JP2015198209A - Circuit board and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a circuit board excellent in bond strength between an insulation substrate and a metal plate bonded to the insulation substrate and including a wiring circuit formed thereon and also excellent in bonding reliability by reducing the occurrence of peeling, warpage or the like due to thermal cycles from low temperatures to high temperatures.SOLUTION: A circuit board includes an insulation substrate, a metal plate bonded to one surface or both surfaces of the insulation substrate, and a bonding layer bonding the insulation substrate with the metal plate. The bonding layer comprises: a metal coating formed on one surface or both surfaces of the insulation substrate and made of active metal capable of forming an eutectic with Ni; and a Ni sintered layer formed by sintering Ni particles. Further, Ni particles in the Ni sintered layer are Ni fine particles having an average particle size of 15-150 nm as measured through SEM observation, and the thickness of the Ni sintered layer is 10-200 μm.

Description

  The present invention relates to a circuit board suitable for applications such as power semiconductor devices and a manufacturing method thereof, and in particular, between an insulating substrate made of a ceramic material and a metal plate bonded to the insulating substrate to form a wiring circuit. The present invention relates to a circuit board excellent in bonding strength, reduced in warp and peeling due to a cooling cycle from low temperature to high temperature, and excellent in bonding reliability between an insulating substrate and a metal plate, and a manufacturing method thereof.

Power semiconductor devices are widely used as, for example, inverters for motor control systems that can operate under conditions of high voltage and large current.In general, aluminum nitride (AlN), silicon nitride (Si ₃ N ₄ ), On one or both sides of an insulating substrate made of a ceramic material such as alumina (Al ₂ O ₃ ), a circuit pattern or a metal plate made of a metal having excellent conductivity such as Cu, Cu alloy, Al or Al alloy (hereinafter, any of these) One or both of the circuit patterns and the metal plate are simply referred to as a “metal plate”).

However, a circuit board in which a metal plate is bonded to one or both sides of such an insulating substrate is exposed to a high temperature in a bonding process in which the circuit board is bonded to its support member by soldering or the like during device manufacture. When used, there are many opportunities to be exposed to large temperature changes, such as periodic heat generation due to its operation / rest and cooling, and when exposed to such large temperature changes, the ceramic material constituting the insulating substrate Due to the large difference in thermal expansion coefficient with the metal plate, a large thermal stress acts between the insulating substrate and the metal plate, resulting in a decrease in bonding strength and warping of the circuit board. In addition, peeling may occur between the insulating substrate and the metal plate. For example, the linear thermal expansion coefficient (CTE: 40 to 400 ° C.) of a silicon nitride substrate used as an insulating substrate is (2.6 to 2.8) × 10 ⁻⁶ / K, whereas it is used as a metal plate. The Cu plate has a linear thermal expansion coefficient (CTE: 0 to 100 ° C.) of 17 × 10 ⁻⁶ / K, and there is a large difference in thermal expansion coefficient between the silicon nitride substrate and the Cu plate.

  Therefore, in the past, various problems caused by the difference in the coefficient of thermal expansion between the insulating substrate and the metal plate in such a circuit board, particularly the bonding strength between the insulating substrate and the metal plate and the thermal cycle characteristics. Various proposals have been made to solve the problem.

  For example, in Patent Document 1, when a nitride-based ceramic member (insulating substrate) and a metal member are joined with an Ag—Cu brazing material layer containing an active metal selected from Ti, Zr, and Nb. , A structure in which the Ag component and the Cu component in the Ag-Cu-based brazing material layer are melted apart to form a structure, which is generated in the cooling process after joining the ceramic member and the metal member having different coefficients of thermal expansion. There has been proposed a ceramic-metal joint that can solve problems such as cracking and breakage caused by the cooling process after joining and the load of the cooling cycle during use due to residual stress and external stress applied from the outside. .

  In Patent Document 2, a bonding agent containing metal fine particles having an average particle diameter of 1 to 100 nm and an active metal selected from Ti, Zr, Hf, and Nb is interposed between an insulating substrate and a metal plate. There has been proposed a method of manufacturing a circuit board with less defects and excellent bonding reliability by heating to a bonding temperature lower than the melting point of the metal fine particles and bonding the insulating substrate and the metal plate.

  Furthermore, in Patent Document 3, a layer containing metal nanoparticles is interposed between a ceramic substrate and a metal plate, and a heat treatment is performed at 200 to 300 ° C. to form a sintered layer in which the metal nanoparticles are sintered. The sintered layer is bonded to the ceramic substrate by an anchor effect in which metal nanoparticles are sintered on the surface of the ceramic substrate, and bonded to the metal plate by metal bonding. It has been proposed to manufacture a ceramic circuit board for a semiconductor module that relieves the thermal stress on the metal plate and has a relatively thick metal plate and has an excellent heat dissipation effect.

  Furthermore, Patent Document 4 includes a support member made of Al or an Al alloy, a bonding layer made of silver or a silver-containing composite material, a non-oxide insulating substrate such as a nitride, and the bonding layer. A circuit wiring board made of Al, Al alloy, or the like is laminated in this order, and an oxide layer is formed on both surfaces of the insulating substrate. A bonding material made of an agent is sandwiched between an insulating substrate and a circuit wiring board, etc., and formed by a bonding technique in which the metal oxide particles are reduced and sintered under heat and pressure, thereby resulting in a temperature cycle under high temperature conditions. There has been proposed a circuit board for a semiconductor module that reduces the occurrence of warpage and has excellent bonding reliability and heat dissipation.

  By the way, in recent years, environmentally friendly electric vehicles are rapidly spreading along with the growing awareness of the environment. In such electric vehicles, inverters that can operate under high voltage and high current. For example, power semiconductor devices are used. In the field of such electric vehicles, there is a demand for the development of smaller, lower-cost, high-efficiency electric systems for further spread. However, further downsizing, cost reduction, and higher efficiency are demanded.

