IPC 7711A.pdf - 第274页

PROCEDURE 1. Clean the area. 2. Remove the defective land and a short length of the connecting conductor if any. (See Figure 1.) 3. Use the knife and scrape off any epoxy residue, contamination or burned mate- rial from …

OUTLINE

This method is used to replace damaged and lifted lands. The damaged lands are

replaced with new dry film, adhesive backed lands. The new lands are bonded to the

printed wiring board surface using a bonding press or bonding iron.

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 integrity of the electrical connection. If a com-

ponent 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 and have a dry film adhesive coating on the back. 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

Buffer

Cleaner

Epoxy

Heat Lamp

Polyimide Tape

Knife

Liquid Flux

Microscope

Replacement Lands,

Adhesive Backed

Scraper

Solder

Soldering Iron

Tweezers

Wipes

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 Scrape off the adhesive

bonding ﬁlm from solder joint area.

Figure 4 Cut out the new land.

7721A

Repair and

Modification of

Printed Boards and

Electronic Assemblies

Revision:

Date: 2/98

Land Repair,

Film Adhesive Method

Number: 4.5.2

Product Class: R, F

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

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

PROCEDURE

1. Clean the area.

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

any. (See Figure 1.)

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.)

NOTE

The new replacement land may be trimmed from copper sheet.

9. Before trimming out the new land carefully scrape off the adhesive film from the

solder joint connection area on the back of the new land. (See Figure 3.)

CAUTION

Scrape off the epoxy backing only from the joint connection area. When han-

dling the replacement land avoid touching the adhesive 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 land. Cut out from the plated side. Cut the length to

provide the maximum allowable conductor overlap for soldering. Minimum 2

times the conductor width. (See Figure 4.)

11. Place a piece of tape over the top surface of the new land. Place the new land

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

ment. Leave the tape in place during the bonding cycle. (See Figure 5.)

12. Select a bonding tip with a shape to match the shape of the new land.

NOTE

The Bonding Tip should be as small as possible but should completely cover the

entire surface of the new land.

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 land. Apply pressure as recom-

mended in the manual of the repair system or repair kit of the manufacturer.

(See Figure 6.)

Figure 5 Place the new land in place

using tape.

Figure 6 Bonding systems.

Figure 7 Completed land repair.

IPC-7721A

Number: 4.5.2

Revision:

Date: 2/98

Subject: Land Repair, Film Adhesive Method

Page2of4

Provided by IHS under license with IPC

Not for Resale

No reproduction or networking permitted without license from IHS

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

CAUTION

Excessive bonding pressure may cause measling in the printed wiring board

surface or the new conductor to slide out of position.

14. After the bonding cycle remove the tape used for alignment. The land is fully

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

15. If the new land 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

land 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 land 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. Remove tape and clean the area.

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

manufacturers 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.

18. Carefully remove any excess bonding film inside the plated hole using 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.

19. Install the proper component and solder in place.

NOTE

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 sol-

der 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 Pro-

cedures.

20. 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: 4.5.2

Revision:

Date: 2/98

Subject: Land Repair, Film Adhesive Method

Page3of4

Provided by IHS under license with IPC

Not for Resale

No reproduction or networking permitted without license from IHS

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