4.5.2 Land Repair, Film Adhesive Method

Procedure

1. 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. 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 on the surface, they should be repaired. Refer to the 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 a copper sheet.
9. 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 two times the circuit width. (See Figure 4)
11. Place a piece of High-Temperature 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. 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. 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. High-Temperature 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. Remove the tape and clean the area.
16. 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.
17. Carefully remove any excess bonding film 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 land width and spacing.
3. Electrical continuity measurement.