  In order to meet these demands, instead of silicon (Si) substrate devices (Si devices) that have been used as power semiconductor devices in inverter systems so far, they have superior breakdown electric field strength and thermal conductivity. Silicon carbide (SiC) substrate devices that can operate at a current density two to three times that of the device, operate at a high temperature of 200 ° C or higher, and sometimes at a high temperature of 250 ° C or higher. Development of (SiC devices) is advancing, and development of large-capacity devices with a withstand voltage of 600 to 1200 V and a rated current of 100 to 400 A is expected for in-vehicle applications.

  Against this background, circuit boards are also required to have higher bonding strength and bonding reliability especially at high temperatures. For example, in Patent Document 1 and Patent Document 3, the temperature is −40 ° C. to 125 ° C. A thermal cycle test in a temperature range is performed, and in Patent Document 4, only a thermal cycle test in a temperature range of −45 ° C. to 200 ° C. is performed. It cannot be said that the cold-heat cycle characteristics are achieved.

Japanese Patent Laid-Open No. 05-201,777 JP 2006-120,973 A JP 2006-228,804 A JP 2012-138,541 A

  Therefore, the present inventors have excellent bonding strength between an insulating substrate made of a ceramic material and a metal plate bonded to the insulating substrate to form a wiring circuit, and warp or peel off due to a cooling cycle from low temperature to high temperature. As a result of intensive investigations to develop a circuit board that can reduce the occurrence of defects and improve reliability, a bonding layer for bonding between an insulating substrate and a metal plate is formed with a metal film of an active metal and a predetermined thickness. By forming the Ni sintered layer, the problem based on the difference in thermal expansion coefficient between the insulating substrate and the metal plate can be solved, and a circuit board having excellent bonding strength and bonding reliability can be obtained. The present invention has been completed.

Accordingly, an object of the present invention is excellent in bonding strength between an insulating substrate and a metal plate bonded to the insulating substrate to form a wiring circuit, and is also warped or peeled off by a cooling cycle from a low temperature to a high temperature. It is an object of the present invention to provide a circuit board that is excellent in bonding reliability by reducing the occurrence of the above.
Another object of the present invention is to provide a method of manufacturing a circuit board having excellent bonding strength and bonding reliability.

  That is, the present invention is a circuit board having an insulating substrate, a metal plate bonded to one or both surfaces of the insulating substrate, and a bonding layer for bonding between the insulating substrate and the metal plate. Is formed of an active metal capable of forming a eutectic with Ni and formed on one or both surfaces of the insulating substrate, and between the metal coating and the metal plate, and Ni particles are sintered. The Ni sintered layer is composed of Ni sintered layers bonded to each other. The Ni sintered layer is Ni fine particles having an average particle diameter of 15 to 150 nm measured by SEM observation, and has a thickness of 10 to 200 μm. There is a circuit board characterized by being.

  Further, the present invention is a circuit board having an insulating substrate, a metal plate bonded to one or both surfaces of the insulating substrate, and a bonding layer for bonding between the insulating substrate and the metal plate, the bonding layer Is formed of an active metal capable of forming a eutectic with Ni and formed on one or both sides of the insulating substrate and between the metal coating and the metal plate, and Ni particles are sintered. The Ni sintered layer is composed of Ni sintered layers bonded to each other. The Ni sintered layer has Ni particles whose average particle diameter is 15 to 150 nm measured by SEM observation and an average particle diameter of 0.1 mm measured by SEM observation. The ratio of the cross-sectional area (Sn) of the Ni fine particles to the sum of the cross-sectional area (Sn) of the Ni fine particles and the cross-sectional area (Sm) of the Ni fine particles. / (Sn + Sm)] is 0.2 to 0.3, and The thickness of the i sintered layer is a circuit board, which is a 10 to 200 [mu] m.

  Further, the present invention is the above-described method for producing a circuit board, wherein an active metal metal film capable of forming a eutectic with Ni is formed on one or both surfaces of the insulating substrate, and the obtained metal film and / or A Ni bonding agent containing Ni particles is applied to the surface of the metal plate, and then the insulating substrate and the metal plate are overlapped with the Ni bonding agent coating layer sandwiched between 250 ° C. and 400 ° C. in a reducing atmosphere. The coating layer is sintered by heating at a temperature of 10 to 200 μm in thickness to form a Ni sintered layer, and the metal coating formed on the surface of the insulating substrate and the Ni sintered layer are insulated as a bonding layer. A circuit board manufacturing method is characterized in that a substrate and a metal plate are joined together.

  In the present invention, the insulating substrate constituting the circuit board is a substrate made of a ceramic material such as an oxide such as alumina or zirconia, a nitride such as aluminum nitride or silicon nitride, or a carbide such as silicon carbide. Can be mentioned. In particular, when the circuit board is required to have high thermal conductivity in applications such as in-vehicle applications, a nitride-based or carbide-based ceramic material is preferable.

  In the present invention, the metal plate constituting the circuit board is not particularly limited as long as it is excellent in conductivity, thermal conductivity and the like and can be used for the circuit board. Specifically, Cu or Cu alloy is used. , Al, Al alloy, W, Mo, etc., preferably a metal plate made of Cu or Cu alloy. If necessary, the surface of these metal plates can be formed to a desired thickness by means such as electroless plating. A metal plate provided with a plating layer such as Ni / Au (outermost surface: Au) or Ni / Ag (outermost surface: Ag) (the thickness of the plating layer is usually Ni layer: about 1 to 10 μm, Au Layer: about 0.01 to 0.3 μm, and Ag layer: about 0.01 to 0.3 μm). The thickness of the metal plate is not particularly limited as long as it can be used for a circuit board, and is usually 0.1 mm or more, preferably 0.2 mm or more and 0.5 mm or less.

