JP6199778B2 - Circuit board and conductor paste for circuit board - Google Patents

Description

  The present invention relates to a circuit board used for a ceramic electronic material such as a power semiconductor. Specifically, the present invention relates to a circuit board provided with a conductor pattern having an electrical resistivity of less than 20 μΩ.

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, provides a conductive paste (eg, copper paste) composed of metal powder (eg, copper), glass frit (inorganic binder), resin (organic binder), solvent, etc. on the surface of a ceramic substrate. And it can produce by drying and baking.

JP 05-325636 A JP 2006-260951 A JP 2004-056148 A JP 2004-134378 A

  In such a circuit board, with recent high performance such as miniaturization, high density and high speed of semiconductor devices, heat cycle resistance (for example, when a heat cycle is repeated in a temperature range of −40 to 250 ° C.) It is required to reduce the resistance of the conductor pattern while maintaining the bonding strength between the substrate and the conductor pattern.

In order to further reduce the resistance of the conductor pattern, it is considered effective to reduce the content of non-conductive components, such as glass, which hinder electrical conduction. However, this may lead to a decrease in bondability (for example, heat cycle resistance) between the substrate and the conductor pattern. That is, since glass generally has a relatively low coefficient of thermal expansion compared to metal (for example, copper), the higher the glass content, the lower the coefficient of thermal expansion of the conductor pattern. In other words, when the glass content is simply reduced, the thermal expansion coefficient of the conductor pattern increases, and when a substrate having a low thermal expansion coefficient (for example, a substrate made of nitride ceramics) is used, There is a risk that the consistency of the thermal expansion coefficient cannot be obtained and problems such as peeling occur.
Due to such a contradiction, it has been difficult to realize a significant reduction in resistance of the conductor pattern.

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

In order to realize a circuit board having these two contradictory characteristics, the present inventor has repeatedly studied from various angles. As a result, means for solving this problem have been found and the present invention has been completed.
That is, according to the present invention, a circuit board provided with an insulating substrate made of ceramics and a glassless conductor 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 includes a copper component and an inorganic filler component. The inorganic filler component is substantially free of glass, average particle diameter (D ₅₀₎ is configured with the following particle 50μm or 10 [mu] m. And the volume thermal expansion coefficient of the said conductor layer is 12 ppm / degrees C or less. Moreover, the electrical resistivity of the said conductor pattern is less than 20 microhm * cm.

  By interposing the copper plating layer between the insulating substrate and the conductor layer, it is possible to realize a circuit substrate in which the insulating substrate and the conductor pattern are firmly integrated without including a glass component in the conductor layer. Further, by including an inorganic filler in the conductor layer, the inorganic filler 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 expansion coefficient”) is 12 ppm. / ° C. or less. Thereby, high durability is realizable also with respect to a low-temperature-high temperature heat cycle. Furthermore, by making the conductive pattern glass-free and making the average particle diameter of the inorganic filler within the above range, excellent electrical conductivity (electric resistivity is 20 μΩ · cm or less, particularly electric resistivity is 10 μΩ · cm or less). Can be realized.

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 the present specification, the “thermal expansion coefficient” means a room temperature to 300 ° C. (for example, 25 to 300 ° C.) based on a general differential expansion thermal mechanical analysis (TMA) unless otherwise specified. Or an arithmetic average value (average volume thermal expansion coefficient) of volume expansion measured in a temperature range of 30 to 300 ° C. Further, in this specification, “electric resistivity” refers to a value measured by a four-terminal four-probe method using a general resistivity meter.
Further, “substantially free of glass” means that the glass component is not actively contained at least, and for example, it is acceptable to mix in a very small amount as an inevitable impurity.

In a preferred embodiment of the circuit board disclosed herein, when the total volume of the copper component and the inorganic filler component is 100% by volume, the volume ratio of the inorganic filler component is 25% by volume or more and 45% by volume. It is as follows.
By making the content rate of an inorganic filler component into the said range, the low resistance of a conductor layer and the maintenance improvement of bondability (for example, heat cycle resistance) can be made compatible at a high level. 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 copper component is obtained by sintering copper powder having an average particle diameter of 1 μm or more and 10 μm or less.
By setting the average particle diameter of the copper powder (raw material) within the above range, the copper particles can be sintered by low-temperature firing (for example, firing at 500 ° C. or less), and a dense conductor layer can be realized.

