JP2016092126A - Circuit board and conductor paste for circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a circuit board provided with conductor patterns having reduced electrical resistivity and excellent heat cycle resistance.SOLUTION: A circuit board 1 includes an insulating substrate 2 made of ceramic and glassless conductor patterns 4 and 6 formed on surfaces of the insulating substrate 2. The conductor patterns 4 and 6 include copper plating layers 4a and 6a in contact with the insulating substrate 2 and conductor layers 4b and 6b formed on the copper plating layers 4a and 6a. The conductor layers 4b and 6b do not contain a glass component and contain a copper component and a conductive filler component. The content of the conductive filler component in the conductor layers 4b and 6b is 50 to 200 pts.mass inclusive based on 100 pts.mass of the copper component. The volumetric thermal expansion coefficient of the conductor layers 4b and 6b is 13.5 ppm/°C or less. The electrical resistivity of the conductor patterns 4 and 6 is less than 20 μΩ cm.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a circuit board used for a ceramic electronic material such as a power semiconductor.

In recent years, next-generation semiconductor devices (typically power devices) used for power control of converters and inverters have been actively researched and developed.
As one of peripheral technologies of this semiconductor device, there is a circuit board for mounting the semiconductor device. A circuit board, for example, has a conductive pattern (metal layer) with high electrical and thermal conductivity on the surface of an electrically insulating substrate, and functions as a wiring circuit or a function to release heat generated in a semiconductor device (heat dissipation) Function).
Such a circuit board, for example, by applying a conductive paste (for example, copper paste) composed of a metal powder (for example, copper), an inorganic filler (for example, glass frit), a resin, a solvent, etc. to the surface of a ceramic substrate, It can be produced by drying and baking. Prior art documents related to this include Patent Documents 1 to 6 and Non-Patent Document 1.

JP 05-325636 A JP 2006-260951 A JP 2004-056148 A JP 2004-134378 A JP 05-144316 A JP 2002-009411 A

Takayuki Ogawa, “Copper paste for through-holes for double-sided substrates”, HARIMA TECHNOLOGY REPORT, [online], May 21, 2013, No. 115, Retrieved from the Internet: http://www.harima.co.jp/ randd / technology_report /

  By the way, in such a circuit board, with the recent high performance such as miniaturization, high density and high speed of the semiconductor device, the resistance of the conductor pattern is reduced and the heat cycle resistance is improved (for example, −40 to 250). There is a demand for improvement in bondability between the substrate and the conductor pattern when the heat cycle is repeated in the temperature range of ° C.

As one measure for reducing the resistance of the conductor pattern, it is conceivable to reduce the content of a non-conductive component that becomes an obstacle to electrical conduction, for example, the inorganic filler. However, if the content of the inorganic filler is simply reduced, the bondability with the substrate may be lowered. Furthermore, when the thermal expansion coefficient of the conductor pattern is increased, for example, when a substrate having a low thermal expansion coefficient (for example, a substrate made of nitride ceramics) is used, the bondability (for example, heat cycle resistance) is lowered. There is a fear.
Further, as one measure for maintaining conductivity, a plating process may be performed on the surface of the conductor layer in order to prevent copper oxidation. However, when the conductive pattern includes a non-conductive inorganic filler, plating may not be locally applied to the part, and so-called pits may be generated. This does not immediately lead to a decrease in bondability, but the oxidation may gradually occur inside the conductor pattern and the conductivity may decrease.

  This invention is made | formed in view of this point, The objective is to provide a circuit board provided with the conductor pattern with which electrical resistivity was reduced and it was excellent also in heat cycle resistance. Another object is to provide a conductor paste for forming such a conductor pattern.

As a result of repeated studies from various angles, the present inventor has come up with the idea of using a conductive filler instead of an inorganic filler such as glass frit or silica. And further examination was repeated and it came to complete this invention.
That is, according to the present invention, a circuit board including an insulating substrate made of ceramics and a glass-less conductive pattern formed on the surface of the insulating substrate is provided. The conductor pattern includes a copper plating layer in contact with the insulating substrate and a conductor layer formed on the copper plating layer. The conductor layer does not include a glass component, but includes a copper component and a conductive filler component. The content rate of the said conductive filler component is 50 to 200 mass parts with respect to 100 mass parts of said copper components. The conductor layer has a volume thermal expansion coefficient of 13.5 ppm / ° C. or less. The electrical resistivity of the conductor pattern is less than 20 μΩ · cm.

By including the conductive filler in the above proportion in the conductor layer, the conductive filler component plays a role of adjusting the coefficient of thermal expansion, and the volume thermal expansion coefficient of the conductor layer (hereinafter sometimes simply referred to as “thermal coefficient of expansion”). .) Can be stably controlled to 13.5 ppm / ° C. or less. Thereby, high durability is realizable also with respect to a low-temperature-high temperature heat cycle.
In addition, by interposing a copper plating layer between the insulating substrate and the conductor layer, it is possible to realize a circuit board in which the insulating substrate and the conductor pattern are firmly integrated without including a glass component in the conductor layer. it can. Furthermore, the electroconductivity (electrical resistivity is 20 microhm * cm or less) is realizable by making a conductor pattern glassless.
In addition, by using a conductive filler, it is possible to prevent the generation of pits and to realize a conductor pattern having no defect on the nickel-gold plating surface.
Therefore, according to the present invention, it is possible to realize a circuit board with reduced electrical resistivity and excellent heat cycle resistance.

  In the present specification, “thermal expansion coefficient” means room temperature to 300 ° C. (for example, 30 to 300 ° C.) based on a general differential expansion thermal mechanical analysis (TMA) unless otherwise specified. ) Refers to the average value of volume expansion coefficient (volume average thermal expansion coefficient) measured in the temperature range. Further, in this specification, “electric resistivity” refers to a value measured by a four-terminal four-probe method using a general resistivity meter.

