Material Separation
Printed circuit board defects can arise when trapped moisture or volatile compounds vaporize during high-temperature assembly processes. The occurrence of outgassing delamination causes internal layers of the substrate to separate, creating voids or blistering. This physical failure disrupts the electrical and mechanical integrity of the multilayer board.
Visual inspection or acoustic microscopy can detect these internal separations after the board exits the reflow oven.
Thermal Expansion
Moisture absorbed by the epoxy resin or fiberglass core expands rapidly when the temperature of the board exceeds the boiling point of water. If the rate of vaporization exceeds the diffusion rate through the polymer matrix, high internal pressure builds. This localized pressure overcomes the adhesion between the prepreg and copper foil layers.
High-density boards with large ground planes are especially susceptible because copper sheets block the escape of steam.
Prevention Method
Baking boards in specialized ovens before the assembly process removes the moisture that drives this defect. This preparation step involves heating the boards at a temperature below their glass transition point for several hours to allow trapped gases to escape. SMT facilities enforce strict post-bake storage limits to ensure that boards do not re-absorb moisture from the ambient factory air before reflow soldering.
By controlling the environmental exposure of the boards, manufacturers prevent outgassing delamination and ensure long-term reliability in harsh operating conditions. In-line humidity sensors monitor storage cabinets to confirm that the storage conditions never rise above five percent relative humidity.
