JP2009054667A - Multiplayer printed circuit board, connection structure of the multilayer printed circuit board and coaxial connector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multiplayer printed circuit board and a connection structure which can reduce the reflection of a signal on an interface between a coaxial connector and the multiplayer printed circuit board and can be put into practical use at a low cost by securing the continuity of an electromagnetic field distribution at the interface at a higher level. <P>SOLUTION: A multiplayer printed circuit board 1 has a microstrip line 2 as a signal layer, and a plurality of grounding layers 3a, 4a, 5a, 6a, 7a provided on the lower part of the microstrip line 2 to be electrically connected mutually. Notches K3, K4, K5, K6 are provided in at least some grounding layers 3a, 4a, 5a, 6a of the plurality of grounding layers 3a, 4a, 5a, 6a, 7a, and the sizes of the notches K3, K4, K5, K6 are made different for each of the grounding layers 3a, 4a, 5a, 6a. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a multilayer printed circuit board and a connection structure between the multilayer printed circuit board and a coaxial connector.

  With the recent increase in the speed of electronic information devices represented by computers, it has become necessary to transmit digital signals having a high frequency exceeding GHz between LSIs and printed boards. Conventionally, when transmitting a digital signal that is not high-speed between printed circuit boards, a flat cable having a large number of signal lines arranged in parallel on the same plane has been used. On the other hand, when transmitting a high-speed digital signal, a coaxial cable whose characteristic impedance is designed and controlled is mainly used, and a coaxial connector such as an SMA connector is used at the end of the cable.

  For example, Patent Documents 1, 2, and 3 disclose a connection structure between a microstrip line formed on a printed board and a connector connected thereto.

  Patent Document 1 discloses a connection structure between a connector and a circuit board that can obtain a reflection characteristic equivalent to that of a K connector by using a connector that is simpler to process and assemble a module base than a K connector such as an SMA connector. It is intended to provide. For this purpose, in the invention described in this document, two ground pads are provided on both sides of the signal line on the board at the joint between the signal line of the circuit board and the coaxial connector, The distance between the pads is made smaller than the diameter of the dielectric of the coaxial connector.

  Patent document 2 aims at providing the connection structure of a coaxial connector and a multilayer printed circuit board which can prevent peeling of a conductor pattern and deterioration of a transmission characteristic by the connection of a coaxial connector and a multilayer printed circuit board. For this purpose, in the invention described in this document, in the structure for connecting the central conductor of the coaxial connector and the microstrip line of the multilayer printed circuit board, the width of the connection portion of the microstrip line to which the coaxial connector is solder-connected. Is wider than the other parts, and a notch is provided in the inner layer of the multilayer printed circuit board facing the connection so that the characteristic impedance of the connection is equal to the characteristic impedance of the coaxial connector. .

Patent Document 3 aims to provide a high-frequency connector that facilitates matching of a high-frequency signal at a connection point between a dielectric and a circuit board. For this purpose, in the invention described in the same document, the center connected to the outer conductor of the coaxial line for transmitting a high-frequency signal and the distance between the inner conductor of the coaxial line and the frame is changed. A conductor, and a derivative that maintains a distance between the center conductor and the ground, and this derivative has a part of its outer peripheral surface cut away, and has a cross-sectional area toward the circuit board side on which the high-frequency signal is transmitted. It is configured to decrease.
JP-A-10-327004 (paragraphs 0005 and 0006) JP-A-6-350312 (paragraphs 0006 and 0007) JP-A-5-242934 (paragraphs 0004 and 0005)

  Transmission lines such as microstrip lines and coaxial cables that transmit digital signals with high frequency components exceeding GHz, that is, high-speed digital signals, have a cross-sectional structure based on the electromagnetic field theory, and the transmission line characteristic impedance. Is designed to a certain value. This is to avoid reflection of signal components on the discontinuous surface of the characteristic impedance when transmission lines with different characteristic impedances are connected. In other words, by making the characteristic impedance constant, the signal can be efficiently transmitted. This is because transmission is possible. Further, since it is difficult to set the characteristic impedance to a desired value at the connection interface between the coaxial connector for connecting the coaxial cable and the printed circuit board, the devices as disclosed in Patent Documents 1, 2, and 3 are devised.

