Note: Descriptions are shown in the official language in which they were submitted.
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MOLDED PLASTIC CASING WITH `~
ELECTROMAGNETIC SHIELDING STRUCTURE
Field of the Invention
This invention relates to a shielding structure
for a molded plastic casin~ with a high frequency
-functioning circuit built therein.
Background of the Invention
An ultimate object of communications is ~ ;
naturally to immediately transmit or exchange a will or
information from any place to any person at any time,
and moblle communications have been and are being
developed gradually in addltion to conventional
communlcations between flxed points. Moblle
communications include communications be-tween a mobile
body such as a ship, an automobile or an aircraft and a
general subscriber's statlon, an offlce or the like and
communications between mobile bodies, and automobile
telephones, portable telephones, cordless telephones are
included in such mobile communications.
Among ~uch mobile communlcatlons, wlreless
apparatus such as portable telephones or -the like ~ ;
require use of a thin caslng due to a demand for
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reduction in size and weight, and electronic par-ts
moun-ted in a high density are accommodated in such
casing. Since a high frequency band of 800 to 900 MHz
called quasl-microwave band is utilized for such radio
equipment, it is required to strengthen electromagnetic
shielding of the inside of a casing while reducing the
weight of -the casing to prevent various possible
impediments which may arise from electromagnetic
interference.
10In a conventional construction wherein -the
inside of a molded plastic casing such as a casing of a
portable telephone set is divided in-to two sections by a
printed circult board, U-shaped springs are soldered to
ground patterns of the printed clrcuit board while a
metal film is formed by platlng, elec-trostatlc painting,
vapor deposition of aluminum or the like on an inner
face of the molded plastic caslng having ribs, and the
U-shaped springs are angaged wlth the rlbs to establish
contact therebetween.
With such conven-tional electromagnetic shielding
structure, however, since U-shaped springs are soldered
to a printed circuit board, there is a problem that many ~ .
steps are required for mounting of such springs.
Besides, as reduction in size and weight of a radio
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appara-tus of a portable telephone set or the like
proceeds, electronic parts must necessarily be mounted
in a high density on a princed circuit board, and such
conventional electromagnetic shielding structure cannot
cope with such high densi-ty mounting of electronic
parts.
Summary of the Invention
Aceordingly, lt is an obJect of the present
invention to provide an eleetromagnetie shielding
strueture for a molded plastic easing by whieh the
inside of the easing in whieh a high frequeney
funetioning elreuit ls aecommodated can be
eleetromagnetleally shlelded wlth a simple structure.
In aeeordanea with an aspeet of the present
invention, there is provided a molded plastie casing,
eomprising: a metal film formed on an inner ~aee of the
casing: a prlnted eireuit board aeeommodated in the
inside of the easing in sueh a manner as to divide the
inside of the easing into two chambers, the printed
eireuit board having a metal eore embedded therein and
having a plurallty of plated through-holes formed
therein, the printed eireuit board having hiBh frequeney ~ .
functioning clrcuits mounted on the opposite faces
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-thereof; a plurality of metal lands formed on the
opposite faces along a peripheral portion of the printed
circuit board and individually connected to the metal
core by way of the plated through-holes: and a plurality
of U-shaped leaf springs mounted at the peripheral
portion of the printed circuit board in individual
contact with the metal lands. each of the U-shaped leaf
springs havlng a tongue formed integrally thereon and
held in resilien-t contact with the metal film.
In accordance with another aspect of the presen-t
invention, there is provided a molded plastic casing,
comprising: a metal film formed on an inner face of the
casing: a printed clrcuit board accommodated in the ~ `
inside of the casing in such a manner as to divide the
inside of the casing into two chambers. the prlnted
circuit board having a metal core embedded therein, the
metal core being exposed over a predetermined wid-th
along an entire perlphery of the prlnted circuit board,
the prin-ted circuit board having high frequency
functioning circuits mounted on the opposite faces
thereof: and a plurality of U-shaped leaf springs ` :`~
mounted at the periphery o-f the printed circui-t board
along which the metal core is exposed in such a manner
as to grip -the me-tal core. each of the U-shaped leaf
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springs having a tongue formed integrally thereon and ::
held in resilient contact with the metal film. :
Alternatively, the metal core of the printed
circuit board may be exposed at only one of -the opposite
faces thereof over a predetermined vidth along an entir0
periphery of the printed circuit board. .
