IPC 7711A.pdf - 第33页

OUTLINE Surface contaminants can significantly effect soldering, bond- ing, coating and the electrical characteristics of printed board and assemblies. This procedure outlines the cleaning meth- ods for printed wiring bo…

NOTES

IPC-7711A/7721A

Number: 2.1

Revision: A

Date: 5/02

Subject: Handling Electronic Assemblies

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Not for Resale

No reproduction or networking permitted without license from IHS

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OUTLINE

Surface contaminants can significantly effect soldering, bond-

ing, coating and the electrical characteristics of printed board

and assemblies. This procedure outlines the cleaning meth-

ods for printed wiring boards and assemblies.

REFERENCES

NAWCWPNS Final report for NON-ODS cleaning of electron-

ics and avionics report of October 10, 1995.

BACKGROUND

In the past few years, the Environmental Protection Agency

(EPA) has been actively involved in reducing the production of

chlorofluorocarbons (CFC’s). Through their efforts, and the

Montreal Protocol, the production of CFC’s have been frozen

to 1986 levels with requirements to further decrease to zero

production by the year 2000. The London Amendments (June

1990) to the protocol are even more restrictive.

Cleaning of the PCB is an important part of any rework/repair

process. The different cleaning processes are dependent

upon the type of flux used in the soldering process or the type

of contaminate to be removed. A general rule of thumb is ‘‘like

dissolves like,’’ which is a quick way of saying that usually

organic/nonpolar contaminants are best removed by nonpolar

solvents and inorganic/polar contaminants are best removed

by polar solvents.

A desirable cleaning medium should:

A. Not be harmful to employees or the environment.

B. Possess excellent wetting ability.

C. Dissolve and removes both soluble and particulate con-

taminants.

D. Be compatible with the PCB assembly.

E. Be stable during use.

INTRODUCTION

If rework/repair operations are performed in a facility that has

an automated cleaning systems (i.e., batch, in-line, aqueous,

semi aqueous, or solvent), then such equipment should be

used to clean the assembly.

If an automated system is not available, the cleaning method

that follows should be used to reduce surface contamination

prior to using adhesives, coating materials or soldering. A

cleaning step after soldering is used to ensure that surface

contaminants are not trapped beneath conformal coatings or

encapsulants, nor will they contribute to future functional

assembly problems.

LIMITATIONS

1. The ability of solvent based cleaning solutions to remove

flux residue containing polyglycols should be assessed

since not all solvent based cleaning solutions will remove

polyglycols.

2. A de-ionized (DI) water rinse should follow IPA/DI clean-

ing except that a water rinse for double sided printed wir-

ing boards with plated through holes may not be

required.

3. Potable (drinking) water should not be used as a final

rinse due to the potential of contaminating the printed

wiring board assembly with chlorine, fluorine and halides.

4. When automated cleaning is used for assemblies that

have been conformally coated, it is important that the

cleaning process is compatible with the type of coating

used and with any unsealed components. The coating

should be checked to ensure that the coating will not be

degraded by the cleaning process.

TOOLS AND MATERIALS

Black Light

Brush, Soft Bristles

Cleaner, Aqueous or

Semi-Aqueous

Containers

De-ionized Water (DI)

Gloves

Isopropyl Alcohol (IPA)

Oven

Wipes, Lint Free

PROCEDURE

CAUTION

Use clean gloves during this entire operation.

NOTE

To reduce solvent volumes, mixtures of IPA with water and

IPA with solvent are available in pressurized containers. The

propellants are HFC’s. These containers may be fitted with a

bristle brush spray attachments for additional cleaning action.

1. Clean the board in an Aqueous or Semi-Aqueous

cleaner, or pour approximately 10 ml per 4 square inches

of effected area.

Product Class: R, F, W, C

Skill Level: Intermediate

Level of Conformance: High

7711A/7721A

General Information and

Common Procedures

Revision:

Date: 2/98

Cleaning

Number: 2.2

Material in this manual, IPC-7711 Rework of Electronic Assemblies, 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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2. Scrub the board vigorously with a continually wet soft

bristle brush for 10 seconds.

3. Rinse the area with 10 ml per 26 square centimeters of

clean Isopropyl Alcohol to effectively remove all potentially

harmful residues.

4. Handle the board by the edges and blot the excess Iso-

propyl Alcohol with clean, lint free cloth.

5. Examine board visually for cleanliness. The use of a black

light will help detect contaminants that will fluoresce.

6. Dry boards in oven, if desired.

7. If the boards or assemblies are to be stored before use

or coating, remove them from the oven and allow to cool

until they can be handled. Place the boards or assem-

blies into self sealing bags with packages of desiccant.

EVALUATION

1. Visually examine and test for cleanliness using IPC-TM-

650, Test Method 2.3.25 or 2.3.26

NOTES

IPC-7711A/7721A

Number: 2.2

Revision:

Date: 2/98

Subject: Cleaning

Page2of2

Provided by IHS under license with IPC

Not for Resale

No reproduction or networking permitted without license from IHS

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