  However, the connection structure disclosed in Patent Document 1 has a problem that signal reflection cannot be sufficiently suppressed. Specifically, in this document, although the impedance matching is devised by devising the pad shape on the printed circuit board, signal reflection occurs because the physical shape at the interface between the coaxial connector and the printed circuit board is discontinuous. It will be.

  More specifically, the coaxial cable and the microstrip line formed on the printed board both transmit a TEM wave (Transverse Electromagnetic Wave) as a signal. Here, when considering the distribution of the electromagnetic field in the cross section perpendicular to the traveling direction of the signal component, in the coaxial cable, the electric lines of force are distributed radially from the central conductor toward the outer conductor, In the printed circuit board on which the microstrip line is formed, electric lines of force are distributed from the microstrip line on the upper side toward the ground layer on the lower side. Therefore, although the coaxial cable and the microstrip line formed on the printed circuit board both transmit TEM waves as signals, the electric field distribution of the transmitted TEM waves and the magnetic field distribution formed at the same time are different. The electromagnetic field distribution is discontinuous at the interface between the coaxial connector to which the coaxial cable is connected and the printed circuit board on which the microstrip line is formed. As a result, signal reflection occurs at the interface between the coaxial connector and the printed circuit board.

  In Patent Document 2, the shape of the multilayer printed circuit board is devised to solve this problem. However, most of the connectors on the market are not shaped like that of the same document, and it is necessary to make a special order for the connector to realize the technology of this document. There is a problem that it is practically difficult to use in a strongly required field.

  In Patent Document 3, the shape of the coaxial connector is devised so that the electromagnetic field distribution transitions gently. However, the shape of a commercially available coaxial connector is not the same as that of the same document, and it is necessary to specially order the coaxial connector to realize the technology of the same document. Another problem is that the continuity of the electromagnetic field distribution between the coaxial connector to which the coaxial cable is connected and the printed circuit board on which the microstrip line is formed is still insufficient.

  The first object of the present invention is to solve the above problems. More specifically, by ensuring the continuity of the electromagnetic field distribution at the interface between the coaxial connector and the multilayer printed circuit board at a higher level, signal reflection at the interface can be reduced and can be put into practical use at low cost. It is to provide a multilayer printed circuit board.

  The second object of the present invention is to solve the above problems. More specifically, by ensuring the continuity of the electromagnetic field distribution at the interface between the coaxial connector and the multilayer printed circuit board at a higher level, signal reflection at the interface can be reduced and can be put into practical use at low cost. An object of the present invention is to provide a connection structure between a multilayer printed board and a coaxial connector.

  A multilayer printed board of the present invention for solving the above problems is a multilayer printed board having a signal layer and a plurality of ground layers provided below the signal layer and electrically connected to each other, A notch is provided in at least a part of the ground layers of the plurality of ground layers, and the size of the notch is different for each ground layer.

  In a preferred aspect of the multilayer printed board of the present invention, the plurality of ground layers are arranged substantially in parallel with a predetermined interval, and are arranged so that the notches overlap.

  In a preferred aspect of the multilayer printed board according to the present invention, the cutout portion of the first ground layer closest to the signal layer is made the largest, and as the distance from the first ground layer increases, the ground layer is cut. Gradually reduce the size of the notch.

  In a preferred aspect of the multilayer printed board according to the present invention, the size of each notch from the first ground layer to the last ground layer provided with the notch is tapered.

  In a preferred aspect of the multilayer printed board of the present invention, the shape of the notch is any one of a trapezoid, a triangle, and a quadrangle.

  In a preferred aspect of the multilayer printed board of the present invention, the contour of the notch is formed by an exponential function curve or a parabolic curve.

