Preventing air voids in potting applications

Paul Whitehead, Strategic Accounts Manager at Intertronics, shares insights on how manufacturers can prevent the introduction of voids during the potting compound processing.

Processing considerations

Proper storage is crucial to prevent moisture absorption by potting compounds, especially hygroscopic ones. Handling materials in line with manufacturer recommendations is essential to avoid future issues. Non-contact mixing methods, such as planetary centrifugal mixers or automated metering systems, typically introduce less air. Regular maintenance of mixing equipment and careful replenishing can help minimize air inclusion. If air entrapment is unavoidable, consider degassing as a solution.

Degassing techniques

Low viscosity materials may self-degas adequately. For higher viscosity products, vacuum degassing can expedite the process. However, caution is necessary to prevent volatile constituents from evaporating. Centrifugal force can also aid degassing, particularly in planetary centrifugal mixers. Care must be taken not to separate fillers or heavier components during centrifugal action. In critical applications, vacuum mixing can be employed for effective degassing.

Application methods

During application, it's vital to avoid introducing air. Techniques to minimise air bubbles include staged pouring or injection, tilting assemblies, filling from the bottom, and preheating to reduce viscosity. Vacuum potting or vacuum degassing before curing can be useful in challenging geometrical situations. Vibrating tables can help release trapped air, and pressurised feed systems should be used cautiously to prevent air saturation.

Contamination and cure

Uncured potting compounds can react with contaminants, leading to adhesion issues, delamination, or gas bubble formation. Using cleaned and dried assemblies can resolve contamination problems. Shrinkage during curing may create voids, which can be minimised by applying materials in stages.

Avoiding voids is critical for PCB performance. Manufacturers can achieve reliable and long-lasting parts by carefully addressing each stage of the potting process.