JP2006210742A - Shield case for electronic equipment and eletronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a radiation noise caused by a resonance of a shield case which builds in a printed circuit board. <P>SOLUTION: The shield case 10 comprising a rectangular upper wall 12 and a side wall 13 has an opening 14 which draws a cable of the printed circuit board 1 fixed to a bottom wall 11 through a spacer 2, and a notch 15 formed in the wall 12 and the wall 13 striding across each ridge line which surrounds the wall 12. The notch 15 suppresses a flow-in of a current caused by a standing wave in the central part of the rectangular wall 12 to reduce the resonance of the shield case. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a shield case for an electronic device and an electronic device for storing a printed circuit board in order to prevent radiation noise of the electronic device.

  With the recent increase in speed and performance of electronic devices, the effect of radiation noise generated by electronic devices on other electronic devices has become a problem. The influence of this radiation noise on other electronic devices is called EMI (Electro Magnetic Interference) and causes malfunction of the electronic devices. For this reason, the frequency band which becomes a problem regarding radiation noise is defined, and the amount of radiation from electronic equipment is regulated. In addition, electronic device manufacturers need to design and manufacture products that conform to this regulation.

  Radiation noise from an electronic device is radiated from a printed circuit board or a cable connected between the printed circuit boards. In particular, radiation noise from a printed circuit board has become a problem as a radiation noise radiation source due to an increase in the speed of a signal wired on the printed circuit board. Therefore, in order to suppress radiation noise from the printed circuit board, the radiation noise radiated to the outside of the electronic device is reduced by housing the printed circuit board in a conductive shielding case.

  However, it has been known that when a shield case is used, radiation noise is deteriorated due to a resonance phenomenon caused by the size of the shield case.

  As a technique for suppressing such a resonance phenomenon, for example, as described in Non-Patent Document 1, the resonance frequency of the shield case is set to a [m], the height, width, and height of the shield case, respectively. Since b [m] and c [m] are expressed by the equation (1), the resonance frequency can be moved to a frequency that does not cause a problem in the noise standard by reducing the size. There has been known a technique of suppressing the resonance phenomenon by partitioning with an elastic member to reduce the internal size.

ここで、ｍ、ｎ、ｐはそれぞれ０、１、２、・・・
ｖは電磁波の伝播速度

Here, m, n, and p are 0, 1, 2,.
v is the propagation speed of the electromagnetic wave

Further, in Patent Document 1, in order to partition the inside of the shield case (housing), a ground plane is formed on the front surface and the back surface of the printed circuit board (printed wiring board), and a partition plate formed of a conductive material is provided. By contacting the ground surface of the printed circuit board and the inner wall of the shield case made of a conductive material, the resonance frequency of the shield case and the frequency of radiation noise (electromagnetic waves) generated from the printed circuit board can be avoided. , Reducing radiated noise.
JP-A-5-129790 Kouichi Kento and Goichiro Yamazaki, “Detailed Electromagnetics Seminar” Kyoritsu Shuppan (December 15, 1970) P347

  However, in the configuration in which the inside of the shield case disclosed in Non-Patent Document 1 is partitioned by a conductive member, the printed circuit board must be divided into small sizes so as to enter the partition plate. It is necessary and takes a lot of work. In addition to the need for a separate conductive member for partitioning the shield case, there is a problem in that the number of boards increases and the number of cables that transmit between the boards that are divided into small parts increases, which increases costs.

  Moreover, in the structure which provides the partition plate which contacts the ground surface of a printed circuit board in the shield case disclosed by patent document 1, you have to form the ground surface on a printed circuit board in the position which provides a partition plate. Therefore, there is a problem that the component mountable area on the printed circuit is narrowed, and restrictions on component placement become severe. Furthermore, problems with heat dissipation have occurred in printed circuit boards that generate a large amount of heat. Moreover, there are problems that assembly workability is deteriorated by providing the partition plate, and that the weight of the shield case is increased.

