JP2019186332A - Print circuit board - Google Patents

Abstract

To reduce radiation noise generated from a print circuit board.SOLUTION: In a print circuit board 1 with at least two grounding points 7 mounted with an electronic component 6 that operate with a pulse signal and electrically connected to a frame ground 4, the grounding points 7 are arranged so as to include at least one other ground point 7 that is less than a half wavelength corresponding to a predetermined frequency among frequencies that are equal to or higher than the reciprocal of a value obtained by multiplying a rise time or a fall time of the pulse signal by a circle ratio, and an electronic component 6 is arranged on the print circuit board 1 having a length less than one fourth wavelength corresponding to the predetermined frequency from any one of the grounding points 7 or less than half the length between two nearest grounding points.SELECTED DRAWING: Figure 1

Description

  The present application relates to a printed circuit board.

  In recent electronic circuits, there is an increasing demand for electronic components that operate at a high frequency, and a demand for miniaturization of devices. On the other hand, in the design of equipment, a more strict design based on EMC (Electro-Magnetic Compatibility) standard is required.

  However, electronic components that generate pulse signals, such as a gate drive signal output from an IC (integrated circuit) of a DC / DC converter that converts the oscillation circuit and clock signal of a microcomputer into a predetermined voltage, are themselves noise sources. Thus, noise propagation to the surroundings causes deterioration of EMI (Electro-Mgnetic Interference) performance (especially EMI radiation) of the device. In particular, a signal having a frequency of the order of kilohertz or higher or a signal having a high voltage level tends to increase the noise level, and affects the high frequency region as harmonic noise having a frequency that is an integral multiple of the fundamental wave.

  Incidentally, the ground layer in the printed circuit board is a ground of an electronic circuit formed on the circuit board, and is a so-called signal ground. This signal ground is connected to a case formed of a metal casing, a frame ground of a heat sink, or a ground on the power supply side directly to form a current feedback path. At this time, the ground layer in the printed circuit board can be regarded as a flat conductor. However, the grounding point connected to the frame ground has a length up to the conductor end of the printed circuit board. That is, with respect to the grounding point on the printed circuit board connected to the frame ground, which is a reference potential, the conductor portion having a length from the grounding point has an inductance, and it corresponds to the board shape such as the length and width of the conductor. A resonant circuit (antenna characteristics) is created. That is, there is a problem that the substrate itself becomes a resonator, and harmonic components of electromagnetic noise generated from the electronic components are amplified by resonance at the resonance frequency and its periphery, and the noise level becomes high.

  In order to reduce the noise generated from these printed circuit boards, through holes connected to the ground layer arranged in the printed circuit board are provided, and through holes are formed at intervals sufficiently smaller than the wavelength corresponding to the maximum frequency of the electromagnetic wave to be suppressed. By arranging, resonance in a desired frequency band or less is suppressed and noise propagation is reduced (see, for example, Patent Document 1).

  In addition, the dielectric component provided on the ground layer at the position that becomes the resonance point of the substrate is arranged so as to contact the housing that houses the printed wiring board, and the resonance frequency of the substrate is shifted to the high frequency side. (For example, refer to Patent Document 2).

International Publication No. 2017/006552 JP 2010-73900 A

However, Patent Document 1 is effective in avoiding resonance between the power supply layer and the signal ground in the electronic circuit, but does not consider the resonance of the ground layer itself.
Further, Patent Document 2 does not mention the degree of shift of the resonance frequency, and only by placing a dielectric at the resonance point (resonance antinode) with respect to the ground point screwed to the casing of the printed circuit board. Resonance with harmonic noise that depends on the characteristics of the component may not be avoided.

  This application has been made to solve the above-described problems. The grounding point connected to the frame ground is arranged according to the characteristics of the electronic component serving as the excitation source, and has a higher frequency than the frequency band in which resonance is to be avoided. An object of the present invention is to provide a printed board capable of shifting the resonance frequency to the side and suppressing radiation noise generated from the board itself.

