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30 DESIGN007 MAGAZINE I DECEMBER 2020 and are generally applied much thicker than this. The increased thickness leads to a signifi- cant increase in weight and often results in a greater per-unit price than a coating. However, the increased thickness does mean that the PCB is far better protected against chemical attack, particularly in the cases of prolonged immersion. Also, a resin can provide superior protection against physical shock (depending upon the formulation) since the bulk of the resin will help to dissipate the forces. A layer of dark- coloured resin can also completely hide the PCB, which allows for some security of the design. Depending on the choice of the resin, removal of the resin can also result in the destruction of the PCB. With so many varying options to protect electronic circuitry, there's a lot of ground to cover, and depending on the application, sometimes a conformal coat- ing may be more suitable—particularly with the two-part coating series that performs like a resin. 2. What is a conformal coating? Conformal coatings can be used to protect the PCBs in a variety of applications, ensuring optimum performance in the harshest of con- ditions. They are generally thin films applied in the 25–250-micron dry film thickness range, leading to a minimal weight increase of the assembly. Conformal coatings conform to the contours of the board, providing maximum protection with minimal weight or dimen- sional change to the PCB. This is possibly the primary advantage of conformal coatings over potting and encapsulation resins. Often, coatings are clear, so the coated com- ponents are easy to identify, and the coat- ing can be easily reworked and components replaced as required. The chemical and ther- mal resistance of coatings is generally good for short exposures. A coating applies relatively little stress upon the components. This is a particular advantage where a component has thin leads or legs. The majority of coatings are 1K (single-component) systems, which have a long useable life, a low curing or drying tem- perature, and short drying time. Being a single-part solution, they are clearly easier to process and apply; however, the majority of 1K coatings are solvent based in order to modify their viscosity for applica- tion purposes. Conventionally, coatings can be applied manually by use of a paintbrush, spray gun, or even manually dipped. Increas- ingly, however, coatings are applied by robotic selective coating systems to provide a more controlled and more consistent process. 3. Is it possible that a conformal coating can perform like a resin? To confuse matters further, the simple answer to this is yes! We've developed a wide range of two-part (2K) conformal coatings, which com- bine the protection and properties of a resin with the ease of application of a conformal coating but without the use of solvents, giv- ing them an environmental advantage. The 2K coatings provide excellent coverage, and their superior flexibility offers protection of delicate components. 2K coatings also deliver excellent mechani- cal properties and abrasion resistance, but, being two-part, they require more sophisti- cated application equipment than 1K coatings, and they are more difficult to remove, making board repair more difficult. Based on similar two-part chemistry to resins, 2K coatings are designed to be applied by selective coating equipment in the range of 200–400 microns (0.2–0.4 millimetres), combining many of the advantages of both technologies and mini- mising many of the drawbacks of each. 4. What are some key differences between resins and coatings? The most noticeable differences are the methods of application (aerosol, conformal coating spray equipment, manual spray gun, and brushing for coatings, compared to mix- ing and dispensing equipment and resin packs for resins). The materials are applied at differ- ent thicknesses (<100 microns for conformal coatings, <500 microns for 1% solids coatings, and >500 microns for resins). Coatings are generally approved to international standards (IEC-1086), military standards (MIL-I-46058C),

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