JP2007305756A - Circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a circuit board which stabilizes the characteristic impedance in signal transmitting via-holes piercing an insulation layer. <P>SOLUTION: Signal transmission channels 2a, 2b are formed at both sides of an insulation layer 1, and connected through signal transmitting via-holes 3 piercing the insulation layer 1 with a cylindrical slit 6 so formed in the insulation layer 1 as to surround the via-holes 3. A conductor material filled in the slit forms a cylindrical conductor 7 set to the ground potential, and the distance (d) between the via-holes 3 and the slit 6 (conductor 7) and the depth of the slit 6 from the surface of the insulation layer 1, i.e., the width W of the conductor 7 is adjusted to control the characteristic impedance (Zo) of the signal transmitting via-hole 3 for a suitable value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a circuit board capable of stabilizing characteristic impedance in a signal transmission line.

  For example, in a circuit board on which a device operating in a high frequency band is mounted, it is necessary to match the characteristic impedance (Zo) of the signal transmission path with the input / output impedance of the device in order to suppress the occurrence of signal reflection and waveform distortion. In order to match the characteristic impedance of the signal transmission path described above, a strip structure or microstrip structure in which an insulating layer of an appropriate thickness is sandwiched in a signal transmission path (strip line) with an appropriate pattern width and the ground layer is opposed is adopted. Has been.

  FIG. 6 shows an example of the basic configuration of the above-described strip structure, which is shown in a sectional view in a state cut in a direction perpendicular to the longitudinal direction of the signal transmission path. In this strip structure, a plurality of signal transmission paths 23 are formed in the center of the insulating layers denoted by reference numerals 21 and 22, and copper foils 24 and 25 are attached to the upper and lower surfaces of the insulating layers 21 and 22, respectively. Has been. By setting the copper foils 24 and 25 to the ground potential, each signal transmission line 23 can obtain a predetermined characteristic impedance between the copper foils 24 and 25 and the ground layer.

  FIG. 7 shows an example of the basic configuration of the above-described microstrip structure, which is also shown in a sectional view in a state cut in a direction perpendicular to the longitudinal direction of the signal transmission path, as in FIG. In this microstrip structure, a plurality of signal transmission paths 23 are formed on one surface of an insulating layer indicated by reference numeral 22, and a copper foil 25 is adhered to the other surface of the insulating layer 22. By setting the copper foil 25 to the ground potential, each signal transmission line 23 can obtain a predetermined characteristic impedance with the ground layer formed by the copper foil 25.

  The characteristic impedance (Zo) of the signal transmission path 23 in the circuit board constituting the strip structure or the microstrip structure is the reactance L per unit length of the signal transmission path and the unit between the signal transmission path and the ground layer. The value approximates the square root of the ratio of the capacitance C per area (reactance L / capacitance C). The characteristic impedance is generally selected to be approximately 50Ω at a single end and approximately 100Ω at a differential.

  Incidentally, in recent years, the above-described electronic devices are also more densely integrated, and there is a growing demand for higher density mounting of the devices and the like. In order to meet such technical demands, a configuration is adopted in which via holes for signal transmission are appropriately formed in the insulating layer, and signal transmission lines patterned on the insulating layer are connected via the via holes. There are cases where it must be done.

  As a result, line characteristics for high frequency signals in the via hole portion become a problem, and the characteristic impedance of the signal transmission via hole portion becomes inconsistent with the characteristic impedance in the signal transmission path patterned on the insulating layer. A problem occurs.

  In other words, mismatching in characteristic impedance occurs between the signal transmission path and the signal transmission via hole, thereby causing signal reflection and waveform distortion in that portion, thereby significantly reducing or inhibiting the transmission characteristics of high-frequency signals. This will cause a technical problem.

Therefore, in order to stabilize the characteristic impedance of the signal transmission via hole portion, by forming a plurality of via holes having a ground potential around the via hole, the characteristic impedance of the signal transmission via hole is changed to the plurality of grounding potentials. A configuration obtained with a via hole is disclosed in Patent Document 1.
Japanese Patent Laid-Open No. 5-206678

  FIG. 8 is a plan view showing the configuration of the wiring board disclosed in Patent Document 1. Reference numeral 31 denotes a signal transmission via hole penetrating the board (insulating layer), and reference numeral 32 denotes an insulating layer. A signal transmission path patterned on the upper surface is shown. That is, the signal transmission via hole 31 is connected to the signal transmission path 32 patterned on the upper surface of the insulating layer, and at the same time to the signal transmission path (not shown) formed on the back surface of the insulating layer. The signal transmission path is configured to be connected to each other via a layer.

