Factors to consider in the choice for electrical potting compound
Why epoxy is a preferred potting compound
Electrical potting compound plays a crucial role in the assembly and long-term protection for delicate and sensitive electronic components. When properly selected, electrical potting compound can provide the necessary defense against a wide variety of environmental, thermal, mechanical and electrical conditions that would otherwise damage the electronic components. Although there is a large variety of materials used as electrical potting compound, epoxy remains to be the most popular and widely used but the wrong choice for epoxy formulation can cause damage by curing in a such a way that will cause unwanted heat and stress on the electronic component.
The importance of considering dwell time
The reasons why epoxy is favored as a potting compound is the balance of electrical, mechanical, thermal, chemical and adhesion properties. One of the usual mistakes in encapsulation design is limited understanding of thermal conditions since engineers may simply base their choices upon the maximum and minimum application temperatures expected. This often leads to a wrong choice of the electrical potting compound because of the failure to account for dwell and ramp times. Dwell time is the length of time the potting compound remains at a given temperature. An epoxy potting compound can withstand short temperature spikes above their recommended continuous use temperatures.
Why ramp time is important
Ramp time is the speed of temperature changes that can likewise lead to a wrong choice for potting compound. Fast ramp times and thermal shock go hand in hand and if the engineers ignore these factors they may end up using an electrical potting compound that may not hold up to thermal cycling without cracking.
Why fast cure times need consideration
It is normally expected for engineers to choose an electrical potting compound with fast cure time however it is important to consider that fast cure times have the tendency to generate a larger exotherm than slower reactions which eventually raises the possibility for thermal damage. In addition, fast cure times have higher possibility to create entrapped bubbles that can reduce the electrical potting compound’s electrical and mechanical properties. Potting compounds work best if they have good adhesion to substrates but many of the polymers used for electronic housings and potted components have low surface energies and fail to bond well. Poor adhesion is usually fixed during the design process with the use of surface treatments and primers. Another problem that has to be considered is potting with a large horizontal surface since once the top has been filled; it can entrap moisture and air that can create damages to the electrical components.