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The Importance of Surface Pretreatment in Electronics Coating
By Mary Battiste, Director of Marketing — North America, Plasmatreat USA C
onformal coating in electronics refers to a thin protective film or layer applied to electronic circuit boards and
components. The primary purpose of confor- mal coating is to protect electronic assem- blies from environmental factors that can lead to corrosion due to the penetration of moisture, accumulation of dust, damage from chemicals and other contaminants. This pro- tective layer helps enhance the reliability and longevity of electronic devices, especially in challenging or harsh operating conditions. The conformal coating material is usual- ly a liquid that can be applied through meth-
Temperature Stability: Enhances the elec- tronic device’s ability to withstand tempera- ture variations.
UV Protection: Some coatings offer protec- tion against ultraviolet (UV) radiation, which can be important for outdoor and space appli- cations.
Conformal coating is commonly used in
industries such as automotive, aerospace, medical devices, and industrial electronics, where reliability and performance under challenging conditions are crucial.
Surface Pretreatment Before applying conformal coating
in electronics, proper pretreatment is essential to ensure the effective- ness of the coating and to maxi- mize the protection of electronic components. The pretreatment process typically involves several steps to clean, prepare, and con- dition the surfaces of the circuit boards and components. Common pretreatment steps
A PCB being treated with plasma.
ods such as spraying, dipping, or brushing. Once applied, it conforms to the contours of the components and circuitry, providing a protective barrier. Common conformal coat- ing materials include acrylics, silicones, ure- thanes, and epoxies. Key benefits of confor- mal coating include:
Corrosion Protection: Shields metallic electronic components from corrosive ele- ments, extending their lifespan.
Environmental Protection: Guards against moisture, dust, radiation and other environ- mental factors that could otherwise damage sensitive electronics.
Insulation: Provides an additional layer of insulation, preventing short circuits or elec- trical malfunctions.
Chemical Resistance: Some conformal coat- ings offer resistance to various chemicals, ensuring compatibility with the application environment.
include cleaning, surface prepara- tion, masking, deionized water rinse, drying, surface activation, and compatibility testing.
Prior to coating, it’s crucial to
remove any contaminants such as dust, grease, oils, flux residues, and other particles. This can be done through various cleaning methods, including ultrasonic cleaning, vapor degreas- ing, solvent cleaning or plasma. The surfaces of electronic components
may have oxide layers, especially on metal parts. Pretreatment may involve processes like abrasion or chemical treatments to remove these oxide layers and promote bet- ter coating adhesion. In some cases, certain areas of the elec-
tronic assembly may need to be masked or covered to prevent the conformal coating from being applied. This is common when specific components or areas should remain uncoated for functional reasons. A deionized water rinse may be used as a final cleaning step to remove any remain-
Coating delamination on a PCB without plasma treatment.
a small amount of coating to a test area and checking for any adverse reactions with the components or materials.
Considerations for Pretreatment Not pretreating the surface before apply-
ing conformal coating can result in incomplete coverage, bubbling or blistering, cracking, and curing issues. Sometimes there is an incompat- ible coating-substrate combination, which results in the coating detaching from the sub- strate leaving areas unprotected. Proper pretreatment plays a crucial role
in addressing and preventing these issues associated with conformal coating for elec- tronics. Proper pretreatment can enhance
Continued on next page
ing residues from the cleaning process. This helps ensure that the surface is free of any potentially harmful substances. After cleaning, it is important to thor-
oughly dry the electronic components. This can be done through various methods such as air drying, forced hot air drying, or baking, depending on the specific requirements of the conformal coating material. In some cases, a surface activation step
may be included to enhance the adhesion of the conformal coating. This can involve plas- ma treatment or the application of adhesion promoters. Before applying the conformal coating to
the entire assembly, it is advisable to conduct compatibility testing. This involves applying
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