JP3554193B2 - High frequency wiring board and method of manufacturing the same - Google Patents

Description

【００６１】
但し、Ａ，Ｂ_１ 、Ｂ_２ は下記数２の（２）（３）（４）式により計算する。
【００６２】
【数２】

【００６３】
ここで、（１）式のｔａｎδ_１ とｔａｎδ_２ はそれぞれ誘電体円柱２３と誘電体基板２２の誘電正接、μは導体層２１の透磁率、ωは２πｆ_０ 、∬｜Ｈ｜^２ ｄＳは上下の金属層界面での磁界の積分、Ｗ^ｅ は共振器の電界エネルギー、Ｗ_ｄ１ ^ｅ とＷ_ｄ２ ^ｅ は誘電体円柱２３内と誘電体基板２２内の電界エネルギーである。
【００６４】
なお、Ｗ^ｅ 、Ｗ_ｄ１ ^ｅ 、Ｗ_ｄ２ ^ｅ の計算に必要な誘電体円柱２３と誘電体基板２２の比誘電率ε’_１、ε’_２やｔａｎδ_１ とｔａｎδ_２ は前記文献１に開示された誘電体円柱共振器法や、小林、佐藤らの「信学技法ＭＷ８７−７」（１９８７年）に開示された空洞共振器法によって測定する。
【００６５】
なお、図２の誘電体円柱２３としてＣ軸に垂直な端面を持つサファイア（直径ｄ＝１０．０００ｍｍ、高さｔ＝５．００４ｍｍ）を使用した。この測定結果を中心導体の誘電体基板接着面の界面導電率として表１に示した。
【００６６】
実施例２
誘電体基板として、アルミナを９３重量％、または９９．５重量％、残部がＳｉＯ_２ 、ＣａＯ，ＭｇＯの助剤成分からなる混合粉末をシート状に成形し、その表面にタングステンペーストを用いてスロット孔を有するグランド層のパターンに印刷塗布し、その表面にグリーンシートを積層一体化した後、これを１６５０℃にて焼成して、グランド層を有するセラミック基板を作製した。
【００６７】
そして、このセラミック基板に対して、適宜鏡面研磨した後、実施例１と全く同様にして誘電体基板の表裏に中心導体を形成し、全長５０ｍｍで電磁結合部を２個含む伝送特性評価用の高周波用配線基板を作製し、実施例１と同様にして、１０ＧＨｚにおける伝送特性および１２ＧＨｚにおける中心導体の誘電体基板との界面導電率を測定した。結果は、表１に示した。
【００６８】
【表１】

【００６９】
表１に示すように、中心導体を誘電体基板と同時焼成によって形成した場合、界面導電率は３．１×１０^７ Ω^−１ｍ^−１と低く、伝送特性も低いものであったが、本発明に従い、中心導体を薄膜形成法によって形成することにより、界面導電率は３．７×１０^７ Ω^−１ｍ^−１以上となった。特に、表面粗さ（Ｒａ）が０．５μｍ以下の誘電体基板表面に薄膜形成法によって形成すると、σは４．０×１０^７ Ω^−１ｍ^−１と非常に高くなり、それと同時に、伝送特性も大きく向上した。
【００７０】
【発明の効果】
以上詳述した通り、本発明の高周波用配線基板は、誘電体基板の内部に形成されるグランド層を誘電体層との同時焼成により形成し、かつ誘電体基板の表面の中心導体を薄膜形成法によって形成することにより、前記中心導体の誘電体基板接着面の界面導電率を小さくでき、線路としての伝送損失を小さくできる。従って、この中心導体とグランド層を具備する線路を電磁結合構造を具備するパッケージに適用することにより、パッケージにおける高周波信号の伝送損失をさらに小さくできる。
【図面の簡単な説明】
【図１】本発明の高周波用配線基板の一例を示す概略断面図である。
【図２】本発明の高周波用配線基板における導体層の界面導電率測定に用いられる誘電体共振器の構造を示す概略図である。
【符号の説明】
１ 高周波用配線基板
２ 誘電体基板
３ 蓋体
４ キャビティ
５ 高周波素子
６ 第１の中心導体
７ 第２の中心導体
８、１０ グランド層
９ スロット孔
１１ ビアホール導体
２０ 誘電体共振器
２１ 導体層
２２ 誘電体基板
２３ 誘電体円柱[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a high-frequency wiring board on which a high-frequency circuit element in a microwave band to a millimeter-wave band is mounted. And a method for manufacturing the same.