  The present invention has been made in view of the above-mentioned unsolved problems of the prior art, and an object thereof is to provide a shield case for electronic equipment and an electronic equipment capable of effectively reducing radiation noise with an extremely simple configuration. To do.

  In order to achieve the above object, a shield case for an electronic device according to the present invention is a shield case for an electronic device that accommodates a printed circuit board, and has a plurality of rectangular portions joined to each other along a ridgeline. A cutout opening straddling the ridgeline is formed in one rectangular portion and the rectangular portion joined thereto.

  Since only the notch opening for reducing radiation noise is processed in the shield case, the number of substrates is not increased, and cables and partition plates for transmitting between the substrates are not required. Therefore, there is an advantage that the cost is not high and the assembling workability is good, and the weight of the shield case itself can be reduced.

  Further, since there are no restrictions on the printed circuit board, there is no need to change the circuit configuration of the printed circuit board, and the mountable area on the printed circuit board is not reduced.

  Embodiments of the present invention will be described with reference to the drawings.

  FIG. 1A is a perspective view showing a shield case of Example 1 according to the present invention, and FIG. 1B is a perspective view showing a printed circuit board built in the shield case and a bottom wall of the shield case.

  As shown in FIG. 1, in an electronic device in which a printed circuit board 1 is accommodated in a shield case 10, four conductive spacers 2 are provided on the bottom surface of the printed circuit board 1, and the printed circuit board 1 has spacers 2. Via the bottom wall 11 of the shield case 10. The shield case 10 has a bottom wall 11, a top wall 12, and four side walls 13 which are rectangular portions, and an opening 14 for drawing out a cable is formed in one of the four side walls. Of the rectangular parts constituting the shield case 10, a total of four notch openings are formed across the ridge line between the upper wall 12 and the side walls 13 which are the first rectangular part having the largest area. 15 is formed.

  Although the spacer 2 for fixing the printed circuit board 1 to the bottom wall 11 of the shield case 10 has been described as being conductive, it may be non-conductive.

  Further, as shown in FIG. 2, instead of the rectangular portion constituting the bottom wall 11 of the shield case 10, the conductive separate sheet metal 3 can be fixed to the spacer 2 of the printed circuit board 1. According to this configuration, it is only necessary to cover the shield case 10 for housing the printed circuit board 1 from above, and the work for making an electrical connection with the separate sheet metal 3 can be performed from the top. Workability is further improved.

  In both configurations of FIGS. 1 and 2, the effect of suppressing the resonance phenomenon becomes more prominent by arranging the position of the notch 15 at the center of the ridgeline.

  Further, if the length of the notch 15 is formed to be half or less of the wavelength of the upper limit frequency determined by the noise standard, not only the slot resonance due to the notch 15 is suppressed, but also leakage from the shield case 10 occurs. Radiation noise can be further reduced.

  Further, by forming the notch 15, the heat dissipation effect is increased, and the temperature rise in the shield case 10 due to heat generated from the printed circuit board 1 can be suppressed.

(Experimental example 1)
In FIG. 3, the shield case composed of the bottom wall 11, the top wall 12 and the side wall 13 which is a complete conductor has a size of 310 mm in the X direction, 210 mm in the Y direction, 50 mm in the Z direction, and a thickness of 1.0 mm. is there. The center of the opening 14 through which the cable is drawn is provided at a location of −100 mm in the X direction, 105 mm in the Y direction, and 0 mm in the Z direction from the origin, where the center of the shield case 10 is the origin. The size is 10 mm in the Z direction and 30 mm in the X direction.

  The four cutouts 15 have a length in the longitudinal direction of 20 mm and a length in the short direction of 10 mm, and straddle the ridgeline between each side wall 13 at the center of each side of the upper wall 12 of the shield case 10. It is formed with.

