JP2011176301A - Substrate for mounting element and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a substrate for mounting an element having sulfuration resistance improved by increasing the planarity of the surface of a thick conductor layer. <P>SOLUTION: The substrate 10 for mounting an element includes a structure that, on a surface of an LTCC substrate 1, the thick conductor layer 2 is formed as an element connection terminal. The thick conductor layer 2 is formed of a metal composed mainly of silver Ag or copper Cu and formed by printing and firing metal paste. The thick conductor layer 2 has its surface flattened by wet blast processing to a surface roughness Ra of at most 0.02 μm. An Ni/Au-plated layer 3 is formed on the thick conductor layer 2, so that the surface of the thick conductor layer 2 is completely covered without any space. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an element mounting substrate and a method for manufacturing the same, and more particularly, an element mounting substrate having high flatness on the surface of a thick film conductor layer formed on the substrate surface and excellent in resistance to sulfur, and such a substrate. It relates to a method of manufacturing.

  In recent years, the use of low-temperature (simultaneous) fired ceramic substrates (LTCC substrates) having an excellent feature of low dielectric constant and low wiring resistance has been expanded with the high density mounting of electronic devices and the increase in processing speed. In addition, use of an LTCC substrate has been studied as a substrate for mounting a semiconductor element such as a light emitting diode (LED) element.

  The LTCC substrate is fired at a temperature of about 800 to 1000 ° C., which is lower than the firing temperature of normal ceramics. It is manufactured by firing after being integrated by thermocompression bonding.

  A thick film conductor layer is formed on the surface of the LTCC substrate by printing and baking a paste mainly composed of a conductor metal such as silver (Ag) or copper (Cu). Of these thick film conductor layers, the terminal portion (electrode) that is particularly connected to the element is provided with nickel (Ni) plating and gold in order to maintain wire bondability, adhesion strength, and weather resistance. Multilayer plating (Ni / Au plating) of (Au) plating is performed. Such Ni / Au plating provides sulfidation resistance and prevents the thick film conductor layer from being discolored by reacting with sulfur (S) in the air or the like.

  However, in recent years, a substrate for mounting an LED element or the like has been required to have high sulfidation resistance, and a conventional plating thickness (Ni plating thickness of 3 to 5 μm / Au required for a wire bonding portion) is required. In the plating thickness of 0.1 to 0.3 μm, the Ni / Au plating portion has a black discoloration in the sulfidation test according to JIS-C-60068-2-43, and the sulfidation test cannot be passed. It was.

According to the study by the present inventors, it has been found that the cause of such discoloration of the Ni / Au plating portion is that nickel sulfide is generated by the Ni plating layer exposed on the surface.
In other words, since the thick film conductors such as Ag have grain boundary voids and surface irregularities, even if the Ni plating layer is formed, the voids and surface irregularities remain, and even if the uppermost Au plating is applied Since the Ni plating layer cannot be covered, the Ni plating layer which is the base layer of the Au plating layer is exposed on the surface. And it is thought that black nickel sulfide generate | occur | produced because this exposed Ni plating layer and sulfur (S) content react.

  Conventionally, as a technique for preventing such sulfidation (discoloration) of the connection terminal part (electrode), a method of applying a protective coating with a silicone resin or the like on the Ni plating layer or a conductor constituting the thick film conductor layer has been used. Such as a method of reducing the particle size of the Ag powder, improving the sinterability and making the grain boundary less likely to remain, forming a thick Au layer by paste printing instead of plating, or increasing the thickness of the Au plating layer, etc. Methods are known.

  However, if the particle size of the Ag powder is reduced and the sinterability is improved, the timing of firing shrinkage with the substrate is not matched, and the substrate is warped. Further, when a thick Au layer is formed or the Au plating layer is thick, there is a problem that the cost is remarkably increased.

  In addition, as a technology to improve the plating properties by treating the surface of the conductor layer formed on the LTCC substrate, the surface of the LTCC substrate is wet-blasted before the plating process, and the surface of the conductor layer is raised. There has been proposed a method for removing the damaged glass (for example, see Patent Document 1).

  However, with this method, voids in the grain boundaries and surface irregularities of the thick film conductor (Ag) are eliminated, and the resistance to sulfidation cannot be improved. That is, Patent Document 1 does not describe in detail the conditions for wet blasting, but blasting for glass removal involves removing a hard substance called glass by crushing it with a short blast. Yes, under the blasting conditions for such a purpose, the gaps between the conductor (Ag) particles are filled and the unevenness is eliminated, and the surface of the conductor layer can be completely covered with an Au plating layer having a normal thickness. It was difficult to make it flat (smooth).

