Non-Perpendicular High-G Shock on Potted Fine Pitch Electronics Under Sustained High Temperature Aging

Fine pitch electronic components in the defense and aerospace applications, experience high thermo-mechanical loads. To study and understand these scenarios, the printed circuit boards with components are usually tested at 0-degree drop angle. But the angle of shock varies a lot in real life scenarios. Change in drop angle, could change the mode of shock propagation throughout the board, which further affects the solder-joint reliability of the components on the board. Studying board level drop tests with change in drop angle would be more relatable to the real-life drop scenarios. Potting is one of the most cost-effective restraint mechanisms, it protects the components from shock, vibration, moisture and heat. Exposure to high temperature is very common in these applications. But properties of the potting compounds changes with long term exposure to high temperature. Potted test vehicles are exposed to a temperature of 100C for 30 and 60days. Long term storage at high temperature, is intended to help in understanding the change in potting compound properties and their impact on reliability. A circular board with surface mount components is tested at g-levels of 10,000g and 25,000g and three different angles of 0-degree, 30-degree, 60-degree. Understanding effect on shock-propagation and component reliability with respect to drop angle variation and long-term thermal aging, is the focus on this paper. To make simulation predictions of the drop angle variation, an explicit finite model of the drop assembly has been created to predict and compare with the experimental results.