  The content ratio of the conductive filler component in the conductor layer is preferably 75 parts by mass or more with respect to 100 parts by mass of the copper component. Thereby, when a board | substrate with a small thermal expansion coefficient is used, the more excellent heat cycle resistance is realizable, for example. For this reason, the effect of this invention can be exhibited at a higher level.

  The content of the conductive filler component in the conductor layer is preferably 150 parts by mass or less with respect to 100 parts by mass of the copper component. Since the conductive filler component has lower conductivity than the copper component, the resistance of the conductor layer can be further reduced by setting the content ratio of the conductive filler component in the above range. Therefore, the effect of the present invention can be exhibited at a higher level.

In a preferred embodiment of the circuit board disclosed herein, the average particle diameter of the conductive filler component is 4 μm or more and 50 μm or less. Thereby, the handleability of a conductive filler and the workability | operativity at the time of conductor layer formation can be improved. Moreover, the electrical resistance of the conductor layer can be reduced without hindering sintering (sintering) between the copper powders. Furthermore, preferably high mechanical strength can be achieved.
In the present specification, the “average particle size” corresponds to a cumulative 50% from the fine particle side in the volume-based particle size distribution measured by a laser diffraction / light scattering method using a general particle size distribution measuring apparatus. particle size (50% volume average particle diameter _{.D 50} and also referred to as a median diameter.) is intended to refer to.

In a preferred aspect of the circuit board disclosed herein, the insulating substrate is a silicon nitride substrate. The coefficient of thermal expansion of the substrate made of silicon nitride (Si ₃ N ₄ ) is about 2.6 ppm / ° C., which is very small compared to the coefficient of thermal expansion of copper (16 ppm / ° C.). For this reason, the application of the technique disclosed herein is particularly effective.

  In the suitable one aspect | mode of the circuit board disclosed here, the average thickness of the said copper plating layer is 2 micrometers or less. As described above, the ceramic that forms the insulating substrate and the copper that forms the copper plating layer differ greatly in thermal expansion coefficient. For this reason, in order to prevent peeling between the insulating substrate and the copper plating layer, it is effective to keep the thickness of the copper plating layer small and to match the thermal expansion coefficient with the insulating substrate. Thereby, the further outstanding thermal stability (heat cycle resistance) is realizable.

  In a preferred embodiment of the circuit board disclosed herein, the conductor layer has an average thickness of 100 μm or more and 300 μm or less. By increasing the thickness of the conductor layer, it is possible to improve electrical conductivity and heat dissipation. In general, a conductor layer formed to be relatively thick tends to have problems such as peeling and cracking due to repeated low-temperature to high-temperature (for example, −40 to 250 ° C.) heat cycles. However, according to the technique disclosed herein, such a problem can be prevented, and it is possible to achieve both a low resistance of the conductor layer and excellent bonding properties at a high level. Therefore, the present invention has a particularly remarkable effect in such a case.

  In a preferred aspect of the circuit board disclosed herein, the conductive filler component includes at least one selected from the group consisting of chromium, molybdenum, and tungsten. These so-called chromium group metals have a low coefficient of thermal expansion among the metals, and have high chemical stability even in a high temperature environment. For this reason, it can be preferably used in the technology disclosed herein.

Moreover, as another aspect of the present invention, a conductor paste for a circuit board for forming a glassless conductor layer is provided. Such a conductor paste contains copper powder, conductive filler powder, a thermoplastic resin, and a solvent. The content of the conductive filler powder is 50 parts by mass or more and 200 parts by mass or less with respect to 100 parts by mass of the copper component. And when the said conductor paste is provided on a copper plating layer and the said conductor layer is formed, and it is set as a conductor pattern, (1) The volume thermal expansion coefficient of the said conductor layer is 13.5 ppm / degrees C or less, 2) It is realized that the electrical resistivity of the conductor pattern is less than 20 μΩ · cm.
By using such a conductor paste, a conductor layer having a low coefficient of thermal expansion can be realized even without glass. Thereby, for example, it is possible to realize good bonding properties with a ceramic substrate having a small coefficient of thermal expansion (for example, a silicon nitride substrate), and it is possible to realize excellent heat cycle resistance. As a result, a conductor pattern having high thermal stability and further reduced electrical resistivity can be realized.

  In the suitable one aspect | mode of the conductor paste disclosed here, the average particle diameter of the said electroconductive filler powder is 4 micrometers or more and 50 micrometers or less. Thereby, the contact resistance can be further reduced. Furthermore, preferably high mechanical strength can be achieved.

  In the suitable one aspect | mode of the conductor paste disclosed here, the average particle diameter of the said copper powder is below the said average particle diameter of the said electroconductive filler powder. Thereby, the electrical resistance of the conductor layer can be further reduced.

  In a preferred embodiment of the conductor paste disclosed herein, the conductive filler powder contains at least one selected from the group consisting of chromium, molybdenum and tungsten. Thereby, at least one of improvement in electrical conductivity, improvement in thermal conductivity, improvement in mechanical strength, and improvement in heat cycle resistance can be realized.

1 is a cross-sectional view schematically showing a circuit board according to an embodiment.

  Hereinafter, preferred embodiments of the technology disclosed herein will be described. Note that matters other than the matters specifically mentioned in the present specification and necessary for the implementation of the present invention (for example, a general circuit board manufacturing method and a conductor paste preparation method) are the conventional ones in this field. It can be grasped as a design matter of those skilled in the art based on the technology. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

≪Circuit board≫
The circuit board disclosed here includes an insulating substrate made of ceramics and a conductor pattern formed on the surface of the insulating substrate. The conductor pattern includes a copper plating layer in contact with the insulating substrate and a conductor layer formed on the copper plating layer. And the following (A) to (D): (A) the conductor layer does not contain a glass component but contains a copper component and a conductive filler component; (B) the content of the conductive filler component in the conductor layer Is 50 parts by mass or more and 200 parts by mass or less with respect to 100 parts by mass of the copper component; (C) the volume thermal expansion coefficient of the conductor layer is 13.5 ppm / ° C. or less; (D) the conductor The electrical resistivity of the pattern is less than 20 μΩ · cm. Therefore, the other components are not particularly limited, and can be arbitrarily determined according to various uses.