In a preferred aspect of the circuit board disclosed herein, the insulating substrate is a silicon nitride substrate.
The thermal expansion coefficient of the substrate made of silicon nitride (Si ₃ N ₄ ) is about 2.6 ppm / ° C., which is very small compared to the thermal expansion coefficient of copper. 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 embodiment of the circuit board disclosed herein, the inorganic filler is silica and / or zirconium tungstate phosphate. Since zirconium phosphate tungstate shows a negative thermal expansion coefficient, the thermal expansion coefficient of the conductor layer can be effectively reduced. Silica has a thermal expansion coefficient of 0.5 ppm / ° C., which is not as high as that of zirconium phosphate tungstate, but is easily available and inexpensive, and therefore has an excellent total balance.

Moreover, as another aspect of the present invention, a conductor paste for a circuit board for forming a glassless conductor pattern is provided. Such a conductor paste contains copper powder, inorganic filler powder, a thermoplastic resin, and a solvent. The said inorganic filler powder does not contain glass substantially, and an average particle diameter is 10 micrometers or more and 50 micrometers or less. And when the said conductor pattern is formed, the volume thermal expansion coefficient of this conductor pattern is 12 ppm / degrees C or less, and implement | achieves that an electrical resistivity is less than 20 microhm * cm.
By using a conductor paste having such a composition, 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 a preferred embodiment of the conductor paste disclosed herein, when the total volume of the copper powder and the inorganic filler powder is 100% by volume, the volume ratio of the inorganic filler powder is 25% by volume or more and 45% by volume. It is as follows. Moreover, in another suitable one aspect | mode of the conductor paste disclosed here, the average particle diameter of the said copper powder is 1 micrometer or more and 10 micrometers or less.

  In addition, the inorganic filler whose thermal expansion coefficient is small compared with glass is marketed, and the prior art regarding the conductor paste containing this also exists (for example, patent documents 1-4). However, there has been no example of a conductive paste that contains an inorganic filler and does not contain a glass component (glass-free) so as to adjust the thermal expansion coefficient of the conductive layer as in the technique disclosed herein.

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. The following (A) to (D): (A) the conductor pattern is glass-less; (B) the conductor layer is an inorganic filler component other than glass and has an average particle size of 10 μm to 50 μm. (C) the conductor layer has a volume thermal expansion coefficient of 12 ppm / ° C. or less; (D) the conductor pattern has an electrical resistivity of less than 20 μΩ · cm. Characterized by; 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 such 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 And ceramics made of phosphate and the like.
Preferred examples are those having a relatively small 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. Ceramics; carbide ceramics such as silicon carbide (silicon carbide: SiC); composite oxide ceramics such as cordierite (2MgO · 2Al ₂ O ₃ · 5SiO ₂ ) and mullite (3Al ₂ O ₃ · 2SiO ₂ ); Etc.
Among them, ceramic materials having a particularly small 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 has a bending strength of about 600 to 800 MPa, and is particularly excellent in mechanical strength. Therefore, silicon nitride can be preferably used in applications requiring high mechanical strength. Aluminum nitride has a bending strength of about 200 to 400 MPa and cannot be expected to be as durable as silicon nitride, but it has a high thermal conductivity of 150 to 200 W / m · K, which is preferable for applications that require heat dissipation. Can be used.

<Conductor pattern>
The conductor pattern of the circuit board disclosed here is glass-less (glass-free). That is, by not intentionally mixing glass having low electrical conductivity or thermal conductivity, a conductor pattern having excellent electrical conductivity or thermal conductivity can be realized. In the technique disclosed herein, the electrical resistivity of the conductor pattern is less than 20 μΩ · cm, preferably 15 μΩ · cm or less, more preferably 10 μΩ · cm, and particularly 6 μΩ · cm or less.
Such a conductor pattern includes a copper plating layer in contact with the insulating substrate and a conductor layer fixed to the surface of the copper plating layer.