[0002]
[Prior art]
Conventionally, a high-frequency package, which is a typical application example of a high-frequency wiring board that handles microwave or millimeter-wave signals, includes, for example, a high-frequency element in a space formed by a dielectric substrate and a lid made of a dielectric. Is housed and hermetically sealed.
[0003]
For the input and output of high-frequency signals of the high-frequency package having such a structure, usually, a signal transmission line such as a strip line electrically connected to the high-frequency element is pulled out from the inside of the space to the outside through a frame in the lid. This is further disposed on the bottom surface via the side surface of the dielectric substrate, and the connection terminal of the high-frequency package and the wiring layer of the external circuit substrate are connected via an adhesive such as solder. As another example, a high-frequency package in which connection terminals are formed on the bottom surface of a dielectric substrate of a high-frequency package and the connection terminals and the high-frequency element are connected through through holes has been proposed.
[0004]
There is also known a method of forming fine wiring by forming a conductor layer such as a wiring layer and a ground layer on a surface of a wiring board by a thin film forming method.
[0005]
[Problems to be solved by the invention]
When the high-frequency wiring board having the above-described configuration is used in the millimeter wave band, when a signal transmission line such as a strip line is drawn from the inside of the space to the outside through the frame, it is necessary to take impedance matching in the frame passing portion. Therefore, it is necessary to narrow the signal line width. As a result, there is a problem that reflection loss and radiation loss occur in the passing portion and the transmission characteristics of the high-frequency signal deteriorate. In addition, if a through hole is formed on the bottom surface of a dielectric substrate and used as a signal line, the characteristics are sharply degraded at 40 GHz or higher, so that it has been difficult to use it in a high frequency region.
[0006]
Therefore, the present inventors have proposed a wiring board which incorporates an electromagnetic coupling mechanism as a high-frequency wiring board and can transmit a signal line with low loss (Japanese Patent Application Laid-Open No. 9-186268).
[0007]
However, the method for manufacturing the high-frequency wiring board includes a ground layer, a wiring layer, a via hole, etc., which are provided in the dielectric substrate, a high-frequency wiring layer formed on the surface of the dielectric substrate, and a low-frequency signal transmission wiring. All of the conductor layers such as the layer and the ground layer are formed by printing a conductor layer on a dielectric sheet with a conductive paste, laminating the dielectric layers, and co-firing with the dielectric sheet.
[0008]
When the high-frequency wiring layer is formed by the above method, the firing must be performed at a temperature lower than the melting temperature of the conductor layer. Therefore, dielectric materials usable as the dielectric substrate are limited to those that can be fired at a low temperature. Further, since the simultaneous firing temperature of the dielectric sheet and the conductive paste is performed at a high temperature of 850 ° C. or more, diffusion of atoms occurs at the interface between the dielectric sheet and the conductive paste, and the smoothness of the interface is reduced. Since the dielectric substrate is damaged, there is a problem in that the dielectric substrate is discolored, the surface resistance of the conductor layer is increased, and the transmission characteristics of high-frequency signals are significantly reduced. Furthermore, sagging occurs at the end of the wiring layer, resulting in an increase in dielectric loss, a decrease in dimensional accuracy, and a variation in signals due to electromagnetic coupling.
[0009]
Therefore, an object of the present invention is to provide a high-reliability high-frequency wiring board which can reduce transmission loss in a high-frequency transmission line and has a simple structure and which can be miniaturized, and a method for manufacturing the same.
[0010]
[Means for Solving the Problems]
The present inventors have repeatedly studied a structure for reducing the loss in a high-frequency wiring board having a structure for transmitting signals by electromagnetic coupling, and as a result, have found that a ground layer formed inside a dielectric substrate is A central conductor formed on the surface of the dielectric substrate by simultaneous firing with a layer and a thin film forming method, and a line for transmitting a high-frequency signal is formed by electromagnetic coupling between the central conductor and the ground layer. However, the present inventors have found that the transmission loss of a high-frequency signal in a high-frequency transmission line can be reduced by employing this line in a package having an electromagnetic coupling structure previously proposed, and have accomplished the present invention.
[0011]
That is, the high-frequency wiring board of the present invention includes a ceramic dielectric substrate formed by laminating a plurality of dielectric layers, a center conductor provided on at least one surface of the dielectric substrate, and Transmits high-frequency signals by electromagnetic coupling with the provided ground layerConsists of microstrip line or coplanar line with groundAnd a high-frequency transmission line, wherein the ground layer is formed by simultaneous firing with the dielectric substrate, and the center conductor is formed by a thin film forming method. is there.
