JP2008258464A - Circuit board and differential transmission apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a circuit board on which a coil component such as a common-mode filter etc. suitable for suppressing the deterioration of the impedance characteristic is mounted, and to provide a differential transmission apparatus. <P>SOLUTION: This circuit board has the coil component mounted on one main surface thereof and has a ground electrode formed on the other main surface thereof. Terminal electrodes formed on the base of the coil component and electrode pads formed on the one main surface of the circuit board are electrically connected respectively. Electrode non-forming portions are formed on the other main surface so that they includes in the plan view a plurality of portions of the terminal electrodes and the electrode pads interposed and located between the base of the coil component and the one main surface. The electrode non-forming portions are formed by being divided by the ground electrode into two or more portions. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a circuit board, and more particularly to a circuit board on which a coil component such as a common mode filter is mounted and a differential transmission device on which the circuit board is mounted.

  Conventionally, noise countermeasure electronic components in high-speed transmission lines such as USB and IEEE 1394 include a ferrite core attached to the outer periphery of an external connection cable, a chip bead inductor mounted on a substrate and connected to the transmission line, a common mode filter, and the like. Ferrite cores and chip bead inductors act as high impedance due to the high magnetic permeability of the ferrite in the noise frequency band to cut off the noise. The common mode filter functions to block noise by providing high impedance due to the high magnetic permeability of the ferrite with respect to common mode noise in differential transmission. Such components are mainly used in personal computers, digital cameras, portable devices, etc., but with the speeding up of data processing, common mode filters that function in the high frequency band of several hundred MHz and even in the GHz band are required. ing. A common mode filter that is assumed to be used in such a high frequency band is disclosed in Patent Document 1, for example. Patent Document 1 discloses a configuration in which stray capacitance generated between electrode pads of a common mode filter is reduced.

JP 2005-317725 A

  In recent years, with the increase in CPU speed, there has been a demand for noise countermeasure electronic components that support higher-speed transmission such as HDMI and PCI-Express. Various problems will become apparent with higher frequencies such as the problem of stray capacitance. For example, the configuration disclosed in Patent Document 1 is intended to solve the problem of the stray capacitance of the common mode filter itself, but the stray capacitance is not limited to the common mode filter itself, and also occurs in relation to peripheral circuits. A common mode filter is usually mounted on a circuit board such as a printed circuit board. A ground electrode is provided on the back side of the circuit board. Such a ground electrode is indispensable for a circuit board including a shielding effect. Parasitic capacitance is also formed in relation to the ground electrode. The influence of such parasitic capacitance becomes more prominent as it becomes a particularly high frequency band such as a GHz band. The impedance characteristics of the common mode filter are deteriorated. Not only the common mode filter but also other high frequency coil components have such a problem. The present invention has been made in view of such a problem, and provides a circuit board and a differential transmission device mounted with coil components suitable for high frequency transmission accompanying high-speed transmission and suitable for suppressing deterioration of impedance characteristics. .

  The circuit board of the present invention is a circuit board in which a coil component is mounted on one main surface and a ground electrode is formed on the other main surface, the terminal electrode formed on the base of the coil component, and the circuit An electrode pad formed on one main surface of the substrate is electrically connected, and the other main surface has a base of the coil component and the one main surface of the terminal electrode and the electrode pad. An electrode non-formation portion is formed so as to include a plurality of interposition portions located between the electrode and the electrode non-formation portion, and the electrode non-formation portion is divided into two or more by the ground electrode. And According to such a configuration, since the parasitic capacitance formed between the electrode portion adjacent to the coil component and the ground can be suppressed, it is possible to prevent the impedance characteristics from degrading due to the parasitic capacitance being coupled to the inductance of the coil component. can do. If the electrode non-formation part is divided into two or more, the ground electrode can be disposed in a part other than the divided electrode non-formation part, so that the shielding effect can be maintained. In addition, when there is a return current passing through the ground electrode, a path of the return current can be secured between the electrode non-forming portions, which contributes to suppression of noise generation due to the removal of the ground electrode.

