IPC 7711A.pdf - 第269页

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 printed wiring board sur- face using a commercially available epoxy. CAUTION…

8. Select a bonding tip with a shape to match the shape of the lifted land.

NOTE

The bonding tip should be as small as possible but should completely cover the

entire surface of the new land.

9. Position the printed wiring board so that it is flat and stable. Gently place the hot

bonding tip onto the tape covering the new land. Apply pressure and heat as

recommended in the manual of the repair system or repair kit. (See Figure 3).

10. After the bonding cycle remove the tape used for alignment. The film is fully

cured. Carefully clean the area and inspect the land.

NOTE

Double sided and multilayer printed wiring boards, may require an eyelet to

restore the through connection. Refer to section 5.0 Plated Hole Procedures.

11. Carefully remove any excess bonding film 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.

12. Install the proper component and solder in place.

NOTE

This method is used to repair a lifted land, but the repaired land may 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.

13. Replace surface coating to match prior coating as required.

EVALUATION

1. Visual examination and tape test per IPC-TM-650, Test Method 2.4.1.

2. Electrical tests as applicable.

NOTES

IPC-7721A

Number: 4.4.2

Revision:

Date: 2/98

Subject: Lifted Land Repair, Film Adhesive Method

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Provided by IHS under license with IPC

Not for Resale

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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 printed wiring board sur-

face using a commercially available 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. If a component is not

installed, a wire clinched to both sides of the printed wiring board may be used.

CAUTION

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

aged see appropriate procedure.

NOTE

This method uses commercially available replacement lands. The new lands are fab-

ricated 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

Ball mills or drills

Buffer

Cleaner

Epoxy

Heat Lamp

Polyimide Tape

Knife

Liquid Flux

Microscope

Replacement Lands

Scraper

Solder

Soldering Iron

Tweezers

Wipes

PROCEDURE

1. Clean the area.

2. Remove the defective land and a short length of the connecting conductor if

any. (See Figure 1.)

Figure 1 Remove the defective land

and solder resist from the conductor.

Figure 2 Select a replacement land

that matches the missing land.

Figure 3 Cut out the replacement

land.

Figure 4 Place the new land in place

using tape.

7721A

Repair and

Modification of

Printed Boards and

Electronic Assemblies

Revision:

Date: 2/98

Land Repair,

Epoxy Method

Number: 4.5.1

Product Class: R, F

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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Not for Resale

No reproduction or networking permitted without license from IHS

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3. Use the knife and scrape off any epoxy residue, contamination or burned mate-

rial 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 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 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 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 allow-

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

(See Figure 3.)

NOTE

The new replacement land may be trimmed from 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 Polyimide tape over the top surface of the land. Place the new

land into position on the printed wiring board surface using the tape to aid in

alignment. (See Figure 4.)

12. Cure the epoxy per the manufacturer’s instructions.

13. After the epoxy has cured, remove the tape used for the alignment. Carefully

clean the area and inspect the new land for proper alignment.

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.

14. Remove tape and clean the area.

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

manufacturer’s recommended instructions.

NOTE

Additional epoxy can be applied around the perimeter of the new land to pro-

vide additional bond strength.

CAUTION

Some components may be sensitive to high temperature.

16. 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.

Figure 5 Completed repair.

IPC-7721A

Number: 4.5.1

Revision:

Date: 2/98

Subject: Land Repair, Epoxy 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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