JP2005101370A - High frequency wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high frequency wiring board which can obtain good transmission property even in a high frequency signal of 10 GHz or higher by matching propagation modes and characteristic impedances near a junction part between a metallic base and an insulating substrate. <P>SOLUTION: The wiring board has a metallic base 1 with a through hole 1b; a metallic terminal 3 fixed to the through hole 1b via a sealing material 2 interposed therebetween; an insulating substrate 5 which is fixed to the metallic base 1 by joining a wiring conductor 4 to the metallic terminal 3; a same surface grounding conductor 9 which is formed in the same surface of the wiring conductor 4; and a roof-like component T which is electrically connected to the metallic base 1 and the same surface grounding conductor 9 enclosing the metallic terminal 3 coaxially. In the roof-like member T, a small diameter part t is formed in one edge face side so that the opening of the other edge face is larger than the opening of the one edge face at the metallic base 1 side. When the length of the small diameter part t is denoted as L and the distance between an inner circumferential surface in the small diameter part t and the metallic terminal 3 as D, 0.3 mm≤L≤0.8 mm and 0.3 mm≤D≤0.8 mm hold. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a high-frequency wiring board used in a high-frequency region of 10 GHz or more in fields such as optical communication field and millimeter wave communication, and in particular, a high-frequency wiring board with improved transmission characteristics at a connection portion with a coaxial metal substrate. It is about.

  As an example of use of a conventional high-frequency wiring board, for example, an optical semiconductor device used in the field of optical communication is shown in FIG. 2A is a sectional view of the optical semiconductor device, FIG. 2B is a top view of the optical semiconductor device with the lid removed, and FIG. 2C is a bottom view of the optical semiconductor device. It is.

  A conventional optical semiconductor device has an iron semiconductor element S ′ mounting portion 11a at the center of the upper surface, and a through hole 11b having a diameter of 0.5 to 2 mm formed from the upper surface to the lower surface in the vicinity of the mounting portion 11a. A disk-shaped metal base 11 made of a metal such as (Fe) -nickel (Ni) -cobalt (Co) alloy or Fe-Ni alloy and the through hole 11b are inserted, and at least the lower end of the through hole 11b The end portion on the upper surface side fixed through the sealing material 12 so as to protrude from the electrode is electrically connected to the electrode of the optical semiconductor element S ′, such as Fe—Ni—Co alloy or Fe—Ni alloy. A metal terminal 13 made of metal, an optical semiconductor element S ′ mounted on the mounting portion 11a and having an electrode electrically connected to an end portion on the upper surface side of the metal terminal 13, and a main surface facing from one side Has a linear wiring conductor 14 formed over the other side, and An insulating substrate 15 is attached to the metal substrate 11 so that the wiring conductor 14 and a portion protruding to the lower surface side of the metal terminal 13 are joined in parallel and facing each other.

  The metal base 11 and the metal terminal 13 are joined through a sealing material 12 made of insulating glass containing lead as a main component, and the metal base 11 and the metal terminal 13 are connected by the sealing material 12. Are electrically isolated. The optical semiconductor element S ′ is brazed and fixed to the metal substrate 11 with a low melting point brazing material such as gold (Au) -tin (Sn) having a melting point of 200 to 400 ° C., and the electrode of the optical semiconductor element S ′ is fixed. It is electrically connected to the metal terminal 13 through the bonding wire 16.

  Further, on the upper surface of the metal base 11, a first lid 17a made of Fe-Ni-Co alloy or the like is provided on the outer peripheral portion within a width of 1 mm from the outer peripheral end for the purpose of protecting the optical semiconductor element S '. An optical semiconductor device as a product is obtained by bonding a second lid body 17b fixed by welding, seam welding, brazing, or the like and further fixing the optical fiber 18 thereon.

  In this optical semiconductor device, an optical semiconductor element S ′ is optically excited by a drive signal supplied from an external electric circuit (not shown), and the excited light is transmitted through an optical isolator (not shown) for returning light. The optical fiber 18 is used for high-capacity optical communication and the like by being transferred to and from the optical fiber 18. The adaptation range is widely used in the range of transmission distance of 40 km or less and transmission capacity of 2.5 GHz or less.

