KR101017943B1 - Printed circuit board using electric resistive materials - Google Patents

Abstract

The present invention relates to a printed circuit board structure in which an electrically resistive material is used. According to the present invention, at least two printed circuit boards are arranged at predetermined intervals by a slot; A connection member connecting the printed circuit boards to each other; And the connection member is an electrically resistive material having a predetermined conductivity, and the conductivity is determined based on signal transmission and noise transmission characteristics between the printed circuit boards and has a range of 300 to 500 s / m. Have The electrically resistive material forms a new path of parallel resistance in the feedback current plane of the slotted printed circuit board. According to the present invention, there is an advantage that can suppress the transmission of noise and unwanted electromagnetic radiation emissions by compensating the flow of the feedback current in the printed circuit board and blocking the transmission path of the unnecessary electromagnetic waves.

Printed Circuit Boards, Electrically Resistant Materials, Signal Integrity, Unnecessary Electromagnetic Waves and Noise Isolation

Description

Printed Circuit Board Structure Using Electrical Resistant Material {PRINTED CIRCUIT BOARD USING ELECTRIC RESISTIVE MATERIALS}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed circuit board (PCB), and more particularly, to a printed circuit board in which unwanted electromagnetic waves are suppressed and signal transmission characteristics are improved through conductivity of an electrically resistive material.

Due to the development of semiconductor device technology, information and communication devices are getting faster and smaller, so that the operating frequency of the system increases more than several orders of magnitude and the driving voltage is gradually decreasing. As a result, signal integrity and EMI issues for power stage noise are becoming important factors in determining the performance of the overall system.

In particular, Simultaneous Switching Noise (SSN) or Ground Bounce Noise (GBN) generated by simultaneous switching of various devices may cause unstable potential between the power plane and the ground plane. It causes logical errors in the operation of digital devices on the substrate.

1 and 2 show a test substrate and a noise transfer characteristic graph which is a simulation result of the test substrate in order to explain these noise transfer characteristics.

As shown in FIG. 1, the test substrate is a width (a): 100 mm, length (b): 50 mm, thickness (d): 0.6 mm, and an FR-4 substrate having ε _r : 4.3 and tan δ: 0.02. It was.

2 shows the amount of power that noise generated from the noise source source s of the test substrate is received at an arbitrary point v.

The simulation results show that the noise caused by the parallel plate along with the noise component is generated. This resonance is generated by the size of the test substrate and is summarized in Equation (1).

Equation (1):

Where c is the speed of light [m / s], ε _r : dielectric constant, m and n: resonant mode, a, b: substrate size.

The amount of noise transmitted by the unwanted noise component and the parallel plate resonance causes a disturbance of the normal operation of the analog circuit existing on one power supply stage.

On the other hand, noise generated in the digital circuit affects the analog circuit, which causes the normal operation to be disturbed. In particular, phase sensitive circuits (phase-locked loops (PLL), audio and video equipment, which are sensitive to electromagnetic waves, can be seriously affected.) Electromagnetic emissions from I / O cables can cause an increase in the overall EMI level. Becomes

Therefore, a method of forming a slot in the printed circuit board is used to block the noise transfer.

3 shows a slotted printed circuit board structure. 3, an analog circuit region 30, a digital circuit region 32, and an I / O cable region 34 are formed on a printed circuit board, which is an analog circuit region 30 and a digital circuit region 32. , Between the I / O cable regions 34 is divided by slots 36. This suppresses the transmission of noise to different areas.

FIG. 4 is a graph showing noise transfer characteristics when the printed circuit board is divided as shown in FIG. 3. Looking at the graph, it can be seen that noise generated in each circuit region of the printed circuit board is formed at -3dB or less.

However, suppression of noise propagation by the slots causes serious problems with signal integrity because of dividing the feedback current plane of the signal line, and also raises unnecessary electromagnetic radiation emission levels, which eventually leads to malfunction of the entire system and of other electronic devices. It causes.

5A and 5B show a microstrip line having a slotted ground plane and an equivalent circuit thereof. In this way, if the slot 50 is present in the ground plane 52, it can be equivalently implemented as a series capacitance 56, but the signal is isolated under the influence of the serial capacitance 56 seriously affects the signal integrity.

For example, FIG. 6 is a result graph for simulation for explaining signal distortion in the printed circuit board of FIG. 5A. FIG. 6A is a frequency response characteristic graph and FIG. 6B is a time domain response characteristic graph. The printed circuit board used in the simulation is a FR-4 substrate with width (a): 100mm, length (b): 50mm, thickness (d): 0.6mm, line: 50Ω, ε _r : 4.4, tanδ: 0.02 Was used. The simulation used 'HFSS v10', a 3D electromagnetic field analysis tool, and ADS was used for time domain simulation. The source used for the time domain analysis was applied at a frequency of 100 MHz, 3.3 Vp-p, and 50% duty cycle.

