Once a PCB has been assembled, the biggest threat is often not the design but the operating environment. Moisture, condensation, dust and corrosive gases can slowly corrode solder joints, cause leakage currents and eventually short circuits. A conformal coating is a thin protective film applied over the PCBA to separate the circuit from that environment.
There are many types of conformal coating. The wrong choice may not fail straight away, but it can cost you later in rework, in production or after the product reaches the field. This guide covers the four questions to answer before you choose, how the four main materials differ, and which types suit which applications.
Contents
Four questions to answer first
1. Operating environment
What temperature range will the product run at? Will it see high humidity, condensation, chemicals or corrosive gases such as sulfur compounds? Outdoor, automotive and indoor appliance products need very different levels of protection.
2. Rework and repair
If components may need to be replaced during production or servicing, choose a coating that is easy to remove. Some materials are almost impossible to remove once cured, which makes rework expensive.
3. Coating process and throughput
Will you spray, brush or dip? Do you need a material that works with automated spray equipment? How soon the board can move to the next process step directly affects throughput.
4. Certifications and regulations
Does your customer or end product require UL 94 V-0, IPC-CC-830B, military or automotive OEM specifications? Do you need RoHS compliance or a solvent system free of toluene and xylene?
The answers to these four questions largely decide which material you need.
Comparing the four main materials
Conformal coatings are grouped into four main types by resin:
In short:
- Acrylic: the easiest to rework and apply, and the most widely used. Its weakness is poor resistance to chemical solvents.
- Polyurethane: good moisture, chemical and abrasion resistance for harsher environments, but difficult to remove for rework, and sensitive to moisture while wet.
- Silicone: good heat resistance and flexibility, suited to outdoor and high-temperature use. Abrasion resistance is low, it scratches easily, and residues can contaminate other processes during rework.
- Epoxy: good moisture, abrasion and chemical resistance with a very strong film, but extremely difficult to remove once cured and less flexible than the other types.
Want to compare the specifications and certifications of each product?
Recommended products by material
Acrylic: rework, general industrial and appliances
- SL 1307 FLZ (Peters, Germany): operating temperature -65 to +125 ℃; UL94 and UL746E recognized; passed the IPC-TM-650 fungus test (growth rating 0) and the four-gas corrosion test. Adjustable viscosity for different coating methods.
- SL 1307 FLZ/234 (Peters, Germany): the same series, additionally qualified to MIL-I-46058C and IEC 61086-2 (Class II) for military and high-reliability products.
- SL 1309 N (Peters, Germany): operating temperature -40 to +130 ℃; fungus resistance to MIL-STD-810 E or RTCA DO 160 E: 2004 Section 13; passed the four-gas corrosion test.
- 419D (MG Chemicals, Canada): toluene- and xylene-free; ready for the next process step in 10 minutes; operating temperature -65 to +125 ℃; UL 94 V-0 and IPC-CC-830B. Removable with thinner 4352 or a thermal stripper for easy rework.
Polyurethane: chemical environments, automotive, flexible circuits
- SL 1301 ECO-FLZ (Peters, Germany): operating temperature -40 to +140 ℃; UL 94 V-0; passed the four-gas corrosion test to DIN EN 60068-2-60 and BMW GS95003-4, making it a good fit for automotive electronics. Free of toluene, xylene and C9 aromatic solvents.
- SL 1400 ECO-FLZ (Peters, Germany): operating temperature -65 to +140 ℃; excellent chemical resistance; RoHS, WEEE and ELV compliant; adjustable viscosity, suitable for flexible circuits.
- 4223F (MG Chemicals, Canada): operating temperature -40 to +145 ℃; resists water, solvents and most household chemicals; ready for the next step in 15 minutes and fully cured in 2 hours at 100 °C; suitable for automated spray equipment.
Silicone: high-temperature environments
- 422B (MG Chemicals, Canada): operating temperature -40 to +200 ℃ with continuous operation up to 200 ℃; UL 94 V-0; excellent corrosion resistance.
Epoxy: high strength or optical clarity
- 4224 (MG Chemicals, Canada): optically clear, UV-stable and non-yellowing; operating temperature -40 to +200 ℃; excellent chemical and abrasion resistance. A two-part system that needs no special application equipment.
Quick guide by application
If your requirement is already clear, you can also use this table:
| Your requirement | Recommended material |
|---|---|
| Frequent rework in production or service | Acrylic |
| Automotive electronics, corrosive gases | Polyurethane |
| Exposure to chemicals or solvents | Polyurethane |
| Flexible circuits | Polyurethane |
| Long-term operation above 145 ℃ | Silicone |
| Optical clarity, UV-stable, non-yellowing | Epoxy |
| Military specification required | Acrylic |
This table is a starting point, not a conclusion. Coating method, film thickness and the certifications your customer specifies all matter, so we recommend testing samples on your own line first.
How to inspect the coating
Conformal coatings are thin and hard to see with the naked eye. 419D, 4223F, 422B and the SL 1307 FLZ series all fluoresce under UV-A light, so you can quickly spot missed or thin areas and use automated optical inspection.
FAQ
Q: Can a conformal coating be reworked after curing?
It depends on the material. Acrylic is the easiest to remove: 419D can be removed with thinner 4352 or a thermal stripper, and SL 1307 FLZ with the matching thinner V 1307 FLZ. Polyurethane and silicone are harder, and cured epoxy is almost impossible to remove.
Q: What is the difference between a conformal coating and a potting compound?
A conformal coating is a thin film that follows the shape of the board. It adds little weight and does not affect heat dissipation or assembly space. A potting compound fills and encapsulates the whole component or module. It gives more complete protection but adds much more weight, volume and rework difficulty. For general moisture and dust protection of a PCBA, a conformal coating is usually enough.
Q: Within the same material type, how do products differ?
Mainly in operating temperature, curing speed, certifications and solvent system. Both SL 1301 ECO-FLZ and 4223F are polyurethanes, but SL 1301 ECO-FLZ has passed an automotive OEM corrosive gas test, while 4223F suits automated spraying and cures quickly.
Q: Can I test samples first?
Yes. Tell us your application, coating method and expected volume, and we will recommend suitable products and arrange samples.
Not sure which coating fits your product?
Tell us your application, operating temperature and coating method. Our sales team will contact you within one business day to help you choose and arrange samples.
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