In the present invention, the bonding layer for bonding between the insulating substrate and the metal plate is composed of a metal film and a Ni sintered layer.
Here, the metal film constituting the bonding layer is an active metal capable of forming a eutectic with Ni in the Ni bonding agent coating layer in contact with the metal film when the Ni sintered layer is formed. Examples of such active metals include Ti, Zr, Hf, and Nb. These can be used alone or in combination with two kinds of active metals. The above can also be used as a mixture. The metal film is formed on the surface of the insulating substrate. Also, as a method of forming the metal film on the surface of the insulating substrate, a metal film having a desired thickness can be formed on the surface of the insulating substrate. Well, a conventionally known method can be adopted, specifically, for example, a vapor deposition method, a sputtering method, a method of placing and depositing the metal foil of the active metal formed by rolling, etc. Can be adopted.

  Further, the thickness of the metal coating formed on the surface of the insulating substrate is not particularly limited, but sufficient bonding strength between the metal plate and the insulating substrate and sufficient mechanical strength of the circuit board are ensured. From this point of view, it is preferably 0.05 μm or more and 1 μm or less, more preferably 0.1 μm or more and 0.9 μm or less. If it is thinner than 0.05 μm, the absolute amount of the titanium-nickel eutectic is insufficient, Depending on the application, the desired bonding strength between the insulating substrate and the metal plate may not be achieved. On the other hand, when the thickness exceeds 1 μm, an excessive amount of titanium-nickel eutectic is formed. There is a possibility that a circuit board having the above cannot be obtained.

  Further, the Ni sintered layer constituting the bonding layer is coated with a Ni bonding agent containing Ni particles on the surface of the metal film formed on the surface of the insulating substrate and / or on the surface of the metal plate, Next, the insulating substrate and the metal plate are overlapped so that the Ni bonding agent coating layer is sandwiched between the metal coating on the surface of the insulating substrate and the metal plate, and the sandwiched coating layer is sintered. In this sintering, Ni particles in the coating layer are sintered at portions where they are in contact with each other, and a so-called neck portion is formed and bonded to form a Ni sintered layer.

  Here, with respect to the thickness of the Ni sintered layer, the thermal stress generated due to the difference in thermal expansion coefficient (thermal expansion coefficient difference) between the insulating substrate and the metal plate is reduced to reduce the desired bonding strength and bonding. In order to obtain reliability, it is usually required to be 10 μm or more and 200 μm or less, preferably 10 μm or more and 100 μm or less. If the thickness of this Ni sintered layer is less than 10 μm, the effect of reducing the stress generated in the entire circuit board is reduced. The ratio of Ni with a certain amount is insufficient, the difference in coefficient of linear expansion between the metal plate and the insulating substrate is directly generated and influenced, the bonding strength is lowered, and the bonding reliability is deteriorated. On the contrary, it is thicker than 200 μm. In this case, if the supply amount of the Ni bonding agent and the process control of the bonding process are taken into consideration, the productivity is deteriorated and the cost is increased, and defects such as voids and cracks may easily enter the Ni sintered layer.

  And about this Ni sintered layer, when observed with a scanning electron microscope (SEM), the Ni particles observed and measured using the SEM image have an average particle size of 15 nm to 150 nm, preferably 80 nm to 110 nm. The following Ni fine particles are preferable, and the standard deviation value of the particle size distribution in the Ni fine particles of the Ni sintered layer is more preferably 20 nm or less, and preferably 18 nm or less. Here, when the average particle diameter measured by SEM observation is less than 15 nm, the particles easily aggregate and are difficult to handle, and the surface area increases and the amount of dispersant required increases. After that, it remains as an organic substance, and the sintering is liable to be hindered, and there is a concern that the bonding strength and the bonding reliability may be lowered. On the contrary, if it exceeds 150 nm, low-temperature baking at 400 ° C. or less becomes difficult. In addition, since the standard deviation value of the particle size distribution of Ni fine particles in the Ni sintered layer is 20 nm or less, the filling rate is increased when two particles having different particle diameters are mixed as compared with the case where the standard deviation is large. Thus, there is an advantage that the bonding strength can be increased.

  Further, in this Ni sintered layer, to increase the packing density of Ni particles to increase the contact area between Ni particles and to reduce the gap between Ni particles, and to obtain further bonding strength and bonding reliability. Further, with respect to Ni particles of the Ni sintered layer, Ni fine particles having an average particle diameter of 15 to 150 nm, preferably 80 to 110 nm, measured by SEM observation, and an average particle diameter of 0.5 to 0.5 measured by SEM observation. Ni fine particles having an average particle diameter of 3 to 7 μm are 10 μm, and the cross-sectional area (Sn) of the Ni fine particles with respect to the sum of the cross-sectional area (Sn) of these Ni fine particles and the cross-sectional area (Sm) of the Ni fine particles. The ratio [Sn / (Sn + Sm)] may be present so that the value is 0.2 to 0.3, and more preferably, the standard deviation value of the particle size distribution in the Ni fine particles of the Ni sintered layer is Ni sintered layer of 20 nm or less, preferably 18 nm or less The standard deviation value of the particle size distribution in the Ni fine particles is 10 μm or less, preferably 5 μm or less. The cross-sectional area of Ni fine particles (Sn) and the cross-sectional area of Ni fine particles (Sm) are first classified as fine particles of 300 nm or less and fine particles of 1 μm or more. The fine particles are calculated in the same manner as in the case of “average particle diameter measured by SEM observation and its standard deviation value” described later.

