JPH1022671A - Shielding mechanism for circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a shielding mechanism for circuit board which has easily handled shielding maternal that are installed in a space between an earth pattern on the circuit board and a wall of a shielding case. SOLUTION: In a space between an earth pattern formed on a board 16 and a wall of a shielding case 13a, 13b, deformable conductive small projections 21 are installed. When the conductive small projections 21 deform, the conduction between the earth pattern and the shielding case can be surely established. Unlike conductive rubber and a springy metallic piece, this shielding material can be handled easily when assembling the board in the shielding case.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shield mechanism for a circuit board incorporated in a communication device such as a satellite communication, a mobile phone, and a mobile phone, and more particularly, to a shield space along a ground pattern formed on a substrate surface. The present invention relates to a shield mechanism for a circuit board formed and confining an electromagnetic wave generated by a circuit block on a board surface in the shield space.

[0002]

2. Description of the Related Art For example, in a circuit board built in a communication device, an electromagnetic wave generated by a circuit block on the circuit board is cut off from a peripheral portion, and an adverse effect on other circuit blocks adjacent to the circuit board on the circuit board may be made. It is required to eliminate adverse effects on peripheral devices other than communication devices. As a result, conventionally, attempts have been made to form a shield space by the substrate surface and the conductive shield case, and to confine electromagnetic waves in the shield space. However, a gap is generated between the wall of the shield case and the ground pattern on the surface of the substrate in accordance with the warpage of the substrate and the dimensional accuracy at the time of molding, and electromagnetic waves leak from the gap.

[0003]

In order to prevent leakage of electromagnetic waves from such a gap, a conductive shielding material may be interposed between the wall of the shield case and the ground pattern. For example, the gap between the shield case wall and the ground pattern is completely closed using a punched sheet of conductive rubber, or metal pieces that exhibit spring force between the shield case wall and the ground pattern are arranged at arbitrary intervals. Or you will. The conductive rubber or metal piece establishes electrical conductivity between the shield case and the ground pattern, and as a result, leakage of electromagnetic waves is eliminated.

However, when the conductive rubber is used, the punched sheet of the conductive rubber becomes relatively large, so that the material cost increases and the handling becomes troublesome when assembling the shield case to the substrate. Also,
When attaching a metal piece having a spring projection, handling is troublesome, such as deformation of the spring projection during assembly.

The present invention has been made in view of the above circumstances, and has as its object to provide a shield mechanism for a circuit board that can easily handle a shielding material.

[0006]

According to the present invention, there is provided, in accordance with the present invention, a ground pattern formed on a surface of a substrate and surrounding a circuit block on the surface of the substrate, and a wall along the ground pattern. A shield case, which is disposed on the substrate surface and has a shield space for accommodating the circuit block and the substrate surface, and a conductive pattern provided in a gap between the ground pattern and a wall of the shield case. A shielding member for preventing a leakage of electromagnetic waves from the shield space through the gap by the shielding member, wherein the shielding member is provided on at least one of the substrate and the shield case. It is characterized by being formed as a deformable conductive small protrusion.

In the shield mechanism for a circuit board according to the present invention, the small conductive protrusions may be plastically deformed between the ground pattern and the wall of the shield case when the substrate and the shield case are fixed to each other. You may make it be crushed.

Further, in the shield mechanism for a circuit board according to the present invention, the board and the shield case may be in contact with each other under a load of at least 2 × 10 ⁻² N. Preferably, in the circuit board shield mechanism according to the present invention, the board and the shield case,
Contact each other under a load of at least 3 × 10 ^-2 N.

Further, in the circuit board shield mechanism according to the present invention, the small conductive protrusion may be formed integrally with the ground pattern. in this case,
The substrate may be formed from a resin material while forming base protrusions on the substrate surface, and the conductive small protrusions may be formed by forming a metal film on the base protrusions.

Further, in the circuit board shield mechanism according to the present invention, the shield case is formed from a resin material while forming a base projection on a wall of the shield case, and a metal film is formed on the base projection. The conductive small protrusion may be formed. The metal film may be formed by depositing copper plating on the base projection and then depositing nickel plating.

Furthermore, in the circuit board shield mechanism according to the present invention, the small conductive protrusions may be arranged at intervals according to the frequency of the electromagnetic wave. In this case, the interval D is D = C / 2fc (C: speed of light, f
c: cut-off frequency).

Further, the ground pattern may be formed on the front and back of the board, the shield case may sandwich the board from the front and back of the board, and the small conductive protrusions may be alternately arranged on the front and back of the board.

Further, it is preferable that the tip of the small conductive projection is formed in a dome shape.

