JP2006173400A - Printed wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To keep characteristic impedance of an entire wiring system as constant as possible, without reducing a wiring width, while suppressing increase of radiation noise caused by a return current. <P>SOLUTION: A printed wiring board including a plurality of conductive layers comprises a wiring pattern 4 formed in a wiring layer; a first power supply plane layer or ground plane layer 2 adjacent to a portion, wherein the characteristic impedance is relatively high in its wiring pattern; and a second power supply plane layer or ground plane layer 3 adjacent to portions 5, 6, of the wiring pattern, wherein the characteristic impedance is relatively low. The distance between the wiring pattern and the second power supply plane layer or ground plane layer 3 is set greater than the distance between the wiring pattern and the first power supply plane layer or the ground plane layer 2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a printed wiring board, and more particularly to a multilayer printed wiring board that uses high-speed signals that require characteristic impedance adjustment.

  In a signal path such as a wiring pattern on a printed wiring board, the characteristic impedance changes at the connection point with the mounting point such as the wiring pattern branch point or IC terminal or connector, resulting in a discontinuity in the characteristic impedance. At the discontinuous point, reflection and attenuation of the signal flowing through the wiring pattern occurs. Since this phenomenon becomes particularly prominent with high-frequency signals, it is important to adjust the characteristic impedance of each part of the printed wiring board through which the high-frequency signal flows so that the characteristic impedance is as constant as possible in the entire system.

  The main factors that determine the characteristic impedance on a multilayer printed wiring board composed of a plurality of layers are the cross-sectional shape of the wiring pattern, the shape of the power plane or GND (ground) plane that is adjacent to the wiring pattern layer, and the wiring pattern layer In general, the distance between the power supply plane or the GND plane and the dielectric constant of the insulator between the wiring pattern layer and the power supply plane or the GND plane adjacent to the wiring pattern layer are known.

  As a method for actually adjusting the characteristic impedance of the wiring pattern on the printed wiring board, for example, JP-A-9-36504 (Patent Document 1) and JP-A-11-317572 (Patent Document 2). ) And the like, there are known a method of changing the wiring width and a method of making a hole in the adjacent power supply plane or GND plane.

  Here, FIG. 13 is a diagram showing an example in which the conventional wiring width is varied. In FIG. 13, the wiring pattern 4 branches into a wiring pattern 5 and a wiring pattern 6, and the wiring pattern 5 and the wiring pattern 6 are set to have a narrow wiring width in order to match the characteristic impedance with the wiring pattern 4.

  FIG. 14 is a diagram showing an example in which a hole is made in a conventional power plane or GND plane. In FIG. 14, the wiring pattern 4 is branched into a wiring pattern 5 and a wiring pattern 6, and the wiring pattern 5 and the wiring pattern 6 have holes in the power supply / GND plane 9 in order to match the characteristic impedance with the wiring pattern 4. 10 is opened.

  On the other hand, in a printed wiring board through which high-speed signals flow, securing a return current is an important issue. A return current is a current that flows in a reverse direction mainly in a portion close to the signal wiring pattern in the corresponding power plane or GND plane layer with respect to the direction of the signal flowing through the wiring pattern, and an element that impedes this current flow. If there is, there is a problem that radiation noise increases.

Further, when a higher speed signal is handled, signal attenuation due to skin effect, dielectric loss, or the like becomes a problem. In order to mitigate this signal attenuation, keeping the wiring width wide is one of the measures.
JP-A-9-36504 Japanese Patent Laid-Open No. 11-317572

  However, the conventional method of changing the characteristic impedance of the wiring pattern has the following problems.

  First, the method of changing the width of the wiring pattern requires a portion that widens the width of the wiring pattern, which causes a problem that the wiring density decreases. Furthermore, when a higher frequency signal is passed, the wiring width must be narrowed at the portion where the characteristic impedance is desired to be increased, so that there is a problem that the high frequency DC resistance is increased.

  In the method of making a hole in the power plane or GND plane immediately below the wiring pattern layer as in Patent Document 1, a return path (return current path) of a signal passing through the power plane or GND plane cannot be secured, and radiation noise increases. There is a problem of doing.

  Also, as in Patent Document 2, there is a method of making a hole in the peripheral portion without making a hole in the power plane or the GND plane directly below the signal wiring pattern layer in order to secure a return path. Since the conductor of the nearby power plane or GND plane that has the greatest influence on the characteristic impedance of the wiring pattern remains, the characteristic impedance cannot be made sufficiently high.

  In addition, the method of simply changing the insulation thickness between the wiring pattern layer and the power plane or the GND plane cannot secure a return path (return current path) of the power plane or the GND plane, and radiated noise. Since increase is a problem, it is not used for high-speed signals.

