IPC 7711A - 第36页

6. Thickness Coating thickness is determined by visual inspection. Thin coatings show sharp outlines of the components and almost no fillet at intersection points of part leads to the circuit board. Thick coatings reduce…

OUTLINE

This procedure covers the techniques for identifying various

coatings so that the appropriate coating removal method can

be selected.

Conformal Coating Types IPC-CC-830 has superseded

MIL-I-46058 as the primary specification for printed circuit

assembly conformal coatings, and covers the following types

of conformal coatings:

1. Type AR – Acrylic resin (includes lacquers and varnishes)

2. Type ER – Epoxy resin

3. Type SR – Silicone resin

4. Type UR – Polyurethane resin

5. Type XY – Paraxylylene

REFERENCES

2.1 Handling Electronic Assemblies

2.2 Cleaning

2.5 Baking and Preheating

2.6 Epoxy Mixing and Handling

IPC - CC-830

TOOLS AND MATERIALS

Abrasive Discs

Brush

Cleaner

Cleaner Wipes

Cotton Swab

Dental Style Drill

Heated Blade

Knife

Solvent

Thermal Parting Tool

Wood Stick

PROCEDURE

To determine the appropriate coating removal procedure the

coating must first be identified. During original manufacture

the specific coating is usually known. Consequently, the coat-

ing removal methods can usually be specified and based on

the known coatings being used.

When identification of the coating is not available, simple

observation and testing will help identify the coating charac-

teristics so that the proper removal procedure can be speci-

fied.

NOTE

The generic or commercial identification of the coating mate-

rial is not necessary to accomplish coating removal.

1. Hardness

Penetration test in a non-critical area to determine relative

hardness. The harder the coating the more suitable to

pure abrasive techniques. The softer and gummier the

coatings the more suitable to the brushing removal pro-

cedures.

2. Transparency

Obviously transparent coatings are usually more suitable

for removal than the opaque type. Removal methods

used with opaque coatings must be far more controllable

and less sensitive to damaging the covered components

and printed board surfaces and are usually slower.

3. Solubility

Most coatings are soluble; however, the solvent required

to dissolve a specific coating may also attack the board

and/or components. Unless directed by other mainte-

nance actions, the solubility test and solvent use should

be limited to isopropyl alcohol. Test coat the surface in a

noncritical area by brushing on a small quantity and

observing the solubility action.

CAUTION

Printed board assemblies should not be immersed in

harsh solvents.

4. Thermal Removal

Use a thermal parting device with controlled heating and

without a cutting edge to determine whether the coating

can be thermally removed. Start with a low temperature,

approximately 100°C, and increase the temperature until

the coating is removed. If the coating flows or gums up,

the temperature is too hot or the coating is not suitable

for thermal removal.

5. Stripability

Carefully slit the coating with a sharp blade in a non-

critical area and try to peel back from the surface to

determine if this method is feasible. Due to the adhesion

required of coating materials, stripable techniques with-

out chemical aids is usually very limited.

Product Class: R, F, W, C

Skill Level: Advanced

Level of Conformance: High

7711A/7721A

General Information and

Common Procedures

Revision:

Date: 2/98

Coating Removal, Identifi-

cation of Conformal Coating

Number: 2.3.1

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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6. Thickness

Coating thickness is determined by visual inspection. Thin

coatings show sharp outlines of the components and

almost no fillet at intersection points of part leads to the

circuit board. Thick coatings reduce these sharp outlines

and show fillets where part leads intersect with the board.

Coatings thinner than 0.064 cm are considered thin.

Coatings thicker than 0.064 cm are classed as thick.

The specific coating to be removed may have one or

more of these characteristics and consequently the

removal method selected should consider the composite

characteristics.

See Figure 1 for Conformal Coating Identification.

See Table 1 for Conformal Coating Characteristics.

See Table 2 for Conformal Coating Removal Methods.

EVALUATION

NOTES

IPC-7711A/7721A

Number: 2.3.1

Revision:

Date: 2/98

Subject: Coating Removal, Identiﬁcation of Conformal Coating

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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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Figure 1 Conformal Coating Identiﬁcation

CONFORMAL COATING IDENTIFICATION

START

DOES THE

COATING FEEL

SOFT/RUBBERY/

SPONGY

DOES THE

COATING HAVE A

NOTICEABLE

REACTION

TO HEAT

DOES THE

COATING HAVE A

NOTICEABLE

REACTION

TO HEAT

IS THE COATING

THICK AND HAVE A

DULL SURFACE

POLYURETHANE

RTV

ENCAPSULATION

SILICON

RESIN

DOES THE

REACTION FORM A

WHITE POWDER

IDENTIFICATION

COMPLETE

USE TABLE 1 FOR

CONFIRMATION

IS THERE A

REACTION TO

ALCOHOL

ACRYLIC

LACQUER

EPOXY

PARAXYLYLENE

YES

IPC-7711A/7721A

Number: 2.3.1

Revision:

Date: 2/98

Subject: Coating Removal, Identiﬁcation of Conformal Coating

Page3of4

Provided by IHS under license with IPC

Not for Resale

No reproduction or networking permitted without license from IHS

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