[0012]
Here, it is preferable that the thin film forming method is a vapor phase method such as vapor deposition, sputtering, CVD, ion plating, laser ablation, or a plating method.
[0013]
Further, in the dielectric substrate, the surface roughness (Ra) of the center conductor formation surface formed by the thin film formation method is 0.5 μm or less, and the interface conductivity of the center conductor to the dielectric substrate adhesion surface is 3.5 × 10 at 12 GHz⁷Ω^-1・ M^-1As described above, the thickness is desirably 50 μm or less.
[0014]
Further, it is desirable that the dielectric substrate is made of at least one selected from alumina ceramics, mullite ceramics, aluminum nitride ceramics, silicon nitride ceramics, silicon carbide ceramics and glass ceramics having an alumina content of 98% or more. .
[0016]
Further, as a specific example of the high-frequency wiring board of the present invention, a dielectric substrate composed of a plurality of dielectric layers, a high-frequency element mounted on one surface of the dielectric substrate, A first high-frequency transmission line formed by a first center conductor formed on the surface and having one end electrically connected to the high-frequency element, and a ground layer provided inside the dielectric substrate; and the dielectric substrate And a second high-frequency transmission line formed by the ground layer provided inside the dielectric substrate, wherein the second high-frequency transmission line is formed by the ground layer provided inside the dielectric substrate. It is characterized in that it has a structure that is electromagnetically coupled to a second high-frequency transmission line.
[0017]
Further, the method of manufacturing a high-frequency wiring board according to the present invention includes a step of applying a conductive paste to a ground layer pattern on at least one dielectric sheet surface; and a step of coating the dielectric sheet having the ground layer pattern formed thereon. A step of laminating another dielectric sheet on the surface, a step of simultaneously firing the laminate to form a dielectric substrate having a ground layer inside, and a step of forming a central conductor on the surface of the dielectric substrate by a thin film forming method. And a step of forming
[0018]
[Action]
According to the present invention, in a line such as a microstrip including a center conductor and a ground layer, in order to improve the transmission characteristics of the line, the interface resistance of the center conductor bonding surface of the dielectric substrate is reduced and the conductor It is important that the accuracy of the side edges is high. From this point of view, the present invention has found that it is effective to form the center conductor by a thin film forming method in order to reduce the interface resistance of the center conductor to the dielectric substrate bonding surface and increase the accuracy of the side end. .
[0019]
That is, when the central conductor to be the transmission line is formed by a thin film forming method, it can be formed at a low temperature of about 50 to 200 ° C. No diffusion and no roughening of the interface, preventing the increase in the interface resistance of the center conductor with the dielectric substrate and the discoloration of the dielectric substrate, which particularly affect the transmission characteristics of the conductor layer, and lowering the transmission characteristics of high-frequency signals. Can be suppressed.
[0020]
Also, since the dielectric substrate and the center conductor are formed separately, the firing temperature of the dielectric substrate may be equal to or higher than the melting temperature of the center conductor. It is possible to select a conductor that is optimal for the transmission characteristics.
[0021]
Furthermore, according to the thin film forming method, there is almost no sagging to the side end of the center conductor, so that dielectric loss can be reduced, and dimensional accuracy can be increased, so that signals due to electromagnetic coupling can be transmitted accurately and efficiently. Fine wiring is possible on the body surface.
[0022]
According to the wiring board of the present invention, since the first and second high-frequency transmission lines formed on the front and back of the dielectric substrate are electromagnetically coupled via the slot holes provided in the ground layer, the transmission line is made of a dielectric. Since it does not pass through the inside of a wall or pass through a through-hole conductor, it is possible to minimize reflection loss and radiation loss that occur when a high-frequency signal passes through the line, and to achieve low transmission loss. In addition, a semiconductor device that can be reduced in size can be provided. In addition, by forming the center conductor in the line by the thin film forming method, a good signal can be transmitted between the first and second high-frequency transmission lines due to the above-mentioned excellent operation and effect.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a schematic sectional view showing an example of a high-frequency semiconductor package structure which is a typical application example of the high-frequency wiring board according to the present invention.
