JP2014022654A - Print circuit board and electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a print circuit board which can effectively suppress EMI noise radiation without increasing circuit board costs.SOLUTION: In a print circuit board, a power supply layer 11 is laminated on one surface and a ground layer 12 is laminated on the other in the way that they have a core layer 10 in between. A signal wiring layer 14a adjacent to the power supply layer 11 is provided with a signal wiring pattern 15 where high frequency signals flow. In an area opposite to the signal wiring patter 15 of the power supply layer 11, a ground plane 16 for return current is formed, and on both sides of the signal wiring pattern 15, bypass capacitors 17a, 17b are provided for a signal wiring layer 14b positioned opposite the ground plane 16 with respect to the signal wiring pattern 15 respectively. The respective bypass capacitors 17a, 17b are electrically connected to the ground layer 12, the ground plane 16, and the power supply layer 11.

Description

  The present invention relates to a printed circuit board and an electronic apparatus having the printed circuit board.

  An electronic device such as a digital camera or a portable terminal device incorporates a multilayer printed circuit board on which electronic parts such as an IC are mounted.

  By the way, in recent years, due to the increase in signal transmission speed accompanying the improvement in processing capability of electronic devices, signals (high frequency signals) that operate at high speeds such as clock signals and data bus signals on signal lines wired to printed circuit boards It is a source of EMI (Electro Magnetic Interference) noise. For this reason, the cable connected to the signal line or the printed circuit board itself becomes an antenna, and amplified EMI noise is radiated.

  As a measure for suppressing (reducing) the emission of the EMI noise, for example, in the technique described in Patent Document 1, in a printed circuit board having a multilayer structure, a power supply layer is sandwiched from both sides by a ground layer, and the ground layers on both sides are arranged. By connecting the end portions of each other, the EMI noise generated between the power supply layer and the ground layer is prevented from being radiated to the outside.

  By the way, as electronic devices such as digital cameras and portable terminal devices in recent years have increased in function, etc., the number of circuits inside the printed circuit board and the further increase in signal transmission speed have progressed. The number of lines is also increasing, which increases the EMI noise radiated to the outside.

  For this reason, it is effective to further increase the number of ground layers described in Patent Document 1 or to widen (enlarge) the pattern of the ground layer in order to suppress the increase of EMI noise. However, increasing the number of stacked ground layers or widening the pattern of the ground layer increases the number of substrate layers and increases the area of the substrate layer, thereby increasing the substrate cost.

  Accordingly, an object of the present invention is to provide a printed circuit board and an electronic device that can effectively suppress the emission of EMI noise without increasing the substrate cost.

  In order to achieve the above object, the printed circuit board according to the present invention has a power supply layer on one surface and a ground layer on the other surface so as to sandwich the core layer, and further has an insulating layer at least on the power supply layer side. A printed circuit board having a multilayer structure in which a plurality of signal wiring layers are stacked with a signal wiring pattern in which a high-frequency signal flows in a signal wiring layer adjacent to the power supply layer among the plurality of signal wiring layers. A ground plane for return current is formed in a region of the power supply layer facing the signal wiring pattern, and the ground plane is formed with respect to the signal wiring pattern on both sides of the signal wiring pattern. Two bypass capacitors are respectively provided in the signal wiring layer located on the opposite side, and each bypass capacitor includes the ground layer, the ground plane, and It is characterized by being electrically connected to the serial power source layer.

  In the printed circuit board according to the present invention, a ground plane for return current is formed in a region facing the signal wiring pattern of the power supply layer, and the signal wiring pattern is opposite to the ground plane on both sides of the signal wiring pattern. A bypass capacitor is provided in each of the signal wiring layers located on the side, and each bypass capacitor is electrically connected to the ground layer, the ground plane, and the power supply layer.

  With such a structure, EMI noise radiated from the signal wiring pattern can be effectively suppressed without increasing the substrate cost (without increasing the number of ground layers or increasing the pattern of the ground layer). it can.

1 is a perspective view showing a back side of a digital camera as an example of an electronic apparatus according to Embodiment 1 of the present invention. FIG. 2 is an exploded perspective view showing a printed circuit board mounted in the digital camera of FIG. 1. FIG. 3 is a diagram illustrating a cross section of the printed circuit board according to the first embodiment. The figure which shows an example of the wiring pattern through which the high frequency signal formed in the signal wiring layer of a printed circuit board flows. The figure which shows an example of the ground plane for return current formed in the power supply layer of a printed circuit board. FIG. 6 is a diagram illustrating a cross section of a printed circuit board according to a second embodiment. The figure which shows the cross section of the printed circuit board for a comparison.

Hereinafter, the present invention will be described based on the illustrated embodiments.
<Embodiment 1>
FIG. 1 is a perspective view showing the back side of a digital compact camera (hereinafter referred to as “digital camera”) as an example of an electronic apparatus according to Embodiment 1 of the present invention, and FIG. 2 is mounted in the digital camera. It is a disassembled perspective view which shows a printed circuit board.

