PCB Potting Compound Selection Guide

Potting or Encapsulation in PCB refers to the application of liquid potting compounds, which are then cured to form a protective casing. This effectively enhances the overall mechanical performance of the components, making it particularly effective for applications like automobiles that need to withstand prolonged exposure to external shocks and vibrations. Epoxy resin potting compound is the most common in modern electronic manufacturing processes, but it may not always be the optimal solution, such as in cases where moisture resistance is crucial. When selecting the appropriate potting compound for your project, various factors should be considered, including physical, chemical, environmental, and mechanical strength. In this article, TechSparks provides a guide to choosing PCB potting compounds by comparing the characteristics of several common compounds to help you make a more informed decision.

Further Reading: PCB Potting: The Ultimate Guide to Protecting Your Circuit Boards

pcb Potting

Epoxy Resin Potting Compound

As mentioned earlier, this is possibly the most widely used potting compound in PCBA projects. Epoxy resin is a thermosetting polymer that forms a stone-like hard shell upon curing, providing sufficient mechanical performance and confidentiality for PCBA boards. Depending on specific requirements, epoxy resin potting compounds have various variants such as flame retardant, thermally conductive, low viscosity, and high-temperature resistant types. Engineers can choose according to the project’s operating environment, for instance, using high-temperature-resistant types for applications with elevated temperatures, possibly up to 300°C or higher.

Pros:

  • Excellent heat resistance, capable of withstanding temperatures as high as 155°C.
  • Outstanding resistance to acids and chemical corrosion.
  • Simple processing, maintaining consistency in performance before and after curing.
  • Excellent adhesion to various metal substrates and porous substrates.

Cons:

  • Susceptible to cracking due to temperature changes, allowing moisture ingress.
  • Not suitable for flexible PCB as it may compromise their inherent flexibility.
  • Difficult to open after encapsulation, posing challenges for repairs if faults occur.

Polyurethane Potting Compound

Also known as PU potting compounds, are flexible potting compounds that address the shortcomings of epoxy resin when it comes to protecting flexible PCB from physical stress. Although relatively expensive, their versatility justifies the investment.

Pros:

  • Greater adaptability, suitable for almost all substrate materials, including metals, ceramics, and polyimides.
  • Soft material that better absorbs physical impacts and vibrations without cracking or breaking.
  • While its temperature resistance is average, the range (-40°C to 100°C) can be expanded by modifying the formulation.
  • Repairable, advantageous for projects requiring optimization upgrades.

Cons:

  • Processing difficulty, potential for bubble formation during potting, often requiring processing in a vacuum environment.
  • Longer curing time.
  • Not recommended for use with LSE plastics, as it may not wet the plastic sufficiently.

Silicone Potting Compound

It is a high-performance PCB potting compound, with the most common being two-component silicone encapsulants. It includes two main types: condensation type and addition type. The former forms a three-dimensional network structure through the condensation reaction of silicon-hydrogen bonds, offering excellent high-temperature resistance, chemical resistance, and electrical insulation. The latter forms through the addition reaction of silicon-carbon bonds, typically curing faster.

Pros:

  • Operating temperature range from -60°C to 200°C, preventing cracking due to significant temperature changes.
  • Strong electrical performance and insulation ability, capable of withstanding pressures of over 10,000V.
  • Superior heat dissipation, making it suitable for high-power projects.
  • High fluidity in liquid state, ensuring better flow into gaps.
  • No by-products during processing.

Cons:

  • High cost, making it less appealing to some users.
  • Insufficient adhesion may pose a risk of detachment.

Considerations for Choosing PCB Potting Compounds

The three mentioned compounds are classified based on material properties, and PCB potting compounds can also be categorized based on function, flexibility, and hardness. However, regardless of the classification method, choosing based on the properties of the potting compound is always the wisest approach.

Cost is a primary consideration when choosing, with potting processes typically used in automotive and industrial rather than in devices like phones or computers due to cost considerations. When assessing costs, always base it on the overall project rather than just the material price, as different materials may have varying processing difficulties, contributing factors that can increase the overall project cost.

Performance requirements after potting include factors such as heat resistance, mechanical performance, flame resistance, and resistance to temperature changes. When considering these aspects, a comprehensive selection strategy tailored to the specific project needs should be adopted.

Furthermore, some projects may have higher requirements for fast turnovers. This implies the need for potting compounds that cure quickly and are compatible with potting processes. For example, room-temperature curing potting compounds, although less demanding on the process, may cure slowly and have high viscosity, which might not be ideal for high-density PCBs. In contrast, heat-curing potting compounds can be compatible with automated processes, speeding up the entire potting process.

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