IPC 7711A - 第264页

4. Mill into the printed wiring board surface adjacent to the plated hole. The milled holes should be aligned directly above the internal spoke connections. Mill down just deep enough to sever the internal spokes connect…

OUTLINE

This method is used on multilayer printed wiring boards or assemblies to disconnect

an internal connection at a plated hole. A precision drill press is used with a carbide

end mill to make precise cuts at the spokes or internal conductors extending from

the hole.

CAUTION

Extreme care must be taken to prevent damage to adjacent conductors. A micro-

scope must be used during milling when extreme accuracy is required.

REFERENCES

2.1 Handling Electronic Assemblies

2.2 Cleaning

2.5 Baking and Preheating

2.6 Epoxy Mixing and Handling

TOOLS AND MATERIALS

Cleaner

Cleaner Wipes

Color Agent

Continuity Meter

End Mills, Carbide

Epoxy

Epoxy Dispensing System

Heat Lamp

Polyimide Tape

Oven

Microscope

Pin Clamps

Precision Drill Press

PROCEDURE

1. Identify the hole that requires rework and clean the area.

2. Mark the coordinates on the board surface and place the printed wiring board

on the base plate of the precision drill press. (See Figure 1.)

3. Select the appropriate size end mill or drill and insert it into the chuck of the

precision drill press. The cutting tool should be approximately 0.010 - 0.025 mm

greater than the width of the spoke or conductor to be cut. (See Table 1 for

Standard End Mill Sizes.) Set speed to high.

CAUTION

Abrasion operations can generate electrostatic charges.

NOTE

End mills are normally single end, two or four flute high grade solid carbide.

Figure 1 Precision drill press with

base plate.

Figure 2 Plated-through hole with

inner layer spoke connections.

Figure 3 Mill adjacent to the plated

hole to sever spoke connections.

7721A

Repair and

Modification of

Printed Boards and

Electronic Assemblies

Revision:

Date: 2/98

Deleting Inner Layer

Connection At A Plated

Hole, Spoke Cut Method

Number: 4.3.4

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.

Page1of2

Provided by IHS under license with IPC

Not for Resale

No reproduction or networking permitted without license from IHS

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

4. Mill into the printed wiring board surface adjacent to the plated hole. The milled

holes should be aligned directly above the internal spoke connections. Mill down

just deep enough to sever the internal spokes connecting the plated hole to the

internal plane. A microscope must be used for accuracy. Up to 4 milled holes

may be required. Do not drill deeper than needed. (See Figure 3.)

5. Blow away material with air and clean the area.

6. Check continuity to be sure that the internal connection has been deleted. Also

check the continuity and inspect the neighboring conductors to make sure that

none of them have been severed or damaged.

7. Mix the epoxy.

8. Fill the holes with epoxy up to and flush with the surface. Remove excess epoxy.

NOTE

A slight overfill of epoxy may be desired to allow for shrinkage when epoxy

cures.

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

CAUTION

Some components may be sensitive to high temperature.

10. Clean the area.

EVALUATION

1. Visual and electrical examination as required.

NOTES

Table 1 Standard End Mill Sizes

0.381 mm Diameter

0.635 mm Diameter

0.812 mm Diameter

1.016 mm Diameter

1.143 mm Diameter

1.397 mm Diameter

1.575 mm Diameter

2.362 mm Diameter

3.175 mm Diameter

IPC-7721A

Number: 4.3.4

Revision:

Date: 2/98

Subject: Deleting Inner Layer Connection At A Plated Hole, Spoke

Cut Method

Page2of2

Provided by IHS under license with IPC

Not for Resale

No reproduction or networking permitted without license from IHS

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

OUTLINE

This method is used to rebond a lifted land. Liquid epoxy is inserted under and

around the land to bond it back down to the printed wiring board surface.

REFERENCES

2.1 Handling Electronic Assemblies

2.2 Cleaning

2.5 Baking and Preheating

2.6 Epoxy Mixing and Handling

TOOLS AND MATERIALS

Cleaner

Epoxy

Heat Lamp

Polyimide Tape

Knife

Oven

Wipes

PROCEDURE

1. Clean the area.

2. Remove any obstructions that prevent the lifted land from making contact with

the base board surface.

CAUTION

Be careful while cleaning and removing all obstructions, not to stretch or dam-

age the lifted land.

3. Mix the epoxy.

4. Carefully apply a small amount of epoxy under the entire length of the lifted land.

The tip of a knife or scraper may be used to apply the epoxy. (See Figure 1.)

5. Place a piece of Polyimide tape over the lifted land and press the land down into

the epoxy and into contact with the base board material. (See Figure 2.)

6. Apply additional epoxy to the surface of the lifted land and to all sides as

needed.

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

CAUTION

Some components may be sensitive to high temperatures.

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.

8. 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 1 Apply epoxy under the entire

length of the lifted land.

Figure 2 Place tape over the lifted

land.

Figure 3 Completed repair.

7721A

Repair and

Modification of

Printed Boards and

Electronic Assemblies

Revision:

Date: 2/98

Lifted Land Repair,

Epoxy Method

Number: 4.4.1

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.

Page1of2

Provided by IHS under license with IPC

Not for Resale

No reproduction or networking permitted without license from IHS

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