Board Support and Stacking: Preventing Warpage in Multi-Board Assemblies
A two-board assembly is a composite structure: FR-4 expands at ~14 ppm/°C in-plane, aluminum shields at ~23, connectors somewhere between. Fastening hardware manages that mismatch.
Support strategy basics
Rigid threaded standoffs at board corners define the stack; they should carry compressive load, not bending. Mid-board supports prevent membrane vibration but should be slightly compliant — over-constraining a large PCB creates solder-joint fatigue during thermal cycles, the classic cracked-BGA failure.
Three practical rules
- Anchor rigidly at two points, support compliantly everywhere else — the classic one-fixed, rest-floating pattern.
- Keep screw torque low on plastic standoffs; nylon creeps and preload decays within days.
- Give copper pours clearance under metal standoffs: a shorted ground plane is the most common first-article surprise.
Test with thermal cycling
Validate stacks across −40 to +85 °C minimum; warpage and support stress reveal themselves in cycles, not at room temperature. Topprecision supplies matched standoff families in metal and engineering plastic, with thermal-cycle data for common board-stack configurations.
