WO2021131693A1

WO2021131693A1 - Wiring board

Info

Publication number: WO2021131693A1
Application number: PCT/JP2020/045787
Authority: WO
Inventors: 山本　哲也; 孝友緒方; 陽彦伊藤
Original assignee: Ｎｇｋエレクトロデバイス株式会社; 日本碍子株式会社
Priority date: 2019-12-26
Filing date: 2020-12-09
Publication date: 2021-07-01
Also published as: CN114026968B; JP7001876B2; CN114026968A; JPWO2021131693A1; TW202133698A; TWI753709B

Abstract

A wiring board (90) according to the present invention comprises: insulator layers (11, 12) which are formed of a ceramic that contains alumina; and conductive layers (21-23) which are provided on the insulator layers (11, 12). Each one of the conductive layers (21-23) comprises: a plurality of core parts (71) which are dispersed in the conductive layer, while containing molybdenum; and a cover part (72) which covers the surfaces of the plurality of core parts (71), while containing tungsten. The cover part (72) has a lower molybdenum concentration and a higher tungsten concentration in comparison to the core parts (71).

Description

Wiring board

The present invention relates to a wiring board, and more particularly to a wiring board having an insulator layer made of ceramic and a conductive layer provided on the insulator layer.

According to Japanese Patent Application Laid-Open No. 51-107306 (Patent Document 1), electroless gold is applied to a wiring pattern (metallized surface) formed on a ceramic surface containing alumina of an integrated circuit package or an electronic circuit substrate. The technique of plating is being studied. Specifically, a metallized paste containing W and Mo is applied to the ceramic surface, and this is fired at, for example, 1500 ° C. It is claimed that a thick electroless gold plating layer can be formed on the metallized surface formed by this in a short time.

According to International Publication No. 2018/155434 (Patent Document 2), an electroplating method or an electroless plating method is applied to the surfaces of the external electrode and the wiring conductor of the wiring board. For example, a nickel plating layer and a gold plating layer are sequentially formed.

According to Japanese Patent Application Laid-Open No. 2015-88642 (Patent Document 3), a configuration in which a seal ring is bonded on a multilayer ceramic structure is disclosed. The multilayer ceramic structure has a ceramic insulating layer and wiring. For example, the ceramic insulating layer is made of alumina and the wiring is made of tungsten. By welding the lid to the seal ring, an airtightly sealed cavity is obtained. The seal ring consists of, for example, an alloy containing iron, nickel and cobalt.

Japanese Unexamined Patent Publication No. 51-107306 International Publication No. 2018/155434 Japanese Unexamined Patent Publication No. 2015-88642

According to the technique of JP-A-51-107306, it is disclosed that a metallized paste containing W and Mo is fired at a high temperature of 1500 ° C. When the firing temperature is high as described above, according to the study of the present inventor, even if the metal component of the metallized paste is only tungsten, the sintering can easily proceed sufficiently, so that the mechanical strength can be easily secured. it can. When the metal component is only tungsten, high water resistance (corrosion resistance to humidity and moisture) can be obtained as compared with the case where molybdenum is contained. Therefore, unless the purpose is to directly form a thick electroless gold-plated layer on the metallized surface in a short time, the usefulness of JP-A-51-107306 seems to be low. In particular, when the gold-plated layer is formed via the nickel-plated layer as described in International Publication No. 2018/155434, the technique of JP-A-51-107306 does not seem to have any meaning. ..

In recent years, the size of alumina crystal grains constituting the ceramic insulator layer may be reduced in order to increase the mechanical strength of the ceramic insulator layer constituting the wiring board. In this case, the particle size of the alumina powder, which is the material of the ceramic insulator layer, is also reduced, and thus the suitable firing temperature is lowered. Therefore, the material of the conductive layer that constitutes the wiring board by being laminated with the insulator layer also needs to be suitable for low-temperature sintering. From the viewpoint of low-temperature sintering, the metal component of the conductive layer is preferably molybdenum (rather than tungsten) as described in JP-A-2015 / 88642. If the metal component of the metallized paste as the material of the conductive layer is simply tungsten, it is difficult for sintering to proceed sufficiently at a low firing temperature. As a result, the mechanical strength of the conductive layer is lowered. On the other hand, according to the study of the present inventor, when the metal component is simply molybdenum, the water resistance (corrosion resistance to humidity and moisture) of the conductive layer may be insufficient.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a wiring board including a conductive layer having high mechanical strength and high water resistance (corrosion resistance to humidity and moisture). To provide.

