Can someone recommend a conformal coating?

[LPEL98]

I have some boards that are used in automotive apps. They are not
meant to get wet, but you know how that goes - sometimes "stuff"
happens. I know I could reduce my failure rate in the field with a
conformal coating that kept the water out.

My concerns is that a coating might restrict heat transfer and cause
my product to run hotter - that would not be desirable. Also, I am
concerend it would be a real bear to rework boards if they have this
coating on them. Is there some kind of coating that is relatively
easy to remove? I'm thinking something that could be relatively
easily peeled off certain components if they need replaced and the
coating could be re-applied. If you guys have ever used that latex
soldermask stuff - something like that would be great - splooge it on,
and it peels off easily after you're done. Some coatings I've seen
are like varnish and would be a bear to remove. Is there easier ones
out there?

Also, how expensive are these coatings? Say for a 3"x2" board. If it
cost me a nickel or dime a board it would probably be worth it, if it
could be removed easily for rework.

 

[Activ8]

I have some boards that are used in automotive apps. They are not
meant to get wet, but you know how that goes - sometimes "stuff"
happens. I know I could reduce my failure rate in the field with a
conformal coating that kept the water out.

My concerns is that a coating might restrict heat transfer and cause
my product to run hotter - that would not be desirable. Also, I am
concerend it would be a real bear to rework boards if they have this
coating on them. Is there some kind of coating that is relatively
easy to remove? I'm thinking something that could be relatively
easily peeled off certain components if they need replaced and the
coating could be re-applied. If you guys have ever used that latex
soldermask stuff - something like that would be great - splooge it on,
and it peels off easily after you're done. Some coatings I've seen
are like varnish and would be a bear to remove. Is there easier ones
out there?

Also, how expensive are these coatings? Say for a 3"x2" board. If it
cost me a nickel or dime a board it would probably be worth it, if it
could be removed easily for rework.

Did you check MG chemicals?

 

[John Larkin]

I have some boards that are used in automotive apps. They are not
meant to get wet, but you know how that goes - sometimes "stuff"
happens. I know I could reduce my failure rate in the field with a
conformal coating that kept the water out.

My concerns is that a coating might restrict heat transfer and cause
my product to run hotter - that would not be desirable. Also, I am
concerend it would be a real bear to rework boards if they have this
coating on them. Is there some kind of coating that is relatively
easy to remove? I'm thinking something that could be relatively
easily peeled off certain components if they need replaced and the
coating could be re-applied. If you guys have ever used that latex
soldermask stuff - something like that would be great - splooge it on,
and it peels off easily after you're done. Some coatings I've seen
are like varnish and would be a bear to remove. Is there easier ones
out there?

Also, how expensive are these coatings? Say for a 3"x2" board. If it
cost me a nickel or dime a board it would probably be worth it, if it
could be removed easily for rework.

Polyurethane varnish makes a nice conformal coating. A hot iron will
solder right through it.

John

 

[Ken Smith]

I have some boards that are used in automotive apps. They are not
meant to get wet, but you know how that goes - sometimes "stuff"
happens. I know I could reduce my failure rate in the field with a
conformal coating that kept the water out.

Don't bet of finding a conformal coating that really keeps the water out.
They slow it down going both in and out. Fairly soon the PCB is as wet as
the average external. This can be a real bummer in the wetter places.
Make sure you design with large clearances.

Most car makers seem to slop something like DC-5 all over the electronic
connections that are exposed. This seems to be the best thing to do.


[...]

Also, how expensive are these coatings? Say for a 3"x2" board. If it
cost me a nickel or dime a board it would probably be worth it, if it
could be removed easily for rework.

The coatings are so cheap you can call them free. Its the labor of
putting them on that really costs.

If you are coating:

Never use "no-clean" flux.

Design out the air traps as much as you can. ie: No components touching
each other etc.

Clean the boards and then clean them again.

After the coating is "dry". Put the boards in the hot box over night
before you apply power.

 

[LPEL98]

Did you check MG chemicals?

Not yet - was looking for some pointers - thanks for that, I'll check 'em out!

Thanks everyone