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56 DESIGN007 MAGAZINE I NOVEMBER 2022 Mo st resin s ystems in use today are extremely complex products with elaborate chemical formulations. Process characteristics and final properties are usually adjusted by the manufacturer to suit the customer's require- ments, and this necessitates a great deal of skill, knowledge, and experience. Yet resin technology is an oen-overlooked area in electronics manufactur- ing. Over the past few years there have been several major developments in material formula- tion and utilisation that have resulted in extremely effec- tive new products being brought to the market. Epoxy resins are the long- time favourites for potting and encap- sulation, but with for- mulators rapidly reach- ing the limits of what can be achieved with these mate- rials, they have turned to poly- urethane chemistry. is month, I will look at polyurethane-based products that are fast becoming the resins of choice for those requiring high performance with cost-effective pricing. What are the key differences between PU and epoxy encapsulation resins? e main differences are flexibility and hard- ness; epoxies tend to be much more rigid and tough than polyurethanes, offering excellent sealing and ingress protection to the assemblies they are encapsulating, while polyure- thanes are usually a little soer and more flexible, which can often make them more forgiving when consider- ing stresses on delicate components during thermal cycling. ese differences can also influence the temperatures t h e r e s i n s a r e s u i t a b l e f o r . Fo r instance, epoxies are not typically suitable for temperatures below -40°C as they become t o o b r i t t l e , w h i l e p o l y - u r e t h a n e s c a n b e s u i t a b l e for temperatures as low as -60°C. At the top end of the temperature scale, polyurethanes are only suitable up to approxi- mately 130°C—or 150°C in exceptional cases— whereas epoxies can be pushed higher, above 200°C. Encapsulation Resins: PU vs. Epoxy Sensible Design by Beth Massey, ELECTROLUBE

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