<Insulating substrate>
The insulating substrate of the circuit board disclosed here is made of a ceramic material. Examples of ceramic materials include carbide ceramics made of metal carbides; nitride ceramics made of metal nitrides; oxide ceramics made of metal oxides; metal borides, fluorides, hydroxides, carbonates, Examples thereof include ceramics made of phosphate and the like.
As a preferred example, a material having a relatively low coefficient of thermal expansion, specifically, nitrides such as silicon nitride (silicon nitride: Si ₃ N ₄ ), aluminum nitride (aluminum nitride: AlN), boron nitride (BN), etc. Material ceramics; Carbide ceramics such as silicon carbide (silicon carbide: SiC); complex oxide ceramics such as cordierite (2MgO · 2Al ₂ O ₃ · 5SiO ₂ ) and mullite (3Al ₂ O ₃ · 2SiO ₂ ) ;
Among them, ceramic materials having a particularly low coefficient of thermal expansion (and an average volume coefficient of thermal expansion of 30 to 500 ° C. of the material) are exemplified by cordierite (<| 0.1 | ppm / ° C.), boron nitride (1 .4 ppm / ° C.), silicon nitride (2.6 ppm / ° C.), silicon carbide (3.7 ppm / ° C.), aluminum nitride (4.6 ppm / ° C.), mullite (5.0 ppm / ° C.) and the like. In particular, silicon nitride is excellent in mechanical strength with a bending strength of about 600 to 800 MPa. For this reason, it can be preferably used in applications where high mechanical strength is required. Moreover, since aluminum nitride has a high thermal conductivity of 150 to 200 W / m · K, it can be preferably used in applications that require heat dissipation.

<Conductor pattern>
The conductor pattern of the circuit board disclosed here includes a copper plating layer in contact with the insulating substrate, and a conductor layer fixed to the surface of the copper plating layer. Further, the electrical resistivity of the conductor pattern is less than 20 μΩ · cm, preferably 15 μΩ · cm or less, more preferably 10 μΩ · cm or less, and particularly preferably 6 μΩ · cm or less.

The copper plating layer is a so-called adhesive layer for bonding the insulating substrate having a small bonding force and the conductor layer. By providing the copper plating layer, it is possible to realize a circuit board that is firmly integrated without including a glass component (inorganic binder component) in the conductor layer.
Such a copper plating layer is substantially composed of a copper component (for example, 95% by mass or more of the entire copper plating layer). For this reason, the thermal expansion coefficient of a copper plating layer may be substantially equivalent to the thermal expansion coefficient of copper. Therefore, for example, when the insulating substrate is made of a ceramic material having a small coefficient of thermal expansion, the coefficient of thermal expansion may be greatly different between the insulating substrate and the copper plating layer. For example, when the insulating substrate is made of a nitride ceramic, the thermal expansion coefficient of the copper plating layer may be 3 to 5 times or more larger than the thermal expansion coefficient of the insulating substrate. Therefore, in such a case, it is preferable to reduce the thermal stress by reducing the thickness of the copper plating layer.
For the above reasons, in a preferred embodiment, the copper plating layer has an average thickness of 5 μm or less (preferably 3 μm or less, more preferably 2 μm or less). Thereby, it is not necessary to substantially consider the thermal expansion coefficient of the copper plating layer, and the heat cycle resistance can be further improved. The average thickness of the copper plating layer is preferably 0.01 μm or more (preferably 0.05 μm or more, more preferably 0.1 μm or more, for example 0.5 μm or more). Thereby, an insulating substrate and a conductor layer can be joined more stably, and a circuit board with high thermal stability can be realized.

The conductor layer is a part that exhibits a conductive function as a wiring circuit and a heat dissipation function that releases heat generated in the semiconductor device. The conductor layer provided in the circuit board disclosed herein has a coefficient of thermal expansion of 13.5 ppm / ° C. or less (for example, 13.5 to 11.5 ppm / ° C., in one example, 13 ppm / ° C. or less). Thereby, for example, even when an insulating substrate having a relatively small coefficient of thermal expansion is used, excellent heat cycle resistance can be realized.
Such a conductor layer does not include a glass component, typically does not include other non-conductive (insulating) inorganic fillers, and includes a copper component and a conductive filler component. As described above, the glass component has low electrical conductivity and thermal conductivity. For this reason, the conductor layer excellent in electrical conductivity and heat conductivity is realizable by not mixing the said glass component intentionally at least. Furthermore, even when the surface of the conductor layer is plated for the purpose of improving heat cycle resistance, the generation of pits can be highly prevented.

  The copper component is an essential component for imparting electrical conductivity and heat dissipation to the conductor layer. The copper component has an average particle size of 0.1 μm or more (typically 0.5 μm or more, preferably 1 μm or more, for example, 2 μm or more), and 10 μm or less (typically 5 μm or less, for example, 4 μm or less). The copper powder may be sintered. Thereby, a conductor layer can be densified. Moreover, the handling property and workability | operativity at the time of conductor layer formation can be improved.

  The conductive filler component is an essential component (thermal expansion coefficient adjusting material) for adjusting the thermal expansion coefficient of the conductor layer. The conductive filler component has the following properties: (1) Low coefficient of thermal expansion (preferably a coefficient of thermal expansion of 10 ppm / ° C. or less, for example, about 4 to 6 ppm / ° C.); (2) Excellent conductivity (Preferably having an electrical resistivity of 10 μΩ · m or less, for example 6 μΩ · m or less); (3) Chemically stable even in a high temperature range of about 500 ° C. can be preferably used.

