IPC 7711A.pdf - 第297页
14. After the timed bonding cycle lift the bonding iron and remove the tape used for alignment. The pad is fully cured. Carefully clean the area and inspect the new pad for proper alignment. 15. If the new pad has a conn…
4. Scrape off any solder resist or coating from the connecting circuit. (See Figure
2.)
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 in the
surface, they should be repaired. Refer to appropriate procedure.
8. Select a commercially available 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.
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.
9. 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 han-
dling the replacement contact, avoid touching the epoxy backing with your fin-
gers or other materials that may contaminate the surface and reduce the bond
strength.
10. 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.)
11. Place a piece of Polyimide tape over the top surface of the new pad. Place the
new pad into position on the printed wiring board surface using the tape to help
in alignment. Leave the tape in place during the bonding cycle. (See Figure 5.)
12. Select a commercially available 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.
13. Position the printed wiring board so that it is flat and stable. Gently place the hot
bonding tip onto the tape covering the new pad. Apply pressure as recom-
mended in the manual of the repair system or repair kit. (See Figure 6.)
CAUTION
Excessive bonding pressure may cause measling in the printed wiring board
surface or may cause the new pad to slide out of position.
Figure 5 Place the new surface mount
pad in place using tape.
Figure 6 Bonding system.
Figure 7 Completed repair.
IPC-7721A
Number: 4.7.2
Revision:
Date: 2/98
Subject: Surface Mount Pad Repair, Film Adhesive Method
Page2of4
Copyright Association Connecting Electronics Industries
Provided by IHS under license with IPC
Not for Resale
No reproduction or networking permitted without license from IHS
--``,``,-`-`,,`,,`,`,,`---
14. After the timed bonding cycle lift the bonding iron and remove the tape used for
alignment. The pad is fully cured. Carefully clean the area and inspect the new
pad for proper alignment.
15. 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 printed wiring 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 from the related termination. This gap will minimize the
possibility of simultaneous reflow during soldering operations.
16. Mix epoxy and coat the lap solder joint connection. Cure the epoxy per the
manufacturers recommended instructions.
NOTE
Additional epoxy can be applied around the perimeter of the new pad to pro-
vide additional bond strength.
CAUTION
Some components may be sensitive to high temperature.
17. 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.
IPC-7721A
Number: 4.7.2
Revision:
Date: 2/98
Subject: Surface Mount Pad Repair, Film Adhesive Method
Page3of4
Copyright Association Connecting Electronics Industries
Provided by IHS under license with IPC
Not for Resale
No reproduction or networking permitted without license from IHS
--``,``,-`-`,,`,,`,`,,`---
NOTES
IPC-7721A
Number: 4.7.2
Revision:
Date: 2/98
Subject: Surface Mount Pad Repair, Film Adhesive Method
Page4of4
Copyright Association Connecting Electronics Industries
Provided by IHS under license with IPC
Not for Resale
No reproduction or networking permitted without license from IHS
--``,``,-`-`,,`,,`,`,,`---