JP2012060004A - Substrate for mounting element, and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a substrate for mounting an element with improved sulfide resistance by increasing flatness of a surface of a thick film conductor layer.SOLUTION: A substrate 10 for mounting an element has such a structure that a thick film conductor layer 2 which is a terminal for connecting the element is formed on the surface of a ceramic substrate 1. The thick film conductor layer 2 is made of metal mainly of Ag or Cu, and formed by printing and firing metallic paste. The surface of the thick film conductor layer 2 is flattened to surface roughness Ra of 0.02 μm or less by wet-blast treatment. A Ni/Au plating layer 3 is formed on the thick film conductor layer 2, and the surface of the thick film conductor layer 2 is completely covered without a clearance.

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.

  2. Description of the Related Art In recent years, light emitting devices using LED elements are used for backlights or general illumination of mobile phones, large liquid crystal TVs, and the like, as light emitting diode (hereinafter referred to as LED) elements increase in brightness and efficiency. It is like that. Along with this, members with higher performance are required for members around the LED element. For example, a substrate made of a resin material is used as a substrate for mounting the LED element, but is easily deteriorated by heat and light accompanying the increase in brightness of the LED element, and is made of an inorganic material such as ceramics. The use of substrates is being considered.

  Examples of the inorganic material include ceramics such as alumina and aluminum nitride, and low temperature co-fired ceramics (LTCC) which is a composite of glass and ceramic powder such as alumina. And the board | substrate formed from these inorganic materials is called a ceramic substrate in this specification.

  Ceramic substrates are promising as LED element mounting substrates because they have higher durability against heat and light than resin substrates.

  A thick film conductor layer is formed on the surface of the ceramic 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 sulfidation resistance, and a conventional plating thickness (Ni plating thickness 3 to 5 μm / Au plating thickness 0) required for a wire bonding portion is required. In the sulfuration test according to JIS-C-60068-2-43, black discoloration occurred in the Ni / Au plated portion, and there was a problem that the sulfide test could not be passed.

  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 portion (electrode), a method of applying a protective coating with a silicone resin or the like on the Ni plating layer, or a thick film Au by paste printing instead of plating Methods such as forming a layer or increasing the thickness of an Au plating layer are known.

  However, when a thick Au layer is formed or an Au plating layer is thickened, 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 having improved resistance to sulfidation by increasing the flatness of the surface of the thick film conductor layer formed on the ceramic substrate. With the goal.

  The element mounting substrate of the present invention includes a 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 ceramic substrate, and the thick film conductor layer. A conductive metal plating layer formed on the surface of the thick film conductor layer, wherein 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. To do.

  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.

  The element mounting substrate manufacturing method of the present invention includes a step of firing a ceramic composition containing ceramic powder and a sintering aid to obtain a ceramic substrate, and silver (Ag) or copper (Cu) on the surface of the ceramic substrate. And a ceramic paste on which the conductor pattern is formed is re-fired, and silver (Ag) or copper (Cu) is obtained from the metal paste. A step of forming a thick film conductor layer made of a metal as a main component, and wet blasting the thick film conductor layer 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 is flattened by the wet blasting. To.

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, it is preferable that the spray speed of the blast liquid composed of the abrasive and the water is 1.2 to 1.8 kg / cm ² .

  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 ceramic substrate is flattened (smoothed) by wet blasting, and the thick film conductor ( Ag) Since the gap between the particles is filled and the surface roughness Ra is adjusted to 0.02 μm or less, the plating property is good, and the surface of the thick film conductor is completely covered even with a normal Au plating layer. Can do. 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.

