NASA Engineering Bulletin: Chip Resistor Body Cracking Identified in Flight Hardware

SYSTEM ADVISORY: HARDWARE INTEGRITY

NASA Engineering and Safety Center (NESC) has issued Technical Bulletin 26-10, addressing a recurring failure vector in Printed Circuit Board Assemblies (PCBAs): the cracking of chip resistor bodies. According to NASA Breaking News, this technical alert highlights structural vulnerabilities in surface-mount technology (SMT) components frequently utilized across mission-critical avionics.

//Failure Mechanism

The report identifies mechanical and thermal stresses as the primary catalysts for resistor degradation. Specifically, the mismatch in the Coefficient of Thermal Expansion (CTE) between the ceramic resistor body and the PCB substrate leads to structural fatigue. During thermal cycling or mechanical board flexing—common during launch and orbital transitions—the solder joints transmit stress directly to the component body rather than absorbing it. This results in micro-cracks that can lead to open circuits or intermittent signal failure.

//Mitigation Protocols

To preserve mission longevity, the NESC suggests several rigorous quality control measures:
- Component Selection: Preferring resistors with flexible terminations or "soft-term" technology to buffer mechanical strain.
- Layout Optimization: Minimizing board flex near large thermal masses and optimizing solder fillet volume to prevent excessive rigidity.
- Inspection Standards: Enhanced automated optical inspection (AOI) and X-ray analysis to detect hairline fractures before integration.

This bulletin serves as a critical directive for systems engineers to re-evaluate SMT mounting processes to ensure reliability in high-vibration environments. Neglecting these mechanical stressors poses a direct risk to secondary payload integrity and primary bus operations.