Qualification Protocol
Reliability assessment protocols subject electronic assemblies to conditions far exceeding normal operating parameters to precipitate latent defects in a compressed timeframe. Using accelerated stress testing allows a manufacturer to identify failure modes such as solder joint fatigue or dielectric breakdown without waiting for years of field data. This methodology relies on the Arrhenius equation or the Coffin-Manson model to relate high-temperature or high-strain cycles to expected service life.
Failure Mechanism
Mechanical and thermal loads drive the progression of crack growth in heterogeneous materials. During accelerated stress testing, rapid temperature transitions induce differential expansion between the fiberglass substrate and copper traces. These stresses force weak interfaces to delaminate or fracture early in the test sequence.
Brittle intermetallic layers often fail under these conditions before ductile bulk solder yields.
Acceptance Criteria
Verification of product robustness depends on the statistical distribution of failures observed during the trial. Standard procedures for accelerated stress testing require a sample size large enough to establish a confidence interval for the mean time to failure. A batch passes when no functional degradation occurs within the calculated equivalent life cycles.
Post-test cross-sectioning confirms that internal micro-cracking remains within specified limits. Detailed inspection of the copper barrel integrity ensures that no circumferential cracks have separated the circuit path. This final check validates the assembly for long-term deployment.
