Structural Separation
Separation of bonded layers within a printed circuit board indicates a loss of adhesion between dielectric substrates or copper cladding. Delamination occurs when thermal expansion forces exceed the internal bond strength of the materials, creating air gaps or pockets inside the laminated composite. Moisture absorption within the resin matrix accelerates this physical degradation under soldering temperatures.
High localized pressure during the lamination cycle prevents full resin flow and contributes to these internal voids.
Thermal Sensitivity
Repeated exposure to reflow profiles drives volatiles out of the substrate and causes internal pressure to rise. Materials that fail to remain stable at high temperatures experience localized bubbling where the resin pulls away from the fiberglass reinforcement. This detachment reduces the reliability of plated through holes because the unsupported copper barrel fractures under mechanical stress.
Microsectioning reveals the presence of these gaps by exposing the cross-sectional view of the affected layers after thermal shock cycles.
Acceptance Criteria
Evaluation of incoming boards relies on visual inspection of coupons after moisture conditioning and simulated assembly exposure. Standards set strict limits on the size and frequency of internal voids permitted within a panel before the product reaches the assembly floor. Any evidence of separation extending into a plated hole requires the rejection of the entire lot due to the high probability of intermittent electrical failure.
Boards showing these structural defects possess insufficient integrity to survive the mechanical demands of end-use applications.
