IPC 7711A - 第291页

OUTLINE This method is used to replace damaged surface mount pads with commercially available replacement pads. The new pads are bonded to the printed wiring board surface using liquid epoxy. CAUTION It is essential that…

NOTES

IPC-7721A

Number: 4.6.3

Revision:

Date: 2/98

Subject: Edge Contact Repair, Plating Method

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Provided by IHS under license with IPC

Not for Resale

No reproduction or networking permitted without license from IHS

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OUTLINE

This method is used to replace damaged surface mount pads with commercially

available replacement pads. The new pads are bonded to the printed wiring board

surface using liquid epoxy.

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

Buffer

Cleaner

Epoxy

Heat Lamp

Knife

Polyimide Tape

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 conductor. (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.

4. Scrape off any solder resist or coating from the connecting conductor. (See Fig-

ure 2.)

Figure 1 Remove pad.

Figure 2 Scrape off solder resist.

Figure 3 Cut out new pad.

Figure 4 Position pad using tape.

7721A

Repair and

Modification of

Printed Boards and

Electronic Assemblies

Revision:

Date: 2/98

Surface Mount Pad

Repair, Epoxy Method

Number: 4.7.1

Product Class: R, F, C

Skill Level: Advanced

Level of Conformance: Medium

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.

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Provided by IHS under license with IPC

Not for Resale

No reproduction or networking permitted without license from IHS

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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 conductor 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.

9. Cut out and trim the new pad. Cut the length to provide the maximum allow-

able conductor overlap for soldering. Minimum 2 times the conductor width.

(See Figure 3.)

NOTE

The new replacement surface mount pad may be trimmed from copper sheet.

10. Mix the epoxy and apply a small amount to the surface where the new pad will

be placed.

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. (See Figure 4.)

12. Cure the epoxy per the manufacturers instructions.

CAUTION

Some components may be sensitive to high temperature.

13. After the epoxy has cured remove the Polyimide tape used for alignment. Care-

fully clean the area and inspect the new pad for proper alignment.

14. If the new pad has a connecting conductor apply a small amount of liquid flux

to the lap solder joint connection area and solder the conductor from the new

pad to the conductor 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.

15. Mix epoxy and coat the lap solder joint connections. 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.

16. Apply surface coating to match prior coating as required.

Figure 5 Completed repair.

IPC-7721A

Number: 4.7.1

Revision:

Date: 2/98

Subject: Surface Mount Pad Repair, Epoxy Method

Page2of4

Provided by IHS under license with IPC

Not for Resale

No reproduction or networking permitted without license from IHS

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