  Here, if the average particle size of the Ni fine particles measured by this SEM observation is less than 15 nm, it is easy to aggregate and difficult to handle, and the surface area increases and the amount of dispersant required increases, The dispersant remains as an organic substance even after firing, which tends to inhibit sintering, and there is a risk that the joint strength and joint reliability may be reduced. Conversely, if it exceeds 150 nm, low-temperature firing at 400 ° C. or lower becomes difficult, When the average particle size of Ni fine particles measured by SEM observation is less than 0.5 μm, the ratio of the particle size of Ni fine particles to Ni fine particles approaches 1, and the filling rate decreases and the bonding strength decreases. If the thickness exceeds 10 μm, the viscosity of the Ni bonding agent becomes high, and it may be difficult to apply the Ni bonding agent. In addition, since the standard deviation value of the particle size distribution of Ni fine particles in the Ni sintered layer is 20 nm or less, the filling rate is increased when two particles having different particle diameters are mixed as compared with the case where the standard deviation is large. The standard deviation value of the particle size distribution of Ni fine particles in the Ni sintered layer is 10 μm or less, and most of the particles are 20 μm or less, and the viscosity is such that the Ni bonding agent can be applied by printing. Can be held. Further, if the ratio of Ni fine particles [Sn / (Sn + Sm)] is out of the range of 0.2 to 0.3, the filling rate of Ni particles decreases in any case, and Ni fine particles and Ni fine particles It becomes impossible to achieve further improved bonding strength and / or bonding reliability by using a mixture of these. In this case, the thickness of the Ni sintered layer is usually 50 μm to 200 μm, preferably 80 μm to 150 μm.

  In the present invention, a method of manufacturing a circuit board includes a step of forming a metal film made of an active metal capable of forming a eutectic with Ni on one or both surfaces of the insulating substrate, and the metal film and / or the metal plate. The Ni bonding agent containing Ni particles is applied to the surface of the substrate, and the insulating substrate and the metal plate are overlapped so that the Ni bonding agent coating layer is sandwiched, and the coating layer is placed in a reducing atmosphere in that state. And sintering at a temperature of 250 ° C. or higher and 400 ° C. or lower to form a Ni sintered layer having a thickness of 10 to 200 μm.

  In the circuit board manufacturing method of the present invention, in the step of forming the Ni sintered layer, the coating layer containing Ni particles is sintered in a reducing atmosphere, and the reducing atmosphere is a Ni oxide film. An atmosphere that can be reduced, specifically, for example, a hydrogen-containing inert gas atmosphere having hydrogen at a predetermined concentration, and it is necessary to make the hydrogen concentration below the explosion limit for safety reasons. Therefore, nitrogen gas, argon gas, etc. whose hydrogen concentration is 1 vol% or more and 4 vol% or less, Preferably they are 2 vol% or more and 3 vol% or less can be illustrated. The sintering temperature is 250 ° C. or higher and 400 ° C. or lower, preferably 300 ° C. or higher and 400 ° C. or lower. When this sintering temperature exceeds 400 ° C., the thermal stress generated in the cooling process after firing increases. There is a possibility that the bonding strength is reduced, and warping and peeling are likely to occur. In the step of forming the Ni sintered layer, when the coating layer sandwiched between the metal film of the insulating substrate and the metal plate is sintered, the coating layer is placed in the stacking direction of the insulating substrate and the metal plate. It is not always necessary to pressurize, but pressurization may be performed if necessary. By pressurizing, the distance between the particles is reduced, the contact area between the particles is increased, and the sinterability is improved. The filling rate is also increased, voids are reduced, and bonding strength and bonding reliability are further improved.

  In the present invention, the Ni particles contained in the Ni bonding agent can be sintered at a temperature of 250 to 400 ° C. during the sintering of the Ni bonding agent coating layer, and between the Ni particles at this sintering temperature. Therefore, the presence of Ni fine particles protected with a dispersant having an average particle diameter of 15 nm or more and 150 nm or less, preferably an average particle diameter of 80 nm or more and 110 nm or less as measured by SEM is indispensable. In order to increase the packing density of Ni particles to increase the contact area between Ni particles and to reduce the gap between Ni particles, and to obtain further bonding strength and bonding reliability, SEM observation is performed. Ni fine particles protected with a dispersant having an average particle size of 0.5 μm or more and 10 μm or less measured in Step 1 are Ni fine particles relative to the sum of the cross-sectional area (Sn) of these Ni fine particles and the cross-sectional area (Sm) of Ni fine particles. Cross-sectional area ( The ratio [Sn / (Sn + Sm)] may be 0.2 to 0.3. When the average particle size of the Ni fine particles protected with the dispersant in the Ni bonding agent is less than 15 nm, the Ni particles easily aggregate and become difficult to handle, and the surface area increases and the amount of dispersant required Increased, the dispersant remains as an organic substance even after firing, which tends to hinder sintering, and there is a risk that joint strength and joint reliability will be reduced. Conversely, if it exceeds 150 nm, low-temperature firing at 400 ° C. or lower is difficult. Become. When the average particle size of the Ni fine particles protected with the dispersant in the Ni bonding agent is less than 0.5 μm, the ratio of the particle size of the Ni fine particles to the Ni fine particles approaches 1; If the filling rate is lowered, the bonding strength is lowered, the porosity is increased, and the bonding reliability may be reduced. On the contrary, if it exceeds 10 μm, the viscosity of the Ni bonding agent is increased and the application of the Ni bonding agent is performed. If the Ni fine particle ratio [Sn / (Sn + Sm)] is out of the range of 0.2 to 0.3, the Ni particle filling rate will decrease in any case. Further, it is impossible to achieve further improved bonding strength and / or bonding reliability by using a mixture of Ni fine particles and Ni fine particles. In the Ni bonding agent, the ratio of the cross-sectional area (Sn) of the Ni fine particles to the sum of the cross-sectional area (Sn) of the Ni fine particles and the cross-sectional area (Sm) of the Ni fine particles is [Sn / (Sn + Sm)]. In order to make it exist so that it may become 0.2-0.3, the ratio [Sn / (Sn + Sm)] of the said cross-sectional area substantially corresponds to the volume ratio of these Ni fine particles and Ni fine particles in Ni bonding agent. Therefore, these Ni fine particles and Ni fine particles may be present so that the volume ratio is 0.2 to 0.3.