  In recent years, the demand for high-speed communication at a transmission distance of 40 km or less has increased rapidly, and research and development on high-speed and large-capacity transmission has been promoted. In particular, an optical transmission device such as an optical semiconductor device that transmits an optical signal in an optical communication device is attracting attention, and higher output and higher speed of the optical signal are issues for improving the transmission capacity.

The optical output of the conventional optical semiconductor device is about 0.2 to 0.5 mW, and the optical semiconductor element has a driving power of about 5 mW. However, in the optical semiconductor device with higher output, the optical output has been improved to a level of 1 mW, and the optical semiconductor element is required to have a driving power of 10 mW or more. Furthermore, the high-frequency signal used in the conventional optical semiconductor device was about 2.5 GHz, but has been improved to about 10 GHz, and higher output and higher speed have been demanded.
JP-A-8-130266

  However, when an optical semiconductor device mounted with an optical semiconductor element driven by a high-frequency signal of about 10 GHz using a conventional high-frequency wiring board is used, the propagation mode changes in the metallic terminal, and accordingly Since the characteristic impedance also changes, there is a problem that the optical semiconductor element is difficult to operate normally, and the transmission characteristic of a high-frequency signal of 10 GHz or more is greatly deteriorated.

  This is because the portion of the metal terminal that protrudes from the through hole of the metal base does not have a coaxial structure. Therefore, if the frequency of the transmitted high-frequency signal increases, the propagation mode of the portion that does not have the coaxial structure is large. This is because deviation occurs and the characteristic impedance changes greatly accordingly.

  That is, in the conventional configuration, the propagation mode of the high-frequency signal in the metal substrate, the portion located inside the through hole of the metal terminal, and the wiring conductor formed on the insulating substrate is a TEM (Transverse Electro Magnetic) mode, On the other hand, the propagation mode of the portion protruding from the through hole of the metal base of the metal terminal and other than the joint portion with the wiring conductor of the insulating substrate is the TE (Transverse Electric) mode, and thus the high frequency signal. The TEM mode, TE mode, TEM mode, and propagation mode change, so that the characteristic impedance suddenly changes in a stepped manner at the propagation mode changing portion, and the reflection loss of the high-frequency signal increases. .

  The present invention has been made in view of the above problems, and its purpose is to match the propagation mode and characteristic impedance in the vicinity of the junction between the metal substrate and the insulating substrate, and to obtain a high-frequency signal of 10 GHz or higher. An object of the present invention is to provide a high-frequency wiring board capable of obtaining good transmission characteristics.

  The high-frequency wiring board of the present invention includes a metal substrate having a through hole formed from the upper surface to the lower surface, and a sealing material that is inserted into the through hole and at least an end on the lower surface side protrudes from the through hole. And a linear wiring conductor attached to the main surface from one side to the opposite side, and the wiring conductor protrudes from the lower surface side of the metal terminal. A rectangular flat plate-like insulating substrate bonded in parallel to a portion and attached to the metal base; a coplanar ground conductor formed on the same plane as the wiring conductor; and the main surface of the insulating substrate on the main surface. A metal roof-like member electrically connected to the metal base and the same-surface ground conductor, which coaxially surrounds a portion of the manufactured terminal projecting on the lower surface side on the main surface of the insulating substrate. The roof-like member is the metal base A small-diameter portion is formed on the one end surface side so that the opening on the other end surface is larger than the opening on the one end surface, and the length of the small-diameter portion is L, the inner peripheral surface in the small-diameter portion, and the metal terminal Where D is the distance between and 0.3 mm ≦ L ≦ 0.8 mm and 0.3 mm ≦ D ≦ 0.8 mm.

  According to the high-frequency wiring board of the present invention, the metal substrate and the same-surface ground conductor are electrically connected to the main surface of the insulating substrate and the portion protruding to the lower surface side of the metal terminal is coaxially surrounded on the main surface of the insulating substrate. A metal roof-like member connected to each other, and the roof-like member has a small-diameter portion on one end surface side so that the opening on the other end surface is larger than the opening on the one end surface on the metal base side. Where the length of the small diameter portion is L, and the distance between the inner peripheral surface and the metal terminal in the small diameter portion is D, 0.3 mm ≦ L ≦ 0.8 mm and 0.3 mm ≦ D ≦ 0.8 mm Therefore, all the high-frequency signal propagation modes from the metal terminal to the wiring conductor can be set to the TEM mode. Therefore, by suppressing the change in the propagation mode, the characteristic impedance also changes smoothly. As a result, good transmission characteristics can be realized even with a high-frequency signal of 10 GHz or higher.

