IPC-7721(S).pdf - 第48页
NOTES IPC-7721 Number: 2.4.2 Revision: Date: 2/98 Subject: Coating Replacement, Conformal Coatings/Encapsulants P a g e2o f2
OUTLINE
This method is used to replace conformal coatings and encapsulants on printed wir-
ing boards.
REFERENCES
2.1 Handling Electronic Assemblies
2.2 Cleaning
2.5 Baking and Preheating
2.6 Epoxy Mixing and Handling
TOOLS & MATERIALS
Cleaner
Cleaning Wipes
Brush
Epoxy or Replacement Coating
Foam Swab
Heat Lamp
Microscope
Oven
PROCEDURE
1. Clean the area.
CAUTION
Surfaces to be coated must be thoroughly cleaned prior to coating to ensure
adequate adhesion, minimized corrosion, and optimized electrical properties.
2. If needed, apply Polyimide tape to outline the area where the coating will be
applied. (See Figure 1.)
3. If required, bake the printed wiring board prior to the application of the replace-
ment coating.
4. Mix the replacement coating.
5. Apply the replacement coating to the board surface as required. A brush or foam
swab may be used to apply and spread the replacement coating. (See Figure 2.)
For large surfaces, apply the replacement coating with a foam swab to create a
texture.
6. Cure the replacement coating per the manufacturer’s instructions.
CAUTION
Some components may be sensitive to high temperature.
EVALUATION
1. Visual examination for texture, color match, adhesion and coverage.
2. Electrical tests to conductors around the repaired area as applicable.
Figure 1 Apply replacement coating
with foam swab to create a texture.
Figure 2 Repair complete.
7721
Repair and
Modification of
Printed Boards and
Electronic Assemblies
Revision:
Date: 2/98
Coating Replacement,
Conformal Coatings/
Encapsulants
Number: 2.4.2
Product Class: R, F, W, C
Skill Level: Intermediate
Level of Conformance: High
Material in this manual was voluntarily established by Technical Committees of the 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 the ipc.
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NOTES
IPC-7721
Number: 2.4.2
Revision:
Date: 2/98
Subject: Coating Replacement, Conformal Coatings/Encapsulants
Page2of2
OUTLINE
This procedure covers baking and preheating of printed boards and printed board
assemblies to prepare the product for the subsequent operations. Included are steps
for:
A. Baking
Baking is used to eliminate absorbed moisture. Whenever possible printed wir-
ing boards and printed wiring board assemblies should be baked prior to solder-
ing, unsoldering and coating operation to prevent blistering, measling or other
laminate degradation.
B. Preheating
Preheating is used to promote the adhesion of subsequent materials to the
board surfaces and to raise the temperature of the printed wiring board to allow
soldering and unsoldering operations to be completed more quickly.
CAUTION
Baking and preheating procedures must be carefully selected to ensure that tem-
perature and time cycles used do not degrade the product. Environmental conditions
must also be carefully considered to ensure that vapors, gases, etc., generated dur-
ing the heating process do not contaminate the product’s surfaces.
CAUTION
To prevent fluxes or other contaminates from being baked onto the board surface,
thoroughly clean the board or assembly prior to baking or preheating.
REFERENCES
2.1 Handling Electronic Assemblies
2.2 Cleaning
TOOLS & MATERIALS
Cleaner
Cleaning Wipes
Oven
EVALUATION
7721
Repair and
Modification of
Printed Boards and
Electronic Assemblies
Revision:
Date: 2/98
Baking and Preheating
Number: 2.5
Product Class: R, F, W, C
Skill Level: Intermediate
Level of Conformance: High
Material in this manual was voluntarily established by Technical Committees of the 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 the ipc.
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