Here, the Ni bonding agent is a Ni particle slurry or Ni particle paste obtained by dispersing Ni particles in a dispersion medium using a dispersant, preferably a Ni particle paste prepared to a high Ni concentration. is there. The dispersant has a role of suppressing aggregation and a role of suppressing oxidation.
The dispersant for preparing the Ni bonding agent is preferably an organic substance that decomposes or disappears depending on the sintering temperature. Preferably, the dispersant includes a fatty acid, or the fatty acid further includes an aliphatic amine. It is preferable to use a dispersant. Among these, the fatty acid may be either saturated or unsaturated, and may be linear or branched, such as propionic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, C3-C8 saturated fatty acids such as octanoic acid, butenoic acid (crotonic acid, etc.), pentenoic acid, hexenoic acid, heptenoic acid, octenoic acid, sorbic acid (2,4-hexadienoic acid), dodecanoic acid, tetradecanoic acid, Examples include hexadecanoic acid, octadecanoic acid, and oleic acid. The dispersant may contain one of these fatty acids alone or two or more of them. On the other hand, the aliphatic amine may be saturated or unsaturated, and may be any of primary, secondary, and tertiary amines, and may be linear or branched. Examples of such aliphatic amines include propylamine, butylamine, pentylamine, hexylamine, heptylamine, alkylamines such as octylamine, alkenylamines such as allylamine, dodecylamine, tetradecylamine, hexadecylamine, octadecylamine. And oleylamine. The dispersant may contain one of these aliphatic amines alone or two or more thereof.

  In addition, as a dispersion medium for preparing such a Ni bonding agent, at least the sintering of Ni particles is not hindered when forming a Ni sintered layer by sintering a coating layer of Ni bonding agent. It only has to volatilize or disappear. Examples of such a dispersion medium include alcohol solvents such as dodecanol, octanol, oleyl alcohol, ethylene glycol, triethylene glycol, tetraethylene glycol, terpineol, methanol, ethanol, and propanol, and new oil solvents such as hexane and toluene. An organic solvent such as

  In the Ni bonding agent, for example, Ni fine particles protected with a dispersant or Ni fine particles and Ni fine particles are blended in a proportion of 50 to 95% by mass and an organic solvent in a proportion of 5 to 50% by mass. Good. In the Ni bonding agent, an antifoaming agent, a plasticizer, a surfactant, a thickener, a binder, and the like are preferably added to the organic solvent as necessary within a range not impairing the effects of the present invention. It can mix | blend in the range used as mass% or less, More preferably 5 mass% or less.

In the circuit board of the present invention obtained by the method of the present invention, a metal film formed on the surface of the insulating substrate and a Ni sintered layer formed between the metal film and the metal plate are the insulating substrate. In this bonding layer, the metal film on the surface of the insulating substrate and the Ni sintered layer are formed at the bonding portion even at a low firing temperature of 400 ° C. or less. While forming a eutectic of the active metal and Ni in the Ni sintered layer, they are firmly bonded and joined together, and in the Ni sintered layer, Ni particles form a so-called neck portion and are firmly attached to each other. In addition to being bonded, they have a coefficient of thermal expansion between the insulating substrate and the metal plate [Ni linear thermal expansion coefficient (CTE: 0 to 100 ° C.): 13.3 × 10 ⁻⁶ / K]. Problems such as warpage and delamination due to thermal stress caused by large difference in thermal expansion coefficient between substrate and metal plate Thus, the circuit board of the present invention exhibits excellent bonding strength and bonding reliability.

[About the average particle size of Ni particles and its standard deviation value]
In the present invention, “average particle diameter measured by SEM observation and its standard deviation value” are prepared by the following method, and a measurement sample is prepared, and a scanning electron microscope (FE-SEM) [Hitachi Co., Ltd.] It was obtained from the SEM image of the measurement sample photographed by the following method using High Technologies, S-4800].

(1) Acquisition of SEM image The sample for measuring the average particle size of Ni particles in the Ni bonding agent used for preparing the circuit board and its standard deviation value is obtained by SEM using the so-called “dispersion method”. An observation sample is prepared, and the obtained SEM observation sample is observed with a SEM at a magnification of 100,000 to acquire an SEM image. That is, about 1 teaspoon of Ni particle powder to be added to the Ni bonding agent is put into a 10 ml screw tube, about 9 ml of ethanol is added, and after ultrasonic cleaning for 5 minutes, it is left to stand sufficiently, and then screwed. Only the supernatant of the liquid is collected so as not to remove the precipitate generated at the bottom of the tube. Next, the collected supernatant is put in another screw tube, ethanol is added so that the total amount becomes 9 ml, and the operations of ultrasonic cleaning, standing, and collecting the supernatant are repeated twice as described above. Thereafter, the collected supernatant is dropped on a carbon support film and dried to prepare a sample for SEM observation. About the sample for SEM observation prepared in this way, in the case of Ni fine particle, it observes by 100,000 times by SEM, and in the case of Ni fine particle, it observes by 1.5000 times by SEM, SEM images are acquired. An example of the SEM image of the Ni fine particles thus obtained (Ni fine particles in the Ni fine particle paste used in Example 1) is shown in FIG.

  For the sample for measuring the average particle size of Ni particles in the Ni sintered layer of the circuit board and its standard deviation value, first embed the circuit board in a curable epoxy resin, cure the resin, and then use a grindstone cutting machine. It is cut out to a size that fits on the SEM sample stage, and then the cut surface is polished and finished into a cross section for SEM observation. The cross section for SEM observation of the measurement sample prepared in this way is observed with a SEM at a magnification of 100,000 times to obtain an SEM image of Ni fine particles. FIG. 1B shows an example of an SEM image of Ni fine particles in the Ni sintered layer thus obtained (circuit board of Example 1).

