4.5.1 Land Repair, Epoxy Method

Outline

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 baseboard 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.

Minimum Skill Level - Advanced

Conformance Level - Medium

Tools and Materials

Circuit Bond Epoxy Clear, superior strength epoxy in two-compartment plastic packages.

Circuit Frames Circuit Frames for surface mount pad, BGA pad and conductor repair.

Cleaner General purpose cleaner for removing contamination.

Flex-Rack PCB Holder Sturdy rack for PCBs used for rework and positioning.

High Temp Tape Discs High temperature polyimide tape discs, .50" diameter.

Knife with #16 Blades A must-have tool for precise cutting, scraping and trimming.

Microscope Precision microscope with stand and lighting for work and inspection.

Oven General purpose oven for drying, baking and curing epoxies.

Precision Tool Set Nine precision-crafted tools for detailed circuit board work.

Repair Skills Practice Kit Training kit to practice circuit board repair skills prior to testing for certification.

Scraper, Curved Tip Hardened stainless steel tip for scraping solder mask and removing defects.

Soldering Iron Properly maintained soldering iron and properly sized soldering iron tips.

Tweezers Multiple sizes and tip configurations of tweezers for various small parts handling needs.

Wipes Nonabrasive, low-linting wipes for cleanup.

Procedure

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 pad 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)
9. Cut out and trim the new land. Cut the length to provide the maximum allowable circuit overlap for soldering. Minimum two times the circuit width. (See Figure 3)
   Note: The new replacement land may be trimmed from a copper sheet.
10. Mix the epoxy and apply a small amount to the surface where the new land will be placed.
11. Place a piece of High-Temperature Tape over the top surface of the land. Place the new land into position on the circuit board surface using the 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 High-Temperature 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. Remove the 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 temperatures.
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.

Images

Land Repair, Epoxy Method

Remove the defective land and remove soldermask from the connecting circuit.

Select a replacement land that matches the missing land.

Cut out the replacement land.

Apply epoxy to the back surface and hold in place using hight temperature tape.

Completed repair.