The copper plating layer is a so-called adhesive layer for bonding the insulating substrate having a small bonding force and the conductor layer. Thereby, even if an inorganic binder component (glass) is not included in the conductor layer, a strongly integrated circuit board can be realized.
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 the copper plating layer can be approximately equal to the thermal expansion coefficient of copper (16 ppm / ° C.). 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 between the insulating substrate and the copper plating layer may be greatly different. 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 on the circuit board disclosed herein has a volume coefficient of thermal expansion of 12 ppm / ° C. or less (preferably 11.5 ppm / ° C. or less, for example, 9 to 11.5 ppm / ° C.). 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 contains a copper component and an inorganic filler component.
The copper component is a main component of the conductor layer, and is a component for imparting electrical conductivity and heat dissipation to the conductor layer. The copper component has an average particle diameter (D ₅₀ ) of 0.1 μm or more (typically 0.5 μm or more, typically considering the viewpoint of densifying the conductor layer and the handleability and workability when forming the conductor layer. Preferably, it is 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) of copper powder may be sintered (sintered).

In the technology disclosed herein, the inorganic filler component is a so-called thermal expansion coefficient adjusting material. Such an inorganic filler component does not substantially contain glass and is composed of an inorganic material other than glass. Suitable inorganic filler materials include zirconium phosphate compounds; silicon oxide (silica: SiO ₂ ), zirconium dioxide (zirconia: ZrO ₂ ), aluminum oxide (alumina: Al ₂ O ₃ ), magnesium oxide (magnesia: MgO), titanium oxide (titania: _TiO 2), oxide material such as barium titanate (BaTiO _3); cordierite _{(2MgO · 2Al 2 O 3 ·} 5SiO 2), mullite _{(3Al 2 O 3 · 2SiO 2} ), folder Composite oxide materials such as stellite (2MgO · SiO ₂ ); nitride materials such as silicon nitride (silicon nitride: Si ₃ N ₄ ) and aluminum nitride (aluminum nitride: AlN); silicon carbide (silicon carbide: Examples thereof include carbide materials such as SiC).

In a preferred embodiment, the conductor layer contains a zirconium phosphate compound as an inorganic filler component. Since the zirconium phosphate-based compound has a relatively small coefficient of thermal expansion, the coefficient of thermal expansion of the conductor layer can be effectively reduced. Examples of such zirconium phosphate compounds include zirconium phosphate tungstate (Zr ₂ (WO ₄ ) (PO ₄ ) ₂ , ZWP) and zirconium phosphate ((ZrO) ₂ P ₂ O ₇ ). In particular, zirconium tungstate phosphate has a negative coefficient of thermal expansion of −3.1 ppm / ° C., so that the thermal expansion coefficient of the conductor layer can be adjusted to a suitable range with a smaller content. For this reason, the original functionality (conductive function and heat dissipation function) of the conductor layer can be sufficiently exhibited, which is preferable.
Moreover, in another suitable one aspect | mode, the silica as an inorganic filler component is included in the conductor layer. Silica has a thermal expansion coefficient of 0.5 ppm / ° C., which is not as high as that of zirconium tungstate phosphate, but is easy to obtain and inexpensive, and therefore has an excellent total balance.

In the technique disclosed here, the average particle diameter (D ₅₀ ) of the particles constituting the inorganic filler component is 50 μm or less. Thereby, the conductor layer can be excellent in smoothness and uniform. Further, in the technology disclosed herein, the average particle diameter of the particles constituting the inorganic filler component (D ₅₀₎ is more than 10 [mu] m (e.g., 15μm or more). Thereby, the number of contacts between the inorganic filler particles in the conductor layer (the number of interfaces between the particles) can be reduced, and the contact resistance can be reduced. More preferably, high mechanical strength can be realized.
From the viewpoint of reducing the number of contacts between the inorganic filler particles in the conductor layer, the 10% volume average particle diameter (D ₁₀ ) of the particles constituting the inorganic filler component is 0.5 μm or more (for example, 1 μm or more). For example, it is preferable that it is 30 μm or less (for example, 25 μm or less) (however, naturally, D ₅₀ ≧ D ₁₀ ). Further, from the viewpoint of realizing a more homogeneous conductor layer, the 90% volume average particle diameter (D ₉₀ ) of the particles constituting the inorganic filler component is, for example, 20 μm or more (for example, 30 μm or more) and 70 μm or less (for example, 60 μm or less) (Naturally, D ₉₀ ≧ D ₅₀ ).