  In addition, a plurality of via holes 33 having a ground potential are formed around the signal transmission via hole 31 so as to surround the signal transmission via hole 31. Therefore, the signal transmission via hole 31 can obtain a predetermined impedance characteristic with the plurality of ground via holes 33.

  However, according to the configuration of the substrate disclosed in Patent Document 1, since the plurality of ground via holes 33 are formed so as to surround the signal transmission via hole 31, the characteristic impedance in the signal transmission via hole 31 is as described above. For example, when setting to about 50Ω, since the facing area of the ground via hole 13 with respect to the signal transmission via hole 11 is small, it is necessary to make the distance between them extremely close. For this reason, in the layout design of each via hole formed on the insulating layer, there is a problem in that there is a technical limitation in size.

  Further, since the ground via hole 33 is intermittently arranged in the circumferential direction with respect to the signal transmission via hole 31, each signal transmission is performed when a plurality of signal transmission via holes 31 are to be formed on the substrate. Capacitive coupling occurs at least between the via holes 31 and the crosstalk characteristics are deteriorated. Therefore, in order to avoid this, there is a restriction that the interval between the signal transmission via holes 31 must be large. For this reason, the configuration disclosed in Patent Document 1 is difficult to adopt except when it is necessary to strictly control the impedance in the signal transmission via hole.

The present invention has been made paying attention to the above-described problems, and the first problem to be solved by the present invention is to stabilize the characteristic impedance in the signal transmission via hole penetrating the insulating layer. It is to provide a circuit board that can be used.
A second problem to be solved by the present invention is a circuit board capable of stabilizing characteristic impedance in a signal transmission line formed on an insulating layer and improving crosstalk characteristics between the signal transmission lines. It is to provide.

  The circuit board according to the present invention, which has been made to solve the first problem described above, has a signal transmission path formed on each of the insulating layers, and each of the signal transmission via holes penetrating the insulating layer. A circuit board to which a signal transmission path is connected, a cylindrical conductor is formed in a direction orthogonal to the surface of the insulating layer so as to surround the via hole, and the cylindrical conductor is set to a ground potential. Thus, the characteristic impedance of the signal transmission via hole is controlled.

  In this case, in a preferred embodiment, a cylindrical slit is formed in the insulating layer so as to surround the via hole, and the cylindrical conductor is formed by a conductive material embedded in the slit. To be.

  More preferably, a ground layer is formed on each of the upper and lower surfaces of the insulating layer on which the signal transmission via hole and the cylindrical conductor are formed so as to face at least the via hole.

  On the other hand, a circuit board according to the present invention, which has been made to solve the second problem described above, has a direction perpendicular to the surface of the insulating layer along a plurality of signal transmission lines formed on the insulating layer. A conductive layer is formed on each of the upper and lower surfaces of the signal transmission path so as to be parallel to the surface of the insulating layer, and the conductor formed on the insulating layer and the upper and lower surfaces Each of the conductive layers is set to a ground potential, thereby forming a coaxial structure in which the signal transmission path is surrounded by the ground layer at the top, bottom, left and right.

  According to the configuration of the circuit board made to solve the first problem described above, the via hole that interconnects the signal transmission lines formed with the insulating layer interposed therebetween is surrounded by a cylindrical shape. Since the conductor is formed and this conductor is set to the ground potential, the distance between the via hole and the cylindrical conductor, and the width in the thickness direction of the insulating layer in the cylindrical conductor are set. By appropriately adjusting, the characteristic impedance in the via hole portion can be easily controlled.

  In addition, according to the configuration of the circuit board made to solve the second problem described above, the conductor is disposed along the signal transmission path, and the conductive layer is disposed above and below the signal transmission path. Since the structure is configured, it is possible to easily control the impedance characteristics of the signal transmission path by adjusting the distance between the signal transmission path and the conductor and the distance between the signal transmission path and the upper and lower conductive layers. is there. Further, the above-described coaxial structure can improve the crosstalk characteristics between the signal transmission paths.

  FIG. 1 shows an embodiment made to solve the first problem of the present invention described above, and FIG. 1 (A) shows a main portion of a circuit board in a longitudinal sectional view. B) shows the main part of the circuit board as viewed from the upper surface (front surface), and (C) shows the main part of the circuit board as viewed from the lower surface (back surface).