(2) Calculation of the average particle size of Ni particles and the standard deviation value Next, the obtained SEM image is read into software that can perform image processing (such as Microsoft® Office PowerPoint®), and the outermost surface. The particles arranged in the column were visually judged, the edge portion of the primary particle on the outermost surface was traced, the particles were filled one by one, and the reference scale bar was added with a straight line.
Next, the above image was written out in tif format and read into an image analysis tool ImageJ 1.47V (Wayne Rasband, National Institutes of Health, USA. ImageJ is in the public domain.). Then, after converting the read image with the scale bar to gray scale (8bit), measure the length of the scale bar in the image, and from the measured length of the scale bar, the length per pixel of the read image Registered. Next, a portion other than the scale bar was selected to form an image of only particles, and a threshold value was determined in order to binarize the particle image. At that time, the portions where the particles overlap (the neck portion after sintering) were separated from each other by the geometric processing (Watershed processing) and binarized.

Since the binarized image obtained in this way has already identified each particle, the ferret diameter (the longest distance between two points in the particle) is read, and the arithmetic average ferret diameter Was calculated. The ferret diameter at this time corresponds to the diameter when the particle is a true sphere.
As described above, a SEM image (100,000 times) having a viewing angle of 1270 nm × 950 nm is arbitrarily selected, and the arithmetic average ferret diameter is calculated and average particle diameter is calculated for approximately 70 to 100 Ni particles in the SEM image. The standard deviation values were calculated from all ferret diameters using Excel using the STDEV equation.

Since the Ni particles contained in the Ni bonding agent have a sintering temperature of 250 to 400 ° C., the Ni particles after sintering are sintered at the portions in contact with each other, so-called so-called “Ni particles”. It exists in a state where the neck portion is formed and bonded, and the particle size of the Ni particles in the Ni bonding agent is substantially maintained to a measurable level even in the Ni sintered layer after sintering.
That is, in general, in the particle sintering process, (a) acute contact of particles, (b) generation / growth of neck part, generation of open pores, (c) enlargement of neck part / grain boundary, open pores The process proceeds in the order of continuity (network formation), and (d) pore cutting / isolation, annihilation. For example, in Ag nanoparticles and Au nanoparticles, these processes are likely to proceed. Thus, the continuous holes are almost closed and the gaps disappear (for example, see “Sintered Materials Engineering” by Tsuneo Ishida, page 78 of Morikita Publishing Co., Ltd.). On the other hand, in the present invention, as shown in FIG. 2, (a) the sharp contact from the agglomeration of Ni fine particles to (b) the growth / generation of the neck portion b is limited to sintering, (Continuous hole c) remains, and the particle size of Ni particles in the Ni bonding agent is substantially maintained even in the sintered Ni layer after sintering.

  According to the present invention, the bonding strength between the insulating substrate and the metal plate bonded to the insulating substrate to form a wiring circuit and the like is excellent, and the bonding reliability from low temperature to high temperature is excellent. The circuit board which can reduce generation | occurrence | production of the curvature, peeling, etc. at the time of manufacture or use of can be provided. In addition, according to the method of the present invention, a circuit board having excellent bonding strength and bonding reliability can be easily manufactured industrially.

1A is an example of an SEM image obtained by photographing Ni fine particles in the Ni fine particle paste used in Example 1, and FIG. 1B is a circuit board obtained in Example 1. FIG. It is an example of the SEM image which image | photographed the Ni fine particle in the Ni sintered layer in. FIG. 2 is an explanatory view schematically showing a sintered state of Ni fine particles in the present invention. FIG. 3 is an explanatory diagram schematically illustrating the circuit board according to the first embodiment. FIG. 4 is an explanatory diagram schematically illustrating a circuit board according to the second embodiment.

Hereinafter, a circuit board and a method for manufacturing the same according to the present invention will be described in detail based on examples and comparative examples shown in the accompanying drawings.
Here, “the average particle diameter of Ni particles in the Ni sintered layer” was measured according to the above-described method for determining the average particle diameter of Ni particles. The particle size of the Ni particles contained in the Ni bonding agent used for the circuit board preparation is substantially maintained even in the Ni sintered layer after sintering at a sintering temperature of 400 ° C. or less. The description is omitted in the following examples and comparative examples.
In addition, for “the thickness of the metal coating” and “the thickness of the Ni sintered layer”, a measurement sample prepared for measuring the average particle diameter of Ni particles in the Ni sintered layer of the circuit board is used. The cross section for SEM observation of this measurement sample was observed with a SEM at 10,000 to 100,000 times, and obtained using a scale bar.
Furthermore, the “bond strength” between the insulating substrate and the metal plate is determined by measuring the shear strength of the metal plate in a die / shear mode using a bond tester (DAGE Universal Bond Tester: Series 4000). It was.

[First Embodiment]
FIG. 3 schematically shows a circuit board A according to the first embodiment of the present invention. The circuit board A of the first embodiment has a laminated structure in which an insulating substrate 1, a metal plate 2, a metal coating 3a, a Ni sintered layer 3b, and a metal plate 2 are joined in order. The metal coating 3a is formed by depositing an active metal on the surface of the insulating substrate 1, and the Ni sintered layer 3b is obtained by applying a Ni bonding agent containing Ni particles on the surface of the metal coating 3a. A metal plate 2 is overlaid on the coated layer and the coated layer of the Ni bonding agent is sintered. The insulating substrate 1 and the metal plate 2 are formed of the metal coating 3a and the Ni sintered layer 3b. Are joined together as a joining layer.

[Examples 1 to 12 and Comparative Examples 1 to 5]
Ni fine particles having an average particle size of 115 nm, Ni fine particles having an average particle size of 150 nm, or Ni fine particles having an average particle size of 3000 nm coated with oleic acid and oleylamine, 1-octanol having a boiling point of 198 ° C. as a dispersion medium, and a binder An acetal resin was kneaded at a ratio corresponding to 85% by mass, 10% by mass, and 5% by mass, respectively, to prepare a Ni fine particle paste as a Ni bonding agent. In addition, the average particle diameter of Ni particle | grains is the value measured by SEM observation by the method mentioned above.

