JP2013065800A - Printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayer printed wiring board which has high EMC characteristics.SOLUTION: A multilayer printed wiring board includes: a connector; a bypass capacitor connected with the connector; a first land to which the connector is connected; and a second land which is disposed at a position facing the first land at a layer different from that of the first land and is grounded. The object is attained by the multilayer printed wiring board.

Description

  The present invention relates to a printed wiring board, and more particularly to a multilayer printed wiring board provided with a bypass pass capacitor for reducing noise from a connector.

  In recent years, a large number of electronic control units (ECUs) are installed in automobiles and electronic devices that require advanced control. A printed wiring board is disposed inside the electronic control unit (ECU), and a connector is installed on each printed wiring board for inputting and outputting signals to and from other wiring boards inside and outside the ECU. The connectors are connected by a wire harness.

  By the way, there are various noise sources around the ECU, and these noises flow from the wire harness to the electronic circuit in the printed wiring board via the connector. Since such noise causes malfunction of electronic circuits on the printed wiring board, it is common to reduce the noise level by arranging a noise absorbing element in the vicinity of the connector.

  There are various elements such as capacitors, coils, and ferrite beads as noise absorbing elements, but capacitors are often used mainly from the viewpoint of cost. A capacitor provided between the input signal line from the connector and the ground (ground) for this purpose is called a bypass capacitor.

JP 2005-149778 A

  Incidentally, since there is a printed pattern wiring between the connector and the bypass capacitor, there is an inductance caused by this wiring. The reactance increases as the frequency increases due to this inductance. Since the inductance by the wiring and the bypass capacitor are connected in series, there is a problem that it is difficult to sufficiently remove the noise by the bypass capacitor for noise including high frequency components.

  As a countermeasure for this problem, there is a method of reducing inductance by shortening the wiring between the connector and the bypass capacitor. However, the installation of connectors and bypass capacitors requires a suitable space, so there is a limit to shortening the wiring. As another method, there is a method in which a bypass capacitor is formed on the back side where the connector is installed as in the invention described in Patent Document 1, but in order to obtain a sufficient noise reduction effect, a relatively large area is used for the capacitance. It is necessary to form a large capacitor, and there is a problem that an area that can be used for wiring of an electronic circuit is reduced on the surface on which the capacitor is formed. In view of such a background, a multilayer printed wiring board having high EMC (Electromagnetic Compatibility) characteristics has been demanded.

  The above-described problem is that a connector, a bypass capacitor connected to the connector, a first land to which the connector is connected, and a layer different from the first land are arranged at positions facing the first land. And a multi-layer printed wiring board provided with a second land that is grounded. In the present application, the “multilayer printed wiring board” means a printed wiring board having two or more layers, and includes a double-sided printed board in which a printed pattern is formed on both sides of an insulator layer.

  The multilayer printed wiring board has a structure in which the respective layers are electrically separated by providing an insulating layer such as glass epoxy or Teflon between the layers in which the wiring is formed by the printed pattern. Using this structure, by forming a bypass capacitor with lands provided in each layer and an insulator between the layers, it is possible to directly connect the connector and the bypass capacitor, and the inductance between the connector and the bypass capacitor is reduced. It can be greatly reduced. Further, since the land for connecting the connector also serves as one electrode of the bypass capacitor, the required area can be reduced.

  In addition to the above-described configuration, it is desirable to provide a third land that is disposed at a position facing the first land and is grounded in a layer laminated in a different lamination direction from the second land. That is, the first land and the second land are formed by sandwiching the first land to which the connector terminal is connected between the grounded second land and the third land. The two bypass capacitors of the first bypass capacitor and the second bypass capacitor constituted by the first land and the third land can be connected in parallel, and a larger capacitance can be obtained.

  At this time, it is desirable that the area where the first land and the second land face each other is different from the area where the first land and the third land face each other. The inductance due to the wiring and the capacitance of the bypass capacitor form a resonance circuit. The size of the capacitance of the bypass capacitor formed by the land is proportional to the land area. Therefore, it is possible to provide a plurality of different resonance points by changing the areas of the opposed portions of the first bypass capacitor and the second bypass capacitor. This makes it possible to particularly enhance the noise reduction effect of different frequency components among the noise components flowing into the printed wiring board.

  Further, instead of making the area where the first land and the second land oppose each other and the area where the first land and the third land oppose are different (or making the areas different). And the second insulator disposed between the first land and the third land, and the thickness of the first insulator layer disposed between the first land and the second land. The layer thickness may be different. Further, the same effect can be obtained even when insulating materials (prepregs) having different dielectric constants are used for the first insulator layer and the second insulator layer.

  According to the present invention, a multilayer printed wiring board having high EMC characteristics can be provided.