According to FIG. 1, a high-frequency semiconductor package 1 has a cavity 4 formed by a dielectric substrate 2 made of a ceramic dielectric material and a lid 3, and a high-frequency device such as an MMIC or MIC is formed in the cavity 4. 5 is mounted.
[0024]
According to the present invention, the first center conductor 6 electrically connected to the high-frequency element 5 is formed on the surface of the ceramic dielectric substrate 2 in the cavity 4 of the semiconductor device. A second center conductor 7 is formed on the other surface of the substrate 2.
[0025]
On the other hand, a ground layer 8 is formed in substantially the entire surface of the dielectric substrate 2 by simultaneous firing with the ceramic dielectric substrate 2, and both the first center conductor 6 and the second middle conductor 7 A microstrip line that transmits a high-frequency signal by electromagnetic coupling between the center conductor and the ground layer is formed. Note that a pair of ground layers may be provided on both sides of the center conductors 6 and 7 to form a grounded coplanar line.
[0026]
Further, a slot hole 9 is formed in the ground layer 8, and the first center conductor 6 and the second center conductor 7 are separated from each other by the terminal holes of the center conductors 6 and 7 via the slot hole 9. Are formed so as to face each other in the arrangement as shown in FIG. 1, so that the first center conductor 6 and the second center conductor 7 are electromagnetically coupled, and the first center conductor 6 and the second center conductor The transmission of a small loss signal is performed.
[0027]
More specifically, the center conductors 6 and 7 via the slot holes 9 may be formed at opposing positions where the center conductors overlap with each other at a half wavelength of a required frequency transmission signal with the slot holes 9 interposed therebetween. Desirably, the shape of the slot hole 9 is a rectangular hole having a long side and a short side, and the size thereof is appropriately set according to a used frequency and a frequency bandwidth. In particular, the long side of the slot hole is desirably set to a length corresponding to １ ／ wavelength of the signal frequency, and the short side of the slot hole is set to a length corresponding to １ ／ wavelength to 1/50 wavelength. desirable.
[0028]
According to the present invention, these first and second center conductors 6 and 7 are both formed by a vapor phase method such as vapor deposition, sputtering, CVD, ion plating, or laser ablation, or a thin film forming method such as a plating method. The main feature is that by forming this central conductor by a thin film forming method, the conductivity at the interface with the ceramic dielectric substrate 2 can be improved, and the highly accurate side end surface can be formed. Therefore, the transmission characteristics as a micro-toslip line or a grounded coplanar line formed by the center conductors 6 and 7 and the ground layer 8 can be improved, and the first center conductor 6 and the second center conductor 7 are provided. The electromagnetic coupling between the respective lines can be enhanced.
[0029]
The thickness of the center conductors 6 and 7 is preferably 0.5 to 50 μm, particularly 0.5 to 25 μm, and more preferably 0.5 to 10 μm. This is because if the thickness is less than 0.5 μm, the conductor resistance increases, so that transmission loss in the center conductor increases.If the thickness is more than 50 μm, sag occurs on the side end surface of the center conductor, and the dielectric loss increases, This is because roughness is generated at the side end and the dimensional accuracy is deteriorated, so that signal variation due to electromagnetic coupling occurs and the cost is increased.
[0030]
In addition, in order to improve the signal transmission characteristics and electromagnetic coupling of the line having the above-mentioned center conductors 6 and 7, the interface conductivity between the first center conductor 6 and the second center conductor 7 and the dielectric substrate 2 is improved. σ is 3.5 × 10⁷Ω^-1・ M^-1Above, especially 4.0 × 10⁷Ω^-1・ M^-1It is desirable that this is the case.
[0031]
In order to control the interface conductivity σ with the dielectric substrate 2 within the above range, the surface roughness (Ra) of the dielectric substrate 2 when the center conductors 6 and 7 are formed by the thin film forming method is set to 0. It is preferably not more than 0.5 μm, especially not more than 0.3 μm, and more preferably not more than 0.2 μm. As described above, by setting the surface roughness (Ra) of the center conductor forming surface within the above range, the conductivity of the center conductor at the interface with the dielectric substrate can be improved, and the accuracy of the side end portion can be improved. In addition, signal transmission loss in a microstrip line or a coplanar line having a center conductor is reduced. As a result, by applying the high-frequency transmission line having such a configuration to the high-frequency package having the above-described electromagnetic coupling structure, excellent transmission with small transmission loss can be achieved between the first center conductor and the second center conductor. Characteristics are obtained.