  The connection structure between the multilayer printed circuit board and the coaxial connector of the present invention for solving the above problems (in this specification, the connection structure between the multilayer printed circuit board and the coaxial connector may be simply referred to as “connection structure”). A coaxial connector having a central conductor and a cylindrical outer conductor that concentrically surrounds the central conductor is connected to the multilayer printed board of the present invention.

  In a preferred aspect of the connection structure of the present invention, the outer conductor and the plurality of ground layers are connected.

  In a preferred aspect of the connection structure of the present invention, the distance t2 between the signal layer and the ground layer farthest from the signal layer is larger than the distance r between the center conductor and the outer conductor.

  According to the present invention, the notch is provided in at least a part of the plurality of ground layers, and the size of the notch is different for each ground layer. By ensuring a higher level of continuity of the electromagnetic field distribution at the interface with the printed circuit board, signal reflection at the interface can be reduced, and as a result, high-speed signal transmission with high efficiency and quality can be realized. A multilayer printed circuit board can be provided. Moreover, it is not necessary to use a special connector, and a multilayer printed board that can be put into practical use at low cost can be provided.

  According to the present invention, a coaxial connector having a central conductor and a cylindrical outer conductor concentrically surrounding the central conductor is connected to the multilayer printed circuit board of the present invention. By ensuring a higher level of continuity of the electromagnetic field distribution at the interface, it is possible to reduce signal reflection at the interface, and as a result, a connection structure that can realize high-speed signal transmission with high efficiency and quality Can be provided. Further, it is not necessary to use a special connector, and a connection structure that can be put into practical use at a low cost can be provided.

  Hereinafter, examples of the present invention will be described, but the present invention is not limited to the following examples, and can be arbitrarily modified and implemented without departing from the gist of the present invention.

  FIG. 1 is a schematic perspective view showing an example of the connection structure of the present invention. More specifically, FIG. 1 shows an embodiment using a microstrip line as a signal layer. That is, the “signal layer” in the present invention refers to a layer in which signal transmission is performed, and examples of the signal layer include not only a microstrip line but also a layer in which signal wiring is formed. Of the signal layers that can take such various aspects, as an example, in FIG. 1, the signal layer is a microstrip line. FIG. 2 is a schematic cross-sectional view of the A-A ′ plane in FIG. 1. More specifically, FIG. 2 is a schematic cross-sectional view in a plane perpendicular to the multilayer printed board 1 and passing through the center conductor 9 of the coaxial connector 8 and the center of the microstrip line 2. FIG. 3 is a schematic plan view showing a signal layer (microstrip line) and a plurality of ground layers, respectively.

  In the connection structure 20 between the multilayer printed circuit board 1 and the coaxial connector 8, the coaxial connector 8 having the central conductor 9 and the cylindrical outer conductor 10 concentrically surrounding the central conductor 9 is connected to the multilayer printed circuit board 1. It is constituted by.

(Multilayer printed circuit board)
The multilayer printed circuit board 1 has a microstrip line 2 as a signal layer and a plurality of ground layers 3a, 4a, 5a, 6a, and 7a provided below the microstrip line 2 and electrically connected to each other. The notch portions K3, K4, K5, and K6 are provided in the ground layers 3a, 4a, 5a, and 6a, which are at least a part of the plurality of ground layers 3a, 4a, 5a, 6a, and 7a. The sizes of the portions K3, K4, K5, and K6 are different for the ground layers 3a, 4a, 5a, and 6a. As a result, it is possible to reduce the reflection of the signal at the interface by ensuring the continuity of the electromagnetic field distribution at the interface between the coaxial connector 8 and the multilayer printed circuit board 1 at a higher level. It is possible to provide the multilayer printed circuit board 1 capable of realizing high-quality signal transmission with high quality. Moreover, it is not necessary to use a special connector, and the multilayer printed circuit board 1 that can be put into practical use at low cost can be provided. The point that the continuity of the electromagnetic field distribution can be secured at a higher level will be described in detail later.

