4.5.2 Land Repair, Film Adhesive Method

Printed Board Type: R/F
Skill Level: Advanced
Conformance Level: High
Revision: E
Revision Date: Mar 28, 2001

OUTLINE

Damaged Land

This method is used to replace damaged and lifted lands. The damaged lands are replaced with new dry film, adhesive backed lands. The new lands are bonded to the circuit board surface using a bonding press or bonding iron.

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 integrity of 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 and have a dry film adhesive coating on the back. 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
IPC772 4.5.2	Land Repair, Film Adhesive Method

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

TOOLS & MATERIALS
Bonding Iron
Bonding Tips
Bonding System
Circuit Frames, Lands
Cleaner
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: Scrape off the adhesive bonding film from solder joint area on the back of new 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 land 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).
   
   NOTE
   The new replacement land may be trimmed from copper sheet.
   
   

9. Figure 4: Cut out the new land. Cut from the plated side.

   Before trimming out the new land carefully scrape off the adhesive film from the solder joint connection area on the back of the new land. (See Figure 3).
   
   CAUTION
   Scrape off the epoxy backing only from the joint connection area. When handling the replacement land avoid touching the adhesive backing with your fingers or other materials that may contaminate the surface and reduce the bond strength.
   
   
10. Cut out and trim the new land. Cut out from the plated side. Cut the length to provide the maximum allowable circuit overlap for soldering. Minimum 2 times the circuit width. (See Figure 4).
    
    
11. Place a piece of Kapton tape over the top surface of the new land. Place the new land into position on the circuit board surface using the tape to aid in alignment. (See Figure 5).
    
    
12. Select a bonding tip with a shape to match the shape of the new land.
    
    NOTE
    The Bonding Tip should be as small as possible but should completely cover the entire surface of the new land.
    
    

13. Figure 5: Place the new land in place using High Temperature Tape.

    Position the circuit board so that it is flat and stable. Gently place the hot bonding tip onto the tape covering the new land. Apply pressure as recommended in the manual of the repair system or repair kit for 5 seconds to tack the land in place. Carefully peel off the tape. (See Figure 6).
    
    CAUTION
    Excessive bonding pressure may cause measling in the circuit board surface or may cause the new circuit to slide out of position.
    
    
14. Gently place the bonding tip directly onto the land. Apply pressure as recommended in the manual of the repair system or repair kit for an additional 30 seconds to fully bond the land. The bonding film is fully cured. After the bonding cycle remove the tape used for alignment. Carefully clean the area and inspect the land.
    
    
15. 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. Kapton tape may be placed over the top of the new land to prevent excess solder overflow.
    
    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.
    
    

16. Figure 6: Bond the new land with a Bonding System.

    Remove Kapton tape and clean the area.
    
    
17. Mix 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.
    
    

18. Carefully remove any excess bonding film inside the plated hole using 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.
    
    
19. 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.
    
    

20. Figure 7: Completed land repair.

    Apply surface coating to match prior coating as required.

EVALUATION

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