The wiring board of the present invention includes an insulator layer made of ceramic containing alumina and a conductive layer provided on the insulator layer. The conductive layer includes a plurality of core portions dispersed in the conductive layer and containing molybdenum, and a coating portion that covers the surface of each of the plurality of core portions and contains tungsten. The coating has a lower molybdenum concentration and a higher tungsten concentration than the core.

The core portion preferably has a molybdenum concentration of 80 wt% (weight percent) or more and 95 wt% or less.

Molybdenum volume when the conductive layer is regarded as molybdenum atoms and metallic molybdenum containing defined as V _M, tungsten volume of when the conductive layer is regarded as a tungsten atoms containing a metal tungsten is defined as V _W, V _M _{When the sum of V W} and V W is defined as 100% (percentage), V _W is preferably 20% or more and 50% or less.

The wiring board may include a base layer provided directly on the conductive layer and made of a conductor different from gold, and a gold layer provided on the conductive layer at least via the base layer.

The base layer preferably contains nickel.

The wiring board may include a metal frame bonded to the base layer and covered with a gold layer.

According to the present invention, since the conductive layer has a core portion containing molybdenum at a relatively high concentration, the conductive layer can be sufficiently sintered even when the firing temperature in the production of the wiring board is low. Become. As a result, it is easy to secure sufficient mechanical strength of the conductive layer. Further, corrosion of the core portion is suppressed by covering each surface of the core portion with a coating portion containing tungsten at a relatively high concentration. From the above, it is possible to obtain a conductive layer having high mechanical strength and high corrosion resistance against humidity and moisture even when the firing temperature is low.

The objectives, features, aspects, and advantages of the present invention will be made clearer by the following detailed description and accompanying drawings.

It is a top view which shows schematic structure of the wiring board in embodiment of this invention. It is a schematic partial cross-sectional view along the line II-II of FIG. It is sectional drawing which shows typically the fine structure of the conductive layer in FIG. Shown shows a reflected electron image of a cross section of a laminate composed of an insulator layer, a conductive layer having a metal component having a converted volume of tungsten of 0 vol% and a converted volume of molybdenum of 100 vol%, and a nickel-plated layer in an initial state. It is an electron micrograph. 6 is a surface photograph of a laminate composed of an insulator layer and a conductive layer having a metal component having a converted volume of tungsten of 0 vol% and a converted volume of molybdenum of 100 vol% in an initial state by a 20-magnification optical microscope. A surface photograph of a laminate composed of an insulator layer and a conductive layer having a metal component having a converted volume of tungsten of 0 vol% and a converted volume of molybdenum of 100 vol% after a high-temperature and high-humidity test by a 20-magnification optical microscope. Is. After the pressure cooker test, on the insulator layer, the conductive layer having a metal component having a converted volume of tungsten of 0 vol% and the converted volume of molybdenum of 100 vol%, the nickel plating layer formed on the conductive layer, and the nickel plating layer. It is an electron micrograph which shows the reflected electron image of the cross section in the vicinity of the edge of the conductive layer of the laminated body composed of the formed gold plating layer. A surface photograph of a laminate composed of an insulator layer and a conductive layer having a metal component having a converted volume of tungsten of 100 vol% and a converted volume of molybdenum of 0 vol% after a high-temperature and high-humidity test by a 20-magnification optical microscope. Is. Shown shows a reflected electron image of a cross section of a laminate composed of an insulator layer, a conductive layer having a metal component having a converted volume of tungsten of 35 vol% and a converted volume of molybdenum of 65 vol%, and a nickel plating layer in an initial state. It is an electron micrograph. A surface photograph of a laminate composed of an insulator layer and a conductive layer having a metal component having a converted volume of tungsten of 35 vol% and a converted volume of molybdenum of 65 vol% after a high temperature and high humidity test by a 20-magnification optical microscope. Is. Shown shows a reflected electron image of a cross section of a laminate composed of an insulator layer, a conductive layer having a metal component having a converted volume of tungsten of 50 vol% and a converted volume of molybdenum of 50 vol%, and a nickel plating layer in an initial state. It is an electron micrograph. A surface photograph of a laminate composed of an insulator layer and a conductive layer having a metal component having a converted volume of tungsten of 50 vol% and a converted volume of molybdenum of 50 vol% after a high temperature and high humidity test by a 20-magnification optical microscope. Is. Shown shows a reflected electron image of a cross section of a laminate composed of an insulator layer, a conductive layer having a metal component having a converted volume of tungsten of 20 vol% and a converted volume of molybdenum of 80 vol%, and a nickel plating layer in an initial state. It is an electron micrograph. A surface photograph of a laminate composed of an insulator layer and a conductive layer having a metal component having a converted volume of tungsten of 20 vol% and a converted volume of molybdenum of 80 vol% after a high-temperature and high-humidity test by a 20-magnification optical microscope. Is. A laminate composed of an insulator layer in an initial state and a conductive layer having a metal component having a converted volume of tungsten of 35 vol% and a converted volume of molybdenum of 65 vol%, which is the laminate shown in FIG. Is an electron micrograph showing a reflected electron image of a cross section of what was prepared separately. It is a distribution map which shows the concentration distribution of molybdenum measured by EDX of the cross section shown in FIG. 15 in the same field of view as FIG. It is a distribution map which shows the concentration distribution of tungsten measured by EDX of the cross section shown in FIG. 15 in the same field of view as FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings below, the same or corresponding parts are given the same reference numbers, and the explanations are not repeated.

