IPC 7711A.pdf - 第252页

2. Expose CAD generated additive conductor patterns of new conductor revision in isolation layer, copper and solder screens. 3 Print and cure isolation layer of protective epoxy. 4 Print, metalize and cure the new conduc…

OUTLINE

This modification/repair conductive pattern is fabricated via a solder/copper com-

posite of screen printable polymer thick film (PTF). The interconnects are established

at conductor lands and through hole locations of the original conductor. Electrical

continuity is optimized between two or more points of interconnection by solder

fusion of the new conductor pattern to the original etched PCB pattern.

NOTE

This modification/repair method is UL recognized, Type 1 94-V-0. It is compatible

with both digital and analog printed wiring board applications and it has resistance

of less than 3.0 milliohms/sq. It consists of greater than 90% copper and solder. The

resin system employed is thermal setting and adhesion of approximately 1.5 kg on

a 6 mm x 0.6 mm wide strip. It is typically applied to either or both sides of printed

wiring boards on thru-hole or surface mount PCB’s prior to assembly, without any

final solder resist coating. (Line resist coating can be applied and it is considered

optional.)

CAUTION

This modification/repair method can be employed on a single-sided, double-sided or

a multilayer printed wiring board. Its primary application is for signal carrying conduc-

tors. New or additional power distribution should be designed into the new conduc-

tor pattern on the basis of 0.25 mm of line width 2.6 amps of current required, up to

a maximum of 3.4 amps. When applying this method to the wave solder side or a

thru-hole printed wiring board, it should be covered with a solder (line) resist.

REFERENCES

2.1 Handling Electronic Assemblies

2.2 Cleaning

2.5 Baking and Preheating

TOOLS AND MATERIALS

Screen printer/screens with matalizer and IR belt ovens

Modification/repair master artwork

Conductive Ink, directly solderable

SMT compatible solder paste

IR solder reflow (fuse) belt oven

Flux cleaner, deionized water

Electronic multi-point tester

PROCEDURE

1. Convert conductor design revision via CAD to additive layer conductor pattern

including vias to be exposed and etch deletes to be performed.

Figure 1 Isolation layer.

Figure 2 Copper ink is applied.

Figure 3 Solder ink fused to copper

ink.

7721A

Repair and

Modification of

Printed Boards and

Electronic Assemblies

Revision:

Date: 2/98

Conductor Repair/

Modification, Conductive

Ink Method

Number: 4.2.6

Product Class: R, F, C

Skill Level: Expert

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

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

2. Expose CAD generated additive conductor patterns of new conductor revision

in isolation layer, copper and solder screens.

3 Print and cure isolation layer of protective epoxy.

4 Print, metalize and cure the new conductive ink pattern which establishes the

modified/repaired conductor.

5. Print the SMT compatible solder paste on to the cured conductive ink pattern,

totally encompassing the underlying material.

6 Fuse the printed solder paste to form the electrical optimization of the new con-

ductor and the interconnection to the original etched conductor. See reflow sol-

dering (IPC-J-STD-001).

CAUTION

Care should be taken not to add any solder to any unmodified or un-repaired areas

on the printed wiring board. All solder flux residue should be removed to meet IPC-

TM-650, Test Methods 2.3.25 and 2.3.26, ionic contamination requirements.

EVALUATION

Visually examine and conduct dimensional measurement of conductor width and

spacing. Ring-out for electrical continuity to detect for ‘shorts’ or ‘opens.’ This test-

ing can be affected manually via continuity meter, automated electronic point-to-

point tester or via a universal bed of nails electronic tester.

NOTE

Additive Conductor Modification Operations has become an industry standard for

production quantities of PCB modification/repair revisions.

NOTE

Because of the expert level of workmanship required, qualified vendors of the ser-

vice should be considered or the acquisition of dedicated in-house systems and

personnel to perform this work.

NOTES

IPC-7721A

Number: 4.2.6

Revision:

Date: 2/98

Subject: Conductor Repair/Modiﬁcation, Conductive Ink 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 replace damaged or missing conductors on internal layers of

multilayer printed wiring boards.

CAUTION

The conductor widths, spacing and current carrying capacity must not be reduced

below allowable tolerances.

CAUTION

The overlap joint used in this method may cause problems with high frequency cir-

cuitry.

CAUTION

This procedure is complicated and should be attempted only by properly skilled

repair personnel using the best tools and equipment.

REFERENCES

2.1 Handling Electronic Assemblies

2.2 Cleaning

2.5 Baking and Preheating

2.6 Epoxy Mixing and Handling

TOOLS AND MATERIALS

Ball Mills

Buffer

Conductor Foil Jumpers

Cleaner

Cleaning Wipes

Color Agent

Epoxy

Hand Held Drill

Heat Lamp

Polyimide Tape

Knife

Liquid Flux

Microscope

Oven

Scraper

Solder

Soldering Iron

PROCEDURE

1. Locate and determine the coordinates where the repair is to be made. Use films

or master drawings of the board as needed.

NOTE

Obtain as much information as possible on the conductive and non-conductive

layers prior to starting the procedure.

2. Remove components from the immediate area if necessary and clean the area.

Figure 1 Milling into multilayer board

to expose the damaged conductors.

Figure 2 A high quality, hand held

drill.

Figure 3 Remove the remaining board

material with a knife.

Figure 4 Conductor foil jumper in

place ready to be soldered.

7721A

Repair and

Modification of

Printed Boards and

Electronic Assemblies

Revision:

Date: 2/98

Conductor Repair,

Inner Layer Method

Number: 4.2.7

Product Class: R, F

Skill Level: Expert

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

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