Referring to FIG. 6, it can be seen that in slotted printed circuit boards, signals are not maintained in a circular shape due to amplitude distortion and phase distortion, such as ringing and rounding phenomena due to reflection in the slots, as compared with non-formed printed circuit boards. Can be.

This division of the feedback current plane to suppress noise transmission has problems with signal integrity and unnecessary electromagnetic radiation emission.

Therefore, in order to solve this problem, a method of adding a bridge line to an isolated feedback current plane to compensate the flow of the feedback current to ensure signal integrity while effectively suppressing unwanted electromagnetic radiation emission has been proposed.

7A and 7B show test substrates for confirming noise and signal transmission characteristics when a bridge line is used. As shown, it can be seen that the printed circuit boards are connected to each other by the bridges 70 and 72. 8A and 8B are graphs of simulation results using the test substrates of FIGS. 7A and 7B. FIG. 8A is a graph of noise transmission characteristics, and FIG. 8B is a graph of transmission characteristics of a transmission line. Simulation simulated the width of the bridge line from 0.2mm to 1.2mm because the signal width for 50Ω matching of the test board was 1.1mm.

As a result of the simulation, if only the noise transmission path is formed as shown in FIG. 8A, even if the width of the bridge line is minutely changed, it can be seen that noise transmission cannot be effectively blocked because the magnitude of the changing inductance is not large. In addition, as shown in FIG. 8B, as the width of the bridge preference increases, the bending of the track gradually disappears. This is because the larger the width of the bridge line, the more the current of the feedback current is compensated for.

Therefore, considering the noise transfer characteristics and the signal transfer characteristics, when the bridge substrate is used, the width of the bridge line should be large enough to compensate for the signal transfer characteristics.

9A and 9B show graphs of noise transfer and signal transfer characteristics for the bridge substrate and the slot substrate. 9, it can be seen that the noise level is increased by the bridge line making the noise transmission path, and the signal transmission is better than that of the slot substrate because the bridge line compensates the feedback current.

Such a slot substrate has excellent noise transfer characteristics, but has a problem in terms of signal integrity because the feedback current plane by the slot is isolated. In addition, the substrate using the bridge line can compensate for the signal integrity, but since the noise is transmitted through the bridge line, unnecessary electromagnetic waves are transmitted.

SUMMARY OF THE INVENTION An object of the present invention is to provide a printed circuit board structure capable of improving the signal transmission characteristics compared to slot substrates and improving the unnecessary electromagnetic wave transmission characteristics compared to bridge substrates. .

According to a feature of the present invention for achieving the above object, a printed circuit board arranged in at least two at a predetermined interval by a slot; A connection member connecting the printed circuit boards to each other; And the connection member is an electrically resistive material having a predetermined conductivity, and the conductivity is determined based on signal transmission characteristics and noise transmission suppression characteristics between the printed circuit boards, Has a range.

The electrically resistive material forms a new path of parallel resistance in the feedback current plane of the slotted printed circuit board.

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According to the printed circuit board of the present invention having the above configuration has the following effects.

That is, a general slot substrate can suppress unwanted electromagnetic wave transmission characteristics, but has a disadvantage in signal transmission characteristics, and a bridge substrate has excellent signal transmission characteristics but a disadvantage in that unwanted electromagnetic waves are transmitted by a bridge, but in this embodiment, slotted printing By connecting each circuit board with an electrically resistive material, it is possible to ensure signal integrity and effectively suppress noise transfer characteristics and unnecessary electromagnetic radiation emission.

In other words, using a resistive material in a slotted feedback current plane that can be equivalently modeled as a series capacitance in a printed circuit board, a new path of parallel resistance is formed to compensate for the flow of the feedback current and transfer of unnecessary electromagnetic waves. By blocking the path with the resistive component of the electrically resistive material, it is possible to suppress noise transfer characteristics and unwanted electromagnetic radiation emission.

Hereinafter, a printed circuit board structure using an electrically resistive material according to the present invention will be described in detail with reference to a preferred embodiment shown in the accompanying drawings.

This embodiment is to improve signal integrity and noise transfer characteristics by using an electrically resistive material for a printed circuit board.

Figure 10a is a test board for confirming the transmission characteristics of the transmission line according to an embodiment of the present invention, Figure 10b is a test board for confirming the noise transmission characteristics according to an embodiment of the present invention.