<Structure>
FIG. 1 is a plan view schematically showing the configuration of the wiring board 90 according to the present embodiment. FIG. 2 is a schematic partial cross-sectional view taken along line II-II of FIG.

The wiring board 90 is a package used for manufacturing a module. As shown in FIG. 2, the electronic component 81 is mounted on the package, and then the lid 82 is attached to the package to obtain a module having the electronic component 81 in the sealed space.

The wiring board 90 has insulator layers 11 and 12 made of ceramic containing alumina as a main component, and conductive layers 21 to 23 provided on the insulator layers 11 and 12. The alumina content of the ceramic may be 70 wt% or more. Further, the ceramic may contain 10 to 30 wt% of zirconia for the purpose of increasing its strength. Further, the ceramic may contain several% of a glass component for the purpose of increasing the adhesion strength between the insulator layers 11 and 12 and the conductive layers 21 to 23. Further, the wiring board 90 may have a via electrode 26. In the configuration shown in FIG. 2, the conductive layer 21 is laminated on the lower surface of the insulator layer 11, and the conductive layer 22 and the insulator layer 12 are laminated on the upper surface of the insulator layer 11 to insulate. The conductive layer 23 is laminated on the upper surface of the body layer 12. The insulator layer 12 has a frame shape, and a region surrounded by the frame shape on the insulator layer 11 constitutes a cavity for accommodating the electronic component 81. The via electrode 26 connects the conductive layer 21 and the conductive layer 22 to each other by penetrating the insulator layer 11.

The laminate can be formed by forming a plurality of green sheets, printing a metallized paste on each green sheet, laminating these green sheets, and firing. Insulator layers 11 and 12 are formed by sintering the green sheet, and conductive layers 21 to 23 and via electrodes 26 are formed by sintering the metallized paste. The metallized paste has a solvent and a powder dispersed therein. This powder contains a powder of metallic molybdenum and a powder of metallic tungsten. The metallized paste may further contain a powder of the additive, preferably having a composition similar to that of the insulator layers 11 and 12.

In the present embodiment, the wiring board 90 further has a base plating layer 31 to 33 (base layer), an intermediate plating layer 41 to 43, and an Au plating layer 51 to 53 (gold layer). The intermediate plating layers 41 to 43 may be omitted. Further, in the present embodiment, the wiring board 90 further has a metal frame body 62 welded by the brazing material portion 61.

Each of the base plating layers 31 to 33 is provided directly on the conductive layers 21 to 23. The base plating layers 31 to 33 are made of a conductor different from gold, preferably containing nickel, and are made of, for example, nickel or a nickel-cobalt alloy. The intermediate plating layers 41 to 43 are made of a conductor different from gold, preferably nickel-containing, and are made of, for example, nickel or a nickel-cobalt alloy.

The Au plating layer 51 is provided on the conductive layer 21 at least via the base plating layer 31, and the Au plating layer 52 is provided on the conductive layer 22 via at least the base plating layer 32. 53 is provided on the conductive layer 23 via at least the base plating layer 33. Specifically, the Au plating layer 51 is provided on the base plating layer 31 via the intermediate plating layer 41. The Au plating layer 52 is provided on the base plating layer 32 via the intermediate plating layer 42. The Au plating layer 53 is provided on the base plating layer 33 via an intermediate plating layer 43. More specifically, the Au plating layer 53 is placed on the base plating layer 33 with a brazing material portion 61 and a metal frame 62. And is provided via an intermediate plating layer 43.