[0014]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

[First Embodiment] FIG. 1 shows a portable telephone PT as a portable wireless device containing a circuit board to which a circuit board shield mechanism according to a first embodiment of the present invention is applied. If this mobile phone PT is used, radio waves can be transmitted and received through the antenna 10. An electronic circuit (not shown) for transmitting and receiving radio waves is housed in the design case 11 of the mobile phone PT. In this mobile phone PT,
By opening the protective cover 12 attached to the design case 11, operation buttons (not shown) necessary for dialing and the like are exposed.

An electronic circuit composed of a plurality of circuit blocks, for example, a transmitting circuit and a receiving circuit, is housed in a box-shaped shield case 13 as shown in FIG. The shield case 13 is composed of a pair of upper and lower case halves 13a and 13b that are overlapped with each other to form a housing space therein. Each of the case halves 13a and 13b is formed by injection molding using, for example, an ABS resin, and a metal film such as a nickel film or a copper film is formed on the entire surface including the inner surface to be a conductor. The case halves 13a and 13b are fixed to each other by a pair of screws 14 and a plurality of engagement mechanisms 15 (see also FIG. 4) for replenishing these screw connections.

The electronic circuit is mounted on the front and back of the board 16 and housed in the shield case 13. As shown in FIG. 3, an earth pattern 17 surrounding the electronic circuit is formed on the front and back surfaces 16a and 16b of the substrate 16. Earth pattern 1
7 is a hole 1 surrounding the screw through hole provided in the substrate 16.
7a are formed.

As shown in FIG. 4, when the two case halves 13a and 13b are connected to each other, the substrate 16 is fixed in the accommodation space by the case halves 13a and 13b. In the present embodiment, the substrate 16 is sandwiched between the step 18 formed on the peripheral wall of the upper half 13a and the upper end 19 of the peripheral wall of the lower half 13b. Through this sandwiching, the wall of the shield case 13 along the ground pattern 17 on the substrate 16 (see FIG. 5) forms a shield space 20 for accommodating the circuit block with the surface of the substrate 16.

A gap is formed between the ground pattern 17 and the wall of the shield case 13 facing the ground pattern 17. In this gap, small conductive projections as a shielding material protrude from the shield case 13 at a predetermined interval D corresponding to the frequency of the electromagnetic wave to be shielded. Since these small conductive projections form continuous conductivity between the ground pattern 17 and the shield case 13, leakage of the electromagnetic wave from the shield space 20 through the gap is prevented. As shown in FIG. 5, the interval D is determined according to D = C / 2fc (C: speed of light, fc: cutoff frequency). If the small conductive protrusions 21 are arranged at intervals smaller than the calculated D, leakage of electromagnetic waves can be prevented.

Next, a method for forming the circuit board shield mechanism according to this embodiment will be described in detail. First, the substrate 16 and the shield case 13 are prepared. The ground pattern 17 is formed on the substrate 13 by forming a metal film such as gold plating.
To form A circuit block is formed in a section surrounded by the ground pattern 17.

On the other hand, the upper and lower halves 13 of the shield case 13
a and 13b are formed through injection molding using a plastic material such as ABS resin. During molding,
Base protrusions are formed at intervals D on the walls of the upper and lower halves 13a and 13b. The smaller the base protrusion, the better
Therefore, it is formed to the minimum size that can be formed by injection molding.

Subsequently, the surfaces of the upper and lower halves 13a and 13b are subjected to a conductive treatment, that is, a metal film is formed. For metal film formation, a material such as copper or nickel is used, and a film formation method such as plating, vapor deposition (particularly, vacuum vapor deposition), or sputtering is employed. As a result, a metal film is formed on the base protrusion, and the conductive small protrusion 21 is formed. As shown in FIG. 6, according to such forming and film formation, for example, a diameter of 0.4 m
m, and a conductive small protrusion 21 having a height of 0.25 mm is obtained. Moreover, the tip of the small conductive protrusion 21 is formed in a dome shape.

Subsequently, as shown in FIG.
a, 13b, the upper and lower halves 13a,
13b are fixed to each other with screws 14. As shown in FIG. 6, in the shield case 13, since the substrate facing surface 13 c of the wall of the shield case 13 is recessed by 0.15 mm with respect to the substrate contact surface 22 a of the screw boss 22, the screw 14
The substrate contact surface 22a of the screw boss 22 by tightening
Is pressed against the substrate 16, a gap of 0.15 mm is formed between the wall of the shield case 13 and the substrate 16.

Here, as shown in FIG. 6, since the small conductive protrusion 21 protrudes from the substrate contact surface 22a by 0.1 mm, the dome-shaped tip of the small conductive protrusion 21 is deformed by tightening the screw 14. While being in contact with the ground pattern 17 on the substrate 16, the contact is securely made. As a result, the ground pattern 17
And continuous conductivity between the shield case 13 is reliably established. In addition, according to the deformation of the small conductive protrusions 21, the ground pattern 17 and the shield case 13
The conductive small projections 21 exhibit any rigidity even when a load is applied to reduce the gap with the wall, so that the rigidity of the entire assembly constituted by the substrate 16 and the shield case 13 can be increased. it can.

