Definition

Thermal cycling describes repeated temperature fluctuations experienced by a PCB during operation or environmental exposure. Each heating and cooling cycle causes materials to expand and contract at different rates according to their CTE. Over time, this mechanical stress leads to solder joint fatigue, via barrel cracking, or delamination at interfaces between dissimilar materials. Design mitigations include: selecting materials with matched CTE, using filled vias for high-aspect-ratio holes, adding teardrops at pad-trace junctions to reduce stress concentration, and specifying high-Tg laminates. Thermal cycling tests (e.g., -40°C to +125°C for 1000 cycles) simulate years of field use during qualification.