Common types of sealing methods

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By Todd Boedecker | Sep 14, 2020
An elastomer keypad

When designing an electronic product, one important consideration is preventing unwanted substances from getting inside of the device. While internal components are typically protected by the main enclosure, any openings related to buttons, switches, and/or screens on the user interface can potentially allow for ingress of dust, liquids, and other substances that can cause possible damage or malfunction.

Fortunately, there are several methods to control, mitigate, and even eliminate liquid and particulate ingress. Below, we’ll be going over a few of the most common sealing methods.

What is sealing?

Liquid, chemicals, and dust can find their way inside of a product at any point where components meet. Sealing is the process of shoring up these connection points or openings to ensure undesired liquids or particles don’t affect function. But what are key considerations when it comes to sealing?

One of the most important factors when deciding on a type of seal is the level of protection required. In many industries, being able to withstand harsh environments or heavy cleaning while staying functional is paramount to the success of a product. For regulated industries, electronic devices often need to meet certain standards for the ability to resist liquids, chemicals, and other particles. Standards such as the National Electrical Manufacture Association (NEMA) 250 rating and Ingress Protection (IP) ratings per IEC EN 60529 are commonly used to define ingress requirements.

Another important consideration when designing sealing for a part is the amount of physical space available, as enough room is needed to achieve the required sealing. The look of a part can also play a large role here, as any visible sealants or adhesives may need to meet aesthetic requirements.

The overall construction of the part can dictate the sealing method as well. Sealing methods involving elastomer are generally only used on parts that are already committed to an elastomer construction, while a perimeter adhesive seal may only be viable for other constructions.

Common types of sealing methods:

  • Perimeter adhesive sealing: One of the most common methods of sealing, this involves using an adhesive to adhere a graphic overlay to the front of the component. The adhesive goes completely around the perimeter underneath the overlay, preventing any liquid or chemical ingress. Because it requires a specific amount and type of adhesive for an effective seal, the available space on the bezel and under the overlay is an important consideration. Also, any other functional layers underneath the graphic overlay need to be accounted for in the sealing design.
  • Front surface sealing: If there are any gaps or areas in which there can be potential for ingress on the front of a bezel or case, front surface sealing can be an effective option. For this method, a sealing compound is dispensed into a gap around any areas in which particulates or liquids could enter (typically the part perimeter). While this provides an effective seal, the sealant is typically black and cannot be matched to other colors, so it may not work with all aesthetic requirements.
  • Rear surface sealing: Similar to front surface sealing, rear surface sealing seals off any openings around tails or cables that come through the rear housing of the device. Because the sealant is added to the back of the case where it generally can’t be seen, this is a good option for any device where there might be stringent visual requirements on the front. Many devices are designed with this in mind to avoid aesthetic issues.
  • Front surface compression: Similar to a television remote, the elastomer rises through the bezel or case to seal off openings. The elastomer is molded to be compression sealed to the front of the part and offers a high level of protection from liquids and chemicals. As the seal is fashioned out of molded elastomer, usage of this sealing method is contingent on elastomer being an integral part of the product design.
  • Wrap around elastomer: As shown in the image, with this sealing method, the silicone rubber keypad is molded to wrap around the edge of the part, sealing off the front and edges of a device. While this offers a high level of protection for internal components, like with front surface compression sealing, it requires a part where elastomer is already part of the design. Due to the use of compression molded elastomer, this undercut feature can generally be tooled and produced with little to no added expense.

Ultimately, choosing the most optimal sealing method comes down to the specific requirements of the project. To discuss which sealing method is right for your next product, schedule a consultation with our experts.