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
>
>***************************************************************************
>* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
>***************************************************************************
>* To unsubscribe from this list at any time, send a message to: *
>* [log in to unmask] with <subject: unsubscribe> and no text. *
>***************************************************************************
>
>
>.
>
>
>
Bob Neves
Director of Technical Services
MICROTEK LABORATORIES
(800) 878-6601
[log in to unmask]
http://www.TheTestLab.com
***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To unsubscribe from this list at any time, send a message to: *
* [log in to unmask] with <subject: unsubscribe> and no text. *
***************************************************************************
Received: from camelot.dsccc.com by inet.dsccc.com with SMTP
(IMA Internet Exchange 2.02 Enterprise) id 24AE8600; Thu, 26 Sep 96 15:32:32
-0500
Received: from offramp.dsccc.com (onramp.dsccc.com [192.1.1.139]) by
camelot.dsccc.com (8.6.11/8.6.10) with SMTP id OAA05693; Thu, 26 Sep 1996
14:51:54 -0500
Received: by offramp.dsccc.com (5.67b/SMI-V1.8)
id AA20296; Thu, 26 Sep 1996 14:52:41 -0500
Received: from ipc.org(168.113.24.64) by offramp via smap (V1.3mjr)
id sma020136; Thu Sep 26 14:52:10 1996
Received: from ipc.org by simon.ipc.org via SMTP (940816.SGI.8.6.9/940406.SGI)
id OAA06024; Thu, 26 Sep 1996 14:42:03 -0700
Resent-Date: Thu, 26 Sep 1996 14:42:03 -0700
Received: by ipc.org (Smail3.1.28.1 #2)
id m0v6LBU-0000UsC; Thu, 26 Sep 96 13:29 CDT
Resent-Sender: [log in to unmask]
Old-Return-Path: <[log in to unmask]>
Message-Id: <[log in to unmask]>
X-Sender: [log in to unmask]
X-Mailer: Windows Eudora Pro Version 2.2 (32)
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
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)
Resent-Message-Id: <"8Oo8y3.0.FdG.xjiIo"@ipc>
Resent-From: [log in to unmask]
X-Mailing-List: <[log in to unmask]> archive/latest/6497
X-Loop: [log in to unmask]
Precedence: list
Resent-Sender: [log in to unmask]
***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To unsubscribe from this list at any time, send a message to: *
* [log in to unmask] with <subject: unsubscribe> and no text. *
***************************************************************************
|
