JP6333048B2 - Multilayer circuit board - Google Patents

Description

  The present invention relates to a multilayer circuit board formed by laminating an insulator layer and a conductor layer, and more particularly to a high-frequency signal transmission technique.

  As is well known, in a multilayer circuit board on which a high-frequency circuit is mounted, a technique such as a strip line, a microstrip line, or a coplanar line is used as a transmission line for a high-frequency signal. When two transmission lines are crossed in such a multilayer circuit board, signal lines corresponding to the central conductor of each transmission line are formed in different conductor layers at least at the crossing portion. The one described in Patent Document 1 is a simple superposition of two microstrip line structures, and between the signal line related to the first microstrip line and the signal line related to the second microstrip line, The ground conductor according to the first microstrip line is arranged. In the device described in Patent Document 2, the signal lines of the first and second microstrip lines are formed on the surface of the multilayer circuit board, respectively, while the ground conductor is formed on the back surface of the multilayer circuit board. That is, a common ground conductor is used for the first and second microstrip lines. At the intersection of the microstrip lines, the signal line of the first microstrip line is formed in the inner layer of the multilayer circuit board, and both ends thereof are connected to the signal lines on the surface layer through through holes.

JP 2002-368507 A JP 2011-055328 A

  By the way, with recent demands for downsizing, thinning, and high functionality of electronic devices, there has been an increasing demand for further thinning and narrower wiring pitches in multilayer circuit boards. On the other hand, when transmitting a high frequency signal in a multilayer circuit board, the discontinuity of the characteristic impedance of the transmission line becomes a problem. This is because reflection of a high frequency signal occurs in the discontinuous portion, thereby causing loss of the transmission signal and distortion or rounding of the waveform. On the other hand, when the transmission lines intersect on the multilayer circuit board as described above, signal interference between the transmission lines becomes a problem.

  With respect to such a problem, in Patent Document 1, since a ground conductor is interposed between the signal line of the first microstrip line and the signal line of the second microstrip line, the transmission signal is isolated. Can be ensured, and the ground conductor forming layer is always required, so that it is not suitable for thinning.

  On the other hand, in the thing of patent document 2, in the location where transmission lines cross | intersect, the parallel resonant circuit which resonates at a use frequency is arrange | positioned, and the isolation | separation at a resonant frequency is ensured. In such a structure, it is not necessary to arrange a ground conductor between the transmission lines, which contributes to a reduction in thickness. However, since the lines are connected by an inductor by wiring, there is a problem that isolation is worsened when the resonance frequency is shifted. In addition, since inductors and capacitors are formed by wiring and insulating layers of the multilayer circuit board, there is a possibility that the resonance frequency may vary due to variations in manufacturing, and it is therefore difficult to ensure constant isolation. There is also. Furthermore, there is a problem that the structure cannot be adopted when the signal frequencies between the transmission lines are different.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a multilayer circuit board having a transmission line crossing structure that has good high-frequency characteristics and can be easily reduced in thickness. is there.

  In order to achieve the above object, the present invention provides a multilayer circuit board formed by laminating a conductor layer and an insulator layer, wherein the first conductor layer is spaced apart from the first signal line and the first signal line. A first ground conductor is formed, and the second conductor layer facing the first conductor layer via the insulator layer is spaced apart from the second signal line and the second signal line. A second ground conductor is formed, the first signal line intersects with the second signal line when projected in the thickness direction of the multilayer circuit board, and the distance between the first ground conductor and the first signal line is first. In addition, the interval between the second signal lines is smaller than the interval other than the intersection, and the interval between the second ground conductor and the second signal line is smaller than the interval other than the intersection in the intersection. The first signal line is at the intersection with the second signal line. The second signal line is formed to have the same line width from an intersection with the first signal line to a portion other than the intersection. To do.

  According to the present invention, in the portion other than the intersection of the first signal line and the second signal line, the first signal line formed in the first conductor layer and the second ground conductor formed in the second conductor layer. A microstrip line is formed, and the microstrip line can be formed by the second signal line formed in the second conductor layer and the first ground conductor formed in the first conductor layer. At the same time, at the intersection of the first signal line and the second signal line, a coplanar line is formed by the first signal line and the first ground conductor formed in the first conductor layer, and the second signal layer is formed in the second conductor layer. A coplanar line can be formed by the two signal lines and the second ground conductor. This makes it possible to reduce the thickness of the multilayer circuit board having the crossing structure of the transmission lines. In addition, since each ground conductor is disposed in the same layer and in the vicinity of each signal line, the coplanar line is not easily affected by signal lines and ground conductors formed in other layers. Thereby, the isolation of the first signal line and the second signal line can be easily ensured.