  Therefore, the present invention has been made in view of the above-described problems, and its purpose is to keep the characteristic impedance of the entire wiring system as constant as possible without reducing the wiring width while suppressing an increase in radiation noise caused by the return current. Is to be able to keep on.

  Another object of the present invention is to improve the degree of freedom in designing a printed wiring board.

  Still another object of the present invention is to make it possible to keep the wiring pattern of the wiring layer constant, and to meet the demands for improved design flexibility and high-density mounting.

  In order to solve the above-described problems and achieve the object, a printed wiring board according to the present invention is a printed wiring board having a plurality of conductive layers, a wiring pattern formed in the wiring layer, and a characteristic impedance of the wiring pattern. A first power plane layer or a ground plane layer adjacent to a relatively high portion, and a second power plane layer or a ground plane layer adjacent to a portion where the characteristic impedance of the wiring pattern is relatively low. The distance between the wiring pattern and the second power plane layer or ground plane layer is set larger than the distance between the wiring pattern and the first power plane layer or ground plane layer. To do.

  In the printed wiring board according to the present invention, the first power plane layer or ground plane layer and the second power plane layer or ground plane layer are electrically connected by via holes. To do.

  In the printed wiring board according to the present invention, the first power plane layer or ground plane layer and the second power plane layer or ground plane layer are electrically connected by a built-in capacitor. And

  In the printed wiring board according to the present invention, the impedance in the wiring pattern is adjusted by changing the width of the second power plane layer or the ground plane layer.

  According to the present invention, it is possible to keep the characteristic impedance of the entire wiring system as constant as possible without reducing the wiring width while suppressing an increase in radiation noise caused by the return current.

  In addition, it is possible to improve the degree of freedom in designing the printed wiring board.

  In addition, it is possible to keep the wiring pattern of the wiring layer constant, and it is possible to meet the demand for higher design freedom and high-density mounting.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings.

  In the following embodiment, when a part having a low characteristic impedance occurs in the wiring pattern for some reason, the characteristic impedance of the wiring pattern having the low characteristic impedance is increased and matched with the characteristic impedance of the other part of the wiring pattern. explain.

(First embodiment)
FIG. 1 is a perspective view showing a part of a printed wiring board according to the first embodiment of the present invention.

  FIG. 1 shows a printed wiring board cut into a rectangle in the plane direction. In practice, each wiring pattern and a plane layer are spread beyond the cut surface. 2 is a plan view of FIG. 1 as viewed from above, and FIG. 3 is a side view of FIG.

  1 to 3, a wiring pattern 4 having a branch point 4a branches into a wiring pattern 5 and a wiring pattern 6 at the branch point 4a. When the wiring pattern is branched in this way, since the branched wiring patterns 5 and 6 are in a state in which resistors are connected in parallel, the characteristic impedance of the wiring patterns 5 and 6 is lowered. In order to keep the characteristic impedance as constant as possible in the entire wiring pattern system, it is necessary to increase the reduced characteristic impedance of the wiring patterns 5 and 6.

  Therefore, in this embodiment, the power plane layer or GND (ground) plane layer 2 that determines the characteristic impedance of the wiring pattern 4 and the power plane layer or GND plane layer that determines the characteristic impedance of the wiring patterns 5 and 6 after branching. 3 are arranged in different layers. More specifically, the power supply / GND plane layer 3 adjacent to the wiring patterns 5 and 6 after branching is arranged farther from the wiring pattern than the power supply / GND plane layer 2 adjacent to the wiring pattern 4 before branching. . In this way, it is possible to increase the characteristic impedance of the wiring patterns 5 and 6 that are lowered by branching, and to approach the characteristic impedance of the wiring pattern 4 before branching.

  The plane adjacent to the wiring patterns 4, 5, and 6 may be a power plane or a GND plane. In the embodiment of the present invention, the expression power / GND plane layer is used in either sense. The power supply / GND plane layer 2 and the power supply / GND plane layer 3 are connected to each other through a via hole 1 for securing a return current immediately below the branch point 4a. Instead of via hole 1, power supply / GND plane layer 2 and power supply / GND plane layer 3 may be connected by a built-in capacitor.

  In this embodiment, the wiring widths of the wiring pattern 4 before branching and the wiring patterns 5 and 6 after branching are the same, but they may be completely different from each other. In such a case, the distance between the wiring patterns 5 and 6 and the power supply / GND pattern 3 is adjusted to increase the characteristic impedance according to the degree of decrease in the characteristic impedance of the wiring patterns 5 and 6 after branching. Adjust it.

(Second Embodiment)
FIG. 4 is a perspective view showing a part of a printed wiring board according to the second embodiment of the present invention.

  FIG. 4 shows a printed wiring board cut into a rectangle in the plane direction. In practice, each wiring pattern and a plane layer are spread beyond the cut surface. 5 is a plan view of FIG. 4 as viewed from above, and FIG. 6 is a side view of FIG.