[0032]
In addition, from the viewpoint of increasing the interface conductivity and reducing the transmission loss of a high-frequency signal, the first center conductor 6 and the second center conductor 7 are made of low-resistance conductors such as Cu, Ag, and Au as conductors. It is desirable to use.
[0033]
At this time, a buffer film made of a metal compound such as Ta, Ti, Ni, Cr, or Pd may be formed on the dielectric substrate side in order to enhance the adhesion to the dielectric substrate 2. When Cu is used as the wiring layer, it is desirable to plate the surface of the wiring layer with Au or the like to prevent oxidation.
[0034]
In the wiring board of the present invention, the dielectric material constituting the dielectric substrate 2 includes alumina ceramics, mullite ceramics, aluminum nitride ceramics, silicon nitride ceramics, silicon carbide ceramics, and glass ceramics having an alumina content of 98% or more. It is desirable to use a material having a small dielectric loss even in a high frequency region such as the above. In particular, glass ceramics and high-purity alumina ceramics are preferably used in that they have excellent surface smoothness when the dielectric substrate surface is baked. In particular, for alumina ceramics, the dielectric loss (tan δ) at 10 GHz is 10 × 10 when the alumina content is about 90%.^-4, 5 × 10 when the alumina content is 98% or more^-4When the alumina content is 99% or more, 3 × 10^-4In particular, it is desirable to use a high-purity alumina ceramic having an alumina content of 99% or more because of the following.
[0035]
Since the ground layer 8 is formed by simultaneous firing with the dielectric substrate 2, the dielectric layer 2 is formed from a metal group used as a low-resistance conductor such as Ag, Cu, or Au, or a normal conductor such as W or Mo. A metal that can be co-fired is used in accordance with the material of.
[0036]
The lid 3 is made of a conductive material capable of preventing the electromagnetic wave from the cavity 4 from leaking to the outside or leaking the electromagnetic wave to the outside, and a metal, a conductive ceramic, a ceramic metal composite material or the like can be used. Alternatively, a conductive material may be applied to the surface of the insulating base, but a metal is preferred from the viewpoint of cost.
[0037]
In the high-frequency wiring board 1 of the present invention, the first and second center conductors 6 and 7 are paired on the surface of the dielectric substrate 2. It may be formed. Further, a ground layer, a capacitor, a resistor, an inductor, and the like, a low-frequency transmission line, and the like may be formed on the surface or inside of the dielectric substrate 2 by simultaneous firing or a thick film forming method. In addition, inside the dielectric substrate 2, via holes and low-frequency transmission lines may be formed by simultaneous firing in addition to the ground layer 8. However, capacitors, resistors, inductors, low-frequency transmission lines, ground layers, and the like formed on the surface of the dielectric substrate are desirably formed together with the central conductor by a thin-film forming method.
[0038]
Further, the end of the second high-frequency transmission line formed on the bottom surface of the dielectric substrate 2 is connected to another first center conductor connected to another high-frequency element by electromagnetic coupling or the like, and the like. It is also possible to form a module substrate provided with the high-frequency element described above.
[0039]
In addition to the high-frequency wiring substrate 1 having a structure in which the high-frequency element 5 shown in FIG. 1 is hermetically sealed in a cavity 4 formed by the dielectric substrate 2 and the lid 3, instead of using the lid, Alternatively, the high-frequency element 5 may be resin-sealed on the surface of the dielectric substrate 2 with a resin such as an epoxy resin.
[0040]
In addition, a ground layer 10 is formed on the surface of the dielectric substrate 2 at the interface with the lid 3, and is electrically connected to the ground layer 8 via the via-hole conductor 11, so that the high-frequency element 5 and the first central conductor 6 are formed. Is electromagnetically shielded from the outside, malfunctions due to the influence of external electromagnetic waves and adverse effects on adjacent circuits can be prevented, and the reliability of the high-frequency wiring board can be improved.
[0041]
The high-frequency element 5 can be connected without transmission loss by being directly mounted on the center conductor 6 with solder, gold bumps, or the like, but is not limited to this. Can be connected by a wire bonding, or can be connected to a substrate made of polyimide or the like by a conductor plate having a conductor made of Cu or the like, or can be flip-chip mounted.
[0042]
Next, a method for manufacturing the high-frequency wiring board of the present invention will be described.
(1) A raw material of a substance constituting the dielectric substrate 2 is mixed, an organic binder is added, and then a sheet is formed to form a dielectric sheet.
