Polyurethane electrical potting compound
Electronic components and assemblies require a substantial amount of protection from moisture, thermal shock, vibrations and extremely low temperatures. There are different encapsulating compounds available from epoxies, silicone and polyurethane. Epoxies are generally hard and tough materials that can provide excellent mechanical properties, good chemical resistance and excellent adhesion but they are unable to protect sensitive components during thermal cycling and may provide stress during exothermic cure. Silicone offers excellent protection during high operating temperatures but it does not provide good adhesion and it is quite expensive. Conventional polyurethane can be formulated to be flexible or rigid with low peak exothermic temperature during cure but it can be penetrated by water during particularly high temperatures. New generation polyurethane has been developed to provide a unique combination of properties:
- Excellent hydrolytic stability
- Low temperature performance
- Fast cure with low exotherm and low shrinkage
Hydrolytic stability means electronic insulation and integrity is maintained in the presence of moisture or even at elevated temperatures. The hydrocarbon content of the resin imparts hydrolytic stability and low moisture permeability that surpasses other types of urethanes. Polyurethane formulations as electrical potting compound can exceed the 28-day requirement of passing Naval Avionic tests which demonstrates that the product is virtually unaffected by moisture at high temperatures. Polyurethane products also have an elongation of 130% at -20oF and do not become brittle up to -70oF. The ability to maintain flexibility at low temperatures allows the electrical potting compound to encapsulate delicate electric components in a stress-free environment. It also provides a cushioning medium for the components and their connections.
Tailoring cure speed and pot life to requirements
The cure speed of polyurethane at room temperature can be accelerated for faster process time and less work in progress. At 20 to 2350 curing versions, polyurethane electrical potting compound exhibits little to no shrinkage and very low exotherm. Faster curing formulations have low peak exothermic temperatures of 30oF to 60oF in a 300 gram mass. This is a very attractive feature when the electrical potting compound is necessary for mass applications and/or high volume production where processing speed is very critical. Other potting compounds and materials are known to generate a lot of heat during curing in large masses or when formulated for fast curing.
The ability of an electrical potting compound to maintain integrity in a wet and hot environment is reassuring. This means that electronic design engineers have a solution for demanding environments because it clearly outperforms most conventional materials. It is important to guarantee that the end user of the electronic product will not worry about shock and vibration damage in the presence of moisture and high temperature.