Conformal coating advice?

Go To Last Post
9 posts / 0 new
Author
Message
#1
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hi All

 

I have circuits that are going to be placed outdoors in IP casing, is it still necessary to use a conformal coating spray?

 

If so , i would like to hear some advice on the best way to use conformal coating.

 

Does conformal coating cause any issues on tracks that are impedance control , therefore effecting RF performance by any chance?

Thanks

Regards

DJ

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

djoshi wrote:
I have circuits that are going to be placed outdoors in IP casing, is it still necessary to use a conformal coating spray?

Even with an air tight case, the air inside will have moisture, and so it can condense on your board, unless you want to seal the case while in pure Nitrogen.

You can place a desiccant packet in the case to absorb the moisture and you may not need conformal coating, it depends on your application (as you have not told us the environment your product will be used in).

 

djoshi wrote:
Does conformal coating cause any issues on tracks that are impedance control , therefore effecting RF performance by any chance?

I don't have any experience with that, but have seen CC on rf circuits, so it can be done.  Check with your CC manufacturer to get their advise. 

 

Jim

 

 

(Possum Lodge oath) Quando omni flunkus, moritati.

"I thought growing old would take longer"

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hi Jim

 

The device will be used in tropical climate countries, where during day it will be hot and during the night temperatures will drop.

 

Thanks i will try giving one of them a call for advice.

Thanks

Regards

DJ

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

With that kind of temperature cycling, it WILL suck humid air into the enclosure. IP64, for example, only guarantees performance for the equivalent of wind-driven rain for a few minutes. The enclosure does NOT have to be hermetically sealed to do that. Without a total seal, it will suck humid air in, which  will condense when it cools. 

 

I have had some of my products in such environments for periods exceeding 6 months. They have all used desiccant bags and have had no problems. I have no doubt that if they were there a LONG time, the desiccant would eventually reach its capacity and the whole thing would start to fail. All that depends on the volume of the enclosure, the volume of the desiccant, and the moisture in the air that is pulled in. For my stuff, I would NOT use a conformal coating. That makes it almost impossible to work on if anything ever goes wrong.

 

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

ki0bk wrote:
Check with your CC manufacturer to get their advise

+1

 

Or, better still, discuss your application in detail with a number of manufacturers

Top Tips:

  1. How to properly post source code - see: https://www.avrfreaks.net/comment... - also how to properly include images/pictures
  2. "Garbage" characters on a serial terminal are (almost?) invariably due to wrong baud rate - see: https://learn.sparkfun.com/tutorials/serial-communication
  3. Wrong baud rate is usually due to not running at the speed you thought; check by blinking a LED to see if you get the speed you expected
  4. Difference between a crystal, and a crystal oscillatorhttps://www.avrfreaks.net/comment...
  5. When your question is resolved, mark the solution: https://www.avrfreaks.net/comment...
  6. Beginner's "Getting Started" tips: https://www.avrfreaks.net/comment...
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I would NOT use a conformal coating. That makes it almost impossible to work on if anything ever goes wrong.

Why? It is usually solder friendly so you can replace parts and respray. I have been doing repairs on a outdoor system installed about 10 years ago and I can replace even chips with a solder pad underneath.

 

There are also around 25,000 boards with conformal coating (mandatory in the standard) that are mounted on poles in roadways, many of them near sea shores where the salty air would absolutely destroy electronics stuff without coating.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I did a lot of marine installations, both onshore and offshore. No conformal coating. I had one unit returned for refurb after 10+ years on the bow of a supertanker. The alum enclosure was heavily decroded, but the electronics were near pristine.
Desiccant bags are more effective in my experience.
Conformal coating can cause issues with rf - by causing physical stress on the items coated and by the permittivity of the stuff. Some rf module manufacturers specifically state not to coat.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Even with an air tight case

That's one of the worst things to do...now moisture gets microscopically sucked in (or the original air volume condenses), and become trapped inside.  Dessicant helps, we used micron-level breathing plugs (similar to goretex) to let the humidity back out.  Our boards were parylene coated (it's by far the best as far as coverage $$$).  We also had some that had more of a rubbery "rtv style" 1/2 inch thick coating, you could xacto away & repair...but not as vapor proof as parylene.

Many many years ago, simply used a can of krylon clear coat spray.  Those were the days of sweet smelling vapors.

 

It also depends A LOT on the sensitivity of the electronics...A 2K/5K divider & an LM7805 could care less....a 2 meg feedback resistor on a 10uV offset feedback amp might be much more affected.  So, keep moisture in mind during the curcuit design.

Many circuits you can spray with a hose & they keep on chugging.

 

Coatings are always a headache in preventing coating places you don't want coated (like connectors, sockets), or ingress into pots.   Use the temporary rubber "peelaway" to try to shield those.

 

 For instance, a RF device operating at C band can accommodate a parylene coating with a low impact on signal performance; however, a Ka band device operating at 40 GHz coated with parylene would see such a large performance shift to render the device unusable. This performance impact due to conventional conformal coatings is typically seen starting at X-band (8-12 GHz) and increases over higher RF frequencies, at which point hermetic packaging is seen as the only high-reliability option for environmental protection. 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

Last Edited: Mon. Jun 22, 2020 - 11:28 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

We used conformal coating and then cast the electronics in silicone resin in rigid metal tubes, with polystyrene beads to provide expansion room. Used in high vibration (10,000g) wide temperature range (-40C - 150C) wet environments (drilling mud is corrosive and electrolytic).

 

Neil