  On the front and back surfaces of the insulating layer 1 constituting the circuit board, signal transmission paths 2a and 2b are respectively formed with the insulating layer 1 therebetween. In the example shown in FIG. 1, the signal transmission lines 2 a and 2 b are formed in directions orthogonal to each other on the front and back of the insulating layer 1. The signal transmission paths 2 a and 2 b formed on the front and back sides of the insulating layer 1 are connected through signal transmission via holes 3 that penetrate the insulating layer 1.

  The signal transmission via hole 3 is formed by, for example, forming a through hole 4 so as to penetrate the insulating layer 1 using laser light, and burying the through hole 4 with, for example, a plating method or a conductive paste. can do.

  On the other hand, a cylindrical slit 6 is formed in the direction perpendicular to the surface of the insulating layer so as to surround the via hole 3, and a conductive material is embedded in the slit 6 so that the cylindrical conductive A body 7 is formed. The slit 6 can be formed by using, for example, laser light, and the conductor 7 in the slit 6 can be formed by, for example, a plating embedding process.

  In the embodiment shown in FIG. 1, the slit 6 is formed in a C shape so as to avoid the position of the signal transmission path 2 a formed on the surface of the insulating layer 1. The slit 6 is concentrically formed with respect to the through hole 4 at a distance d from the through hole 4 and has a depth W from the surface of the insulating layer 1. A part of the conductive material (conductor 7) embedded in the slit 6 is connected to a ground line 8 formed on the back surface of the insulating layer 1 via a connection portion 9.

  According to the circuit board having the above-described configuration, the cylindrical conductor 7 set to the ground potential is disposed so as to surround the signal transmission via hole 3, so that the distance between the via hole 3 and the slit 6 (conductor 7). By adjusting d and the depth of the slit 6 from the surface of the insulating layer 1, that is, the width W of the conductor 7, the characteristic impedance (Zo) of the signal transmission via hole 3 is controlled to an appropriate value. be able to.

  Further, according to the circuit board having the above-described configuration, the cylindrical conductor 7 set to the ground potential is disposed so as to surround the signal transmission via hole 3, and therefore the signal transmission via hole 3 is adjacent to the substrate. Even when is formed, it is possible to effectively prevent the cylindrical conductor 7 from causing capacitive coupling in the mutual via holes 3. Therefore, it is possible to reduce the degree of restriction on the position of the signal transmission via hole 3 on the circuit board.

  Next, FIG. 2 and FIG. 3 show another embodiment made to solve the first problem of the present invention, and FIG. 2 shows the main part of the circuit board in a longitudinal sectional view. FIG. 3 is a cross-sectional view as seen in the direction of the arrow from the line AA in FIG.

  In the embodiment shown in FIGS. 2 and 3, the signal transmission via hole 3 already described with reference to FIG. 1 is formed adjacently on the substrate and surrounds each via hole 3 so as to surround the ground. A cylindrical conductor 7 set at a potential is arranged. Therefore, in FIG. 2 and FIG. 3, representative parts corresponding to the respective parts shown in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the embodiment shown in FIG. 2 and FIG. 3, a multilayer circuit board is configured with respect to the configuration of FIG. 1, and the signal transmission via hole 3 and the cylindrical conductor 7 surrounding it are formed. In addition, ground layers 11 and 12 are laminated on the upper and lower surfaces of the insulating layer 1 so as to face each other.

  According to the configuration described above, the cylindrical conductor 7 formed along the peripheral side surface of the signal transmission via hole 3 can mainly control the characteristic impedance in the via hole 3, and the cylindrical conductor 7 can be controlled. Since the via hole 3 is surrounded by the upper and lower ground layers 11 and 12, capacitive coupling between the via holes can be reduced. Therefore, according to the configuration described above, crosstalk characteristics between via holes can be further improved as compared with the configuration shown in FIG.

  In the embodiment shown in FIGS. 2 and 3, the upper and lower ground layers 11 and 12 are formed over the entire surface of the substrate, but the upper and lower ground layers 11 and 12 are arranged at the positions where the via holes are arranged. Even if it is formed so as to partially face each other, the same effect can be obtained.

  4 and 5 show an embodiment made to solve the second problem of the present invention described above. 4 is a longitudinal sectional view showing the main part of the circuit board, and FIG. 5 is a sectional view of the circuit board as viewed in the direction of the arrow from the line BB in FIG.