  Next, when preparing the circuit board A according to the first embodiment, first, a silicon nitride substrate having a size of 15 mm × 15 mm × 0.6 mm used as the insulating substrate 1 is shown in Table 1 on one side. Active metal was vapor-deposited to form a metal vapor-deposited film having the metal species and thickness shown in Table 1 as the metal coating 3a. Next, the above-mentioned Ni bonding agent is applied onto the formed metal coating 3a by printing, and then has a size of 10 mm in length × 10 mm in width on the coating layer of the Ni bonding agent and is shown in Table 1. A metal plate 2 having a metal type and a thickness was placed, and the space between the coating layer and the metal plate 2 was averaged by applying pressure from the upper surface of the metal plate 2 to room temperature at 5 MPa for 10 seconds. Thereafter, the Ni layer 3b having the thickness shown in Table 1 is formed by sintering the coating layer at a temperature shown in Table 1 in a nitrogen gas atmosphere with a hydrogen concentration of 3 vol%. The insulating substrate 1 and the metal plate 2 were bonded using the bonding layer 3b as a bonding layer.

  About the circuit board of each Example and Comparative Example prepared as described above, the bond strength was measured using a bond tester (DAGE Universal Bond Tester: Series 4000) and the shear strength of the metal plate was measured. Asked. For bonding reliability, a vapor phase thermal shock test apparatus (ESPEC TSA-72ES-W) was used, and cooling at −40 ° C. for 30 minutes and heating at 250 ° C. for 30 minutes was taken as 100 cycles. The thermal cycle test is repeated, the test piece after the test is observed, whether or not the metal plate is peeled off from the insulating substrate, and when the circuit board is placed on the surface plate, The warpage and lifting at the center were visually observed and evaluated according to the following criteria.

Bonding reliability (double-circle): The metal plate does not peel from the insulating substrate, and no warping or lifting is observed before and after the thermal cycle test.
Bonding reliability ○: The metal plate is not peeled off from the insulating substrate, but warpage or lifting of 1 mm or less is observed after the thermal cycle test.
Bonding reliability Δ: The metal plate is not peeled from the insulating substrate, but the bonding strength after the test is 1 kgf / mm ² or less.
Bonding reliability x: The metal plate is peeled from the insulating substrate.
The results are shown in Table 1.

As apparent from the results shown in Table 1, in the case of Examples 1 to 12 in the circuit board A of the first embodiment, the bonding strength is 1 kgf / mm ² or more before and after the thermal cycle test, Further, the metal plate was not peeled off from the insulating substrate, and the warping and floating of the insulating substrate were within 1 mm, and both the bonding strength and bonding reliability were excellent.
On the other hand, in the case of Comparative Examples 1 to 5, the bonding strength before the thermal cycle test or after the thermal cycle test is lower than 1 kgf / mm ² , or the metal plate is easily peeled after the thermal cycle test. Was lower than 1 kgf / mm ² . In the case of Comparative Example 3 where the joining temperature was 200 ° C., the Ni fine particles used as the Ni particles were not sintered, and the Ni sintered layer was not formed. Moreover, in the case of the comparative example 4 whose joining temperature is 450 degreeC, the joining strength before a thermal cycle test was low, and peeling generate | occur | produced after the thermal cycle test, but this is when cooling from junction temperature to room temperature. It is presumed that the temperature difference between the insulating substrate and the metal plate is large, the thermal stress due to the difference in thermal expansion between the insulating substrate and the metal plate is large, and the bonding layer is defective.

[Second Embodiment: Examples 13 to 25 and Comparative Examples 6 to 11]
FIG. 4 schematically shows a circuit board B according to the second embodiment of the present invention. Unlike the circuit board A of the first embodiment, the circuit board B of the second embodiment is an olein shown in Table 2 as a Ni bonding agent for forming the Ni sintered layer 3b of the bonding layer. Ni fine particles Sn having an average particle diameter of 115 nm, Ni fine particles Sn having an average particle diameter of 150 nm, Ni fine particles Sm having an average particle diameter of 1 μm, and Ni fine particles Sm having an average particle diameter of 3 μm coated with acid and oleylamine are used. These Ni fine particles Sn (Ni particles) and Ni fine particles Sm (Ni particles) added at the Ni fine particle ratio [Sn / (Sn + Sm)] shown in Table 2 were used. In addition, the average particle diameter of Ni particle | grains is the value measured by SEM observation by the method mentioned above.
About points other than the above, it is the same as that of the case of 1st Embodiment A, and also performed the measurement of the joint strength, and the thermal cycle test similarly.
The results are shown in Table 2.

As is apparent from the results shown in Table 2, in the case of Examples 12 to 25 in the circuit board B of the second embodiment, the bonding strength is 1 kgf / mm ² or more before and after the thermal cycle test. In addition, the metal plate is not peeled off from the insulating substrate, and the warping and floating of the insulating substrate are within 1 mm except in Examples 23 and 24, and both the bonding strength and the bonding reliability are excellent. It was.
On the other hand, in the case of Comparative Examples 6 to 11, the bonding strength before the thermal cycle test or after the thermal cycle test is lower than 1 kgf / mm ² , or the metal plate is easily peeled after the thermal cycle test. Was lower than 1 kgf / mm ² . In the case of Comparative Example 8 where the bonding temperature was 200 ° C., the Ni fine particles used as the Ni particles were not sintered, and the Ni sintered layer was not formed. Moreover, in the case of the comparative example 9 whose joining temperature is 450 degreeC, the joining strength before a thermal cycle test was low, and peeling generate | occur | produced after the thermal cycle test, but this is when cooling from junction temperature to room temperature. It is presumed that the temperature difference between the insulating substrate and the metal plate is large, the thermal stress due to the difference in thermal expansion between the insulating substrate and the metal plate is large, and the bonding layer is defective. Further, in the case of Comparative Examples 10 and 11 where the ratio of Ni fine particles [Sn / (Sn + Sm)] is 0.1 or 0.8, both the bonding strength and the bonding reliability before the thermal cycle test are low. This is presumably due to the fact that the Ni fine particle Sm was added and the filling rate of the Ni particles was lowered, and the contact area between the Ni particles was reduced and the bonding strength was lowered.

