2.3.5 Coating Removal, Grinding/Scraping Method

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

Coating Removal Required At Outlined Area

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.

ACCEPTABILITY REFERENCES
IPC-A-600 2.0	Externally Observable Characteristics
IPC-A-610 10.0	Laminate Conditions
PROCEDURE REFERENCE
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

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

TOOLS & MATERIALS
Ball Mills
Brushes
Cleaner
Micro-Drill System
Microscope
Knife
Rubberized Abrasives
Scraper
Wipes
Wood Sticks

PROCEDURE SCRAPING

1. Clean the area.
   
   

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

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

   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).

Figure 4: Removal complete.

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.
   
   

   Figure 5: Micro-Drill System.