AVR-Chat

I am looking for a Conformal Coating/Potting Compound that I can coat boards with to
protect them from moisture that can be removed (component-safe solvent?) to do
repairs.

The boards will have SMT, through-hole as well as DB-25, jumper pins, headers, etc.
Obviously I’d protect the DB-25, jumper pins, headers, etc. during the coating
process.

I have found "Techspray 2108-12S" $21 spray can at Mouser that says it can be easily
removed for rework.  Is this a cost effective approach?

Spray, brush, or dip would be fine with me.

BTW:  I am planning on coating the DB-25, headers, etc. (i.e.: connecting pins) with
a non-conducting grease, etc. to protect them from moisture in the field.
 
Cheers,

Chuck Hackett
"Good judgment comes from experience, experience comes from bad judgment"
7.5" gauge Union Pacific Northern (4-8-4) 844 http://www.whitetrout.net/Chuck

On Sat, Oct 2, 2010 at 10:27 AM, Chuck Hackett <egroupscdh@up844.us> wrote:

> I am looking for a Conformal Coating/Potting Compound that I can coat boards with to
> protect them from moisture that can be removed (component-safe solvent?) to do
> repairs.

A few things to keep in mind with Coatings:

A very common misconception is that Conformal Coating is a Hermetic Seal.

As Conformal Coating is not a hermetic seal, what real happens is the
impurities in the water are kept away from the circuit, but the water
itself reaches the traces over time. Since the water is now fairly
devoid of contaminates the water acts more like a dielectric
insulator. You never notice it in a low impedance digital circuit, but
unless debugging is an obsession don't let it get near a RF tuning
circuit or a high impedance Wireless Sensor Network circuit.

> BTW: I am planning on coating the DB-25, headers, etc. (i.e.: connecting pins) with
> a non-conducting grease, etc. to protect them from moisture in the field.

Coatings, don't know about grease, will migrate up pins. Grease
doesn't strike me as a good thing here, but can't really express why.

Different compounds can interact.  Recently had a problem where the
volume of a device was traced to the interaction of two compounds used
to pop a transformer.  Either compound alone had no effect on the
volume.

Account for out-gassing.

--
http://blog.softwaresafety.net/
http://www.designer-iii.com/
http://www.wearablesmartsensors.com/

Re non-conducting grease.   Why non-conducting on something you want to
conduct?    If you do some googling you will find it somewhat of a
controversy as to whether or not you should put a dielectric (i.e.,
non-conducting) corrosion protection on connector pins.

 

Chemtronics makes an electrically conductive grease but it is incredibly
expensive per unit weight (Digi-Key sells it).   Instead I use "NO-OX-ID
A-Special" from Sanchem, which is much more reasonably priced, on all my
boat connections that are exposed to the elements.   

 

http://www.sanchem.com/aSpecialE.html

 

Being conductive you don't want it to short out adjacent pins, so be careful
applying it!      The technique I use depends on the connector.    Sometimes
I'll use both this grease and an anti-corrosion spray, for example, on wires
going into a Eurostyle terminal block I'll poke the bare wire end into the
grease, screw it in place and then spray anti-corrosion stuff over the
completed terminal block.

 

Steve

From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf
Of Chuck Hackett
Sent: Saturday, October 02, 2010 7:27 AM
To: AVR-Chat
Subject: [AVR-Chat] PCB Coating

 

  

I am looking for a Conformal Coating/Potting Compound that I can coat boards
with to
protect them from moisture that can be removed (component-safe solvent?) to
do
repairs.

The boards will have SMT, through-hole as well as DB-25, jumper pins,
headers, etc.
Obviously I'd protect the DB-25, jumper pins, headers, etc. during the
coating
process.

I have found "Techspray 2108-12S" $21 spray can at Mouser that says it can
be easily
removed for rework. Is this a cost effective approach?

Spray, brush, or dip would be fine with me.

BTW: I am planning on coating the DB-25, headers, etc. (i.e.: connecting
pins) with
a non-conducting grease, etc. to protect them from moisture in the field.
 
