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52 SMT Magazine • March 2015 by kevin Balben delo High-Reliability Thanks to Adhesives artICle Protecting electronic components from thermal, mechanical and chemical stress is be- coming increasingly important in many indus- tries. While application-friendly packaging is one way to ensure components' stability, highly reliable encapsulants are playing a more impor- tant role as well. DELO Industrial Adhesives' product special- ist Kevin Balben explains the correct uses of to- day's encapsulants and compounds and clarifies the myths that surround them. True or False? When using encapsulants and casting com- pounds in electronic production, there is no al- ternative to heat curing in ovens. True. While users have a choice between heat curing and light curing, the latter is used in a handful of applications including those that use connectors, switches and relays. Light cur- ing acrylates are ideal for these applications and enable extremely short cycle times. As soon as components are exposed to harsh environmental conditions, heat-curing epoxy resins are the only game in town. These robust products contain an anhydride hardener acti- vated by heat. Therefore, curing requires tem- peratures between +100°C and +180°C. For demanding conditions there are no alternatives to heat curing. Thermodes and induction are forms of heat curing and work faster than a normal oven, but are still slower than light curing. Users cannot always use in- duction or thermodes because the geometry and size of the parts may not allow it. For the most part, there is no way around air convec- tion ovens. Temperature and freedom from tensions are conflicting goals when trying to optimize the curing process. True. The higher the temperature, the faster the adhesive cures. Thus, high temperatures are good for fast processes. At the same time, high tension causes a great deal of warping since the polymer network is created through heat and shrinks during cooling. If warping is too intense, the materials should be cured at lower temperatures for a few

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