JP2006278448A - Wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wiring board having proper transmission characteristics of high-frequency signals. <P>SOLUTION: In the wiring board, a signal line 2 is located inside an insulating substrate 1 and a conductor layer 5, a part of which faces the signal line 2, is located between the signal line 2 and one principal plane of the insulation substrate 1, and a connection pad 3 electrically connected to the signal line 2 via a via conductor 4 extended via a region, where the conductor layer 5 is not formed is formed on one principal plane of the insulation substrate 1. The connection pad 3 is so arranged such that the periphery thereof overlaps the conductor layer 5 in top view, with an air gap 1a formed in between the connection pad 3 and the conductor layer 5 in the overlapped portion 1c. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a wiring board for mounting electronic components such as semiconductor elements and capacitive elements.

  Conventionally, as wiring boards used for mounting electronic components such as semiconductor elements and capacitive elements, ceramic sintered bodies such as aluminum oxide sintered bodies and glass ceramic sintered bodies, epoxy resins, polyimide resins, etc. An insulating substrate made of an electrically insulating material such as an organic resin or a composite material formed by bonding an inorganic powder such as aluminum oxide with an organic resin such as an epoxy resin, and a metal material such as tungsten, molybdenum, copper, or silver, A signal line for signal transmission formed on the insulating substrate, a connection pad formed on one main surface of the insulating substrate, a via conductor formed so as to electrically connect the signal line and the connection pad, and a signal The thing of the structure which comprised the conductor layer formed in the inside of the insulated substrate facing the track | line was known. The conductor layer is disposed between the signal line and one main surface of the insulating substrate, and has a function of generating an electrostatic capacitance (capacitance) between the signal line and controlling the impedance of the signal line.

  In such a wiring board, an electronic component is mounted on another main surface or the like opposite to one main surface of an insulating substrate provided with a connection pad, and an electrode of the electronic component is bonded to an exposed portion of a signal line with a bonding wire, solder, or the like. And an electronic device is configured by sealing the electronic component with a lid, a sealing resin, or the like.

  Electronic components include semiconductor integrated circuit elements such as IC and LSI, LD (semiconductor laser), LED (light emitting diode), PD (photodiode), CCD (charge coupled device), line sensor, image sensor, etc. Semiconductor elements, semiconductor elements for MEMS (Micro Electro Mechanical System), vibrators such as piezoelectric vibrators and crystal vibrators, capacitive elements, and other various electronic components are used. Used as a part of electronic devices such as telephones, computers and routers.

  Then, the connection pads of such an electronic device are electrically and mechanically connected to the connection terminals of the external electric circuit board via a bonding material such as solder, so that the electrodes of the electronic components are connected to the signal lines, via conductors and It is electrically connected to the external electric circuit board via the connection pad.

The connection pad requires a relatively large area in order to secure the connection strength to the external electric circuit board, and is formed to have a circular shape with a diameter of about 0.8 mm, for example.
JP 2003-142627 A JP 2002-314028 A

  In recent years, for example, high-frequency signals of 800 MHz to several tens of GHz band have to be transmitted along with higher frequency of signals used in electronic devices such as high-speed computing of computers, high-speed Internet communication or in-vehicle collision prevention sensors. Has arisen.

  However, when the area of the connection pad is increased as in the conventional wiring board described above, when a high frequency signal is transmitted, a capacitance is generated between the connection pad and the conductor layer located immediately above the connection pad. In this portion, the impedance of the connection pad is lowered, impedance mismatching occurs, high-frequency signals are not transmitted well, and it is impossible to ensure electrical reliability.

  The present invention has been devised in order to eliminate the above-mentioned drawbacks, and an object of the present invention is to provide a wiring board that has good high-frequency signal transmission characteristics and can be reliably connected to an external electric circuit board. It is in.

  In the wiring board of the present invention, a signal line is disposed inside an insulating substrate, and a conductor layer partially opposed to the signal line is disposed between the signal line and one main surface of the insulating substrate. A wiring board comprising a connection pad electrically connected to the signal line via a via conductor penetrating a non-formation region of the conductor layer on one main surface of the board, and an outer peripheral portion of the connection pad However, it is disposed so as to overlap with the conductor layer in a plan view, and a gap is provided between the connection pad and the conductor layer of the overlapping portion.

  In the wiring board of the present invention, an opening surrounding the connection pad and communicating with the gap is provided on one main surface of the insulating substrate, and a part of the conductor layer is exposed inside the opening. It is characterized by being.

  Furthermore, the wiring board of the present invention is characterized in that the conductor layer is a ground conductor layer or a feed conductor layer.