10A and 10B, it can be seen that the electrically resistive material 110 and 210 are connected between the substrates along the transmission line. Substrates in which the electrically resistive materials 110 and 210 are used will hereinafter be referred to as resistive substrates 100 and 200. The electrically resistive material 110 and 210 generally mean a material having an electrical resistive component, and refers to a material having conductivity. The electrically resistive material 110, 210 is used as a shield to shield electromagnetic waves or used as an absorber.

In the present embodiment, the electrically resistive material 110 or 210 compensates for the feedback current of the feedback current plane in the slot substrate, and removes the noise transmission path through the resistor with a loss effect. Best of all, if the conductivity is properly selected, it can compensate for the feedback current. Conductivity measurements are normally specified in MIL-DTL-83528C, but are generally measured in the form of 4-probes. In the case of 4-probe measurement, it is necessary to use a probe that minimizes the contact resistance between the probe and the specimen in order to reduce the measurement error.

11 shows signal transmission characteristics and noise transmission characteristics in the resistive substrates 100 and 200 when the electrically resistive material is used.

As shown in FIGS. 11A and 11B, the signal transmission characteristics and the noise transmission characteristics according to the conversion of the conductivity were simulated. The resistivity material used in the simulation was fixed at a thickness of 0.25 mm, a width of 1 mm, and a slot of 1 mm. The conductivity was simulated with varying 100 to 900 s / m.

The simulation results show that the use of materials with high conductivity improves signal transfer but increases noise transfer, while the materials with low conductivity improves noise transfer but poor signal transfer. can do.

That is why it is important to choose an electrically resistive material with adequate conductivity. In this embodiment, an electrically resistive material having a conductivity of 400 s / m is used.

Next, the comparison of the characteristics of a slot substrate, a bridge substrate, and a resistive substrate is demonstrated.

This is shown in the characteristic graph shown in FIG. 12A and 12B are graphs comparing signal transmission characteristics and noise transmission characteristics of a slot substrate, a bridge substrate, and a resistive substrate, and FIG. 12C is an enlarged graph of signal transmission characteristics of a bridge substrate and a resistive substrate. Indicates.

12A and 12B, it can be seen that the resistive substrate improves the signal transfer characteristic similarly to the signal transfer characteristic of the bridge substrate and effectively suppresses the noise transfer characteristic in comparison with the bridge line. Referring to FIG. 12C in the signal transmission characteristic, the resistive substrate and the bridge substrate are almost similar. In particular, it was confirmed that suppressing the resonance phenomenon occurring in the vicinity of 500MHz, the noise transfer characteristics improved from about 1kHz or less to about 10kHz or more.

13 is a graph showing signal transmission characteristics in the time domain.

The signal was applied at a frequency of 100 MHz, 3.3 Vp-p, and 50% duty cycle to confirm the signal propagation characteristics in the time domain.

This shows that a voltage drop of about 0.5V occurred due to the passage of the electrically resistive material, but the resistive substrate showed little difference compared to the bridge substrate. It can also be seen that the signal integrity is significantly improved compared to the slot substrate.

On the other hand, the present embodiment compares the characteristics of the slot substrate, the bridge substrate, and the resistive substrate with respect to crosstalk which causes severe signal distortion during high-speed signal transmission.

FIG. 14 shows substrates for measuring crosstalk, FIG. 14A is a reference substrate, FIG. 14B is a slot substrate, FIG. 14C is a bridge substrate, and FIG. 14D is a perspective view of a resistive substrate.

The transmission lines of the respective substrates shown in Fig. 14 were matched with a microstrip type and each line was 50 mV. The width of the track was 1.1 mm, and the distance between the track and the track was 3 mm. The input signal was a high frequency signal with a frequency of 100 MHz, 3.3 Vp-p, and 50% duty cycle.

This simulation result is shown in FIG.

FIG. 15A is a graph of a near-end crosstalk phenomenon, and FIG. 15B is a graph of a far-end crosstalk phenomenon. NEXT is a crosstalk effect caused by an electromagnetic field that interferes with signals of adjacent wires, and FEXT is a phenomenon in which interference by input signals in opposite directions attenuates input signals.

The NEXT simulation results show that slot substrates exhibit crosstalk of up to 800 m Vp-p and resistive substrates up to 300 m Vp-p with a voltage suppression effect of about 500 m Vp-p.

Next, to confirm the unwanted electromagnetic radiation emission for each substrate, the noise source as the source of unwanted electromagnetic radiation emission was used the 'The Comparison Noise Emitter III (CNE III)' of 'York EMC Services Ltd.'.

