The need to keep components dry between the time of manufacture and the point of reflow soldering led to the development of Moisture Barrier Bags.
Sometimes called Vapor Barrier Bags, they are made from multiple layers of plastic and aluminium that control moisture vapor leakage.
It’s also a protective packaging process that can prevent oxidation.
MBBs are increasingly used to pack other goods or moisture sensitive assemblies/devices for long term (up to 1 year) storage and transport.
Moisture Vapor Transmission Rate
The rate at which water vapor passes through a specific area of barrier material. As MVTR is reduced, dry storage time is increased and desiccant loading is reduced.
MVTR is measured in grams of water per 100 square inches of barrier per 24 hours ( gms / 100in² / 24 hours)
IPC/Jedec J STD 033 (electronic application)
EIA 583 for storage with a known humidity level
MIL P116 General application
Calculation of desiccant to be included
Application; dry storage of SMDs
- What you need to know: Bag size, Bag MVTR, Storage time in months, desiccant capacity at 10%RH & 25°C.
- Formula: Units = (0.304 x Months x Bag MVTR x Bag Area) / Moisture Capacity
- Example: 10” x 20” inch Barrier Bag, with a 0.0006 MVTR and a12 month storage time. Find Bag Area: 10” x 20” x 2 sides = 400 inches².
- Apply Formula: Units = (0.304 x 400 in² x 0.0006 MVTR x 12 months) / 2,9 g/unit
- Units = 0.3 : use 1/2 unit of Desiccant.
When the desiccant capacity at 10% RH and 25°C is not known the quantity needed can be estimated using the following simplified equation. U = 5 X 10-3 A
- U = Amount of desiccant in UNITS
- A = Total exposed surface area of the MBB in square inches
Items to consider when selecting a moisture barrier bag
- Very good MVTR (0,0006 g/100 sq inch /day)
- The lower the MVTR the longer we can store the product and less desiccant we have to use
- Very good mechanical resistance (155µ )
- Purchase price
- ESD safe
- MSL label (JEP113) printed on the bag
- Additional flap length for reuse
Download the complete Moisture Barrier Bags Tutorial