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

  1 to 2 are sectional views showing an element mounting board 10 of the present invention. The element mounting substrate 10 has a ceramic substrate 1 made of a sintered body mainly composed of alumina or aluminum nitride, and one main surface (upper surface in the figure) is an element (semiconductor element) such as an LED element. It becomes the mounting surface 1a mounted. The shape, thickness, size and the like of the ceramic substrate 1 are not particularly limited. The ceramic substrate 1 may have a planar shape as shown in FIG. 1 or a shape in which a side wall 1b is provided at the end of the substrate and a mounting surface 1a is formed in the cavity as shown in FIG. But you can. Moreover, the raw material composition of the sintered body of the glass ceramic composition constituting the ceramic 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 ceramic 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 2, the thick film conductor layer 2 can be formed at the same height as the mounting surface 1a. 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 also be formed as a terminal (electrode) for external connection on the non-mounting surface 1b which is the main surface opposite to the mounting surface 1a of the ceramic 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 a metal such as silver (Ag) or copper (Cu) formed on the surface of the ceramic 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. Green sheet is a ceramic composition containing ceramic powder and sintering aid. Add a binder, plasticizer, solvent, etc., if necessary, to prepare a slurry, which is formed into a sheet by the doctor blade method. And can be formed by drying.

As the ceramic powder, alumina powder or aluminum nitride powder can be used . The 50% particle size (D ₅₀ ) of the ceramic powder is preferably 0.5 μm or more and 2 μm or less. If D ₅₀ of the ceramic powder is less than 0.5μm, the ceramic powder is easily aggregated to handle not only difficult, it is difficult to uniformly disperse. On the other hand, when D ₅₀ exceeds 2 μm, there is a risk of insufficient sintering. In the present specification, the particle size is obtained by a particle size measuring apparatus using a laser diffraction / scattering method.

As the sintering aid, those conventionally used in the production of ceramic substrates can be used. For example, a mixture of SiO ₂ and an alkaline earth metal oxide and a rare earth element oxide (particularly, a Y ₂ O ₃ -based auxiliary containing Y ₂ O ₃ as a main component) can be suitably used. The D ₅₀ of the sintering aid is preferably 0.5 μm or more and 4 μm or less.

  By mixing and mixing such ceramic powder and sintering aid such that the ceramic powder is 80 mass% to 99 mass% and the sintering auxiliary is 1 mass% to 20 mass%, the ceramic is mixed. A composition can be obtained, and a slurry can be obtained by adding a binder and, if necessary, a plasticizer, a solvent and the like to the 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 dimensional angle 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.

[Green sheet firing]
By heating the unfired green sheet at a temperature of 500 ° C. or more and 600 ° C. or less, degreasing is performed to decompose and remove a binder such as a resin contained in the green sheet. In the case of stacking unfired green sheets, the above-described degreasing is performed after a plurality of sheets are stacked while being aligned and heated and pressed to be integrated. Then, it heats at the temperature of about 1100-2200 degreeC further, the ceramic composition which comprises a green sheet is baked, and it is set as a ceramic substrate.

[Print metal paste]
By printing a conductive metal paste on the surface of the ceramic substrate by a method such as screen printing, an unfired conductor pattern is formed. 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, a metal paste containing a small amount of glass frit may be used in order to ensure sufficient adhesion between the conductor metal and the ceramic substrate.

[Baking of metal paste (refire)]
After printing the metal paste, the metal paste formed inside the ceramic substrate (via hole) and on the front surface (front and back surfaces) is fired by firing at 500 to 1000 ° C., and the main component is silver (Ag) or copper (Cu). A thick film conductor layer made of metal is formed.

[Wet (wet) blasting]
Wet blasting is performed on the thick film conductor layer formed on the surface of the ceramic 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 injection speed (pressure), the treatment 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. If the particle size of the abrasive is less than 25 μm, the abrasive will enter the cutting groove of the ceramic substrate, 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 it becomes difficult to sufficiently planarize the surface of the thick film conductor layer. 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.

Moreover, it is preferable that the flow rate (injection speed) which injects the blast liquid mixed by such a ratio shall be 1.2-1.8 kg / cm < ² >. When the blasting liquid spray rate 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. It becomes difficult to achieve sufficient planarization. Therefore, it becomes difficult to impart good sulfidation resistance. When the blast liquid spray rate 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 the wet blasting process, it is possible to adopt a method of injecting a blast liquid from an injection port arranged about 5 cm above the conveying surface toward the thick film conductor layer of the ceramic substrate that is continuously conveyed by the belt conveyor. 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 becomes difficult.

