Circuit Board Repair and Rework Guide > 2.0 Basic Procedures > 2.3.5 Coating Removal, Grinding / Scraping Method

2.3.5 Coating Removal, Grinding / Scraping Method

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

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 References
CTC	1.0	Foreword
CTC	2.1	Handling Electronic Assemblies
CTC	2.2.1	Cleaning, Local
CTC	2.2.2	Cleaning, Aqueous Batch Process
CTC	2.3.1	Coating Removal, Identification of Coatings
CTC	2.4.1	Coating Replacement, Solder Mask
CTC	2.4.2	Coating Replacement, Conformal Coatings/Encapsulants
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

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

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

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

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.

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.

Figure 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.

Figure 4: Removal complete.

Evaluation

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

Figure 5: Micro-Drill System.