How to Waterproof a PCB

Have you heard someone talking about waterproofing a PCB and you wondered what it is all about? It is imperative to mention that the process can be tough, but at the end of the day, it helps to further strengthen the circuit board.

In this article, we take you down the road on why PCBs are waterproofed, including the evolutions in the process.

What is PCB Waterproofing?

To put it simply, it is the process of protecting the Printed Circuit Board (PCB) from water. But water is not the only reason for using the protective measure.

It is common knowledge that PCBs are exposed to a wide range of environments, most especially in the factory. However, the common environment is the exposure to wetness and this is what you want to avoid.

It is also possible for the performance of the circuit board to be negatively affected by other factors, ranging from the steam/heat and chemical emanating from the factory.

Given the above factors, you see reasons why it is important to waterproof a PCB. But the question is, “how do I go about it?”

Waterproofing Processes for PCBs

Here, we talk about some of the steps you can take to protect your Printed Circuit Board (PCB) from water, chemicals and a wide range of other complicating environments that could hamper the board’s performance.

1. Use the Conformal Waterproof Coating

When it comes to the protection of PCBs, one of the core factors to consider is the exposure to water. You don’t want water to penetrate the board and to be sure of that, it is imperative to use a corresponding proofing method.

The conformal waterproof coating is one of the best waterproofing methods for circuit boards. Below are additional pieces of information on how it works:

How It Works

The process simply requires the spraying of specific liquid compounds on the PCB’s surface to make it waterproof. Usually, the compounds used here are required to have specific attributes, such as being elastic and thin.

The following are examples of the compounds used for conformal waterproof coating for PCBs:

  • Silicon
  • Epoxy and;
  • Urethane

Widespread Usage

Although the conformal waterproof coating is used for protecting the circuit board from water, it can also be used for other purposes. These other purposes include upping the board’s resistance to corrosion and dust.

Downsides to Conformal Waterproof Coating

On the contrary, you may not want to use this waterproofing method for your circuit board for different reasons. Here are some of the reasons:

Damage is not Entirely Ruled Out

While the coating is elastic and can help keep out water from penetrating the circuit board, it is not entirely full-proof.

It has been noticed that the conformal waterproof coating may be able to keep out water, but a similar protection is not top-notch when the board is exposed to corrosive and humid/wet environments.

Low Adhesion Strength

Perhaps, one major reason why the coating lets water pass into the board when exposed to wet environments is because of the low adhesion strength. In this sense, the adhesion is not strong enough to prevent water from sipping into the circuit board.

2. Seal the Connectors on the PCB

Now that we have ascertained that the conformal waterproof coating process is not entirely full-proof, we can consider other options. One popular option is to seal the connectors and that’s for a good reason.

These connectors are in the path of water, when in use and considering that they are used for sensor, wire and terminal connection; you don’t want to take any chances.

How to Seal

To seal or close the connectors, all you have to do is to pick any waterproof material. There are lots of them out there, ranging from acrylic, silicone, epoxy and urethane.

PCB Considerations

While sealing the connectors can help prevent water from entering the board, it is also possible for the process to be faulty.

You see, the materials used for the connectors’ sealing may not measure up in extreme wet environments. That is why it is recommended that the circuit boards to have the connectors sealed are not to be used in applications that require exposure to wet or humid environments. That is why this process is not a great deal for PCBs used in the marine market.

3. Apply Waterproofing Materials Directly on the PCB

You can make a direct application of the choice waterproofing materials on the surface of the PCB, preferably on the top-most/outer layer of the board.

Here are some of the things you want to know about how this process works:

Material Form

The common materials used for this PCB waterproofing process are the Parylene C and Parylene N. They are high-density polymers, capable of being made into thin layers.

The Waterproofing Method

These materials are first applied on the surface of the board. Although they are in the liquid form, it doesn’t take a long time before they become solid, thus, protecting that surface from water exposure.