  The wiring board according to the present invention is configured so that the outer peripheral portion of the connection pad is arranged so as to overlap the conductor layer in a plan view, and the gap is provided between the connection pad and the conductor layer of the overlap portion. Air having a low dielectric constant exists in a part of the insulating substrate (dielectric) interposed between the pad and the conductor layer, thereby reducing the generation of capacitance between the connection pad and the conductor layer, and the impedance of the connection pad. Reduction can be effectively suppressed. Therefore, it is possible to obtain a wiring board with excellent impedance matching and excellent high-frequency signal transmission characteristics.

  Further, according to the wiring board of the present invention, since the outer peripheral portion of the connection pad is arranged so as to overlap the conductor layer in a plan view, a non-formation region for preventing an electrical short circuit with the via conductor is provided. Except for this, it is possible to generate a capacitance with the signal wiring with a sufficient length, and thereby the impedance of the signal line can be effectively controlled.

  Furthermore, according to the wiring board of the present invention, an opening surrounding the connection pad and communicating with the gap is provided on one main surface of the insulating substrate, and a part of the conductor layer is exposed inside the opening, thereby connecting Air can be interposed between the conductor layer and the connection pad at a portion surrounding the pad, and the capacitance between the connection pad and the conductor layer can be further reduced. Thereby, the impedance reduction of the connection pad can be prevented more effectively, and the transmission characteristics of the high frequency signal can be further improved.

  Furthermore, according to the wiring board of the present invention, by using the conductor layer as a ground conductor layer or a feeding conductor layer, the conductor layer is a so-called solid wiring in which only the periphery of other signal line via conductors is not formed. can do. Thereby, wherever the signal line is formed in the same layer, the capacitance with the signal line inside the wiring board can be made substantially constant, and the impedance with the signal line can be efficiently maintained.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a sectional view showing an example of an embodiment of a wiring board according to the present invention. In FIG. 1, 1 is an insulating substrate, 2 is a signal line, 3 is a connection pad, 4 is a via conductor, 5 is a conductor layer, 1a is a gap formed in the insulating substrate 1, these insulating substrate 1, signal line 2, the wiring board 9 is constituted by the connection pads 3, the via conductors 4, the conductor layer 5, and the gap 1a.

  The insulating substrate 1 is an aluminum oxide sintered body, a glass ceramic sintered body, an aluminum nitride sintered body, a ceramic sintered body such as a mullite sintered body, an organic resin such as an epoxy resin or a polyimide resin, or an aluminum oxide. Etc. are formed of an electrically insulating material such as a composite material formed by bonding an inorganic powder such as an epoxy resin with an organic resin.

  When the insulating substrate 1 is made of, for example, an aluminum oxide sintered body, it is manufactured as follows. First, an appropriate organic binder and solvent are added to and mixed with raw material powders such as aluminum oxide, silicon oxide, calcium oxide, and magnesium oxide to produce a mud-like ceramic slurry. A ceramic green sheet (ceramic green sheet) is obtained by forming a sheet by employing the sheet forming technique. Thereafter, ceramic green sheets are laminated in the predetermined order in the vertical direction to form a green ceramic molded body. The green ceramic body is fired in a reducing atmosphere at a high temperature of about 1600 ° C., whereby the insulating substrate 1 is manufactured.

  The insulating substrate 1 has a signal line 2 and a conductor layer 5 inside, and a plurality of connection pads 3 on the main surface, and a plurality of via conductors 4 that electrically connect the signal line 2 and the connection pads 3 to each other. Is formed so as to penetrate through the non-formation region of the conductor layer 5. The reason why the conductor layer 5 is not formed in the portion where the via conductor 4 penetrates is to avoid an electrical short circuit between the via conductor 4 and the conductor layer 5.

  Further, the signal line 2, the conductor layer 5 and the connection pad 3 are made of a metal material such as tungsten, molybdenum, copper, silver, or palladium. For example, when made of tungsten, an organic solvent and a binder are added to and kneaded with tungsten powder. The produced metal paste is formed by printing in a predetermined pattern on a ceramic green sheet to be the insulating substrate 1.

  The signal line 2, the connection pad 3, and the via conductor 4 are electrically connected to the electrodes of the electronic component and function as conductive paths that lead out to the outside.

  The conductor layer 5 forms a predetermined capacitance with the signal line 2 and functions to control the impedance of the signal line with this capacitance.

