2.3.2 Coating Removal, Solvent Method

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.

Coating Removal Required
At Outlined Area

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

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.

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

Acceptability References
IPC-A-600	2.0	Externally Observable Characteristics
IPC-A-610	10.0	Laminate Conditions

Procedure References
CTC	1.0	Foreword
CTC	2.1	Handling Electronic Assemblies
CTC	2.2	Cleaning
CTC	2.3.1	Coating Removal, Identification of Coatings
CTC	2.4.1	Coating Replacement, Solder Mask
CTC	2.4.2	Coating Replacement, Conformal Coatings/Encapsulants
IPC 7721	2.3.2	Coating Removal, Solvent Method

Tools and Materials
Brushes
Coating Remover Solvent
Foam Swabs
Knife
Tape, Kapton
Thermal Parting Tool
Wood Sticks

Figure 1: Apply Kapton tape to outline area for coating removal.

Procedure - Local Spot Removal

1.	Apply Kapton tape to outline the area where the coating needs to be removed. (See Figure 1).

Figure 2: Apply solvent with a foam swab to remove coating.

	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.

Figure 3: Removal complete.

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.