[0043]
(2) A conductor paste containing a metal constituting the ground layer 8 is printed on at least one layer of the surface of (1) on a ground layer pattern having slot holes by a screen printing method or the like, and if necessary, the dielectric material is used. A through hole is formed in a predetermined portion of the sheet and the conductive paste is filled.
[0044]
(3) The dielectric sheet of (1) is laminated on the surface of the sheet of (2) and pressed. At this time, when there are a plurality of sheets (2), the sheets are stacked while being aligned.
(4) The laminate of (3) is fired.
[0045]
(5) Wiring patterns of the center conductors 6 and 7 having a thickness of 0.5 to 50 μm are formed on both surfaces of the ceramic substrate obtained in (4) by a thin film forming method. As a method of forming a thin film, a method of forming a wiring pattern by a vapor phase method such as vapor deposition, sputtering, CVD, ion plating, or laser ablation using a mask on the surface of the dielectric substrate 2, plating on the surface of the dielectric substrate 2 After a conductor film is formed by a method such as the above, a metal foil is formed on another film by a method of forming a wiring pattern by a photolithography method and plating, and the wiring patterned by a photolithography method is transferred to the surface of the dielectric substrate 2. Is desirable.
[0046]
At the time of forming the thin film, it is desirable that the surface roughness (Ra) of the ceramic substrate is 0.5 μm or less. In order to achieve such surface roughness, the surface of the obtained ceramic substrate is mirror-polished. Alternatively, a ceramic substrate material that can form a smooth baked surface without mirror polishing is selected.
[0047]
The low-frequency signal transmission lines other than the center conductors 6 and 7 and the ground layer 8, the ground layer, and the conductor layers such as resistors, capacitors, and inductors are formed on the surface of the dielectric substrate 2 from the viewpoint of simplicity of the process. It is preferable that the conductor layer to be formed is formed by a thin film forming method, and the conductor layer to be formed inside the dielectric substrate 2 is formed by simultaneous firing with the dielectric substrate 2.
[0048]
【Example】
Example 1 (1) A raw material containing 75% by weight of borosilicate glass and 25% by weight of alumina powder was mixed, an organic binder was added, and then formed into a sheet to form a green sheet.
[0049]
(2) A Cu paste was printed on the surface of (1) in a pattern of the ground layer 8 having slot holes.
[0050]
(3) The dielectric sheet of (1) was laminated on the surface of the sheet of (2) and pressed.
[0051]
(4) The laminate of (3) was fired at 920 ° C. in a nitrogen atmosphere. The surface roughness (Ra) of the obtained ceramic substrate was 0.78 μm.
[0052]
(5) A ceramic substrate having the average surface roughness (Ra) shown in Table 1 is prepared by appropriately mirror-finishing both surfaces of the ceramic substrate of (4), and then NiCr is 0.05 μm thick and made of Cu by sputtering. A wiring pattern of the center conductors 6 and 7 having a thickness of 2.3 μm was formed, and the surface thereof was plated with gold (the entire thickness of the center conductor was 3 μm).
[0053]
According to the above-mentioned method, a high-frequency wiring board having a total length of 50 mm and including two electromagnetic coupling portions was manufactured, and the transmission characteristics (measurement frequency 10 GHz) of the line end were measured with a network analyzer. The results are shown in Table 1.
[0054]
For comparison, the center conductors 6 and 7 were formed by applying a copper paste and then simultaneously firing the glass ceramic. The thickness of the center conductor was 15 μm. Then, the transmission characteristics were measured in the same manner as described above, and the results are shown in Table 1.
[0055]
Further, a conductor layer having the same thickness as the center conductor was formed on the entire surface of the dielectric substrate by the same thin film forming method as described above, and the interface conductivity between this conductor layer and the dielectric substrate was measured. The interface conductivity was measured by the dielectric cylinder resonator method described below.
[0056]
In this dielectric cylinder resonator method, a dielectric substrate in which a metal layer is applied to both end surfaces or one end surface of a dielectric cylinder made of a dielectric material whose relative dielectric constant and dielectric loss tangent are known, has a predetermined relationship. This is a method of measuring the conductivity at the interface between the metal layer and the dielectric substrate, that is, at the metal layer interface, by forming a dielectric resonator by attaching the dielectric resonators as described above.