  As shown in FIGS. 1 and 2, the digital camera 1 of the present embodiment has a camera outer frame formed by joining the outer peripheral edge portions of the front case 2 and the rear case 3, and the camera operation is performed inside this. A printed circuit board 5 on which a plurality of electronic components 4 such as ICs for performing control and the like are mounted is disposed (details of the printed circuit board 5 which is a feature of the present invention will be described later).

  On the rear case 3 side, a monitor screen 6, operation buttons 7 and the like are provided. Further, a USB connector 8 is provided on the printed circuit board 5 as an input / output interface on the side surface of the digital camera 1, and the USB connector 8 is used for transmitting a signal to / from an external device such as a printer. A USB cable 9 is detachably connected. The USB connector 8 is provided with a cover case (not shown). When the USB cable 9 is not connected, the surface of the USB connector 8 is covered with this cover case. A lens barrel (not shown) having a photographing lens system is provided on the front side of the front case 2.

(Printed circuit board 5)
Next, details of the printed circuit board 5 according to Embodiment 1 of the present invention will be described.

  FIG. 3 is a view showing a cross section of the printed circuit board 5. As shown in FIG. 3, this printed circuit board 5 is a multilayer board (six-layer board in the figure), and has a power supply layer 11 on one side (upper side in the figure) and the other side (lower side in the figure) across the core layer 10. In addition, a ground (GND) layer 12 is laminated. Further, signal wiring layers 14a and 14b each having a wiring pattern formed thereon are laminated on the upper surface side of the power supply layer 11, and the insulating layers 13c and 13d are also formed on the lower surface side of the ground layer 12. The signal wiring layers 14c and 14d having the wiring patterns formed thereon are laminated.

  In the present embodiment, the signal wiring pattern 15 in the signal wiring layer 14a located on the opposite side of the power supply layer 11 from the ground layer 12 is a signal wiring through which a high-frequency signal flows, and the signal wiring pattern 15 generates EMI noise. It becomes a noise source that causes radiation (hereinafter, this signal wiring pattern 15 is referred to as “high-speed signal wiring 15”).

  For example, in the signal wiring layer of the printed circuit board as shown in FIG. 4, when a plurality of signal wirings 30 (corresponding to the high-speed signal wirings 15) through which high-frequency signals flow are patterned, the plurality of signal wirings 30 are This is a noise source that causes EMI noise to be emitted.

  A return current ground plane 16 is provided in a region of the power supply layer 11 facing the high-speed signal wiring 15. The width of the ground plane 16 (the width in the left-right direction in FIG. 3) is formed wider than the width of the high-speed signal wiring 15. The ground plane 16 and the ground layer 12 are via-connected at two locations on both sides.

  For example, in the power supply layer of the printed circuit board as shown in FIG. 5, the ground plane 31 provided in the center corresponds to the ground plane 16 for return current.

  In the present embodiment, bypass capacitors 17 a and 17 b are provided on the signal wiring layer 14 b, which is the surface layer of the printed circuit board 5, at positions facing both sides of the ground plane 16 of the power supply layer 11. The bypass capacitors 17a and 17b are via-connected to the power supply layer 11, the ground layer 12, and the ground plane 16. An insulating pattern 18 is provided on both sides of the bypass capacitors 17a and 17b of the signal wiring layer 14b which is the surface layer.

  As described above, according to the printed circuit board 5 of the present embodiment, the return current of the high-speed signal wiring 15 can be ensured by providing the ground plane 16 for the return current with respect to the high-speed signal wiring 15 in the power supply layer 11. In addition, the capacitor electrode plate is formed by adjoining the power supply layer 11 and the ground layer 12 with the core layer 10 interposed therebetween. Further, bypass capacitors 17 a and 17 b provided in the signal wiring layer 14 b are via-connected to the power supply layer 11, the ground plane 16, and the ground layer 12.

  As a result, EMI noise radiated from the high-speed signal wiring 15 can be effectively suppressed without increasing the substrate cost (without increasing the number of ground layers or widening the pattern of the ground layer).

  Furthermore, according to the printed circuit board 5 of the present embodiment, for example, even when the ground plane 16 provided in the power supply layer 11 cannot be physically wide, the bypass capacitors 17a and 17b provided in the signal wiring layer 14b are connected to the power supply layer 11. Since the ground plane 16 and the ground layer 12 are via-connected, a stable ground can be formed and radiation of EMI noise can be sufficiently suppressed.

<Embodiment 2>
FIG. 6 is a view showing a cross section of a printed circuit board according to Embodiment 2 of the present invention. In addition, the same code | symbol is attached | subjected to the member which has the same function as the printed circuit board of Embodiment 1 shown in FIG. 3, and the overlapping description is abbreviate | omitted.

  As shown in FIG. 6, the printed circuit board 5a of the present embodiment has a structure in which a ground pattern 19 for return current is provided at a position facing the high-speed signal wiring 15 in the signal wiring layer 14b as a surface layer. . The ground pattern 19 is via-connected to the ground plane 16 at two locations. Other structures are the same as those of the printed circuit board of the first embodiment.

