JPH11298096A - Low emi feeding-wiring structure, circuit board using the same and low emi electronic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lessen unwanted electromagnetic radiations from feeding and high speed signal wirings by forming a parallel coupling structure of signal or power feed wiring and ground wiring, having the same width with a dielectric layer inserted therebetween to dispose the wirings near to each other face to face. SOLUTION: Wirings 1, 3 having the same width are disposed on the opposite faces of a dielectric layer 2. Self inductances L1, L2 and mutual inductance M exist on each of two parallel wiring boards. The current flows in the reverse direction on a signal or power feed wiring to a ground wiring, so that the effective inductance Le is represented by L3=L1+L2-2M. A relation M=k(L1L2)<1/2> holds between the self inductances L1, L2 and a mutual inductance M, and k is called the coupling factor. The parallel coupling structure has a strong coupling between both wirings, hence the mutual inductance is high and effective inductance L3 is low. Thus unwanted electromagnetic radiations from the feed and high speed signal wirings can be lessened.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-speed signal circuit board used for an electronic device, and more particularly to a power supply / wiring structure for suppressing unnecessary electromagnetic radiation.

[0002]

2. Description of the Related Art Unnecessary electromagnetic radiation has increased in recent years due to the speeding-up of electronic devices, and it has become essential to apply EMI regulations in commercializing devices. Unwanted electromagnetic radiation is generated from each part in the electronic circuit device. Power supply and high-speed signal wiring in the multilayer printed circuit board are the dominant factors, and the magnitude of the current flowing through these wirings or the inductance of the wirings The increase in unwanted electromagnetic radiation increases with the introduction to Electromagnetic Compatibility.
/ Paul, Clayton R. (1992) P731-P737.

[0003] Since recent electronic circuit devices operate at high speed and change in power supply current at high speed, power supply in a multilayer printed circuit board and unnecessary electromagnetic radiation from high-speed signal wiring become important problems. At present, more effective countermeasures against this unnecessary electromagnetic radiation are required.

[0004]

In the current high-speed electronic circuit device, power supply and high-speed signal wiring in a multilayer printed circuit board can be cited as dominant factors of unnecessary electromagnetic radiation. These wirings have an effective inductance Le determined by physical dimensions. Here, this effective inductance Le
Fluctuates the current flowing through the device, a noise voltage Vn is generated.
The noise voltage Vn is determined by the fluctuation speed di / of the power supply current determined by the effective inductance Le and the operating speed of the driving element.
Using dt, Vn = Le × di / dt. Since the noise voltage fluctuates the power supply voltage, the unnecessary electromagnetic radiation increases as the noise voltage increases.

A conventional multilayer printed circuit board generally has a power supply / wiring structure using a solid layer for the ground as shown in FIG. However, a multi-layer substrate requires through holes for connecting signals between different layers, and as shown in FIG. 5, a clearance hole may be provided in the solid layer to avoid a short circuit with the through hole. This clearance hole hinders the ideal path of the return current flowing through the solid layer, amplifies the inductance of the current path,
In addition, since the return current flowing through the solid layer flows so as to largely detour, the area of the current loop increases, and the unnecessary electromagnetic radiation also increases.

Therefore, in order to reduce the unnecessary electromagnetic radiation from these wirings, it is necessary to suppress the spread of the current, to make the area of the current loop as small as possible, and to reduce the effective inductance Le of the wirings.

An object of the present invention is to reduce unnecessary electromagnetic radiation from power supply and high-speed signal wiring in a multilayer printed circuit board, and specifically to reduce the effective inductance Le of the wiring.

[0008]

The power supply and high-speed signal wiring formed in the multilayer printed circuit board include a signal or power supply wiring and a ground wiring through which a return current flows. The present invention provides a parallel-coupling structure in which a signal or power supply wiring and a ground wiring having the same width are arranged close to each other with a dielectric layer interposed therebetween, thereby reducing the wiring inductance. By suppressing the spread of current in the substrate, it is possible to reduce unnecessary electromagnetic radiation from power supply and high-speed signal wiring.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments.

(Embodiment 1) Hereinafter, a first embodiment of the present invention will be described. FIG. 1 shows a printed circuit board having a wiring structure which is the basis of the present invention. This wiring is composed of a wiring 1 disposed close to the opposing surface with a dielectric layer 2 interposed therebetween, and a ground wiring 3 having the same wiring width as 1.

FIG. 2 shows a cross section of the wiring structure of FIG.
In the present wiring structure, since the dielectric thickness d (= distance between the wirings) is much smaller than the wiring width W, the signal or power supply wiring 1 and the ground wiring 3 are close to each other. Always wired in parallel in the direction.