  In FIG. 4, unlike the first embodiment, the wiring pattern 7 does not have a branch point, and its wiring width is also constant. In this case, the characteristic impedance of the wiring pattern 7 is normally constant and should not change. However, in this embodiment, as shown in FIGS. 5 and 6, the wiring pattern 7 is connected to the connector 20 at the end thereof. In such a case, the characteristic impedance of the wiring pattern 7 becomes low at the peripheral portion 7 b of the connector 20. In order to keep the characteristic impedance as constant as possible in the entire wiring pattern system, it is necessary to increase the characteristic impedance of the connector peripheral portion 7b of the lowered wiring pattern 7.

  Therefore, in the present embodiment, the power supply / GND plane layer 2 that determines the characteristic impedance of the wiring pattern portion 7a away from the connector of the wiring pattern 7 and the power supply / GND plane layer 3 that determines the characteristic impedance of the connector peripheral portion 7b are provided. Arrange in different layers. More specifically, the power supply / GND plane layer 3 adjacent to the connector peripheral portion 7b is disposed farther from the wiring pattern than the power supply / GND plane layer 2 adjacent to the wiring pattern portion 7a. In this way, the characteristic impedance of the connector peripheral portion 7b, which has been lowered, can be increased and brought close to the characteristic impedance of the wiring pattern portion 7a.

  The power supply / GND plane layer 2 and the power supply / GND plane layer 3 are connected to each other through a via hole 1 for securing a return current immediately below a portion where the characteristic impedance of the wiring pattern 7 changes. Instead of via hole 1, power supply / GND plane layer 2 and power supply / GND plane layer 3 may be connected by a built-in capacitor.

  In the present embodiment, the case where the characteristic impedance of the wiring pattern 7 is reduced due to the connector 20 has been described. However, the case where the characteristic impedance of the wiring pattern is low due to a pad for inspection or other reasons is also described above. The characteristic impedance can be made constant by using a method of changing the distance between the wiring pattern and the power source / GND plane layer.

(Third embodiment)
FIG. 7 is a plan view showing a part of a printed wiring board according to the third embodiment of the present invention.

  In the third embodiment, like the second embodiment, even when the wiring width of the wiring pattern 7 does not change, the wiring pattern is present due to the presence of a connector, an inspection pad, etc. as described above or for other reasons. 7 shows another method for increasing the characteristic impedance of the portion where the characteristic impedance is lowered when the characteristic impedance 7 is changed.

  In the present embodiment, first, as in the second embodiment, the power supply / GND plane layer 3 adjacent to the wiring pattern portion 7c having a low characteristic impedance is replaced with the power supply / GND plane layer 2 adjacent to the wiring pattern portion 7a. More away from the wiring pattern. As a result, the characteristic impedance of the wiring pattern portion 7c having a low characteristic impedance can be increased and brought close to the characteristic impedance of the wiring pattern portion 7a. After that, the width of the power / GND plane layer 3 is further reduced. As a result, the characteristic impedance of the wiring pattern portion 7c whose characteristic impedance has been lowered can be further increased and brought closer to the characteristic impedance of the wiring pattern portion 7a.

  The power supply / GND plane layer 2 and the power supply / GND plane layer 3 are connected to each other through a via hole 1 for securing a return current immediately below a portion where the characteristic impedance of the wiring pattern 7 changes. Further, the power supply / GND plane layer 2 and the power supply / GND plane layer 3 may be connected by a built-in capacitor instead of the via hole 1.

(Fourth embodiment)
FIG. 8 is a plan view showing a part of a printed wiring board according to the fourth embodiment of the present invention, and FIG. 9 is a side view of FIG.

  In the fourth embodiment, as in the second embodiment, even when the wiring width of the wiring pattern 7 does not change, the wiring pattern is present due to the presence of connectors, inspection pads, etc. as described above or for other reasons. 7 shows a technique for increasing the characteristic impedance of the portion where the characteristic impedance has decreased stepwise when the characteristic impedance 7 is changed stepwise.

  In FIG. 8, it is assumed that the characteristic impedance of the wiring pattern 7 gradually decreases in the order of the wiring pattern portions 7a, 7d, and 7e due to the presence of a connector, an inspection pad, or the like. In this case, as shown in FIG. 10, the power supply / GND plane layer 2 adjacent to the wiring pattern portion 7a, the power supply / GND plane layer 3 adjacent to the wiring pattern portion 7d, and the power supply / GND adjacent to the wiring pattern portion 7e. The distance from the wiring pattern 7 is gradually increased in the order of the plane layer 8.

  As a result, the characteristic impedance of the wiring pattern portion 7d having a low characteristic impedance can be increased, and the characteristic impedance of the wiring pattern portion 7e can be further increased to approach the characteristic impedance of the wiring pattern portion 7a.

