JP2005085847A - Cabinet structure enclosing printed wiring board, and circuit packaging unit of electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cabinet structure which encloses a printed wiring board and reduces radiated noise even when six surface shield structure cannot be taken by constraint of product size etc., and the circuit packaging unit of an electronic apparatus. <P>SOLUTION: In a structure, the printed wiring board 1 on which at least one electronic component (IC) is mounted is attached on a first conductive member 20 whose size is identical to or greater than that of the printed wiring board 1, and a second conductive member 10 is further attached on the upper surface of the printed wiring board 1. It is characterized by installing structure wherein an electronic component 2 which is operated by internal clock of the highest frequency in the electronic components (ICs) mounted on the printed wiring board 1, external clock wiring which is arranged on the printed wiring board 1 and transmits a signal of the highest frequency, and an area of the electronic component to which the clock wiring is connected, are arranged so as to be covered with the second conductive member 10. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a housing structure of an electronic device having a printed wiring board therein, and to a housing that suppresses radiation noise generated from the printed wiring board or from a cable by devising the housing structure in the vicinity of the printed wiring board. Concerning body structure.

JP-A-7-94885 Japanese Patent Laid-Open No. 10-208791

  Conventionally, radiated noise generated from electronic devices has been voluntarily regulated by, for example, VCCI (Industrial Regulation Committee for Information Processing Devices, etc.) in Japan, and regulated by FCC in the United States. Therefore, electronic devices are required to satisfy such a regulation value, and countermeasures against radiation noise are performed by combining various means so that the value becomes smaller than the regulation value.

  As a means for suppressing radiation noise from a printed wiring board in an electronic device, a means for suppressing the electromagnetic wave from leaking outside by placing the printed wiring board in a box having a six-sided shield structure has been widely used. An example of this method will be described with reference to FIGS. A plurality of ICs such as IC2, IC3, and IC4 constituting a digital circuit are mounted and operated on the printed wiring board 1 in FIG. When these ICs actually operate and a current flows through the circuit, an electromagnetic field is generated, which becomes a part of an electromagnetic wave and causes radiation noise.

  FIG. 9 is a diagram in which the printed wiring board described in FIG. 8 is housed in a metallic shield box 30. The ground of the printed wiring board 1 and the shield box 30 are fixed and grounded via a conductive connecting member 31. If the printed wiring board is placed in a shield box with no defects as shown in Fig. 9, radiation noise can be completely suppressed. However, in actual products, the shield box has defects due to various factors such as cable outlets. Electromagnetic waves leak out.

  Patent Document 1 is an example of a method for reducing radiation noise by such a method. In this example, the structure is such that a plurality of multilayer printed wiring boards are accommodated in a sub-rack of a shield structure, and an object is to reduce electromagnetic waves leaking from defects generated in order to allow the printed wiring board to be taken in and out. In such a structure, it is necessary to prevent a defect such as a gap as much as possible so that electromagnetic waves generated from the printed wiring board are not leaked to the outside.

  In addition, means for suppressing electromagnetic waves generated from a printed circuit board by using a printed wiring board as close as possible to a sheet metal having as little defects as possible is also used. The principle will be briefly described with reference to FIGS.

  The printed wiring board of FIG. 10 is mounted with many electronic components such as IC2 operating at the highest internal clock operating frequency on the printed wiring board, and other IC3 and IC4. An external clock signal having the highest frequency is transmitted from IC2 to IC3 through signal lines 5 and 6 on the printed wiring board. The signal line 5 is a signal line arranged on the lower layer of the printed wiring board, and the signal line 6 is a signal line arranged on the upper surface of the printed wiring board. Signal lines arranged in different layers are electrically connected via via holes 7. The signal lines 8 and 9 are signal lines arranged on the lower surface and the upper surface of the printed wiring board, respectively, but are normal control signal lines that do not transmit an external clock signal having the highest frequency. Reference numerals 100 and 101 schematically represent high-frequency currents of the external clock signals flowing through the signal lines 5 and 6 at a certain moment.

