Would suggest making sure the mask thickness if sufficient, and may
required 2 coats of material.  Adhesion can be also improved by the
micro-etching process similar to inner layers, or oxide if a replacement
is not being used.  

Jeffrey Bush
Director, Quality Assurance and Technical Support

                   76 Technology Drive - POB 1890
                       Brattleboro, Vermont 05302
                            802.257.4571.21
                             http://www.vtcircuits.com
 

-----Original Message-----
From: John Parsons [mailto:[log in to unmask]] 
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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Technet Mail List provided as a service by IPC using LISTSERV 1.8e
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To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
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