Preferable examples satisfying such properties include chromium group metals, that is, chromium (Cr), molybdenum (Mo), and tungsten (W). Chromium group metals have a relatively low coefficient of thermal expansion among the metals. For this reason, the thermal expansion coefficient of the said conductor layer can be effectively reduced by including a chromium group metal in a conductor layer. Among these, tungsten has an average coefficient of thermal expansion of 0 to 100 ° C., which is 4.5 ppm / ° C., which is the smallest among all metals. For this reason, the thermal expansion coefficient of the conductor layer can be adjusted to a suitable range with a smaller content ratio, which is preferable.
Molybdenum has an extremely low electrical resistivity and is excellent in electrical conductivity and thermal conductivity. Furthermore, the mechanical strength at high temperature is also high. Therefore, the original functionality (conductive function and heat dissipation function) of the conductor layer can be exhibited at a higher level, which is preferable.

The conductive filler component may have an average particle size of 0.5 μm or more (typically 1 μm or more, preferably 2 μm or more, for example, 4 μm or more). Thereby, the electrical resistance of a conductor layer can be reduced, without preventing sintering (sintering) of copper powders. Furthermore, preferably high mechanical strength can be achieved.
Further, from the viewpoint of making the conductor layer excellent in smoothness and uniform, the average particle diameter is preferably 50 μm or less (typically 30 μm or less, for example, 20 μm or less).

  In a preferred embodiment, the average particle diameter of the particles constituting the conductive filler component is larger than the average particle diameter of the particles constituting the copper component in the conductor layer. For example, the average particle diameter of the particles constituting the conductive filler component is preferably about 1.2 to 3 times larger than the average particle diameter of the particles constituting the copper component. Thereby, the resistance of the conductor layer is further reduced, and higher conductivity can be realized.

  The shape of the particles constituting the conductive filler component can be, for example, spherical, elliptical, crushed, or fibrous. From the viewpoint of realizing a conductor layer having higher smoothness and homogeneity, for example, an average aspect ratio (major axis / minor axis ratio) of approximately 1 to 1.5 (for example, 1 to 1.3), spherical, elliptical, or Crushed particles are preferred.

In the technology disclosed herein, the conductive filler component is 50 parts by mass or more (typically 55 parts by mass or more, for example, 75% by mass or more, and further 100 parts by mass or more) with respect to 100 parts by mass of the copper component. Include at a rate of. Thereby, the thermal expansion coefficient of the conductor layer can be adjusted to a suitable range (relatively small), and the thermal expansion coefficient can be matched with the insulating substrate. As a result, problems such as interfacial peeling can be prevented to a high degree, and a conductor layer having high heat cycle resistance can be realized.
Moreover, the upper limit of the content rate of an electroconductive filler component is 200 mass parts or less (typically 180 mass parts or less, for example, 150 mass% or less) with respect to 100 mass parts of copper components. Thereby, it is possible to realize a conductor layer that is excellent in bondability with the copper plating layer and has high electrical conductivity and heat dissipation.

In the conductor layer, for example, when the total volume of the copper component and the conductive filler component is 100% by volume, the volume ratio of the copper component is 55% by volume to 80% by volume (for example, 60% by volume to 75% by volume). Or less). In other words, the volume ratio of the conductive filler component is preferably 20% by volume or more and 45% by volume or less (for example, 25% by volume or more and 40% by volume or less).
The conductor layer may contain components other than the copper component and the conductive filler component (for example, various additives that can be generally used in this kind of field) as long as the effects of the present invention are not significantly reduced.

  The size and thickness of the conductor layer may be determined in consideration of, for example, the dimensions, height, and spacing (arrangement) of the semiconductor device to be mounted (connected), but from the viewpoint of ensuring conductivity and heat dissipation. It is preferable to form a relatively thick conductor layer in as wide a region as possible. For this reason, the thickness of the conductor layer is preferably 100 μm or more (typically 120 μm or more, for example, 150 μm or more). In addition, the upper limit of the thickness is preferably, for example, 300 μm or less (for example, 250 μm or less) from the viewpoint of durability and ease of manufacture.

<Nickel-gold plating layer>
In a preferred embodiment of the circuit board disclosed herein, the surface of the conductor layer is provided with a nickel plating layer and / or a gold plating layer. Thereby, it is possible to highly prevent the conductor layer from being oxidized even in a high temperature environment. Therefore, the heat cycle resistance can be further improved.

<Embodiment>
Hereinafter, a circuit board according to an embodiment will be described with reference to FIG. In addition, in the following drawings, the same code | symbol is attached | subjected and demonstrated to the member and site | part which show | plays the same effect | action, and the overlapping description may be abbreviate | omitted or simplified. The embodiments described in the drawings are modeled as necessary to clearly explain the present invention, and do not necessarily accurately reflect the dimensional relationship (length, width, thickness, etc.) of the actual circuit board. It is not a thing.

In the embodiment shown in FIG. 1, the circuit board 1 includes conductor patterns 4 and 6 on the surface of an insulating substrate (ceramic substrate) 2. On one surface of the insulating substrate 2, a conductor pattern (wiring circuit) 4 is formed in accordance with a predetermined design drawing. In this embodiment, a plurality of (in this case, a total of seven) conductor patterns 4 having different sizes (lengths, etc.) and thicknesses are formed on the insulating substrate 2. Each conductor pattern 4 includes a copper plating layer 4a and a conductor layer (wiring layer) 4b. A conductive pattern (heat radiation layer) 6 is formed on the other surface of the insulating substrate 2 over almost the entire surface. The conductor pattern 6 is composed of a copper plating layer 6 a and a conductor layer 6 b as in the wiring circuit 4.
In addition, the conductor pattern may be provided on both surfaces of the insulating substrate 2 as shown in FIG. 1, or may be provided only on one surface. Further, the number of conductor patterns may be one as in the heat dissipation layer 6 of FIG. 1 or a plurality of conductor patterns as in the wiring circuit 4 of FIG. Further, the conductor pattern may be provided on a part of the insulating substrate 2 or may be provided over almost the entire surface of the insulating substrate 2. Furthermore, for example, for the purpose of improving heat cycle resistance and preventing corrosion, a plating layer (for example, a nickel plating layer or a gold plating layer) may be provided on the surface of the conductor layers 4b and 6b.