  FIG. 11 is a view in which the printed wiring board 1 of FIG. 10 is arranged on a first conductive member (metal sheet metal) 20 and fixed via an attachment jig 21. When a signal is transmitted to the signal line in FIG. 10, a reverse current that cancels the magnetic field flows through the ground in the vicinity of the signal line. However, in many cases, the ground on the printed wiring board does not necessarily have an ideal ground structure due to the convenience of wiring design. Therefore, a ground current that completely cancels the electromagnetic field of the signal line cannot flow.

  In that case, when the first conductive member (metal sheet metal) 20 is disposed, a ground current that cancels the difference between the electromagnetic field generated by the high-frequency current flowing through the signal line of the printed wiring board 1 and the ground pattern is the first conductive member. Flowing through (metal sheet metal) 20, generation of radiation noise can be suppressed.

  An example in which a printed wiring board is brought close to a plain sheet metal with few defects is also shown in Patent Document 2 and the like. In this example, radiation from the cable is also caused by bringing the cable closer to the sheet metal. Suppressed.

  However, as described above, the method of covering the printed wiring board, which is the radiation noise source, with the six-side shield box structure is sufficient if the electronic device as a product is large to some extent and has enough space, In many cases, this method cannot be used for products with complicated products or shapes.

  In such a case, a method of suppressing radiation noise generated from the printed wiring board is used by using a method in which the printed wiring board is brought close to a plain conductive member, for example, a first conductive member (metal sheet metal). However, in recent years, the operating frequency of digital circuits has increased, and it has become difficult to satisfy the regulation value only by such means. Further, the closer the printed wiring board is to the plain conductive member, the better. However, depending on the product, it may be difficult to bring it closer.

  The object of the present invention is further improved in the case where a six-side shield structure cannot be obtained due to product size restrictions, etc., or when it is not sufficient to bring a printed wiring board close to a sheet metal such as metal due to the recent increase in frequency of digital circuits. Is to reduce radiation noise by adding a conductive member as small as possible when it is difficult to bring a printed wiring board close to a stable sheet metal as a frame ground due to the structure of the electronic device as a product.

  In order to achieve the above object, in the present invention, a printed wiring board on which one or more electronic components are mounted is attached to a first conductive member having the same size as or larger than the size of the printed wiring board. In the structure in which the second conductive member is further attached to the upper surface, the electronic component operating at the highest internal clock frequency among the electronic components mounted on the printed wiring board and the highest disposed on the printed wiring board It is characterized in that the second conductive member covers the external clock wiring for transmitting a frequency signal and the area of the electronic component to which the clock wiring is connected.

  According to the present invention, a second conductive member is disposed in the vicinity of a portion that causes large radiation noise on a printed wiring board, and the first conductive member and the second conductive member are disposed on both sides of the printed wiring board. Thus, radiation noise can be reduced by canceling out the electromagnetic field imbalance caused by the current flowing in the signal line and the ground wiring on the printed wiring board.

  Furthermore, a radiation noise reduction effect can be achieved by adopting a structure in which at least one of the two sides in the vertical direction or the two sides in the horizontal direction of the second conductive member is electrically connected to the first conductive member. Can be increased.

  Furthermore, by using a member made of a flexible conductive material or a member made of a composite material of a conductive material and an insulating material as the second conductive member, the second conductive member is arranged close to a circuit portion that causes radiation noise. Therefore, radiation noise can be reduced more effectively.

  Moreover, if such a mounting form is used for a circuit mounting unit of an electronic device, the level of radiation noise of the electronic device can be reduced.

  First, the principle of the present invention will be described in detail with reference to FIGS.

  The printed wiring board shown in FIG. 1 is mounted with a number of electronic components such as IC2 that operates at the highest operating frequency among the ICs mounted on the printed wiring board, and other IC3 and IC4. Has been. Many other electronic components are mounted on an actual printed wiring board, but are simplified. In this example, the external clock signal having the highest frequency is also transmitted from the IC 2 whose clock inside the IC operates at the highest operating frequency to the IC 3 through the signal lines 5 and 6 on the printed wiring board. The signal line 5 is a signal line arranged on the lower layer of the printed wiring board, and the signal line 6 is a signal line arranged on the upper surface of the printed wiring board. The signal lines 5 and 6 arranged in different layers are electrically connected via the via hole 7. Furthermore, the conductive member 10 is disposed so as to cover the area of the external clock wiring 5, the external clock wiring 6, and the IC2 and IC3 to which the clock wiring is connected, which transmits the signal line of the highest frequency disposed on the printed wiring board 1. To do. The signal lines 8 and 9 are signal lines arranged on the lower surface and the upper surface of the printed wiring board, respectively, but are normal control signal lines that do not transmit an external clock signal having the highest frequency. Numbers 100 and 101 schematically represent high-frequency currents of the external clock signals flowing in the signal lines 5 and 6 at a certain moment.

