UV-Cure Touchup and Parylene Coating

UV curing, a photochemical process utilized to preserve conformal coatings, adhesives and inks, offers a range of enhanced properties compared to traditional curing methods. By exposing coatings or other substances to intense UV light for drying (curing), this technique delivers immediate results, boosting production speed and minimizing the need for setup and cleanup procedures. Reduced operational expenses and heightened production efficiency are additional benefits of UV curing across various coating materials and processes.

In these cases, the consequent superior bonding between coating and substrate is environmentally friendly, saving energy without need for emissions’ controls. The diminished incidence of process/product rejection offers the additional benefits of:

• Better adhesion and bond strength
• Durable yet elastic coating surfaces
• Enhanced resistance to abrasion/surface scratching,
• Improved protection against exposure to chemicals and solvents.

Procedurally, the photochemical reaction essential to the UV curing process mixes liquid monomers and oligomers with minute traces of photoinitiators, which are subsequently exposed to UV energy. In the UV curing process, ultraviolet light interacts with specially formulated chemistries to cure coatings more rapidly than possible with traditional methodologies. The photoinitiators absorb the UV energy from the process light source, either arc light or laser light. The resultant chemical reaction converts liquid coating formulation into a stable, cured film in a matter of seconds.

Parylene and UV Light   

Although Parylene boasts numerous applications and advantages as a conformal coating, its resistance to UV radiation is generally limited. While it maintains stability when used indoors, most types of Parylene are not advised for prolonged outdoor use due to exposure to direct sunlight in the operating environment.

The UV stability of Parylenes C and N typically lasts for about 100 hours. In contrast, Parylene HT® and AF-4 excel in this aspect, offering UV protection for over 2,000 hours when tested against ASTM G 154 standards. This exceptional performance surpasses that of rival conformal coatings such as acrylic, epoxy, silicone and urethane.

After Parylene has been deposited, if there were any masking areas, the masking materials are removed. It is fairly common for the Parylene film around the de-masking area to be minimally damaged by the de-masking process. This can result in “fingers” along the edges of the Parylene masking line or even large tears. Sometimes, it is critical that the edges that were created be sealed to prevent any possibility of moisture or other chemicals penetrating the side edges.

These edges or other imperfections can be repaired by applying a liquid conformal coating. Urethane is commonly chosen for its similarity to Parylene properties. Occasionally, customers may ask for a UV curable liquid touchup material. However, it’s advised against using any UV curing method with Parylene coating due to the potential film degradation.

Although effective for its intended purposes, this method is largely incompatible with Parylene’s chemical vapor deposition (CVD) process, significantly limiting its suitability with Parylene.