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2.3.2 Coating Removal, Solvent Method
Outline
This procedure uses a solvent to remove surface coatings. This procedure can be used for spot or overall coating removal of conformal coatings or solder resists.

Approved solvents may be used to remove specific soluble type coatings on a spot basis by brushing or swabbing the local area with the controlled application of solvent until the area is free of the coating material.

If warranted, all the soluble type coating can be removed by immersing and brushing the entire printed board or printed board assembly.

To determine the appropriate coating removal procedure the coating must first be identified. Refer to procedure number 2.3.1.

Note
Coating removal may require the use of one or more methods.

Caution
Determine, on a module by module basis, the hazards to parts, etc., by short term immersion in the removal solvents. If chloride based or other harsh solvents are used, extreme care must be exercised to prevent damage to base material, component parts, plated-through holes, and solder joints. Some solvent coating removal methods can cause expansion or swelling of the base material which can degrade the printed board or printed board assembly. Under no circumstances should these solvents be used except in a closely controlled process. It is recommended that the printed board or printed board assembly be inspected to ensure that no damage has occurred.

Before using any solvent refer to Material Safety Data Sheets

Minimum Skill Level - Advanced
Recommended for technicians with soldering and component rework skills and exposure to most repair/rework procedures, but lacking extensive experience.

Conformance Level - High
This procedure most closely duplicates the physical characteristics of the original, and most probably complies with all the functional, environmental and serviceability factors.

Acceptability References
IPC-A-600 2.0 IPC-A-600 2.0 Externally Observable Characteristics
IPC-A-610 10.0 Laminate Conditions
Procedure References
1.0 Foreword
2.1 Handling Electronic Assemblies
2.2 Cleaning
2.3.1 Coating Removal, Identification Of Coatings
2.4.1 Coating Replacement, Solder Mask
2.4.2 Coating Replacement, Conformal Coatings/Encapsulants
IPC7721 2.3.2 Coating Removal, Solvent Method
Tools and Materials
CircuitMedic Part
Cleaning Brushes
Disposable brushes for use with solvents for cleaning and application of coatings.
CircuitMedic Part
Coating Remover Pen
For precise removal of silicone, acrylic and urethane coatings from circuit boards.
CircuitMedic Part
Foam Swab
Ideal for absorbing cleaning solvents, and applying color agents and epoxies.
CircuitMedic Part
High Temp Tape Discs
High temperature polyimide tape discs, .50" diameter.
CircuitMedic Part
Knife with #16 Blades
A must-have tool for precise cutting, scraping and trimming.
CircuitMedic Part
Mixing Picks
Unique mixing sticks have a paddle shape on one and sharp pick on the opposite end.
Thermal Part Tool
Thermal Parting Tool
Thermal removal tool using controlled heat through specially shaped tips.
Images and Figures
2.3.2 Coating Removal, Solvent Method
Coating Removal Required At Outlined Area
2.3.2 Coating Removal, Solvent Method
Figure 1: Apply Kapton tape to outline area for coating removal.
2.3.2 Coating Removal, Solvent Method
Figure 2: Apply solvent with a foam swab to remove coating.
2.3.2 Coating Removal, Solvent Method
Figure 3: Removal complete.

Procedure - Local Spot Removal 
  1. Apply High Temperature Tape to outline the area where the coating needs to be removed. (See Figure 1)

    Dip the end of a foam swab in stripping solution and apply a small amount to the coating to be removed. (See Figure 2)

    Note
    Since various substances may be used as coatings, the time required for a given coating to dissolve or soften will vary. Reapply solvent several times as most solvents evaporate rapidly.

  2. Rub the treated surface carefully with a brush or wood stick to dislodge the coating. A wedge shaped applicator tip, knife, or heated blade may be effective in removing some coatings, particularly polyurethanes.

  3. Neutralize or clean the stripped area and dry.

Procedure - Overall Removal

  1. A single step for removal of all the coating may be completed by providing a continuous flow of solvent.

    Alternately, process the board in a series of tanks containing mild solvent, starting with a high contamination tank and progressing sequentially to a final, fresh solvent tank.

Evaluation

  1. Visual examination or UV light may be used to verify complete removal of coating.

Procedure for reference only.