1st thing to be said; I work for a company that supplies Desiccant Dry cabinets to the electronics industry for the storage of moisture sensitive components. The answer here really lies in inventory management/control. Ultimately you want to avoid baking where possible, and this can be achieved with some kind of tracking system (automatic or manual, but this will be a necessity) and a dry storage cabinet. IPC/JEDEC J-STD 033a states; �4.1.2 Short Duration Exposure Previously dry SMD packages, which have been exposed only to ambient conditions not exceeding 30�C/60% RH may be adequately dried by room temperature desiccation using dry pack or a dry cabinet.�
So by controlling the total floor exposure time components are permitted (dependant upon their MS Level) and utilizing a dry storage cabinet, you can avoid baking altogether.
One of the suggestions in the posts above was to use Moisture Barrier Bags (MBB) with a bag of silica gel desiccant. There are a number of thoughts/concerns that come up here.
1)How fresh is the desiccant that is being used? And how will you maintain and verify it's 'activity'? 2)Can you guarantee that the bags will not be punctured or otherwise sealed improperly? 3)What is the propensity of the component carrier to absorb moisture, and how much �unplanned� moisture is going into the bag with the carrier? 4)Personal thoughts on a vacuum sealer�. I�ve seen set-ups where you can practically scan the barcode through the MBB the vacuum has sealed it so tight, and I wonder how there is sufficient space/pressure for the moisture to defuse out of the component to be captured by the desiccant.
Desiccant dry cabinets are able to maintain an RH level of less than 1%, they auto recycle their synthetic desiccant to ensure that it is always at it's most active. They are basicaly a "plug in and forget" type of solution for this problem.
If you are interested you can find a number of resources on this topic of MSD storage and handling as well as (of course) product information on our website, which is; www.drycabinets.com
As one of the posters mentioned above; We will also be exhibiting at APEX this year (2004), our booth number is 1417, stop by and see us.
Hope this helps.
Kevin McCarten
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