Japanese Patent No. 4089902

  The present invention has been made to solve the above-described problems, and provides an element mounting substrate with improved sulfidation resistance by increasing the flatness of the surface of the thick film conductor layer formed on the substrate. With the goal.

  The element mounting substrate of the present invention includes a low-temperature fired ceramic substrate, a thick film conductor layer made of a metal mainly composed of silver (Ag) or copper (Cu), formed on the surface of the low-temperature fired ceramic substrate, A conductive metal plating layer is formed on the thick film conductor layer, and the surface of the thick film conductor layer is flattened by wet blasting and has a surface roughness Ra of 0.02 μm or less. It is characterized by that.

  The conductive metal plating layer is preferably a Ni—Au plating layer in which a nickel (Ni) plating layer and a gold (Au) plating layer are laminated.

  In the method for manufacturing an element mounting substrate of the present invention, a metal paste mainly composed of silver (Ag) or copper (Cu) is printed on the surface of a substrate made of a glass ceramic composition containing glass powder and a ceramic filler. Then, a step of forming a conductor pattern, and firing the substrate on which the conductor pattern is formed, sintering the glass ceramic composition and firing the metal paste, silver (Ag) or copper (Cu) Forming a thick film conductor layer made of a metal having a main component, and subjecting the thick film conductor layer to wet blasting to flatten the surface of the thick film conductor layer to a surface roughness Ra of 0.02 μm or less. And a step of forming a nickel (Ni) -gold (Au) plating layer on the thick film conductor layer whose surface has been flattened by the wet blasting. The features.

The abrasive used for the wet blast treatment is preferably a ceramic powder having a particle size of 25 to 150 μm, and the medium is preferably water. The mixing ratio of the abrasive is preferably 20 to 60% by volume with respect to the total amount of the abrasive and the water. Furthermore, in the wet blasting process, the blast liquid composed of the abrasive and the water is injected at a pressure of 1.2 to 1.8 kg / cm ² from a nozzle having an injection port having a diameter of 5 to 10 mm. It is preferable.

  According to the present invention, the thick film conductor layer made of a metal such as silver (Ag) or copper (Cu) formed on the surface of the low-temperature fired ceramic substrate is flattened (smoothed) by wet blasting, so that the thick film Since the gap between the conductor (Ag) particles is filled and the surface roughness Ra is adjusted to 0.02 μm or less, the plating property is good, and even with a normal thickness Au plating layer, the thick film conductor surface is completely covered Can be covered. Therefore, an element mounting substrate having excellent sulfidation resistance can be obtained.

It is sectional drawing which shows an example of the element mounting substrate of this invention. It is sectional drawing which shows the other example of the element mounting board | substrate of this invention. It is sectional drawing which shows the 3rd example of the element mounting substrate of this invention. It is sectional drawing which shows the 4th example of the element mounting board | substrate of this invention.

  Hereinafter, embodiments of the present invention will be described in detail.

  1 to 4 are cross-sectional views showing the element mounting substrate 10 of the present invention. The element mounting substrate 10 has a low-temperature fired ceramic substrate (LTCC substrate) 1 made of a sintered body of a glass ceramic composition containing glass powder and a ceramic filler, and one main surface (upper surface in the figure) is It is a mounting surface 1a on which an element (semiconductor element) such as an LED element is mounted. The shape, thickness, size, etc. of the LTCC substrate 1 are not particularly limited. The LTCC substrate 1 may be planar as shown in FIGS. 1 and 2, or as shown in FIGS. 3 and 4, a side wall 1b is provided at the end of the substrate, and a mounting surface 1a is provided in the cavity. It may have a formed shape. Moreover, the raw material composition of the sintered body of the glass ceramic composition constituting the LTCC substrate 1, the sintering conditions, and the like will be described in the manufacturing method described later.

