Quick answer: The desiccant clause of a J-STD-033 dry pack procedure should do more than name a part number. It should record how the quantity per bag was calculated (bag WVTR at its test condition, bag area, required shelf life and the desiccant's capacity per unit), how desiccant is stored and how long a bag of desiccant may be open, the incoming check that proves it is still active, where it goes in the bag next to the humidity indicator card, and which indicator reading triggers a re-bake or repack. Recording the inputs, not only the answer, is what lets the site change bag, desiccant or shelf life later without starting over.
Procedures written when a line starts tend to stay unchanged for years. That makes the first version of a moisture-sensitive device (MSD) handling procedure unusually important. SEMI's 300 mm Fab Outlook, as reported by Evertiq on 15 October 2026, projects the number of Americas 300 mm fabs or lines starting operations rising from 13 in 2026 to 23 in 2027. Each new site, and the assembly and EMS operations around it, will write or adopt a dry pack procedure.
Where the desiccant sits in the dry pack
IPC/JEDEC J-STD-033 describes dry packing for surface-mount devices: components on reels or in trays, a humidity indicator card (HIC) and desiccant, sealed in a moisture barrier bag (MBB). The desiccant's job is to absorb the moisture that permeates the bag during its shelf life, keeping the HIC, and the parts, below the limit for their moisture sensitivity level.
The desiccant clause, item by item
1. Quantity per bag, with the calculation
J-STD-033 gives a formula of the form U = (0.304 × M × WVTR × A) / D, where U is the number of desiccant units, M the required shelf life in months, WVTR the bag's water vapour transmission rate, A the bag's surface area and D the moisture capacity of one unit as defined in the standard. Write all four inputs into the procedure, with the WVTR's test condition and the source of the capacity figure. If the bag supplier, bag size or shelf life changes, the procedure then tells the engineer exactly what to recalculate. Worked methods are in desiccant sizing with JEDEC and isotherms, and unit definitions in desiccant units, MIL-D-3464 and JEDEC.
2. Desiccant type and its capacity evidence
Name the desiccant type and require the supplier to provide capacity data at the low humidity the bag is meant to hold, with the test temperature, humidity and method. This matters most if you consider a material other than the classic clay or silica gel units: ask any supplier, ATMOSIScience included, how their unit equivalence was derived. Plant-fiber desiccant does not yet have a published J-STD-033 unit value, so its use in a dry pack has to rest on your own qualification data.
3. Storage and open time
Desiccant starts loading as soon as its own container is opened. The clause should state how unopened desiccant is stored, the maximum time a desiccant container may stay open on the packing bench, and what happens to partly used containers (reseal, re-dry or discard).
4. Incoming and point-of-use checks
Specify a check that proves desiccant is still active before it goes into a bag: weight gain against a fresh reference sample, or loss on drying against the supplier's limit. See LOD as an incoming QC test.
5. Placement and line safety
State where the desiccant goes relative to the reel and the HIC, and require a format that cannot shed particles into the bag. Static, dust and metal detection considerations are covered in line-safe desiccants.
6. HIC reading and actions
Link the HIC spots to actions on opening: within limit, use; above limit, follow the bake or re-dry rules for that MSL. See humidity indicator cards and RH points.
7. Records
Record the bag seal date and time, desiccant lot, quantity used and the operator. When a lot of parts fails a moisture check later, these records are what separate a desiccant problem from a bag or process problem.
A template you can adapt
| Field | Example entry |
|---|---|
| Bag | Supplier, part number, size, WVTR and its test condition |
| Shelf life required | Months from seal, per MSL policy |
| Desiccant | Type, supplier, capacity per unit with test condition and source document |
| Units per bag | Calculated value and rounding rule |
| Storage and open time | Sealed storage location; maximum open minutes per container |
| Incoming check | Method, sample size and acceptance limit |
| HIC actions | Reading thresholds and the action for each |
Beyond the reel: other electronics packs
Many electronics products are not dry-packed reels: finished boards, modules, appliances and spares shipped in cartons. Those use the same sizing logic without the J-STD-033 framework. See desiccant for electronics and PCB condensation and the desiccant sizing calculator.
Frequently asked questions
What does J-STD-033 say about desiccant?
It sets how dry packs for moisture-sensitive devices are built and how the desiccant quantity is calculated from bag WVTR, area, required shelf life and desiccant capacity. Use the current revision of the standard itself for exact definitions.
How many desiccant units go in a moisture barrier bag?
It is calculated per bag from the formula's inputs. Two bags of different size or barrier need different quantities.
Can a plant-fiber desiccant be used in a dry pack?
Only with your own qualification data. There is no published J-STD-033 unit value for fiber desiccant, so the procedure would have to cite measured capacity at the bag's target humidity.
How long can desiccant stay open on the packing bench?
Set a written limit based on your room humidity and verify it with weight-gain checks. Reseal partly used containers immediately.
Get capacity data for your dry pack calculation
Tell ATMOSIScience the bag, target humidity and shelf life your procedure needs. We will share measured capacity at that condition and how it was tested, so your engineers can decide on evidence.
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