The metal frame body 62 is joined to the base plating layer 33 by the brazing material portion 61. The metal frame 62 is covered with the Au plating layer 53 via the intermediate plating layer 43. The lid 82 will be welded onto the plated metal frame 62. The metal frame 62 is made of a metal, and this metal may be an alloy.

FIG. 3 is a cross-sectional view schematically showing the fine structure of the conductive layers 21 to 23 (FIG. 2). In FIG. 3, the covering portion 72 is shown in white without hatching in order to make the figure easier to see.

The conductive layers 21 to 23 have a plurality of core portions 71 dispersed in the conductive layers 21 to 23 and a coating portion 72 that covers the surface of each of the plurality of core portions 71 as a microstructure that can be observed with a microscope. including. Each of the conductive layers 21 to 23 preferably further includes an alumina-containing additive portion 73 as a microstructure that can be observed with a microscope. In that case, both the conductive layers 21 to 23 and the insulator layer containing alumina are included. The joint strength between 11 and 12 is increased. The additive portion 73 may contain a glass component, which promotes sintering of the conductive layers 21 to 23. It is preferable that the covering portion 72 completely covers the surface of each of the plurality of core portions 71, but the present invention is not limited to this, and a part of the plurality of core portions 71 is exposed without being covered by the covering portion 72. You may. That is, it is sufficient that the surface of most of the core portions 71 among the plurality of core portions 71 is covered with the covering portion 72. As shown in FIG. 3, in an observation example in a field of view including several tens of core portions 71, the outline of each core portion 71 is relative to the total value of the outline lengths of each core portion 71. The total length of the portions forming the boundary line with the covering portion 72 was 80% or more.

The core portion 71 contains a molybdenum atom, preferably has a molybdenum concentration of 80 wt% or more and 95 wt% or less, and may be substantially composed of molybdenum. The covering portion 72 contains a tungsten atom and has a lower molybdenum concentration and a higher tungsten concentration than the core portion 71.

Molybdenum atoms conductive layers 21 to 23 contain the converted volume of molybdenum when regarded as metallic molybdenum is defined as V _M, in terms of tungsten in the case where the conductive layers 21 to 23 is regarded as a tungsten atom and a metal tungsten containing the volume is defined as _{V W,} defining the sum of these terms the volume _{V M} and _{V W} to 100%. Under these definitions, the converted volume V _W is preferably in the range of 20% or more and 50% or less. To obtain such a composition, the metallized paste which is a material of the conductive layers 21 to 23, and the powder of the powder and metallic tungsten metal molybdenum, volume ratio satisfies the above range V _M: at V _W It suffices if it is mixed. In the structure shown in FIG. 3, the alloying between the molybdenum and tungsten is preferably not very advanced, ignoring the effect of alloying, the conductive layers 21 to 23, in terms of volume V _M Corresponds to the volume of the core portion 71, and the converted volume V _W corresponds to the volume of the covering portion 72. The metal components in the conductive layers 21 to 23 may be substantially only molybdenum and tungsten.

<Effect>
According to the present embodiment, since the conductive layers 21 to 23 have the core portion 71 containing molybdenum at a relatively high concentration, the conductive layer is formed even when the firing temperature in the production of the wiring board 90 is low. 21 to 23 are sufficiently easy to sinter. As a result, it is easy to secure sufficient mechanical strength of the conductive layers 21 to 23. Further, the coating portion 72 containing tungsten in a relatively high concentration covers each surface of the core portion 71, so that the corrosion of the core portion 71 is suppressed. From the above, it is possible to obtain conductive layers 21 to 23 having high mechanical strength and high corrosion resistance against humidity and moisture even when the firing temperature is low.

The core portion 71 preferably has a molybdenum concentration of 80 wt% or more and 95 wt% or less. This makes it easier for the conductive layers 21 to 23 to sinter. When the concentration is less than 80 wt%, the molybdenum concentration of the covering portion 72 is relatively increased. In this case, the moisture resistance of the covering portion 72 itself is lowered. On the other hand, if the concentration exceeds 95 wt%, the moisture resistance of the core portion 71 decreases. In this case, the portion of the surface of the core portion 71 that is not covered with the covering portion 72 is particularly susceptible to corrosion.