  On the mounting surface 1 a of the LTCC substrate 1, a thick film conductor layer 2 that is a connection terminal (electrode) that is electrically connected to an element such as an LED element is formed. The thick film conductor layer 2 is composed of a conductor metal mainly composed of silver (Ag) or copper (Cu), and is formed by printing and baking a conductor metal paste by screen printing or the like, as will be described later. ing. As shown in FIGS. 1 and 3, the thick film conductor layer 2 can be formed at the same height as the mounting surface 1a. Moreover, as shown in FIG. 2 and FIG. 4, the recessed part 1c may be formed in the mounting surface 1a, and the thick film conductor layer 2 may be formed in the recessed part 1c (bottom surface). The surfaces of these thick film conductor layers 2 are flattened (smoothed) by wet blasting and have a surface roughness Ra of 0.02 μm or less. The Ni / Au plating layer having a laminated structure of a nickel (Ni) plating layer and a gold (Au) plating layer formed thereon on the thick film conductor layer 2 whose surface is flattened in this way. 3 is formed, and the surface of the thick film conductor layer 2 is completely covered without a gap. When the surface roughness Ra of the thick film conductor layer 2 exceeds 0.02 μm, it is difficult to completely cover the surface of the thick film conductor layer 2 with the Ni / Au plating layer 3 and the sulfidation resistance becomes insufficient. . The surface roughness Ra of the thick film conductor layer 3 is more preferably 0.01 μm or less.

  The thick film conductor layer 2 can be formed as a terminal (electrode) for external connection also on the non-mounting surface 1b which is the main surface opposite to the mounting surface 1a of the LTCC substrate 1. In such a structure, it is preferable that the surface of the thick film conductor layer 2 formed on the non-mounting surface 1b is flattened by wet blasting similarly to the thick film conductor layer 3 formed on the mounting surface 1a. That is, the thick film conductor layer 2 formed on the non-mounting surface 1b is also flattened by wet blasting so as to have a surface roughness Ra of 0.02 μm or less, and the Ni / Au plating layer 3 is formed thereon. It is preferable to have a structure in which the formed thick film conductor layer 2 is completely covered with no gaps. Reference numeral 4 in the drawing denotes a through conductor portion that electrically connects the element connection terminal on the mounting surface 1a and the external connection terminal on the non-mounting surface 1b.

  In the element mounting substrate 10 of the present invention, the thick film conductor layer 2 made of metal such as silver (Ag) or copper (Cu) formed on the surface of the LTCC substrate 1 has a surface roughness Ra by wet blasting. Since it is flattened to 0.02 μm or less, and the Ni / Au plating layer 3 is formed thereon, and the surface of the thick film conductor layer 2 is completely covered without any gap, discoloration occurs in the sulfidation test. No sulfidation resistance.

  The element mounting substrate 1 of the present invention can be manufactured as follows.

[Formation of green sheets]
First, a green sheet is formed. The green sheet is prepared by adding a binder, and optionally a plasticizer, a solvent, etc. to a glass ceramic composition containing glass powder and a ceramic filler, and forming this into a sheet by the doctor blade method or the like. It can be formed by drying.

  The glass powder is not necessarily limited, but a glass transition point (Tg) of 550 ° C. or higher and 700 ° C. or lower is preferable. When the glass transition point (Tg) is lower than 550 ° C., degreasing described later may be difficult. When the glass transition point (Tg) is higher than 700 ° C., the shrinkage start temperature is increased, and the dimensional accuracy may be decreased.

As the glass powder, for example, SiO ₂ is selected from 57 to 65 mol%, B ₂ O ₃ is 13 to 18 mol%, CaO is 9 to 23 mol%, Al ₂ O ₃ is ₃ to 8 mol%, K ₂ O and Na ₂ O are selected. Glass powder containing a total of at least one of 0.5 to 6 mol% is used. The 50% particle size (D ₅₀ ) of the glass powder is preferably 0.5 μm or more and 2 μm or less. If D ₅₀ of the glass powder is less than 0.5μm, the glass powder is likely to agglomerate, handle not only difficult, it is difficult to uniformly disperse. On the other hand, when D ₅₀ exceeds 2 μm, the glass softening temperature may increase or the sintering may be insufficient. In this specification, the particle diameter is obtained by a laser diffraction / scattering method.

As the ceramic filler, those conventionally used for manufacturing LTCC substrates can be used. For example, alumina powder, zirconia powder, a mixture of alumina powder and zirconia powder, or the like can be suitably used. The D ₅₀ of the ceramic filler is preferably 0.5 μm or more and 4 μm or less.

  A glass ceramic composition is prepared by mixing and mixing such glass powder and ceramic filler such that the glass powder is 30% by mass to 50% by mass and the ceramic filler is 50% by mass to 70% by mass. A slurry can be obtained by adding a binder, and if necessary, a plasticizer, a solvent and the like to the glass ceramic composition.