  As an example of a preferred aspect of the present invention, the distance between the first ground conductor and the first signal line has an influence on the characteristic impedance of the first signal line, and the first signal line is intersected at the first and second signal lines. The distance to the ground conductor is more dominant than the distance to the second ground conductor, and the distance to the second ground conductor is set to be more dominant than the distance to the first ground conductor except for the intersection. The distance between the second ground conductor and the second signal line has an influence on the characteristic impedance of the second signal line, and the distance from the second ground conductor at the intersection of the first and second signal lines is the first. The distance is more dominant than the distance to the ground conductor, and the distance from the first ground conductor is set to be more dominant than the distance from the second ground conductor except at the intersection.

  As described above, according to the multilayer circuit board according to the present invention, it is possible to easily realize thinning with good high-frequency characteristics while having a cross structure of transmission lines.

Surface view of multilayer circuit board Simulation results of pass characteristics Isolation simulation results

  An intersecting structure of multilayer circuit boards according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a surface view of a multilayer circuit board. In FIG. 1, (a) is a surface view seen from one main surface side of the multilayer circuit board, and (b) is a surface view seen from the other main surface side of the multilayer circuit board.

  A multilayer circuit board 10 according to the present embodiment is a double-sided board in which conductor layers and insulator layers are laminated, and conductor layers 100 and 200 are formed on both sides of one insulator layer as shown in FIG. It is. That is, the first conductor layer 100 is formed on one main surface of the multilayer circuit board 10, the second conductor layer 200 is formed on the other main surface, and the insulator layer 300 is interposed between the conductor layers 100 and 200. Is formed. As shown in FIG. 1A, the first conductor layer 100 includes a first signal line 110 for transmitting a high-frequency signal, and a first ground conductor formed at an interval from the first signal line 110. 150 is formed. The first ground conductor 150 is a so-called “solid ground”, and is a wiring (including the first signal line 110), land, through-hole, and terminal necessary for a high-frequency circuit constituted by the multilayer circuit board 10. It is formed entirely in a region excluding electrodes. Similarly, as shown in FIG. 1B, the second conductor layer 200 has a second signal line 210 for transmitting a high-frequency signal, and a second signal line 210 formed at an interval from the second signal line 210. Two ground conductors 250 are formed. The second ground conductor 250 is a so-called “solid ground”, and is a wiring (including the second signal line 210), a land, a through hole, and a terminal necessary for a high-frequency circuit constituted by the multilayer circuit board 10. It is formed entirely in a region excluding electrodes. The first ground conductor 150 and the second ground conductor 250 are electrically connected through a through hole (not shown).

  In the multilayer circuit board 10 according to the present invention, the first signal line 110 intersects the second signal line 210 when projected onto the second conductor layer 200 in the thickness direction of the multilayer circuit board 10. The feature of the present invention is the structure of the first conductor layer 100 and the second conductor layer 200 at the intersection between the first signal line 110 and the second signal line 210. The feature of the present invention is the structure of the first signal line 110 at the intersection of the first signal line 110 and the second signal line 210.

  As shown in FIG. 1A, the first signal line 110 has a constant width W15 except at the intersection with the second signal line 210, and approaches the intersection with the second signal line 210. The width gradually decreases, and the width W10 is smaller than the width W15 at and near the intersection. In addition, the gap G10 between the first signal line 110 and the first ground conductor 150 formed in the first conductor layer 100 at the intersection is larger than the gap G15 between the first signal line 110 and the first ground conductor 150 in the area other than the intersection. It is getting smaller. Specifically, the edge of the first ground conductor 150 facing the first signal line 110 gradually approaches the first signal line 110 as it approaches the intersection, and in the vicinity of the intersection, Overhangs to form the gap G15. In other words, the first ground conductor 150 is formed in a trapezoidal shape in the direction of the first signal line 110 in the vicinity of the intersection. The position where the extension of the first ground conductor 150 starts substantially coincides with the position where the width of the first signal line 110 starts to decrease in the length direction of the first signal line 110.