An undesired electromagnetic radiation emission measurement result graph is shown in FIG.

Referring to Fig. 16, since the slot substrate is a substrate in which noise transfer characteristics are suppressed, the characteristics of the undesired electromagnetic wave emission effect are better than those of other test substrates.

In addition, the resistive substrate can improve the results up to 12 dBu V / m from 500 MHz to 900 MHz compared to the bridge substrate. The measured results are shown in Table 2.

TABLE 2

frequency Radiated Emission (dBu V / m) Slot board Bridge board Resistive substrate 73.8 MHz 28.3 32.2 30.5 103.6 MHz 33.2 43.2 40.6 288.6 MHz 29 38.5 34.1 588.9 MHz 24.8 39.1 28.3 706.8 MHz 26.3 43.2 32.2

 As described above, according to the present embodiment, a method of guaranteeing signal integrity and effectively suppressing noise transmission characteristics and unnecessary electromagnetic radiation emission by using an electrically resistive material is proposed. In other words, the electrically resistive material compensates for the flow of the feedback current by forming a new path of parallel resistance in the slotted feedback current plane that can be equivalently modeled in series capacitance, and blocks the transmission path of the undesired electromagnetic wave as a resistance component. And suppressing unwanted electromagnetic radiation emission.

Although described with reference to the illustrated embodiment of the present invention as described above, this is merely exemplary, those skilled in the art to which the present invention pertains various modifications without departing from the spirit and scope of the present invention. It will be apparent that other embodiments may be modified and equivalent. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

1 is a perspective view of a test substrate for explaining general noise transfer characteristics.

Figure 2 is a graph of noise transfer characteristics of the test substrate of Figure 1;

3 is a schematic diagram of a slotted printed circuit board.

4 is a noise transfer characteristic graph of FIG.

5A and 5B are microstriplines with slotted ground planes and equivalent circuit diagrams thereof.

FIG. 6 is a result graph for simulation for explaining signal distortion in the printed circuit board of FIG. 5, FIG. 6A is a graph of frequency response characteristic, and FIG. 6B is a graph of time domain response characteristic.

7A and 7B are structural diagrams of test boards for confirming noise and signal transmission characteristics when a bridge line is used.

8A and 8B are graphs of the results of the simulation using the test substrates of FIGS. 7A and 7B. FIG. 8A is a graph of noise transmission characteristics, and FIG. 8B is a graph of transmission characteristics of a transmission line.

9A and 9B are graphs of noise transfer characteristics and signal transfer characteristics for a bridge substrate and a slot substrate.

10 is a structural diagram of a printed circuit board according to an embodiment of the present invention;

Figure 10a is a test board for confirming the transmission characteristics of the transmission line,

Figure 10b is a test board for confirming the noise transfer characteristics.

FIG. 11 is a graph of signal transmission characteristics and noise transmission characteristics of the resistive substrate of FIG. 10; FIG.

12 is a graph comparing characteristics of a resistive substrate with a slot substrate and a bridge substrate according to an embodiment of the present invention;

12A and 12B are graphs comparing signal transmission characteristics and noise transmission characteristics for a slot substrate, a bridge substrate, and a resistive substrate.

12C is an enlarged graph of FIG. 12A and illustrates a graph of signal transmission characteristics between a bridge substrate and a resistive substrate.

FIG. 13 is a graph showing signal transmission characteristics in the time domain for each substrate of FIG. 12; FIG.

Fig. 14 is a substrate provided for explaining a crosstalk phenomenon for the resistive substrate of the present invention, Fig. 14A is a reference substrate, Fig. 14B is a slot substrate, Fig. 14C is a bridge substrate, and Fig. 14D is a perspective view of the resistive substrate.

15 is a graph showing a crosstalk phenomenon for the substrates shown in FIG.

15a is a graph of a near-end crosstalk phenomenon,

15B is a graph of far-end crosstalk (FEXT) phenomenon.

Fig. 16 is a graph showing the measurement result of the unnecessary electromagnetic radiation emission of the resistive substrate according to the embodiment of the present invention.

Claims (3)

A printed circuit board arranged in at least two at predetermined intervals by a slot; And, A connection member connecting the printed circuit boards to each other; And including The connecting member is an electrically resistive material having a predetermined conductivity, and the conductivity is determined based on signal transmission characteristics and noise transmission suppression characteristics between the printed circuit boards, and has a range of 300 to 500 s / m. Printed circuit board structure. The method of claim 1, Wherein the electrically resistive material forms a new path of parallel resistance in the feedback current plane of the slotted printed circuit board. delete

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