Wrapping sheet for electronic parts

A wrapping sheet is provided to keep electronic parts in an excellent dry condition and let static electricity caused by the friction of materials release to the outside. The wrapping sheet for enveloping electronic parts comprises an air permeable sheet at one side, an air non-permeable sheet with a conductive layer on the other side, separate pouchy portions formed between both the sheets, and silica gel and conductive foam beads enclosed in each separate pouchy portion.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a wrapping sheet for enveloping liquid crystal 
parts, electronic parts such as IC, LSI and VLSI, and other precision 
parts. 
2. Description of the Prior Art 
In case of storing and transporting electronic parts such as IC and LSI, 
water can attach to the electronic parts or moisture can soak into them 
under the dew point, and as a result the electric leak arises in the 
electronic parts or the conduction defect, disconnection and other error 
functioning occur in them due to the corrosion of the parts. For that 
reason the electronic parts must be stored and transported in the dry 
condition, so that until now desiccant has been used to keep them in the 
dry condition. However, when the particles of desiccant or the sheets of 
plastic material for enclosing the desiccant rub mutually during the 
transportation, such friction generates static electricity. The amount of 
the static electricity is increased especially, because the humidity is 
lowered with the desiccant. Since MOS type IC has the extremely thin oxide 
film for insulating its gate electrode, the discharge of the generated 
static electricity destroyed the insulation, and it was a problem that the 
semiconductors of the IC were affected adversely. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to provide a wrapping 
sheet for electronic parts which is capable of keeping the electronic 
parts in an excellent dry condition and at the same time favorably 
resolving the bad influence on the electronic parts due to the static 
electricity generated increasingly in that dry condition. 
The foregoing object of the present invention is accomplished by providing 
a wrapping sheet for electronic parts comprising an air permeable sheet on 
one side, an air non-permeable sheet with a conductive layer on the other 
side, separate pouchy portions between both the sheets, and silica gel and 
conductive foam beads enclosed in each separate pouchy portion. The object 
is also accomplished by providing a wrapping sheet described above wherein 
a transparent portion is formed on said non-permeable sheet in each 
separate pouchy portion. 
The wrapping sheet is capable of removing the moisture around the 
electronic parts favorably with the silica gel enclosed in the separate 
pouchy portions. Also the wrapping sheet is capable of favorably 
protecting the electronic parts owing to its high shielding effect against 
the static electricity. This effect results from the fact that the static 
electricity generated due to the friction of the silica gel and so on is 
released through the conductive form beads to the outside non-permeable 
sheet, which also releases the static electricity outside through its 
conductive layer. In addition, the cushiony effect of the form beads can 
prevent effectively the silica gel from being crushed and can protect the 
electronic parts from the outer shock favorably. 
The transparent portion formed on the non-permeable sheet in the separate 
pouchy portion makes it possible to check the water absorbing capacity of 
the inner silica gel from the outside therethrough.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The embodiment of this invention will be explained on the bases of the 
drawings hereinafter. 
FIG. 1 is a perspective view of a wrapping sheet for enveloping electronic 
parts. 
An electronic parts 1, which is a substrate installed with IC, LSI and so 
on, is first enveloped by the wrapping sheet 2 around its outer surface, 
kept airtight in an airtight bag 18, and then, packed in the outer box 26, 
stored and transported. 
The wrapping sheet 2, as shown in FIG. 2, consists of sheets which form a 
plurality of separate pouchy portions 3, 3, 3 at predetermined intervals. 
Each separate pouchy portion 3 encloses silica gel 15 and foam beads 16 to 
be mentioned later. 
FIG. 3 is a sectional view of a principal portion of the wrapping sheet 2. 
The said separate pouchy portion 3 is partitioned off from the sheet, 
pouched and formed by the seal portion 5 made up by heat-sealing an inner 
sheet 6 and an outer sheet 7. Before making up the seal portion 5, the 
silica gel 15 and the foam beads 16 are enclosed in each separate pouchy 
portion 3. 
Incidentally, the foam beads 16 can be either foamed in the separate pouchy 
portion 3 by heating after enclosed therein or can be foamed beforehand 
and enclosed in the separate pouchy portion 3. 
And the inner sheet 6 is formed with an air permeable film and the outer 
sheet 7 is formed with an air non-permeable film. 
The details of each part is shown in FIG. 4, an enlarged outlined, 
constitutional view. The said inner sheet 6 consists of an inner film 8 
and an inner non-woven fabric 9. On the other hand, the said outer sheet 7 
consists of the four layers, that is, a charge-preventive guard layer 11, 
an evaporated metal layer 12, an insulator layer 13 and an adhesive layer 
32. 
Further, the inner film 8 has a structure in which there are formed a lot 
of through holes 8a, 8a with the size of 1-2 .mu. so that gas and vapor 
can be passed through but liquid such as water cannot. 
Next, each layer of the said outer sheet 7 will be explained. The 
charge-preventive guard layer 11 in the outermost side is kneaded or 
coated with polyamide or polyimide. The metal steam-welded layer 12 in the 
second outermost side is mixed with metal powder such as carbon black, Cu, 
Ni, Ag and A1. The insulator layer 13 on the third layer consists of a 
polyester film mixed with mica powder. The adhesive layer 32 in the 
innermost side consists of polyethylene kneaded with polyamide or 
polyimide. 
Further, a transparent portion 4 is formed in part of the outer sheet 7 by 
means of the punching process so as to be capable of observing the inside 
of the separate pouchy portion 3. In the transparent portion 4, letters 
such as a name of goods are written down in a conductive ink 14 in which 
powder such as carbon black or silver powder is mixed. 
Furthermore, particles of a water absorbing polymer 17 may be enclosed in 
the said separate pouchy portion 3b in addition to the silica gel 15. This 
water absorbing polymer 17 can assist the absorbing capacity of the silica 
gel 15 by absorbing a large quantity of water in case that the humidity 
becomes extremely high in the surroundings after reaching the dew point. 
The foam beads 16 which are enclosed in the separate pouchy portion 3 
together with the silica gel 15 consist of polystyrene or polyethylene in 
which black carbon is mixed. The foam beads 16 have cushioning property 
after foaming process and can efficiently prevent the particles of silica 
gel 15 from rubbing mutually and breaking down. Further, in case that 
static electricity occurs due to the friction of the silica gel 15 at the 
time of enclosing them in the separate pouchy portion 3, the foam beads 16 
can release static electricity through the inner black carbon to the 
outside. The foam beads 16 are also capable of protecting the electronic 
parts 1 from the outer shock by displaying their cushioning capacity. 
The electronic parts 1 can be kept in a dry condition by enveloping it with 
the wrapping sheet 2 of this invention because the silica gel 15 and the 
water absorbing polymer 17 can efficiently absorb the moisture around the 
electronic parts 1. And the electronic parts 1 are never affected by 
static electricity because static electricity caused by the friction of 
the silica gel 15 and so on can be released through the foam beads 16, the 
adhesive layer 32, the evaporated metal layer 12 and the charge-preventive 
guard layer 11. 
Further, the electronic parts 1 is never affected by microwave because 
outer microwave is efficiently shut out by the insulator layer 13.