  In a preferred embodiment, the average particle size of the particles constituting the inorganic filler component is larger than the average particle size of the particles constituting the copper component in the conductor layer. For example, the average particle diameter of the particles constituting the inorganic filler component is preferably about 2 to 10 times larger than the average particle diameter of the particles constituting the copper component. Thereby, the resistance in the conductor layer is further reduced, and higher conductivity can be realized.

The specific surface area of the particles constituting the inorganic filler component is usually 5 m ² / g or less, typically 3 m ² / g or less, for example, about 0.1 to ^2.5 m ² / g. Thereby, the contact area of the inorganic filler particles in the conductor layer can be reduced, and the contact resistance can be further reduced. In the present specification, the “specific surface area” means a gas adsorption amount measured by a gas adsorption method (a constant capacity adsorption method) using nitrogen (N ₂ ) gas as an adsorbate, and a BET method (for example, BET1 The value (m ² / g) analyzed by the point method.
Moreover, the shape of the particles constituting the inorganic filler component can be, for example, spherical, elliptical, crushed, fibrous or the like. 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.

Although the content rate of the copper component in a conductor layer is not specifically limited, For example, when the total volume of a copper component and an inorganic filler component is 100 volume%, the volume ratio of a copper component is 55 volume% or more and 75 volume% or less. There should be. 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. The content ratio of the inorganic filler component (thermal expansion coefficient adjusting material) in the conductor layer is not particularly limited. For example, when the total volume of the copper component and the inorganic filler component is 100% by volume, the volume of the inorganic filler component The ratio is preferably 25% by volume or more and 45% by volume or less. Thereby, the coefficient of thermal expansion of the conductor layer can be kept relatively small, and matching of the coefficient of thermal expansion with the insulating substrate can be achieved. As a result, defects such as peeling can be prevented, and a conductor layer having high heat cycle resistance can be realized.
The conductor layer may contain components other than the copper component and the inorganic 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.

<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 a conductor pattern 4 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. Also, one conductor 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 6a and a conductor layer 6b, similarly to the wiring circuit.
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 conductor pattern 6 in FIG. 1 or a plurality of conductor patterns as in the conductor pattern 4 in FIG. 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, inorganic 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, inorganic filler powder, thermoplastic resin, and solvent. And the following conditions (a) and (b): (a) The inorganic filler powder does not substantially contain glass, and the average particle diameter (D ₅₀ ) is 10 μm or more and 50 μm or less; (b) the above When the conductor pattern is formed, it is preferable that the conductor pattern has a volume thermal expansion coefficient of 12 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 (eg, 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.

  Although the content ratio of the copper powder in the conductor paste is not particularly limited, it is typically 50% by mass or more (for example, 60% by mass or more, preferably 70% by mass or more, more preferably 75% by mass or more) of the entire conductor paste. Thus, it is good to be 98% by mass or less (typically 90% by mass or less, for example, 85% 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 inorganic filler powder is a so-called thermal expansion coefficient adjusting material for adjusting the thermal expansion coefficient of the conductor pattern. As the inorganic filler powder, inorganic substances other than glass, for example, silica and zirconium phosphate compounds as described above may be used. The particles constituting the inorganic filler powder preferably have an average particle size of 10 μm or more and 50 μm or less. By using such an inorganic 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 pattern is 12 ppm / ° C. or less). In a preferred embodiment, the average particle size of the inorganic filler powder is larger than the average particle size of the copper powder. Thereby, a conductive pattern with higher conductivity can be formed.

