"85/85" is the environmental test that appears most often on quotation requests, and many teams price it as though it were a fixed package. The conclusion first: 85/85 is only a temperature-humidity point — 85 °C at 85 %RH. What actually sets the severity is three other things: the duration, whether bias is applied, and what is checked afterwards. None of the three has a universal answer; the mounting position and the OEM technical agreement decide.
1. What 85/85 actually stresses
In a constant 85 °C / 85 %RH environment, moisture keeps diffusing into packages, interfaces and gaps. It forces out three classes of failure:
- Insulation degradation: a water film builds a creepage path across the PCB surface and interfaces, leakage current rises, and the problem appears first between high-voltage and low-voltage circuits;
- Electrochemical migration: under bias, metal ions migrate along glass fibres and interfaces, dendrites grow and eventually short;
- Corrosion: platings, solder joints and connector contact areas oxidise and corrode under sustained humidity.
How this divides work with constant and cyclic damp heat we covered separately (cyclic versus constant damp heat: stopping the silent killer in PCBA and connectors). One line to add here: temperature cycling stresses the mechanical fatigue of expansion and contraction and looks for cracking; 85/85 stresses the slow electrical attack of moisture and looks for leakage. Different mechanisms, and neither replaces the other.
2. Common duration bands
| Duration | Typical use | Note |
|---|---|---|
| 168 h | Fast exploratory work on components and modules, comparing material options | Lowest cost, limited evidential weight |
| 504 h | Mid-level check under some corporate internal specifications | The compromise between exploratory and validation |
| 1000 h | The mainstream band for automotive volume-part life validation | Automotive projects usually start here |
| 2000 h | Tightened requirement from some carmakers on 800 V high-voltage platforms | High-voltage parts, long-life applications |
The band figures come from public market information and common technical agreement language. The same words "85/85" carry completely different weight when a 168-hour report and a 1000-hour report land on an OEM reviewer's desk — which is exactly why it becomes a price lever: drop the band, the fee drops immediately, and the report is still called an "85/85 report".
3. How automotive 85/85 differs from consumer 85/85
The same 85 °C / 85 %RH, and the difference concentrates in three points.
1. Bias or no bias. Component-level steady-state damp heat life tests (such as JEDEC JESD22-A101) normally run powered — electrochemical migration is only activated under bias. An unpowered 85/85 is closer to a storage test: it catches moisture absorption and corrosion but not dendrite shorts. When an OEM borrows this condition to assess a component, whether it is powered and with what load has to be stated in the test outline.
2. Different acceptance items. Consumer work looks at appearance and basic function. Automotive parts are usually also checked for insulation resistance, dielectric strength, contact resistance drift and shift in key parameters — "still powers up afterwards" and "still compliant afterwards" are two different things.
3. Different tests on either side. In an automotive flow, 85/85 rarely stands alone; it is usually combined with temperature cycling and IP protection testing (such as IP69K high-pressure jet) into a climatic stress package. GB/T 28046.4 and ISO 16750-4 contain separate damp heat clauses that complement steady-state 85/85 — problems that only surface under combined stress cannot be seen by running 85/85 alone.
4. Setting the conditions: three things to settle before submitting samples
Duration follows the mounting position and the target customer: cabin parts and high-voltage parts are not on the same scale, and whatever the OEM agreement says is what applies — do not drop the band on your own initiative.
Sample state: powered or unpowered, no load or loaded, monitored in-line during the test or not — this decides which class of failure the test can expose. When TMC LAB takes on 85/85 work, the sample state and acceptance items go into the test outline and are confirmed before the chamber starts, so it does not turn out afterwards that a key parameter was never monitored.
Acceptance basis: what is measured after the test and what counts as a pass, written into the outline. When the report goes to an OEM for review, complete acceptance items are the minimum requirement.
5. A few honest words
Using 85/85 for exploratory work during development is far cheaper than dealing with a batch problem after volume production. If the band is uncertain, set it from the target customer's technical agreement; if the agreement is silent, start from the industry convention for that mounting position and write the reasoning into the test request form — that form becomes the basis for the report being accepted later.
To confirm the band against a standard condition table, start with the clause breakdown on the GB/T 28046 environmental testing and ISO 16750 pages, then check it against the target customer's technical agreement.
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.