  In order to investigate the effect of reducing the resonance frequency due to the cutout 15 of the shield case 10, a dipole antenna 20 is inserted in the shield case 10 as a noise wave source instead of the printed circuit board 1 as shown in FIG. The radiation noise intensity was simulated using The dipole antenna 20 is made of a perfect conductor, has a diameter of 1 mm, a length of 10 mm, and is fed from the center. Further, the dipole antenna 20 was set as a Sin wave having a frequency component of 10 MHz to 1 GHz in increments of 10 MHz and having a uniform 1 V amplitude for each frequency. The direction of the dipole antenna 20 is the Z direction, and is arranged at the center (origin) of the shield case 10.

  For comparison, as shown in FIG. 4, a similar simulation was performed for a shield case having a bottom wall 11, an upper wall 12, a side wall 13, and an opening 14 and not having a notch.

  FIGS. 5A and 5B are the results of simulation using the method of moments for the radiation noise intensity at a position 3 m away from the center (origin) of the shield case of this experimental example. Fig.5 (a) has shown the intensity | strength of the horizontal polarization of the radiation noise in each frequency. The horizontal axis represents frequency, the vertical axis represents radiation noise intensity, and the frequency band is 810 MHz to 910 MHz. FIG. 5B shows the intensity of vertically polarized radiation noise at each frequency. The horizontal axis is frequency, the vertical axis is radiation noise intensity, and the frequency band is 810 MHz to 910 MHz.

  As can be seen from FIGS. 5A and 5B, the resonance phenomenon occurs at 860 MHz. Since the resonance frequency of the shield case calculated from the equation (1) is about 860 MHz, it can be seen that the resonance phenomenon of 860 MHz is due to the shield case resonance.

  6 (a) and 6 (b) perform a simulation of the radiation noise intensity at a position 3 m away from the center (origin) of the shield case using the same moment method for the shield case of the comparative example shown in FIG. It is a result. FIG. 6A shows the intensity of horizontally polarized radiation noise at each frequency. The horizontal axis represents frequency, the vertical axis represents radiation noise intensity, and the frequency band is 810 MHz to 910 MHz. FIG. 6B shows the intensity of vertically polarized radiation noise at each frequency. The horizontal axis represents frequency, the vertical axis represents radiation noise intensity, and the frequency band is 810 MHz to 910 MHz.

  As can be seen from FIGS. 6A and 6B, a resonance phenomenon occurs at 860 MHz. When the radiation noise intensity of Experimental Example 1 shown in FIG. 5 and the radiation noise intensity of the comparative example at 860 MHz, which is the resonance frequency of the shield case, are compared, the horizontal polarization is 6.23 dBμV / m and the vertical polarization is 4. It can be seen that the radiation noise is suppressed at 88 dBμV / m.

  As described above, the shield case structure of the present embodiment only processes the cutouts in the shield case, so the number of boards does not increase, and cables and partition plates for transmitting between the boards are not required. In addition, the assembly workability is good and the weight of the shield case itself can be reduced.

  Further, since there are no restrictions on the printed circuit board, it is not necessary to change the circuit configuration of the printed circuit board, and further, the mountable area on the printed circuit board is not reduced.

  By using the shield case in electronic devices such as copiers (multifunction devices), printers, fax machines, scanners, etc., radiation noise radiated from these can be greatly suppressed, The influence can be greatly suppressed.

  FIG. 7 shows a shield case according to the second embodiment. As in the first embodiment, the cutout 15 is formed across all the ridge lines of the shield case 10 including the bottom wall 11, the upper wall 12, and the side wall 13.

  Thus, by forming the notch 15 also in the height direction of the sides constituting the ridge line of the shield case 10, the resonance phenomenon in the height direction of the shield case 10 can also be suppressed. it can.

  By arranging the positions of the notches 15 in the central part of the side, the effect of suppressing the resonance phenomenon becomes more remarkable.

  Further, the heat dissipation effect is increased by increasing the number of the notches 15, and the temperature rise in the shield case 10 due to heat generated from the printed circuit board 1 can be further suppressed.

