Katherine,
Here are my answers to your questions :
1. If you are looking for dry bags you should probably consider the bags
that are used to package moisture-sensitive components. Take note that these
bags are normally used in combination with desiccant. This is required for
long term storage since the bags are never perfectly hermetic. The key
specification is the Water Vapor Transmission Rate (WVTR). The highest
quality of bags, as required by J-STD-033 must meet a WVTR of <= 0.002
gm/100 in2 in 24 hrs at 40C. I can point you to a few good suppliers if you
want.
2. I really don't think that a zip-lock type of seal can be efficient to
keep moisture out of a dry bag.
3. The same suppliers that offer dry bags typically offer different models
of HIC as well
4. I am not aware of any standard for PCB dry storage. I believe that this
will vary for every type of board and your supplier might be the best source
of information on this subject.
Francois Monette
Cogiscan Inc.
50 De Gaspe, Suite A5
Bromont, Quebec, Canada, J2L 2N8
Tel : (450)534-2644
Fax: (450)534-0092
www.cogiscan.com
------------------------------
Date: Tue, 18 Dec 2001 10:35:58 -0500
From: "Lambert, Katherine A." <[log in to unmask]>
Subject: Board baking & sealable bags
Hi folks,
Currently we bake our boards and store them in nitrogen cabinets until we
are ready to use the boards on our automated line. Typically, turn around
is fairly quick - within a week - but occasionally is more than a month due
to other part shortages.
We are trying to streamline the process a bit and get rid of the nitrogen
cabinets as they take up a lot of space, and the boards become separated
from the rest of the kit, etc.
We are looking at a bake & bag process. We would bake the boards, seal them
in appropriate bags with a humidity indicator card, and send them to the
assembly area with the rest of the kit. Desiccants are not an option as
they typically have caused our panelized boards to break. We have a variety
of board types - polyimide, epoxy-glass, etc. Since the folks around here
like a one-size-fits-all process, we need to develop the process around the
most sensitive board type.
Now for the questions:
1. Where is a good source for information regarding sealable or resealable
bags that are reasonably impermeable to ambient humidity? Our relative
humidity levels typically run between 30% & 50%
2. We have a bag sealer, but will a zip-lock type bag work just as well?
3. Where is a good source for information regarding humidity indicator
cards?
4. Is there any reliable information regarding how long a baked board can be
exposed to ambient humidity before it has to be rebaked?
Thanks for any insight you can provide.
Kathie Lambert
Process Engineer
Northrop Grumman
Baltimore, MD
410-765-9746
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