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Removing Conformal Coating

Posted by Sean Horn

Friday, November 11, 2016 7:43

@ 7:43 AM

Conformally coated PCBs are expected to work without fail, largely because of the protection the coatings provide them.  In addition to PCB-manufacturing issues, coating problems can trigger failure mechanisms for the assembly.  For instance,

  • Conformal coating applied incorrectly can cause PCB malfunction.
  • Selecting the wrong coating material from among acrylic, epoxy, parylene, silicone or urethane can be a source of board failure, if it does not support the PCB’s operating environment.

Removing the coating may be necessary if these conditions prevail.

Reliable Methods of Removing Conformal Coating

Coating removal methods are determined by their impact on the film, its thickness, and effect on the substrate.  Major removal methods include:

One needs to match the appropriate removal method to the coating material, its age, thickness and the board’s specific function.

Removal According to Coating Material

Since the possibility of defective coating or PCB components can develop after manufacture, removal strategies are an integral element of design, based largely on the assembly’s specific coating material and operational function.

Summary

Because the process of removing conformal coating from PCBs can vary from simple to complex, it is important to correctly match the removal methodology with both the type of coating material used, and the project/purpose of the circuit board.  Stripping fluids that work for some materials (acrylic) may be useless for others (parylene).  Determining the appropriate coating erasure procedure assures optimal removal without interfering with PCB function after it has been recoated.  THF is the only chemical solvent that consistently removes parylene from assembly substrates; the limited chemical options remaining are highly specialized and seldom applied.  Abrasion and scraping techniques work best for parylene films; laser may also develop further as a major parylene removal process.  Mechanical and plasma-based techniques are useful for spot-removal assignments.

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