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2.3.5 Coating Removal, Grinding/Scraping Method

 
Outline
This coating removal method uses various grinding and scraping tools, depending on the composition of the coating material. A knife or dental-style scraper is normally used when a scraping method is desired. A handheld drill is normally used when a grinding technique is desired. A wide variety of rotary abrasive materials, including ball mills, may be required.

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

Caution: Abrasion operations can generate electrostatic charges.

Minimum Skill Level - Expert
Recommended for technicians with advanced soldering and component rework skills and extensive experience in most repair/rework procedures.

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 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 2.3.5 Coating Removal, Grinding/Scraping Method
Kits and Systems
110-4106
Micro Drill System
Versatile power tool for milling, drilling, grinding, cutting and sanding circuit boards.
201-7100
Precision Tool Set
Nine precision-crafted tools for detailed circuit board work.
Tools and Materials
115-3136
Abrader
Mild abrasive for removing oxides and contaminants.
cutting
Ball Mills, Abrasives, Cutting Tools
Ball mills, abrasives and cutting tools for working on circuit boards.
235-2106-5
Cleaning Brushes
Disposable brushes for solvent cleaning and application of coatings.
355-0614
Knife with #16 Blades
A must-have tool for precise cutting, scraping and trimming.
335-3197
Scraper, Curved Tip
Hardened stainless steel tip for scraping solder mask and removing defects.
Additional Items and Supplies
Cleaner
Cleaner
General purpose cleaner for removing contamination.
Microscope
Microscope
Precision microscope with stand and lighting for work and inspection.
Wipes
Wipes
Nonabrasive, low-linting wipes for cleanup.
Images and Figures
2.3.5 Coating Removal, Grinding/Scraping Method
Coating Removal Required At Outlined Area
2.3.5 Coating Removal, Grinding/Scraping Method
Figure 1: Scrape away damaged or unwanted coating with a knife or scraper.
2.3.5 Coating Removal, Grinding/Scraping Method
Figure 2: Rubberized abrasives are best used to remove thin, hard coatings.

2.3.5 Coating Removal, Grinding/Scraping Method
Figure 3: Rotary brushes are best used to remove soft coatings.
2.3.5 Coating Removal, Grinding/Scraping Method
Figure 4: Removal complete.
2.3.5 Coating Removal, Grinding/Scraping Method
Figure 5: Micro-Drill System.

Procedure - Scraping
  1. Clean the area.
  2. Remove the damaged or unwanted coating or solder mask using a knife or scraper. Hold the blade perpendicular to the coating and scrape from side to side until the desired material is removed. (See Figure 1)
  3. Remove all loose material and clean the area.
Procedure - Grinding
  1. Clean the area.
  2. Insert an abrasive tip into the handheld drill. Abrade away the damaged or unwanted coating. Move the tool from side to side to prevent damage to the circuit board surface. (See Figure 2)
  3. Remove all loose material and clean the area.
Note: Rubberized abrasives of the proper grade and grit are ideally suited for removing thin hard coatings from flat surfaces but not for soft coatings since these would cause the abrasive to "load up" with coating material and become ineffective.

Rotary brushes are better suited than rubberized abrasives on contoured or irregular surfaces, such as soldered connections, etc. since the bristles will conform to surface irregularities while removing hard or soft coatings. (See Figure 3)

Note: The procedure for removing thick coatings is primarily to reduce their thickness to a thin coating and then to remove the remaining thin coating by the scraping method.

Evaluation
  1. Visual examination or UV light may be used to verify the complete removal of the coating.
Procedure for reference only.