K2 - Board Cleaning and Conformal Coating

[John Huggins, kx4o]

All,

Being in the electronics biz, we usually wash boards post assembly with
the usual products and in accordance with IPC610, etc.  Often, the boards
are sprayed with conformal coating: Some to handle "condensing
environments" and others just because someone wanted it.  My operating
locations will include salty beaches and moist mountains.

I couldn't find details in the K2 manual concerning these steps.  I did
find a few posts in old Elecraft archives, but need to ask...

Are there any components used in the K2 boards that will not tolerate
typical board washing procedures? (Most modern components expect this
step, but some don't - often switches)

Is there any reason not to conformal coat the boards once complete? (Cost
is no object to make this last a long time in beach environments)

Thanks.

John
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[Don Wilhelm-4]

  John,

Cleaning the K2 (K1, KX1 too) boards is not recommended.  The flux is
not corrosive in its native state, but in repairing many Elecraft
transceivers, I have seen cases where attempts at cleaning the boards
resulted in failures due to leakage paths created - after being
subjected to cleaning compounds, enough residue remains to cause
problems.  Any fluid running under connectors or under ICs, relays, or
other components can (and has) caused problems.

Yes, the switches should be avoided, the toroids may be another
candidate depending on the cleaning method.  The LCD and the bargraph on
the front panel are examples that come to my mind.

However, you sound like you have professional cleaning tools at your
disposal, so clean the boards at your own risk.

I have repaired several transceivers that were used in a beach
environment, and not one of those repairs could I attribute to the
environment - the exterior may have taken a beating from the salt air,
corroding the BNC connector shells, the outside of the key jack, but the
boards inside the enclosure remained free of any apparent corrosion.  
 From the evidence I have seen conformal coating is unnecessary.  I do
not know if it would do any harm.  It may make future component removal
difficult.

73,
Don W3FPR

On 6/1/2011 3:05 PM, John Huggins, kx4o wrote:

> All,
>
> Being in the electronics biz, we usually wash boards post assembly with
> the usual products and in accordance with IPC610, etc.  Often, the boards
> are sprayed with conformal coating: Some to handle "condensing
> environments" and others just because someone wanted it.  My operating
> locations will include salty beaches and moist mountains.
>
> I couldn't find details in the K2 manual concerning these steps.  I did
> find a few posts in old Elecraft archives, but need to ask...
>
> Are there any components used in the K2 boards that will not tolerate
> typical board washing procedures? (Most modern components expect this
> step, but some don't - often switches)
>
> Is there any reason not to conformal coat the boards once complete? (Cost
> is no object to make this last a long time in beach environments)
>
>

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[Fred Townsend]

John I helped develop some the cleaning systems for delicate boards
including RF assemblies. I have done a great deal of conformal coatings.
Conformal coatings are not to be taken lightly. There are major tradeoffs.
First the cleaning.

Alcohol, on a Q-Tip,  may be used for spot cleaning. Dunk cleaning will
leave a flux residue in many shaft encoders, switches, connectors, and
sockets. Alcohol will also dissolve some of the lubricants used on some
types of switches. I wouldn't dunk clean even if I had a forbidden Freon
degreaser.

Conformal coatings are useful on assemblies like VCOs where mechanical
stability is needed. They are also useful for high voltage circuits or
circuits that are sensitive to leakage. It is a given that connectors and
other contact surfaces must be masked before sealing. Conformal coatings
will detune tank circuits where the air dielectric is replaced by conformal
coating. They also make component replacement and reworking of boards
hazardous and extremely difficult.  Melting the coating with a soldering
iron will cause a decomposition that emits hazardous gases and leaves an
acidic residue that is almost impossible to remove. Therefore rework must be
done by cutting through and removing of the coating before de-soldering.

In short I do not see a significant benefit to conformal coating of Elecraft
boards with the possible exception of VFOs, direct synthesis, and other
boards that might be sensitive to microphonics.

73
de Fred, AE6QL


-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of John Huggins, kx4o
Sent: Wednesday, June 01, 2011 12:05 PM
To: [hidden email]
Subject: [Elecraft] K2 - Board Cleaning and Conformal Coating

All,

Being in the electronics biz, we usually wash boards post assembly with the
usual products and in accordance with IPC610, etc.  Often, the boards are
sprayed with conformal coating: Some to handle "condensing environments" and
others just because someone wanted it.  My operating locations will include
salty beaches and moist mountains.

I couldn't find details in the K2 manual concerning these steps.  I did find
a few posts in old Elecraft archives, but need to ask...

Are there any components used in the K2 boards that will not tolerate
typical board washing procedures? (Most modern components expect this step,
but some don't - often switches)

Is there any reason not to conformal coat the boards once complete? (Cost is
no object to make this last a long time in beach environments)

Thanks.

John
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[IZ2NYY]

Hy John, my approach is merely practical. I usually say "if it works this way, that's good as it is!". My K2' boards work without having been cleaned and i'm happy this way.

IMHO


Pippo
IZ2NYY