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Conformal Coating Coverage on Side of IC

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Conformal Coating Coverage on Side of IC | 17 September, 2009

Does anyone have a reference to a spec for this? We have a tall SMT IC that we coat with AR coating in a Asymtek spray coating machine. We do not have the angle head option to spray from a 45 so the sides of tall parts are sometimes left uncovered. The leads are all covered fine. I have looked in IPC-CC-830, J-STD-001, IPC-610 and cant find a specific reference to this. Only that it "coats device edges". That probably means vertical sides as well.

What do you guys think?

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Conformal Coating Coverage on Side of IC | 18 September, 2009

There is no specification that covers all the peculiar possible situations in conformal coating.

The user and the supplier should define and document coating requirements on the assembly drawing, since they are specific to the product.

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Conformal Coating Coverage on Side of IC | 21 September, 2009

Thanks for the reply. I didnt consider this too peculiar a situation however, since pretty much anyone who coats boards with a thin material like acrylic prob has come across this.

Maybe its time to invest in some machine upgrades!


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Conformal Coating Coverage on Side of IC | 21 September, 2009

10.4. Pre-Cure Examination. Immediately after material application, the uncured conformal coating shall be examined for: a. Bubbles and Air Entrapments. These defects shall be broken by vacuum, with a sharp probe, or other appropriate tools. b. Bridging. Conformal coating material shall not be allowed to bridge between the bottom of ceramic-bodied DIP's or surface mounted parts and the PWB, or between the part lead and the PWB, thereby negating stress relief. 10.5. Post Cure Examination. After the cure cycle, the conformally coated PWB or PWA shall be examined to assure that the following conditions are met. See Figure 10-2 through Figure 10-5 for additional requirements. a. Conformal coating is uniform in color, thickness, and texture, tack-free, and shows proper adhesion to all coated surfaces. b. Conformal coating shall cover all areas as specified on the engineering documentation, have a smooth continuous surface, and follow the contours of the PWA. Minor pull back from sharp points and edges is permissible unless otherwise specified on engineering documentation. c. Conformal coating is free from contamination. d. Terminals shall be conformal coating encapsulated, including the insulation gap of the wire, unless it is a solder ball type connection (as in a high voltage connection). This is normally applied with a brush after the initial conformal coating application. e. Conformal coating may bridge between adjacent part leads providing stress reliefs are not negated. f. Conformal coating shall not exhibit discoloration (due to such things as excessive curing oven temperature, contamination, etc.) [Workmanship Standard for Staking and Conformal Coating of Printed Wiring Boards and Electronic Assemblies, NASA-STD-8739.1, August 6, 1999]

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Conformal Coating Coverage on Side of IC | 22 September, 2009

Good ol NASA... thanks Dave

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