I have been thinking about your reply and the article from Peter Duncan
sent me an article promoting a combination of heat and vacuum as a
method for drying components. I am still having trouble accepting the
notion that the relationship between the boiling point of water and
pressure are not significant in the "popcorn effect".

Can we make popcorn (real popcorn) at reduced temperature and higher
elevation. A qualified Yes, because the water boils at a lower
temperature. But no if the water is driven off before the corn cooks
enough to become "popcorn". Can we bake a cake at higher elevation. No,
because water boils out of the mixture at a temperature too low to allow
cooking to take place (chemical changes to the proteins and sugars in
the mixture).

What about making popcorn under increased pressure. Sorry, in a
submarine popcorn is a problem. When the boiling point of water is too
high the corn burns before the water turns to steam.

Ahhhh. Here is a novel idea. Reflow under increased pressure. If the
water in the package cannot turn quickly to vapor, it cannot damage the
components. Is there a patent here?

The problem I see is that nobody has qualified the low pressure
processes. I think it is a promising solution, the trouble is we haven't
established the relationship between temperature and pressure to safely
dry the package.

> -----Original Message-----
> From: Paul Signorelli [mailto:[log in to unmask]]
> Sent: Tuesday, December 10, 2002 9:31 AM
> To: [log in to unmask]
> Subject: RE: [TN] Vacuum
>
>
> Hi Guy,
> i think the technical reason is that the vacuum helps the
> molecular desorption process at the exposed surface of the
> molding compound. That is a rate controlling step...The bulk
> diffusion in the mold compound is considered a thermodynamic
> process (i think the compound is essentially an
> incompressable material in a thermodynamic sense), Then the
> vacuum would not change the diffusion process very much but
> may flatten the line a bit faster only if the desorbtion
> process is faster.. It may not really help but it is an easy
> way to get <5 % RH
>
> Paul Signorelli
> Reliability Engineer
> Sanmina-SCI Corporation, Plant 432
> 702 Bandley Dr.
> Fountain, CO 80817
>
> eMail address: [log in to unmask]
> Phone: 719-382-2352,   Fax: 719-382-2520
>
> >>> "Guy Ramsey" <[log in to unmask]> 12/10/02 06:26AM >>>
> Good point, quantity of water per unit volume is the issue.
> And you may be right about not seeing vacuum in a solid. But
> then, it wouldn't be sucking but simple dispersion acting on
> the moisture within the hydroscopic solid. Things that make
> you go hummm.
>
> > -----Original Message-----
> > From: Paul Signorelli [mailto:[log in to unmask]]
> > Sent: Monday, December 09, 2002 10:23 AM
> > To: [log in to unmask]
> > Subject: Re: [TN] Vacuum
> >
> >
> > Thanks for checking that out Guy...
> > i don't think the vapor inside the parts see a vacuum, they
> > only see the sucking action on the diffusion barrier. You
> > can't lower the boiling point inside the part, if the vacuum
> > can't get to the moisture inside. It is different with
> > themperature exposure, there the moisture does get exposed to
> > direct heat. These MS parts are semi-hermetic and vacuum
> > drying might be the best way to desorb them... i have seen
> > very little written about this.  i run a vacuum chamber at
> > 40C for drying out plastic BGA's on reels.
> > The question is how time does the vacuum procedure save ?
> > i just use shop vacuum, not a high vacuum pump.
> > At 6000 feet there isn't much air around anyway.
> > The suggests the fact that the RH is not the important
> > factor, it is the Absoulte Humidity. a completely different
> subject...
> >
> > Paul Signorelli
> > Reliability Engineer
> > Sanmina-SCI Corporation, Plant 432
> > 702 Bandley Dr.
> > Fountain, CO 80817
> >
> > eMail address: [log in to unmask]
> > Phone: 719-382-2352,   Fax: 719-382-2520
> >
> > >>> [log in to unmask] 12/09/02 06:20AM >>>
> > Sorry, I couldn't follow up on this thread last week. And I
> > wish I had hard data to support my statement. Steve had it
> > right. I am aware that some companies are combining heat with
> > vacuum to reduce temperature demands for resetting Moisture
> > Sensitive Devices. One of the Intersil link that Steve
> > provided last week contained equations for absorption and
> > desorption. These do not include pressure (which changes the
> > boiling point). I have not been able to find any work that
> > includes this variable. I did go home one evening and dig out
> > an old college physics text. The whole thing is a lot more
> > complex than would first appear.
> >
> > I don't think there is a serious danger posed to components
> > unless you "significantly"  exceed the boiling point of water
> > at a given pressure. But what is "significant"? I can't put
> > my finger on it. J-STD-033A has bake-out temps of 125 degrees
> > C for users, and 150 degrees C for supplier bake prior to Dry
> > Pak. Does that mean that bake out at 50 degrees C above the
> > boiling point of water at 0.2 bar (about 12,000 meters
> > altitude)? I don't think so.
> >
> > -----Original Message-----
> > From: TechNet [mailto:[log in to unmask]] On Behalf Of Mary Jane Chism
> > Sent: Friday, December 06, 2002 2:12 PM
> > To: [log in to unmask]
> > Subject: Re: [TN] Vacuum
> >
> >
> >
> > Guy,
> > I am gathering information of the rules and regulations of
> > MSD (Moisture Sensitive Devices). I am in the process of
> > developing a training class for MSDs. Please explain how
> > vacuum would damage the device. Are you talking of a physical
> > aspect of damage, esd damage, etc.? Apparently, I need to
> > learn more about these before I teach the class.  Thanks.
> >
> > Mary Jane Chism
> > Technical Trainer
> > Kimball Electronics Group
> >
> > -----Original Message-----
> > From: Guy Ramsey [mailto:[log in to unmask]]
> > Sent: Friday, December 06, 2002 1:39 PM
> > To: [log in to unmask]
> > Subject: Re: [TN] Vacuum
> >
> >
> > Yes.
> > Moisture sensitive components can be damaged by vacuum.
> >
> > > -----Original Message-----
> > > From: TechNet [mailto:[log in to unmask]] On Behalf Of Stolar, Paul W
> > > Sent: Friday, December 06, 2002 11:33 AM
> > > To: [log in to unmask]
> > > Subject: [TN] Vacuum
> > >
> > >
> > > Has anyone ever heard of vacuum damaging components?
> > >

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