Thin PCBs (typically with a thickness below 0.8mm) are prone to bending failure during thermal cycling tests due to their low structural rigidity and inconsistent thermal expansion coefficients of layered materials, and this failure can be effectively prevented through material optimization, structural design improvement, and process parameter control. Thermal cycling environments with alternating high and low temperatures cause periodic expansion and contraction of PCB substrates, copper foils, and solder masks. Thin boards lack sufficient mechanical strength to resist thermal stress, resulting in irreversible bending, warpage, or even layer cracking, which seriously affects assembly yield and product reliability. Therefore, targeted prevention measures must be implemented in the design and manufacturing stages.

Material selection optimization is the foundation of preventing thermal cycling bending failure. Prioritizing high-rigidity, low-thermal-expansion substrate materials such as modified epoxy resin and high-Tg substrates can reduce the thermal expansion coefficient difference between the substrate and copper foil, minimizing thermal stress generated during temperature changes. Meanwhile, choosing high-elongation copper foil with good ductility can enhance the PCB’s ability to withstand cyclic stress and avoid copper foil cracking caused by repeated bending. For ultra-thin PCBs used in wearable devices and flexible modules, appropriately increasing the core substrate thickness in local areas can balance overall rigidity without affecting lightweight requirements.

Structural design and manufacturing process optimization further improve the thermal cycling resistance of thin PCBs. In the design phase, uniform layout of copper areas is essential to avoid uneven copper distribution that causes inconsistent thermal expansion and contraction. Empty large copper-free areas and excessive concentrated copper layouts should be eliminated, and symmetric stack-up structure must be strictly followed to ensure balanced stress on the upper and lower layers of the PCB. In the production process, controlling lamination temperature, pressure, and cooling rate can reduce residual stress inside the board. In addition, adopting staged thermal cycling pre-treatment before formal testing can release internal stress in advance, effectively avoiding sudden bending failure during subsequent long-term thermal cycling tests.