We request PCB suppliers to do a final baking before vaccume seal PCBs in 
a pack of 20 (board size of 6" x 4") with a desiccant pack before 
shipment. Suppliers mark the date of baking on cartons for receiving and 
internal usage control. We only re-bake the PCBs if date of use is > 3 
months from date of baking. 

PCBs are stored in original carton boxs (sealed) until go to Pick & Place 
machine and this helps to slow down the moisture absortion.

regards.
----------------------[Reply - Original Message]----------------------

Sent by:"Dill, Norm J" <[log in to unmask]>
 
    Our air conditioning system here mixes in a large volumes of outside 
air 
to help control the inside temperature while economizing on energy costs. 
 As a result, the inside and outside humidity levels are very similar.
     Our PWB s (FR4 & polyimide) are purchased and stored with desiccant 
included in each package of 10.  At best, this results in slightly higher 
costs from our suppliers, extra handling in our stock room and later 
baking 
steps.
    We are considering restructuring our PWB stocking procedures.
    Does anyone have pro/con examples of board storage in this kind of 
environment?  For example, does the desiccant actually keep the boards 
from 
absorbing moisture during high humidity days?  What would be expected if 
the 
boards were wrapped/stored in slip sheets and bound with duct tape or left 
open on the shelf?  If the humidity was controlled, could the desiccant 
and 
some baking steps be eliminated without an increase in warpage problems.
     Any opinions, examples or references will be appreciated.

     Norm Dill
     [log in to unmask]


=====================================================================