When the converted volume V _{W of} tungsten is 20% or more, the covering portion 72 containing tungsten can more sufficiently cover each surface of the core portion 71. If converted volume V _W is less than 50%, can be more ensured converted volume V _M of molybdenum, sintering of the conductive layers 21 to 23, it is possible to proceed more thoroughly.

Assuming that the Au plating layers 51 to 53 are directly bonded to the conductive layers 21 to 23, the Au plating layers 51 to 53 are easily peeled off. Therefore, it is preferable that the Au plating layers 51 to 53 are provided via the base plating layers 31 to 33 directly provided on the conductive layers 21 to 23.

It is preferable that the base plating layers 31 to 33 contain nickel. In this case, the nickel in the base plating layers 31 to 33 is alloyed with the tungsten or molybdenum in the conductive layers 21 to 23, so that the base plating layers 31 to 33 are firmly bonded to the conductive layers 21 to 23.

The wiring board 90 may include a metal frame 62 (FIG. 2) bonded to the base plating layers 31 to 33 and covered with Au plating layers 51 to 53. Since the metal frame 62 is a relatively thick member, there is a relatively high possibility that a large external force will be received from the lateral direction in FIG. 2 for some reason. Further, the metal frame body 62 is likely to receive a force applied to the lid 82, which is a large member, due to some factor, almost as it is. Therefore, a large force may be applied to the conductive layer 23 that supports the metal frame body 62. Even in such a case, since the base plating layer 33 is firmly bonded to the conductive layer 23, the occurrence of peeling on the conductive layer 23 is prevented. This prevents the occurrence of leak paths on the conductive layer 23 due to peeling. Further, the high mechanical strength of the conductive layer 23 prevents the conductive layer 23 from being destroyed due to the large force described above. As a result, the occurrence of leak paths is more reliably prevented.

<Experiment>
A cross-sectional photograph (FIG. 4, FIG. 7, FIG. 9, FIG. 11, and FIG. 13) showing a reflected electron image and a surface photograph (FIG. 5, FIG. 6, FIG. 8, FIG. 10, FIG. 12 and with reference to FIG. 14) and, on the alumina layer (insulator layer) 10 corresponding to the insulating

layers

11 and 12, by the ratio of the converted volume _{V M} and _{V W} to form a different conductive layer 20 , Multiple types of laminates (samples) were formed. Then, the corrosion resistance to humidity and moisture, specifically, the oxidation resistance was examined.

First, with reference to FIGS. 4 to _{_{7, V W: V M =}} 0: the 100 samples of the experimental results will be described below.

FIG. 4 shows a cross section of a sample to which the Ni plating layer 40 is attached for convenience of observation in the initial state (in other words, the state before being exposed to an environment that easily promotes oxidation). In this sample, unlike the above-described embodiment, tungsten was not added, so that the core portion 71 and the additive portion 73 were distributed without the coating portion 72 (FIG. 3).

FIG. 5 shows the surface of the sample without the plating layer in the initial state. The surface image of the conductive layer 20 by a 20-magnification optical microscope is almost white, indicating that the conductive layer 20 has not yet been oxidized. FIG. 6 shows the surface of the sample after the high temperature and high humidity test. The high temperature and high humidity test described in the present specification was performed under the conditions of a temperature of 85 ° C., a relative humidity of 85%, and a period of 96 hours. The surface image of the conductive layer 20 by a 20-magnification optical microscope was substantially black, indicating that the conductive layer 20 was considerably oxidized.

FIG. 7 shows a cross section of the sample with the Ni plating layer 40 and the Au plating layer 50 after the pressure cooker test (PCT) near the end of the conductive layer 20 (the position indicated by the broken line ED). The PCT was performed under the conditions of a temperature of 121 ° C., a relative humidity of 100%, a pressure of 2 atm, and a period of 1000 hours. Immediately to the left of the broken line ED (FIG. 7), an abnormality was observed at the interface between the end of the conductive layer 20 and the Ni plating layer 40. This indicates that corrosion has occurred.

Above, from the results of FIGS. 4 to _{_{7, V W: V M =}} 0: 100 of the samples were found to be less corrosion resistance to humidity and moisture.