FIG. 3 shows a conceptual diagram of the inductance of the wiring. Two parallel wiring boards like this wiring structure have their own inductances L1 and L2 and mutual inductance M. In addition, since currents flow in opposite directions in the signal or power supply wiring and the ground wiring, the effective inductance Le is Le = L1 + L2-2−M.
It is represented by The relationship of M = k√L1 · L2 is established between the self inductances L1 and L2 and the mutual inductance M. Here, the coefficient k is called a coupling coefficient, and indicates L1 and L2, that is, how much the signal or power supply wiring and the ground wiring are magnetically coupled. Since the parallel coupling structure like the present wiring structure has strong coupling between the two wirings, the mutual inductance is large and the effective inductance Le is small. Therefore, unnecessary electromagnetic radiation from power supply and high-speed signal wiring can be reduced.

(Embodiment 2) Hereinafter, a second embodiment of the present invention will be described. FIG. 6 shows a printed circuit board wired by the parallel connection structure of the first embodiment. The printed circuit board 5 is a double-sided printed circuit board and includes a semiconductor element 4, a signal or power supply wiring 1 connecting the semiconductor element 4, and a ground wiring 3.

FIG. 7 shows the concept of the substrate current distribution in this embodiment. By laying the power supply and high-speed signal wiring in a parallel-coupling structure, the current path is limited and the spread of the current is suppressed, so that the current loop is minimized, and thus unnecessary electromagnetic radiation from the power supply and high-speed signal wiring can be reduced. . Further, currents flowing in opposite directions flow through the power supply, the high-speed signal wiring, and the ground wiring, so that the magnetic fields between the wirings always cancel each other, and unnecessary electromagnetic radiation can be reduced. This has performance equal to or better than wiring with a multi-layer substrate of two or more layers.

(Embodiment 3) Hereinafter, a third embodiment of the present invention will be described. FIG. 8 shows a printed circuit board wired by the parallel connection structure of the first embodiment. The printed board 6 is a multilayer printed board having two or more layers, and includes the semiconductor element 4, the power supply and high-speed signal wiring 1 connecting the semiconductor elements 4, the ground wiring 3, the through hole 7, and the like. In FIG. 8, the through hole 7 and the clearance 8 provided in the ground layer of the substrate 6 make it impossible to route the ground wiring 3 parallel to the power supply and high-speed signal wiring 1, so that as shown in the enlarged view of the substrate in FIG. , So as to bypass the through hole 7. Although the overall wiring length is long, the current loop is minimized by holding the parallel coupling structure, and the increase of unnecessary electromagnetic radiation is suppressed.

[0016]

FIG. 10 shows the results obtained by analyzing the effective inductance Le of the parallel coupling structure and the single strip structure by electromagnetic field analysis. Here, the wiring width W was used as a parameter. The effective inductance Le of the parallel coupling structure having strong coupling is much smaller than that of the single strip structure having no coupling. According to FIG. 10, the wiring width is 1 [mm].
By doing so, the effective inductance Le can be reduced to 1/10 or less. Therefore, the noise voltage generated by the flow of the high-frequency current is also reduced to 1/10, and unnecessary electromagnetic radiation is reduced to
It can be reduced to 0 or less.

Further, since the power supply and high-speed signal wiring and the ground wiring are always wired in parallel, the return current does not spread and the current loop area is minimized, so that unnecessary electromagnetic radiation can be reduced. Even with a two-layer double-sided board, ground wiring is always provided on the opposite side of the power supply and high-speed signal wiring. Leads to a reduction in

[Brief description of the drawings]

FIG. 1 is a perspective view illustrating a power supply / signal wiring structure according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a power supply / signal wiring structure according to the first embodiment of the present invention.

FIG. 3 is a conceptual diagram illustrating inductance of a power supply / signal wiring.

FIG. 4 is a perspective view showing a conventional power supply / signal wiring structure.

FIG. 5 is a diagram showing a problem in a conventional substrate.

FIG. 6 is a perspective view showing a substrate according to a second embodiment of the present invention.

FIG. 7 is a conceptual diagram of a current distribution according to a second embodiment of the present invention.

FIG. 8 is a perspective view showing a substrate according to a third embodiment of the present invention.

FIG. 9 is an enlarged view showing a substrate according to a third embodiment of the present invention.

FIG. 10 is a characteristic diagram showing the relationship between the wiring width and the inductance according to the effect of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Power supply / signal wiring, 2 ... Dielectric, 3 ... Ground wiring,
4 ... Semiconductor element, 5 ... Printed board (double-sided board), 6 ...
Printed circuit board (multilayer board of two or more layers), 7: through hole, 8: clearance.

Claims (3)

[Claims] In a multilayer printed circuit board having two or more layers, a dielectric is sandwiched between a signal or power supply wiring and a ground wiring, and furthermore, the wiring is opposed by a width equal to or greater than the thickness of the dielectric, thereby increasing the inductance of the wiring. To reduce
A low EMI power supply / wiring structure characterized by suppressing noise voltage. 2. A circuit board using a low EMI power supply and wiring structure, wherein the wiring structure according to claim 1 is applied and wiring is performed between semiconductor elements. 3. A low EMI electronic device using the circuit board according to claim 2.