My experience with equipment that gets transported into different climatic
conditions is that you at least have to be below 3ug/inch2.
As you move equipment from a cooler environment into a warmer environment
the RH on the surface of the equipment and inside the equipment can reach
100% and result in condensation and make all the available "dirt" mobile.
In addition you have to watch out for high levels of voltage gradients, as
those areas seem to attract all mobile dirt in the equipment with typically
bad results. And of course the smallest available spaces (like under
resistors and capacitors) are catch basins for bad stuff.
(Like a roach motel: dirt goes in but does not come out!)

In an other experience like yours, where we had "localized" equipment
failures, we traced those back to the presence of oil refineries nearby
spewing some undesirable "dirt" into the air and into the equipment.

By the way, the contamination detected by the Omega meter can not only come
from the solder materials, but also from dirty raw boards or from dirty
components!!

And please, don't coat "dirty" boards.

Have fun,

Ahne Oosterhof.




-----Original Message-----
From:   TechNet [mailto:[log in to unmask]] On Behalf Of Chuck Mays
Sent:   Sunday, May 27, 2001 21:04
To:     [log in to unmask]
Subject:        [TN] Ionic contamination limit for PWA with 0402 sized components

I have a problem with a small mobile product that is failing in field
trials.  One area we have considered is a combination of RH and the level
of ionic contamination affecting high impedance areas of the PWA to cause
the problem.

An external lab checked a sample of the PWA's using the Omega method and
found the average level to be about 18 ug/sq.in.

Most of the failures in field trials have occurred not too far from the bay
in one of the suburbs of Sydney where the field trials are in progress.
The temperature is not high (15 - 20 degrees C).

My questions are:
1.  Does anyone have experience that indicates that the 10ug/sq.in. level
for ionic contamination is OK for PWAs that use 0402 sized components?
2.  Is it possible to determine an impedance above which one should be
concerned with a level of ionic contamination for a given voltage?
3.  If it turns out that for this design, RH and the level of ionic
contamination are causing the problem, can the situation be improved by
conformally coating the board or areas of the board?  (If so, can someone
please point me to the applicable standards for conformal coating?  Thanks.)

Best Regards,

Chuck Mays

Invetech Operation Pty Ltd
[log in to unmask]

Tel 613 9211 7700
Fax 613 9211 7702

The information contained in this message and any attachments is
confidential and intended for the named recipient(s).  If you have received
this message in error, please contact the sender by return e-mail and
destroy the message and any attachments.

Any opinions or undertakings expressed in this message are those of the
individual sender except where the sender expressly and with authority
states them to be the opinions of Invetech.

----------------------------------------------------------------------------
-----
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send the following message: SET
Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases >
E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700
ext.5315
----------------------------------------------------------------------------
-----

---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------