Meaning
Long term structural decline of materials occurs during prolonged exposure to elevated temperatures. Studies on thermal aging degradation help manufacturers estimate the operational lifespan of electronic assemblies in hot environments. This process involves the growth of brittle intermetallic layers and the coarsening of the solder grain structure over months or years.
Microstructural Change
Diffusion of atoms at the interface between the solder and the pad continues even after the initial reflow is complete. During thermal aging degradation, the copper or nickel from the pad moves into the solder to form thicker layers of intermetallic compounds. These layers are much harder and more brittle than the surrounding metal, which creates a point of weakness.
The solder itself also changes, as the small grains join together to form larger structures that are less resistant to fatigue.
Mechanical Failure
Weakening of the bond leads to a higher probability of joint separation under the stress of thermal cycling. As thermal aging degradation progresses, the ability of the joint to absorb mechanical energy decreases markedly. Components that once passed drop tests may fail easily after they have been in service for a long period.
Lifecycle Validation
Reliability testing in Chinese labs often includes accelerated aging in ovens to simulate years of use in just a few weeks. These tests provide the data needed to prove that a product meets the warranty requirements set by the customer. Reports documenting the effects of thermal aging degradation are essential for the certification of products used in critical infrastructure.
Maintaining these records allows the manufacturer to defend their material choices and process settings against claims of premature product failure.
