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Electronic Issue of Adhesive Tech center's Newsletter Winter 1998 Volume IV Issue One
IN THIS ISSUE Encapsulating Systems ARALDITE and ARATHANE ENCAPSULATING SYSTEMS 
Guidelines For Optimizing Encapsulant Performance After an encapsulating system is selected, proper processing is vital to optimize system performance Processing and encapsulating system involves three steps: • Preparation of the casting mix • Casting • Gelation and cure Casting Mix Preparation:Before removing system components from the container, stir materials thoroughly. This is paricularily important for prefilled systems because filler may have settled during storage. In addition, resins with a high filler content should be heated in an oven overnight at 60 to 80C (140 to 178 F) in their original containers before mixing. This facilitate stirring and pouring. NOTE: Preheating hardeners is not recommended. To combine resin and hardener, mix encapsulating system components with a low viscosity of less than 3,000cP at room temperature either manually or in an open mixer. Resin systems with a higher viscosity should be preheated to 40C-50C (104F to 122F) before the room temperature hardener is added. To improve system uniformity and dielectrical properties, degas the blended casting mix under a vacuum of more than 28 inches of mercury before pouring. Casting To cast resin systems with a long work life, pour mixed components by hand or from a batch mixer into an open mold at atmospheric pressure. However, if the encapsulating system has a short work life, or for long production runs, use of continuous -type mixing and metering equipment is preferable. In many cases, it is advantageous to preheat electronic assemblies to a temperature 20C to 30C higher than the processing temperature of the mix to facilitate part wetting and help remove trapped air. To prevent foaming under a vacuum, the pressure in the cssting chamber should be higher that the vacuum used to prepare individual system components. Gelation and Cure: Curing is typically conducted according to the schedule recommended in the product data sheet. Room-temperature systems cure at about 25C (77F). Depending upon the reactivity of the casting mix and the ambient shop temperature, cure time is usually from 12 to 72 hours. The cure cycle of an encapsulating system can be accelerated by post curing at elevated temperatures. Heat-cure systems are typically cured at temperatures abobe 90C (194F). However, some encapsulating systems can be cured at temperatures slightly above 80C (176F0. To minmimize internal stress, cure encapsulants in two stages: gelation followed by postcuring. This ensures good high temperature and thermal cycling performance. NOTE: The exothermic heat liberated during the cure process, especially for room-temperature-cure systems, can produce internal casting temperatures that are significantly higher than the cure temperature of the encapsulating system. For further details on system handling and mixing, contact 1-800--323-5158. SAFETY /HANDLING PRECAUTIONS: IT IS IMPORTANT THAT THE MATERIAL DATA SHEETS FOR EACH ENCAPSULATING PRODUCT BE READ AND UNDERSTOOD BEFORE USING THE PRODUCT. Ciba supplies customers throughout the world with epoxy and polyurethane encapsulants and potting materials. The systems protect electrical circuits, transformers, capacitors, modules and sensors used in the automotive industry as well as in consumer and professional electronics. Among Ciba’s broad range of encapsulating products are systems designed for both room temperature and heat curing. Each product features its own advantages. However, in general, Ciba systems fall into three different classes: ROOM-TEMPERATURE-CURE EPOXIES HEAT-CURE EPOXIES POLYURETHANES These systems provide: •Proven performance history •Easy handling and adaptabillity to high speed dispensing equipment •Good mechanical and dielecttric properties •Good resistance to thermal shock and aging •Good chemical resistance Guide to Selecting Ciba Encapsulating Materials
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