4.7.2 Surface Mount Pad Repair, Film Adhesive Method

Clean the area.

Remove the defective pad and a short length of the connecting circuit. (See Figure 1).

Use a knife and scrape off any epoxy residue, contamination or burned material from the board surface.

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

Clean the area.

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.

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.

Select a replacement surface mount pad that most closely matches the surface mount pad to be replaced. If a special size or shape is needed they can be custom fabricated. (See Figure 2).

Note
New surface mount pads are fabricated from copper foil. The foil is plated on the top side with solder, and an adhesive bonding film is applied to the bottom side.

Before trimming out the new pad carefully scrape off the adhesive bonding film from the solder joint connection area on the back of the new pad. (See Figure 3).

Caution
Scrape off the epoxy backing only from the joint connection area. When handling the replacement contact, avoid touching the epoxy backing with your fingers or other materials that may contaminate the surface and reduce the bond strength.

Cut out and trim the new pad. 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).

Place a piece of Kapton tape over the top surface of the new pad. Place the new pad into position on the circuit board surface using the Kapton tape to help in alignment. (See Figure 5).

Select a bonding tip with a shape to match the shape of the new pad. See bonding tip chart in the replacement parts section of the manual provided with the repair system or repair kit.

Note
The tip used for bonding should be as small as possible but should completely cover the entire surface of the new pad.

Position the circuit board so that it is flat and stable. Gently place the hot bonding tip onto the kapton tape covering the new pad. Apply pressure as recommended in the manual of the repair system or repair kit for 5 seconds to tack the new pad 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 pad to slide out of position.

Gently place the bonding tip directly onto the new pad. Apply pressure as recommended in the manual of the repair system or repair kit for an additional 30 seconds to fully bond the pad. After the bonding cycle remove the tape used for alignment. The new pad is fully cured. Carefully clean the area and inspect the new pad for proper alignment.

If the new pad 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 pad 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 pad 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.

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

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

Caution
Some components may be sensitive to high temperature.

Apply surface coating to match prior coating as required.

Visual examination.

Measurement of new pad width and spacing.

Electrical continuity measurement.