JP2009260124A - Printed circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a printed circuit board which solves the problem that the path of return current for a transmission signal flowing on a microstrip line around a hollow becomes long to be a cause of unnecessary radiation noise, and suppresses occurrence of the unnecessary radiation noise owing to the presence of the hollow, in a printed circuit board having inner layer planes, wherein each inner layer plane is provided with the hollow. <P>SOLUTION: The printed circuit board having two or more inner layer plane layers is characterized in that an RC snubber is arranged at a part where voltage fluctuation is caused in the inner layer plane. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a printed circuit board having an inner layer plane and having a cutout in the inner layer plane, and more particularly to a printed circuit board in which generation of unnecessary radiation noise due to the presence of the cutout is suppressed.

  In general, the width of a component mounting pad (hereinafter simply referred to as a pad) on a printed circuit board is larger than the width of a microstrip line connected to the pad, so that the capacitance per unit length of the pad is less than that of the microstrip line. It becomes larger than the electrostatic capacity per unit length. Therefore, the characteristic impedance of the pad is smaller than the characteristic impedance of the microstrip line.

  Therefore, as a technique for matching the characteristic impedance of these pads and the characteristic impedance of the microstrip line, there is a technique of hollowing out the conductor of the inner layer plane immediately below the pads. According to this technology, the distance between the pad and the inner layer plane is increased, and the capacitance of the pad is reduced, so that a decrease in the characteristic impedance of the pad is suppressed, so that the characteristic impedance of the pad is changed to that of the microstrip line. Can be combined.

Japanese Patent No. 2654414

  By providing the above-described cutout in the inner plane, the return current path for the transmission signal flowing through the microstrip line around the cutout becomes long. This causes a phenomenon that near magnetic field noise is generated. In particular, when the ground potential fluctuates due to common mode noise, it causes unnecessary radiation noise.

  Therefore, the problem to be solved by the present invention is that the generation of unnecessary radiation noise due to the presence of the cutout is suppressed in the printed circuit board having the inner layer plane and the cutout provided in the inner layer plane. An object is to obtain a printed circuit board.

  The invention described in claim 1 for solving the above-mentioned problem is characterized in that, in a printed circuit board having two or more inner plane layers, an RC snubber is arranged at a location where voltage fluctuation occurs in the inner layer plane. It is a printed circuit board. The RC snubber here refers to a series circuit composed of a resistor and a capacitor.

  According to the first aspect of the present invention, the signal frequency at which noise is generated is shifted to a higher frequency, and the resistor consumes noise, so that unnecessary radiation noise can be suppressed.

  FIG. 1 is a plan view of a sample substrate 100 for measurement. FIG. 2 is a rear view of the sample substrate 100. This sample substrate 100 has a length in the longitudinal direction of 100 mm, a length in the short direction of 12 mm, the number of layers is 4, the distance between the signal layer and the ground layer immediately below is 0.12 mm, and the first ground of the inner layer The distance between the layer and the second ground layer is 1.2 mm.

  The pattern length of the sample substrate 100 is 82 mm, and a pad 101 is provided at the center. The pad 101 has a longitudinal direction of 2.0 mm and a lateral direction of 1.5 mm. In the first ground layer, a hollow (not shown) is provided immediately below the pad 101. The dimension of the cutout is 2.2 mm in the longitudinal direction and 1.7 mm in the lateral direction.

  FIG. 3 is a schematic cross-sectional view showing a connection structure with the SMA connector 102 in the sample substrate 100. In the sample substrate 100, the first ground layer and the second ground layer are short-circuited when the SAM connector 102 is inserted into the through hole.

  FIG. 4 is a schematic diagram showing a state of measurement of electromagnetic wave radiation of the sample substrate 100. Referring to FIG. 4, the sample board 100 is connected to the port 1 (indicated by P1) of the network analyzer 103 via the cable 105 and the SMA connector 102, and the dipole antenna is similarly connected to port 2 (indicated by P2). 104 were connected, these were installed at intervals of 10 cm, and S21 was measured.

  Further, a second sample substrate (not shown) having a structure similar to that of the sample substrate 100 and not provided with the first ground layer was prepared, and this was measured by the same method as described above.

  As a result of the above measurement, S21 was −55 dB in the second sample substrate when the frequency of the measurement signal was 2 GHz. On the other hand, in the sample substrate 100, S21 was −45 dB. That is, in the sample substrate 100, S21 increased compared to the second sample substrate, and it was confirmed that there was radiation.

  Here, a sample substrate 100 in which an RC snubber composed of a 10Ω resistor and a 1 pF capacitor was connected between the first ground layer and the second ground layer was prepared. The RC snubber was attached at the location indicated by the arrow in FIG. Moreover, the schematic cross section which shows the connection structure of RC snubber in FIG. 6 is shown. When the electromagnetic wave radiation was measured by the same method as described above, S21 was -70 dB when the frequency of the measurement signal was 2 GHz. That is, it was confirmed that electromagnetic radiation was reduced by connecting the RC snubber.

Explanation of symbols

100 Sample substrate 101 Pad 102 SMA connector 103 Network analyzer 104 Dipole antenna 105 Cable

The top view of a sample board | substrate. The rear view of a sample board | substrate. The schematic cross section which shows the connection structure with the SMA connector in a sample board | substrate. The schematic diagram which shows the mode of the measurement of the electromagnetic wave radiation of a sample board | substrate. The figure which shows the location which attaches RC snubber. The schematic cross section which shows the connection structure of RC snubber.

Claims (1)

A printed circuit board having two or more inner plane layers, wherein an RC snubber is arranged at a location where voltage fluctuation occurs in the inner layer plane.

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