  Next, an optical semiconductor device as an embodiment of the high frequency wiring board of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1A is a cross-sectional view showing an example of an embodiment of an optical semiconductor device using the high-frequency wiring board of the present invention. FIG. 1B and FIG. It is the top view and bottom view in the state where the cover of the optical semiconductor device shown in a) was removed.

  In these drawings, 1 is a metal substrate, 2 is a sealing material, 3 is a metal terminal, 4 is a wiring conductor, 5 is an insulating substrate, T is a metal roof-like member, and S is an optical semiconductor element. These constitute an optical semiconductor device.

  The metal substrate 1 has a function of mounting the optical semiconductor element S and dissipating heat generated by the optical semiconductor element S, and has a circular shape, a semicircular shape, a rectangular shape, etc., and a thickness of 0.5 to 2 mm. It is flat and has a mounting portion 1a for mounting the optical semiconductor element S on its upper surface, and a through hole 1b having a diameter of 0.5 to 2 mm formed from the upper surface to the lower surface in the vicinity of the mounting portion 1a.

  Such a metal substrate 1 is made of a metal such as an Fe—Ni—Co alloy or an Fe—Ni alloy. For example, when the metal substrate 1 is made of an Fe—Ni—Co alloy, the ingot (lumps) It is manufactured in a predetermined shape by applying a conventionally known metal processing method such as punching.

  Further, a Ni layer having a thickness of 0.5 to 9 μm and an Au layer having a thickness of 0.5 to 5 μm, which have excellent corrosion resistance and excellent wettability with a brazing material, are sequentially deposited on the surface of the metal substrate 1 by a plating method. Thus, it is possible to effectively prevent the metal substrate 1 from being oxidatively corroded and to braze each component to the metal substrate 1 satisfactorily.

  The thickness of the metal substrate 1 is preferably 0.5 mm or more. When the thickness is less than 0.5 mm, the welding conditions are used when the first lid body 7a and the second lid body 7b described later are welded to the metal substrate 1. The metal substrate 1 tends to bend and deform easily due to (temperature, etc.), and if it exceeds 2 mm, the thickness of the semiconductor element storage package or the semiconductor device becomes unnecessarily thick and it is difficult to reduce the size. Tend. Therefore, the thickness of the metal substrate 1 is preferably 0.5 to 2 mm.

  1A to 1C show an example in which one semiconductor element S is mounted and one through hole 1b is formed, but a plurality of semiconductor elements S are mounted and a plurality of semiconductor elements S are mounted. The through hole 1b may be formed.

  A metal terminal 3 is fixed to a through hole 1 b formed in the metal base 1 through a sealing material 2. The metal terminal 3 has a function of transmitting a high-frequency signal transmitted and received by the optical semiconductor element S to a wiring conductor on the insulating substrate. The metal terminal 3 is fixed via a sealing material 2 so that at least an end portion on the lower surface side of the metal substrate 1 protrudes from the through hole 1b by about 1 to 20 mm, and is attached to an insulating substrate 5 described later. It is electrically connected to the formed wiring conductor 4.

  The metal terminal 3 is made of a metal such as an Fe—Ni—Co alloy or an Fe—Ni alloy. For example, when the metal terminal 3 is made of an Fe—Ni—Co alloy, the ingot is rolled or punched. By applying a conventionally known metal processing method such as the above, a pin having a length of 1.5 to 22 mm and a diameter of 0.1 to 1 mm is manufactured.

  If the length of the portion of the metal terminal 3 that protrudes from the lower surface of the metal base 1 is less than 1 mm, it tends to be difficult to firmly join the wiring conductor 4 and brazing material to be described later. If it exceeds 20 mm, the length of the insulating substrate 5 becomes unnecessarily long, and it tends to be difficult to reduce the size of the optical semiconductor device. Therefore, it is preferable to fix the metal terminal 3 via the sealing material 2 so that at least the end portion on the lower surface side of the metal substrate 1 protrudes from the through hole 1b by about 1 to 20 mm.

