conformal coating

[FunkyPunk FieldEffectTrollsistor]

A part is also a sealed assembly!

No shit, dumbfuck.

Ifsaid 'sealed assenbly' get BAKED in an oven, there will be NO water in
it, and if said assembly is subsequently sealed further, there is going
to be a greater NO water content level in it, THEREFORE, if an entire
assembly get baked, as is the STANDARD procedure for assemblies prior to
sealing operations, then there will be NO water INSIDE the seal.

AFTER the sealing operation, there will be no water getting in as well.

Where your brain went askew is unknown.

So if a small sealed assembly can't
keep the water out, a big one can't either.

If only we could have kept your mother from getting any water, we would
then not have to listen to your utter stupidity.

Ofcourse you can use
better materials which slow down the ingress of moisture but
eventually you'll have moisture inside.

You're an idiot. There are coated assemblies out there in the harshest
of environs that have lasted for decades.

That should be a hint for you, and your blatant Obama styled lies.

 

[MooseFET]

The diffusion rate of water and gas in polymers is orders of magnitude
higher than in metals, so anything protected only by polymers will
eventually become wet.  Any polymer, including Parylene.  Nice
hermetically sealed metal boxes (i.e. *not* sealed with polymer
O-rings!) will keep things inside dry for thousands of years.

Even with O-rings in the design, it is darn good. The cross sectional
area of the O-ring is very small.

ASCII art:

MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM <- Metal
MMMMMMMMMMMMMMMMM MMMMMMMMMMMMMMM
MMMMMMMMMMMMMMM MMMMMMMMMMMMM ------
Exposed area
MMMMMMMMMMMMMMM MMMMMMMMMMMMM ------
MMMMMMMMMMMMMMMMM MMMMMMMMMMMMMMM
MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM

In a well designed housing, the exposed area is a tiny fraction of the
diameter of the O-ring.

 

[Jon Kirwan]

Even with O-rings in the design, it is darn good. The cross sectional
area of the O-ring is very small.

ASCII art:

MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM <- Metal
MMMMMMMMMMMMMMMMM MMMMMMMMMMMMMMM
MMMMMMMMMMMMMMM MMMMMMMMMMMMM ------
Exposed area
MMMMMMMMMMMMMMM MMMMMMMMMMMMM ------
MMMMMMMMMMMMMMMMM MMMMMMMMMMMMMMM
MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM

In a well designed housing, the exposed area is a tiny fraction of the
diameter of the O-ring.

Yes, but didn't Phil say "orders of magnitude?" A little "linear"
trimming of exposed area and a little added path length doesn't seem
to compensate for "orders of magnitude."

Jon

 

[Nico Coesel]

The diffusion rate of water and gas in polymers is orders of magnitude
higher than in metals, so anything protected only by polymers will
eventually become wet. Any polymer, including Parylene. Nice
hermetically sealed metal boxes (i.e. *not* sealed with polymer
O-rings!) will keep things inside dry for thousands of years.

If you do not include moisture coming in from the cables (between the
copper strand or between the copper and the insulation).

 

[FunkyPunk FieldEffectTrollsistor]

Yes, but didn't Phil say "orders of magnitude?" A little "linear"
trimming of exposed area and a little added path length doesn't seem
to compensate for "orders of magnitude."

Jon

Neoprene O-rings can degrade faster than the materials used in coatings.

The arguments some of you dopes make are hilarious.

I work with fully ruggedized gear every day. I have seen several
sealing methods, and even utilize conduction cooling in several cases.

Any clue as to why we do not have moisture entrapment or moisture attack
problems?

 

[FunkyPunk FieldEffectTrollsistor]

If you do not include moisture coming in from the cables (between the
copper strand or between the copper and the insulation).

Ever heard of hermetic pass thrus?

There are several ways of sealing off a raw circuit card assembly
without a case.

 

[Jon Kirwan]

Neoprene O-rings can degrade faster than the materials used in coatings.

The arguments some of you dopes make are hilarious.

I work with fully ruggedized gear every day. I have seen several
sealing methods, and even utilize conduction cooling in several cases.

Any clue as to why we do not have moisture entrapment or moisture attack
problems?

I'm just a hobbyist with modest math skills. However, I do have a
feel for what "orders of magnitude" means and can compare that with
linear path length changes in geometry. I'll leave it to the "big
boys" to work out what is practical for specifics and watch.

Jon

 

[MooseFET]

Yes, but didn't Phil say "orders of magnitude?"  A little "linear"
trimming of exposed area and a little added path length doesn't seem
to compensate for "orders of magnitude."

A totally hermetic housing is better, but O-rings on aluminum produces
a housing that will last many years in water.

I know of systems that used a hygroscopic material in one of the
optical components that have been used in the ocean for about 10 years
now without a failure. The O-rings have continued to work over very
wide temperature ranges and repeated changes in pressures.

These were just simple Viton, not the newer materials.

 

[MooseFET]

If you do not include moisture coming in from the cables (between the
copper strand or between the copper and the insulation).

That needn't happen if you put in metal to ceramic penetrators or
connectors. You can bring signals in and out and keep the housing
hermetic.

Even just stripping the middle of the the wires, soldering the
section and then potting it in place reduces the rate that water gets
in.

 

[Jon Kirwan]

A totally hermetic housing is better, but O-rings on aluminum produces
a housing that will last many years in water.