  Further, in the circuit board, it is preferable that the electrode non-forming portion is formed for each of the plurality of interposed portions and is separated from each other via the ground electrode. According to this configuration, it is only necessary to form the electrode non-forming portion in the minimum necessary portion, and the proportion of the ground electrode portion can be increased accordingly, which is preferable in maintaining the shielding effect.

  Furthermore, in the circuit board, it is preferable that a winding axis direction of a coil constituting the coil component is a direction substantially orthogonal to the ground electrode. When the winding axis of the coil formed on the coil component, that is, the direction perpendicular to the coil surface is substantially orthogonal to the ground electrode provided on the circuit board, the area where the coil conductor faces the ground electrode increases, so the parasitic capacitance Easy to form. Therefore, the above-described configuration is more effective when applied when the winding axis direction of the coil is substantially orthogonal to the ground electrode.

  Further, in the circuit board, the coil is preferably a planar spiral coil. A coil component using a planar spiral coil contributes to a reduction in height, but has a large area facing the ground electrode. By adopting the above configuration, it is possible to suppress parasitic capacitance, and it is possible to realize a low-profile coil component having excellent impedance characteristics.

  Furthermore, in the circuit board, the coil component is preferably a common mode filter. The above-described configuration is suitable when a common mode filter that is mounted as a chip element and is required to support high frequencies is used.

  The differential transmission device of the present invention is a differential transmission device equipped with the circuit board. The circuit board can be mounted on a device, a cable or the like having a differential transmission transmission and / or reception function to constitute a differential transmission device.

  According to the electronic component of the present invention, it is possible to provide a circuit board and a differential transmission device equipped with a coil component suitable for suppressing deterioration of impedance characteristics.

(First embodiment)
Hereinafter, although specific embodiment of this invention is described, this invention is not limited to this embodiment. As a first embodiment of the coil component of the present invention, a common mode filter will be described as an example with reference to FIG. The coil component is not limited to the common mode filter, and may be another noise filter or an inductor. However, the common mode filter has a strong demand for high frequency and low profile, and is a coil component suitable for application of the configuration according to the present invention. 1A is a front view of a common mode filter, FIG. 1B is a bottom view of the common mode filter, FIG. 1C is a plan view of one main surface of the circuit board, and FIG. The top view which looked at the main surface of the mounted circuit board, (e) is sectional drawing of (d), (f) is the bottom view which looked at the other main surface of the circuit board which mounted the common mode filter. The common mode filter shown in FIG. 1 is a laminated common mode filter, and its structure is shown in FIG. FIG. 5A is a cross-sectional view of the common mode filter. FIG. 5B is an exploded perspective view showing the layer structure and electrode structure inside the base 2 other than the terminal electrode 1 in FIG. Note that the thickness of the insulating layer is exaggerated. The first planar spiral line 13a is formed on the insulating layer 12a, the second planar spiral line 13b is formed on the insulating layer 12b, and the first planar spiral line 13a and the second planar spiral line 13b are interposed via the insulating layer 12b. The planar spiral line 13b is arranged so as to be opposed. A magnetic layer 11a and a magnetic layer 11b are disposed on opposite sides of the first planar spiral line 13a and the second planar spiral line 13b, respectively. In the configuration shown in FIG. 5, the insulating layer portion 16 composed of the insulating layers 12a, 12b, 12c, and 12d is fixed in close contact with the magnetic layer 11a and the magnetic layer 11b. The insulating layer portion 16 is a nonmagnetic layer. The first lead line 15a is formed on the insulating layer 12c, and is electrically connected to one end on the spiral center side of the first planar spiral line 13a through a via electrode 14a formed in the insulating layer 12a. . The second lead-out line 15b is formed on the insulating layer 12d, and is electrically connected to one end on the spiral center side of the second planar spiral line 13b through a via electrode 14b formed in the insulating layer 12d. ing. The other ends of the first planar spiral line 13a and the second planar spiral line 13b are led out to one side surface of the base 2 and connected to separate electrode terminals 1 to form a pair of input terminals or a pair of output terminals. To do. On the other hand, the other ends of the first lead-out line 15a and the second lead-out line 15b are led out to the other side face opposite to the one side face of the base 2 and connected to separate electrode terminals 1, respectively, and a pair of output terminals Alternatively, a pair of input terminals is configured.

