity) controls for up to 20 years. In contrast, the electronics for most commercial applications tend to be active for most of their lifetime and the operating environment is more predictable. This difference makes the thermal management task for the artillery application challenging. The ability to accurately analyze these designs requires the use of fully coupled thermal-stress transient-analysis with accurate material properties over the full temperature range. To highlight the thermal-stress transient effects, the potted configuration of a typical electronics assembly is analyzed. The thermal analysis indicates that significant stresses can develop in critical locations as a result of temperature cycles. The structural dynamic responses of unpotted and potted assemblies, subjected to gun-launch environments, are also compared. The results indicate that for the potted design, the dynamic response of the processor board is attenuated by the potting material.

Thermomechanical Impact of Polyurethane Potting on Gun Launched Electronics

“…One drawback of this study is that the viscoelastic model employed is limited to a frequency range that falls below the vibratory frequencies the potted assembly is subjected to during gun launch (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). Further studies into the highfrequency material behavior are underway to determine the impact on the material behavior and structural stability of the electronic assembly.…”

“…e speci�c heat varies by about 50%. Chao et al have shown that the potting would be expected to have signi�cant thermal mismatch issues based on the coefficients of thermal expansion for the potting and the ceramic chips [16]. For thermal expansion issues, ringed potting should be considered over fully potted models.…”

“…Material testing reveals that the mechanical properties of the potting material employed for this analysis change signi�cantly with temperature. Because of this and as supported by [3,6,7,[16][17][18]] the potting material potentially imposes additional risks to the mechanical stability of the electronics assembly. e material evaluated in this study is not an ideal potting solution because of its thermomechanical issues.…”

“…It is important that engineers understand the severity of gun launch and the harsh thermal loads to which the potting material and the potted assemblies are subjected to [3]. To improve tolerance to high-shock and vibratory loads, viscoelastic materials are traditionally employed as potting compounds.…”

“…Most studies on the use of FEA to model-potted electronics focus on the thermomechanical impact of potting materials on the integrated circuits and electronic components [3,5,6]. It has been well documented that under high thermal loads, the potting material imparts large stresses on the electronic components.…”