2.3.5 Coating Removal, Grinding/Scraping Method

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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 typically used when a grinding technique is preferred. Various rotary abrasive materials, including ball mills, may be required. The coating must first be identified to determine the appropriate coating removal procedure. 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, Materials and Supplies

Abrader
Mild abrasive for removing oxides and contaminants.

Ball Mills, Abrasives, Cutting Tools
Ball mills, abrasives and cutting tools for working on circuit boards.

Flex-Rack PCB Holder
Sturdy rack for PCBs used for rework and positioning.

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

Cleaner
General purpose cleaner for removing contamination.

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

Micro Drill System
Versatile power tool for milling, drilling, grinding, cutting and sanding.

Microscope
Precision microscope with stand and lighting for work and inspection.

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

Scraper, Curved Tip
Hardened stainless steel tip for scraping solder mask and removing defects.

Wipes
Nonabrasive, low-linting wipes for cleanup.

Procedure

Scraping

Clean the area.
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)
Remove all loose material and clean the area.

Grinding

Clean the area.
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)
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 remove the remaining thin coating by scraping.

Evaluation

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

Images and Figures

Coating Removal, Grinding/Scraping Method

Figure 1. The area requiring coating removal is identified.

Figure 2. Scrape away damaged or unwanted coating with a knife or scraper.

Figure 3. Rubberized abrasives are best used to remove thin, hard coatings.

Figure 4. Rotary brushes are best used to remove soft coatings.

Figure 5. Continue as needed until the required coating material is removed,

2.3.5 Coating Removal, Grinding/Scraping Method

Mechanically remove conformal coatings using precision grinding or scraping techniques. Includes tool selection, depth control and surface protection methods to avoid damage to traces and laminate. Minimum Skill Level: Expert Conformance Level: High

Mechanically remove conformal coatings using precision grinding or scraping techniques. Includes tool selection, depth control and surface protection methods to avoid damage to traces and laminate.

Minimum Skill Level: Expert
Conformance Level: High