I know of systems that used a hygroscopic material in one of the
optical components that have been used in the ocean for about 10 years
now without a failure. The O-rings have continued to work over very
wide temperature ranges and repeated changes in pressures.

These were just simple Viton, not the newer materials.

Which meets an application need. But that doesn't appear disagree
with Phil's comment, since he was using "eventually" in context with
"thousands of years" and "orders of magnitude." Thanks for the
additional explanation.

Jon

 

[FunkyPunk FieldEffectTrollsistor]

A totally hermetic housing is better, but O-rings on aluminum produces
a housing that will last many years in water.

I know of systems that used a hygroscopic material in one of the
optical components that have been used in the ocean for about 10 years
now without a failure. The O-rings have continued to work over very
wide temperature ranges and repeated changes in pressures.

These were just simple Viton, not the newer materials.

Simple O-ring seals, when properly implemented, are typically good down
to 600' depths.

 

[FunkyPunk FieldEffectTrollsistor]

Even just stripping the middle of the the wires, soldering the
section and then potting it in place reduces the rate that water gets
in.

What a totally retarded methodology.

 

[ROB L]

How long do you need it to work for.  A coating just slows the
progress of the salt and water working its way towards the PCB.
Potting is thicker so it works longer.


Put it in a sealed housing and drop the coating?


Does it travel to the destination by air?  Does it get exposed to sun
light.



I have lots and lots of experience of unsuitable ones.  I gave up long
ago and went the sealed housing route.



- Show quoted text -

a sealed housing is not an option.

The saline moisture transport is principally through the atmosphere
and whilst I have some experience of conformal coatings I am concerned
about the saline content of the atmosphere, and any condensate, and
its affect on the coating.

The pcb holds an optical sensor & 'tronics and its housing is
transparent to visible, IR & UV. It is for outside use.
This pcb is quite small (~60x55mm), is all extra low volatge, and
production will be 100k+ p.a

I need a reliable dipping conformal coating that resists the salt in
the atmosphere.

thanks

 

[ChairmanOfTheBored]

a sealed housing is not an option.

The saline moisture transport is principally through the atmosphere
and whilst I have some experience of conformal coatings I am concerned
about the saline content of the atmosphere, and any condensate, and
its affect on the coating.

The pcb holds an optical sensor & 'tronics and its housing is
transparent to visible, IR & UV. It is for outside use.
This pcb is quite small (~60x55mm), is all extra low volatge, and
production will be 100k+ p.a

I need a reliable dipping conformal coating that resists the salt in
the atmosphere.

thanks

That small of a board at that number of production... You do not need
to service it. Make 'em, pot 'em and forget about it.

Use stycast. It fully hardens, and NOTHING gets in. You conformal coat
the PCB assy. Then, after a cure period, you dip it in stycast.

The conform is enough done right, but hard potting media IS what you
want, and servicing them is more costly than simply making more would be.
So make 110k of them hard potted.

 

[ROB L]

 That small of a board at that number of production...  You do not need
to service it.  Make 'em, pot 'em and forget about it.

 Use stycast.  It fully hardens, and NOTHING gets in.  You conformal coat
the PCB assy.  Then, after a cure period, you dip it in stycast.

  The conform is enough done right, but hard potting media IS what you
want, and servicing them is more costly than simply making more would be.
So make 110k of them hard potted.- Hide quoted text -

- Show quoted text -

You are correct in that servicing is not an issue.
I do not know of stycast - is this just another epoxy?

 

[MooseFET]

Which meets an application need.  But that doesn't appear disagree
with Phil's comment, since he was using "eventually" in context with
"thousands of years" and "orders of magnitude."  Thanks for the
additional explanation.

I was giving scale to the numbers not disagreeing.

"orders of magnitude" could mean many of them.

 

[MooseFET]

A totally hermetic housing is better, but O-rings on aluminum produces
a housing that will last many years in water.

BTW: One of the systems that has run a long time is housed in a
titanium housing. The O-ring seal is good to the bottom of the ocean
but the aluminum housing suddenly gets a lot smaller at only a couple
of thousand PSI.

 

[MooseFET]

 Simple O-ring seals, when properly implemented, are typically good down
to 600' depths.

300 PSI! You must have a moron doing the design of the O-ring seal.
Read the data sheet and follow the suggested design and you'll do
better.

 

[MooseFET]

a sealed housing is not an option.

The saline moisture transport is principally through the atmosphere
and whilst I have some experience of conformal coatings I am concerned
about the saline content of the atmosphere, and any condensate, and
its affect on the coating.

The pcb holds an optical sensor & 'tronics and its housing is
transparent to visible, IR & UV. It is for outside use.
This pcb is quite small (~60x55mm), is all extra low volatge, and
production will be 100k+ p.a

I need a reliable dipping conformal coating that resists the salt in
the atmosphere.

Try Sylgard. The light may go through well enough.

 

[Rich Grise]

I need a conformal coating that will protect a pcb in a saline
atmosphere, maybe even the odd small drop of saline will land on the
pcb.
The temperature is room temp and the pcb dissipates only the odd mW
(no hot components)

Potting is not an option but dipping is!! (odd I know but
nevertheless)

Has ayone knowledge/experience of a suitable conformal coating?

Do you googlers even KNOW ABOUT the search side of google?

Searching "conformal coating" with quotes returns "about 163,000" hits.

Now, go and do your own homework first.

Good Luck!
Rich