It is a perspective view of the multilayer printed wiring board which is one Embodiment of this invention. It is the wiring diagram (a) of the upper layer of the multilayer printed wiring board which is one Embodiment of this invention, and the wiring diagram (b) of a lower layer. It is an equivalent circuit diagram of one embodiment of the present invention. It is a figure which shows the EMC characteristic of the multilayer printed wiring board which is one Embodiment of this invention. It is a wiring diagram ((a) is an upper layer, (b) is an intermediate | middle layer, (c) is a lower layer) of the multilayer printed wiring board which is other embodiment of this invention. It is the equivalent circuit schematic of other embodiment of this invention.

  FIG. 1 is a perspective view of a printed wiring board 1 according to an embodiment of the present invention. The printed wiring board 1 is a double-sided board, and wiring layers 2 and 4 are formed on the upper and lower sides of an insulating substrate 3, respectively. An electronic circuit is formed on each of the wiring layers 2 and 4 by printed wiring using copper foil. A connector 5 is disposed on the upper layer 2.

  2A and 2B show wiring diagrams of the upper layer 2 and the lower layer 4 in the vicinity of the connector 5, respectively. In the upper layer 2, through holes 20 and lands 21 for inserting the respective terminals of the connector 5 are formed, and the terminals of the connector 5 and the lands 21 are connected. The land 21 has a rectangular shape so as not to short-circuit with the adjacent land 22 and to take as large an area as possible. In addition, a bypass capacitor 24 for reducing noise flowing in from the connector is attached, and a terminal 23 of the connector and the bypass capacitor 24 are connected by a wiring 23 with a printed pattern.

  In the lower layer 4, a through hole 40 for inserting a terminal of the connector 5 and a land 42 for soldering the terminal are formed. Around the land 42, a land 41 that is grounded is formed. The land 41 and the land 42 are insulated. 2B is a conceptual land, and is not a land independent of the surrounding ground wiring but a part of the ground wiring of the solid wiring. In the present application, such wiring is also referred to as “land”.

  In the printed wiring board 1 of the present embodiment, the bypass capacitor is attached to the upper layer 2, but it can also be designed to be arranged in the lower layer 4. The wiring connecting the connector 5 and the bypass capacitor 24 does not need to be arranged in the same layer as the bypass capacitor 24, and may be provided in another layer.

  FIG. 3 shows an equivalent circuit diagram near the terminals of the connector 5. The terminal 50 of the connector is connected to the bypass capacitor 24 via the wiring 23. Since the wiring 23 has an inductance, the inductance 23 and the bypass capacitor 24 are connected in series. Further, the land 21 of the upper layer 2 forms a bypass capacitor 51 together with the land 41 of the lower layer 4 facing each other with the insulating base 3 interposed therebetween. The land bypass capacitor 51 is connected in parallel with the wiring inductance 23.

  As is apparent from the equivalent circuit of FIG. 3, the bypass capacitors 24 and 51 and the inductance 23 form a resonance circuit. The resonance point (resonance frequency) can be determined by the capacitances of the bypass capacitors 24 and 51 and the inductance 23. Among these, the capacitance of the bypass capacitor 51 formed by the land is determined by the dielectric constant of the insulating base 3, the thickness of the base 3, and the areas of the opposing lands 21 and 41. In the multilayer printed wiring board 1, since the land 41 in the lower layer 4 is a solid wiring, the resonance point can be determined by changing the area of the land 21 in the upper layer.

  FIG. 4 shows experimental results of EMC (Electromagnetic Compatibility) characteristics of the multilayer printed wiring board 1. In the experiment, noise was input from the outside through the connector 5, and the noise level (noise current amount) at which the electronic circuit formed on the printed wiring board 1 caused an abnormal operation was examined. In FIG. 4, the horizontal axis represents the noise frequency, and the vertical axis represents the noise level that causes abnormal operation. The higher the noise level that causes abnormal operation, the higher the EMC characteristics. The solid line 30 shows the frequency characteristics when there is no bypass capacitor 51 formed by the lands 21 and 41 (that is, only the bypass capacitor 24), and the broken line 31 shows the case where there is the bypass capacitor 51 formed by the lands 21 and 41. Shows frequency characteristics.

  As is clear from the comparison between the solid line 30 and the broken line 31, it can be seen that the presence of the bypass capacitor 51 formed by the lands 21 and 41 improves the EMC characteristics particularly in the high frequency component. It can also be seen that the EMC characteristics are greatly improved near the resonance point 32.

  FIG. 5 is a wiring diagram of each wiring layer of a three-layer printed wiring board according to another embodiment of the present invention. In the figure, (a) is an upper layer 70, (b) is an intermediate layer 80, and (c) is a lower layer 90 wiring diagram. Each layer is electrically insulated by an insulating base, and a connector and a PIBUS capacitor are arranged on the upper layer 70. A land 83 having connector terminals connected to the intermediate layer 80 is formed, and a land 73 on the upper layer 70 and a land 93 on the lower layer 90 are formed at positions facing the land 83. The land 73 of the upper layer 70 and the land 93 of the lower layer 90 are grounded.

