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2. Details


2.1 Dry pack packing
NEC Electronics uses dry packs to prevent moisture absorption for peace-of-mind soldering.
The following explains the moisture absorption characteristics of dry packs.

2.1.1 Complete dry pack and simple dry pack 2.1.2 Long-term storage of complete dry pack
2.1.3 Resealing of complete dry pack  


2.1.1 Complete dry pack and simple dry pack
Figure 2.1 shows the moisture absorption characteristics when a QFP thin type package (thickness 1.5mm) packed in complete dry pack and simple dry pack are left in an ambience of 40 and 90%. The figure shows that while the simple dry pack product absorbs a considerable amount of moisture, the complete dry pack product absorbs hardly any.


Complete dry pack
In this form of packing, a bag for the moisture absorption device is sealed together with a desiccant made from aluminum laminate.

Simple dry pack
A transparent plastic bag used for devices for which anti-moisture absorption measures are not taken.
 Figure2-1Complete dry pack and simple dry pack

Figure2-1 Complete dry pack and simple dry pack

2.1.2 Long-term storage of complete dry pack
Figure 2-2 shows the moisture characteristics of a complete dry pack. First, three each of a QFP thin and thick package (1.5mm and 3.7mm respectively) are made up with a complete dry pack . One each is then left in a tank at 40 and 90% for 0 hours, one month, and one year. This figure shows that the complete dry pack does not absorb moisture even after one year, and thus is moisture-proof.


Figure 2-2 Long-term storage characteristics of complete dry pack
Figure 2-2 Long-term storage characteristics of complete dry pack

2.1.3 Resealing of complete dry pack
Procedures when all the complete dry packed products cannot be installed and are resealed using tape are as follows.

(1) Moisture absorption      (2)Restrictions


(1) Moisture absorption
In Figure 2-3, a thin QFP package (1.5mm) is placed in an aluminum laminate bag with desiccant, then temporarily resealed using cellophane tape or vinyl tape, and left in an ambience of 40 and 90%. Figure 2-4 shows the resulting moisture absorption characteristics.
This shows the package to be highly effective, as it has hardly absorbed any moisture even after being resealed. It is recommended that the storage condition be kept at 168H or less in this case, as the effectiveness will be reduced when temperature and humidity rise after resealing.

Figure 2-3 Moisture absorption characteristics of resealed aluminum laminate bag

Figure 2-3 Moisture absorption characteristics of resealed aluminum laminate bag


Figure 2-4 Method of resealing aluminum laminate bag

Figure 2-4 Method of resealing aluminum laminate bag


(2) Restrictions
When using tape for resealing , take care with the following.
(a) Resealing should be performed within the time limit after opening a dry pack and in accordance with the method shown in Figure 2-4. Resealing should be only be performed once.
(b) The limit for resealing is 168 hours.
(c) The sealed time after resealing is not to be included in the expiry time after opening the dry pack.
*For the time limit after opening the dry pack, see the soldering conditions for each product.
The following is an example of storage time calculations for resealing.

example: After opening a dry pack, if the product must be used within 72 hours, the storage time shall be as shown below.
Figure 2-5 example of storage time calculation for resealing
Figure 2-5 example of storage time calculation for resealing
The time limit after opening the dry pack is X+Z=72H; the storage time after sealing by tape is Y=168H. Therefore the total storage time will be 240H.



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