Damp heat testing verifies stability in hot-humid environments, focusing on insulation performance, moisture absorption, coating adhesion and corrosion tendency. The two test types cycle differently and therefore expose different failure modes.
How the two tests differ
Steady-state damp heat: temperature and humidity are held constant (for example 40 C / 93% RH), primarily examining performance loss and insulation resistance decay from long-term moisture absorption.
Cyclic damp heat: temperature and humidity vary in cycles (for example 23 C to 55 C), alternating condensation and drying. This is closer to real day-night temperature swings and dew formation, and exposes seal failure and condensation ingress.
What is examined
Insulation resistance: moisture absorption lowers the resistance of insulating materials, which can lead to leakage and breakdown.
Coating and plating adhesion: repeated damp heat blisters and flakes coatings that are not well bonded.
Appearance: rust spots, discolouration, white bloom.
Function: moisture causes parameter drift or failure.
Mechanical properties: plastic parts change dimension and modulus after absorbing moisture.
Common failures and root causes
PCBA corrosion → incomplete conformal coating coverage, or a mismatch between the coating and component stress.
Rising connector contact resistance → high plating porosity or insufficient mating force, letting moisture into the interface.
Water ingress into the enclosure → a sealing design problem, with latches or gaskets failing.
Flex cable breakage → the FPC-to-connector crimp corrodes in damp conditions and contact resistance rises.
Fogging of optical parts → seal failure lets moisture inside, affecting display and light transmission.
Frequently asked questions
My product is not sealed — does it still need damp heat testing?
Yes. The protection strategy for open products is conformal coating rather than enclosure sealing. Conformal coating covers components and solder joints on the board, but connectors and uncoated interfaces remain weak points. The test must specify whether condensation is permitted on the product, to avoid a wrong verdict.
Can other tests be run after damp heat?
Yes, but the sequence matters. After damp heat the product has absorbed moisture, so going straight into vibration or shock can accelerate failure and produce an overly severe result. The usual practice is to recover the product under standard conditions after damp heat, then continue.
Service notes
Our laboratory holds both CMA and CNAS accreditation, covers about 10,000 m2 and runs more than 500 sets of equipment. All testing is carried out in our own laboratories — nothing is subcontracted. Plant visits and on-site witnessed testing are welcome.
Scheduling follows the actual project pipeline. You can state your preferred lead time when you submit samples; we will confirm a feasible plan against current capacity and keep you updated at each milestone. Once the report is issued we send the electronic copy; corrective-action advice can be arranged separately.