  The upper layer 70 is formed with through holes 71 for inserting connector terminals and lands 72 for soldering the terminals. Around the land 72, a grounded land 73 is formed. Similar to FIG. 2B, the land 73 indicated by a broken line is a conceptual land, and is not a land independent of the surrounding ground wiring but a part of the ground wiring of the solid wiring. Further, a through hole 75 for inserting one end of the bypass capacitor 77 and a land 75 for soldering are formed. The other end of the bypass capacitor 75 is connected to the ground wiring. The lands 72 and 75 are insulated from the ground wiring.

  A through hole 81 and a land 83 for inserting a connector terminal are formed in the intermediate layer 80, and the connector terminal and the land 83 are connected to each other. The land 83 has a rectangular shape so as not to short-circuit with the adjacent land 82 and to take as large an area as possible. A through hole 84 for inserting one end of the bypass capacitor 74 is formed, and one end of the bypass capacitor 74 is connected to the land 83 via the wiring 85.

  The lower layer 90 is formed with a through hole 91 for inserting a connector terminal and a land 92 for soldering the terminal. A grounded land 93 is formed around the land 92. Although the land 93 is electrically coupled to the ground wiring, it is not a solid wiring like the ground wiring of the upper layer 73 but is formed in a rectangular shape. The area of the land 93 in the lower layer 90 is different from the area of the land 73 in the upper layer 70. Although a through hole and a land for inserting the other end of the bypass capacitor 77 are formed in the lower layer 90, they are not shown in order to avoid complexity.

  FIG. 6 shows an equivalent circuit diagram near the connector terminal of the three-layer printed wiring board. The terminal 53 of the connector is connected to a bypass capacitor 77 via a wiring 85. The wiring 85 has an inductance. The wiring inductance 85 and the bypass capacitor 77 are connected in series. The land 83 of the intermediate layer 80 is between the bypass capacitor 54 between the land 73 of the upper layer 70 facing the insulating base and the land 93 of the lower layer 90 facing the land of the insulating base. Each of the bypass capacitors 55 is formed. The bypass capacitors 54 and 55 are connected in parallel with the inductance 85.

  In the three-layer printed wiring board of this embodiment, the bypass capacitors 54 and 55 connected in parallel are formed by the three lands 73, 83, and 93, so that a larger capacitance can be obtained. Thereby, the noise reduction effect can be enhanced. Further, since the area where the land 73 of the upper layer 70 and the land 83 of the intermediate layer 80 face each other is different from the area where the land 93 of the lower layer 90 and the land 83 of the intermediate layer 80 face each other, it has a plurality of different resonance points. A resonant circuit can be formed. In addition, since the lands 73 and 93 that are grounded are formed in the upper and lower layers of the signal line land 83, an effect as a shield can be expected.

  The technical idea according to the present invention has been described in detail with reference to specific embodiments. However, various changes and modifications may be made by those skilled in the art to which the present invention pertains without departing from the spirit and scope of the claims. It is clear that can be added. For example, the shape of the land does not have to be rectangular, and the design can be changed as appropriate so that a sufficient capacity can be obtained. Further, the connector, the bypass capacitor, and the wiring connecting them need not be in the same layer and can be changed as appropriate.

  Further, instead of making the area where the upper land and the intermediate land face each other and the area where the intermediate land and the lower land face different from each other as shown in FIG. And the thickness of the first insulator layer disposed between the upper layer and the intermediate layer is different from the thickness of the second insulator layer disposed between the intermediate layer and the lower layer. Also good. In adjusting the thickness of the insulator layer (base), the thickness of the material (prepreg) constituting the insulator layer may be adjusted, or the number of prepregs having a predetermined thickness may be adjusted. . Further, prepregs having different dielectric constants may be used for the first insulator and the second insulator. In this way, by appropriately setting the opposing area of the land, the thickness of the prepreg, the number of sheets, the dielectric constant, etc., it is possible to set so as to obtain a desired capacity by these correlations, and it has a desired resonance point. A resonant circuit can be formed.

DESCRIPTION OF SYMBOLS 1 Printed wiring board 2 and 70 Upper layer 3 Base | substrate 4, 90 Lower layer 5 Connector 21, 22, 41, 73, 83, 93 Land 24, 77 Bypass capacitor 80 Middle layer

Claims (4)

A connector;
A bypass capacitor connected to the connector;
A first land to which the connector is connected;
A second land disposed on a layer different from the first land, at a position facing the first land, and grounded;
Multi-layer printed wiring board with   2. The multilayer printed wiring according to claim 1, further comprising: a third land disposed in a position opposed to the first land and grounded in a layer laminated in a different lamination direction from the second land. Board.   The area of the portion where the first land and the second land face each other is different from the area of the portion where the first land and the third land face each other. Multilayer printed wiring board.   The thickness of the first insulator layer disposed between the first land and the second land, and the thickness of the second insulator layer disposed between the first land and the third land The multilayer printed wiring board according to claim 1, wherein:

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