  Such a circuit board may be excellent in various properties such as electrical conductivity, heat dissipation, and mechanical strength, and the insulating board and the conductor pattern may be firmly integrated. Therefore, the circuit board disclosed here can be suitably used as a member constituting a ceramic electronic material such as a power semiconductor.

≪Circuit board manufacturing method≫
Although the manufacturing method of such a circuit board is not specifically limited, For example, the following processes:
(1) Applying copper plating to the surface of an insulating substrate made of ceramics;
(2) preparing a conductor paste containing copper powder, conductive filler powder, thermoplastic resin and solvent;
(3) Applying the prepared conductive paste onto an insulating substrate that has been subjected to copper plating; and (4) Applying the insulating substrate to which the conductive paste has been applied above the burn-out temperature of the thermoplastic resin in an inert atmosphere. Fired with to form a conductor pattern;
Can be produced by a method including: Hereinafter, each process is demonstrated in order.

<1. Copper plating treatment>
First, a copper plating process is performed on the surface of the insulating substrate. The copper plating treatment can be formed, for example, by a conventionally known general electroless plating technique. That is, first, adjustment is made so that nuclei are formed by a nucleation component such as palladium, and electroless copper plating is preferably performed thereon. Thereby, the nucleation component can be physically bonded to the surface of the insulating substrate to form a copper plating layer firmly fixed to the surface of the insulating substrate. The detailed procedure of the copper plating process will be described in later examples.

<2. Preparation of conductor paste>
Next, a conductor paste (copper paste) is prepared. The conductor paste typically includes copper powder, conductive filler powder, a thermoplastic resin, and a solvent. Moreover, a glass component is not included. And the following conditions: The content rate of the said electroconductive filler powder is 50 to 200 mass parts with respect to 100 mass parts of the said copper component; The said conductor paste is provided on a copper plating layer, and it is the said. When the conductor layer is formed into a conductor pattern, the conductor layer preferably has a volume thermal expansion coefficient of 13.5 ppm / ° C. or less and an electrical resistivity of less than 20 μΩ · cm. In addition, it does not specifically limit about another component, It can determine arbitrarily according to various uses.

Copper powder is a component for imparting electrical conductivity and heat dissipation to the conductor pattern.
In the present specification, “copper powder” refers to an aggregate of particles mainly composed of copper (Cu), and is typically an aggregate of particles composed of simple copper, for example, mainly composed of copper. Even if it contains a trace amount of impurities other than alloys and copper, it can be included in the “copper powder” as long as it is an aggregate of particles mainly composed of copper.

  As the particles constituting the copper powder, for example, particles having a size (particle diameter) suitable for sintering at a low temperature (500 ° C. or less) may be used. Specifically, those having an average particle size of 10 μm or less are preferable, and those having an average particle size of 5 μm or less (for example, 4 μm or less) are more preferable. Since the firing temperature can be set to 500 ° C. or lower, which is lower than the conventional temperature, thermal shrinkage (distortion due to thermal stress) caused by firing can be suppressed. Therefore, the conductor pattern excellent in adhesiveness with a base material (here copper plating layer) is realizable. In addition, there is an effect that a highly dense conductor pattern can be formed. The lower limit is not particularly limited, but in consideration of handling properties and workability, a lower limit value of 0.1 μm or more (typically 0.5 μm or more, preferably 1 μm or more, for example, 2 μm or more) may be used. Moreover, the shape of the particles constituting the copper powder can be, for example, spherical, scaly, conical, fibrous or the like. Among these, spherical or scale-like particles are preferably used for reasons such as easy filling and easy formation of dense conductor patterns. According to the conductor paste using the copper powder having such an average particle diameter and / or particle shape, a conductor pattern excellent in electric conductivity and heat dissipation can be formed.

  The content ratio of the copper powder in the conductor paste is 35% by mass or more (for example, 40% by mass or more) of the entire conductor paste, and is preferably 70% by mass or less (for example, 60% by mass or less). Thereby, the denseness of a conductor pattern can be improved and high electrical conductivity and heat dissipation can be formed.

The conductive filler powder is a so-called thermal expansion coefficient adjusting material for adjusting the thermal expansion coefficient of the conductor pattern. As the conductive filler powder, an inorganic substance having conductivity, for example, a chromium group metal as described above may be used. The particles constituting the conductive filler powder have an average particle size of 0.5 μm or more (typically 1 μm or more, preferably 2 μm or more, for example, 4 μm or more), and 50 μm or less (typically 30 μm or less). For example, 20 μm or less). By using such a conductive filler powder, it is possible to stably form a conductor pattern having a low resistance and a low coefficient of thermal expansion (for example, the coefficient of thermal expansion of the conductor layer is 13.5 ppm / ° C. or less). it can. In addition, it is possible to highly prevent the occurrence of problems such as ignition during work.
In a preferred embodiment, the average particle size of the conductive filler powder is greater than or equal to the average particle size of the copper powder. In other words, the average particle diameter of the copper powder is equal to or less than the average particle diameter of the conductive filler powder. Thereby, it is possible to form a conductor pattern that is more excellent in electrical conductivity.

In the technique disclosed herein, the conductive filler powder is 50 parts by mass or more (typically 55 parts by mass or more, for example, 75% by mass or more, and further 100 parts by mass or more) with respect to 100 parts by mass of the above components. However, it is included at a ratio of 200 parts by mass or less (typically 180 parts by mass or less, for example, 150% by mass or less).
The content of the conductive filler powder in the conductor paste is typically 25% by mass or more (typically 30% by mass or more, for example, 35% by mass or more) of the entire conductor paste, and 60% by mass or less ( It is typically 55% by mass or less, for example, 50% by mass or less.
According to such a configuration, it is possible to suitably match the thermal expansion coefficient with the insulating substrate, and it is possible to suppress the occurrence of defects such as peeling. Moreover, the conductor pattern which was further excellent in electrical conductivity and heat dissipation can be formed by restraining the content rate of electroconductive filler powder to the required minimum.

