Key takeaways
Cyclic damp heat (GB/T 2423.4) produces condensation during the ramp-up phase and is far harsher on PCBA and connectors than steady-state damp heat (GB/T 2423.3): the condensation film lowers insulation resistance and drives electrochemical migration (CAF) and mould corrosion. Automotive electronics normally use the climatic clauses of the GB/T 28046 series, and whether the sample is powered or biased during the test makes a large difference to the conclusion.
On a report, a damp heat test is a single line — "insulation resistance meets the requirement after the test". What it actually hunts is the hardest class of vehicle fault to reproduce: the occasional false actuation in the rainy season, the unit that fails on power-up after storage, the intermittent communication dropout. The common driver behind all of them is condensation.
1. Why cyclic damp heat is stricter
Steady-state damp heat (GB/T 2423.3) holds temperature and humidity constant, examining moisture absorption and stable corrosion. Cyclic damp heat (GB/T 2423.4) drives the sample surface below the chamber dew point during the ramp-up phase, so water droplets condense on the surface — and the water film is the active medium for insulation degradation and electrochemical migration. The repeated "condense, then dry" action within a cycle is closer to real storage and service than constant humidity.
2. Three typical failures
First, falling insulation resistance: the water film bridges creepage paths, and the problem shows between high-voltage and low-voltage circuits first. Second, electrochemical migration (CAF / dendrite): under bias, metal ions migrate along glass fibres and interfaces and eventually form dendritic shorts — common on PCBA. Third, corrosion: platings and solder joints fail under the combined action of damp heat and salt, with the connector contact area usually the first to show it.
3. How to plan it for automotive parts
The GB/T 28046 series sets conditions and severities for climatic tests from the OEM's point of view, and they are often combined with temperature cycling and salt mist into a "climate pack". The sample state has to be fixed in advance: powered or unpowered, with or without bias, loaded or unloaded — that alone determines which class of problem the test can expose. For seals and connectors, run it at the pre-compliance stage; that is when most problems surface.
4. What design can do about it
Conformal coating, hydrophobic layout, creepage distance and aperture design, and seal selection are the four common engineering counters to damp heat risk. The value of pre-compliance testing is to verify those counters early, not to wait for a failed unit to arrive at the laboratory in search of a root cause.
Turnaround time is arranged according to the actual project. You are welcome to state your target date when submitting samples; we will check it against the current schedule, confirm a feasible plan with you, and update you at each milestone.