The printed circuit board disclosed in the present application is a printed circuit board on which electronic components that operate with a pulse signal are mounted and at least two or more grounding points that are electrically connected to the frame ground. Among the points, the second ground point is arranged at a distance of less than ½ wavelength of a predetermined frequency that is equal to or greater than the reciprocal of the value obtained by multiplying the rise time or the fall time of the pulse signal by the circle ratio from the first ground point. And
The electronic component is connected to the first ground point from the first ground point or the second ground point, on a printed circuit board having a wavelength less than ¼ wavelength of the predetermined frequency, or from the first ground point or the second ground point. And a second grounding point, which is disposed on a printed circuit board having a distance less than ½ of the distance between the second grounding point and the second grounding point.

  According to the printed circuit board disclosed in the present application, by arranging the ground point according to the electronic component serving as the excitation source, the resonant frequency of the substrate itself is changed, and at a predetermined frequency with respect to the harmonic noise generated from the electronic component. By avoiding resonance, a noise level at a predetermined frequency or lower can be suppressed.

1A is a schematic cross-sectional view of a printed circuit board in the first embodiment, and FIG. 1B is a schematic cross-sectional view of another printed circuit board in the first embodiment. 2A is a diagram for explaining a pulse signal of the electronic component according to the first embodiment, and FIG. 2B is a diagram for explaining the attenuation characteristics of harmonic noise generated from the pulse signal shown in FIG. 2A. 6 is a diagram illustrating an example of frequency characteristic analysis of a printed circuit board according to Embodiment 1. FIG. 3 is a plan view illustrating a configuration example of a printed circuit board according to Embodiment 1. FIG. 6 is a plan view showing another configuration example of the printed circuit board in the first embodiment. FIG. 6 is a diagram illustrating a connection example between the printed circuit board and the frame ground in Embodiment 1. FIG.

Embodiment 1 FIG.
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, exemplary embodiments preferable for the present application will be described with reference to the drawings. However, the material, shape, arrangement, and the like of the component parts described in this embodiment are not limited to the embodiment disclosed in the present application unless otherwise specified.

Embodiment 1 FIG.
FIG. 1A is a schematic cross-sectional view of the printed circuit board in the first embodiment. In FIG. 1A, the printed circuit board 1 is a multilayer printed circuit board in which the inner layer is a ground plane 3 that serves as a signal ground layer of an electronic circuit, and the surface layer includes a signal line layer of the electronic circuit and a power supply layer 2. In the signal line layer and the power supply layer 2, a thin wiring pattern or a plane-like conductor is also included, and a ground pattern can also be arranged. On the other hand, the ground plane 3 is a plain-shaped conductor extending over the entire substrate surface.

  The ground pattern formed on the signal line layer and the power supply layer 2 is electrically connected to the ground plane 3 through the ground via 5, and a plurality of ground patterns exist on the printed circuit board 1 according to the circuit pattern. The grounding points 7 are the ground vias 5 that are electrically connected to the external frame ground 4, and are arranged on the printed circuit board 1 at least two points. The frame ground 4 is connected to a power source supplied from the outside and grounded. The power source of the electronic circuit formed on the printed circuit board 1 is supplied from the ground plane 3 serving as a signal ground layer via the frame ground 4. Return to the power supply side. The frame ground 4 is preferably a metal housing such as a heat sink or a metal case. Note that the ground shown in the present embodiment is not limited to the zero potential, but means the ground to which the lowest potential is applied on the electronic circuit including the power source. For example, in an automobile, the vehicle body itself is at ground potential, and grounding is ensured by bringing a heat sink or a metal case into contact with a metal part of the vehicle body and fastening.

  Basically, various electronic components constituting an electronic circuit are mounted on the surface layers on both sides of the printed circuit board 1. In particular, the electronic component 6 shown in FIG. 1A outputs a pulse-like signal as an excitation source. An electronic component is shown. Here, the pulse signal is a clock signal, a digital communication signal, a gate drive signal for driving a semiconductor element, or the like. Examples of electronic components that mainly output these pulse signals include a microcomputer having a clock circuit, a power supply IC including a DC / DC converter that performs voltage conversion, and a driver IC for driving a semiconductor element.

  At this time, since the ground plane 3 serving as the signal ground layer is grounded via the frame ground 4, the ground plane 3 has a considerable impedance with respect to the ground potential, and strictly speaking, does not have the same potential as the ground portion. . Therefore, a resonance phenomenon is caused at a specific frequency depending on the magnitude of the impedance (inductance or stray capacitance) with respect to the frame ground 4.