The thermoplastic resin is a bonding component (organic binder component) for temporarily fixing a solid content (copper powder or conductive filler powder) in the conductor paste after the conductor paste is dried.
As the thermoplastic resin, a resin that is soluble in the solvent to be used (typically an organic solvent) and is thermally decomposed by burning at a low temperature of 500 ° C. or lower in an inert gas atmosphere can be preferably used. . Preferable examples (and its burn-off temperature) include acrylic resins (including methacrylic resins) such as acrylic (250 ° C.), polymethyl methacrylate, polyethyl methacrylate, polybutyl acrylate; polyacetal resins (310 ° C. ); Polyvinyl acetal resins such as polyvinyl butyral (460 ° C.), copolymers of polyvinyl alcohol and ethylene; polystyrene resins such as polystyrene (410 ° C.), acrylonitrile / butadiene / styrene copolymers (ABS resin) And polyolefin resins such as polyethylene, polypropylene (445 ° C.), and cyclic olefins.

  The content of the thermoplastic resin in the conductive paste is not particularly limited because it may vary depending on the particle size of the copper powder or conductive filler powder, for example, but it is the minimum necessary to temporarily fix the copper powder and conductive filler powder. It is preferable to reduce to this amount. That is, the content of the thermoplastic resin in the conductor paste is 0.05% by mass or more (typically 0.1% by mass or more) of the entire conductor paste, and 1% by mass or less (typically 0%). 0.5 mass% or less, for example, 0.3 mass% or less). A conductive pattern can be stably formed by setting it as 0.05 mass% or more. Moreover, by setting it as 1 mass% or less, for example, even when a conductor pattern having a thickness of 100 μm or more is formed, the resin component can be suitably burned out by low-temperature firing at 500 ° C. or less. As a result, it is difficult for the resin to remain in the conductor pattern, and it is possible to form a conductor pattern excellent in heat dissipation and electrical conductivity while ensuring the bonding property.

  The solvent dissolves or disperses the constituents of the conductor paste disclosed herein (that is, copper powder, conductive filler powder, and thermoplastic resin as a solid content), and at the same time, improves the viscosity of the solvent. It also has the role of preventing sagging and bleeding during coating. Since the conductive paste is used to form a conductive pattern on a circuit board, workability and formability can be improved by preparing it in a paste form (including ink form and slurry form). It is possible to stably form a conductive pattern.

As the solvent, a highly viscous organic solvent having a viscosity at 20 ° C. of 200 to 2000 mPa · s (for example, 250 to 1700 mPa · s) can be preferably used. Thereby, the fall of the viscosity of the conductor paste accompanying the reduction | decrease of the said thermoplastic resin can be compensated, and malfunctions, such as a coating defect and a joining defect, can be prevented suitably. As the highly viscous organic solvent, an organic solvent containing at least one polyol (for example, diols or triols) can be preferably used. Specific examples (and their viscosities) include octanediol (271 mPa · s) and Nika MARS (1650 mPa · s). NAKAMA MARS is a solvent manufactured by Nippon Kayaku Yakuhin Co., Ltd., and is a mixture of isomers such as 2,4-diethyl-1,5-pentanediol and 2-butyl-2-ethyl-1,3-propanediol. is there.
In the present specification, “viscosity” refers to a value measured using a general viscometer when the liquid temperature is 20 ° C. For example, it means a value measured using a parallel disk type rotational viscometer (B type viscometer) at a rotational speed of the rotor of 20 rpm.

The amount of the solvent to be used is an amount that can uniformly dissolve or disperse the above components, and may be adjusted so as to have a viscosity suitable for coating in consideration of, for example, the thickness of the conductor pattern to be formed. The content of the solvent in the conductor paste is not particularly limited, but is typically 1% by mass or more (typically 2% by mass or more, for example, 3% by mass or more) of the entire conductor paste, and 10% by mass or less. (Typically 9% by mass or less, for example, 8% by mass or less).
Furthermore, the ratio of the total of the thermoplastic resin and the solvent in the conductor paste is preferably about 10% by mass or less (typically 1 to 10% by mass, for example, 3 to 10% by mass). Thus, by increasing the proportion of the copper powder and the conductive filler powder, for example, even a conductor pattern having a thickness of 100 μm or more can be densely and stably formed.

  Note that various additives may be added to the conductor paste in addition to the main constituent components for the purpose of adjusting the conductor paste to suitable properties (for example, viscosity, pH, bonding strength, etc.). . Examples of such additives include surfactants, antifoaming agents, plasticizers, thickeners, antioxidants, dispersants, pH adjusters, preservatives, colorants and the like.

  Conductor paste by blending the above components (for example, copper powder, conductive filler powder, thermoplastic resin and solvent) at a predetermined ratio and kneading them by a conventionally known dispersion / kneading technique (for example, roll mill, mixer, etc.). (Copper paste) can be prepared. The conductor paste thus prepared can be sintered at a lower temperature (typically 500 ° C. or less, for example, 400 to 500 ° C.) compared to the conventional one, and has excellent electrical conductivity, heat dissipation, and heat cycle resistance. It is characterized in that an excellent conductor pattern can be realized. Therefore, it can be preferably used for the purpose of forming a wiring circuit or a heat dissipation layer on an insulating substrate made of ceramics.

<3. Application of conductor paste>
Next, the conductor paste is applied to the surface of the insulating substrate that has been subjected to copper plating. Conventionally known methods (for example, screen printing method, metal mask printing method, gravure printing method, doctor blade method, dispenser coating method, dip coating method, ink jet method, etc.) are applied to conductor paste (typically coating). ) Can be used. Of these, the printing method can be preferably employed. By using the printing method, for example, coating corresponding to a wiring pattern having a complicated shape (for example, having a different thickness or size) can be performed easily and accurately.