  In the embodiment shown in FIGS. 4 and 5, a plurality of signal transmission lines 2 are formed on the insulating layer 1, and perpendicular to the surface of the insulating layer 1 along each signal transmission line 2. The conductor 7 is formed in the direction to be. Each conductor 7 forms a slit in a direction perpendicular to the surface of the insulating layer 1 using, for example, laser light, as in the example already described with reference to FIG. Can be formed.

  On the other hand, conductive layers 11 and 12 are laminated on both the upper and lower surfaces of the insulating layer 1 so as to face the signal transmission path 2, and the conductive layers 11 and 12 are set to the ground potential. The conductive layers 11 and 12 are configured to function as a ground layer. Each conductor 7 formed between the signal transmission paths 2 is connected to the ground layer 12 at an appropriate position as indicated by reference numeral 12a.

  According to the configuration described above, the left and right direction of each signal transmission line 2 is surrounded by the conductor 7 formed in a direction orthogonal to the surface of the insulating layer 1, and the vertical direction of each signal transmission line 2 is parallel to the surface of the insulating layer 1. A coaxial structure surrounded by the conductive layers 11 and 12 is formed. With this configuration, the characteristic impedance of each signal transmission path 2 is controlled by adjusting the distance between each signal transmission path 2 and the left and right conductors 7 and the distance between each signal transmission path 2 and the upper and lower conductive layers 11 and 12. can do.

  In addition, according to the configuration shown in FIGS. 4 and 5, each signal transmission line 2 functions as a coaxial cable, and shield effect against high frequency signals or noise radiated from a power supply line through which a relatively large current flows. Shield effect can be demonstrated. Furthermore, the crosstalk characteristic between the adjacent signal transmission lines 2 can be effectively improved.

  Note that the above-described embodiment shows the minimum necessary configuration, and may be formed in a multilayer structure as needed. In addition, the signal transmission path in the above description is not only superimposed with a control signal including, for example, a clock signal transmitted and received between the devices, but may be used as a power supply line for driving the devices. Further, the ground layer and the ground line in the above description may be set to the reference potential of the circuit or may be set to the power supply line.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing, the top view, and the reverse view which showed 1st Embodiment of the circuit board concerning this invention. It is sectional drawing which similarly showed 2nd Embodiment of the circuit board. It is sectional drawing of the state seen from the AA line in FIG. 2 in the arrow direction. It is sectional drawing which similarly showed 3rd Embodiment of the circuit board. It is sectional drawing of the state seen from the BB line in FIG. 4 in the arrow direction. It is sectional drawing which showed the basic structural example of the conventional strip structure. It is sectional drawing which showed the basic structural example of the conventional microstrip structure. It is the top view which showed the example of control of the characteristic impedance in the conventional via-hole part.

Explanation of symbols

1 Insulating layer 2, 2a, 2b Signal transmission path 3 Signal transmission via hole 4 Through hole 4
6 Slit 7 Cylindrical Conductor 8 Ground Line 9 Connection Portion 11, 12 Conductive Layer (Ground Layer)
12a connection

Claims (4)

A circuit board in which a signal transmission path is formed on each of the insulating layers, and each signal transmission path is connected via a signal transmission via hole penetrating the insulating layer,
A cylindrical conductor is formed in a direction perpendicular to the surface of the insulating layer so as to surround the via hole, and the characteristic impedance in the signal transmission via hole is controlled by setting the cylindrical conductor to a ground potential. A circuit board characterized by being configured to do so.   2. A cylindrical slit is formed in the insulating layer so as to surround the via hole, and the cylindrical conductor is formed of a conductive material embedded in the slit. Circuit board.   The ground layer is formed on each of the upper and lower surfaces of the insulating layer on which the signal transmission via hole and the cylindrical conductor are formed so as to face at least the via hole. 2. The circuit board described in 2. Conductors are respectively formed in a direction perpendicular to the surface of the insulating layer along a plurality of signal transmission paths formed on the insulating layer, and the signal is parallel to the surface of the insulating layer. Conductive layers are formed on both the upper and lower sides of the transmission line,
A circuit having a coaxial structure in which the conductor layer formed on the insulating layer and the conductive layers on both the upper and lower surfaces are respectively set to a ground potential so that the upper, lower, left, and right sides of the signal transmission path are surrounded by the ground layer. substrate.

Images