Cheers,

Chuck Hackett
"Good judgment comes from experience, experience comes from bad judgment"
7.5" gauge Union Pacific Northern (4-8-4) 844
http://www.whitetrout.net/Chuck





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[Non-text portions of this message have been removed]

We use 3 different coatings at work. They go from soft to hard. I can get you the info later. The boards range from commerical to military boards. Analog and RF. Not sure how much work you want to put into getting it off vice protection of the coating. If you are thinking about potting we have options for that too.

If you want protected connectors I would look at AMP connectors, cost more but worth it, instead of the standard DB25 connector. Non-conductive grease may work but it can be messy and needs to be replaced every now and then.

Brian

--- In AVR-Chat@yahoogroups.com, "Chuck Hackett" <egroupscdh@...> wrote:

>
> I am looking for a Conformal Coating/Potting Compound that I can coat boards with to
> protect them from moisture that can be removed (component-safe solvent?) to do
> repairs.
> 
> The boards will have SMT, through-hole as well as DB-25, jumper pins, headers, etc.
> Obviously I'd protect the DB-25, jumper pins, headers, etc. during the coating
> process.
> 
> I have found "Techspray 2108-12S" $21 spray can at Mouser that says it can be easily
> removed for rework.  Is this a cost effective approach?
> 
> Spray, brush, or dip would be fine with me.
> 
> BTW:  I am planning on coating the DB-25, headers, etc. (i.e.: connecting pins) with
> a non-conducting grease, etc. to protect them from moisture in the field.
>  
> Cheers,
> 
> Chuck Hackett
> "Good judgment comes from experience, experience comes from bad judgment"
> 7.5" gauge Union Pacific Northern (4-8-4) 844 http://www.whitetrout.net/Chuck
>

What I've come across in many automotive devices is a potting compound that
is almost like kids slime. Looks glossy, but is jelly soft. I suppose it it
allows thermal expansion, and offers a huge physical barrier to dirt, but I
don't know if it's servicable. Most likely not. It's all throw-away today.

Another interesting find is conformal coatings that have been selectively
applied. Looks like it was done with a CNC nozzle.
Not that I've looked for the source of these compounds.

For general use I use Plasticote 70. You can solder 'through' it for
re-work.
http://www.crcind.com.au/catalogue.nsf/Web_Brands/055F762AEDF54A80CA2569AC001973B5?openDocument

Regards
Roland


On 2 October 2010 16:27, Chuck Hackett <egroupscdh@up844.us> wrote:

>
>
> I am looking for a Conformal Coating/Potting Compound that I can coat
> boards with to
> protect them from moisture that can be removed (component-safe solvent?) to
> do
> repairs.
>
> The boards will have SMT, through-hole as well as DB-25, jumper pins,
> headers, etc.
> Obviously I�d protect the DB-25, jumper pins, headers, etc. during the
> coating
> process.
>
> I have found "Techspray 2108-12S" $21 spray can at Mouser that says it can
> be easily
> removed for rework. Is this a cost effective approach?
>
> Spray, brush, or dip would be fine with me.
>
> BTW: I am planning on coating the DB-25, headers, etc. (i.e.: connecting
> pins) with
> a non-conducting grease, etc. to protect them from moisture in the field.
>
> Cheers,
>
> Chuck Hackett
> "Good judgment comes from experience, experience comes from bad judgment"
> 7.5" gauge Union Pacific Northern (4-8-4) 844
> http://www.whitetrout.net/Chuck
>
>  
>


[Non-text portions of this message have been removed]

--- In AVR-Chat@yahoogroups.com, "Chuck Hackett" <egroupscdh@...> wrote:
>
> I am looking for a Conformal Coating/Potting Compound that I can coat boards with to
> protect them from moisture that can be removed (component-safe solvent?) to do
> repairs.

>I am looking for a Conformal Coating/Potting Compound that I can coat
>boards with to protect them from moisture that can be removed (component-
>safe solvent?) to do repairs.


Working in the railway area (passenger information systems) we have to coat all our electronic devices against moisture and (often conductive) dust. I had a look at what we use and if you google for "sl1360 conformal coating" and maybe "Lackwerke Peters" you should find the stuff (and maybe even some source in your area) very easily.

The coating can be brushed and sprayed and is available in different colours but we use mostly the transparent variant. While wet it will fluoresce in UV to check for even coating. You can solder thru it (if really necessary - it will get brown and stink!) but I don't know whether there is a solvent to remove it completely (ask the manufacturer?).

HTH,
Stefan