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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 hand held 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
Tools and Materials
CircuitMedic Part
Abrader
Mild abrasive for removing oxides and contaminates from conductive surfaces.
CircuitMedic Part
Alcohol Swab
Self-saturating Isopropyl alcohol swab. Squeeze handle to release alcohol.
CircuitMedic Part
Ball Mills, Abrasives, Cutting Tools
Ball mills, abrasives and cutting tools for working on circuit boards.
Cleaner
Cleaner
General purpose cleaner for removing contamination.
CircuitMedic Part
Cleaning Brushes
Disposable brushes for use with solvents for cleaning and application of coatings.
CircuitMedic Part
Knife with #16 Blades
A must-have tool for precise cutting, scraping and trimming.
Microscope
Microscope
It is a challenge to undertake precision repair without a good microscope.
CircuitMedic Part
Micro Drill System
Versatile power tool for milling, drilling, grinding, cutting and sanding circuit boards.
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 hand held 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 complete removal of coating.

Procedure for reference only.