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J-STD-001 & IPC-A-610 Updates for Conformal Coating: An Insider's Guide
Rework and touchup procedures required to be documented and available for review, and any reworked area should meet the requirements of the assembly drawing. If thickness measurements were required in the reworked area, the validation process should be documented and available for review, and coating touchup around sensitive components should be applied as close to the original coating thickness as possible.
J-STD-001F contained several items additional to those defined in Revision E, including cleaning procedures and handling precautions before coating Class 3 work, conformal coating requirements used for tin whisker risk mitigation, the use of masking materials, and avoidance of contaminating residues. Regarding coating distribution and uniformity, it was acknowledged that these would depend partly on the method of application and might affect visual appearance and corner coverage. Some variation in visual appearance of the conformal coating was expected and was acceptable. Other additional items included requirements for transparency, acceptable levels and positions of bubbles, voids and delamination, foreign object debris and freedom from visual defects such as dewetting, measling, peeling, wrinkles cracks, ripples, and fisheyes.
Revision F of IPC-A-610 required that conformal coatings should be transparent, uniform in colour and consistency and shoud uniformly cover the board and components. Uniform coating distribution depended partly on the method of application and might affect visual appearance and corner coverage. Assemblies coated by dipping might have a drip line or localized build-up of the edge of the board. This build-up might contain a small amount of bubbles but would not affect the functionality or reliability of the coating. IPC-A-610F gave photographic examples of acceptable coverage and definitions of coverage defects. Default thicknesses values were shown for various coating types, although it was stressed that if the engineering drawing specified thickness, then the drawing was predominant. A new item in Revision F concerned the use of conformal coatings for electrical insulation.
The NASA J-STD-001FS Space Addendum was currently at the ballot stage, and this defined particular procedures and precautions for cleaning and drying before coating, mixing records for coatings, coating, curing inspection, and rework.
Pauls’ presentation prompted many questions from webinar participants, and he responded energetically and constructively, going to considerable lengths to give informative and definitive explanations, resorting only occasionally to his favourite “it depends…”
Doug Pauls has been a contributor to SMART Group events for as many years as I can remember, and has participated in numerous conferences in the UK. He has always shared his knowledge and experience generously and with an occasional flash of ironic humour, and this webinar conveyed a wealth of up-to-the-minute information on essential industry standards.
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