  As the binder, for example, polyvinyl butyral, acrylic resin and the like can be suitably used. As the plasticizer, for example, dibutyl phthalate, dioctyl phthalate, butyl benzyl phthalate and the like can be used. As the solvent, aromatic or alcoholic organic solvents such as toluene, xylene and butanol can be used. Further, a dispersant or a leveling agent can be used in combination.

  The green sheet thus formed can be cut into a predetermined dimension angle by using a punching die or a punching machine, and at the same time, via holes for interlayer connection can be punched and formed at predetermined positions.

[Print metal paste]
An unfired conductor pattern is formed by printing a conductive metal paste on the surface of the green sheet by a method such as screen printing. In addition, an unfired interlayer connection portion is formed by filling a conductor metal paste into the via hole for interlayer connection described above. As the conductive metal paste, for example, a paste made by adding a vehicle such as ethyl cellulose to a metal powder containing silver (Ag) or copper (Cu) as a main component and, if necessary, a solvent or the like is used. As the metal powder, silver (Ag) powder, mixed powder of silver and palladium, mixed powder of silver and platinum, and the like are preferably used. In the present invention, since the glass component contained in the green sheet can sufficiently secure the adhesion between the conductor metal and the substrate, the glass frit is prevented from increasing the electrical resistance (resistance value) of the conductor metal. It is preferable to use a metal paste in which is not blended.

[Lamination and firing of green sheets]
A plurality of green sheets on which unfired conductor patterns are formed are stacked and integrated by heating and pressing, and then heated at a temperature of 500 ° C. or higher and 600 ° C. or lower to be included in the green sheet. Degreasing is performed to decompose and remove the binder such as resin. Then, the glass ceramic composition which further heats at the temperature of about 800-1000 degreeC and comprises a green sheet is baked. By this firing, the metal paste formed in the glass ceramic substrate and on the front surface (front and back surfaces) is simultaneously fired to form a thick film conductor layer made of a metal mainly composed of silver (Ag) or copper (Cu).

[Wet (wet) blasting]
Wet blasting is performed on the thick film conductor layer formed on the surface of the glass ceramic substrate (LTCC substrate). That is, a blast liquid obtained by mixing an abrasive (blast powder) with a liquid medium (for example, water) is sprayed (sprayed) onto the thick film conductor layer at a high pressure. By this wet blast treatment, the gaps between the conductor particles are filled, and the surface of the thick film conductor layer is flattened (smoothed). The surface roughness Ra of the thick film conductor layer after the treatment can be set to 0.02 μm or less by adjusting the particle size of the abrasive, the blast liquid spraying speed, the spraying pressure, the processing time, and the like.

As the abrasive, for example, ceramic powder such as alumina or zirconia can be used. In order to increase the efficiency of blasting, it is preferable to use crushed alumina powder. The particle size of the abrasive is preferably in the range of 25 to 150 μm. When the particle size of the abrasive is less than 25 μm, the abrasive enters into the cutting groove of the LTCC substrate, etc., which may become a foreign substance and hinder the mounting of the element. On the other hand, when the particle size of the abrasive exceeds 150 μm, the thick film conductor layer in the vicinity of the cavity wall surface that is the element mounting portion cannot be efficiently blasted. The 50% particle size (D ₅₀ ) of the abrasive is preferably in the range of 80 to 100 μm. A more preferable D ₅₀ is 90 μm.

  The mixing ratio of the abrasive (blast powder) and the liquid medium (for example, water) is 20 to 60% by volume of the abrasive as a whole. When the mixing ratio of the abrasive is less than 20% by volume, the efficiency of wet blasting is remarkably reduced, and the surface of the thick film conductor layer cannot be sufficiently flattened. On the other hand, when the ratio of the abrasive exceeds 60% by volume, the viscosity of the blast liquid becomes too high, and the blasting efficiency is lowered. The most preferable mixing ratio is a ratio of 40% by volume of abrasive and 60% by volume of water.

