Conformal coatings provide reliable working security for PCBs. 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 depends largely on the coating material used. Except for epoxy, liquid resins of acrylic, silicone and urethane 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.
For other methods:
- 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; used for all coating types but urethane, in specialized situations.
- Difficult to manage thermal methods can weaken solder joints and overheat components, leaving surface residue while causing delamination/discoloration. Best used for spot-removal for all coatings but 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 effecting coating removal include:
- type of coating material used,
- its applied-thickness,
- the PCB’s project/purpose,
- its operating conditions, and
- the precise reasons for removal.
Determining the appropriate removal procedure assures optimal removal without interfering with PCB function after it has been recoated. When selecting a firm to remove ineffective conformal films, seek one that:
- recognizes how the diversity of application/performance circumstances leading to the coating’s failure
- requires project-specific removal processes.
Since no single removal process is applicable to film-removal, procedural inconsistencies are rampant. Firms providing clients optimal results offer a diversity of methodological alternatives for coating removal, supporting the process most suited to the particular project.
Choose a firm that understands risk is inherent in any conformal coating removal and values safeguarding board components 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. Both client and coating service firm benefit from when the firm has a good in-house removal operation. Because a wide range of removal options can exist for a single coating the question is: “Which choice makes the most sense: solvent, abrasion, plasma, or even thermal removal/stripping services, or any of the remaining recommended methods, used individually or in combination?”
You’ll be most confident in the outcome when you’re included in the decision-making process. Damaged PCBs are similar to hospital patients. Some need only a few stitches for repair, while others require brain surgery. For reliable results, each removal project must follow established, verified procedures that can be customized as needed, understood and agreed-upon by the client.
Diamond M.T. stands out among conformal coating firms, providing world-class services in all areas, including film removal. Our client consultation personnel work according to your designated guidelines and needs, developing best-practice, mutually agreed-upon solutions when procedural confusion arises. Diamond’s documented removal standards outline specific processes for each type of removal project, which are then customized to the conditions of the job, as the necessity arises. Highly-skilled, comprehensively-trained technicians working with up-to-date equipment assure quality coating removal every time!
To learn more about conformal coating removal services, download our whitepaper now: