IPC 7711A - 第39页

OUTLINE This procedure uses a solvent to remove surface coatings. This procedure can be use for spot or overall coating removal of conformal coatings or solder resists. Approved solvents may be used to remove specific so…

Table 1 Conformal Coating Characteristics

Characteristics

Conformal Coating Type

Epoxy Acrylic

Poly-

urethane

Silicone

Resin

Para-

xylylene

Hard UUU

Medium Hard UU

Soft UU

Heat Reaction UUU

Surface Bond - Very Strong UUU

Surface Bond - Strong UU

Surface Bond - Medium UU

Surface Bond - Light U

Solvent Reaction U

Non-porous Surface UUU U

Glossy Surface UUU

Semi-glossy Surface UU

Dull Surface U

Rubbery Surface U

Brittle UU

Chips UU

Peels and Flakes UU U

Stretches UU

Scratch, Dent, Bend, Tear UUU

Table 2 Conformal Coating Removal Methods

Conformal Coating

Removal Method

2.3.2

Solvent Method

2.3.3

Peeling Method

2.3.4

Thermal

Method

2.3.5

Grinding

Scraping

Method

2.3.6

Micro Blasting

Method

Paraxylyene 1 2 3

Epoxy 123

Acrylic 1 2 3 4

Polyurethane 3 1 2 4

Silicone Thin 1 2 3 4

Silicone Thick 1 2

NOTE: The preferred order for applying removal methods to speciﬁc coatings is numerically indicated. These removal methods are listed in ascending order.

More than one method may be required.

IPC-7711A/7721A

Number: 2.3.1

Revision:

Date: 2/98

Subject: Coating Removal, Identiﬁcation of Conformal Coating

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OUTLINE

This procedure uses a solvent to remove surface coatings. This procedure can be

use for spot or overall coating removal of conformal coatings or solder resists.

Approved solvents may be used to remove specific soluble type coatings on a spot

basis by brushing or swabbing the local area with the controlled application of sol-

vent until the area is free of the coating material.

If warranted, all the soluble type coating can be removed by immersing and brush-

ing the entire printed board or printed board assembly.

To determine the appropriate coating removal procedure the coating must first be

identified. Refer to procedure number 2.3.1.

NOTE

Coating removal may require the use of one or more methods.

CAUTION

Determine, on a module by module basis, the hazards to parts, etc., by short term

immersion in the removal solvents. If chloride based or other harsh solvents are

used, extreme care must be exercised to prevent damage to base material, compo-

nent parts, plated-through holes, and solder joints. Some solvent coating removal

methods can cause expansion or swelling of the base material which can degrade

the printed board or printed board assembly. Under no circumstances should these

solvents be used except in a closely controlled process. It is recommended that the

printed board or printed board assembly be inspected to ensure that no damage has

occurred.

Before using any solvent refer to Material Safety Data Sheets.

REFERENCES

2.1 Handling Electronic Assemblies

2.2 Cleaning

2.3.1 Coating Removal, Identification of Conformal Coatings

2.4.1 Coating Replacement, Solder Resist

2.4.2 Coating Replacement, Conformal Coatings/Encapsulants

TOOLS AND MATERIALS

Brush

Cotton Swab

Polyimide Tape

Knife

Suitable Solvent

Thermal Parting Tool

Wood Stick

Figure 1 Apply tape to outline for

coating removal.

Figure 2 Apply solvent with foam

swab to remove coating.

7711A/7721A

General

Information and

Common Procedures

Revision:

Date: 2/98

Coating Removal,

Solvent Method

Number: 2.3.2

Product Class: R, F, W, C

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.

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PROCEDURE – LOCAL SPOT REMOVAL

1. Apply Polyimide tape to outline the area where the coating needs to be removed.

(See Figure 1.)

2. Dip the end of a foam swab in stripping solution and apply a small amount to the

area of coating to be removed. (See Figure 2.)

As an alternative, a small cotton patch can be cut to the size of the area masked

(see Figure 1), saturated with the stripping solution, and pressed into intimate

contact with the surface of the coating to be removed. The patch will retard the

evaporation of certain solvents and reduce exposure time.

NOTE

Since various substances may be used as coatings, the time required for a given

coating to dissolve or soften will vary. Reapply solvent several times as most sol-

vents evaporate rapidly.

3. Rub the treated surface carefully with a brush or wood stick to dislodge the coat-

ing. A wedge shaped applicator tip, knife, or heated blade may be effective in

removing some coatings, particularly polyurethanes.

4. Neutralize or clean the stripped area and dry.

PROCEDURE – OVERALL REMOVAL

1. A single step for removal of all the coating may be completed by providing a con-

tinuous flow of solvent.

Alternately, process the board in a series of tanks containing mild solvent, start-

ing with a high contamination tank and progressing sequentially to a final, fresh

solvent tank.

EVALUATION

1. Visual examination or UV light may be used to verify complete removal of coating.

NOTES

Coating Removal Required at Outlined Areas

IPC-7711A/7721A

Number: 2.3.2

Revision:

Date: 2/98

Subject: Coating Removal, Solvent Method

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Provided by IHS under license with IPC

Not for Resale

No reproduction or networking permitted without license from IHS

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