  Similarly to the first signal line 110, the second signal line 210 has a gap G20 between the second signal line 210 and the second ground conductor 250 formed in the second conductor layer 200 at the intersection. The distance G25 between the second signal line 210 and the second ground conductor 250 is smaller. However, unlike the first signal line 110, the second signal line 210 extends at least from the intersection with the first signal line 110 to a portion other than the intersection, in other words, from the intersection to the second signal line 210. The line width is the same (constant) over the length direction. On the other hand, as with the first ground conductor 150, the edge of the second ground conductor 250 facing the second signal line 210 gradually approaches the second signal line 210 as it approaches the intersection, and in the vicinity of the intersection. The second signal line 210 is formed so as to protrude from the gap G25. In other words, the second ground conductor 250 is formed in a trapezoidal shape in the direction of the second signal line 210 near the intersection.

  Here, the first signal line 110 constitutes the internal conductor of the microstrip line in relation to the second ground conductor 250 formed in the second conductor layer 200 except at the intersection with the second signal line 210. It is like that. That is, the characteristic impedance of the first signal line 110 is such that the distance from the second ground conductor 250 formed in the second conductor layer 200, that is, the thickness of the insulator layer 300 is the same as that of the first conductor layer 100 except at the intersection. The dimensions and the like of each part are defined so as to be more dominant than the gap G10 with respect to the formed first ground conductor 150. On the other hand, the first signal line 110 forms an internal conductor of the coplanar line at the intersection with the second signal line 210 in relation to the first ground conductor 150 formed in the first conductor layer 100. ing. That is, the characteristic impedance of the first signal line 110 is such that the gap G15 between the first signal line 110 and the first ground conductor 150 formed in the first conductor layer 100 is the second ground conductor formed in the second conductor layer 200 at the intersection. The dimensions and the like of each part are defined so as to be more dominant than the distance from 250, that is, the thickness of the insulating layer 300. In addition, the characteristic impedance of the first signal line 110 is constant over the whole regardless of the intersection with the second signal line 210, that is, the characteristic impedance discontinuity does not occur. The dimensions of each part are specified. The characteristic points relating to the characteristic impedance as described above are the same for the second signal line 210.

  According to the multilayer circuit board 10 according to the present embodiment, an insulator is provided between the first conductor layer 100 in which the first signal line 110 is formed and the second conductor layer 200 in which the second signal line 210 is formed. Since only the layer 300 exists, the thickness can be easily reduced. Further, by adjusting the distance between the signal lines 110 and 210 and the ground conductors 150 and 250, it is possible to easily prevent the occurrence of discontinuity in characteristic impedance. In particular, in the present embodiment, since the line width of the first signal line 110 is narrower at the intersection between the first signal line 110 and the second signal line 210 than at the intersection other than the first signal line 110, Can easily make the characteristic impedance constant over the entire portion regardless of the intersection.

  Further, according to the multilayer circuit board 10 according to the present embodiment, since the ground conductors 150 and 250 are arranged in the vicinity of the signal lines 110 and 210 and in the same layer at the intersection, they are formed in other layers. Insensitive to signal lines and ground conductors. Thereby, the isolation between the first signal line 110 and the second signal line 210 can be easily ensured. In particular, in the present embodiment, the line width of the first signal line 110 is narrower at the intersection between the first signal line 110 and the second signal line 210 than at the intersection other than the intersection. Can be secured more easily.

  As mentioned above, although embodiment of this invention was explained in full detail, this invention is not limited to this. For example, in each of the above embodiments, a double-sided board in which conductor layers are formed on both sides of one insulator layer has been described. However, the present invention is a multi-layer circuit board having three or more conductor layers including a surface conductor layer. However, the present invention can be applied. In this case, the conductor layers facing each other with one insulator layer therebetween correspond to the first conductor layer and the second conductor layer of the present invention, respectively. In such a case, either the first conductor layer or the second conductor layer may be formed as a surface layer of the multilayer circuit board, or both layers may be formed as the inner layer of the multilayer circuit board. Also good.

  With respect to the multilayer circuit board according to the example of the present invention, pass characteristics and isolation were obtained by simulation. An example shall have the structure of the said embodiment. In this embodiment, the line length of the first signal line is 5 mm, the thickness is 13 μm, the width of the first signal line other than the intersection is 85 μm, the width of the first signal line at the intersection is 56 μm, and the first signal line is other than the intersection. The distance between one signal line and the ground conductor was 170 μm, and the distance between the first signal line and the first ground conductor at the intersection was 25 μm. In this embodiment, the line length of the second signal line is 5 mm, the width is constant and 85 μm, the thickness is 13 μm, the distance between the second signal line and the second ground conductor other than the intersection is 170 μm, and the second signal line at the intersection is The distance between the two signal lines and the second ground conductor was 38 um. In this example, the thickness of the insulator layer was 44 um.

