How to Source Conformal Coating Removal Services

Conformal coatings protect PCBs and ensure they work reliably throughout their expected operational life. However, poor coating application or selection of the wrong coating material can cause assembly malfunction. In other cases, poorly manufactured PCBs may need component repair/replacement. When these problems arise, coating removal is necessary.

Removal Methods

Removal depends largely on the coating material used. Acrylic, silicone and urethane coatings respond to chemical solvents for either spot- or complete surface coating removal. However, no single solvent works effectively for every liquid coating material, so appropriate selection of solvent type is necessary.

Most acrylic coatings respond to removal by the solvent butyrolactone. Silicone is best removed with methylene chloride/hydrocarbon-based solvents. Activators of ethylene glycol ether-base/alkaline or methanol-base/alkaline remove urethane conformal coatings efficiently. Chemically-resistant Parylene coatings require specialized removal methods. Parylene normally responds only to tetrahydrofuran for solvent removal.

Other removal methods include:

• Micro abrasive blasting (abrasion) can be used for all types of conformal films and specified for a project focus of any size, large or small.
• Versatile oxygen-based plasma is very effective for Parylene removal and can be used for liquid coatings.
• Laser ablation works well with Parylene, converting solid coating back to gas or plasma, with very precise, but slow, results.
• Time-consuming cut/peel/sand/scrape mechanical removal processes require thorough masking and can easily damage components. This method can be used for all coating types except urethane and is typically for specialized situations.
• Difficult to manage thermal methods can weaken solder joints and overheat components, leaving surface residue while causing delamination/discoloration. It is best used for spot removal on all coatings except urethane.

Choosing a Dependable Removal Company

Because poor coating application, selection of the wrong coating material or inadequate board-manufacture may generate assembly malfunction, removal strategies are fundamental to PCB design. No single approach or rule governs conformal coating removal. Processes are a function of a PCB’s applied coating material and the unit’s operational requirements. Factors affecting coating removal include:

• The type of coating material used
• The coating’s applied thickness
• The product’s end use
• Expected operating conditions
• The reasons for removal

Determining the appropriate removal procedure assures optimal removal without interfering with PCB function after it has been recoated. When selecting a company to remove ineffective conformal films, seek one that:

• Recognizes how the diversity of application/performance circumstances leads to the coating’s failure
• Identifies project-specific removal processes

Since no single removal process is applicable to film-removal, procedural inconsistencies are rampant. Companies providing optimal results offer a diversity of methodological alternatives for coating removal, supporting the process most suited to the particular project.

The company performing the removal must understand that risk is inherent in any conformal coating removal and board components need to be safeguarded during the process. Good removal always focuses on component compatibility as a key consideration, emphasizing mild but effective film-stripping procedures, whenever possible. This should be as true for chemical solvent removal, as it is for mechanical peeling, or any of the other removal procedures.

While a far greater number of PCBs are damaged during original manufacture than during the coating process, conformal films still must be removed before any repairs can begin. Damaged PCBs vary in the amount of repair that is required. Some need only need minimal repairs, while others require extensive rework. For reliable results, each removal project must follow established, verified procedures that can be customized as needed, understood and agreed-upon by the client.