Use Case

Ideally, the materials used for this process have a thickness of at least 0.05mm or 2 mils. When compared to the traditional varnish, such as the epoxy resin, the Parylene C and Parylene N materials are thinner.

Notwithstanding, you can be confident that the waterproofing protection the materials offer can help the Printed Circuit Board (PCB) function effectively in the special purpose and the heavy-duty electronic boards.

4. Consider Using a Water-Resistant PCB Substrate

Most of the other waterproofing methods discussed in this article center on applying the protective coatings or materials on the side or on the surface of the board.

Yet, it is possible to protect the circuit board from the inside. That is where the use of a water-resistant substrate comes in.

What is a PCB Substrate?

Generally, the work of the substrate is to separate the copper(s) and the prepreg layer in a circuit board.

In terms of the protective properties, the substrate helps to bolster the structure and to improve the strength of the circuit board.

Internal Waterproofing

Using the PCB substrate requires making an internal protection of the board. That way, the board is protected both from water penetration and swelling.

Choice of PCB Substrate

The choice of a substrate solely depends on the water absorption rate. You don’t want to use a substrate that cannot keep water away for long, as that would defeat the purpose of using it in the first place.

In this regard, using the moisture-resistant substrate is better. A good example of one is the FR-4 material, which has 0.10% of water absorption.

Besides the FR-4 material, the following are some of the alternative PCB substrates you can use for waterproofing purposes:

  • Ceramic
  • FR-1: this PCB substrate is better when used with either the single or the double-layered circuit boards.
  • PTEF: consider using this moisture-resistant material for either the high-frequency or high-speed PCBs.

5. Use Waterproofing Enclosures

Often times, the waterproofing enclosures are mistaken for the conformal waterproofing coating methods. They are quite different, but let us explain what the former means before we point out the differences.

The waterproofing enclosures are boxes made from the following materials: stainless steel, plastic, steel and silicon.

How They Work?

The enclosures simply do as the name suggests “closing.” Ideally, the waterproofing enclosures or boxes are used to cover the circuit board and isolate the same from the surrounding environment.

Differences between Waterproofing Enclosures and Conformal Coating

The core difference between the two is that the enclosures isolate the circuit board from the humid/wet environment, while the conformal coating process involves spraying (liquid) compounds on the PCB’s surface to bolster the water-resistance.

The second difference is the extent of the water-resistance. On the one hand, the conformal coating method is not entirely waterproof, because of the low adhesion strength that could let water into the PCB. On the other hand, the waterproofing enclosures can improve the PCB’s resistance to water because of the isolation capabilities, thereby, reducing the chances of water reaching the board.

Combining the Waterproofing Enclosures and Conformal Coating Methods

Is it possible to combine the two for the best results? Ordinarily, the conformal coating method is ideal for PCBs that do not have a direct exposure to water, while the waterproofing enclosures are used when contact with water is expected.

However, you may want to combine both the conformal coating and waterproofing enclosures if there is a possibility of the circuit board’s exposure to or use in the high humid/wet areas. By this combination, the circuit board will have a higher protection against corrosion and water.

Choosing the Waterproof Application Process

There are three (3) major processes to applying waterproofing materials on a PCB. They are:

  • Manual Spray: the manual method of applying the waterproofing materials helps to assure the accuracy of applying the materials where they are needed on the circuit board. The manual spray process is commonly used when you don’t have a special laiting machine.
  • Dispensing: paint is stored in a hopper and pumped into a spray gun, from where it is applied to the circuit board.
  • Dipping: you can also consider the third option of dipping the Printed Circuit Board (PCB) into the paint tank to be coated. However, you may not want to use this option because of the uneven coating that comes about because most of the coat sticks to the surface than on the areas it is needed.

Final Words

Waterproofing a PCB is an important step towards improving the durability. With the right waterproofing method, you can be sure to protect the circuit components and the board in general.

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