  The sealing material 2 has a function of securing an insulating interval between the metal base 1 and the metal terminal 3 and fixing the metal terminal 3 to the through hole 1b of the metal base 1, and is usually made of glass or ceramic. Inorganic materials such as are used.

  For example, the metal terminal 3 is formed of a glass ring having a thickness equal to the thickness of the metal substrate 1, an outer diameter smaller than the diameter of the through hole 1 b, and an inner diameter larger than the outer diameter of the metal terminal 3. Then, the metal terminal 3 is inserted into the ring, and then the glass is heated and melted at a predetermined temperature, whereby the outer peripheral surface of the metal terminal 3 is hermetically fixed to the inner surface of the through hole 1b.

  In addition, a rectangular flat plate-like insulating substrate 5 having a linear wiring conductor 4 attached to the lower surface of the metal base 1 from one side to the other side facing the main surface is connected to the wiring conductor 4 of the metal terminal 3. Attached in parallel to the portion protruding to the lower surface side.

  Further, the same surface ground conductor 9 is formed at equal intervals on both sides of the wiring conductor 4 on the main surface of the insulating substrate 5. Thereby, the ground potential of the wiring conductor 4 can be strengthened and the transmission characteristics can be improved.

  The insulating substrate 5 has a function of supporting the wiring conductor 4 and is made of a thermosetting resin such as polyimide resin or epoxy resin, an aluminum oxide sintered body, an aluminum nitride sintered body, a mullite sintered body, or a carbonized body. It is made of an inorganic material such as a silicon-based sintered body, a silicon nitride-based sintered body, or a glass-ceramic. For example, in the case of an aluminum oxide-based sintered body, aluminum oxide, silicon oxide, magnesium oxide, calcium oxide, etc. Add a suitable organic binder, solvent, plasticizer, and dispersant to ceramic raw material powder to make a mud, and form it into a sheet by using the well-known doctor blade method. Sheets are obtained, and then these ceramic green sheets are subjected to appropriate punching, laminating, and cutting processes for insulating substrates. It is manufactured by along with obtaining a green ceramic body use firing the green ceramic body at a temperature of about 1600 ° C..

  The wiring conductor 4 has a function of transmitting an electric signal between the optical semiconductor element S and an external electric circuit, and is formed in a straight line from one side to the other side facing the main surface of the insulating substrate 5.

  Such a wiring conductor 4 is generally formed by copper plating when the insulating substrate 5 is made of a thermosetting resin such as polyimide resin or epoxy resin, and the insulating substrate 5 is made of an inorganic material such as an aluminum oxide sintered body. In the case, it is made of tungsten, molybdenum, manganese, etc. For example, if the insulating substrate 5 is made of an aluminum oxide sintered body, a metal paste obtained by adding an organic solvent and a solvent to the tungsten powder, It is formed on the main surface of the insulating substrate 5 by printing and applying in a predetermined pattern to the ceramic green sheet as the main surface in advance by screen printing, and firing the ceramic green sheet.

  The wiring conductor 4 has a Ni layer having a thickness of 0.5 to 9 μm, an Au layer having a thickness of 0.5 to 5 μm, etc. to prevent oxidation and to firmly connect the bonding wire 6 and the metal terminal 3 to the surface. It is preferable to sequentially deposit the metal layers by plating.

  The insulating substrate 5 is printed on the surface of the wiring conductor 4 with solder or a low melting point brazing material such as Au—Sn having a melting point of 200 to 400 ° C. using a conventionally known screen printing method. The metal base 1 to which the metal terminal 3 is fixed is placed so that the wiring conductor 4 and the portion of the metal terminal 3 protruding on the lower surface side of the metal base 1 are parallel and facing each other. The metal substrate 1 is fixed by heating at a temperature.

