If you remember, what was the Relative Humidity in the Plant?
----------
From: TechNet-request
To: technet; Bob Neves
Cc: mttc
Subject: Re[2]: ASSY Moisture Release Rates and Prebake Parameters
Date: Friday, September 27, 1996 09:16
Doug:
Another interesting part of the experiment is to weigh the
samples that had been baked to remove the moisture, after they
had again been exposed to the normal plant atmosphere. In a
similar study done in a previous life, we weighed the samples
every 15 mimites after removal from the oven. We found that 60%
of the moisture returned to the samples within 2 hours and 90%
returned within 24 hours. This indicated to us that if we were
to gain any advantage from baking the PWBs, we had to process
those boards within 2 hours.
Harry O'Halloran
______________________________ Reply Separator
_________________________________
Subject: Re: ASSY Moisture Release Rates and Prebake Parameters
Author: Bob Neves <[log in to unmask]> at INET
Date: 9/26/96 11:46 AM
Doug,
There are several factors other than PWB substrate material which will also
influence moisture release rates: Percentage Copper (planes & circuits);
Thickness; Storage Environment; Soldermask; and probably a few others that
don't come to mind right now. The point is that it is going to be difficult
to throw a specific "one time fits all" into moisture prebakes.
The longer your PWB's bake, the more likely solderability problems will
creep
in due to oxide formation and intermetallic growth acceleration. Obviously
an
inert environment will retard oxidation, but will do little for heat
accelerated intermetallic growth.
The easiest way to calculate the best prebake times for your set of PWB
moisture circumstances is to perform a simple weight loss study. Take a
couple of your ready to assemble PWB's and cut them into 2" x 2" squares.
Very accurately weigh and number each sample with a laboratory scale. Place
all of the samples into your prebake oven, removing samples at 15 minute
intervals. Immediately re-weigh the removed samples, and calculate the
percentage weight loss due to moisture. It will become very clear where the
weight loss percentage levels flatten out, allowing you to calculate your
point of diminishing "prebake time" returns.
At 08:26 AM 9/26/96 -0700, you wrote:
>We are looking for reports or other references for moisture release rates
>for different PWB substrate materials. Also recommended prebake parameters
>for time and temperature in air and for other atmospheres. Any leads will
be
>appreciated
>
>Mel Parrish
>We can be reached at: e-mail: [log in to unmask]
>Manufacturing Technology Training Center (MTTC), Inc
>543 Graaf Street Phone 619 446-5571
>Ridgecrest CA 93555 Fax 619 446-4337
>Home Page: http://www1.ridgecrest.ca.us/~mttc/mttc.htm
>Bulletin Board: 619 446-4087
>
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Bob Neves
Director of Technical Services
MICROTEK LABORATORIES
(800) 878-6601
[log in to unmask]
http://www.TheTestLab.com
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Date: Thu, 26 Sep 1996 11:46:51 -0700
To: [log in to unmask]
From: Bob Neves <[log in to unmask]>
Subject: Re: ASSY Moisture Release Rates and Prebake Parameters
Cc: [log in to unmask] (Doug Whitnell)
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