Now this discussion is headed in the right direction. With HP consultancy
help, it took me three months to develop a MSD and vacuum seal procedure
meeting specified requirements.
Five years ago, HP and others, performed similar experiments to TI. The
results were the same.
Yes, the operators have some problems but not when properly trained, made
responsible, and made accountable. One is the tendancy for an individual to
crank up the vacuum ruining what's inside and, two, getting their little
fingers caught in the heat sealing mechanism.
No matter the process, once properly developed, works just fine, thank you.
The has been shown at many places from distributors, don't trust them here,
to dock to stock, if any in a Lean Mfg capability. Then, when opened,
storing unused parts in an intert atmosphere, as Nitrogen, then rebaking
when time specified exceeded.
It's all there folks so no opinions needed. Just the facts will do.
MoonMan
----- Original Message -----
From: "Francois Monette" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, May 02, 2002 9:50 AM
Subject: [TN] Vacuum Seal and MSD
> Steve,
>
> Here is some more information that will explain and support what I said
> earlier. There are always many ways to skin a cat, but only one that is
the
> industry standard.
>
> The proper guidelines for bag sealing are actually specified in the JEDEC
> standard EIA/JEP124 section 5.2.1 Packing moisture-sensitive components :
> "...Partially or lightly evacuate the bag to reduce packaging bulk and
heat
> seal the bag as close to the end as possible following the heat sealing
> equipment manufacturer's guidelines. The bag should not be completely
> evacuated since this will reduce the effectiveness of the desiccant and
> possibly damage the content..."
>
> As far as I know there are two technical reasons to explain this :
>
> 1. With a tight vacuum, the desiccant is squeezed between the bag and the
> stack of trays. There is no surface contact with any air that would allow
it
> to pull moisture from everywhere inside the bag.
>
> 2. A high vacuum will slowly pull the outside air and the humidity that it
> contains through the bag. Over time the moisture content inside the bag
will
> increase faster than with no vacuum.
>
> I am aware of some experiments that were made by TI a couple years ago. It
> showed that when dry bags were opened, after 1.5 years, bags with low
vacuum
> had less than 10% RH inside, while bags with high vacuum had 15% RH
inside.
>
> Of course you could use a vacuum sealer with very low vacuum but not all
> machine types can be set at low values. Many people use machines
originally
> designed for the food industry and even at the lowest setting they will
pull
> too much vacuum. Also I have seen that over time people tend to crank up
the
> vacuum level (that warm and fuzzy feeling once again). And trust me, you
can
> pull a high vacuum inside a dry bag. When you can read the marking that is
> embossed in your JEDEC tray you know you're in trouble...I personally
think
> that it is safer to use a standard heat sealer and ask your operators to
> remove the excess air before sealing.
>
> And yes I know, many suppliers are not aware of this very important
> specification. Feel free to point them to the right document.
>
> Regards,
>
> François Monette
> Cogiscan Inc.
> Tel : 450-534-2644
> Fax : 450-534-0092
> E-mail : [log in to unmask]
> www.cogiscan.com
>
>
>
> Date: Wed, 1 May 2002 20:39:32 EDT
> From: [log in to unmask]
> Subject: Re: vacuum seal and MSD
>
> Hi Earl!
>
> Nice procedure. But this thread has raised a few questions that I'm trying
> to
> sort out.
>
> There have been a few responses that have said that vacuum sealing is
> actually not a good thing. Then there was the response that you shouldn't
> use
> dessicants when vacuum sealing...these differing views have come from well
> respected people. Which only confuses me more...
>
> I originally thought that vacuum sealing was probably about the best thing
> you could do to preserve shelf life...but now I'm not so sure...or shall I
> say from the reponses from a few have posed some questions, and now I'm
not
> so sure....
>
> Is there anything out there that can settle the questions about this
issue?
> Anyone?
>
> -Steve Gregory-
>
> ------------------------------
>
> Date: Wed, 1 May 2002 22:52:44 EDT
> From: [log in to unmask]
> Subject: [TN} Vacuum Sealing...
>
> Why is this there this disparity? Don't understand it at all..
>
> Why is there so many differing opinions concerning component storage?
>
> Geeze, this is really weird! We don't know about this subject at all, do
we?
>
> -Steve Gregory-
>
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