The “dam & fill” process with two materials is mainly used in cases where a component needs to be protected with an optically-transparent encapsulant or if a conventional glob-top material is too viscous to flow around and underneath fine wires. Optically transparent encapsulants usually have a low viscosity. A dam is therefore applied around the component first to prevent the potting material from flowing all over the substrate.
Epo-Tek OG116-31 is a UV-curable epoxy. Due to its thixotropic nature it is often used as a dam. It can be cured with UV-light in a very short time. Afterwards the encapsulant – either also a UV-cure or a thermoset material - can be applied.
Epo-Tek OG198-55 has an even higher thixotropy than OG116-31.
Both products have an extraordinary chemical and humidity resistance and a high glass transition temperature (Tg >110°C).
As most UV-cure epoxies, both OG116-31 and OG198-55 are cationic products. Ionic polymerization is initiated by photo-generated ions. The cure process continues until all polymers are consumed. Generally, cationic products have the benefits of less shrinkage and higher adhesion over free radical cured systems and are not adversely impacted by an oxygen rich curing environment.
SOURCE: John P. Kummer GmbH