  As described above, according to the printed circuit board 5a of the present embodiment, the ground pattern 19 is provided on the signal wiring layer 14b which is the surface layer, so that the ground planes for return currents are provided above and below the high-speed signal wiring 15, respectively. 16 and a ground pattern 19 are provided, and the ground plane 16 and the ground pattern 19 are via-connected at two locations.

  As a result, the high-speed signal wiring 15 shields the four directions on the upper and lower sides and both sides of the high-speed signal wiring 15, so that EMI noise radiated from the high-speed signal wiring 15 can be more effectively suppressed.

  FIG. 7 is a view showing a cross section of a printed circuit board for comparison with the printed circuit boards according to the first and second embodiments of the present invention. In addition, the same code | symbol is attached | subjected to the member which has the same function as the printed circuit board of Embodiment 1 shown in FIG. 3, and the overlapping description is abbreviate | omitted.

  As shown in FIG. 7, this comparative printed circuit board 5b is provided with the bypass capacitors 17a and 17b provided in the signal wiring layer 14b which is the surface layer of the printed circuit board of the first and second embodiments, and the ground pattern 19. Absent. Specifically, as described in the first embodiment, the ground plane 16 for return current is only provided in the region of the power supply layer 11 facing the high-speed signal wiring 15.

  In the printed circuit board 5b having the structure as shown in FIG. 7, the ground plane 16 for return current is provided in the power supply layer 11 with respect to the high-speed signal wiring 15, so that EMI noise radiated from the high-speed signal wiring 15 is reduced. it can. However, for example, when the ground plane 16 provided in the power supply layer 11 cannot be physically widened or when the ground plane 16 and the ground layer 12 cannot be connected at multiple points by vias, the impedance of the ground plane 16 cannot be lowered. , Radiation of EMI noise cannot be sufficiently suppressed.

  Table 1 below shows measurement results (NO. 1 to 7) of EMI noise (EMI radiation noise) by the structure of the printed circuit board 5 according to the first embodiment.

  In this noise measurement, electronic devices equipped with the printed circuit board having the structure according to the first embodiment are operated at different frequencies (NO.1: 67.63 MHz to NO.7: 934.99 MHz), and the EMI noise CISPR22 standard is set. EMI noise (noise level) was measured as to whether or not it was satisfied.

  The EMI noise that seems to be caused by the high-speed signal wiring 15 (signal wiring 30 in FIG. 4) was generally measured at a multiple of the operating frequency of 27 MHz. The EMI noise (noise level) measured at a multiple of 27 MHz is 188.999 MHz (NO.3), 323.74 MHz (NO.5), and 350.73 MHz (NO.6) in Table 1.

  As is apparent from this measurement result, EMI noise of multiples of 27 MHz other than the frequencies of No. 3, 5, and 6 was suppressed, and the level was such that measurement was not possible.

  In addition, at the frequencies of NO.3, 5, and 6, the margin value for the regulation value of the CISPR22 reference value for EMI noise on the right side of Table 1 is at least for both the horizontal and vertical polarization of the antenna used for measurement. It was 8.5 dB or more, and the effect of the present invention sufficient for EMI noise was obtained.

  Each embodiment described above is an example of a printed circuit board built in a digital camera. However, in addition to this, for example, a printed circuit board built in an electronic device such as a mobile terminal device is similarly used. The present invention can be applied.

1 Digital camera (electronic equipment)
2 Front case 3 Rear case 4 Electronic component 5, 5a, 5b Printed circuit board 10 Core layer 11 Power supply layer 12 Ground layer 15 High-speed signal wiring (signal wiring pattern)
16 Ground plane 17a, 17b Bypass capacitor 19 Ground pattern

JP 2003-218541 A

Claims (4)

A multilayer in which a power layer is laminated on one surface and a ground layer is laminated on the other surface so that the core layer is sandwiched, and a plurality of signal wiring layers are laminated at least on the power layer side with an insulating layer interposed therebetween A printed circuit board having a structure,
Among the plurality of signal wiring layers, a signal wiring layer adjacent to the power supply layer is provided with a signal wiring pattern through which a high-frequency signal flows,
In a region facing the signal wiring pattern of the power supply layer, a ground plane for return current is formed,
A bypass capacitor is provided on each side of the signal wiring pattern on the signal wiring layer located on the opposite side of the ground plane with respect to the signal wiring pattern,
The printed circuit board, wherein each bypass capacitor is electrically connected to the ground layer, the ground plane, and the power supply layer.   The printed circuit board according to claim 1, wherein the ground layer and the ground plane are via-connected in at least two places.   A ground pattern is formed in the signal wiring layer provided with each bypass capacitor so as to be positioned between the respective bypass capacitors, and the ground plane and the ground pattern are surrounded at least by surrounding the signal wiring pattern. 3. The printed circuit board according to claim 1, wherein vias are connected at two locations.   An electronic apparatus comprising the printed circuit board according to any one of claims 1 to 3.