  FIGS. 1A and 1B show the configuration of the terminal electrode of the common mode filter having the configuration shown in FIG. Further, as shown in FIG. 1C, four main surfaces 3 of the wiring board 17 on which the common mode filter is mounted are provided with four terminals for electrical connection with terminal electrodes formed on the common mode filter. Electrode pads are respectively formed at positions corresponding to the terminal electrodes of the common mode filter. The electrode pad is formed larger than the mounting surface side portion of the terminal electrode of the common mode filter. As shown in FIG. 1 (d), the electrode pad protrudes when the common mode filter is mounted. ing. The terminal electrode 1 of the common mode filter and the electrode pad 4 of the circuit board are electrically joined by solder (not shown). Further, illustration of wiring portions on the circuit board connected to the electrode pads is omitted. As shown in FIG. 1F, the ground electrode 6 is widely formed on the other main surface 5 of the circuit board 17 including the common mode filter mounting portion.

  Here, in the embodiment shown in FIG. 1, the electrode non-formation portion 7 in which the ground electrode is not formed is formed on the other main surface 5 of the circuit board 17. Moreover, the electrode non-forming portion 7 includes a plurality of interposed portions 8 located between the base 2 of the common mode filter and one main surface 3 of the terminal electrode 1 and the electrode pad 4 in a plan view. Is formed. Here, as shown in the sectional view (e), the intervening portion refers to the portion of the terminal electrode 1 that is sandwiched between the base 2 and one main surface 3 and the base of the electrode pad 4. 2 and a portion located between one main surface 3 and the main surface 3. The horizontal line portion shown in FIG. 1 (f) becomes the interposed portion 8, and the portion corresponding to the portion surrounded by the dotted line in the electrode pad does not become the interposed portion. As shown in FIGS. 1E and 1F, the electrode non-forming portion 7 is formed so as to include the interposed portion 8 in a plan view as viewed from a direction perpendicular to the main surface of the circuit board. On the other main surface of the substrate 17, there is no ground electrode facing the interposed portion 8. Among the electrode portions related to the common mode filter and its mounting, the interposed portion is close to the other main surface, and it is easy to form a parasitic capacitance. On the other hand, by providing the above-described configuration relating to the electrode non-forming portion, it is difficult to form parasitic capacitance.

  Furthermore, the embodiment shown in FIG. 1 is characterized in that the electrode non-forming portion 7 is formed by being divided into two by the ground electrode. If the ground electrode is not formed on the entire portion facing the common mode filter in order to suppress the parasitic capacitance caused by the interposed portion, the shielding effect by the ground electrode is impaired, and noise enters and exits significantly. End up. In addition, when there is a common mode return current via the ground electrode, the return current bypasses the periphery where the ground electrode is removed, so the current is concentrated and the path becomes longer, which may be a new noise source. . On the other hand, as shown in FIG. 1, the electrode non-formation part 7 formed so as to include the interposed part 8 in a plan view is divided and formed, and a ground electrode is formed between the divided electrode non-formation parts. Is preferably provided. Since all the ground electrodes facing the common mode filter are not removed, the shielding effect is also maintained, and the path of the common mode return current is shortened, contributing to the dispersion of the current. In the embodiment shown in FIG. 1, each electrode non-forming portion is configured to include an interposed portion related to a pair of input terminals and an interposed portion related to a pair of output terminals. In addition, the electrode non-forming portion 7 is formed so as to include the interposed portion 8 in plan view. However, if this is too large, the characteristic impedance of the microstrip line changes, so the area of the electrode non-forming portion 7 is As long as the installation part 8 is included, it is more preferable to make it necessary minimum. For example, the outer edge of the electrode non-forming part 7 and the outer edge of the interposed part 8 may be substantially matched.