The above and o-ther obJects, features and .
advantages of the present invention and the manner of
realizing them will become more apparent, and the
invention itself will best be understood, from a study
of the following description and appended claims with
reference to the a-ttached drawings showing some
preferred embodiments of the invention.
Brief Description of the Drawings
FIG. 1 is an explosed sectional view o-E a first
embodiment of the present invention:
FIG. 2 is an enlarged sectlonal view of a leaf
spring mounting portion of the firs-t embodiment;
FIG. 3 is a perspective view of a leaf spring
with a tongue:
FIG. 4A is a sectional view of a leaf spring
mounting portion according to a second embodiment of the
present invention: :
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FIG. 4B is a sectional view of a leaf spring
moun-ting portion according to a third embodiment of the
present invention: and
FIG. 5 is a sectional view wherein the present
invention is applied to a molded plastic casing of a
portable telephone set.
Description of the Preferred Embodiments
Referring to FIG. 1, there is shown an exploded
sectional view of a first embodiment of the present
invention. A molded plastic casing 2 is constituted ` ,
from a front casing 4 and a rear casing 6. A step 4a is
formed along an entire periphery of an openlng portion
of the front casing 4. and a plurallty of rlbs ~ are
formed in a substantially equidistantly spaced
relatlonshlp from each other on an lnner face of the
front caslng 4. A vapor deposlted fllm 10 of alumlnum --
is formed on the entire lnner face of -the front casing
4. The aluminum vapor deposited film 10 may be replaced
by a plated film of aluminum or such film may otherwise
be formed by electrostatic painting.
A step 6a which is so shaped as -to just fit with
the step 4a of the front casing 4 is formed at an
opening portion of the rear caising 6, and a plurality of
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ribs 12 are -formed at locations of an inner face thereof
corresponding to the ribs 8 of the front casing 4. A
vapor deposited film 14 of aluminum is formed on the
entire inner face of the rear casing 6 similarly to the
front casing 4. Similarly, the aluminum vapor deposi-ted
film 14 may be raplaced by a plated film of aluminum or
such film may otherwise be formed by electrostatic
painting.
Reference numeral l6 denotes a metal core
printed circuit board, which has a core 18 of aluminum
embedded therein. The core 18 i~ plated with copper or
nickel so as to provide connection between the core 18
and plated through-holes 20. A plurality of metal lands
22 are formed on the opposite front and rear faces along
a periphery of the metal core printed eircuit board 16
and are eonneeted -to the aluminum eore 18 by way of the
plated through-holes 20.
Referenee numeral 24 denotes a leaf spring
having a plurality of ton8ues 24a formed integrally ~:
thereon as shown in a perspeetive vlew of FIG. 3. The
leaf spring 24 has a substantially U-shape in section
and is mounted at a portion of each pair of lands 22
formed on the fron-t and rear faces of the metal core
printed circuit board 16 as shown in an enlarged
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sectional view of FIG. 2. Such leaf springs 24 are
mounted on four sides of the metal core printed circuit
board 16.
In assembling the molded plastic casing 2, the
fron-t casing 4 and the rear casing 6 are fitted at -the
steps 4a and 6a thereof with each other in such a manner
that the metal core printed circuit board 16 is held
between the ribs 8 of the front casin~ 4 and the ribs 12
of the rear casing 6. Then, the front casing 4 and the
rear casing 6 are coupled integrally with each other by
means of screws not shown. As a result of such
assembly, the tongues 24a of the leaf springs 24 are
contacted resiliantly with the aluminum vapor deposited
fllm lO oi' the front caslng 4, and consequently, the two ::
chambers formed in the inside of tho caslng 2 can be
electromagnetlcally shielded completely. For example,
logic clrcuit parts are carried on the front surface of '
-the metal core printed circuit board 16 while
transmitter/receiver circuit parts are carried on the
20 rear surface of the metal core printed circuit board 16. ~.