  Since the ground point 7 connected to the frame ground 4 serves as a resonance node in the ground plane 3, the ground point 7 can be regarded as a half wavelength, and the end of the ground plane 3 can be regarded as an open end. Therefore, the frequency corresponding to the quarter wavelength becomes the resonance frequency between the ground point 7 and the end of the ground plane 3.

  The arrangement of the grounding points 7 in FIG. 1A is arranged such that at least one other grounding point 7 is included in a distance of less than ½ wavelength according to a predetermined frequency. That is, at each grounding point 7 in FIG. 1A, the length of the distance between the nearest grounding points 7 is less than ½ wavelength.

  Furthermore, it is preferable that at least one or more grounding points 7 are included at a distance of less than a quarter wavelength corresponding to a predetermined frequency from the end of any ground plane 3. That is, the distance between the ground point 7 and the end of the ground plane 3 in FIG. 1A is set to less than ¼ wavelength.

  Here, one wavelength corresponding to a predetermined frequency is calculated from the relationship between the propagation speed / frequency of electromagnetic waves, and the propagation speed is determined by the relative dielectric constant of the printed circuit board 1.

  FIG. 2A shows a pulse signal, and FIG. 2B shows the attenuation characteristics of harmonic noise generated from the pulse signal. As shown in FIG. 2B, as a tendency of the attenuation characteristic of the harmonic noise generated from the pulse signal shown in FIG. 2A, the harmonic envelope has an area having a certain level from DC when the frequency axis is logarithmically, It has a region that attenuates according to the frequency with an inclination of 20 dB / dec and a region that attenuates at 40 dB / dec on the high frequency side. At this time, the frequency of the inflection point that begins to attenuate at 20 dB / dec is 1 / (π × tw), and can be calculated as a guide by the pulse width tw. The frequency of the inflection point at which attenuation begins at 40 dB / dec is 1 / (π × tr), and tr can be calculated as a guideline as the rise time tr1 or the fall time tr2 of the pulse signal shown in FIG. 2A.

  Here, the predetermined frequency is a frequency at which resonance is desired to be avoided among frequencies of 1 / (π × tr) or more shown in FIG. 2B, and the distance between the ground points 7 is set to 1 according to the predetermined frequency. By setting the distance between the ground point and the end of the ground plane 3 to less than ¼ wavelength, the resonant frequency present in the printed circuit board 1 is shifted to a higher frequency side than the predetermined frequency, thereby reducing noise at the predetermined frequency. The level can be suppressed. In addition, by shifting the resonance frequency to the high frequency side, the resonance frequency can be shifted to a frequency band where harmonic noise is further attenuated by the attenuation characteristic shown in FIG. 2B, and the peak level is also suppressed.

  At this time, the pulse signal having the rise time tr1 or the fall time tr2 shown in FIG. 2A is a signal having the fastest rise time or fall time among the pulse signals generated on the configured electronic circuit, or the most pulsed signal. It is preferable that the signal has a large voltage amplitude. Basically, the higher the frequency or the larger the voltage amplitude, the greater the energy of the noise, the higher the harmonic noise affects the high frequency region, and the easier it is to propagate noise due to crosstalk. In the pulse signal shown in FIG. 2A, it is assumed that the rise time tr1 and the fall time tr2 are the same. However, when each time is different, a predetermined frequency or the like is calculated with reference to the earlier time.

  FIG. 3 is an example of the analysis result of the frequency characteristics of the potential of the ground plane 3 which is the signal ground layer, and shows the effect when the number of grounding points 7 is increased. By increasing the number of grounding points 7 and decreasing the distance between the grounding points 7 and the distance between the grounding point 7 and the end of the ground plane 3, the resonance frequency of the ground plane 3 itself shifts to the high frequency side. The noise level tends to attenuate. By arranging the ground point 7 based on the wavelength corresponding to the frequency at which resonance is to be avoided, the radiation noise level at a predetermined frequency can be suppressed.