In order to achieve such deformation of the small conductive protrusions 21, it is preferable that the base protrusions of the shield case 13 are formed of a deformable plastic material, and a conductive film is formed on the surface of the base protrusions. . Therefore, the material of the base projection is not limited to the above-described ABS resin, and may be any material that achieves deformation. Even if the base projection itself has conductivity and the base projection is used as it is as the small conductive projection 21. Good. Also,
The conductive film may be any material having any flexibility that does not cause a crack due to deformation of the base projection. As a result of experiments by the inventor, good conductivity was obtained particularly in a film formed by superimposing nickel plating on an undercoat of copper plating. However, good deformation can be obtained even with nickel plating alone. Moreover, as described above, the conductive small protrusion 21
Are arranged at a predetermined interval D, the load acts intensively on the dome-shaped tip of the small conductive protrusion 21, and together with the shape, the dome-shaped tip can be easily deformed. At this time, if the ground pattern 17 and the shield case 13 are brought into contact with each other only by the small conductive protrusions 21, the contact portion is set in common for all products, so that the shield characteristics for each product are stabilized. be able to.

In addition, although only a pair of screws 14 are used for fixing the upper and lower halves 13a and 13b, the engaging mechanisms 15 are arranged at appropriate intervals as shown in FIG. The upper and lower halves 13a, 13b are securely fixed to each other by the engagement mechanism 15 of the above. By eliminating the use of screws as much as possible, the assembling work can be simplified. Moreover, the conductive small protrusion 21
Can be formed when the shield case 13 is converted into a conductor, so that the manufacturing cost and the productivity can be reduced by omitting the manufacturing process such as attaching the shielding material or reducing the number of parts.

FIG. 7 shows the relationship between the tightening force of the screw 14 and the degree of achievement of the conductivity of the small conductive protrusion 21 between the shield case 13 and the ground pattern 17 in the circuit board shielding mechanism thus obtained. Is shown. In FIG. 7, the fastening force of the screw 14 is represented by a load pressing the small conductive protrusion 21 against the ground pattern 17. This load is adjusted by the rigidity of the shield case 13 and the degree of protrusion of the projection. On the other hand, the degree of achievement of conductivity is determined by the small conductive protrusions 21.
Represented by the electrical resistance achieved through The lower the resistance, the better the conductivity between the shield case and the ground pattern. As is clear from FIG. 7, according to the conductive small projections 21 according to the present embodiment, when a load of ² × 10 ⁻² N is applied, almost stable conduction is established, and the load becomes 3%.
If it exceeds x10 ^-2 N, stable electric conductivity is assured. Therefore, even if a small load is applied and the vibration or the like is applied, the conductivity is not affected.

[Second Embodiment] FIG. 8 shows a circuit board shield mechanism according to a second embodiment of the present invention. In the second embodiment, the conductive small protrusions 2 are alternately arranged on the front and back of the substrate 16.
1 is arranged. As a result, the shield cases 13a, 1
When the substrate 3b sandwiches the substrate 16 from the front and back, pressing force is alternately applied to the front and back of the substrate, so that the small conductive protrusions 21 reliably contact the ground pattern. Note that the same components as those in the first embodiment described above are denoted by the same reference numerals, and detailed description thereof will be omitted.

[Third Embodiment] FIG. 9 shows a circuit board shield mechanism according to a third embodiment of the present invention. In the third embodiment, the small conductive protrusions 21 are formed integrally with the ground pattern. The small conductive projections 21 are easily formed by resin-molding the substrate together with the base projections, and then forming a metal film on the base projections. The conductive small protrusions can be formed at the same time as the formation of the ground pattern, and the manufacturing cost can be reduced and the productivity can be improved by omitting the manufacturing process such as attaching the shielding material or reducing the number of parts. The same components as those in the first and second embodiments described above are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0030]

As described above, according to the present invention, deformable conductive small projections are provided in the gap between the ground pattern on the substrate and the wall of the shield case. Continuous conductivity between the ground pattern and the shield case is reliably established, and therefore, unlike conductive rubber and spring metal pieces, it is possible to provide a shield material that is easy to handle when assembling the shield case to the board. it can.

Moreover, if the small conductive projection is deformed, the small projection exerts rigidity even if a load for reducing the space between the ground pattern and the wall of the shield case is applied after the deformation. And the shield case can increase the rigidity of the entire assembly.

² × 10 ^-2 between substrate and shield case
When they are brought into contact with each other with a load of N, almost stable continuous conductivity is established. When this load is set to 3 × 10 ⁻² N, stable conductivity is assured. Therefore,
Even if vibration or the like is applied, the conductivity is not affected.

