Automotive electronics operate in far harsher conditions than typical consumer products. Road salt in winter, heat, humidity and condensation in the engine bay and underbody, years of thermal cycling and sulfur-bearing gases in the air all slowly attack the solder joints and traces on a circuit board. For products such as ECUs, BMSs, on-board chargers (OBCs) and EV chargers, OEMs and Tier 1 suppliers almost always require environmental testing — and the test specified most often is salt spray testing.
Conformal coating is one of the key lines of defense that gets a PCBA through these tests, but “coated” does not mean “will pass”. This article covers the common salt spray standards, the other tests OEMs usually require alongside it, the most common reasons for failure, and what to look for when selecting an automotive conformal coating.
Contents
What does a salt spray test measure?
In a salt spray test, samples are placed in a test chamber where a salt solution fog creates a highly corrosive environment, accelerating long-term corrosion into a short time. For a PCBA, it tests whether the coating can keep out salt and moisture so that solder joints, traces and component leads show no corrosion, leakage current or functional failure after the test.
Common standards fall into two groups:
| Type | Common standards | Test method |
|---|---|---|
| Continuous salt spray | ISO 9227 (neutral salt spray, NSS), ASTM B117, IEC 60068-2-11 (Ka) | Continuous fog of approx. 5% sodium chloride solution at 35°C; simple conditions that are easy to compare |
| Cyclic salt spray | IEC 60068-2-52 (Kb) | Salt fog alternating with humid storage (plus a drying phase at some severities); closer to the wet/dry changes of real use |
Continuous salt spray is well suited to comparing different materials or coatings. Cyclic salt spray, with its wet/dry alternation, is closer to what a vehicle actually experiences on the road, and many OEM specifications use this type. ISO 16750-4, the climatic load standard for automotive electronics, also lists salt spray as one of its tests.
Which test to run, for how many cycles or hours, and at which severity is defined by the OEM’s or customer’s specification. Get the complete test specification at project kick-off before deciding on coating chemistry and film thickness.
Beyond salt spray: other tests OEMs often require
Salt spray only simulates one source of corrosion — salt. Automotive electronics validation usually includes the following tests as well, and the conformal coating has to be chosen with all of them in mind:
| Test | What it simulates | What it requires of the coating |
|---|---|---|
| Flowing mixed gas corrosion (IEC 60068-2-60, Ke) | Corrosive gases containing sulfur, chlorine, etc. | Barrier against corrosive gases |
| Damp heat, cyclic (IEC 60068-2-30, Db) | Condensation from high humidity and temperature changes | Moisture and condensation resistance |
| Thermal shock (IEC 60068-2-14, Na) | Rapid temperature changes | Flexibility — no cracking or delamination |
| OEM-specific standards (e.g. BMW GS 95003-4) | Combined conditions defined by the OEM | As specified |
The flowing mixed gas corrosion test is especially closely tied to the conformal coating. Peters’ SL 1301 ECO-FLZ and SL 1307 FLZ series have both passed four-gas corrosion testing according to DIN EN 60068-2-60 and BMW GS 95003-4.
Where do salt spray failures usually come from?
When a board fails, the first thought is often “the coating isn’t good enough”, but in practice the application itself is the more common cause:
1. Coating too thin on sharp points and edges
Surface tension pulls coating away from component leads, solder joint peaks and board edges, so the film there is often only a fraction of the thickness on flat areas — and these are the first places salt spray breaks through.
2. Insufficient or uneven film thickness
Only one coat applied to keep up with output, or the spray angle leaves shadowed areas on the far side of components uncoated. Confirm film thickness by measurement, not by experience.
3. Bubbles, pinholes and dewetting
Any bubble or pinhole that goes through the coating is a path for salt water. For the causes of and fixes for these coating defects, see Conformal Coating Bubbles and Peeling: Common Causes and How to Fix Them.
4. Masking boundaries
At connectors, test points and other masked areas, the coating at the masking boundary tends to lift or be incomplete, and salt seeps in from there.
5. Board cleanliness
Flux residue absorbs moisture in salt spray and damp heat conditions and also weakens adhesion, so under-film corrosion often appears after testing.
Tip: Inspecting under UV-A light after coating is the fastest way to find missed and thin areas before sending boards for testing. The SL 1307 FLZ series, 419D, 4223F and 422B all contain a fluorescent tracer.
