Circuit Board Repair Guide > Basic Circuit Board Repair Procedures > 2.3.5 Coating Removal Using Grinding / Scraping Method

Coating Removal Using Grinding / Scraping Method

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Repair a Conductor | Plated Hole Repair | Base Board Repair | Replace Solder Mask or Coatings

This coating removal procedure covers the use of various grinding and scraping tools to remove coatings.

A knife or dental style scraper is used when a scraping method is desired. A hand held drill is 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. Coating Removal, Identification of Coatings.

Caution
Abrasion operations can generate electrostatic charges.

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

Related Procedure References
CTC 1.0 Foreword - Circuit Board Repair Guide
CTC 2.1 Handling Electronic Assemblies
CTC 2.2.1 How to Clean a Circuit Board
CTC 2.2.2 Cleaning Circuit Boards, Aqueous Batch Process
CTC 2.4.1 Replace Solder Mask or Coatings on Printed Circuit Boards
CTC 2.4.2 Replace Conformal Coatings and Encapsulants on Circuit Boards
IPC 7721 2.3.5 Coating Removal, Grinding/Scraping Method

Tools and Materials
Ball Mills
Brushes
Cleaner
Micro Drill System
Microscope
Knife
Rubberized Abrasives
Scraper
Wipes
Wood Sticks
 
Coating removal required at outlined area
Coating Removal Required
At Outlined Area


Printed Board Type: R/F/W/C  |  Skill Level: Expert  |  Conformance Level: High  |  Rev.: E  |  Rev. Date: Jul 7, 2000

Scrape damaged coating with knife

Fig. 1: Scrape away damaged or unwanted coating with a knife or scraper.


Rubberized abrasives to remove thin, hard coatings

Fig. 2: Rubberized abrasives are
best used to remove thin, hard
coatings.


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 remove soft coatings

Fig. 3: Rotary brushes are best
used to remove soft coatings.


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.

Verify complete removal of coating

Fig. 4: Coating removal complete.


Evaluation
   
1.  Visual examination or UV light may be used to verify complete removal of  coating.
   
Micro Drill System used for milling, drilling, grinding, cutting and sanding circuit boards

Fig. 5: Micro Drill System.
 




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