  The content of the inorganic filler powder (thermal expansion coefficient adjusting material) in the conductor paste is not particularly limited because it may vary depending on, for example, the thickness of the conductor pattern to be formed, but typically 1% by mass or more of the entire conductor paste ( It is typically 5% by mass or more, for example, 10% by mass or more, and may be 30% by mass or less (typically 25% by mass or less, for example, 20% by mass or less). The volume ratio of the inorganic filler powder when the total volume of the copper powder and the inorganic filler powder is 100% by volume is preferably 25% by volume or more and 45% by volume or less. According to this configuration, for example, even when a conductive pattern (typically a conductive layer) is formed relatively thick, the thermal expansion coefficient can be matched with that of the insulating substrate, resulting in problems such as peeling. Can be suppressed. Moreover, the conductor pattern which was further excellent in electrical conductivity and heat dissipation can be formed by restraining the content rate of an inorganic 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 inorganic 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 conductor paste is not particularly limited because it may vary depending on the particle size of the copper powder or the inorganic filler powder, for example, but the minimum amount necessary for temporarily fixing the copper powder and the inorganic filler powder. It is preferable to reduce to. That is, the content of the thermoplastic resin in the conductor paste is 0.1% by mass or more (typically 0.15% 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 conductor pattern can be stably formed by setting it as 0.1 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 constituent components of the conductor paste disclosed herein (that is, copper powder, inorganic filler powder, and thermoplastic resin as a solid content), and at the same time, improves the viscosity of the solvent and applies the solvent. It also has the role of preventing sagging and bleeding during construction. 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 0.1% by mass or more (typically 1% by mass or more, for example, 5% by mass or more) of the entire conductor paste, and is 20% by mass. % Or less (typically 15% by mass or less, for example, 10% by mass or less).
Furthermore, the ratio of the total of the thermoplastic resin and the solvent in the conductor paste is preferably 10% by mass or less (typically 1 to 10% by mass, for example, 5 to 10% by mass). Thus, by increasing the ratio of the copper powder and the inorganic filler powder, 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.

  The above-described components (for example, copper powder, inorganic filler powder, thermoplastic resin and solvent) are prepared at a predetermined ratio, and kneaded by a conventionally known dispersion / kneading technique (for example, a roll mill, a mixer, etc.), thereby producing a conductive paste ( Copper paste) can be prepared. The conductive paste thus prepared can be sintered at a lower temperature (typically 500 ° C. or lower, for example, 400 to 500 ° C.) compared to the conventional one, and has 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. In addition, in the range of the said calcination temperature, since a change of a composition or a property (for example, softening etc.) does not arise in an inorganic filler component, the property equivalent to the state of the material contained in a conductor paste is maintained.

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. Accordingly, for example, even when other plating treatment (for example, nickel-gold plating treatment) is performed on the surface of the conductor layer, the plating layer can be prevented from growing on the non-formation portion of the conductor pattern, and the withstand voltage can be prevented from being lowered. be able to.
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 plating or gold plating) 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 an inorganic filler component are formed in this order on the surface of an insulating substrate made of ceramics is suitably manufactured. Can do.
The volume thermal expansion coefficient of such a conductor layer may be 12 ppm / ° C. or less (for example, 9 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).

  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. In consideration of cost and manufacturing stability, for example, a conductive layer is formed by performing electrolytic composite plating (plating method that creates a state in which inorganic 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 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, the inorganic filler powder (F1 to F4), the thermoplastic resin, and the solvent shown in Table 2 were prepared. These materials were mixed at the ratios shown in Table 4 to prepare conductor pastes (S1 to S13).

  Next, the prepared conductor paste (S1 to S13) 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 pattern 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 of about 100 to 150 μm was formed on the surface of the copper plating layer.
Then, the electroless copper plating on the silicon nitride substrate was removed by etching. 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 13) 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.
The properties of the used inorganic filler powder are summarized in Table 4. In Table 4, “D ₁₀ ”, “D ₅₀ ”, and “D ₉₀ ” are the volume-based particle size distribution measured by particle size distribution measurement based on a general laser diffraction / light scattering method, respectively, from the fine particle side. The particle diameter corresponds to 10% cumulative, 50% cumulative, and 90% cumulative. The “volume ratio” is the volume ratio occupied by the inorganic filler powder when the total volume of the copper powder and the inorganic filler powder is 100% by volume.

[Electrical characteristics]
About the conductor layer of the obtained circuit boards (Examples 1 to 7), electric 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 Table 4.

[Jointability]
About the said circuit board (Example 1- Example 7), 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 column of “Jointability” in Table 4. In Table 4, “◯” indicates that no defects in appearance such as distortion or cracking were observed in the conductor pattern even after the heat cycle, and that both were well bonded. This indicates that a defect in appearance was confirmed and / or that both were separated.

