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The top of the enclosure I am building is going to be the PCB. The PCB has a 7-segment LCD and the leads are somewhat exposed. Is there an insulation material I can brush on or squeeze on that will stick and cover the leads and prevent accidental shorts?

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There are a wide range of compounds termed "conformal coatings" which provide varying degrees of insulation of the boards electrical conductors. Many of these can be applied by some or all of dipping, brushing or spraying. (A few are applied under very specialised vacuum conditions - not applicable here).

The main role of a conformal coating is protection of the PCBA from environmental factors, humidity, oxidation, corrosives, ...) with insulation being an important but secondary role.

You can get two pot epoxy coatings - which is a far more aggressive approach than you need.

A thin layer of a neutral cure silicone rubber will do a good job of insulation and isolation. Do not use acetic acid cure silicone rubber.


Wikipedia - conformal coating


Dow Corning - Conformal Coating Grand Masters [tm]

DC Conformal Coatings tutorial - 12 pages !

Ive used this DC CC - effective but environmentally nasty

DC - specific products technical notes


Humi seal conformal coatings training !!!

  • A Conformal coating is a protective chemical coating or polymer film 25-75µm thick (50µm typical) that ‘conforms’ to the circuit board topology. Its purpose is to protect electronic circuits from harsh environments that may contain moisture and or chemical contaminants. By being electrically insulating, it maintains long-term surface insulation resistance (SIR) levels and thus ensures the operational integrity of the assembly. It also provides a barrier to air-borne contaminants from the operating environment, such as salt-spray, thus preventing corrosion.

MG chemicals CCs

  • Example - 422b silicne CC

    • Ideal for high temperature environments. Silicone Conformal Coating (422B) is a flexible finish product that provides a protective coating for printed circuit boards against moisture, corrosion, and thermal shock. It protects and insulates electrical and electronic components and assemblies, including generators, motors, transformers, relays, and solenoid coils. For spraying, liquid can be thinned using M.G. Thinner Cleaner. Thin up to one half part thinner to one part coating.

Specific insulating coatings

Masterbond CCs

DIMAC CC video presentation

http://www.dowcorning.com/content/etronics/etronicscoat/

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  • \$\begingroup\$ Thanks, it was a lot of reading but I understand the choices and tradeoffs much better. \$\endgroup\$ – BSEE Aug 28 '12 at 20:08
  • \$\begingroup\$ I did some research and acrylic is the least expensive. Although I may go for a softer silicone in the end so I can rework. \$\endgroup\$ – BSEE Sep 7 '12 at 1:36
  • \$\begingroup\$ You can burn off/solder through acrylic with a soldering iron. Not so with silicone. \$\endgroup\$ – Jon Watte Feb 24 '16 at 22:48
  • \$\begingroup\$ @JonWatte Yes, but/and. | I'm wondering if he REALLY meant Acrylic - as opposed to eg Polyurethane (because it is liable to be cheapest and is common and ) ... . Polyurethane can be soldered through BUT be wary of the fumes which, AFAIK, may end up with free cyanide . I imagine these are unlikely to be lethal (I may be wrong :-( ), but also liable to not be wholly benign. | Silicone rubbers can in almost all cases be scraped off well enough to resolder. \$\endgroup\$ – Russell McMahon Feb 25 '16 at 7:00
  • \$\begingroup\$ Acrylic is actually at least as easily available if you search for "conformal coating." For example, the only CC product that Jameco sells is brush-on Acrylic. (If you go down to the Home Depot, the selection is more urethane-based, like you suggest!) \$\endgroup\$ – Jon Watte Feb 26 '16 at 19:07
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Here's an answer from 2012 which was deleted. It is NOT mine - but the advice is good enough that it seems sad to let it go to waste for some future seeker. So:

________________

If you can have adequate room for applying the conformal coating, great.

Also if you can control the quality of application to insure a sufficient thickness to prevent puncturing the coating when the metal panel is forced against it , great.

Otherwise I can recommend a mylar material that comes in large rolls and various thicknesses e.g. 1 or 2 mil , where the roll can be cut on a band-saw into the desired width and cut on anvil paper cutters to desired length. UL approved my use for HV open frame power supply insulation with 8 mil thickness.

It is very hard but flexible material and economical by the roll. Any suitable adhesive for applying to board will do.

It is a common item at plastic distributors in most cities.

Here is a manufacturer thereof - one of the biggest - Dupont Teijin. Mylar is a DuPont trademark but other people make similar under other (or the same :-) ) names.

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