  In the multilayer printed circuit board 1, as shown in FIG. 1, a plurality of ground layers 3a, 4a, 5a, 6a, 7a are arranged substantially in parallel with a predetermined interval, and the ground layers 3a, 4a, 5a, 6a are arranged. The cutout portions K3, K4, K5, and K6 in FIG. The ground layers 3a, 4a, 5a, 6a, and 7a are not shown in FIGS. 1 and 2, but are electrically connected to each other through vias or the like, and the ground layers have the same potential. A dielectric layer is provided between the microstrip line 2 and the ground layer 3a and between the ground layers 3a, 4a, 5a, 6a, and 7a, but is not shown in FIGS. Furthermore, the multilayer printed circuit board 1 is a six-layer board of a microstrip line 2 and ground layers 3a, 4a, 5a, 6a, and 7a, but there are a power supply layer, other signal layers, and other ground layers not shown here. It doesn't matter.

  In the multilayer printed circuit board 1, as shown in FIG. 3, the cutout portion K3 in the first ground layer 3a closest to the microstrip line 2 is made the largest, and the distance from the first ground layer 3a increases. The sizes of the cutout portions K4, K5, and K6 of the ground layers 4a, 5a, and 6a are gradually reduced. That is, the cutout portions K3, K4, K5, and K6 of the ground layers 3a, 4a, 5a, and 6a are formed so as to gradually decrease from the first ground layer 3a that is closest to the microstrip line 2. ing. More specifically, the shapes of the cutout portions K3, K4, K5, and K6 of the ground layers 3a, 4a, 5a, and 6a are trapezoidal, and the ground layer 3a (second layer: first ground layer) As the cutout portion K3, the cutout portion K4 of the ground layer 4a (third layer), the cutout portion K5 of the ground layer 5a (fourth layer), and the cutout portion K6 of the ground layer 6a (fifth layer) are obtained. The trapezoidal area of the notch is formed to be small. The ground layer 7a (sixth layer) is not provided with a notch. By forming the cutout portions of the ground layers 3a, 4a, 5a, and 6a as described above, the last contact where the cutout portions are provided from the first ground layer 3a as shown in FIGS. The cutouts K3, K4, K5, and K6 up to the formation 6a are formed in a tapered shape.

  Thus, the cutout portions K3, K4, K5, and K6 are the largest in the first ground layer 3a close to the surface of the multilayer printed circuit board 1, and become smaller as the lower layer is reached, and finally the cutout portions in the ground layer 7a. There is no notch. When the notches K3, K4, K5, and K6 formed in the ground layers 3a, 4a, 5a, and 6a are viewed from the direction perpendicular to the substrate surface (ground layer) as shown in FIG. That is, the ground layers 3a, 4a, 5a, 6a are arranged so as to overlap when viewed in plan. As a result, as shown in FIGS. 1 and 2, when viewed from the substrate surface side, when the ground layers 3a, 4a, 5a, and 6a are viewed in plan, the notches K3, K4, K5, and K6 are tapered. It is arranged to become. Further, the microstrip line 2 is arranged above the notches K3, K4, K5, K6, and the multilayer printed board 1 is formed. Here, the notches K3, K4, K5, and K6 are formed in four layers up to the ground layers 3a, 4a, 5a, and 6a, but the number of layers may be increased or decreased.

  As described above, in the multilayer printed circuit board 1, a plurality of ground layers 3 a, 4 a, 5 a, 6 a, 7 a connected to each other by vias or the like are provided below the microstrip line 2, and the ground layers 3 a, 4 a are provided. , 5a and 6a are formed with notches K3, K4, K5 and K6 having different sizes at the substrate ends of the conductor surfaces. The notches K3, K4, K5, and K6 are arranged so as to overlap when viewed from the direction perpendicular to the substrate surface (ground layer), and further, the layers farther from the microstrip line 2 are the notches K3. , K4, K5, and K6 are formed to be small. As a result, the notches K3, K4, K5, and K6 are tapered when viewed from the substrate surface side. By adopting the multilayer printed board 1 having such a shape, it becomes easy to ensure the continuity of the electromagnetic field distribution at the interface between the coaxial connector 8 and the multilayer printed board 1 at a higher level. Therefore, the continuity of this electromagnetic field distribution will be described next.

