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. The coating must first be identified to determine the appropriate coating removal procedure. 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 the base material, 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 the Material Safety Data Sheets.

Minimum Skill Level - Advanced

Conformance Level - High

Tools and Materials

Cleaning Brushes Disposable brushes for solvent cleaning and application of coatings.

Coating Remover Pen For precise removal of silicone, acrylic and urethane coatings from circuit boards.

Foam Swab, Small Swabs for use with solvents and application of color agents and epoxies.

High Temp Tape Discs High temperature polyimide tape discs, .50" diameter.

Knife with #16 Blades A must-have tool for precise cutting, scraping and trimming.

Mixing Picks Disposable mixing sticks for mixing and applying adhesives.

Precision Tool Set Nine precision-crafted tools for detailed circuit board work.

Thermal Parting Tool Thermal removal tool using controlled heat through specially shaped tips.

Procedure

Local Spot Removal

1. Apply High-Temperature Tape to outline the area where the coating needs to be removed. (See Figure 1)
2. 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 coating to dissolve or soften will vary. Reapply the solvent several times, as most solvents evaporate rapidly.
3. 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 effectively remove some coatings, particularly polyurethanes.
4. Neutralize or clean the stripped area and dry.

Overall Removal

1. Providing a continuous flow of solvent may complete a single step for removing all the coating. 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 the complete removal of the coating.

Images

Coating Removal, Solvent Method

The area requiring coating removal is identified.

Apply high-temperature tape to outline the area where the coating needs to be removed.

Dip the end of a foam swab in a stripping solution and apply a small amount to the coating to be removed.

Neutralize or clean the stripped area and dry.