IPC 7711A - 第296页

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…

OUTLINE

This method is used to replace damaged surface mount pads with new dry film,

adhesive backed pads. The new pads are bonded to the printed wiring board sur-

face using a specially designed bonding press or bonding iron.

CAUTION

It is essential that the board surface be smooth and flat. If the base material is dam-

aged see appropriate procedure.

NOTE

This method uses commercially available replacement surface mount pads. The new

pads 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

they can be custom fabricated.

REFERENCES

2.1 Handling Electronic Assemblies

2.2 Cleaning

2.5 Baking and Preheating

2.6 Epoxy Mixing and Handling

TOOLS & MATERIALS

Bonding Iron

Bonding System

Bonding Tips

Cleaner

Epoxy

Heat Lamp

Polyimide Tape

Knife

Liquid Flux

Microscope

Oven

Replacement Surface

Mount Pads

Scraper

Solder

Soldering Iron

Tweezers

Wipes

PROCEDURE

1. Clean the area.

2. Remove the defective pad and a short length of the connecting circuit. (See

Figure 1.)

3. Use a knife and scrape off any epoxy residue, contamination or burned material

from the board surface.

CAUTION

Abrasion operations can generate electrostatic charges.

Figure 1 Remove the defective

surface mount pad and soldermask.

Figure 2 Scrape off solder resist.

Figure 3 Scrape off the adhesive

bonding ﬁlm from solder joint area.

Figure 4 Cut out the new surface

mount pad.

7721A

Repair and

Modification of

Printed Boards and

Electronic Assemblies

Revision:

Date: 2/98

Surface Mount Pad

Repair, Film Adhesive

Method

Number: 4.7.2

Product Class: R, F, C

Skill Level: Advanced

Level of Conformance: High

Material in this manual was voluntarily established by Technical Committees of IPC. This material is advisory only and its use

or adaptation is entirely voluntary. IPC disclaims all liability of any kind as to the use, application, or adaptation of this material.

Users are also wholly responsible for protecting themselves against all claims or liabilities for patent infringement. Equipment

referenced is for the convenience of the user and does not imply endorsement by IPC.

Page1of4

Provided by IHS under license with IPC

Not for Resale

No reproduction or networking permitted without license from IHS

--``,``,-`-`,,`,,`,`,,`---

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

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

Provided by IHS under license with IPC

Not for Resale

No reproduction or networking permitted without license from IHS

--``,``,-`-`,,`,,`,`,,`---