  In this case, the above-mentioned non-formation region of the conductor layer 5 is preferably wide in order to prevent an electrical short circuit with the via conductor 4, but if it is too wide, the function of controlling the impedance of the signal line 2 is hindered. Therefore, it is preferable to make the non-formation region as narrow as possible within the range in which an electrical short circuit between the via conductor 4 and the conductor layer 5 can be effectively prevented. When the insulating substrate 1 is made of a ceramic material such as an aluminum oxide sintered body, the non-formation region is formed from the side surface of the via conductor 4 to the outside, for example, in the range of about 50 μm to 150 μm. Further, in the non-formed region, it is preferable that the distance from the side surface of the via conductor 4 to the outer edge (conductor layer 5) of the non-formed region is substantially equal throughout the circumference of the via conductor 4.

  In addition, the via conductor 4 is preferably formed so that the cross section (cross section perpendicular to the direction in which the signal is transmitted) has a circular shape from the viewpoint of high frequency characteristics, and the size is 50 μm to 200 μm in diameter. It is desirable to set the degree. In this case, as described above, the non-formation region is preferably arranged concentrically with the via conductor 4 and is formed in an annular shape having an inner diameter of about 250 μm and an outer diameter of about 800 μm concentrically with the via conductor 4. It is particularly desirable.

  The via conductor 4 is made of the same metal material as that of the signal line 2 and the conductor layer 5. For example, a via hole is previously formed in a portion of the ceramic green sheet to be the insulating substrate 1 where the connection pad 3 is formed. The ceramic green sheet is formed by printing and filling a metal paste similar to the metal paste used for forming the signal line 2 by a conventionally known screen printing method in the surface and in the through hole.

  The wiring board 9 has an electronic component (not shown) mounted on the main surface of the insulating substrate 1, and the electrodes of the electronic component are electrically connected to the signal line 2 and the conductor layer 5 via bonding wires or solder. An electronic device such as an RF module is configured by sealing electronic components with a lid or a sealing resin as necessary, and the connection pad 3 is connected to an external electric circuit board (not shown) as a connection terminal Are connected to each other via a connecting material made of solder or the like, whereby the electrodes of the electronic component are electrically connected to an external electric circuit via the signal line 2, the via conductor 4 and the connection pad 3.

  Note that the signal line 2 transmits a high-frequency signal of 800 MHz to several tens GHz or the like for oscillation in an RF module, for example. In addition to such a high-frequency signal, a signal line for transmitting a low-frequency signal such as a KHz band may be formed.

  Further, the conductor layer 5 is disposed between the signal line 2 and one main surface of the insulating substrate 1 so as to partially face the signal line 2. Thereby, the capacitance between the signal line 2 and the conductor layer 5 is kept constant, and the impedance of the signal line 2 is kept substantially constant. Thereby, a high frequency signal can be transmitted through the signal line 2.

And the connection pad 3 of the wiring board 9 mentioned above is arrange | positioned so that the outer peripheral part may overlap with the conductor layer 5 seeing through a plane, Between the connection pad 3 and the conductor layer 5 of this superimposition part 1c, Therefore, air having a low dielectric constant (for example, aluminum oxide material) is formed in a part of the insulating substrate 1 (dielectric) interposed between the connection pad 3 and the conductor layer 5 located in the overlapping portion 1c. Therefore, the generation of capacitance between the connection pad 3 and the conductor layer 5 is reduced, and the connection pad 3 has a portion that is less than the dielectric constant of the ceramics such as a sintered body. It is possible to match the impedance by suppressing the occurrence of the problem that the impedance is lowered, and to provide the wiring board 9 having excellent high-frequency signal transmission characteristics.

  The shape of the gap 1a is an annular or elliptical ring shape, a rectangular frame shape, a combination of a plurality of straight lines and curves, etc. in plan view, and in particular, a shape having no corners such as an annular shape and an elliptical ring shape. When the connection pad 3 is connected to an external electric circuit, it is preferable because the stress concentration is small.

  In order to achieve better impedance matching, the gap 1a is preferably disposed so as to surround the connection pad 3 all around, but a part thereof may be connected to the insulating substrate 1 in plan view. Absent.

  Further, when the gap 1a has a shape with an inner periphery and an outer periphery surrounding the connection pad 3, such as an annular shape or an elliptical shape, in plan view, the shape is different between the inner periphery and the outer periphery. May be.

  When the gap portion 1a is formed in a ring shape or a frame shape, the outer circumference of the gap portion 1a is at least the outer circumference of the connection pad 3 in order to reduce the capacitance between the conductor layer 5 and the connection pad 3 and prevent the impedance from decreasing. It is preferable to provide it so that it may reach.

  However, if the gap 1a is too large, the strength of the insulating substrate 1 may be reduced. Therefore, when the gap 1a is extended outside the overlapping portion in plan view, the connection pad 3 It is preferable to set the width between the outer peripheral edge of the gap and the outer peripheral edge of the gap portion 1a to be about 150 μm.