<4. Firing>
Next, the applied conductor paste is typically pre-dried at an appropriate temperature (typically 30 to 150 ° C., for example 80 to 120 ° C.).
Thereafter, firing is performed for a predetermined time at a temperature at which the copper in the conductor paste can be sufficiently sintered. The firing temperature is set higher than the temperature at which the thermoplastic resin used burns out. Preferably, the temperature is set at a relatively low temperature, for example, not less than the burn-out temperature of the thermoplastic resin and not more than 500 ° C. (typically 350 to 500 ° C., for example, 400 to 500 ° C.). Thereby, the thermal contraction (distortion by a thermal stress) at the time of baking can be suppressed to the minimum. The firing time is usually about 0.1 to 5 hours (typically 0.5 to 3 hours). The atmosphere during firing is preferably an inert gas atmosphere from the viewpoint of preventing copper oxidation. Here, the inert gas atmosphere can be defined as an atmosphere substantially free of oxygen and hydrocarbon gas. Typical atmospheric gases include nitrogen gas and rare gases such as argon and helium.
Thereby, the thermoplastic resin and the solvent in the conductor paste are almost completely burned out by firing. At the same time, the copper component is sintered, and the conductor layer is firmly fixed to the surface of the copper plating layer. Note that, within the above firing temperature range, the conductive filler component does not change in composition or properties (for example, softening, etc.), and therefore maintains the same properties as the material contained in the conductor paste.

Next, typically, the substrate after baking is subjected to an etching process. The etching process can be performed by a conventionally known general method. That is, the copper plating (specifically, the palladium component in the copper plating) adhering to the portion (conductor pattern non-formed portion) where the conductor paste has not been applied / fired is removed. Thereby, for example, also when performing other plating treatments on the surface of the conductor layer, it is possible to prevent the plating layer from growing on the portion where the conductor pattern is not formed, and to prevent a decrease in withstand voltage.
Furthermore, for the purpose of improving heat cycle resistance and preventing corrosion, the surface of the conductor layer can be subjected to plating treatment (for example, nickel-gold plating treatment) again.

By such a method, a circuit board in which a copper plating layer and a conductor layer substantially consisting of a copper component and a conductive filler component are formed in this order on the surface of an insulating substrate made of ceramics is suitably manufactured. be able to.
The volume thermal expansion coefficient of the conductor layer may be 13.5 ppm / ° C. or less (for example, 13.5 to 11.5 ppm / ° C.). In addition, the electrical resistivity of the conductor pattern composed of the copper plating layer and the conductor layer may be less than 20 μΩ · cm (preferably 15 μΩ · cm or less, more preferably 10 μΩ · cm or less).

  In addition, in the manufacturing method shown here, although the conductor layer is formed by preparing conductor paste and providing this conductor paste on the surface of a copper plating layer, it is not limited to this aspect. For example, in consideration of cost and manufacturing stability, a conductive layer is formed by performing electrolytic composite plating (plating method for creating a state in which conductive filler is dispersed in copper plating) on an electroless copper plating pattern. You can also. In particular, when a relatively thick conductor layer is formed, the plating rate is required, so that electrolytic plating is more advantageous than electroless copper plating from the viewpoint of work efficiency.

  EXAMPLES Examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the following examples.

Here, a conductor pattern was formed on an insulating substrate, and the bondability between the substrate and the conductor pattern, the presence or absence of pits, and the electrical characteristics of the conductor pattern were evaluated.
Specifically, first, an electroless copper plating process was performed on a commercially available silicon nitride substrate (manufactured by Mitsubishi Materials). Table 1 shows the conditions for electroless copper plating. Thereby, a copper plating layer having an average thickness of 1.5 μm was formed on the entire surface of the silicon nitride substrate.

  Next, the copper powder, inorganic filler powder (F1 to F6), thermoplastic resin, and solvent shown in Table 2 were prepared. These materials were mixed in proportions shown in Tables 4 and 5 to prepare conductor pastes (S1 to S24).

  Next, the prepared conductor paste (S1 to S24) was stencil printed on the surface of the silicon nitride substrate with the copper plating layer by a doctor blade method. The printing pattern was a 30 mm × 30 mm square, and the printing thickness (metal mask hole) was 0.18 mm.

Next, the silicon nitride substrate with the conductor paste was heated and dried (120 ° C., 3 hours) on a hot plate, and then baked at 500 ° C. for 1 hour in a nitrogen gas atmosphere. As a result, a conductor pattern (copper plating layer + conductor layer) of about 100 to 150 μm was formed on the surface of the copper plating layer.
Then, the electroless copper plating (on the portion where the conductor pattern was not formed) on the silicon nitride substrate was removed by treating with an etching solution for dissolving copper for a short time. Table 3 shows the etching conditions.

Here, in order to further provide heat cycle resistance, the conductor layer was coated with nickel plating and gold plating. Thereby, the circuit board (Example 1-Example 24) provided with the copper plating layer, the conductor layer, and nickel-gold plating in this order on the surface of the silicon nitride substrate was produced.
Tables 4 and 5 show the content ratio (parts by mass) of the inorganic filler component with respect to 100 parts by mass of the copper component in the conductor layer.

[Measurement of volume average thermal expansion coefficient]
Separately, a sample for measuring the coefficient of thermal expansion was prepared using the conductor paste (S1 to S24). Specifically, the conductor paste was press-molded into a predetermined shape (for example, a disk shape), dried at 120 ° C., and then fired at 500 ° C. for 1 hour in a nitrogen gas atmosphere. Thus, a measurement sample was produced. This sample was placed in differential expansion type thermomechanical analysis (TMA), the volume expansion coefficient was measured in the temperature range of room temperature to 300 ° C., and the average value was obtained.