Next, with reference to FIG. _{_{8, V W: V M =}} 100: 0 Sample experimental results will be described. FIG. 8 shows the surface of a sample without a plating layer after a high temperature and high humidity test. The surface image of the conductive layer 20 by a 20-magnification optical microscope was almost white, indicating that the conductive layer 20 was hardly oxidized. _{_{Therefore, V W: V M = 100}} : 0, it was found that higher corrosion resistance to humidity and moisture. On the other hand, since the conductive layer 20 of this sample does not contain molybdenum, it has only low mechanical strength.

Next, with reference to FIGS. 9 and _{_{10, V W: V M =}} 35: For a sample of experimental results 65 will be described below. FIG. 9 shows a cross section of a sample to which the Ni plating layer 40 is attached for convenience of observation in the initial state. In this sample, as described with reference to FIG. 3 in the above-described embodiment, the core portion 71 (gray portion of the conductive layer 20 in FIG. 9) and the covering portion 72 (white portion of the conductive layer 20 in FIG. 9) The portion) and the additive portion 73 (the black portion of the conductive layer 20 in FIG. 9) were distributed, and the coating portion 72 almost completely covered the surface of each of the core portions 71. FIG. 10 shows the surface of a sample without a plating layer after a high temperature and high humidity test. The surface image of the conductive layer 20 by a 20-magnification optical microscope exhibited a bright color closer to white as compared with FIG. _This, V _W: compared with the case of _{_{100, V W:: V M}} = 0 V M = 35: 65 is more in the case of indicating that the oxidation of the conductive layer 20 is suppressed.

Next, with reference to FIGS. 11 and _{_{12, V W: V M =}} 50: Experimental results of 50 samples will be described below. FIG. 11 shows a cross section of a sample to which the Ni plating layer 40 is attached for convenience of observation in the initial state. Also in this sample, the coating portion 72 almost completely covered each surface of the core portion 71. FIG. 12 shows the surface of the sample without the plating layer after the high temperature and high humidity test. The surface image of the conductive layer 20 by a 20-magnification optical microscope exhibited a bright color closer to white as compared with FIG. _This, V _W: compared with the case of _{_{100, V W:: V M}} = 0 V M = 50: 50 is more in the case of indicating that the oxidation of the conductive layer 20 is suppressed.

Next, with reference to FIGS. 13 and _{_{14, V W: V M =}} 20: for 80 samples of experimental results will be described below. FIG. 13 shows a cross section of a sample to which the Ni plating layer 40 is attached for convenience of observation in the initial state. In this sample, the coating portion 72 roughly covered each surface of the core portion 71. However, as compared with the samples of FIGS. 9 and 11, there was a portion where the surface of the core portion 71 seemed to be exposed. As a result of performing the image analysis of FIG. 13 using the image analysis software ImageJ, the boundary line between the outer line of each core portion 71 and the covering portion 72 is relative to the total value of the lengths of the outer lines of each core portion 71. The total length of the portions forming the sword was 80% or more. FIG. 14 shows the surface of a sample without a plating layer after a high temperature and high humidity test. The surface image of the conductive layer 20 of this sample by a 20-magnification optical microscope is slightly blacker and darker than the samples of FIGS. 10 and 12, but has a brighter color closer to white than that of FIG. Presented. _This, V _W: compared with the case of _{_{100, V W:: V M}} = 0 V M = 20: 80 is more in the case of indicating that the oxidation of the conductive layer 20 is suppressed.

Generally, the higher the atomic number, the higher the signal strength of the reflected electron, so the reflected electron image has a higher whiteness. From this, it is estimated that in FIG. 13, the core portion 71, which is a gray portion, has a high molybdenum concentration, and the coating portion 72, which is a white portion, has a high tungsten concentration.

In order to verify the above estimation, EDX (Energy-Dispersive X-Ray Spectrometry) was performed together with the observation of the reflected electron image. The cross section of the observation sample was made by ion milling, and carbon vapor deposition was performed on it. Hitachi High-Technologies S-3400N was used for observing the backscattered electron image. Genesis MX4 manufactured by EDAX was used for EDX. The acceleration voltage in EDX was 10 kV, and the signal strength was measured by scanning for 150 seconds in the measurement field of view.

15 to 17 are similarly _V W and Figure _9: V M = _35: the analysis results for the samples having a composition ratio of 65. However, this sample was prepared separately from the sample shown in FIG. 9 for convenience of observation. FIG. 15 shows a reflected electron image of a cross section of the sample without the Ni plating layer 40 (see FIG. 9) in the initial state. FIG. 16 shows the results of measuring the distribution of molybdenum concentration in the same field of view as in FIG. 15 with EDX. FIG. 17 shows the result of measuring the distribution of the tungsten concentration in the same field of view as in FIG. 15 with EDX. The visual field range of the conductive layer was about 24 μm × about 12 μm. Arrow 1 in FIGS. 15 to 17 indicates the position of the core portion 71. Similarly, the arrow 2 indicates the position of the covering portion 72.