If the small conductive protrusions are formed integrally with the ground pattern, the small conductive protrusions can be formed at the same time as the formation of the ground pattern. This eliminates the manufacturing process of attaching the shielding material and reduces the number of parts. By doing so, reduction in manufacturing cost and improvement in productivity can be achieved. The small conductive protrusions are easily formed by resin-molding the substrate together with the base protrusions, and then forming a metal film on the base protrusions.

Further, even if the small conductive protrusions are formed integrally with the shield case, the manufacturing process such as the attachment of the shield can be omitted, and the number of parts can be reduced. In particular, if a metal film is formed by overcoating of copper plating and nickel plating, excellent conductive performance can be obtained.

Furthermore, if the small conductive protrusions are arranged at an arbitrary interval according to the frequency of the electromagnetic wave, when the substrate and the shield case are relatively fixed, a load applied by the fixation is applied to the small conductive protrusions. By acting intensively, the small conductive protrusion can be reliably deformed. Moreover, this interval D
Is determined from D = C / 2fc, the cutoff frequency f
The electromagnetic wave c does not leak from the shield space.

Furthermore, if the small conductive protrusions are arranged differently on the front and back of the substrate, the pressing force is applied alternately on the front and back of the substrate when the shield case sandwiches the substrate from the front and back of the substrate. It can be securely held.

Furthermore, if the tip of the small conductive protrusion is formed in a dome shape, reliable contact of the small conductive protrusion can be achieved.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a mobile phone.

FIG. 2 is an enlarged external view of a shield case to which the circuit board shield mechanism according to the first embodiment of the present invention is applied.

FIG. 3 is a plan view showing the front and back surfaces of a substrate.

FIG. 4 is a cross-sectional view of a shield case in which conductive small protrusions are emphasized.

FIG. 5 is a plan view showing the inner surfaces of the upper and lower halves of the shield case.

FIG. 6 is an enlarged view of a small conductive protrusion.

FIG. 7 is a graph showing the relationship between the screw tightening load and the degree of achieving conduction.

FIG. 8 is a view showing a circuit board shield mechanism according to a second embodiment of the present invention.

FIG. 9 is a view showing a circuit board shield mechanism according to a third embodiment of the present invention.

[Explanation of symbols]

13 shield case, 16 substrate, 17 ground pattern, 20 shield space, 21 small conductive protrusions.

Claims (12)

[Claims] 1. An earth pattern formed on a surface of a substrate and surrounding a circuit block on the surface of the substrate, and a wall along the earth pattern is disposed on the surface of the substrate so as to house the circuit block. A shield case forming a shield space between the ground pattern and a wall of the shield case, and a conductive shield material provided in a gap between the ground pattern and the wall of the shield case. A circuit board shielding mechanism for preventing leakage of electromagnetic waves from a space, wherein the shielding member is formed as a deformable small conductive projection provided on at least one of the substrate and the shield case. For shield mechanism. 2. The method according to claim 1, wherein the conductive small protrusion is plastically or elastically deformed between the ground pattern and a wall of the shield case when the substrate and the shield case are fixed to each other. The shield mechanism for a circuit board described in the above. 3. The shield mechanism according to claim 1, wherein the board and the shield case are in contact with each other under a load of at least 2 × 10 ⁻² N. 4. The shield mechanism according to claim 3, wherein the board and the shield case are in contact with each other under a load of at least 3 × 10 ⁻² N. 5. The shield mechanism according to claim 1, wherein the small conductive protrusion is formed integrally with the ground pattern. 6. The substrate is formed from a resin material while a base projection is formed on the surface of the substrate, and the conductive small projection is formed by applying a metal film to the base projection. Item 6. A shield mechanism for a circuit board according to item 5. 7. The shield case is formed from a resin material while a base protrusion is formed on a wall of the shield case, and the conductive small protrusion is formed by forming a metal film on the base protrusion. The shield mechanism for a circuit board according to any one of claims 1 to 4, wherein 8. The circuit board according to claim 6, wherein the metal film is formed by depositing a copper plating film on the base projection and then overlaying a nickel plating film. For shield mechanism. 9. The small conductive protrusions are arranged at intervals according to the frequency of the electromagnetic wave.
9. The shield mechanism for a circuit board according to any one of 8. 10. The interval D is defined as D = C / 2fc (C:
10. The circuit board shield mechanism according to claim 9, wherein the shield speed is determined from the speed of light and fc: cutoff frequency. 11. The ground pattern is formed on the front and back of the substrate, the shield case sandwiches the substrate from the front and back of the substrate, and the small conductive protrusions are alternately arranged on the front and back of the substrate. A circuit board shield mechanism according to claim 10. 12. The shield mechanism for a circuit board according to claim 1, wherein a tip of said small conductive projection is formed in a dome shape.