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November 2004

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Subject:
From:
"Barmuta, Mike" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Barmuta, Mike
Date:
Wed, 17 Nov 2004 13:27:07 -0800
Content-Type:
text/plain
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text/plain (175 lines)
Hi John; I think the questions is... what are you asking the mask to do? I
don't think you are asking it to be a "soldermask". Is it an anti-humidity
coating, a dielectric coating, an environmental coating, an anti-corrosion
coating, etc.

Work with your customer to try and clearly define what are the specific
requirements and to what level of performance are they needed for the
finished product. It may be difficult to nail down, because they may not
know, but you will be in a much better position to define which path to
take. It may be conformal coating, burying circuitry in additional layers,
multiple masks and adhesion promoters, a different final plating finish,
encapsulation/potting, etc.

Right now you are just trying to be a good supplier offering to help in any
way you can
but I don't think you have all the information you need to help them with
the correct solution. Good luck.


                                                                Regards

Michael Barmuta

Staff Engineer

Fluke Corp.

Everett WA

425-446-6076

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of John Parsons
Sent: Wednesday, November 17, 2004 12:55 PM
To: [log in to unmask]
Subject: Re: [TN] Alternatives to Conformal Coating?


Jean-Francois,

If it is a bad idea then you are not alone.  Another on the list suggested
it and it is something we discussed here as well but I forgot to add it to
the list.  What we need to do is compare the cost of building a multilayer
board against the increased cost of doing it right with conformal coating.

Thanks
John

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Bissonnette,
Jean-Francois
Sent: Wednesday, November 17, 2004 11:49 AM
To: [log in to unmask]
Subject: Re: [TN] Alternatives to Conformal Coating?


Well not knowing exactly if it was done before or even if this feasable, my
answer to that may have a place in the wall of shame or just be interesting.

This would not protect the components nor the soldered connection but it
would protect all the traces.  Would it be possible to keep the connections
in the internal layer, leaving both external layers with only the lands to
solder the components on?

(ready to blush in shame)

JF

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of John Parsons
Sent: Wednesday, November 17, 2004 2:08 PM
To: [log in to unmask]
Subject: [TN] Alternatives to Conformal Coating?


Greetings all,

We are a fab shop and are looking for a solution to a problem being
experienced by one of our customers.  They have a board which resides in a
somewhat hostile environment
        - steam/salt water vapour
        - board carries 20Amp current
        - susceptible to multiple thermal excursions which put further
stress on
the unit
The problem, as one might expect, is that the soldermask is not man enough
for the job.  Some units have exhibited significant solder mask flaking from
the conductors after as little as 4 hours of operation.  FYI, board is
double sided with 3oz base Cu.

The product is currently only in the prototype stage but production volumes
are expected to be in the 100,000-250,000 units annually.  We have proposed
the obvious solution of utilizing a conformal coating post assy but that is
an option they would initially prefer to avoid due to the inherent costs
involved.  They would like us to first exhaust any possibility that the
problem can be averted from the pcb fabrication level.  I should also
mention that the expected lifespan of the unit is a maximum of 1000hrs and
likely only several hundred hours.

Some options that have been discussed are; (in no particular order of
likelihood to succeed of fail!)
        - multiple coating of soldermask
        - micro etch of copper prior to mask application (currently pumice
scrub)
        - conductor pacification with oxide alternative.  If this does not
provide
additional bite for the mask it may provide additional protection from
corrosion once the mask has pealed off.

Any ideas from the lot of you?  Are there properties to specialty solder
masks which might be beneficial in this application?  Any options to
conformal coating??

Regards
John Parsons

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