4.5.1 Land Repair, Epoxy Method

Printed Board Type: R/F
Skill Level: Advanced
Conformance Level: Medium
Revision: D
Revision Date: Jul 7, 2000

OUTLINE

Damaged Land

This method is used to replace damaged and lifted lands. The damaged lands are replaced with new lands. The new lands are bonded to the circuit board surface using epoxy.

CAUTION
This method is used to replace a damaged or missing land, but the new land will not have an intermetallic connection to the remaining plated hole. The solder joint of the replaced component will restore the electrical connection.

CAUTION
It is essential that the board surface be smooth and flat. If the base board is damaged see appropriate procedure.

NOTE
This method uses new lands that are fabricated from copper foil. They are available in hundreds of sizes and shapes and are generally supplied solder plated. If a special size or shape is needed it can be custom fabricated.  

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
2.5	Baking and Preheating
2.7	Epoxy Mixing and Handling
IPC7721 4.5.1	Land Repair, Epoxy Method

Figure 1: Remove the defective land and remove soldermask from the connecting circuit.

TOOLS & MATERIALS
Bonding System
Circuit Frames, Lands
Cleaner
Convection Oven
Epoxy
Flux, Liquid
Knife
Land Repair Kit
Microscope
Scraper
Solder
Soldering Iron
Tape, Kapton
Tweezers
Wipes

PROCEDURE

1. Figure 2: Select a replacement land that matches the missing land.

   Clean the area
   
   
2. Remove the defective land and a short length of the connecting circuit if any. (See Figure 1).
   
   
3. Use the knife and scrape off any epoxy residue, contamination or burned material from the board surface.

   
   CAUTION
   Abrasion operations can generate electrostatic charges. 
   
   

4. Scrape off any solder mask or coating from the connecting circuit. (See Figure 1).
   
   

5. Figure 3: Cut out the replacement land.

   Clean the area
   
   
6. Apply a small amount of liquid flux to the connection area on the board surface and tin with solder. Clean the area. The length of the overlap solder connection should be a minimum of 2 times the circuit width.
   
   
7. The area for the new pad on the board surface must be smooth and flat. If internal fibers of the board are exposed or if there are deep scratches in the surface they should be repaired. Refer to appropriate procedure.
   
   
8. Select a replacement land that most closely matches the land to be replaced. (See Figure 2).
   
   
9. Cut out and trim the new land. Cut the length to provide the maximum allowable circuit overlap for soldering. Minimum 2 times the circuit width. (See Figure 3).

   
   NOTE
   The new replacement land may be trimmed from copper sheet. 
   
   

10. Figure 4: Place the new land in place using Kapton tape.

    Mix the epoxy and apply a small amount to the surface where the new land will be placed.
    
    

11. Place a piece of Kapton tape over the top surface of the land. Place the new land into position on the circuit board surface using the Kapton tape to aid in alignment. (See Figure 4).
    
    
12. Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling.
    
    
13. After the epoxy has cured, remove the Kapton tape used for the alignment. Carefully clean the area and inspect the new land for proper alignment.
    
    
14. If the new land has a connecting circuit apply a small amount of liquid flux to the lap solder joint connection area and solder the circuit from the new land to the circuit on the circuit board surface. Use minimal flux and solder to ensure a reliable connection. Tape may be placed over the top of the new land to prevent excess solder.

    
    NOTE
    If the configuration permits, the overlap solder joint connection should be a minimum of 3.00 mm (0.125") from the related termination. This gap will minimize the possibility of simultaneous reflow during soldering operations. Refer to 7.1 Soldering Basics. 
    
    

15. Figure 5: Completed repair.

    Remove Kapton tape and clean the area.
    
    

16. Mix the epoxy and coat the lap solder joint connections. Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling.

    
    NOTE
    Additional epoxy can be applied around the perimeter of the new land to provide additional bond strength.

    
    CAUTION
    Some components may be sensitive to high temperature. 
    
    

17. Carefully remove any excess epoxy inside the plated hole using a ball mill or drill bit. Turn the ball mill or drill bit by hand to prevent damage to the wall of the plated through hole.
    
    

18. Install the proper component and solder in place.

    
    NOTE
    This method is used to replace a damaged or missing land, but the new land will not have an intermetallic connection to the remaining plated hole. The solder joint of the replaced component will restore the integrity of the electrical connection or an eyelet or buss wire may be used. See Plated Hole Repair Procedures. 
    
    

19. Apply surface coating to match prior coating as required.

EVALUATION

1. Visual examination.
   
   
2. Measurement of new pad width and spacing.
   
   
3. Electrical continuity measurement.