  In the high frequency wiring board of the present invention, the metal substrate 1 is electrically connected to the main surface of the insulating substrate 5 and the portion protruding from the lower surface side of the metal terminal 3 is coaxially surrounded by the main surface of the insulating substrate 5. A metal roof-like member T connected to the metal base 1 is provided, and the roof-like member T is arranged on one end surface side so that the opening on the other end surface is larger than the opening on the one end surface on the metal base 1 side. A small-diameter portion t is formed, where L is the length of the small-diameter portion t, and D is the distance between the inner peripheral surface of the small-diameter portion t and the metal terminal 3, and 0.3 mm ≦ L ≦ 0.8 mm and 0.3 mm ≦ D ≦ 0.8 mm.

  Thereby, all the propagation modes of the high frequency signal from the metal terminal 3 to the wiring conductor 4 can be set to the TEM mode. Therefore, by suppressing the change in the propagation mode, the characteristic impedance also changes smoothly. As a result, good transmission characteristics can be realized even with a high-frequency signal of 10 GHz or higher.

  In addition, the metal roof-like member T is formed as a structure that covers a side surface of a portion of the metal terminal 3 protruding to the lower surface side of the metal base 1 with a gap interposed, and has a length of about 1 to 20 mm. From the viewpoint of the characteristic impedance matching, it is important to cover the entire portion of the metal terminal 3 protruding from the lower surface side of the metal base 1 on the side of the wiring conductor 4 from the main surface of the insulating substrate 5 coaxially. It is.

  The roof-like member T has a thickness of about 0.5 to 2 mm and a cross-section of a semi-annular shape in which the ring is cut in half, a rectangular outer periphery and inner periphery, and either the outer periphery or the inner periphery. A semicircular shape and a rectangular shape on the other side are used.

  Further, in the portion other than the small-diameter portion t of the roof-shaped member T, the distance between the inner peripheral surface and the metal terminal 3 is larger than the distance D between the inner peripheral surface and the metal terminal 3 in the small-diameter portion t. It is large and is preferably 0.7 to 1.56 mm. If the distance between the inner peripheral surface of the roof-like member T and the metal terminal 3 is less than 0.7 mm, the characteristic impedance tends to increase at the tip of the metal terminal 3, and as a result, reflection at the time of high-frequency input / output Loss increases and the operability of the optical semiconductor element S is likely to deteriorate. On the other hand, when it exceeds 1.56 mm, a higher-order mode tends to occur at the tip of the metal terminal 3, and as a result, reflection loss at the time of high-frequency input / output becomes large, and the operability of the optical semiconductor element deteriorates. It becomes easy.

  Such a metal roof-like member T is made of a metal such as an Fe—Ni—Co alloy, for example, a conventionally well-known metal processing such as cutting or MIM (metal injection mold) of an ingot of an Fe—Ni—Co alloy. By applying the method, a predetermined shape is produced.

  The metal roof-like member T is made of a silver (Ag) -copper (Cu) having a melting point of 700 to 900 ° C. on a metal layer such as a metallized layer previously deposited on the main surface of the metal substrate 1 and the insulating substrate 5. ) Or the like. In addition, it is preferable that a Ni layer having a thickness of 0.5 to 9 μm and an Au layer having a thickness of 0.5 to 5 μm, which have excellent corrosion resistance and excellent wettability with a brazing material, be sequentially deposited on the surface by a plating method. It is possible to effectively prevent the metal roof-like member T from being oxidatively corroded and to braze well.

  Further, the metal roof-like member T may be integrally formed with the metal base 1 described above. When the metal base 1 and the metal roof-like member T are integrally formed, the above-described cutting, MIM, or the like is performed. It is manufactured by a conventionally known metal processing method.

  Then, the optical semiconductor element S is mounted on the mounting portion 1a via an Au—Sn low melting point brazing material, and the electrodes are electrically connected to the end portion on the upper surface side of the metal terminal 3, the bonding wire 6, and the like. The first lid 7a made of Fe-Ni-Co alloy or the like is connected to the upper surface of the metal substrate 1 for the purpose of protecting the optical semiconductor element S, and then YAG laser welding, seam welding or the like. It is fixed by brazing. Further, the second lid 7b in which the optical fiber 8 and an optical isolator (not shown) for preventing return light are bonded to the outer peripheral portion (the bowl-shaped portion) of the first lid 7 with a resin adhesive. Are joined by YAG laser welding or the like to become an optical semiconductor device as a product.

