IPC 7711A - 第32页

NOTES IPC-771 1A/7721A Number: 2.1 Revision: A Date: 5/02 Subject: Handling Electronic Assemblies P a g e4o f4 Copyright Association Connecting Electronics Industries Provided by IHS under license with IPC Not for Resale…

Handling Electronic Assemblies

If no ESDS markings are on an assembly, it still needs to be

handled as if it were an ESDS assembly. However, ESDS

components and electronic assemblies need to be identified

by suitable EOS/ESD labels. Many sensitive assemblies will

also be marked on the assembly itself, usually on an edge

connector. To prevent ESD and EOS damage to sensitive

components, all handling, unpacking, assembly and testing

must be performed at a static controlled work station.

Avoid contaminating solderable surfaces prior to soldering.

Whatever comes in contact with these surfaces must be

clean. When boards are removed from their protective wrap-

pings, handle them with great care. Touch only the edges

away from any edge connector tabs. Where a firm grip on the

board is required due to any mechanical assembly procedure,

gloves meeting EOS/ESD requirements need to be worn.

These principles are especially critical when no-clean pro-

cesses are employed.

Handling After Solder

After soldering and cleaning operations, the handling of elec-

tronic assemblies still requires great care. Finger prints are

extremely hard to remove and will often show up in confor-

mally coated boards after humidity or environmental testing.

Gloves or other protective handling devices need to be used

to prevent such contamination. Use mechanical racking or

baskets with full ESD protection when handling during clean-

ing operations.

Common Tools and Equipment

Work environments require tools and equipment to conduct

electronic assembly operations. The following information is

provided as guidance regarding the use of common equip-

ment. EIA-625 provides more specific information.

Table 3 General Rules for

Handling Electronic Assemblies

1. Keep work stations clean and neat. There must not be

any eating, drinking, or use of tobacco products in the

work area.

2. Minimize the handling of electronic assemblies and

components to prevent damage.

3 When gloves are used, they need to be changed as

frequently as necessary to prevent contamination from

dirty gloves.

4. Solderable surfaces are not to be handled with bare

hands or fingers. Body oils and salts reduce solderabil-

ity, promote corrosion and dendritic growth. They can

also cause poor adhesion of subsequent coatings or

encapsulates.

5. Do not use hand creams or lotions containing silicone

since they can cause solderability and conformal coat-

ing adhesion problems..

6. Never stack electronic assemblies or physical damage

may occur. Special racks need to be provided in

assembly areas for temporary storage.

7. Always assume the items are ESDS even if they are not

marked.

8. Personnel must be trained and follow appropriate ESD

practices and procedures.

9. Never transport ESDS devices unless proper packaging

is applied.

IPC-7711A/7721A

Number: 2.1

Revision: A

Date: 5/02

Subject: Handling Electronic Assemblies

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Not for Resale

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NOTES

IPC-7711A/7721A

Number: 2.1

Revision: A

Date: 5/02

Subject: Handling Electronic Assemblies

Page4of4

Provided by IHS under license with IPC

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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Provided by IHS under license with IPC

Not for Resale

No reproduction or networking permitted without license from IHS

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