  FIG. 2 is a view in which the printed wiring board 1 of FIG. 1 is disposed on a first conductive member (metal sheet metal) 20 and fixed via an attachment jig 21. Further, the conductive member 10 described in FIG. 1 is disposed on the printed wiring board 1.

  In FIG. 2, when a signal is transmitted to a signal line, a reverse current that cancels the magnetic field flows through the ground near the signal line. However, in many cases, the ground on the printed wiring board does not necessarily have an ideal ground structure due to the convenience of wiring design. Therefore, a ground current that completely cancels the electromagnetic field of the signal line cannot flow.

  In that case, when the first conductive member (metal sheet metal) 20 is arranged, a ground current that cancels the difference between the electromagnetic fields generated in the printed wiring board 1 flows to the first conductive member (metal sheet metal) 20 and radiates. Generation of noise can be suppressed. At this time, the major cause of radiation noise is the circuit part (inside IC2 in FIG. 1) that operates with the clock inside the IC of the highest frequency in the printed wiring board and the highest frequency in the printed wiring board. 1 is a circuit portion transmitting the external clock (in FIG. 1, the IC 2, the signal lines 5 and 6, the via hole 7, and a ground pattern of a printed wiring board (not shown)). Here, the closer the above circuit and the first conductive member (metal sheet metal) are, the more the cancellation effect can be expected. However, in many cases, the IC mounting surface is at a position facing the first conductive member (metal sheet metal). However, since it is arranged on the opposite side (the upper surface of the printed wiring board 1 in FIG. 2), it is located far from the first conductive member (metal plate) 20. The external clock signal line 5 disposed on the lower surface of the printed wiring board 1 is located close to the first conductive member (metal sheet metal) 20, but is externally disposed on the upper surface of the printed wiring board 1. The clock signal line 6 is at a far position. In this case, if there is a defect in the ground pattern of the printed wiring board 1 near the signal line 6, it causes a large amount of radiation noise.

  In the present invention, the second conductive member 10 is disposed in the vicinity of a portion that causes large radiation noise on the printed wiring board, and the first conductive member (metal sheet metal) 20 and the second conductive member 20 are disposed on both sides of the printed wiring board. By disposing the conductive member 10, radiation noise can be efficiently reduced by canceling out the unbalanced electromagnetic field caused by the current flowing in the signal line and the ground line on the printed wiring board.

  Furthermore, the effect is enhanced by adopting a structure in which at least one of the two sides in the vertical direction or the two sides in the horizontal direction of the second conductive member 10 is electrically connected to the first conductive member. be able to.

  Furthermore, by using a member made of a flexible conductive material or a composite member of a conductive material and an insulating material for the second conductive member 20, the second conductive member 20 is arranged closer to a circuit part that causes radiation noise. Can do.

  Moreover, if such a mounting form is used for a circuit mounting unit of an electronic device, the level of radiation noise of the electronic device can be reduced.

  Next, embodiments of the present invention will be described in detail.