In the EDX measurement shown in FIG. 16, the higher the whiteness, the higher the molybdenum concentration. Since the coating portion 72 indicated by the arrow 2 has a lower whiteness than the core portion 71 indicated by the arrow 1, it can be said that the coating portion 72 has a lower molybdenum concentration than the core portion 71.

In the EDX measurement shown in FIG. 17, the higher the whiteness, the higher the tungsten concentration. Since the covering portion 72 indicated by the arrow 2 has a higher whiteness than the core portion 71 indicated by the arrow 1, it can be said that the covering portion 72 has a higher tungsten concentration than the core portion 71.

Next, the element concentration of the core portion 71 was measured by EDX by irradiating the vicinity of the central portion of the core portion 71 with an electron beam. Specifically, three core portions having different positions were arbitrarily selected, and measurements were taken at positions A to C near the center of each. The results are shown in Table 1 below.

From this measurement result, it was found that the molybdenum concentration in the core portion was 80 wt% to 95 wt%. Moreover, this measurement similar to the measurement, like _V W and Sample _11: a sample having a 50 ratio, sample Like _V W in Figure _{13:: V M = 50 V} M = 20: 80 ratio of It was also performed with the sample to have, and the result was the same as in Table 1.

When the molybdenum concentration of the core portion 71 is less than 80 wt%, the molybdenum concentration of the coating portion 72 is relatively high. In this case, the moisture resistance of the covering portion 72 itself is lowered, and as shown in FIG. 6, oxidative corrosion may proceed after the high temperature and high humidity test. On the other hand, when the molybdenum concentration of the core portion 71 exceeds 95 wt%, the moisture resistance of the core portion 71 is lowered. In this case, as shown in FIG. 6, oxidative corrosion may particularly progress after the high temperature and high humidity test on the portion of the surface of the core portion 71 that is not covered by the coating portion 72.

Next, the element concentration was measured by EDX while irradiating the entire surface of the conductor layer 20 of FIG. 15 with an electron beam. As a result, the weight percent ratio of tungsten to molybdenum was substantially the same as the weight percent ratio of metal molybdenum to metal tungsten in the metallized paste which is the material of the conductor layer 20.

Although the present invention has been described in detail, the above description is exemplary in all embodiments and the invention is not limited thereto. It is understood that innumerable variations not illustrated can be assumed without departing from the scope of the present invention.

10: Alumina layer (insulator layer)
11, 12: Insulator layer 20 to 23: Conductive layer 26: Via electrode 31 to 33: Base plating layer (base layer)
40: Ni plating layer 41 to 43: Intermediate plating layer 50 to 53: Au plating layer (gold layer)
61: Wax material part 62: Metal frame body 71: Core part 72: Coating part 73: Additive material part 81: Electronic parts 82: Lid 90: Wiring board

Claims

An insulator layer made of ceramic containing alumina,
The conductive layer provided on the insulator layer and
The conductive layer is provided with
A plurality of core portions dispersed in the conductive layer and containing molybdenum,
A covering portion that covers the surface of each of the plurality of core portions and contains tungsten,
A wiring board, wherein the covering portion has a lower molybdenum concentration and a higher tungsten concentration as compared with the core portion.
The wiring board according to claim 1, wherein the core portion has a molybdenum concentration of 80% by weight or more and 95% by weight or less.
The molybdenum volume when the conductive layer is regarded as a molybdenum atoms containing a molybdenum metal is defined as V M, tungsten volume of when the conductive layer is regarded as a tungsten atoms containing a metal tungsten is defined as V W, When defining the sum of V M and V W and 100%, V W is less than 50 percent over 20 percent, the wiring board according to claim 1 or 2.
A base layer provided directly on the conductive layer and made of a conductor different from gold,
A gold layer provided on the conductive layer at least via the base layer, and
The wiring board according to any one of claims 1 to 3, further comprising.
The wiring board according to claim 4, wherein the base layer contains nickel.
The wiring board according to claim 4 or 5, further comprising a metal frame bonded to the base layer and covered with the gold layer.