Further, the pressure for injecting the blast liquid mixed at such a ratio is preferably 1.2 to 1.8 kg / cm ² when the injection port of the boron carbide nozzle has a diameter of 8 mm. When the spray pressure of the blast liquid is less than 1.2 kg / cm ² , an effect is observed in removing the glass that is raised on the surface of the thick film conductor layer, but the surface roughness Ra of the thick film conductor layer is 0.02 μm or less. Such a sufficient flattening cannot be performed. Therefore, good sulfidation resistance cannot be imparted. When the spray pressure of the blast liquid exceeds 1.8 kg / cm ² , alumina powder as a blast material adheres to the surface of the thick film conductor layer, and the effect of flattening the surface becomes small.

  In addition, the diameter of the nozzle of the boron carbide nozzle can be 5 to 10 mm. If the diameter of the injection port is less than 5 mm, the flow velocity becomes too high, and not only the thick film conductor layer but also a large amount of glass on the glass ceramic substrate is removed to reduce the strength, or to the surface of the thick film conductor layer. Alumina powder, which is a blast material, adheres, and the effect of flattening the surface is reduced. If it exceeds 10 mm, an effect is observed in removing the glass that has been raised on the surface of the thick film conductor layer, but sufficient flattening may be performed so that the surface roughness Ra of the thick film conductor layer is 0.02 μm or less. It becomes difficult.

  In the wet blasting process, a method of injecting blast liquid from an injection port of a boron carbide nozzle disposed about 5 cm above the conveying surface toward the thick film conductor layer of the LTCC substrate that is continuously conveyed by the belt conveyor. Can be taken. The conveying speed of the conveyor is preferably 1 to 1.5 m / min. When the conveying speed is less than 1 m / min, alumina powder as a blast material adheres to the thick film conductor layer, and the effect of flattening the surface is small. When the conveyance speed exceeds 1.5 m / min, the effect of blasting is small, and flattening sufficient for preventing sulfidation cannot be performed.

[Plating process]
On the thick film conductor layer whose surface roughness Ra is flattened to 0.02 μm or less by wet blasting, Ni plating is performed and then Au plating is performed to form a Ni / Au plating layer. The Ni plating is formed to a thickness of 5 to 10 μm by electroplating using, for example, a nickel sulfamate bath. The gold plating can be formed to a thickness of 0.2 to 0.5 μm by electroplating using, for example, a potassium gold cyanide bath.

  Since wet blasting is applied to the lower thick film conductor layer in the previous step, the gaps between the conductor (for example, Ag) particles are filled, the unevenness is smoothed, and the surface roughness Ra is flattened to 0.02 μm or less. The thick film conductor layer can be completely covered with the Ni / Au plating layer having the above thickness. Therefore, the Ni plating layer is not exposed and has excellent sulfidation resistance. Even if the Ni / Au plating layer is not coated with a protective coating such as a silicone resin, JIS-C-60068-2-43. In the sulfidation test based on the above, it is possible to obtain an Au plating film free from black defects due to the precipitation of nickel sulfide on the surface of the Au plating film.

  Examples of the present invention will be described below. The present invention is not limited to these examples. The element mounting substrate 10 having the structure shown in FIG. 1 was produced by the method described below.

First, the green sheet for main bodies for producing the element mounting substrate 10 was produced. Green sheets for the body, SiO ₂ is _60.4mol%, B 2 _{O 3} is 15.6mol%, _Al 2 _{O 3} is 6 mol%, CaO is 15mol%, _{K 2} O is 1mol%, Na ₂ O is 2 mol% The raw materials were blended and mixed so as to become, and the raw material mixture was put in a platinum crucible and melted at 1600 ° C. for 60 minutes, and then the molten glass was poured out and cooled. This glass was crushed for 40 hours by an alumina ball mill to produce a glass powder for a substrate body. In addition, ethyl alcohol was used as a solvent for pulverization.

  A glass ceramic composition was produced by mixing and mixing the glass powder for substrate main body at 40% by mass and the alumina filler (trade name: AL-45H, manufactured by Showa Denko KK) at 60% by mass. 50 g of this glass ceramic composition, 15 g of an organic solvent (toluene, xylene, 2-propanol, 2-butanol mixed at a mass ratio of 4: 2: 2: 1), plasticizer (di-2-ethylhexyl phthalate) 2.5 g, 5 g of polyvinyl butyral as a binder (Denka Co., Ltd., trade name: PVK # 3000K) and 0.5 g of a dispersant (Bik Chemie, trade name: BYK180) were blended and mixed to prepare a slurry. .

  This slurry was applied onto a PET film by a doctor blade method and dried to produce a green sheet for a main body having a thickness after firing of 0.15 mm.

