Multifunctional card having an electromagnetic wave protection

A multifunctional card includes a substrate having a semiconductor circuit, and a housing, made of an insulating material, for housing the substrate. The housing comprises two pieces of housing halves to be fitted to contain the substrate therein. In the housing, a sheet-like member constituted by metal and insulating layers put on one another is positioned between the substrate and the housing to cover at least central portion of the substrate with the insulating layer inside. The metal layer is electrically connected to ground portions of the substrate, the ground portions of the substrate being formed so as to contact with a ground portion of a main apparatus.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a multifunctional IC card having an 
electromagnetic wave protection means. 
2. Description of the Related Art 
A large number of multifunctional IC cards, such as memory cassettes, 
currently employ a housing made of a plastic material in consideration of 
cost or a request from a customer. The plastic housing does not shield an 
electromagnetic wave as well as metal case. However, no 
anti-electromagnetic wave countermeasure is usually taken. Furthermore, in 
a multifunctional IC card or an intelligent card incorporating a 
semiconductor device such as a CPU integrated circuit (IC) chip, 
electromagnetic wave noise is generated from clocks operating the CPU. 
This noise causes a disturbance in a device outside the card. However, no 
countermeasure against electromagnetic wave noise generated in a card 
comprising a CPU is taken. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a multifunctional card 
having an electromagnetic wave protection means, which can be manufactured 
at a relatively low cost. 
In order to achieve the above object, there is provided a multifunctional 
IC card comprising a circuit substrate having a semiconductor such as an 
integrated circuit (IC) chip circuit, and a housing, made of an insulating 
material, for housing the substrate, wherein the housing comprises two 
pieces of housing halves to be fitted to contain the substrate therein, in 
the housing, a sheet-like member constituted by metal and insulating 
layers put on one another is positioned between the substrate and the 
housing to cover at least central portions of the substrate with the 
insulating layer inside, the metal layer being electrically connected to a 
ground portion of the substrate, the ground portion of the substrate being 
formed so as to contact with a ground portion of a main apparatus. 
The sheet-like member can be formed to a bag-like shape capable of housing 
the substrate, or a sheet-like shape or a ribbon-like shape arranged so as 
to cover the upper and lower surfaces of the substrate. 
According to the above-described multifunctional card, electromagnetic wave 
noise internally generated from the card can be shielded by the metal 
layer, thus preventing disturbances to other devices. Similarly, external 
electromagnetic wave noise can be shielded by the metal layer, and hence 
an erroneous operation in the card can be prevented. 
Since the sheet-like member has an insulating layer, and the insulating 
layer is arranged inside, contact between the metal layer and elements and 
wiring lines on the substrate can be prevented. 
When static discharge occurs through a mating portion or a seam between the 
first and second housing halves of the housing, the static is discharged 
onto the metal layer. In this case, only the metal layer is charged, and 
the static does not reach the inside of the card. Once the card has been 
removed from a main apparatus, the electrostatic charged in the metal 
layer is subjected to natural discharge. On the other hand, once the card 
has been connected to the main apparatus, the static charged in the metal 
layer is discharged onto the main apparatus side because the ground 
portion in the card is in contact with the ground portion of the main 
apparatus. As described above, the present invention also comprises an 
antistatic countermeasure. 
As described above, the present invention comprises the sheet-like member 
in the housing, which has a simple structure, that is, the structure 
constituted by the metal and insulating layers put on one another, thereby 
providing a relatively low-cost multifunctional card which can shield 
internal and external electromagnetic wave noise and prevent an erroneous 
operation, and which is effective in preventing the static related 
destruction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As shown in FIGS. 1 and 2, a flat housing made of an insulating material, 
such as plastics, comprises first and second housing halves 1 and 2 which 
are fitted and constitute upper and lower portions of the housing, and 
houses a circuit substrate such as a printed circuit board 3. The 
substrate 3 contained within the housing comprises a connector 4, 
integrated circuit (IC) chips 5, and ground pads 6 which are formed so as 
to be brought into contact with ground portions of a main apparatus. A 
bag-like sheet-like member 7 is constituted by a thin-film member having a 
two-layer structure consisting of metal and insulating layers 71 and 72 
put on one another. For example, the thin-film member is constituted by a 
layer made of a plastic material, e.g., a thermoelastic material, such as 
PET (polyethylene terephthalate), and having a surface entirely plated or 
coated by copper, or a surface having a multilayer plated structure 
constituted by a lower copper plating layer and an upper nickel plating 
layer. The sheet-like member 7 houses the substrate 3 while the insulating 
layer 72 is located inside. The sheet-like member 7 is located between the 
substrate 3 and the first and second housing halves 1 and 2. Metal 
portions on the surface of the sheet-like member 7 are connected to the 
ground pads 6 at the end portions of the opening of the sheet-like member 
7, in whatever method suitable Since the insulating layer 72 is located 
inside, the metal layer 71 is not brought into contact with elements or 
wiring lines on the substrate 3, and hence a short circuit can be 
prevented. 
A function and effect of the embodiment will be described below. 
Electromagnetic wave noise generated from a CPU inside the card is 
shielded by the sheet-like member 7, and hence does not influence other 
devices outside the card. External electromagnetic wave noise is also 
shielded by the sheet-like member 7 so that an erroneous operation in the 
multifunctional card can be prevented. 
An antistatic countermeasure will be described below. When static discharge 
occurs and the charge enters the multifunctional card through the mating 
portion between the first and second housing halves 1 and 2, with the card 
already pulled from the main apparatus, the static is discharged onto the 
sheet-like member 7, and does not reach the substrate inside the card. The 
charge in the thin-film member is subjected to natural discharged. 
Similarly, the static generated from a human body and the like upon 
pulling of the card from the main apparatus is discharged onto the 
sheet-like member. Since the ground portions of the multifunctional card 
are connected to the ground terminals of the main apparatus in this state, 
the static is discharged onto the main apparatus side through the ground 
pads of the card and the ground portions, thereby protecting the 
semiconductor circuits on the substrate from the static related 
destruction. 
Since a sheet-like member having a card size can be standardized, the cost 
can be minimized. 
In the embodiment, the bag-like member 7 is used. However, instead of the 
member 7, a sheet-like or a ribbon-like member constituted by a thin-film 
member having a two-layer structure consisting of metal and insulating 
layers can be used. The sheet-like member is used to cover the central 
portions of the upper and lower surfaces of the substrate with the 
insulating layer arranged inside. A peripheral portion of the substrate is 
not covered. In practice, however, most of electromagnetic wave noise 
entering through the peripheral portion of the substrate can be shielded. 
In addition, since the static is discharged onto the metal portion near 
the edge of the sheet-like member, an influence on the elements on the 
substrate is small. Hence, the sheet-like member can be satisfactorily 
used in practice.