  The high-frequency wiring boards of the present invention and comparative examples were configured as follows. First, an insulating substrate 5 made of an aluminum oxide sintered body having a thickness of 0.5 mm, a length of 10 mm, and a width of 6 mm, in which a pattern to be the wiring conductor 4 and the same surface ground conductor 9 was formed on the main surface, was produced. The insulating substrate 5 had a relative dielectric constant of 8.6, the wiring conductor 4 had a width of 0.27 mm, a length of 10 mm, and a thickness of 0.015 mm.

  Next, a cylindrical metal substrate 1 having a diameter of 3.2 mm and a thickness of 1.0 mm, which is formed by integrating the roof-shaped member T, was made of an Fe—Ni—Co alloy. The roof-like member T has a semi-cylindrical shape, the length is 2.5 mm, the radius of the inner periphery other than the small diameter portion t is 1 mm, and the distance between the inner peripheral surface of the small diameter portion t and the metal terminal 3. D and the length L of the small diameter portion t are as shown in Table 1.

  And in the center part of the metal base | substrate 1, the circular through-hole 1b with a diameter of 1.16 mm for inserting the metal terminals 3 by punching was formed.

  Then, a metal terminal 3 having a diameter of 0.22 mm was inserted into the through hole 1 b of the metal substrate 1 and joined with the sealing material 2. The sealing material 2 was glass having a relative dielectric constant of 4. As a result, Samples 1 to 10 for the present invention and for comparison were obtained.

  About these samples, the reflection loss S11 of 1 GHz to 50 GHz was measured using a high-frequency three-dimensional structure simulator (HFSS manufactured by Ansoft).

Table 1 shows the worst reflection loss S11 in the above frequency range for each sample.

  From Table 1, it was found that for samples 3 to 5, 8, and 9, which are the high-frequency wiring boards of the present invention, the reflection loss S11 was -15 dB or less and good characteristics were obtained. On the other hand, in samples 1, 2, 6, 7, and 10 of the comparative example, it was found that the reflection loss S11 increased and exceeded -15 dB.

  Note that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the present invention. For example, in the best mode for carrying out the above, the metal substrate has a so-called package structure on which an optical semiconductor element is mounted, but this may be a coaxial connector.

(A) is sectional drawing which shows an example of embodiment of the optical semiconductor device using the high frequency wiring board of this invention, (b) is a top view in the state which removed the cover of the optical semiconductor device of (a), (C) is a bottom view of the optical semiconductor device of (a). (A) is sectional drawing of the optical semiconductor device using the conventional high frequency wiring board, (b) is a top view in the state which removed the cover of the optical semiconductor device of (a), (c) is (a). It is a bottom view of an optical semiconductor device.

Explanation of symbols

1 .... Metal base 1a ... Mounting part 1b ... Through hole 2 .... Sealing material 3 .... Metal terminal 4 .... Wiring conductor 5 .... Insulation substrate S ... Optical semiconductor element T ...... Roof-like member t ... Small diameter part

Claims (1)

A metal base having a through hole formed from the upper surface to the lower surface, and a metal terminal inserted through the through hole and fixed through a sealing material so that at least an end on the lower surface side protrudes from the through hole And a linear wiring conductor deposited from one side to the opposite side on the main surface, and the wiring conductor is joined in parallel to a portion projecting to the lower surface side of the metal terminal, and the metal A rectangular flat plate-like insulating substrate attached to the base, a coplanar ground conductor formed on the same surface as the wiring conductor, and the main surface of the insulating substrate projecting to the lower surface side of the metal terminal A metal roof-like member electrically surrounding the metal base and the same-surface ground conductor, which surrounds the portion coaxially on the main surface of the insulating substrate, and the roof-like member comprises: The other end face than the opening of the one end face on the metal substrate side When the small diameter portion is formed on the one end surface side so that the opening becomes large, the length of the small diameter portion is L, and the distance between the inner peripheral surface of the small diameter portion and the metal terminal is D 0.3 mm ≦ L ≦ 0.8 mm and 0.3 mm ≦ D ≦ 0.8 mm.

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