  As Comparative Example 1, an example in which the first and second transmission lines are configured by microstrip lines was prepared. In Comparative Example 1, the line length of the first and second signal lines was 5 mm, the width was 85 μm, the thickness was 13 μm, the thickness of the insulator layer was 44 μm, and the distance between each signal line and the ground conductor was 170 μm.

  Further, as Comparative Example 2, an example in which the first and second transmission lines are configured by coplanar lines was prepared. In Comparative Example 2, the line length of the first and second signal lines was 5 mm, the width was 56 μm, the thickness was 13 μm, the thickness of the insulator layer was 44 μm, and the distance between each signal line and the ground conductor was 25 μm.

  In Example and Comparative Examples 1 and 2, one end of the first signal line is port 1, the other end is port 2, one end of the second signal line is port 3, and the other end is port 4. A sine wave of 1 GHz to 6 GHz is applied between port 1 and port 2, and a predetermined load (impedance element) is connected between port 3 and port 4. In such a situation, S21, which is one of the S parameters, is obtained as the evaluation value of the pass characteristic, and S41 is obtained as the evaluation value of the isolation. 2 and 3 show the simulation results.

  As shown in each figure, according to the present invention, it was found that although the pass characteristic was slightly inferior to Comparative Example 1, the isolation was greatly improved. On the other hand, in comparison with Comparative Example 2, it was confirmed that there was a great advantage with respect to the pass characteristics, although the isolation was inferior. In the design of a realistic high-frequency circuit, when a coplanar line as in Comparative Example 2 is used, the conductor loss increases because the width of the signal line is smaller than that of the microstrip line. However, since high processing accuracy is required for a constant characteristic impedance, it is not realistic in a scene where high density, narrow pitch, and thinning are required. Therefore, although the realistic comparison object of the present invention is Comparative Example 1, as described above, although the pass characteristics are slightly inferior, the isolation is good, so a scene where high density, narrow pitch, and thinning are required. It was verified that it is very effective.

  DESCRIPTION OF SYMBOLS 10,20 ... Multilayer circuit board, 100 ... 1st conductor layer, 200 ... 2nd conductor layer, 110 ... 1st signal line, 210 ... 2nd signal line, 150 ... 1st ground conductor, 250 ... 2nd ground conductor, 300: Insulator layer.

Claims (5)

A multilayer circuit board formed by laminating a conductor layer and an insulator layer,
The first conductor layer is formed with a first signal line and a first ground conductor that is spaced from the first signal line,
The second conductor layer facing the first conductor layer with the insulator layer interposed therebetween is provided with a second signal line and a second ground conductor disposed at a distance from the second signal line,
The first signal line intersects the second signal line when projected in the thickness direction of the multilayer circuit board;
The distance between the first ground conductor and the first signal line is smaller at the intersection of the first and second signal lines than at the area other than the intersection, and the distance between the second ground conductor and the second signal line is The intersection is formed smaller than the interval other than the intersection,
The first signal line is formed to have a narrower line width at the intersection with the second signal line than at the intersection other than the first signal line,
Said second signal line, the multi-layer circuit board line width over a portion other than the crossing portion from the intersection of the first signal line is you characterized in that it is formed in the same. The distance between the first ground conductor and the first signal line has an influence on the characteristic impedance of the first signal line, and the distance from the first ground conductor at the intersection of the first and second signal lines is the second ground conductor. The distance to the second ground conductor is set to be more dominant than the distance to the first ground conductor except at the intersection.
The distance between the second ground conductor and the second signal line has an influence on the characteristic impedance of the second signal line, and the distance from the second ground conductor at the intersection of the first and second signal lines is the same as the distance from the first ground conductor. The distance from the first ground conductor is set to be more dominant than the distance from the second ground conductor except at the intersection. Multilayer circuit board. The first signal line forms a part of a coplanar line at an intersection with the second signal line and forms a part of a microstrip line at a portion other than the intersection,
2. The second signal line forms a part of a coplanar line at an intersection with the first signal line and forms a part of a microstrip line at a portion other than the intersection. 2. The multilayer circuit board according to 2. The first signal line has a constant characteristic impedance at an intersection with the second signal line and at a portion other than the intersection,
4. The multilayer circuit board according to claim 1, wherein the second signal line has a constant characteristic impedance at an intersection with the first signal line and at a portion other than the intersection. 5. The multilayer circuit board is a double-sided board in which the first conductor layer is formed on one surface of one of the insulator layers, and the second conductor layer is formed on the other surface of the insulator layer.
The multilayer circuit board according to any one of claims 1 to 4, wherein the multilayer circuit board is provided.

Images