  FIG. 1 is a top view after electronic components are mounted on a printed wiring board. The printed wiring board 1 includes a CPU IC 2 that operates at 1 GHz, which is the highest operating frequency among the ICs mounted on the printed wiring board, and many other electronic components such as other ICs 3 and 4. Has been implemented. There are many other electronic components, signal lines, and ground patterns in the actual printed wiring board, but they are simplified. In this embodiment, an external clock signal having a maximum frequency of 133 MHz is also transmitted from IC2 to IC3 through signal lines 5 and 6 on the printed wiring board. The signal line 5 is a signal line arranged on the lower layer of the printed wiring board, and the signal line 6 is a signal line arranged on the upper surface of the printed wiring board. The signal lines 5 and 6 arranged in different layers are electrically connected via the via hole 7. Further, among the ICs mounted on the printed wiring board, the IC IC 2 of the CPU that operates at 1 GHz which is the highest operating frequency of the clock inside the IC, and 133 MHz which is the highest frequency disposed on the printed wiring board 1. The conductive member 10 is disposed so as to cover the external clock wiring 5, the external clock wiring 6, and the IC2 and IC3 areas to which the clock wiring is connected. The conductive member 10 is represented by a perspective view so that the positional relationship with the electronic component can be understood. The signal lines 8 and 9 are signal lines arranged on the lower surface and the upper surface of the printed wiring board, respectively, but are normal control signal lines that do not transmit an external clock signal having the highest frequency. Reference numerals 100 and 101 schematically represent high-frequency currents of the external clock signals flowing through the signal lines 5 and 6 at a certain moment.

  FIG. 2 shows that the printed wiring board 1 of FIG. 1 is placed on the first conductive member (metal sheet metal) 20 with the surface on which the IC 2 or the like is mounted as it is, and is attached via a mounting jig 21. FIG. Further, among the ICs described with reference to FIG. 1, the CPU internal IC 2 operating at the highest operating frequency of 1 GHz and the external clock transmitting the highest frequency signal line disposed on the printed wiring board 1. The conductive member 10 is disposed so as to cover the area of the wiring 5, the external clock wiring 6, and the IC2 and IC3 to which the clock wiring is connected.

  In FIG. 2, when a signal is transmitted to a signal line, a reverse current that cancels the magnetic field flows through the ground near the signal line. However, in many cases, the ground on the printed wiring board does not necessarily have an ideal ground structure due to the convenience of wiring design. Therefore, a ground current that completely cancels the electromagnetic field of the signal line cannot flow.

  In that case, when the first conductive member (metal sheet metal) 20 is arranged, a ground current that cancels the difference between the electromagnetic fields generated in the printed wiring board 1 flows to the first conductive member (metal sheet metal) 20 and radiates. Generation of noise can be suppressed. At this time, the major cause of radiation noise is the circuit part (inside IC2 in FIG. 1) that operates with the clock inside the IC of the highest frequency in the printed wiring board and the highest frequency in the printed wiring board. 1 is a circuit portion transmitting the external clock (in FIG. 1, the IC 2, the signal lines 5 and 6, the via hole 7, and a ground pattern of a printed wiring board (not shown)). Here, the closer the circuit and the first conductive member (metal sheet metal) are, the more the cancellation effect can be expected. In many cases, the surface on which the IC is mounted is opposite to the first conductive member (metal sheet metal). Since it is arranged on the opposite side (the upper surface of the printed wiring board 1 in FIG. 2) instead of the position, it is far from the first conductive member (metal sheet metal) 20. The external clock signal line 5 disposed on the lower surface of the printed wiring board 1 is located close to the first conductive member (metal sheet metal) 20, but is externally disposed on the upper surface of the printed wiring board 1. The clock signal line 6 is at a far position. In this case, if there is a defect in the ground pattern of the printed wiring board 1 existing in the vicinity of the signal line 6, this causes a large amount of radiation noise.

  In the present invention, a second conductive member 10 is disposed in the vicinity of a portion that causes large radiation noise on a printed wiring board, and a first conductive member (metal) that is a first conductive member is disposed on both sides of the printed wiring board. By disposing the (sheet metal) 20 and the second conductive member 10, the radiation noise is reduced by canceling out the unbalance of the electromagnetic field caused by the current flowing in the signal line and the ground line on the printed wiring board.

  3 and 4 show a second embodiment of the present invention.

  FIG. 3 is a top view after electronic components are mounted on the printed wiring board. Instead of the conductive member 10 of FIG. 1, a conductive member 11 extending in the vertical direction is arranged. The conductive member 11 is a perspective view so that the positional relationship with components and signal lines mounted on the printed wiring board 1 can be understood.