  Generally, when connecting a coaxial connector and a multilayer printed circuit board via a connector, a central conductor of the coaxial connector and a signal layer of the multilayer printed circuit board are connected to form a signal line, and a plurality of outer conductors and the multilayer printed circuit board are connected. Connect to the ground layer. In the case of a multilayer printed circuit board used in a digital device such as a computer, between a signal layer on the surface of the multilayer printed circuit board and a ground layer closest to the signal layer among a plurality of ground layers provided below the signal layer, In addition, a dielectric layer having a thickness of about several hundred μm exists between each of the plurality of ground layers. A downward electromagnetic field from the signal layer toward the ground layer is formed in the dielectric layer by the signal propagated as the TEM wave.

  On the other hand, the electromagnetic field formed by the TEM wave propagating in the coaxial connector spreads in the vertical and horizontal directions from the center conductor toward the outer conductor. For this reason, when a coaxial connector and a multilayer printed board not provided with a predetermined notch in the ground layer are connected via a connector, a downward electromagnetic wave from the signal layer formed in the multilayer printed board toward the ground layer is formed. The field and the radial electromagnetic field formed in the coaxial connector are not continuously connected. In particular, in a multilayer printed board used in a digital device such as a computer, the distance between each ground layer is about 100 to 200 μm, whereas the distance between the center conductor and the outer conductor in the coaxial connector is often larger than this. For example, in the case of an SMA connector, the distance between the center conductor and the outer conductor is about 1 mm. Therefore, when the central conductor of the coaxial connector and the signal layer of the multilayer printed circuit board are connected on the same plane, part of the electromagnetic field formed by the coaxial connector is below the ground layer at the connection interface. As a result, the electromagnetic field leaks to the back side of the ground layer. In such a case, even if the coaxial connector and the signal layer (for example, a microstrip line) on the multilayer printed board are designed to have the same characteristic impedance, an electromagnetic field leaks at the interface between the coaxial connector and the multilayer printed board. This makes it difficult to transmit signals with high efficiency and quality.

  Therefore, in the present invention, as shown in FIGS. 1 to 3 as an example, trapezoidal notches K3 and K4 are formed at the substrate ends of the conductor surfaces of the plurality of ground layers 3a, 4a, 5a and 6a of the multilayer printed board 1. , K5, and K6, and the cutout portions K3, K4, K5, and K6 are arranged and overlapped so as to overlap when viewed from the direction perpendicular to the substrate surface (ground layer). Then, the cutout portion K3 of the first ground layer 3a is maximized, and the areas of the cutout portions K4, K5, and K6 are made smaller in the ground layers 4a, 5a, and 6a farther from the first ground layer 3a. The notches K3, K4, K5, and K6 are arranged so as to be tapered when viewed from the substrate surface. By adopting such a configuration, the electromagnetic field formed by the microstrip line 2 as the signal layer and the ground layers 3a, 4a, 5a, 6a, and 7a in the vicinity of the interface between the multilayer printed circuit board 1 and the coaxial connector 8 is radial. It tends to be formed and approaches the radial electromagnetic field formed between the center conductor 9 and the outer conductor 10 of the coaxial connector 8. As a result, signal reflection at the interface can be reduced by ensuring the continuity of the electromagnetic field distribution at the interface between the coaxial connector 8 and the multilayer printed board 1 at a higher level.

  1 to 3, the trapezoids of the cutout portions K3, K4, K5, and K6 of the ground layers 3a, 4a, 5a, and 6a are line symmetric with respect to the microstrip line 2 that is the signal layer. Has been placed. Since the shapes of the cutout portions K3, K4, K5, and K6 of the ground layers 3a, 4a, 5a, and 6a are arranged symmetrically about the microstrip line 2, it is easy to make the electromagnetic field distribution uniform. For this reason, the effect of the present invention is easily exhibited. However, it is sufficient that the continuity of the predetermined electromagnetic field is ensured, and the shape of the cutout portion of the ground layer does not have to be line symmetric about the signal layer.