An example of the arrangement of electronic components serving as excitation sources will be described below.
In the electronic component 6 shown in FIG. 1A, it is preferable to avoid the arrangement of the ground plane 3 at the resonance point portion depending on the arrangement position of the ground point 7. For example, in FIG. 1A, the electronic component 6 is disposed so as to be sandwiched between the ground point 7 and the end of the ground plane 3, and is disposed less than a quarter wavelength corresponding to a predetermined frequency from the ground point 7. . Alternatively, as shown in FIG. 1B, when the electronic component 6 is disposed so as to be sandwiched between the grounding points 7, the distance of the electronic component 6 from the nearest grounding point 7a is the two nearest grounding points. It arrange | positions so that it may become less than 1/2 of the distance L between the grounding point 7a and the grounding point 7b. At this time, the case where there is only one ground point within a half wavelength around the electronic component 6 is regarded as an arrangement between the ground point and the end of the ground plane 3. If there are two or more grounding points within the range, it is considered as an arrangement between the grounding points. It is preferable to arrange the electronic component 6 on a substrate closer to the grounding point 7, and voltage excitation can be suppressed by placing the electronic component 6 serving as an excitation source in the vicinity of the grounding point 7 serving as a resonance node. The noise level suppression effect is increased. In FIG. 1, the distance is based on the center position of the electronic component 6. However, if the site that is the excitation source on the electronic component is clear, the excitation site may be the center position.

  The shape of the ground plane 3 and the shape of the printed circuit board 1 may be arbitrary. For example, FIG. 4 shows a case where the ground plane 3 is L-shaped, and FIG. 5 shows a case where the ground plane 3 is annular. The ground plane 3 may be either an inner layer or a surface layer, and the plane shape need not match the substrate shape. As for the arrangement of each grounding point 7, any other grounding point 7 is disposed at a wavelength less than ½ wavelength of the predetermined frequency. Also in the electronic component 6, the contact between the nearest grounding point 7 and the nearest two points is connected. The distance between the points is less than ½ of the distance L. At this time, in order to avoid resonance at a predetermined frequency, as indicated by the broken line in FIG. 4 or FIG. 5, any distance from the end of any ground plane to a distance less than ¼ wavelength corresponding to the predetermined frequency. Such a grounding point 7 is preferable, and the plane shape may be changed by chamfering as necessary.

  FIG. 6 shows an example of connection between the printed circuit board 1 and the frame ground 4. The printed circuit board 1 is surrounded by the resin case 13 and insulated from the heat sink 11. The heat sink 11 is a frame ground, and the ground terminal 9 is fastened to the heat sink 11 by the fastening member 8. A portion extending from the ground terminal 9 is passed through a via serving as a ground point 7 of the printed circuit board 1. At this time, a ground pad 12 is provided on the surface layer, and the protruding portion of the ground terminal 9 and the ground pad 12 are joined with the solder 10, thereby making the heat sink 11 conductive and fixing the printed circuit board 1. According to this configuration, the frame ground 4 and the ground plane 3 can be electrically connected and the printed circuit board 1 can be fixed. FIG. 6 shows a DC / DC converter circuit or an inverter circuit that performs power conversion such as DC / AC and an application to a control board for driving and controlling the DC / DC converter circuit. Used for heat dissipation of semiconductor elements. At this time, the signal terminal is extended from the semiconductor element mounted on the heat sink 11 to the printed circuit board 1 side and, like the ground terminal 9, is passed through vias electrically connected to each related signal line, and then on the surface layer. The provided pad part and the extension part of the signal terminal are joined with solder. A board | substrate can be fixed more by increasing a junction location.

The characteristics of the printed circuit board according to the first embodiment are summarized as follows.
Features 1.
An electronic component 6 that operates with a pulse signal is mounted, and has at least two or more grounding points 7 that are electrically connected to the frame ground 4. Of the two or more grounding points 7, the first contact The second grounding point 7b is arranged at a distance less than ½ wavelength of a predetermined frequency equal to or larger than the reciprocal of the value obtained by multiplying the rise time or the fall time of the pulse signal by the circularity from the point 7a,
The electronic component 6 is supplied from the first grounding point 7a or the second grounding point 7b, on the printed circuit board 1 having a wavelength less than ¼ wavelength, or from the first grounding point 7a or the second grounding point 7b. The first grounding point 7a and the second grounding point 7b are arranged on a printed circuit board having a distance less than ½ of the distance L.

Feature 2.
The grounding point 7 is a ground via 5 and is characterized in that it is electrically connected to a plain signal ground layer (ground plane 3) that applies a ground potential to an electronic circuit including the electronic component 6.

Feature 3.
The grounding point 7 is disposed from a plane end of the signal ground layer (the ground plane 3) at less than a quarter wavelength of the predetermined frequency.

