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5 Simple Steps to Eliminate Bubbles in Potting Encapsulants

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Encapsulant solutions are commonly used to enhance protection of circuit boards from environmental and liquid contaminants, chemical attack, and electrical shortages. While potting materials provide many positive attributes when used to protect PCBs, sometimes other issues arise during and post application of these compounds. This blog focuses on “bubbles” forming within the encapsulant itself.

Some causes of bubbles . . .

  • Moisture contamination in some coating can cause bubbling
    • Moisture can come from many sources, such as the prepolymer, catalyst, adhesive or primer. Moisture reacts with the isocyanate in a polymer, which then produces carbon dioxide. CO2 vapor manifests itself within the encapsulant as a bubble. Note: moisture contamination originating in either the adhesive or primer produces small bubbles visible only at the bond line.
  • Mold moisture contamination
    • Molds insufficiently annealed (above the boiling point of water) may experience surface moisture or condensation. In high-humidity environments, condensation will form if the mold is cooled but not reheated afterward. Also, if water-based mold-release agents are improperly applied, a resultant can be moisture contamination of the encapsulant. This typically results in surface bubbles.
  • Insufficient degassing of encapsulant during manufacturing and filling
    • Small bubbles will most assuredly form if the prepolymer is not degassed properly or the finished product is not degassed sufficiently prior to filling and/or pouring during application.
  • Incorrect technique of application
    • Please ensure that splashing, especially with low viscosity encapsulants, is minimized or eliminated altogether to prevent turbulence in the liquid from creating bubbles.
  • Applicator not sealed properly
    • Perform routine checks on your applicator system to make sure that all seals/gaskets are functioning properly with no potential for moisture contaminated air to seep into the system.

Here are 5 logical and fairly easy steps to take in order to alleviate bubbles in your encapsulant:

  1. Package/store liquid encapsulant under a (dry) nitrogen blanket
    1. Atmospheric moisture has extremely low to no potential of intrusion into your encapsulant’s container when nitrogen is used to cover/protect the liquid.
  1. Prepare mold efficiently and effectively
    1. Develop a step-by-step annealing/preheating process to make certain that your mold is moisture free.
  1. Degas potting components properly and completely
    1. Determine and implement the best degassing process (e.g., centrifugation after filling, if applicable) for your encapsulant material, the result being a bubble-free liquid.
  1. Enhance efficiency of application technique (to minimize splash and turbulence)
    1. If possible, automate the dispensing of the liquid potting material to ensure minimal turbulence while pouring. If you must dispense manually, make sure all personnel responsible for this function are properly trained.
  1. Determine that applicator is completely sealed
    1. Work with your equipment supplier and your engineering/maintenance department to understand how to properly maintain your equipment so it is working up to specification and is leak free.

Encapsulants are great for ensuring high-quality PCB performance. But, as with any tool, they must be carefully and precisely used in order to guarantee maximum performance. Additionally, they must be carefully maintained, prior to use, in order to prevent any defects (e.g., bubbles) from manifesting themselves. Please contact your HumiSeal representative or the HumiSeal Technical Support hotline with inquiries, for more information, or for help with potting encapsulant concerns.

Encapsulation Solutions brochure

 

This entry was posted in Humiseal, Encapsulants on April 16, 2018 by Humiseal Editor
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