We once did an experiment that seemed to indicate that plastic can absorb
water vapor faster than liquid water. The rate was also temperature
dependent. But, it seems from my experience, that spending 10 minutes in the
wash is a little, but not much worse, than 10 minutes at 50% RH.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Kane, Amol (349)
Sent: Wednesday, September 06, 2006 1:18 PM
To: [log in to unmask]
Subject: Re: [TN] Populated board bake out after 1st side reflow/DI wash
Okay, I am intrigued, what is the difference between the moisture absorbed
over time and the moisture (water) absorbed in the aqueous wash?
Amol Kane
M.S (Industrial Eng.)
Process Engineer
Harvard Custom Manufacturing, Inc.
941 Route 38 Owego, NY 13827
Phone: (607) 687-7669 x349
Fax: (607) 687-9733
[log in to unmask]
www.harvardgrp.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Wednesday, September 06, 2006 1:07 PM
To: [log in to unmask]
Subject: Re: [TN] Populated board bake out after 1st side reflow/DI
wash
Hi Joe!
Going through a aqueous cleaner won't cause problems with 2nd side
reflow. The moisture that you have to worry about is the moisture that
is absorbed over time. Sticking to the floor life time guidelines that
go along with the limits of each part, i.e.; Level 1, 2, 3, etc., is
what you need to be concerned about. You don't need to re-bake the
assemblies if you're within the floor life of the part.
-Steve Gregory-
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Macko, Joe @ IEC
Sent: Wednesday, September 06, 2006 11:31 AM
To: [log in to unmask]
Subject: [TN] Populated board bake out after 1st side reflow/DI wash
Fellow techs,
Hello.
A general question came up about the need to re-bake a double sided
board after 1st side reflow/DI wash before starting 2nd side assembly.
The concern is that the board (or mounted MSDs) may absorb enough
moisture going through the high-pressure DI water in-line cleaner to
potentially cause a problem during 2nd side reflow. There are some MSDs
mounted on the 1st side but both sides are assembled before exceeding
any of the component's floor life. It has been suggested that some level
of bake out should be performed after 1st side cleaning to prevent
potential problems during 2nd side reflow but the push back is that this
adds cost, handling, etc... that may introduce its own associated
problems and is not really necessary.
Thanks again. It is great to have a knowledgeable forum such as TechNet.
Joe
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