What must a good compliant coating guarantee?

To ensure optimal protection of printed circuit boards, a good coating must meet certain basic requirements and characteristics:

• Electrical insulation of surfaces
• Surface insulation resistance (SIR)
• Elasticity
• Adhesion
• Thermal aging
• Thermal cycle / thermal shock
• Moisture barrier
• Salt spray resistance
• UV resistance
• Corrosive gas resistance
• Solvent resistance

The compliant coating must ensure high electrical insulation between contacts. Before environmental testing, the surface electrical resistance must be at least 10¹⁰ ohms and must not fall below 10⁸ ohms after testing.

Products such as DOWSIL CC-2588 and Electrolube AFA have been designed specifically to provide excellent, long-lasting electrical insulation, even in harsh environmental conditions.

Surface insulation resistance (SIR)

The ability of a compliant coating to maintain its electrical properties is critical for long-term protection. The most common tests include:

• Dielectric strength
• Dielectric constant
• Surface insulation resistance
• Comparative tracking index (CTI)
• Dispersion coefficient

In this area, DOWSIL 1-2577 and Electrolube AFA-S guarantee high performance thanks to their stable and homogeneous composition, ensuring a constant level of insulation.

Coating flexibility

The conformal coating must remain elastic to adapt to the thermal expansion of the printed circuit board (PCB). To test this property, a strip of coated copper is bent around a 3 mm diameter pin without the coating breaking or peeling off.

Elastoplastic silicones, such as DOWSIL 1-2620, and elastomeric silicones, such as DOWSIL 3-1965, are ideal for this application due to their ability to adapt to substrate deformation without breaking.

Adhesion of the conformal coating to the PCB

A good conformal coating must adhere firmly to the substrate. To check adhesion, the cross test is used: adhesive tape is applied to the engraved area and then removed to assess any detachment.

Products such as Electrolube UVCL and DOWSIL SE9187L, thanks to their anhydrous composition and strong internal cohesion, guarantee excellent adhesion to various types of printed circuit boards, even under dynamic conditions or when subject to vibration.

Thermal aging of conformal coating for PCBs

The compliant coating must be resistant to accelerated aging according to UL746 tests, which include:

• 24 hours of immersion in water
• 24 hours at a temperature of 105 °C
• 96 hours with 90% relative humidity at a temperature of 35 °C
• 8 hours at a temperature of -70 °C The cycle is repeated three times to simulate years of exposure to environmental conditions.

In this area, DOWSIL 1-2577LV and Electrolube DCA stand out for their chemical and thermal stability, proving their effectiveness even after repeated environmental cycles of exposure to high temperatures, cold, and humidity.

Thermal cycle/thermal shock

Coated printed circuit boards must withstand rapid temperature changes, such as those that occur during engine start-up at low temperatures. The tests comply with IEC 60068-2-14 and simulate conditions that vary in short intervals from -40 °C to +100 °C.

Products such as DOWSIL 3-1953, designed for automotive applications, and Electrolube PUC, which is particularly resistant to extreme loads, guarantee effective protection even in the event of significant thermal shocks.

Barrier against humidity

Atmospheric moisture is one of the main causes of corrosion in printed circuit boards. A good conformal coating must prevent moisture penetration and condensation on electronic surfaces.

Salt spray resistance

In marine environments, the combination of water and salt accelerates corrosion. The conformal coating must protect printed circuit boards from the harmful effects of salt spray.

The conformal coating must prevent these phenomena: solutions such as DOWSIL 1-2577 and Electrolube DCR (colored variant of DCA) have been specially developed for use in corrosive environments, extending the service life of printed circuit boards.

UV resistance

Exposure to ultraviolet rays can cause the quality of the conformal coating to deteriorate over time. Tests according to ISO 4892, Part 3, Cycle 1 simulate exposure equivalent to 4 years of aging in a northern European climate.

Transparent silicones, such as DOWSIL 3-1953 and Electrolube APL, offer excellent UV resistance, maintaining transparency and coating integrity even after long cycles of simulated exposure according to ISO 4892.

Resistance to corrosive gases

PCBs must be protected from aggressive atmospheres containing gases such as hydrogen sulfide and sulfur dioxide.

Under BS EN 60068-2-60 test conditions, resistant solutions such as DOWSIL SE9189L and Electrolube UVCL demonstrate high chemical resistance, making them particularly suitable for critical industrial environments.

Resistance to solvents

The compliant coating must maintain its integrity even in the presence of chemical solvents. The IEC 61086-2 standard specifies detailed tests to evaluate resistance to various chemicals used in industry.

Polyurethane products, such as Electrolube PUC, meet these requirements, effectively resisting substances used in manufacturing and maintenance processes.

Md Poland’s support in choosing the ideal conformal coating

In the field of electronics, choosing the right conformal coating means protecting the heart of your devices, ensuring reliable operation even in the most extreme conditions.

Thanks to our technical selection and experience gained in the field, at MD Poland we support customers in choosing the most suitable solution, combining Dowsil and Electrolube certified products with competent and specialized support.

There is a perfectly suited solution for every electronic protection need, and we are here to help you find it. Contact the experts at Md Poland if you need more information on the applications of conformal coatings for printed circuit boards.