JP2006120973A - Circuit board and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the manufacturing method of a circuit board which hardly generates defects and a circuit board using it which is excellent in heat dissipation property, and has high junction strength and is excellent in junction reliability. <P>SOLUTION: An adhesive 3 which comprises metallic fine particle having an average particle diameter of 1 to 100 nm and at least one kind of active metal selected from Ti, Zr, Hf and Nb is interposed between an insulating substrate 1 and a metallic plate 5. The method has a junction process for joining the insulating substrate 1 and the metallic plate 5 by heating a lamination body to a junction temperature less than a melting point of the metallic fine particle. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method of manufacturing a circuit board including a metal plate and an insulating substrate used in a semiconductor device or the like, and in particular, excellent mechanical strength obtained by joining the metal plate and the insulating substrate using metal nanoparticles. The present invention relates to a circuit board having high reliability such as cold-heat cycle characteristics, low cost, and excellent mass productivity, and a manufacturing method thereof.

Conventionally, as an insulating substrate constituting a semiconductor device, a copper (Cu) circuit board or the like is integrally bonded as a wiring layer to the surface of a ceramic sintered body typified by alumina (Al ₂ O ₃ ), aluminum nitride (AlN) or the like. Such circuit boards are widely used.

  These circuit boards are made of metal such as copper (Cu), which has excellent thermal and electrical conductivity, so that the heat generated from the semiconductor device can be quickly released outside the device. Therefore, there is an advantage that the delay and malfunction of the circuit operation of the semiconductor device can be eliminated.

  As a method for forming an electric circuit of such a circuit board, an insulating substrate made of ceramics and a circuit board made of metal are joined. As this joining method, conventionally, a method using a refractory metal such as Mo or W, a method using an active metal such as a group 4A element or a group 5A element, and the like are known. The active metal method is frequently used because sealing properties, high reliability, and the like are obtained.

  The active metal method is a joining method that utilizes the fact that metal elements such as Ti, Zr, Hf, and Nb are easily wetted and react with ceramic materials. Specifically, a brazing material to which an active metal is added is used. It is used as a brazing method used, a method (solid phase diffusion bonding) or the like in which an active metal foil or powder is interposed between an insulating substrate and a metal member.

For example, an active metal such as Ti is added to a eutectic brazing material (Ag: 72% by mass) of Cu and Ag, this is interposed between an insulating substrate and a metal member, and heat-treated at an appropriate temperature for bonding. A method has been proposed. (See Patent Document 1).
Japanese Patent Laid-Open No. 5-201777

  However, despite the high bonding strength required for the joined part between the insulating substrate and the metal member, the thermal expansion coefficient of the ceramic material is smaller than that of the metal material. There was a problem that defects such as cracks and peeling occurred.

  This is because, when a ceramic material and a metal material with significantly different coefficients of thermal expansion are joined, residual stress is caused by the difference in thermal expansion during the cooling process after joining, and the joint strength is greatly reduced due to synergy with external stress. Also, it is a problem that occurs when cracks are generated from the maximum point of stress due to the cooling process after joining or the addition of a thermal cycle, which eventually leads to the destruction of the ceramic material.

  That is, a circuit board excellent in heat dissipation and excellent in bonding strength and reliability has not been provided yet.

  Accordingly, an object of the present invention is to provide a method of manufacturing a circuit board with few occurrences of defects and a circuit board having excellent heat dissipation, high bonding strength, and excellent bonding reliability.

  The method for manufacturing a circuit board according to the present invention includes an insulating substrate, a metal plate, metal fine particles having an average particle diameter of 1 to 100 nm, and at least one active metal selected from Ti, Zr, Hf, and Nb. And a bonding step of bonding the insulating substrate and the metal plate by heating the laminated body to a bonding temperature lower than the melting point of the metal fine particles with a bonding agent containing To do.

  Moreover, as for the manufacturing method of the circuit board of this invention, it is desirable that the said active metal is 2-7 mass% of the metal component contained in the said binder.

  In the method for producing a circuit board according to the present invention, the metal fine particles preferably contain one or more elements selected from the group consisting of iron, silver, copper, nickel, and indium.

  In the method for manufacturing a circuit board according to the present invention, the metal fine particles are preferably formed by coating the periphery of the metal core particles with an organic substance.

  In the circuit board manufacturing method of the present invention, it is desirable that the insulating substrate is at least one ceramic selected from aluminum nitride, silicon nitride, and aluminum oxide.

  In the method for manufacturing a circuit board according to the present invention, it is preferable that the metal plate is made of at least one metal selected from copper, aluminum, tungsten, molybdenum and alloys thereof.

  In the method for manufacturing a circuit board according to the present invention, it is desirable to heat and bond the laminates while pressing them in the lamination direction.

In the method for manufacturing a circuit board according to the present invention, it is desirable to pressurize the laminate with a pressure of 10 to 100 g / cm ² with respect to the area of the joint.

  In the method for manufacturing a circuit board according to the present invention, it is preferable that the bonding is performed at 500 ° C. or less.

  In the method for manufacturing a circuit board according to the present invention, it is preferable that the bonding step is performed in an inert gas atmosphere or in a vacuum.

  The circuit board of the present invention is manufactured by the circuit board manufacturing method described above.

  According to the method for producing a circuit board of the present invention, as the metal forming the connecting agent, metal fine particles having a large surface area and a large sum of surface energies and having an average particle diameter of 1 to 100 nm are used. Bonding is likely to occur, and the insulating substrate and the metal plate can be bonded at a much lower temperature than when using a normal metal powder having an average particle size exceeding 100 nm. The stress resulting from the thermal expansion difference can be significantly reduced.

