Moisture Sensitivity
Plastic IC packages absorb moisture from the surrounding environment. This is a typical characteristic of the materials (mold compound and die attach) used in the construction of plastic packages. The moisture inside the package increases or decreases to reach the relative humidity (RH) of the surrounding environment. Weight gain/loss analysis is used to determine the time it takes for a package to reach moisture saturation or the time required for removing it. This information is used to specify maximum exposure times and minimum dry-baking times for a particular package.
Moisture inside the package turns into steam when the package is exposed to the vapor phase/infrared reflow and/or wave-soldering processes that are common in the fabrication of printed circuit boards (PCBs). The resulting steam and vapor pressure can cause cracking of the package, a phenomenon called popcorning.

Dry-Packing Process
If a package is moisture sensitive (level 2 or higher), it must be dry packaged. Normally, in this process, packages are baked for 24 hours at 125C.±5 C°. Baking time could vary depending on the package type.

Dry Packing
Dry packing consists of baking the packages to reduce moisture to a level not to exceed 0.05% by weight. Then, the units are placed in a moisture-barrier bag, along with desiccant, to keep the moisture inside the bag to a level <20% RH. Each product is labeled as moisture sensitive, outlining the necessary precautions for handling the product. Table 1 shows the floor life for the different package moisture-sensitivity levels.
Table 1 . Floor Life For Different Package Moisture-Sensitive Level 

Note: X=time between bake and dry bake at the manufacturing site
           Y=floor life of package after removal from dry-pack bag
           Z=total soak time
           The values are default values. If the actual time exceeds this value, use the actual time and adjust the soak time.

Typical Packing Method
The typical packing method requires the following materials:
• Stick magazines (shipping tubes), trays, tape and reel
• Desiccant
• Moisture-barrier bag
• Labels [moisture-sensitive identification (MSID) label, dry-pack caution label]
• Humidity-indicator card
Example of tray and tape-and-reel dry pack are shown in Figure 1 and 2.
Figure 1. Tray Box and Sealed Moisture-Barrier Bag (Top), Opened Bag and Tray Stack (Bottom)

 
Figure 2.Dry-Packed Tape-and-Reel Configuration 
 

Moisture-Sensitivity Labeling

Primary and intermediate containers containing moisture-sensitive packages are labeled as
shown in Figures 3 and 4.

Figure 3. Moisture-Sensitive Identification (MSID) Label

The MSID label is applied to the outside of the intermediate container near the TI barcode label.
This label indicates that moisture-sensitive packages are inside.
The moisture-sensitivity caution label (see Figure 4) is applied to the reel (for tape-and-reel configurations) and to the outside of the sealed moisture-barrier bag. This label contains detailed
information specific to the device (moisture-sensitivity level, floor life, etc.).

Figure 4. Moisture Sensitive Caution Label(Levels 2a Through 5a)

The humidity-indicator card (see Figure 5) is placed inside the sealed moisture-barrier bag.
This card verifies that the product has been stored and shipped in a low-humidity environment.

Figure 5. Humidity-Indicator Card