  1 to 3, all of the notches K3, K4, K5, and K6 are trapezoidal, but the shapes of these notches are not necessarily the same. Further, in FIGS. 1 to 3, the cutout portions K3, K4, K5, and K6 are formed in a tapered shape. However, the design is not limited to the tapered shape, and the design may be changed as appropriate.

(Connection structure)
The connection structure 20 is configured by connecting a coaxial connector 8 having a central conductor 9 and a cylindrical outer conductor 10 concentrically surrounding the central conductor 9 to the multilayer printed circuit board 1. More specifically, the coaxial connector 8 is formed of a center conductor 9, a dielectric 12 disposed around the center conductor 9, and an outer conductor 10 disposed around the dielectric 12. By adopting such a connection structure, signal reflection at the interface can be reduced by ensuring a higher level of continuity of the electromagnetic field distribution at the interface between the coaxial connector 8 and the multilayer printed circuit board 1. As a result, the connection structure 20 capable of realizing high-speed signal transmission with good efficiency and quality can be provided. Moreover, it is not necessary to use a special connector, and the connection structure 20 that can be put into practical use at a low cost can be provided. More specifically, the coaxial connector 8 is not specially shaped, and is formed by patterning only the shapes of the ground layers 3a, 4a, 5a, 6a of the multilayer printed circuit board 1. do not need. Therefore, it is possible to realize the connection between the coaxial connector 8 and the multilayer printed circuit board 1 with good efficiency and quality without any additional manufacturing cost.

  As shown in FIG. 1, the multilayer printed circuit board 1 and the coaxial connector 8 in the connection structure 20 transmit signals from the coaxial connector 8 to the multilayer printed circuit board 1 by connecting the center conductor 9 and the microstrip line 2. Is done. Further, the outer conductor 10 and the plurality of ground layers 3a, 4a, 5a, 6a, 7a are connected. More specifically, the outer conductor 10 of the coaxial connector 8 is connected to the ground layers 3 a, 4 a, 5 a, 6 a, and 7 a of the multilayer printed circuit board 1 through the fixing block 11 of the coaxial connector 8.

  Since the connection between the outer conductor 10 and the ground layers 3a, 4a, 5a, 6a, and 7a via the fixed block 11 in the connection structure 20 needs to be electrically connected, the fixed block 11 needs to be a conductor. For example, copper whose surface is gold-plated is suitable. However, the fixed block 11 may be other metal or conductor within the scope of the gist of the present invention. In the present invention, since the plurality of ground layers are electrically connected to each other in the multilayer printed circuit board, the connection between the fixed block and the ground layer of the multilayer printed circuit board is the same as that of the fixed block and the plurality of ground layers. Is not necessary, and the fixed block may be connected to an arbitrary ground layer. From the viewpoint of facilitating stable electrical connection up to a higher frequency, it is preferable to connect the fixed block and the plurality of ground layers with the shortest distance and a wide area. For this reason, as shown in FIGS. 1 and 2, it is more preferable to connect the fixed block 11 to all of the ground layers 3a, 4a, 5a, 6a, and 7a.

  In the connection structure 20, as shown in FIGS. 1 and 2, the notches K3, K4, K5, and K6 of the ground layers 3a, 4a, 5a, and 6a of the multilayer printed circuit board 1 are sequentially reduced in size. The ground layers 3a, 4a, 5a, and 6a are formed so that the conductor surface recedes in a tapered shape from the substrate end. Therefore, the electromagnetic wave formed by the high-speed digital signal transmitted through the coaxial connector 8 is a microstrip formed on the multilayer printed circuit board 1 in accordance with the ground layers 3a, 4a, 5a, and 6a whose conductor surfaces are receding in a tapered shape. Smoothly guided to the track 2. For this reason, there is little reflection of the electromagnetic wave in the interface of the coaxial connector 8 and the multilayer printed circuit board 1, and it becomes easy to implement | achieve signal transmission with sufficient efficiency and quality.

