Meaning
An environmental stress test that exposes electronic assemblies to varying levels of temperature and moisture to identify latent design flaws. This dynamic thermal humidity cycling reveals weaknesses such as delamination, corrosion and solder joint fatigue before a product enters mass production. The test is conducted in a specialized chamber according to standards established by the JEDEC Solid State Technology Association.
Stress Mechanism
Rapid transitions between high and low temperatures cause the different materials in the assembly to expand and contract at different rates. This differential expansion creates mechanical tension at the interfaces between the chips and the board. Adding moisture during the hot phase accelerates the penetration of water vapor into the plastic packaging, which can lead to internal pressure and cracking.
Failure Identification
Inspections are performed after several hundred cycles to look for microscopic cracks or electrical opens. Dye and pry testing or acoustic microscopy are used to see defects that are hidden from the naked eye. This rigorous process reveals whether the combination of materials and manufacturing steps is durable enough for the target environment.
Reliability is confirmed when the electrical resistance of the samples remains within the specified tolerance after the full cycle count.
Reliability Standard
Automotive and aerospace components require more cycles and wider temperature ranges than consumer electronics due to their harsher operating requirements.