[0057]
The principle of this measuring method is that a conductor plate (usually, the diameter of the dielectric cylinder, which is sufficiently large so that the edge effect is negligible) is provided on both end surfaces of the dielectric cylinder having a predetermined dimensional ratio (height t / diameter d). When a conductor plate having a diameter D about three times as large as d is provided in parallel and sandwiched to form an electromagnetic field resonator, TE_omnThis is because the high-frequency current flowing through the conductor plate in the resonance mode is distributed only on the short-circuit surface, that is, only at the interface between the dielectric and the conductor.
[0058]
More specifically, as shown in FIG. 2, a dielectric substrate 22 having a conductor layer 21 formed on the surface is attached to an end face of a dielectric cylinder 23 having a predetermined dimensional ratio (height t / diameter d). The dielectric resonator 20 is configured so that the dielectric substrate 22 of the wiring substrate is in contact with the end surface of the dielectric cylinder 23 and is sandwiched from both ends.
[0059]
In the dielectric resonator 20, TE_omnThe high-frequency current flowing through the conductor layer 21 in the mode (m = 1, 2, 3,..., N = 1, 2, 3,...) Is distributed only at the interface between the conductor layer 21 and the dielectric substrate 22. Using the measured TE_omnMode (m = 1, 2, 3,..., N = 1, 2, 3,...) Resonance frequency f₀And no-load Q and Qu, the interface conductivity σ is given by the following equation (1)._intCan be calculated.
[0060]
(Equation 1)

[0061]
However, A, B₁, B₂Is calculated by the following equations (2), (3) and (4).
[0062]
(Equation 2)

[0063]
Here, tan δ in equation (1)₁And tan δ₂Is the dielectric loss tangent between the dielectric cylinder 23 and the dielectric substrate 22, μ is the magnetic permeability of the conductor layer 21, and ω is 2πf.₀, ∬ | H |²dS is the integral of the magnetic field at the interface between the upper and lower metal layers, W^eIs the electric field energy of the resonator, W_d1 ^eAnd W_d2 ^eIs the electric field energy in the dielectric cylinder 23 and in the dielectric substrate 22.
[0064]
Note that W^e, W_d1 ^e, W_d2 ^eDielectric constant ε ′ of the dielectric cylinder 23 and the dielectric substrate 22 necessary for the calculation of₁, Ε '₂And tanδ₁And tan δ₂Is measured by the dielectric cylinder resonator method disclosed in the above-mentioned document 1 or the cavity resonator method disclosed in “Religion Technique MW87-7” by Kobayashi and Sato (1987).
[0065]
In addition, sapphire (diameter d = 10000 mm, height t = 5.004 mm) having an end surface perpendicular to the C axis was used as the dielectric cylinder 23 in FIG. The measurement results are shown in Table 1 as the interface conductivity of the center conductor on the dielectric substrate bonding surface.
[0066]
Example 2
As a dielectric substrate, 93% by weight or 99.5% by weight of alumina, the remainder being SiO₂, A mixed powder comprising auxiliary components of CaO and MgO was formed into a sheet, and the surface thereof was printed and coated with a tungsten paste on a pattern of a ground layer having slot holes, and a green sheet was integrally laminated on the surface. Thereafter, this was fired at 1650 ° C. to produce a ceramic substrate having a ground layer.
[0067]
Then, after appropriately mirror-polishing the ceramic substrate, center conductors are formed on the front and back surfaces of the dielectric substrate in exactly the same manner as in Example 1, and a total length of 50 mm is used for evaluating transmission characteristics including two electromagnetic coupling portions. A high-frequency wiring board was prepared, and the transmission characteristics at 10 GHz and the interface conductivity between the center conductor and the dielectric substrate at 12 GHz were measured in the same manner as in Example 1. The results are shown in Table 1.
[0068]
[Table 1]

[0069]
As shown in Table 1, when the center conductor was formed by simultaneous firing with the dielectric substrate, the interface conductivity was 3.1 × 10⁷Ω^-1m^-1However, according to the present invention, by forming the center conductor by a thin film forming method, the interface conductivity is 3.7 × 10⁷Ω^-1m^-1That's all. In particular, when formed on the surface of a dielectric substrate having a surface roughness (Ra) of 0.5 μm or less by a thin film forming method, σ becomes 4.0 × 10⁷Ω^-1m^-1And the transmission characteristics were greatly improved.
