Richard,
Since I am really not a PWB guy, please take this with whatever size grain
of salt you wish.
Even if you were able to pull the board down to a few millitorr, I cannot
see how only 60 minutes is going to accomplish much. However, if it did, 1
hour is certainly less time than 8. Maybe I missed something.
In microelectronics applications, where hermetic packages were created, we
would vac bake at 125-150°C for 16-72 hrs, depending on the particular
device, application, etc. I believe that most of the time we would be in
the 100-200mT range.
Since components within the assembly were predominantly non-organic, one
would think that our times were long, but residual gas analysis of sealed
assemblies directed our process conditions. It is very interesting how much
moisture can be adsorbed on/in plated surfaces and other surfaces within the
module. And we did not have wet 'ol laminiate inside to pollute the
atmosphere within the package...
The caveat is that this may be an entirely ultra right/left wing comparison
to a PWB. We were seeking internal moisture levels in the 10's of PPM
moisture. I wouldn't think that you needed such low levels.
I just find it hard to comprehend that a significant amount of the moisture
in a board [that has sat out in room air for any length of time] can be
expelled in only 60 minutes [at what vac level], with/without the addition
of heat.
If the moisture were to come out of the board that quickly, would one have
to be concerned about delamination, etc. due to the vac process alone?
Certainly, you are speaking of bare boards - right? Be interesting to see
how well can-type electrolytics held up on a vacuum!
You may just have to do some testing of your own...
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of SALA GABRIELE
Sent: Friday, June 01, 2012 11:53 AM
To: [log in to unmask]
Subject: [TN] R: [TN] Vacuum Drying of PCB's
Hello Rich,
by using Vacuum Drying method to dry-off the PCBs, compared to a classic
baking method this one provides plenty of benefits in terms of time
reduction for a cycle, vacuum helps moisture diffusion, also as we know
moisture boiling point temperature under vacuum is lower then in open
atmosphere that means thermal stress reduction on PCB/Laminates.
Furthermore, by using Vacuum, other significant benefit is no oxidation of
PCB metal surfaces, plus heavy Power consume reduction
In the other hands, cost and serviceability of vacuum machine should be more
expensive then classic electrical oven. Also the cost should be higher.
Let's wait for someone who experimented or are using VD.
Regards
Gabriele
-----Messaggio originale-----
Da: TechNet [mailto:[log in to unmask]] Per conto di Richard Kraszewski
Inviato: venerdì 1 giugno 2012 16.48
A: [log in to unmask]
Oggetto: [TN] Vacuum Drying of PCB's
I would appreciate anyone sharing their thoughts on vacuum drying of PCB's.
What conditions do you use? (Time, temp and vacuum)
I realize it can be used to reduce required peak temperature but is there
potentially any time reduction benefit to using vacuum?
I saw a paper from the "Electronic Components and Systems Division within
German Electrical and Electronic Manufacturers´Association Working Group",
entitled
"Recommendation & Guideline Values for drying for bare PCBs"
The offered a rather paltry reduction in drying time of 60 minutes from 8
hours if vacuum was used. Doesn't seem like much of a benefit.
Rich Kraszewski/PLEXUS
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