What to look for in an automotive conformal coating
When selecting a conformal coating for automotive use, we recommend confirming the following, in order:
1. Mounting location and temperature range
Temperature and humidity differ greatly between the cabin, the underbody and areas near the engine. Confirm your product’s operating temperature range first, then compare it with the coating’s operating temperature.
2. Corrosive environment
Besides salt spray, does the product also need to pass corrosive gas or damp heat testing? Polyurethanes, with better moisture and chemical resistance, usually have more margin than acrylics in harsh corrosive environments.
3. Thermal cycling
Almost every automotive product has to survive thermal shock. A coating that is too hard or too thick tends to crack first at component leads and corners, and salt spray gets in through the cracks.
4. Rework requirements
Automotive lines usually need to repair and rework boards, so confirm whether the coating can later be removed locally and recoated.
5. Certifications and environmental regulations
OEMs usually require flame-retardancy certification such as UL 94, and compliance with environmental regulations such as ELV (End-of-Life Vehicles Directive) and RoHS. Confirm at project kick-off that the corresponding documents are available.
Based on these criteria, common choices for automotive electronics include:
- SL 1301 ECO-FLZ (Peters, Germany, polyurethane): operating temperature -40 to +140 °C, UL 94 V-0, passes four-gas corrosion testing according to DIN EN 60068-2-60 and BMW GS 95003-4. Eco-friendly formulation free of toluene, xylene and C9 aromatic solvents; can be removed for rework by soldering through or mechanically.
- SL 1307 FLZ (Peters, Germany, acrylic): operating temperature -65 to +125 °C, UL 94 and UL 746E certified, and passes the same four-gas corrosion testing. Its fluorescent tracer makes inspection easy, and it can be repaired with V 1307 FLZ thinner, making it a good fit for products that need rework.
- SL 1400 ECO-FLZ (Peters, Germany, polyurethane): operating temperature -65 to +140 °C, excellent chemical resistance, UL 94 V-0 and compliant with RoHS, WEEE and ELV; adjustable viscosity, also suitable for flexible circuits.
- 4223F (MG Chemicals, Canada, polyurethane): operating temperature -40 to +145 °C, good corrosion and chemical resistance, suitable for automated spray equipment, fully cures in 2 hours at 100°C — a good fit for production lines.
Want to compare operating temperatures, certifications and rework methods across products?
Pre-test checklist
1. Get the complete test specification: standard number, severity, number of cycles or hours, and pass criteria (appearance, insulation resistance, functional test).
2. Shortlist 2–3 candidate materials: screen them with the selection criteria above and request samples and technical data from suppliers.
3. Trial-coat your own boards: use the application method and cure conditions you will use in production — don’t rely on datasheet values alone.
4. Measure film thickness and check coverage under UV light: pay special attention to component leads, board edges and masking boundaries.
5. Record pre-test baselines: for example insulation resistance and functional test results, so you have something to compare against after testing.
6. Tear down and analyze after testing: if a board fails, record where the corrosion occurred to determine whether the cause is the material, film thickness or application.
Datasheets and manufacturer test reports show what the material itself can do; your salt spray results depend on your laminate, solder mask, component layout, film thickness and process. That is why you must trial-coat and test your own product to be sure.
FAQ
Q: If a PCBA is conformal coated, will it always pass salt spray testing?
Not necessarily. Conformal coating greatly improves protection, but the result also depends on film thickness, completeness of coverage, board cleanliness and coating quality. Trial-coat under production conditions before testing, and if a board fails, use the corrosion locations to trace back to the coating process.
Q: How long does a salt spray test take?
It depends on the OEM’s or customer’s specification — test hours and cycle counts vary widely between standards and severities. Confirm the specification at project kick-off, then decide on material and film thickness.
Q: Acrylic or polyurethane — which is better for automotive?
For harsh corrosive environments that call for better moisture and chemical resistance, polyurethane is usually the choice, for example SL 1301 ECO-FLZ. If your line has frequent rework, consider the acrylic SL 1307 FLZ, which has passed the same four-gas corrosion testing. Either way, validate by trial-coating your own product.
Q: Can you provide certification documents and technical data?
Yes. Tell us which products and document types you need — for example UL certification, technical data sheets (TDS) or safety data sheets (SDS) — and we will help provide them.
Does your automotive project need to pass salt spray or corrosion testing?
Tell us where the product is mounted, its operating temperature and the test specification your customer requires. Altra will recommend suitable conformal coatings, arrange samples so you can trial-coat your own boards, and provide the technical data and certification documents you need for testing.
