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AUGUST 2019 I SMT007 MAGAZINE 13 thickness and coverage are especially beneficial with regards to tin-whisker mitigation and dielectric re-enforce- ment. 2K materials are also low-odour and solvent-free, providing health and safety benefits in comparison to other chemistries. From rigorous testing, the 2K systems demonstrate very impressive perfor- mance when compared to other coat- ing types. The fact that they can be applied thickly without cracking during thermal shock testing enables a greater degree of component lead coverage to be achieved. This results in improved performance during powered salt spray testing, mixed flowing gas (MFG) test- ing, and condensation testing; tradi- tionally, these gruelling test regimes are commonly used during automotive qualification campaigns. What Are the Key Features and Benefits of 2K Products? The 100% solid material provides increased thickness and coverage, in comparison to sin- gle coating systems. 2K materials have also been developed to successfully endure auto- motive and aerospace thermal shock cycles with minimal impact on solder joint reliability. 2K coating materials can be applied thinly (50– 75 μm). However, they have been designed, formulated, and tested to be applied at much greater thicknesses (250–300 μm) to facilitate superior encapsulation of components and component leads. Further, 2K coatings provide a fast chemical cure with full cure achieved in only 10 minutes at 80°C, significantly improving throughput and reducing work in progress. For instance, the 2K850 is a rapid UV-cure coating system within the 2K range, which is immediately dry to the touch when exposed to regular micro- wave lamps or LED lamps. Following oven cure, the boards can be bagged without resid- ual solvent odour or concerns about sufficient moisture being available to complete cross- linking process. The overall oven lengths can be as short as 700 mm due to the lower inten- sity and longer wavelength light being less hazardous, and conveyors can be repurposed for this purpose (Figure 3). Due to the fact that UV light can be shad- owed by tall components, a secondary cure process is required. The chemical cure of a 2K material is achieved within six hours at a constant and reliable rate without any require- ment for an additional oven process. Unlike traditional single coating systems, 2K materials have a different flow, which can pro- vide improved edge coverage and resolves any issues regarding areas to be left uncoated such as connectors and BGAs. 2K can be applied by selective coating spray and needle dispensing to provide maximum coating accuracy to users. With coating applications, controlling the flow rate at a suitably low level whilst also maintaining the correct mix ratios, is the key challenge and has recently been overcome by the use of specially developed, low-volume progressive cavity pumps. The pumps accu- rately control the flow rates of the individual components of the formulations within ±1%, maintaining control of the volumetric mix ratio and ensuring correct curing and properties of the dispensed materials. Additionally, the spray head velocity can be up to three times faster than traditional 100% solid material Figure 3: UV-LED curing system for 2K coatings.