Thermal Aging
The gradual decline of the structural and electrical properties of a circuit board occurs when the assembly is subjected to high temperatures or repeated thermal cycling. This thermo-mechanical degradation is driven by the mismatch in the coefficient of thermal expansion between the copper conductors and the surrounding organic resin matrix. As the board undergoes heating and cooling, this expansion mismatch generates high stresses that can fracture solder joints, split copper vias and cause delamination within the laminate layers.
It is a major cause of failure in electronics operating in harsh environments like automotive under-hood systems or aerospace applications.
Material Impact
Prolonged exposure to high temperatures can degrade the epoxy resin matrix, which causes the polymer chains to break down and leads to a reduction in the glass transition temperature of the material. This resin breakdown decreases the mechanical strength of the laminate, which makes it more susceptible to cracking and peeling under mechanical vibration or thermal stress. Furthermore, the degradation of the resin-glass interface allows moisture to penetrate the board, which can lead to conductive anodic filament growth and electrical short circuits.
Measuring the rate of this degradation involves using techniques like dynamic mechanical analysis and thermo-gravimetric analysis to monitor the physical properties of the laminate under controlled heating conditions.
Testing Reliability
Engineers use environmental stress screening to simulate this degradation process and evaluate the long-term reliability of board assemblies before they are deployed in the field. This testing process exposes the assemblies to rapid temperature changes and vibration, which accelerates the occurrence of latent defects such as micro-cracks or weak solder joints. By identifying these failure modes early, design teams can modify the board layout or select laminates with better thermal stability to ensure the assembly survive its intended operating life.