[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 is manufactured by the method described below.

First, a green sheet for a main body for producing the element mounting substrate 10 is produced. The green sheet for the main body is 96% by mass of alumina powder (manufactured by Showa Denko KK, trade name: AL-45H), sintering aid (talc powder, SiO ₂ : 65.8% by mass, MgO: 34.2% by mass). The ceramic composition is produced by blending and mixing so that the content is 4% by mass. 50 g of this 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 0.5 g, 5 g of polyvinyl butyral as a binder (trade name: PVK # 3000K, manufactured by Denka) and a dispersant (trade name: BYK180, manufactured by Big Chemie) are mixed and mixed to prepare a slurry.

  This slurry is applied onto a PET film by a doctor blade method and dried to produce a green sheet for main body having a thickness of 1 mm after firing. Thereafter, a through hole having a diameter of 0.3 mm is formed in a portion corresponding to the through conductor using a hole puncher.

  This green sheet for main body is degreased by holding at 550 ° C. for 5 hours, and further fired by holding at 1500 ° C. for 60 minutes to produce an alumina ceramic substrate.

  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, kneading is carried out for 1 hour in a porcelain mortar, and further, dispersion is performed three times with a three roll to produce a metal paste.

  The ceramic substrate surface and through holes are filled with a metal paste by screen printing to form an unfired through conductor paste layer, and an unfired thick film conductor layer is formed to obtain a ceramic substrate with a thick film conductor layer. .

  The ceramic substrate with a thick film conductor layer is held at 870 ° C. for 30 minutes and fired to manufacture the test element mounting substrate 10.

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

The mixing ratio of the abrasive (blast powder) and the liquid medium (water) is 40% by volume of the abrasive as a whole. Furthermore, the flow rate (injection speed) for injecting the blast liquid 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. The blast liquid is jetted from the jetted nozzle, thereby obtaining a thick film conductor surface having a surface roughness Ra of 0.01 μm. In addition, the conveyance speed of a belt conveyor shall be 1.2 m / min.

  A 7 μm Ni plating film is formed on the thick film conductor surface by electroplating in a nickel sulfamate bath, and an Au plating film having a thickness of 0.3 μm is formed on the surface by electroplating in a potassium gold cyanide bath. When the element mounting substrate 10 obtained in this way is exposed for 100 hours in a sulfidation test in accordance with JIS-C-60068-2-43, an Au plating film free from black defects due to precipitation of nickel sulfide is obtained on the surface of the Au plating film. Can do.

  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.

DESCRIPTION OF SYMBOLS 1 ... Ceramic substrate 2 ... Thick film conductor layer 3 ... Ni / Au plating layer 4 ... Penetration conductor part 10 ... Substrate for element mounting

Claims (7)

A 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 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 ceramic substrate contains alumina or aluminum nitride as a main component.   The element mounting substrate according to claim 1, wherein the conductive metal plating layer is a nickel (Ni) -gold (Au) plating layer. Firing a ceramic composition containing ceramic powder and a sintering aid to obtain a ceramic substrate;
Forming a conductive pattern by printing a metal paste mainly composed of silver (Ag) or copper (Cu) on the surface of the ceramic substrate;
Refiring the ceramic substrate on which the conductor pattern is formed, and forming a thick film conductor layer made of a metal mainly composed of silver (Ag) or copper (Cu) from the metal paste;
Performing wet blasting 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. .   The method for manufacturing an element mounting substrate according to claim 4, wherein the abrasive used for the wet blasting treatment is ceramic powder having a particle size of 25 to 150 μm, and the medium is water.   The method for manufacturing an element mounting substrate according to claim 5, wherein a mixing ratio of the abrasive is 20 to 60% by volume with respect to a total amount of the abrasive and the water. Wherein in the wet blasting treatment, the injection speed of the blast liquid consisting of the water and the abrasive, 1.2~1.8kg / cm ² in a claim 5 or 6 device manufacturing method of packaging board according.

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