With so many types of conformal coating and various methods of application, it is important to consider the primary factors of conformal coating, in order to achieve defect-free coating and highest reliability of the final device.
Primary Factors
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Choice of conformal coating
Selecting the right conformal coating is necessary to achieve better protection
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Viscosity
The viscosity of the conformal coating used affects the method of application, cure time, thickness and coverage
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Equipment parameters
For example, the speed and height of application
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Masking keep-out areas
Are there any areas that should not be covered by the conformal coating?
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Curing Method
Depending on their type, thickness, and curing method, conformal coatings can cure between seconds to days.
Apart from the general factors that affect all types of conformal coating, here are some specific factors that are dependent on the application methods:
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Hand Spraying
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Dipping
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However, all these considerations are for naught if the biggest factor is overlooked: Contamination.
Common types of contamination
- Flux residue
- Stray solder/solder balls
- Residue from board fabrication
- Dust from drilling, cutting and scoring
- Fingerprints and skin oils from handling
- Silicon and other oils migrating from other processes
- Dust or dirt in the air/work environment
The presence of contamination can severely affect the conformal coating process and cause defects. Therefore, it is important to ensure that the boards are washed prior to conformal coating.