  In the connection structure 20, as shown in FIGS. 1 and 2, tapered grooves formed by the cutout portions K3, K4, K5, and K6 of the ground layers 3a, 4a, 5a, and 6a and the ground layer 7a are outside. It arrange | positions so that it may become larger than the length of the conductor 10. FIG. This makes it easier to transmit the electromagnetic field formed by the signal transmitted through the coaxial connector 8 to the multilayer printed circuit board 1 without leaking to the back surface of the ground layer 7a. As a result, efficient and high quality signal transmission can be realized.

  In the connection structure 20, as shown in FIG. 2, the distance between the center conductor 9 and the outer conductor 10 is r, the distance from the microstrip line 2 of the multilayer printed board 1 to the first ground layer 3a is t1, When t2 is the distance from the microstrip line 2 of the multilayer printed circuit board 1 to the grounding layer 7a which is the first grounding layer not provided with a notch and is located farthest from the microstrip line 2, t2 is r It is preferable to make it larger than that, that is, t2> r. This makes it easier to transmit the electromagnetic field formed by the signal transmitted through the coaxial connector 8 to the multilayer printed circuit board 1 without leaking to the back surface of the ground layer 7a. More preferably, t1 <r and t2> r. By adopting such a configuration, smooth propagation of electromagnetic waves from the coaxial connector 8 to the multilayer printed circuit board 1 is facilitated, and the effects of the present invention are remarkably exhibited. When t2> r, the number of ground layers may be changed as appropriate. Further, even when t2> r is not satisfied, the effect of the present invention is not lost, so that t2 ≦ r may be satisfied depending on the design of the connector.

(Characteristics of connection structure)
FIG. 4 is a characteristic diagram showing the effect of adopting the connection structure of the present invention. FIG. 5 is another characteristic diagram showing the effect of adopting the connection structure of the present invention. Specifically, FIG. 4 shows the result of obtaining the insertion loss when a signal is transmitted from the coaxial connector 8 to the multilayer printed circuit board 1 by three-dimensional electromagnetic field analysis. FIG. 5 shows the result of obtaining the reflection loss when a signal is transmitted from the coaxial connector 8 to the multilayer printed circuit board 1 by three-dimensional electromagnetic field analysis. 4 and 5, the characteristics indicated by the solid line indicate the insertion loss and the reflection loss in the connection structure 20 shown in FIGS. 4 and 5, the characteristics indicated by the dotted lines are the insertion loss and the connection loss when the connection structure is formed of a multilayer printed board that does not use a tapered structure without providing a predetermined notch in the ground layer (related technology). The reflection loss is shown. The three-dimensional electromagnetic field analysis is performed with a coaxial connector shape equivalent to a commercially available SMA connector having a characteristic impedance of 50Ω and a microstrip line structure designed to be 50Ω on a multilayer glass epoxy substrate.

  As is apparent from FIGS. 4 and 5, in the connection structure 20 of the present invention, the reflection loss is −20 dB or less in the region from 0 to 20 GHz, and it can be seen that the signal is transmitted with almost no reflection. In particular, when the connection structure is formed with a multilayer printed circuit board that does not use a taper structure for the ground layer (related technology), the reflection increases rapidly when the frequency exceeds 16 GHz, and the insertion loss greatly increases accordingly. In the connection structure 20 of the present invention, the reflection does not increase even when the frequency is increased. As a result, the insertion loss at 20 GHz is less than half that of the related art. From this result, it can be seen that the use of the grounding structure of the present invention is extremely effective in transmitting a high-speed digital signal containing a high-frequency component.

(Other embodiments of the ground layer)
The shape of the notch provided in the ground layer can be arbitrarily designed within the scope of the gist of the present invention.

