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56 DESIGN007 MAGAZINE I MARCH 2021 packs for resins. en there is the thickness of the application to consider: <100 microns for conformal coatings, <500 microns for thick coatings, and >500 microns for resins, as well as approval ratings (coatings are generally approved to UL746, while for resins it is very much dependent upon the application). Due to the coating thickness, coatings occupy less volume and give a much smaller increase in overall weight compared to res- ins. ere are both coatings and resins based on epoxy, polyurethane, and silicone chemis- tries, but there are also acrylate, acrylic, and parylene coatings which do not have a direct resin equivalent. Most resins are 100% solids systems, so that few or zero VOCs are released during curing with minimal shrinkage, while many coatings are solvent-based, although there are two-component (2K), UV-curable acrylate systems, and solvent-less silicone coatings that are also 100% solid. In particular, 2K coatings are designed to be applied more thickly, without cracking dur- ing thermal shock testing, and enable a greater degree of component lead coverage to be achieved, resulting in improved performance during thermal shock, powered salt-spray testing, MFG testing and condensation test- ing (traditionally gruelling test regimes, com- monly used during automotive qualification campaigns). e 2K series is also VOC-free, solvent-free, and fast-curing, whether by ther- mal or the revolutionary UV/chemical dual- cure mechanism. 2. What are the main considerations for choosing a resin instead of a coating? e main considerations for choosing between a resin and a conformal coating are normally down to the specifics of the applica- tion. If the housing is designed to be the pri- mary protection against the environment, then a conformal coating is generally a more appropriate choice. However, if the housing is not the primary environmental protection or if the unit involved is to be subject to long-term immersion in various chemicals, then a resin is generally a preferred, more appropriate choice. Also, if there are many tall and heavy compo- nents on a PCB that is expected to encounter significant vibrational loads during use, then an encapsulation resin might be a more appropri- ate choice. Further consideration should also be given if the unit is to be used in a situation where it is not easily accessible or if a long con- tinuous service life is required, in which case a resin might be recommended to provide the extra protection and durability needed. 3. What is the best way to mix a resin pack and what can go wrong? Remove the resin pack from the outer pack- aging. In the case of polyurethane and silicone resins, don't remove it from the foil pack until ready to use. Lay the pack out onto a flat sur- face and remove the centre clip. Use the clip to push the resin from one half of the pack to the other, then pick the pack up in both hands and mix in a circular motion for a couple of min- utes. Place the pack back on the flat surface and use the clip to push the resin from the cor- ners into the centre. Pick the pack up in both hands and continue mixing for a further min- ute. Repeat, pushing the resin from the corners into the centre of the pack, and then continue to mix for another minute to ensure that the material is fully mixed and is a uniform colour. Use the clip to push the mixed resin to the side of the pack with the angled seam. Roll the pack film up so that the pack fits into the hand. Cut Due to the coating thickness, coatings occupy less volume and give a much smaller increase in overall weight compared to resins.