  In the embodiment shown in FIG. 1, since the common mode filter shown in FIG. 5 is used, the winding axis direction of the coil constituting the common mode filter is a direction substantially orthogonal to the ground electrode 6. In the coil having such a configuration, the ratio of the coil surface facing and close to the ground electrode is large, and it is easy to form a parasitic capacitance. However, in the configuration of FIG. The formation of parasitic capacitance can be suppressed. Therefore, the configuration of FIG. 1 is suitable for mounting a common mode filter having such a configuration. In FIG. 1, the common mode filter including the planar spiral coil illustrated in FIG. 5 is used. However, a common mode filter including a helical coil may be used. However, when a common mode filter including a planar spiral coil is used, the ratio facing the ground electrode formed on the other main surface of the circuit board 17 tends to be particularly large. Therefore, the configuration shown in FIG. 1 is particularly suitable when a common mode filter having a planar spiral coil is mounted.

(Second Embodiment)
FIG. 2 shows a second embodiment according to the present invention. The configuration shown in FIG. 2 is a configuration in which the electrode non-forming portion is divided and formed in the same manner as the configuration shown in FIG. It differs from the structure of FIG. 1 by the point formed so that it may contain. The configuration shown in FIG. 2 has an advantage that the path can be shortened when there is a common mode return current because the ground electrode is divided into the non-electrode forming portion and the line extending direction.

(Third embodiment)
The above electrode non-formation part should just divide | segment into 2 or more, and is not restricted to forming in 2 parts. FIG. 3 shows another embodiment in which the configuration of the electrode non-forming portion is different. 3A is also a front view of the common mode filter, FIG. 3B is a bottom view of the common mode filter, FIG. 3C is a plan view of one main surface of the circuit board, and FIG. Is a plan view of the main surface of the circuit board on which the common mode filter is mounted, (e) is a sectional view of (d), and (f) is a bottom view of the other main surface of the circuit board on which the common mode filter is mounted. The figure is shown. As shown in FIG. 3F, in this embodiment, the electrode non-formed portion is divided into four parts. That is, in this embodiment, the electrode non-forming portion is formed for each of the plurality of interposed portions 8 and separated from each other via the ground electrode. Also in this configuration, as shown in FIGS. 3E and 3F, the electrode non-forming portion 7 is formed so as to include the interposed portion 8 in a plan view as viewed from a direction perpendicular to the main surface of the circuit board. ing. In the case of such a configuration, the proportion of the electrode non-forming portion is further reduced as compared with the first embodiment shown in FIG. 1 while preventing the interposed portion 8 from facing the ground electrode on the other main surface of the circuit board 17. In addition, the proportion of the ground electrode can be increased. Therefore, the above-described effects relating to the shield and the return current can be more easily exhibited. In the configuration of FIG. 3, the size of the electrode pad 4 is slightly larger than that of the configuration of FIG. 1, and the electrode pad is larger than the mounting surface side portion of the terminal electrode. As shown to (e), the part from the center of the common mode filter which does not overlap with the terminal electrode 1 among the electrode pads 4 also corresponds to the interposed part.

(Fourth embodiment)
Next, another embodiment in which the configuration of the common mode filter is changed is shown in FIG. The embodiment shown in FIG. 4 has a configuration in which a wound surface-mounted common mode filter is used as the common mode filter. In the wound common mode filter, a base 2 made of a magnetic ferrite core is provided with a pair of windings 10, the ends of the winding are connected to the terminal electrode 1 on one side of the base 2, and the other side is connected to the other side. The magnetic ferrite core 9 is bonded. The terminal electrode on the opposite surface side of the substrate 2 is mounted on the circuit board 17 as the terminal electrode on the mounting surface side. The configuration and mounting method of the electrode non-forming part are the same as in the first embodiment. Also in this case, the electrode non-forming portion 7 includes a plurality of interposed portions 8 located between the terminal electrode 1 and the electrode pad 4 between the base 2 of the common mode filter and the one main surface 3 in a plan view. It is formed as follows. In the configuration shown in FIG. 4, the winding axis of the coil of the common mode filter is parallel to the ground electrode formed on the other main surface of the circuit board. By applying the above configuration according to the part, it is possible to suppress the parasitic capacitance caused by the terminal electrode.

