Parylene Coating Blog by Diamond-MT

Conformal Coating Removal Standards

Posted by Sean Horn on Fri, Feb 17, 2017 @ 08:00 AM

If problems in a conformal coating defy reliable repair, coating removal may be the only solution.  Removing conformal coating from PCBs requires matching removal methodology with coating type and the component’s function.  A variety of factors – bubbles/voids, coating thickness, component failure, inadequate masking, poor adhesion, surface finish, among many others – can necessitate coating removal.     

Recognizing the various types of conformal coatings and their interactions with the parts/materials they cover is as critical to their removal as it is to original covering process.  To accurately determine correct procedural guidelines, consulting prevailing industry standards is recommended.  IPC Standards 7711/7721 delineate recommended procedures for conformal coating removal from, and replacement onto, PCBs.  Their objectives:   

  • Deliver standardized training developed by the industry, recognized, approved and traceable to enhance understanding and appropriate application of removal criteria.
  • Designate accept/reject criteria for these processes that encourage consistent and correct application of benchmarked activities, pertinent to conformal coating removal.
  • Teach methods and processes to assure acceptable workmanship.
  • Communicate methods and techniques that support application of professionally certified standards for coating removal.  

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IPC-7711/7721                    

Coatings must be removed in almost all instances of assembly repair.  In some cases, the films themselves are defective, unable to generate the protective properties that is their purpose.  In others, components covered by coating are inoperative for some reason; conformal films must be removed before repair can begin. 

Successful removal of conformal films largely depends on the levels of operator skill and experience.  Titled Rework, Modification, and Repair of Electronic Assemblies, IPC- 7711/7721 details standards for appropriate removal of conformal coatings, describing “the procedural requirements, tools, materials and methods to be used in the modification, rework, repair, overhaul or restoration of electronic products.”

Certified IPC Standard 7711/7721 is designed to develop and assure acquisition of workmanship skills necessary to safely remove improperly functioning conformal films from substrate surfaces.  Like every other IPC training and certification program, 7711/7721 was “developed by and through consensus of industry [leaders and] … representatives from academia, government agencies, original equipment manufacturers (OEMs), electronic manufacturing service companies (EMSs) and circuit board manufacturing companies, and are used worldwide.”

 A multi-step identification and treatment procedure is mandated by IPC 7711/7721, prior to actual coating removal.  Essential procedural activities include:

  • Product classifications, skill levels, tools and materials.
  • Basic surface mount and through hole component removal.
  • Land preparation and component installation.
  • Primary heating methods: conductive, convective and others.
  • Handling electronic assemblies.
  • Wire splicing procedures.
  • Through hole component removal and installation.
  • Chip and MELF rework procedures.     
  • SOIC/SOT, J-lead and QFP rework.
  • Printed wiring board circuit and laminate repair.
  • Conformal coating removal.

Coating removal methods are outlined on page vi of the IPC 7711/7721

manual, Procedures 2.3.1–2.3.6:

Coating Removal                                                                                                   

          Procedure      Description                Board             Skill            Level of

                                                                    Type               Level           Conformance

           2.3.1             Coating Removal,       R, F, W, C      Advanced    High

                                Identification of

                                Conformal Coating                                                                

           2.3.2             Coating Removal,       R, F, W, C      Advanced     High

                                Solvent Method                                                                     

           2.3.3             Coating Removal,        R, F, W, C      Advanced    High 

                                Peeling Method                                                                      

           2.3.4             Coating Removal,        R, F, W, C      Advanced    High 

                                Thermal Method                                                                    

           2.3.5             Coating Removal,        R, F, W, C      Advanced    High 

                         Grinding/Scraping Method                                                            

           2.3.6              Coating Removal,        R, F, W, C      Advanced    High 

                            Micro Blasting Method                                                              

          Coating replacement procedures appear on page vii, 2.4.1 – 2.4.2:

Coating Replacement                                                                                         

      Procedure          Description                Board            Skill             Level of

                                                                    Type              Level           Conformance

       2.4.1             Coating Replacement,    R, F, W, C     Intermediate      High   

                                  Solder Resist                                                                        

       2.4.2             Coating Replacement,    R, F, W, C     Intermediate      High   

                    Conformal Coatings/Encapsulants                                                     

Major Removal Methods                                     

Depending upon the PCB’s operational requirements, each of the wet coatings – acrylic, epoxy, silicone, urethane – responds best to a particular removal treatment; vapor-deposited parylene similarly reacts best to removal techniques suitably adapted to its use.  IPC-7711/7721 standards detail coating removal methods determined by their impact on the film, its thickness, and effect on the substrate. 

Matching the appropriate removal method to the coating material, its age, thickness and the board’s specific function is the major take-away from IPC-7711/7721.

            Diamond MT removes conformal coating cost-effectively, minimizing downtime and the risks involved to PCB assemblies.  Our established quality program is based on IPC-7711/7721 standards and guidelines.  Combined with knowledge of commercial manufacturing requirements, competitive pricing and on-time delivery, we provide clients superior conformal coating removal services, followed by recoat, if requested.

To learn more about problems with conformal coating and how they can be remedied, download our whitepaper:

Conformal Coating Rework  Whitepaper

Tags: conformal coating removal, conformal coating rework, conformal coating issues, conformal coating defects, conformal coating removal services