[Pit occurrence]
Arbitrary surfaces of the obtained circuit boards (Examples 1 to 24) were observed with a scanning electron microscope (SEM) to confirm the occurrence of pits. The results are shown in the “pit” column of Tables 4 and 5. In Tables 4 and 5, “◯” indicates that no pit was confirmed, and “x” indicates that a pit was confirmed (the surface of the nickel-gold plating was defective).

[Electrical characteristics]
About the conductor pattern of the obtained circuit boards (Examples 1 to 24), electrical resistance was measured by a 4-terminal 4-probe method using a resistivity meter (model: Loresta GP MCP-T610) manufactured by Mitsubishi Chemical Analytech Co., Ltd. The rate was measured. The results are shown in the column “Electric resistivity” in Tables 4 and 5.

[Jointability]
About the said circuit board (Example 1- Example 24), after repeating a heat cycle 200 times between -40-250 degreeC, bondability was evaluated. Specifically, after confirming from the appearance (visually) that there are no defects such as distortion or cracking, it is confirmed whether the conductor pattern can be peeled off the substrate with tweezers, and the mechanical relationship between the substrate and the conductor pattern is confirmed. The joint property was evaluated.
The results are shown in the “Jointability” column of Tables 4 and 5. In Tables 4 and 5, “◯” indicates that no defects in appearance such as distortion or cracking were observed in the conductor pattern even after the heat cycle, and “×” indicates that both were well bonded. This indicates that a defect in appearance was confirmed after the cycle and / or that both were separated.

As shown in Tables 4 and 5, generation of pits was observed in Examples 17 to 24 in which silica having low conductivity or zirconium phosphate tungstate was used as the inorganic filler. On the other hand, in Examples 1 to 16 in which a metal material (tungsten or molybdenum) having excellent conductivity was used as a filler (conductive filler), no pit was generated.
In Examples 1, Example 5, Example 9, Example 13, and Example 14, in which the conductive filler component content was less than 50 parts by mass with respect to 100 parts by mass of the copper component, the electrical resistivity of the conductor pattern was low. The coefficient of thermal expansion exceeded 13.5 ppm / ° C. As a result, the thermal expansion of the conductor pattern with the silicon nitride substrate was not consistent, and in many cases, the conductor pattern was peeled after the heat cycle. On the other hand, as the content of the conductive filler component is increased, the electrical resistivity of the conductor pattern tends to increase. This is presumably because the conductivity of the conductive filler component is lower than that of the copper component.
In contrast to these comparative examples, in Examples 2 to 4, Example 6, Example 7, Example 10, Example 11, Example 15, and Example 16, the electrical resistivity is less than 20 μΩ · cm and the heat cycle resistance (substrate The bondability between the conductor pattern and the conductor pattern was also good.
Such a result supports the technical significance of the invention disclosed herein.

  Further, when tungsten having different average particle diameters is used as the conductive filler (Example 1 to Example 4, Example 5 to Example 8, and Example 9 to Example 12), when tungsten having a large average particle diameter is used, The electrical resistivity was the lowest. This is presumably because the number of contacts between the particles in the conductor layer has decreased.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

1 Circuit board (wiring board)
2 Insulating substrate (ceramic substrate)
4 Conductor pattern (wiring circuit)
4a Copper plating layer 4b Conductor layer (wiring layer)
6 Conductor pattern (heat dissipation layer)
6a Copper plating layer 6b Conductor layer

Claims (12)

A circuit board comprising an insulating substrate made of ceramics, and a glassless conductor pattern formed on the surface of the insulating substrate,
The conductor pattern includes a copper plating layer in contact with the insulating substrate, and a conductor layer formed on the copper plating layer,
The conductor layer does not include a glass component, includes a copper component and a conductive filler component,
The content ratio of the conductive filler component is 50 parts by mass or more and 200 parts by mass or less with respect to 100 parts by mass of the copper component,
The volume thermal expansion coefficient of the conductor layer is 13.5 ppm / ° C. or less,
The circuit board whose electrical resistivity of the said conductor pattern is less than 20 microhm * cm.   The circuit board according to claim 1, wherein a content ratio of the conductive filler component is 75 parts by mass or more with respect to 100 parts by mass of the copper component.   The circuit board according to claim 1 or 2, wherein a content ratio of the conductive filler component is 150 parts by mass or less with respect to 100 parts by mass of the copper component.   The circuit board according to any one of claims 1 to 3, wherein an average particle diameter of the conductive filler component is 4 µm or more and 50 µm or less.   The circuit board according to claim 1, wherein the insulating substrate is a silicon nitride substrate.   The circuit board according to claim 1, wherein an average thickness of the copper plating layer is 2 μm or less.   The circuit board according to claim 1, wherein the conductor layer has an average thickness of 100 μm or more and 300 μm or less.   The circuit board according to claim 1, wherein the conductive filler component includes at least one selected from the group consisting of chromium, molybdenum, and tungsten. A conductive paste for a circuit board for forming a glassless conductive layer,
Including copper powder, conductive filler powder, thermoplastic resin and solvent,
The content ratio of the conductive filler powder is 50 parts by mass or more and 200 parts by mass or less with respect to 100 parts by mass of the copper component,
When the conductor paste is applied on the copper plating layer to form the conductor layer, a conductor pattern is obtained.
The volume thermal expansion coefficient of the conductor layer is 13.5 ppm / ° C. or less,
A conductor paste that realizes that the electrical resistivity of the conductor pattern is less than 20 μΩ · cm.   The conductor paste according to claim 9, wherein the conductive filler powder has an average particle size of 4 μm or more and 50 μm or less.   The conductor paste of Claim 10 whose average particle diameter of the said copper powder is below the said average particle diameter of the said electroconductive filler powder.   The conductor paste according to any one of claims 9 to 11, wherein the conductive filler powder includes at least one selected from the group consisting of chromium, molybdenum, and tungsten.

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