A Comprehensive Guide to Potting PCB Boards

Did you know that printed circuit boards (PCBs) are present in almost all electronic devices? The reliability, durability, and safety of these devices greatly depend on the design and manufacture of their internal PCBs. As such, it has become increasingly important for manufacturers to take measures to better protect them. In this article, FS Technology will introduce a protective measure known as potting, which can prevent damage to the core of these electronic devices.

What is potting PCB?

Potting is a common protective measure used by most PCBA board manufacturers to safeguard electronic circuits against heat, environmental hazards, chemicals, and impacts. This is achieved by filling the enclosure of the PCB board with a potting compound, which acts as an encapsulation resin, thus protecting the entire board and its components. Here are some reasons why you should consider potting PCB board:

Potting enhances electronic performance and circuit dependability by protecting PCBs from tampering, moisture, and voltage leaks. Potting also shields electronics from the effects of vibration and stress, preventing wiring disconnections and early system failure.
Additionally, the PCB and PCB case’s vibration waves may pair, intensifying stress on the PCB and causing early failure. PCBs become stress and vibration resistant through potting.
Also, Encapsulation protects PCBs from dirt and dust, which can cause overheating, signal interference, and decreased speed or performance.
Lastly, PCB board potting improves the security and privacy of the electronic device. The nature of potting makes accessing your PCB and reverse engineering your device incredibly challenging, thereby enhancing the privacy and security of your PCB board.

PCB Potting Compound Guide

Common Potting Compounds

Epoxy

One of the primary advantages of using epoxy potting chemicals is their exceptional adhesion. They can be used for potting PCB without the need for primers. Additionally, they have high stiffness, modulus, and tensile strength, making them ideal for outdoor applications, such as switches, transformers, and agricultural machinery.

Silicone

Silicone PCB potting compounds are renowned for their exceptional elongation capabilities and softness and flexibility. However, silicon’s broad operating temperature range is its most notable feature. Specially formulated silicone potting materials can function at temperatures ranging from -100°F to 200°F. Despite being the most expensive option, silicon is the least stressful material for components.

Polyurethane

Polyurethane’s key benefits are its flexibility, elongation, and resistance to abrasion. Since most potting applications involve devices made up of multiple substrates, such as metal alloys, ceramics, polymers, and glass, flexibility is essential. Therefore, you require a material that can protect each component while maintaining the particular characteristics of each substrate. Specially formulated polyurethane potting chemicals are excellent at achieving this.

How to choose potting material

Hardness

Harder compositions offer better weather and abrasion resistance, as well as IP protection. For those who want a stiff and rigid compound, the best options are urethane and epoxy, which have hardnesses up to 80D. While silicone is highly flexible, it is sufficiently rigid, with hardness ranging from 10A to 60A.

Thermal conductivity

Choose materials with the best thermal conductivity to manage and dissipate the heat produced by your electronic devices easily. Fortunately, silicone, epoxy, and urethane offer excellent thermal conductivity, with silicone being the best.

Viscosity

Most PCB encapsulation applications require low-viscosity, flowable, and self-leveling compounds, which are commonly available. However, if necessary, ask for compounds with a higher viscosity.

Color

If the finished product’s color and visibility are important, you need the proper potting compound color. Otherwise, a deep, opaque hue will suffice. However, keep in mind that translucent materials are necessary for LED visibility.

Process flow of PCB potting board

Prepare

The potting compounds
A container or a bucket
A stirrer
Precision scales
Whenever the resin is ready, you will need the following materials for the PCB board potting process:
Protective mask
Protective neoprene gloves
Protective clothing
Protective glasses
To ensure high-quality results, you need to control the resin. This step requires:
A hot air oven
Hardness tester (analog shore a)

Step by step guide

Pre-bake the PCB enclosure

The resin material polyol is highly sensitive to moisture, so it’s crucial to pre-bake the PCB and its enclosure in an oven at 60°C. This step ensures that the enclosure is free from any moisture, which could otherwise adversely affect the potting process.

Mark the desired resin level

Secondly, it is important to mark the desired resin level on the enclosure to ensure accurate potting and easy reference in the future. Additionally, sensitive components or parts of the circuit board should be masked to prevent any damage during the potting process.

Prepare the resin

Before mixing the polyol and isocyanate materials to create the resin material, you must first wear a protective mask and neoprene gloves. Carefully vary the weight ratio of the resin-to-hardener to create a compound that is hard yet flexible. Experts recommend a 1:6 weight ratio when mixing isocyanate and polyol, respectively.

To prevent the polyol from settling over time due to variations in room temperature, homogenize it using a metal rod before adding it to the mixture.

Use a scale to measure the weight of the bucket before adding polyol into it. Next, add polyol into the bucket while noting the increase in weight and stop pouring when the weight increase (polyol weight) reaches six-sevenths (6/7) of the total weight of the resin to be potted. Then, start pouring isocyanate into the bucket while taking note of the weight difference. Stop pouring when isocyanate makes up one-seventh (1/7) of the total resin weight.

Finally, mix both materials in the bucket using a mechanical stirrer until the mixture is even. This is crucial for the best results and durability of the resin. Don’t forget to mark the desired resin level on the enclosure and mask any sensitive components or parts of the PCB.

Pour the resin into the PCB enclosure

To begin this step, tilt the enclosure at a slight angle of about 3°. This can be achieved by placing a pad or similar item under the enclosure. This helps to prevent air from becoming trapped under the PCB enclosure.

Carefully pour the resin into the PCB enclosure at the marked level you noted in step 2.

Now, allow the potted PCB board and enclosure to pre-cure at room temperature. Afterward, place them in an oven and cure them for 24 hours at 80°C.

Check the final quality

After the 24-hour curing process, remove the PCB board enclosure from the oven. Then, use an analog shore A hardness tester to check the final hardness of the resin at a standard temperature of 20°C. The recommended reading should be between shore A 85 and 90.

Electronic potting is essential for shielding PCB boards and electronic assemblies from dirt, moisture, water, and other types of damage. However, proper preparation and application of potting compounds, and understanding the difference between potting and conformal coatings, are even more critical. Fortunately, now that you understand the fundamentals of potting your PCB board, you can do it with confidence.

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