  The distance between the inner periphery of the gap 1a and the via conductor 4 is preferably about 50 to 150 μm.

  Such a gap 1a is formed, for example, by forming the insulating substrate 1 by laminating a plurality of ceramic green sheets and forming an annular, frame-like through hole surrounding the via conductor 4, It is formed by laminating a plurality of ceramic green sheets so that the through holes communicate with each other vertically.

  The through-holes may have different dimensions depending on each layer, and the through holes are formed by laminating the largest one as the bottom layer, or by laminating the largest one as the bottom layer so that the smallest ones are arranged in order. May be.

  Further, it is not necessary to form the inner surface of the gap portion 1a as a vertical surface, and in consideration of securing the mechanical strength of the insulating substrate 1 around the gap portion 1a, productivity, etc. It may be a curved surface.

  The inner periphery of the gap 1a is closer to the outer edge of the via conductor 4 in plan view in order to reduce the capacitance between the conductor layer 5 and the connection pad 3 and prevent the impedance from decreasing. It is valid.

  Further, the above-described wiring board 9 is provided with an opening 1b surrounding the connection pad 3 and communicating with the gap 1a on one main surface of the insulating substrate 1, and a part of the conductor layer 5 is provided inside the opening 1b. Is exposed.

  As a result, the insulating substrate 1 (dielectric) does not exist between the conductor layer 5 and the connection pad 3 in the portion surrounding the connection pad 3, and only air exists. 5 can be further reduced, the problem that the impedance of the connection pad 3 is lowered can be suppressed more efficiently, and the wiring board 9 having extremely excellent high-frequency signal transmission characteristics can be provided. .

  As for the transmission of high-frequency signals, the lower the electrical resistance, the better the characteristics. Therefore, copper, silver or the like is suitable as the material of the signal line 2, and the pattern of the signal line 2 has a corner portion. A straight line with no corners is desirable, but when it is necessary to bend, it is desirable to form the bent part into an arc shape (design with a corner having a radius without corners).

  Further, when a plurality of signal lines 2 are formed, it is desirable to separate the signal lines as much as possible.

  Furthermore, the conductor layer 5 of the wiring board 9 described above is preferably used as a ground conductor layer or a feed conductor layer.

In this case, since the conductor layer 5 can be a so-called solid wiring in which only the periphery of the via conductor 4 for the other signal line 2 is not formed, the signal line 2 can be formed anywhere on the same layer.
The capacitance with the signal line 2 inside the wiring board 9 can be made constant, and the impedance of the signal line 2 can be efficiently maintained.

  Further, if the conductor layer 5 is a ground conductor layer or a power feeding conductor layer, the grounding or feeding power among the electrodes of the electronic component is electrically connected to the conductor layer to ground or feed the electronic component. This can be performed more efficiently, and electrical characteristics as a wiring board for mounting electronic components can be improved.

  In this case, the conductor layer 5 may be formed over a plurality of layers, and both the ground conductor layer and the feed conductor layer may be provided inside the insulating substrate.

  The connection pad 3 is preferably formed with a relatively large diameter in order to ensure the connection strength to the external electric circuit board. The connection pad 3 is preferably a circular shape without corners so that stress is evenly applied when connected to an external electric circuit and from the viewpoint of high-frequency transmission characteristics, and the size is preferably about 200 μm to 800 μm in diameter. .

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention.

  For example, in the non-formation region of the conductor layer 5, a coat layer made of the same insulating material as that for forming the insulating substrate 1 is formed with the same thickness as the conductor layer 5 to have the same height. It is also possible to improve the reliability by more reliably preventing the occurrence of such problems.

It is sectional drawing which shows an example of embodiment of the wiring board of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Insulating substrate 1a ... Air gap part 1b ... Opening 1c ... Overlapping part 2 ... Signal line 3 ... Connection pad 4 ... Via conductor 5 ... Conductor layer 9 ...・ Wiring board

Claims (3)

A signal line is disposed inside the insulating substrate, and a conductor layer partially opposed to the signal line is disposed between the signal line and one main surface of the insulating substrate, on one main surface of the insulating substrate, A wiring board provided with a connection pad electrically connected to the signal line through a via conductor penetrating a non-formation region of the conductor layer;
The wiring is characterized in that an outer peripheral portion of the connection pad is arranged so as to overlap the conductor layer in a plan view and a gap is provided between the connection pad and the conductor layer of the overlap portion. substrate. An opening surrounding the connection pad and communicating with the gap is provided on one main surface of the insulating substrate, and a part of the conductor layer is exposed inside the opening. The wiring board according to claim 1. The wiring board according to claim 1, wherein the conductor layer is a ground conductor layer or a power feeding conductor layer.

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