  FIG. 6 is another schematic plan view showing a signal layer (microstrip line) and a plurality of ground layers, respectively. As can be seen from FIG. 6, in the ground layers 3b, 4b, 5b, 6b, the notches are formed as triangles. As in the other embodiments, the ground layer 7b is not formed with a notch.

  FIG. 7 is still another schematic plan view showing a signal layer (microstrip line) and a plurality of ground layers, respectively. As can be seen from FIG. 7, in the ground layers 3c, 4c, 5c, and 6c, the notches are formed in a quadrangular shape. More specifically, in the ground layers 3c, 4c, 5c, and 6c, the notch is formed as a square, but the shape of the notch may be a rectangle. As in the other embodiments, the ground layer 7c is not formed with a notch.

  FIG. 8 is still another schematic plan view showing a signal layer (microstrip line) and a plurality of ground layers, respectively. As can be seen from FIG. 8, in the ground layers 3d, 4d, 5d, and 6d, notches are formed by exponential function curves. Specifically, the contour of the notch is formed by an exponential function curve. As in the other embodiments, the ground layer 7d is not formed with a notch.

  While various embodiments have been described above, the present invention is not limited to the above embodiments. For example, you may form the outline of a notch part with a parabolic curve. Moreover, the shape of the notch part of each ground layer does not need to be similar.

It is a typical perspective view which shows an example of the connection structure of this invention. It is typical sectional drawing of the A-A 'surface in FIG. It is the typical top view which took out and showed each signal layer (microstrip line) and a plurality of grounding layers. It is a characteristic view which shows the effect by employ | adopting the connection structure of this invention. It is another characteristic view which shows the effect by employ | adopting the connection structure of this invention. It is the other typical top view which took out and showed each signal layer (microstrip line) and a plurality of grounding layers. FIG. 10 is still another schematic plan view showing a signal layer (microstrip line) and a plurality of ground layers taken out from each other. FIG. 10 is still another schematic plan view showing a signal layer (microstrip line) and a plurality of ground layers taken out from each other.

Explanation of symbols

1 multilayer printed circuit board 2 microstrip line 3 ground layer (first ground layer)
4, 5, 6, 7 Ground layer 8 Coaxial connector 9 Center conductor 10 Outer conductor 11 Fixed block 12 Dielectric 20 Connection structure K3, K4, K5, K6 Notch

Claims (9)

A multilayer printed circuit board having a signal layer and a plurality of ground layers provided below the signal layer and electrically connected to each other;
A multilayer printed circuit board, wherein a notch portion is provided in at least a part of the plurality of ground layers, and the size of the notch portion is different for each ground layer.   The multilayer printed circuit board according to claim 1, wherein the plurality of ground layers are arranged substantially in parallel with a predetermined interval, and are arranged so that the cutout portions overlap each other.   The notch portion in the first ground layer closest to the signal layer is maximized, and the size of the notch portion of the ground layer is gradually reduced as the distance from the first ground layer increases. Item 3. The multilayer printed circuit board according to Item 1 or 2.   The multilayer printed circuit board according to claim 3, wherein the size of each notch from the first ground layer to the last ground layer provided with the notch is tapered.   The multilayer printed circuit board according to any one of claims 1 to 4, wherein a shape of the notch is any one of a trapezoid, a triangle, and a quadrangle.   The multilayer printed circuit board of any one of Claims 1-4 in which the outline of the said notch part is formed with an exponential function curve or a parabolic curve.   A coaxial connector having a central conductor and a cylindrical outer conductor that concentrically surrounds the central conductor is connected to the multilayer printed board according to any one of claims 1 to 6. Connection structure between multilayer printed circuit board and coaxial connector.   The connection structure according to claim 7, wherein the outer conductor and the plurality of ground layers are connected.   The connection structure according to claim 7 or 8, wherein a distance t2 between the signal layer and a ground layer farthest from the signal layer is larger than a distance r between the center conductor and the outer conductor.

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