Two identical products, same test list, same severities — but different results simply because the order of execution is different. This is something that is often overlooked when planning environmental testing.
This article explains why test sequence is part of the test definition, ordering principles, and what needs to be agreed upon before starting.
1. Why sequence matters
Three mechanisms cause order to alter results:
- Cumulative:The former test produces small damage, the latter amplifies it into obvious damage. Vibration testing after the sample has been cracked by thermal cycling gives much worse results than vibration testing on the intact sample.
- Masking:The following test erases the traces of the previous test. Testing water after dust testing may wash away dust and remove evidence of intrusion.
- Material Variation:High temperatures can change the state of the material (stress relaxation, coating transformation), causing subsequent cold testing to no longer accurately evaluate the original material.
Consequence: if the required document clearly states the test sequence, the operator cannot change the order himself. If the documents do not clearly state, it is necessary to agree in writing before testing.
2. General ordering principles
- Don’t destroy first, destroy later.Mild or non-destructive tests should be reserved to utilize the same sample.
- Climate before mechanics.A common sequence is temperature/humidity first, vibration and shock second, as moisture and thermal cycling can weaken the joint before vibration accelerates damage.
- Avoid cross contamination.Corrosion, dust, and solvent tests contaminate the chamber and sample; If performed in advance, they may affect later tests.
- Test the function at a meaningful point.Check after each step or group of steps, depending on the assessment goal.
- The final test should be one where the trace is clearly observed.For example, checking for corrosion, cracking, and deformation requires the sample to have its surface intact.
3. A typical reference sequence
| Step | Test group | Reason for placing in this position |
|---|---|---|
| 1 | Initial check: appearance, function, parameters | Set a benchmark before testing |
| 2 | Dry heat/cold (Test B, Test A) | Non-destructive, shared samples, basic heat resistance test |
| 3 | Temperature change (Test N) | Apply thermal stress to the joint and material, preparing for the following steps |
| 4 | Stable humidity/heat cycle (Cab, Db) | Causes moisture and condensation — causes of insulation degradation |
| 5 | Vibration and shock (Fc/Fh, Ea) | After the joint has been subjected to thermal-humidity stress, vibration amplifies potential damage |
| 6 | Rough handling, falling (Ec) | Simulate the transportation and loading stages |
| 7 | Corrosion (Ka/Kb, Kc/Kd/Ke) | Place it last with the climate-mechanical group to observe corrosion traces on the sample that has been subjected to stress |
| 8 | Final inspection and evaluation | Compare with the initial milestone according to the agreed criteria |
This is a reference string, not a mandatory regulation. The actual sequence must come from the usage environment: if the product is shipped before installation, it may be necessary to bring the roughing group up first.
4. Ordering pairs that cause disagreement
| Pair | Commonly used order | Reason |
|---|---|---|
| Damp heat and salt mist | Hot humidity first, frost later | Salt mist leaves salt residue that affects moisture testing; Conversely, prewetting helps evaluate corrosion in conditions where a wet film has formed |
| Vibration and salt mist | Depends on the goal | If you want to evaluate corrosion at cracked joints, do a vibration test first; If you want to evaluate mechanical durability in a corrosive environment, put corrosion first |
| Welding heat and other environmental testing | Final soldering heat (with components) | The welding process changes the material state, which should not precede initial material evaluation tests |
| Dust and water | Dust first, water later — but it must be clearly stated | Water can wash away dust; If evidence of dust intrusion is required, this must be checked and recorded before water testing |
5. Where functional examinations belong in the sequence
- Before string:required, to have a benchmark for comparison. Without a baseline, deterioration cannot be concluded.
- After each step:suitable when it is necessary to determine which step causes damage — for design analysis.
- After group of steps:suitable for qualitative testing, lower cost but loss of causality.
- During the test:Some tests require continuous functional monitoring or parameter measurements at extreme temperatures; need to be clearly defined from the beginning.
6. When the sequence can be shortened
Can be shortened when the goal is rapid screening (e.g. batch inspection), when the product already has data from previous tests, or when the risk level is low and the customer agrees. Should not be shortened when:
- The results are used to declare conformity or certify according to standards that define their own sequences.
- Customers require the correct string according to their documents.
- The goal is to find the cause of the failure — at which point it is necessary to try to isolate each factor.
7. Common mistakes
- Change the order for convenient operationwithout recording — causing the results to no longer match the requirements.
- Use the same template for all stepswhen the documentation requires a separate sample for each test.
- Do not check appearance between steps,leading to loss of evidence of when the damage occurred.
- Do not clean the chamber between test groups.cause cross contamination.
- Ignore recovery conditions,causes the following test to start while the sample is still in the unfinished state.
8. Frequently asked questions
What if the requirement document gives no sequence?
Propose an authoritative sequence, send the customer written confirmation, and record that sequence in the test report.
Can each test use a separate sample?
Yes, and sometimes necessary, to separate the effects of each agent. The downside is that cumulative effects cannot be detected — which is a real condition.
Vibration before or after damp heat?
Normally, heat is applied first to condition the joint to withstand stress, then vibrate to detect potential damage. But must follow the customer’s requirement or be agreed in advance.
Is recovery time between steps mandatory?
Many tests have provisions for conditions and recovery times before testing or moving forward. Skipping this step may cause erroneous results.
How does sequence affect lead time and cost?
High impact: changing the order can increase the number of temperature ups/downs of the chamber, increase the number of functional tests, and may force additional samples to be used.
What if results across steps are inconsistent?
Fully record the phenomenon, take photos, re-measure relevant parameters, and evaluate according to agreed criteria. An abnormal result should not be “ignored” because it will lose the value of the entire record.
9. Conclusion
In environmental testing, ordering is not an operational detail but part of the test definition. The same list of tests in different orders yields different conclusions, and this should be clearly noted in the records.
Three things to do: build chains based on usage environment, not habits; Agree functional test sequences and scores in writing before testing; and record the execution order and results of each step in the report.
References
- IEC 60068-1 — Environmental testing: General provisions and guidance.
- IEC 60068-2-38 — Combined heat-humidity cycle (Test Z/AD).
- IEC 60068-2-53 — Combined climatic and dynamic testing.
- IEC 60068-2-47 — Specimen mountings for vibration, shock and similar dynamic tests.
- IEC 60068-3-1, 3-4 — Guidelines for cold/dry heat and humidity testing.
Related articles
- Z/AD combined heat-humidity cycle (IEC 60068-2-38) for electronic components
- What is IEC 60068? Structure of the Environmental Testing Standard Set and How to Read Test Codes
- How to Choose Environmental Tests from the Product’s Real Operating Environment
- Pass/Fail Criteria After Environmental Testing and Interim Functional Checks
- What capabilities does a RoHS test room need? ISO/IEC 17025, VILAS and scope of accreditation
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This article is an interpretive content compiled by us;not legal advice. Enterprises need to compare relevant documents/standards verbatim before applying them to specific products.
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