  For example, a normal printed wiring board (PCB) may be used as the circuit board according to the present invention. The circuit board may be a single layer board or a multilayer board. In the case of a multilayer board, the board of each layer constituting the multilayer board corresponds to the circuit board in the present invention. Therefore, in this case, for example, the ground electrode formed between the substrates of the multilayer substrate corresponds to the ground electrode formed on the other main surface. The coil component may be of an array type in which a plurality of coil portions are formed in one chip, such as a common mode filter array.

  The manufacturing method of the coil component represented by the common mode filter is not particularly limited. An example of the manufacturing method will be described with reference to FIG. For the magnetic layers 11a and 11b, a ferrite sintered plate substrate is processed into a predetermined thickness and size. An insulating layer 16 made of a heat-resistant resin such as polyimide, planar spiral lines 13a and 13b made of silver or copper, and lead lines 15a and 15b are laminated on the ferrite substrate as the magnetic layer 11a by photolithography. The lead line and the planar spiral line are electrically connected by vias or the like. A ferrite substrate is bonded thereon as the magnetic layer 11b. For example, the bonding is performed using an adhesive. After cutting, the electrode terminal 1 is formed outside the chip by plating, sputtering, coating, or the like. For the insulating layer 16, the planar spiral lines 13a and 13b, and the lead lines 15a and 15b, an LTCC process in which a silver paste is printed on a ceramic green sheet, laminated, and fired may be applied. The coil component according to the present invention may be manufactured by a multilayer flexible substrate in which thin sheets of polyimide or the like on which an electrode pattern is formed are bonded and laminated.

  The circuit board using a common mode filter as a coil component can be widely applied to a differential transmission device such as a device having a transmission and / or reception function of differential transmission and a cable. By mounting the circuit board of the present invention on a DVD player, a digital TV, an HDTV, a display, a projector or the like that performs differential transmission, it contributes to high performance of these devices.

It is a figure which shows one Embodiment of the circuit board of this invention. It is a figure which shows other embodiment of the circuit board of this invention. It is a figure which shows other embodiment of the circuit board of this invention. It is a figure which shows other embodiment of the circuit board of this invention. It is a figure which shows an example of the common mode filter mounted in the circuit board of this invention.

Explanation of symbols

1: Terminal electrode 2: Base body 3: One main surface 4: Electrode pad 5: The other main surface 6: Ground electrode 7: Electrode non-formation part 8: Interposition part 9: Magnetic ferrite core 10: Winding 11a, 11b : Magnetic layers 12a, 12b, 12c, 12d: Insulating layers 13a, 13b: Planar spiral lines 14a, 14b: Via electrodes 15a, 15b: Lead lines 16: Insulating layers 17: Circuit boards

Claims (6)

A circuit board in which a coil component is mounted on one main surface and a ground electrode is formed on the other main surface,
The terminal electrode formed on the base of the coil component and the electrode pad formed on one main surface of the circuit board are electrically connected,
No electrode is formed on the other main surface so as to include a plurality of interposed portions between the terminal electrode and the electrode pad between the base of the coil component and the one main surface in a plan view. Part is formed,
The circuit board according to claim 1, wherein the electrode non-forming portion is divided into two or more by the ground electrode.   The circuit board according to claim 1, wherein the electrode non-forming portion is formed for each of the plurality of interposed portions and is spaced apart from each other via the ground electrode.   The circuit board according to claim 1 or 2, wherein a winding axis direction of a coil constituting the coil component is a direction substantially orthogonal to the ground electrode.   The circuit board according to claim 1, wherein the coil is a planar spiral coil.   The circuit board according to claim 1, wherein the coil component is a common mode filter.   A differential transmission device on which the circuit board according to claim 5 is mounted.

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