  Note that the power supply / GND plane layer 2 and the power supply / GND plane layer 3 and the power supply / GND plane layer 3 and the power supply / GND plane layer 8 are for securing a return current immediately below the portion where the characteristic impedance of the wiring pattern 7 changes. The via holes 1 are connected to each other. Further, the power supply / GND plane layers may be connected to each other with a built-in capacitor instead of the via hole 1.

(Fifth embodiment)
FIG. 10 is a perspective view showing a part of a printed wiring board according to the fifth embodiment of the present invention, and FIG. 11 is a plan view of FIG. 10 viewed from above.

  This embodiment is substantially the same as the first embodiment, except that the width of the power / GND plane layer 3a adjacent to the wiring pattern 5 and the width of the power / GND plane layer 3b adjacent to the wiring pattern 6 are This is different from the width of the GND plane layer 2.

  By doing in this way, it becomes possible to adjust the degree to which the characteristic impedance of the wiring patterns 5 and 6 whose characteristic impedance is lowered is increased, and the degree of freedom in adjusting the characteristic impedance can be increased.

  FIG. 12 is a diagram illustrating the effects of the first to fifth embodiments.

  When the wiring width of the wiring pattern is not changed and the distance between the wiring pattern and the power supply / GND plane layer is not changed, the characteristic impedance is constant, but is slightly increased by making a hole in the GND plane layer as in the past. It is possible. Furthermore, the characteristic impedance can be further increased by changing the interval between the wiring pattern and the power / GND plane layer or adjusting the width of the power / GND plane layer as in the first to fifth embodiments.

  As described above, according to the above-described embodiment, by changing the distance between the wiring pattern and the power supply / GND plane layer, the characteristic impedance of the wiring pattern can be largely changed as compared with the structure that is not changed. In addition, since the characteristic impedance can be adjusted without forming a wide portion in the wiring pattern, the wiring density of the wiring layer can be kept high. In addition, in the case of higher frequencies, the degree of freedom for widening the wiring width is also improved. Further, it is possible to secure a return path by electrically connecting power supply / GND plane layers having different heights directly below the wiring pattern through via holes.

  Also, by connecting the power supply / GND plane layers of different heights directly below the wiring pattern with built-in capacitors, the power supply / GND plane layers of different layers do not need to be at the same potential. It becomes possible to take.

  In addition, the characteristic impedance can be further adjusted by changing the width of the power / GND plane layer whose distance has been changed.

  In addition, by setting the wiring pattern width to the minimum wiring width, the wiring density of the wiring layer can be increased to the limit determined by the minimum wiring width without worrying about the characteristic impedance. It becomes possible to meet the demand.

It is the perspective view which extracted and showed a part of printed wiring board concerning the 1st Embodiment of this invention. It is the top view which looked at FIG. 1 from the upper surface. FIG. 3 is a side view of FIG. 2. It is the perspective view which extracted and showed a part of printed wiring board concerning the 2nd Embodiment of this invention. It is the top view which looked at FIG. 4 from the upper surface. FIG. 6 is a side view of FIG. 5. It is the top view which extracted and showed a part of printed wiring board concerning the 3rd Embodiment of this invention. It is the top view which extracted and showed a part of printed wiring board concerning the 4th Embodiment of this invention. It is a side view of FIG. It is the perspective view which extracted and showed a part of printed wiring board concerning the 5th Embodiment of this invention. It is the top view which looked at FIG. 10 from the upper surface. It is a figure which shows the effect of 1st thru | or 5th embodiment. It is a figure which shows a prior art example. It is a figure which shows a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Via 2 Power supply / GND plane layer 3 Power supply / GND plane layer 4 Wiring pattern before branching 5 Wiring pattern after branching 6 Wiring pattern after branching 7 Wiring pattern 8 Power supply / GND plane layer 9 Power supply / GND plane layer 10 Hole

Claims (4)

In a printed wiring board having a plurality of conductive layers,
A wiring pattern formed in the wiring layer;
A first power plane layer or a ground plane layer adjacent to a portion having a relatively high characteristic impedance of the wiring pattern;
A second power plane layer or a ground plane layer adjacent to a portion having a relatively low characteristic impedance of the wiring pattern;
The distance between the wiring pattern and the second power plane layer or ground plane layer is set larger than the distance between the wiring pattern and the first power plane layer or ground plane layer. Printed wiring board.   The printed wiring board according to claim 1, wherein the first power plane layer or ground plane layer and the second power plane layer or ground plane layer are electrically connected by a via hole.   2. The printed wiring board according to claim 1, wherein the first power plane layer or ground plane layer and the second power plane layer or ground plane layer are electrically connected by an internal capacitor. .   The printed wiring board according to claim 1, wherein the characteristic impedance in the wiring pattern is adjusted by changing a width of the second power plane layer or the ground plane layer.

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