  a ... acute angle contact of particles, b ... neck part, c ... pores (continuous holes), A, B ... circuit board, 1 ... insulating board, 2 ... metal plate, 3a ... metal coating, 3b ... Ni sintered layer, Sn ... Ni fine particles, Sm ... Ni fine particles.

Claims (17)

A circuit board having an insulating substrate, a metal plate bonded to one or both surfaces of the insulating substrate, and a bonding layer for bonding between the insulating substrate and the metal plate;
The bonding layer is made of an active metal capable of forming a eutectic with Ni and a metal film formed on one or both surfaces of the insulating substrate, and is formed between the metal film and the metal plate, and Ni particles are formed. It consists of Ni sintered layers that are sintered and bonded together,
The Ni sintered layer is a fine Ni substrate having an average particle diameter of 15 to 150 nm measured by SEM observation, and a thickness of 10 to 200 μm.   The circuit board according to claim 1, wherein the Ni fine particles of the Ni sintered layer have a standard deviation value of a particle size distribution of 20 nm or less.   The circuit board according to claim 1, wherein the insulating substrate is made of a nitride-based or carbide-based ceramic material.   The circuit board according to claim 1, wherein the metal film is a Ti film.   The circuit board according to claim 1, wherein the Ni sintered layer has a thickness of 10 to 100 μm. A circuit board having an insulating substrate, a metal plate bonded to one or both surfaces of the insulating substrate, and a bonding layer for bonding between the insulating substrate and the metal plate;
The bonding layer is made of an active metal capable of forming a eutectic with Ni and a metal film formed on one or both surfaces of the insulating substrate, and formed between the metal film and the metal plate, and Ni particles are formed. It consists of Ni sintered layers that are sintered and bonded together,
The Ni sintered layer is a mixture of Ni fine particles having an average particle diameter of 15 to 150 nm measured by SEM observation and Ni fine particles having an average particle diameter of 0.5 to 10 μm measured by SEM observation. In addition, the ratio [Sn / (Sn + Sm)] of the cross-sectional area (Sn) of Ni fine particles to the sum of the cross-sectional area (Sn) of Ni fine particles and the cross-sectional area (Sm) of Ni fine particles is 0.2-0. 3 and the Ni sintered layer has a thickness of 10 to 200 μm.   7. The circuit according to claim 6, wherein the Ni particles of the Ni sintered layer have a standard deviation value of the particle size distribution of Ni fine particles of 20 nm or less and a standard deviation value of the particle size distribution of Ni fine particles of 10 μm or less. substrate.   The circuit board according to claim 6 or 7, wherein the insulating substrate is made of a nitride-based or carbide-based ceramic material.   The circuit board according to claim 6, wherein the metal film is a Ti film.   The circuit board according to claim 6, wherein the Ni sintered layer has a thickness of 50 to 200 μm. A method for producing a circuit board according to any one of claims 1 to 10,
Forming a metal film of an active metal capable of forming a eutectic with Ni on one or both surfaces of the insulating substrate;
Applying a Ni bonding agent containing Ni particles protected with a dispersant to the surface of the obtained metal coating and / or the metal plate;
Next, the insulating substrate and the metal plate are overlapped with the Ni bonding agent coating layer interposed therebetween, and heated in a reducing atmosphere at a temperature of 250 ° C. or more and 400 ° C. or less to sinter the coating layer to have a thickness of 10 to 10. Forming a 200 μm Ni sintered layer;
A method of manufacturing a circuit board, comprising: bonding a metal film formed on a surface of the insulating substrate and the Ni sintered layer to each other between the insulating substrate and the metal plate as a bonding layer.   The Ni particles protected with the dispersant in the Ni bonding agent are Ni fine particles having an average particle diameter of 15 to 150 nm measured by SEM observation, and the thickness of the Ni sintered layer is 50 to 100 μm. The method for manufacturing a circuit board according to claim 11.   The method of manufacturing a circuit board according to claim 12, wherein the Ni fine particles protected with the dispersant in the Ni bonding agent have a standard deviation value of a particle size distribution of 20 nm or less.   The Ni particles protected with the dispersant in the Ni bonding agent include Ni fine particles having an average particle diameter of 15 to 150 nm measured by SEM observation and Ni fine particles having an average particle diameter of 0.5 to 10 μm measured by SEM observation. The ratio of the cross-sectional area (Sn) of the Ni fine particles to the sum of the cross-sectional area (Sn) of the Ni fine particles and the cross-sectional area (Sm) of the Ni fine particles as well as the mixture with the particles [Sn / (Sn + Sm)] The method for manufacturing a circuit board according to claim 11, wherein the value is 0.2 to 0.3, and the thickness of the Ni sintered layer is 50 to 200 μm.   The circuit according to claim 14, wherein the Ni particles of the Ni sintered layer have a standard deviation value of the particle size distribution of Ni fine particles of 20 nm or less and a standard deviation value of the particle size distribution of Ni fine particles of 10 µm or less. A method for manufacturing a substrate.   The method for manufacturing a circuit board according to claim 11, wherein the insulating substrate is made of a nitride-based or carbide-based ceramic material.   The method for manufacturing a circuit board according to claim 11, wherein the metal film is a Ti film.