As shown in Table 4, in Examples 1 and 2 in which spherical silica having an average particle diameter of about 22 μm was used as the inorganic filler, the bondability between the substrate and the conductor pattern was high and the electrical resistivity was less than 20 μΩ · cm. It was.
On the other hand, in Example 7 in which the content of the inorganic filler (spherical silica) was reduced to 20% by volume, the electrical resistivity was reduced, but peeling of the conductor pattern was observed after the heat cycle. This is presumably because the thermal expansion coefficient of the conductor pattern was as high as 13 ppm / ° C. or higher due to the reduction in the proportion of spherical silica, and the thermal expansion consistency with the silicon nitride substrate could not be obtained. Conversely, in Example 8 in which the content of the inorganic filler (spherical silica) was increased to 50% by volume, the heat cycle resistance was excellent, but the electrical resistivity could not fall below 20 μΩ · cm.

In Examples 3 to 5 in which crushed zirconium tungstate phosphate (ZWP) having an average particle diameter of approximately 11 μm is used as the inorganic filler, the bondability between the substrate and the conductor pattern is high and the electrical resistivity is 20 μΩ · cm. It was below. Moreover, when Example 1 and Example 4 or Example 2 and Example 5 with the same content rate of an inorganic filler are compared, Example 4 and Example 5 using ZWP can implement | achieve a lower electrical resistivity. It was. This is considered to be because the volume thermal expansion coefficient of ZWP itself was smaller than that of spherical silica, so that the same volume thermal expansion coefficient could be realized with a small proportion.
On the other hand, in Example 9 where the ZWP ratio was reduced to 21% by volume as in Example 7, the coefficient of thermal expansion of the conductor pattern was as high as 12.5 ppm / ° C, and the conductor pattern was peeled off after the heat cycle. Admitted.

In Examples 10 to 13, in which spherical silica having an average particle diameter of about 3 μm was used as the inorganic filler, the electrical resistivity was higher than that of the inorganic filler having the same content ratio. This is presumably because even though the volume occupation ratio was the same, the number of inorganic filler particles in the conductor layer increased, so that the number of contacts between the particles increased and the contact resistance increased. Furthermore, in Examples 10 to 12, the bondability (heat cycle resistance) was also poor. This is probably because the number of inorganic filler particles in the conductor layer has increased, and the number of contact points of the particles has increased.
To support this, in Example 6 using spherical silica (F1 fine particle cut product) having an average particle diameter of approximately 37 μm as the inorganic filler, the electrical resistivity could be further reduced as compared with Example 1.
These results support the technical significance of the invention disclosed herein.

  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 (10)

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 includes a copper component and an inorganic filler component,
The inorganic filler component is substantially free of glass and is composed of particles having an average particle diameter of 10 μm or more and 50 μm or less,
The volume thermal expansion coefficient of the conductor layer is 12 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 volume ratio of the inorganic filler component is 25% by volume or more and 45% by volume or less when a total volume of the copper component and the inorganic filler component is 100% by volume.   The circuit board according to claim 1, wherein the copper component is obtained by sintering copper powder having an average particle diameter of 1 μm or more and 10 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 an average thickness of the conductor layer is 100 μm or more and 300 μm or less.   The circuit board according to claim 1, wherein the inorganic filler is silica and / or zirconium tungstate phosphate. A conductor paste for a circuit board for forming a glassless conductor pattern,
Including copper powder, inorganic filler powder, thermoplastic resin, and solvent,
The inorganic filler powder is substantially free of glass and has an average particle size of 10 μm or more and 50 μm or less,
A conductor paste that realizes that when the conductor pattern is formed, the conductor pattern has a volume thermal expansion coefficient of 12 ppm / ° C. or less and an electrical resistivity of less than 20 μΩ · cm.   The conductor paste according to claim 8, wherein a volume ratio of the inorganic filler powder is 25% by volume or more and 45% by volume or less when a total volume of the copper powder and the inorganic filler powder is 100% by volume.   The conductor paste of Claim 8 or 9 whose average particle diameter of the said copper powder is 1 micrometer or more and 10 micrometers or less.

Images