  On the other hand, ethyl cellulose as a vehicle is blended with conductive powder (trade name: S400-2, manufactured by Daiken Chemical Industry Co., Ltd.) in a ratio of 90:10 as a solvent so that the solid content becomes 87% by mass. After being dispersed in α-terpineol, the mixture was kneaded in a porcelain mortar for 1 hour, and further dispersed three times with a three roll to produce a metal paste.

  A through hole having a diameter of 0.3 mm is formed in a portion corresponding to the unfired through conductor of the green sheet for the main body by using a hole puncher, and a metal paste is filled by a screen printing method to form an unfired through conductor paste layer. At the same time, an unfired thick film conductor layer was formed to obtain a green sheet for a main body with a thick film conductor layer.

  The green sheet for a main body with a thick film conductor layer obtained above is degreased by holding at 550 ° C. for 5 hours, and further held at 870 ° C. for 30 minutes to be fired to obtain a test element mounting substrate 10. Manufactured.

  The thick film conductor layer corresponding to 2 in the element mounting substrate 10 was wet-blasted under the following conditions.

The mixing ratio of the abrasive (blast powder) and the liquid medium (water) was 40 vol% of the abrasive as a whole. Further, the pressure for injecting the blast liquid mixed at such a ratio is 1.5 kg / cm ^2, and is arranged 5 cm above the conveying surface toward the thick film conductor layer while being continuously conveyed by the belt conveyor. A thick film conductor surface having a surface roughness Ra of 0.01 μm was obtained by injecting blast liquid from an injection port having a diameter of 8 mm of a boron carbide nozzle. The conveyor speed of the belt conveyor was 1.2 m / min.

  A 7 μm Ni plating film is formed on the surface of the obtained thick film conductor by electroplating using a nickel sulfamate bath, and an Au plating film having a thickness of 0.3 μm is formed on the surface by electroplating using a potassium gold cyanide bath. Formed. When the element mounting substrate 10 thus obtained was exposed for 100 hours in a sulfidation test according to JIS-C-60068-2-43, an Au plating film free from black defects due to precipitation of nickel sulfide was formed on the surface of the Au plating film. I was able to get it.

  Although the embodiment of the present invention has been described above, the present invention is not limited to this, and it is obvious that various modifications can be made within the scope of the claims.

1. Low temperature fired ceramic substrate (LTCC substrate)
2 ... Thick film conductor layer 3 ... Ni / Au plating layer 4 ... penetrating conductor 10 ... element mounting substrate

Claims (7)

A low-temperature fired ceramic substrate;
A thick film conductor layer made of a metal mainly composed of silver (Ag) or copper (Cu), formed on the surface of the low-temperature fired ceramic substrate;
A conductive metal plating layer formed on the thick film conductor layer;
The element mounting substrate, wherein the thick film conductor layer has a surface flattened by wet blasting and has a surface roughness Ra of 0.02 μm or less.   The element mounting substrate according to claim 1, wherein the conductive metal plating layer is a nickel (Ni) -gold (Au) plating layer. Forming a conductor pattern by printing a metal paste mainly composed of silver (Ag) or copper (Cu) on the surface of a substrate composed of a glass ceramic composition containing glass powder and a ceramic filler;
A thick film conductor made of a metal mainly composed of silver (Ag) or copper (Cu) by firing the substrate on which the conductor pattern is formed, sintering the glass ceramic composition and firing the metal paste. Forming a layer;
Performing a wet blast treatment on the thick film conductor layer, and planarizing the surface of the thick film conductor layer to a surface roughness Ra of 0.02 μm or less;
Forming a nickel (Ni) -gold (Au) plating layer on the thick film conductor layer whose surface has been planarized by the wet blasting process. .   4. The method for manufacturing an element mounting substrate according to claim 3, wherein the abrasive used for the wet blasting treatment is ceramic powder having a particle size of 25 to 150 [mu] m, and the medium is water.   5. The method for manufacturing an element mounting substrate according to claim 4, wherein the mixing ratio of the abrasive is 20 to 60% by volume with respect to the total amount of the abrasive and the water. 6. The element mounting substrate according to claim 4, wherein, in the wet blasting process, a pressure of a blast liquid composed of the abrasive and the water is 1.2 to 1.8 kg / cm ² . Production method.   The manufacturing method of the element mounting substrate according to claim 6, wherein the blast liquid is sprayed from a nozzle having a spray port having a diameter of 5 to 10 mm.

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