Conformal coatings like parylene are strong and trustworthy, and they make necessary equipment safe to use and safer to rely on for long periods of time. However, even the best conformal coatings sometimes need a bit of help to perform their duties efficiently--and that's where masking comes in. Masking is a specialized process with a lot of variables, and, while it is necessary for many applications, the specifics aren't always well-known. Today, our conformal coating experts will provide a crash-course in masking.
The Basics of Masking
Masking is a process designed to ensure that the functionality of conformal coatings and the items they're protecting, like printed circuit boards, don't interrupt one another. For example, if parylene were to coat batteries, connectors, grounding points, switches, or other delicate components, the overall functionality of the item itself could be limited, and the rest of the coating might be rendered inefficient. Masking keeps this from happening by protecting identified areas from the coating during the application process. The process is specialized, and there are a lot of variables, but the key is to carefully decide which masking systems are most effective given the item itself and the desired functions.
Parylene coating is a versatile and effective conformal coating solution used to protect electronic components. However, the process of applying parylene coating can be challenging since it needs to be applied only on specific areas of the substrate while leaving other areas untouched. To address this issue, masking is used to selectively apply the coating to the required areas while protecting the rest. This blog post will discuss the masking process for parylene coating in detail, including different types of masks, their benefits and limitations, and best practices to ensure the masking process is successful.
Why Masking for Parylene Matters
In many applications across many industries, the masking process is crucial because it ensures that the parylene coating doesn't get in its own way. This means that, sometimes, parylene can cause product failures or interfere with performance if the conformal coating gets somewhere it shouldn't be.
For example, at times parylene's benefits can also be its weaknesses--like when its strong dielectric properties cause it to interrupt electric signals on a PCB--and that's where masking comes in.
The masking process works to protect all the benefits parylene offers while limiting the risks. There are a variety of masking conventions, ranging from different types of liquid latex to tapes, tape dots, and various models of caps and boots.
Types of Masks
There are various types of masks used in parylene coating, including tape masks, liquid latex masks, Kapton® tape masks, and photodefinable masks. Each of these masks has its own benefits and limitations.
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Tape Masks: Tape masks are the most commonly used masks in the parylene coating industry. These masks consist of pressure-sensitive adhesive (PSA) tapes, such as polyester or polyimide, which are cut into specific shapes and sizes to cover areas that need to be protected. The benefits of using tape masks include easy application, low cost, and the ability to withstand high temperatures.
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Liquid Latex Masks: Liquid latex masks are an alternative to tape masks. They are applied by brushing or spraying a liquid latex material onto the substrate's surface, which dries and hardens to create a barrier. The main advantage of liquid latex masks is their ability to conform to irregular surfaces, making them ideal for complex shapes. However, they can be challenging to remove and may leave residue.
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Kapton® Tape Masks: Kapton® tape masks are another type of PSA tape mask that offers high-temperature resistance and can be used in various applications. However, they are not as flexible as other types of masks and may not adhere well to uneven surfaces.
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Photodefinable Masks: Photodefinable masks are a type of mask that is made using photolithography. These masks offer precise control over the location and size of the masked areas, making them ideal for complex geometries. However, they are costly and require specialized equipment and expertise to create.
The Masking Process
The masking process is necessary for making parylene coating as efficient as possible. Let our conformal coating experts explain!
- Step 1. Identify the areas where parylene coating absolutely cannot be placed. This is crucial since it drives the rest of the process and defines future success.
- Step 2. Once the proper areas have been identified, it's time to apply specially-created conformal coating masking materials which will ensure that parylene doesn't coat the areas in question.
- Step 3. Next, the entire device is placed in a vacuum chamber, where the parylene coating is applied. Parylene vapor coats the device, including the masked areas.
- Step 4. After successful parylene deposition, all of the masked areas are cleaned, leaving the specified areas left untouched and functional.
What You Need to Know
Here's a quick look at what you need to know about the parylene masking process.
- Variables. One of the most important parts of the masking process is identifying all of the variables. These include but are not limited to, the type of coating being used, the specific area to be coated, and all involved materials. These variables often have a big impact on the entire process, so knowing what you're dealing with is crucial.
- Parylene masking. It's important to remember that if you're using one of the most trusted and long-lived conformal coatings--parylene--then you'll need to use a unique masking process. Parylene's application is in a gaseous form, so there is often a need to mask more than just a few specific locations.
- Issues. As with anything worth doing, there are a few potential issues to look out for when masking. One of these is electrostatic discharge, defined as too much static electricity, which can be controlled by an ionized air blower; another potential problem is improper timing because the relationship between the masking and coating processes is delicate and any timing issues can cause big risks.
Benefits and Limitations of Masking
Masking is an essential part of the parylene coating process and offers many benefits. By selectively applying the coating, masking ensures that only the required areas are coated, reducing the risk of electrical shorts and improving the device's overall performance. Masking also helps to minimize waste and reduce costs associated with over-coating. However, masking also has some limitations, including the risk of coating defects if the masking process is not done correctly. Improper masking can lead to incomplete coverage or coating defects such as bubbles or delamination.
Although parylene is an essential component of many devices, this coating sometimes needs a little help to do what it does best: provide reliable, trustworthy protection for a long time to come. That little bit of help comes from the masking process--and it's important to understand just why this process is so beneficial in parylene application.
Best Practices for Masking
To ensure a successful masking process, there are some best practices that need to be followed. First, it is crucial to choose the right type of mask for the application. The choice of mask will depend on the substrate's material, the complexity of the masking requirements, and the expected operating conditions. Second, it is essential to clean the substrate thoroughly before applying the mask to ensure that it adheres correctly. Third, the mask should be applied carefully and inspected to ensure that there are no gaps or overlaps that could result in coating defects. Finally, it is important to remove the mask carefully to avoid damaging the coating or leaving residue.
Conclusion
Masking is a critical step in the parylene coating process and is essential for ensuring that the coating is applied only to the required areas. By choosing the right type of mask, following best practices, and carefully inspecting the masked areas, it is possible to achieve high-quality, defect-free coatings.
Interested in more information on the masking process? Looking for conformal coating experts and parylene pros? Contact us today!
