Fred,
        Go to JEDEC's web site and download "IPC/JEDEC J-STD-033  Standard
for Handling, Packing, Shipping and Use of Moisture/Reflow Sensitive Surface
Mount Devices".  It will not only give the formula you are looking for, but
also the basis of setting up your moisture sensitive device handling
procedures.  The formula will require you to know the amount of water the
desiccant will hold for a certain relative humidity.  Intel has a chart you
can use to get that amount.  That document is also downloadable from Intel's
internet site.  It is in their 1999 Packaging Databook chapter 8 page 20.

Good Luck!
Ryan Grant

> -----Original Message-----
> From: Fred Biederman [SMTP:[log in to unmask]]
> Sent: Wednesday, February 16, 2000 6:57 AM
> To:   [log in to unmask]
> Subject:      [TN] Moisture Sensitive parts
>
>      Can anyone show me how to calculate the size of the desiccant bag
> that
>      is required when resealing components into a bag?
>
>      Presently we receive Moisture Sensitive components sealed in a static
>      sensitive bag. We will open the bag and place the SMD parts on the
>      board. After the build these components will be sent to a nitrogen
>      cabinet where they get lost and forgotten. This area creates a lot of
>      scrap.
>
>      We have the vacuum sealer that is gathering dust and needs to be
>      installed.
>
>      I have found a supplier of the desiccant and the Humidity Indicators.
>
>      My goal is to set a procedure for returning these components back to
>      the store room.
>
>      Thank you
>      Fred
>
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