Hi William

You have just opened up an entire can of worms.

First off, why do they ask for the coating? Is it to hide a problem?
Commonly, the smaller track spacing and lower operating voltages are
inducing electro-chemical reactions that cause failure hence the
increased demand for coating.

Then adhesion - does your coating adhere to component surfaces,
plating materials but not to the solder resist? It ain't intelligent,
so how would it know the difference? You need to pay close attention
to the bare board preparation and resist curing then ensure that you
don't apply too much flux or too much heat, before you coat.

Then cleanliness - keep in mind that all fluxes leave residues. Are
they harmful? Maybe....

Lead-free - how are surface contamination levels affected? No-one
knows for sure, but we do know that the higher process temperatures
do produce all sorts of issues including potential flux vitrification
much less board degradation.

I strongly recommend that you have a good read of IPC-J-STD-001D,
A610, CC-830 and the 830 HDBK.

Also keep-in-mind that a coating seals in as well as out so, before
you coat, know what you are putting it over.

I hope this helps.

Graham Naisbitt

[log in to unmask]



On 14 Sep 2006, at 00:27, [log in to unmask] wrote:

> Hi Folks:  My company is beginning to be asked by several
> customers for
> conformal coating on their PCB assemblies.  We are currently
> building to
> IPC-A-610 using a combination of SMT and T/H technology in a  no-
> clean manufacturing
> process flow.  From my old PCB days, I remember  problems with PCB
> cleanliness
> and conformal coating peeling off the PCB  surface.
>
> What are folks using today for a conformal coating in a no-clean
> manufacturing environment?  Do I need to worry about cleanliness at
> all  today?  With
> RoHS and lead-free processing/PCB finishes how are surface
> contamination levels
> affected??
>
> I'm just looking for some basic information to point me in the right
> direction.....rather not have to re-invent the wheel.  Thought this
> would  be the
> perfect forum for this type of question!!!!
>
> Thanks in advance for any help and guidance you folks may
> provide!!!!!!!
>
> Sincerely,
>
> William E. Black
> Medco
> Quality Assurance Manager
> Tel:   1 631 667 9699
> e-mail:  [log in to unmask] (mailto:[log in to unmask])
>
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