  Next, the principle of suppressing the resonance of the shield case 10 by the notch 15 will be described with reference to FIGS. FIG. 8 shows the resonance phenomenon of a shield case composed of a rectangular part having no opening or notch, and the X direction which is the long side of the shield case having no opening or notch as shown in FIG. And a dimension b in the Y direction, which is a short side, and a dimension c in the Z direction, a standing wave Sx standing in the X direction as shown in (b), and a constant wave standing in the Y direction as shown in (c). A standing wave Sy is generated.

  In other words, the shield case resonates at a resonance frequency as shown by the equation (1), and standing waves Sx and Sy as shown in FIGS. 8B and 8C are generated inside the shield case. This is a phenomenon that occurs because there is a relative difference in impedance between the center and the end of the shield case. 9A and 9B show the direction of the current flowing through the shield case at the time of resonance. FIG. 9A shows the current Dx flowing in the X direction, and FIG. 9B flows in the Y direction. Current Dy is shown.

  In this way, since the relative difference in impedance occurs in the shield case, the current Dx in the X direction and the current Dy in the Y direction easily flow from the center of the shield case. Furthermore, as the relative difference in impedance increases, these currents flow more easily, and the currents Dx and Dy flow in a concentrated manner at the central portions AA and BB of the shield case, so that the resonance phenomenon of the shield case occurs. Occurs and emits noise.

  Therefore, as shown in FIG. 10, a notch 15 is formed across the ridge line between the upper wall 12 and the side wall 13 of the shield case, thereby reducing the relative difference in impedance existing at the shield case center and the shield case end. By doing so, the flow of the current D is suppressed. In this way, the radiation noise due to the resonance phenomenon of the shield case is reduced.

  Further, since the currents Dx and Dy flow in a concentrated manner at a location where the relative difference in impedance of the shield case is large, that is, the central portions AA and BB of the shield case, the position of the notch 15 By arranging in the center portion, the effect of suppressing the resonance phenomenon becomes more remarkable.

BRIEF DESCRIPTION OF THE DRAWINGS The shield case of Example 1 which concerns on this invention is shown, (a) is a perspective view which shows the external appearance, (b) is a perspective view which shows the built-in printed circuit board and the bottom wall of a shield case. FIG. 7 shows a modification of the first embodiment, where (a) is a perspective view showing an appearance thereof, and (b) is a perspective view showing a built-in printed circuit board and another sheet metal. It is a figure explaining the simulation model of example 1 of an experiment. It is a figure explaining the simulation model of the comparative experiment example. It is the result of having calculated | required the radiation noise intensity | strength of the shield case of Experimental example 1 by simulation. It is the result of calculating | requiring the radiation noise intensity | strength of the shield case of a comparative experiment example by simulation. 6 is a perspective view showing a shield case according to Embodiment 2. FIG. It is a schematic diagram explaining the resonance phenomenon of a shield case. It is a schematic diagram explaining the resonance phenomenon of a shield case. It is a schematic diagram explaining the suppression principle of the radiation noise by a notch.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Printed circuit board 2 Spacer 3 Sheet metal 10 Shield case 14 Opening 15 Notch

Claims (4)

  A shield case for an electronic device that accommodates a printed circuit board, having a plurality of rectangular portions joined together along a ridgeline, and straddling the ridgeline across at least one rectangular portion and the rectangular portion joined thereto A shield case for electronic equipment, wherein a notch opening is formed.   A shield case for an electronic device for accommodating a printed circuit board, the first rectangular portion having the maximum area, and a plurality of second rectangular portions joined to the first rectangular portion along a ridgeline A shield case for electronic equipment, wherein a cutout opening is formed in the first rectangular portion and the plurality of second rectangular portions so as to straddle the ridgeline.   The shield case for an electronic device according to claim 1, wherein the notch opening is disposed in the center of the ridge line.   An electronic device comprising the shield case for an electronic device according to any one of claims 1 to 3 and a printed circuit board accommodated in the shield case.

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