Referring now to FIG. 4A, there is shown a
sectional view of a leai spring mounting portion of a
second embodiment of the present invention. In the
present embodiment, the core 18 of aluminum is exposed
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fully along an en-tire periphery 18a thereof, and leaf
springs 24 each having a plurality of tongues 24a are
mounted a-t the exposed portion 18a of -the core 18.
Referring now to FIG. 4B, -there is shown a sectional
view of a leaf spring mounting portion of a third
embodiment of the present invention. In the present
embodiment, the core 18 of aluminum is exposed only at
one of the opposlte faces thereof along an en-tire
periphery of an outer peripheral portion 18b thereof,
and leaf springs 24 each having a plurality of tongues
24a are mounted such that tlle exposed core 18b is
gripped by the leaf springs 24.
Where the leaf springs 24 are con-tacted directly
with the core 18 oF the prlnted circui-t board 16 a~
~5 shown in FIG. 4A or 4B, the casing can be -formed wlth a
reduced thickness. Further, pla-ted through-holes for
connecting the core 18 to the leaf springs 24 are
urlnecessary.
Even where an outer peripheral portion o-f a
metal core printed circuit board is worked in such a
manner as shown in FIG. 4A or 4B, if the molded plastic
casing 2 is assembled with the metal core printed
circuit board 16 held between the front casing 4 and the
rear casing 6, then -the tongues 24a of the leaf springs
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24 are contacted resiliently with the aluminum vapor
deposited film 10 formed on -the inner face of the front
casing 4, and consequently, an electromagnetic shielding
effect similar to that of -the first embodiment described
hereinabove can be obtained.
Referring now to FI~. 5, there is shown a
sectional view of a casing of a portable telephone set
to which an electromagnetic shield structure of the
present invention is applied. A molded plastic casing
10 32 of the portable telephone set is cons-tituted from a -
front casing 3~ and a rear casing 36. A plurality of
ribs 38 are prov:ided in a substantially equidistantly
spaced relationship from each other on an inner face of
the front caslng 34. A vapor depos.lt0d film not shown
of aluminum is formed on the entire inner face of the
front casing 34.
A plurality of ribs 40 are formed also at
locations of an inner face of the rear casing 36
opposing to the ribs 38 of the front casing 3~. A ~apor
deposited film not shown of aluminum is formed on the
entire inner face of the rear caslng 36.
A metal core prin-ted circuit board 42 having a
core 44 of aluminum embedded therein is accommodated in
the casing 32. If the front casing 34 and the rear
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casing 36 are secured to each other by means of screws
46 and 48, then the printed circuit board 42 is
supported from the opposite sides thereof by the
opposing ribs 38 and 40 of the front and rear casings 34
and 36. Logic circuit parts not shown of the por-table
telephone set are carried on a front surface of the
printed circuit board 42 while transmi-t-ter/receiver
circuit parts not shown are carried similarly on a rear
surface of the printed circuit board 42.
The core 44 of the printed circuit board 42 is
exposed completely over an entire periphery at an outer
peripheral portion 44a thereof similarly as in the
embodiment shown in FIG. 4A. Thus, if leaf springs 24
each having a plurali-ty of tongues 24a are mounted a-t
the exposed portion 44a of the core 44 of the printed
circuit board 42, then the tongues 2~a thereo~ are
contacted reslllerltly wlth the alumlnum vapor deposlted
film not shown formed on the inner face of the casing 42
so that the two chambers in the casing 32 defined by the
metal core printed circuit board 42 can be
electromagnetically shielded completely.
In each of the embodimen-ts described above, a
core of a metal core printed circuit board has a
function of electromagne-tically shielding two chambers
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defined thereby in a casing and also has a heat
radiating effect as a heat sink.
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