Feature 4.
The rise time or fall time of the pulse signal is characterized by being the fastest rise time or fall time of the pulse signal.

Feature 5.
The rise time or fall time of the pulse signal is the rise time or fall time of the pulse signal having the largest signal amplitude.

Feature 6
The rise time or fall time of the pulse signal is a rise time or fall time of a drive signal for driving a semiconductor element in the DC / DC converter circuit.

  As described above, in the printed circuit board according to the first embodiment, by arranging the ground point according to the characteristics of the electronic component serving as the excitation source, the resonance frequency of the substrate itself is changed, and the harmonics generated from the electronic component. By avoiding resonance at a predetermined frequency with respect to noise, it is possible to suppress the noise level below the predetermined frequency and reduce the peak level by shifting to the high frequency side. In addition, the electronic component is arranged to be less than ¼ wavelength corresponding to a predetermined frequency from the ground point, or from the nearest ground point to less than half of the distance L between the two nearest ground points. Voltage excitation can be suppressed by avoiding the operation at the point, and the noise level can be reduced. Since it does not depend on the ground plane or substrate shape, it can be applied to various control devices and is suitable for a control device having an inverter circuit or a converter circuit.

In the present application, exemplary embodiments are described. However, various features, aspects, and functions described in the embodiments are not limited to application of specific embodiments, and are independent. The present invention can be applied to the embodiments in various combinations.
Accordingly, countless variations that are not illustrated are envisaged within the scope of the technology disclosed herein. For example, the case where at least one component is modified, the case where it is added, or the case where it is omitted are included.

1: printed circuit board, 2: signal line layer and power supply layer, 3: ground plane, 4: frame ground, 5: ground via, 6: electronic component, 7: grounding point, 8: fastening member, 9: grounding terminal, 10 : Solder, 11: Heat sink, 12: Ground pad, 13: Resin case

The printed circuit board disclosed in the present application is a printed circuit board on which electronic components that operate with a pulse signal are mounted and at least two grounding points that are electrically connected to the frame ground . The printed circuit board is connected to the frame ground. A plane signal ground layer that provides a ground potential to an electronic circuit including an electronic component is provided, and the pi ratio is measured from the first grounding point to the rising or falling time of the pulse signal from two or more grounding points. A second grounding point is disposed at a distance less than ½ wavelength of a predetermined frequency equal to or greater than the inverse of the value multiplied by
The electronic component is sandwiched between the first grounding point or the second grounding point and the plain end of the signal ground layer, and ¼ of a predetermined frequency from the first grounding point or the second grounding point. Arranged between the first ground point and the second ground point, and from the first ground point or the second ground point, the first ground point and the second ground point. disposed less than half the distance between the grounding point wherein a is.

Claims (6)

A printed circuit board on which electronic components that operate with a pulse signal are mounted and having at least two grounding points that are electrically connected to the frame ground,
Of the two or more grounding points, a distance from the first grounding point that is less than ½ wavelength of a predetermined frequency that is equal to or greater than the reciprocal of a value obtained by multiplying the rise time or fall time of the pulse signal by the circumference. A second grounding point is arranged,
The electronic component is connected to the printed circuit board having a wavelength less than ¼ of the predetermined frequency from the first ground point or the second ground point, or the first ground point or the second ground point. The printed circuit board is disposed on the printed circuit board having a distance less than ½ of the distance between the first grounding point and the second grounding point.   The printed circuit board according to claim 1, wherein the grounding point is a ground via and is electrically connected to a planar signal ground layer that applies a ground potential to an electronic circuit including the electronic component.   The printed circuit board according to claim 2, wherein the grounding point is disposed at a wavelength less than a quarter wavelength of the predetermined frequency from a plain end of the signal ground layer.   4. The printed circuit board according to claim 1, wherein the rising time or the falling time of the pulse signal is the fastest rising time or the falling time of the pulse signal. 5.   4. The printed circuit board according to claim 1, wherein a rising time or a falling time of the pulse signal is a rising time or a falling time of a pulse signal having the largest signal amplitude. 5.   The rise time or fall time of the pulse signal is a rise time or fall time of a drive signal for driving a semiconductor element in a converter circuit or an inverter circuit. The printed circuit board according to one item.

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