# Mitigating Alumina Substrate Cracking in NASA Printed Circuit Board Assemblies Addressing flexure-induced failures in large-footprint ceramic chip resistors during environmental testing cycles. - **Source:** [NASA](https://www.nasa.gov) - **Published:** 2026-11-03 - **Topic:** [Software & Engineering](https://brifing.si/c/engineering) - **Original article:** - **On Brifing:** https://brifing.si/s/295fc320-584b-43f9-ac1d-10a6c05eed9d ## Rare Failure Identification NASA identified two instances of thick-film chip resistor cracking during thermal cycling following vibration testing. Despite the widespread use of these components, such alumina substrate failures remain rare. The fractures occurred across the short axis, indicating that bending forces, rather than inherent material defects, caused the structural integrity to fail. ## Ruling Out Manufacturing Defects Initial investigations focused on potential lot-wide defects, as both failed resistors originated from the same production batch. However, testing against MIL-PRF-55342 specifications and independent scanning electron microscopy confirmed no pre-existing flaws. The analysis successfully ruled out cyclic fatigue, pointing instead to mechanical stress induced by the board assembly environment. ## Mechanical Stress Drivers The failure analysis highlighted that large 2512 case size resistors are particularly vulnerable when placed near board edges. The orientation of the long axis parallel to the edge increased susceptibility to flexure. Furthermore, excessive solder fillets on top terminations created rigid joints that transferred board-level bending stresses directly into the ceramic. ## Board Mounting and Torque Hard mounting printed circuit boards to rigid frames can store and amplify bow or twist stresses. Suboptimal fastener torquing patterns further concentrate these mechanical loads at specific resistor locations. These installation factors, combined with board flexure, create a high-risk environment for ceramic components that are not properly isolated from structural deformation. ## Strategic Component Orientation To mitigate future risks, engineers must avoid placing large ceramic components with their long axis parallel to board edges. This orientation is highly susceptible to global and local flexure damage. Proper component placement is a critical design step to ensure that mechanical stresses do not compromise the integrity of the brittle substrate. ## Advanced Analytical Requirements Designers should perform finite element analysis to demonstrate adequate stress and displacement margins for large components located near board edges. This analytical approach quantifies the impact of board bow and twist, ensuring that the design can withstand environmental testing without transferring excessive tensile loads to the ceramic body of the resistors. ## Solder Joint Control Controlling solder fillet height is essential to prevent rigid joint formation. Solder must be kept off the top surface of terminations to avoid creating a stiff connection that forces board flexure into the component. Engineers should consult manufacturer guidelines and perform rigorous inspections to verify that solder volumes remain within specified limits. ## Validation Through Thermal Shock Implementing functional thermal shock testing, specifically one to three cycles with a hot-dwell functional test, is recommended prior to vibration testing. This process documents the integrity of the as-built assembly. Such proactive validation steps help identify potential flexure-induced cracking risks before the hardware undergoes more rigorous environmental acceptance testing protocols. ## Sources covering this story - https://www.nasa.gov/centers-and-facilities/nesc/tb-26-10-printed-circuit-board-assembly-chip-resistor-body-cracking/ — --- _Summary written by Brifing from the original reporting. Copyright in the original article belongs to its publisher; read the full piece at the link above._