[0070]
【The invention's effect】
As described in detail above, the high-frequency wiring board of the present invention forms the ground layer formed inside the dielectric substrate by simultaneous firing with the dielectric layer, and forms the center conductor on the surface of the dielectric substrate into a thin film. By forming by the method, the interface conductivity of the center conductor on the dielectric substrate bonding surface can be reduced, and the transmission loss as a line can be reduced. Therefore, by applying the line having the center conductor and the ground layer to a package having an electromagnetic coupling structure, the transmission loss of a high-frequency signal in the package can be further reduced.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view showing an example of a high-frequency wiring board according to the present invention.
FIG. 2 is a schematic view showing the structure of a dielectric resonator used for measuring the interface conductivity of a conductor layer in a high-frequency wiring board according to the present invention.
[Explanation of symbols]
1 high frequency wiring board
2 Dielectric substrate
3 Lid
4 cavities
5 High frequency element
6 First center conductor
7 Second center conductor
8, 10 Ground layer
9 slot holes
11 Via hole conductor
20 Dielectric resonator
21 conductor layer
22 Dielectric substrate
23 Dielectric cylinder

Claims (12)

Electromagnetic coupling between a ceramic dielectric substrate formed by laminating a plurality of dielectric layers, at least a center conductor provided on one surface of the dielectric substrate, and a ground layer provided inside the dielectric substrate A high-frequency transmission line comprising a microstrip line or a coplanar line with a ground for transmitting a high-frequency signal by using the same, wherein the ground layer is formed by simultaneous firing with the dielectric substrate, and the center conductor is formed. A high frequency wiring board formed by a thin film forming method. Claim surface conductivity of the dielectric substrate bonding surface of the center conductor formed by the thin film forming method σ, characterized in that it is ^{3.5 × 10 7 Ω -1 · m} -1 or more at 12 GHz 1 The wiring board for high frequency described. The high-frequency wiring board according to claim 1, wherein the thin film forming method is a vapor phase method such as vapor deposition, sputtering, CVD, ion plating, or laser ablation, or a plating method. The dielectric substrate is made of at least one selected from alumina ceramic, mullite ceramic, aluminum nitride ceramic, silicon nitride ceramic, silicon carbide ceramic and glass ceramic having an alumina content of 98% or more. The high-frequency wiring board according to claim 1. 2. The high-frequency wiring board according to claim 1, wherein the thickness of the center conductor formed by a thin film forming method is 50 μm or less. 2. The high-frequency wiring board according to claim 1, wherein a surface roughness (Ra) of the center conductor bonding surface formed by the thin film forming method of the dielectric substrate is 0.5 μm or less. A dielectric substrate comprising a plurality of dielectric layers; a high-frequency element mounted on one surface of the dielectric substrate; and one end formed on the surface of the dielectric substrate and electrically connected to the high-frequency element A first high-frequency transmission line formed by the first center conductor provided and a ground layer provided inside the dielectric substrate, a second center conductor formed on the other surface of the dielectric substrate, and the dielectric A second high-frequency transmission line formed by the ground layer provided inside the substrate; and a high-frequency transmission line formed by electromagnetically coupling the first high-frequency transmission line and the second high-frequency transmission line. In a wiring board, the first center conductor and the second center conductor are formed by a thin film forming method, and the ground layer is formed by simultaneous firing with the dielectric layer. And the other end of said first high frequency transmission line, and an end portion of the second high-frequency transmission line, formed by electromagnetically connected via the slot hole formed in the ground layer according to claim 7, wherein High frequency wiring board. The high-frequency wiring board according to claim 7 , wherein the thin film forming method is a vapor phase plating method such as vapor deposition, sputtering, CVD, ion plating, and laser ablation. The dielectric substrate is made of at least one selected from alumina ceramic, mullite ceramic, aluminum nitride ceramic, silicon nitride ceramic, silicon carbide ceramic and glass ceramic having an alumina content of 98% or more. The high-frequency wiring board according to claim 7 . 2. The method for manufacturing a high-frequency wiring board according to claim 1, wherein a conductive paste is applied to a ground layer pattern on at least one dielectric sheet surface, and the dielectric layer having the ground layer pattern formed thereon. A step of laminating another dielectric sheet on the surface of the body sheet, a step of simultaneously firing the laminate to form a dielectric substrate having a ground layer inside, and a method of forming a thin film on the surface of the dielectric substrate Forming a central conductor according to the above method. The method for manufacturing a high-frequency wiring board according to claim 11 , wherein the thin film is formed by a vapor phase plating method such as vapor deposition, sputtering, CVD, ion plating, or laser ablation.

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