  4 is arranged on the first conductive member (metal sheet metal) 20 with the printed circuit board 1 of FIG. FIG. Further, among the ICs described in FIG. 3, the CPU IC 2 operating at 1 GHz, which is the highest operating frequency of the internal clock of the IC, and the external clock transmitting the highest frequency signal line disposed on the printed wiring board 1. A conductive member 11 extending in the vertical direction with the shape covering the area of the wiring 5, the external clock wiring 6, and the IC2 and IC3 to which the clock wiring is connected as a basic shape is disposed, and the first conductive member (metal sheet metal) ) 20 is electrically connected. Although the conductive member 11 has such a shape, there is a disadvantage that the occupied area increases, but the radiation noise reduction effect can be further improved.

  5 and 6 show a third embodiment of the present invention.

  Example 2 is the same as Example 2 except that a flexible member in which a copper foil is bonded to a polyester film is used for the conductive member 12 in FIGS. In FIG. 6, the conductive member 12 has a polyester surface facing down to prevent a short circuit with an electronic component. Although not illustrated in the drawing, the first conductive member (metal sheet metal) 20 is fixed and conductive by screws. By using a flexible conductive member, it can be brought closer to the problematic IC or signal line.

  FIG. 7 shows a fourth embodiment of the present invention, and shows a diagram in which the circuit mounting unit shown in FIG. Since a mounting circuit unit is disposed in the mold exterior 50 of the electronic device, and there is a structure 40 unrelated to this unit in the vicinity of the mounting circuit unit, a shield box structure cannot be formed. Even in such a case, radiation noise of the electronic device can be reduced.

The top view which mounted components on the printed wiring board used in 1st Example of this invention The figure which shows 1st Example of this invention The top view which mounted components on the printed wiring board used in 2nd Example of this invention The figure which shows 2nd Example of this invention The top view which mounted components on the printed wiring board used in 3rd Example of this invention The figure which shows 3rd Example of this invention 4th Example of this invention, perspective view which mounted circuit mounting unit in electronic device The top view which mounted components on the printed wiring board for demonstrating the prior art example 1. The figure which shows the prior art example 1 The top view which mounted components on the printed wiring board for demonstrating the prior art example 2. The figure which shows the prior art example 2

Explanation of symbols

1 Printed wiring boards 2, 3, 4 Electronic components (IC)
5, 6, 8, 9 Signal line 7 Via hole 10, 11, 12 Second conductive member 20 First conductive member (metal sheet metal)
21 Jig 30 for Fixing Printed Wiring Board and Conductive Member Shield Box 31 Jig 40 for Fixing Printed Wiring Board in Shield Box Exterior of Electronic Equipment

Claims (8)

A structure in which a printed wiring board on which one or more electronic components are mounted is attached to a first conductive member equal to or larger than the size of the printed wiring board, and a second conductive member is further attached to the upper surface of the printed wiring board In
An electronic component operating with the internal clock of the highest frequency among the electronic components mounted on the printed wiring board,
The external clock wiring that transmits the signal of the highest frequency disposed on the printed wiring board and the area of the electronic component to which the clock wiring is connected,
A housing structure surrounding a printed wiring board, wherein the second conductive member is arranged so as to cover it.   The casing structure surrounding the printed wiring board according to claim 1, wherein the second conductive member has a structure that is electrically connected to a ground of the printed wiring board.   2. The printed wiring according to claim 1, wherein at least one of two sides of the second conductive member in the vertical direction or the horizontal direction is electrically connected to the first conductive member. Enclosure structure surrounding the board.   2. The housing structure surrounding a printed wiring board according to claim 1, wherein the second conductive member is a member made of a flexible conductive material or a composite member of a conductive material and an insulating material.   The printed wiring board on which the electronic component according to claim 1 is mounted is attached to a first conductive member having a size equal to or larger than the size of the printed wiring board, and a second conductive member is further attached to the upper surface of the printed wiring board. A circuit mounting unit for electronic equipment, characterized by having a mounting structure.   The circuit mounting unit for an electronic device according to claim 5, wherein the second conductive member has a housing structure in which the second conductive member is electrically connected to a ground of the printed wiring board.   5. The electronic device according to claim 4, wherein at least one of two sides of the second conductive member in the vertical direction or the horizontal direction is electrically connected to the first conductive member. Circuit mounting unit for 5. The circuit mounting unit for an electronic device according to claim 4, wherein the second conductive member is a member made of a flexible conductive material or a composite member of a conductive material and an insulating material.

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