  Furthermore, by adding at least one element selected from the group of Ti, Zr, Hf, and Nb to the bonding agent, the metal component forming the bonding agent is easily wetted with respect to the insulating substrate. In addition, the bonding strength between the insulating substrate and the metal plate can be remarkably improved because the insulating substrate and the bonding agent easily react with each other.

  The effect of reducing the stress and the effect of improving the bonding strength can be combined, and the circuit board excellent in connection reliability with the insulating substrate and the metal plate can be easily manufactured.

  Moreover, according to the method for manufacturing a circuit board of the present invention, the bonding temperature can be sufficiently lowered by setting the active metal ratio to 2% by mass or more. Moreover, the softness | flexibility of a joining layer can fully be maintained because the ratio of an active metal shall be 7 mass% or less.

  According to the method for manufacturing a circuit board of the present invention, it is desirable to use a metal containing one or more elements selected from the group of iron, silver, copper, nickel, and indium as the metal fine particles.

  For example, when iron (Fe) is used, if the particle size is reduced to 50 nm, the sintering start temperature is 300 to 400 ° C., 20 nm for silver (Ag), 60 to 80 ° C., 50 μm for copper (Cu). When it is about 200 ° C. and nickel (Ni) is 20 nm, it becomes possible to sinter at a temperature of 200 ° C. or less (Noboru Ichinose, et al. “Introduction to Ultrafine Particle Technology” (1988.7 Ohm) P.26. ~ 29).

  In addition, by coating the periphery of the metal core particles with an organic material to form metal fine particles, the metal fine particles can be stably and uniformly dispersed in an organic solvent, and high property stability is imparted to the metal fine particles. It becomes possible to do.

  In addition, by using a ceramic made of a material selected from aluminum nitride, silicon nitride, and aluminum oxide as the insulating substrate, it is possible to increase the thermal conductivity of the insulating substrate and obtain an excellent circuit substrate with high heat dissipation. In addition, it is possible to increase the strength of the insulating substrate and prevent the insulating substrate from being damaged by thermal stress.

  Further, by forming the metal plate with a metal made of at least one of copper, aluminum, tungsten, molybdenum and alloys thereof, it becomes possible to reduce the electrical resistance, suppress the heat generation of the metal circuit, Since the conductivity can be increased, high heat dissipation can be realized.

  In addition, in the bonding process, it is possible to firmly bond the metal plate and the insulating substrate by heating the laminated body of the insulating substrate and the metal plate laminated via the bonding agent while applying a predetermined pressure. Become.

By making this pressurizing pressure within a range of 10 to 100 g / cm ² with respect to the area of the joint, the metal plate follows the fine irregularities of the insulating substrate and prevents the joint defect and optimizes the joint thickness. It becomes possible to keep it.

  Moreover, by reducing the bonding temperature to 500 ° C. or less, it is possible to reduce thermal stress due to the difference in thermal expansion coefficient between the insulating substrate and the metal plate, and to prevent cracks occurring in the ceramics, A highly reliable circuit board having excellent mechanical strength can be obtained.

  Further, by performing the bonding step in an inert gas atmosphere or in a vacuum, oxidation of the metal plate and the bonding agent can be prevented, and good bonding can be performed.

  According to the circuit board manufacturing method of the present invention described above, when an insulating substrate made of ceramics and a metal plate made of metal can be joined, both can be joined more firmly and the joint temperature can be significantly reduced. It is possible to reduce the thermal stress caused by the difference in thermal expansion coefficient between the insulating substrate and the metal plate, and to prevent cracks occurring in the insulating substrate, and it has excellent mechanical strength and high reliability. A substrate can be obtained.

  That is, according to the circuit board manufacturing method of the present invention, it is possible to obtain a circuit board that is inexpensive, excellent in heat dissipation, and excellent in mechanical strength and reliability.

  In the method of manufacturing a circuit board according to the present invention, a bonding agent 3 is formed on the surface of an insulating substrate 1 made of ceramic as shown in FIG. 1A as shown in FIG. As shown in FIG. 1, the metal plate 5 is disposed on the bonding agent 3 to produce a laminated body 7, and the laminated body 7 is processed at a predetermined temperature, whereby the bonding agent as shown in FIG. 3, the method of manufacturing the circuit board 9 in which the insulating substrate 1 and the metal plate 5 are firmly bonded to each other.

  Below, the manufacturing method of the circuit board of this invention is demonstrated in detail.

  According to the manufacturing method of the circuit board 9 of the present invention, as the metal component in the bonding agent 3 for bonding the insulating substrate 1 and the metal plate 5, fine metal particles having an average particle diameter of 1 to 100 nm, Ti, Zr, Hf It is important to contain at least one active metal selected from Nb.

  That is, by using metal fine particles, the bonding temperature between the insulating substrate 1 and the metal plate 5 can be lowered, and at least one active metal selected from Ti, Zr, Hf, and Nb is further added. By adding, the wettability and reactivity between the bonding agent 3 and the insulating substrate 1 are improved, so that the bonding temperature can be further lowered, and the stress based on the difference in thermal expansion coefficient between the insulating substrate 1 and the metal plate 5 Can be significantly reduced, and the bonding strength between the insulating substrate 1 and the metal plate 5 can be improved. Therefore, the combined reliability of the insulating substrate 1 and the metal plate 5 is combined. Therefore, it is possible to easily produce the circuit board 9 excellent in the above.

  As described above, the average particle diameter of the metal fine particles needs to be 1 to 100 nm, but is more preferably 10 nm or more and 70 nm or less, and particularly preferably 20 nm or more and 50 nm or less.

  The addition amount of the active metal is preferably 2% by mass or more, and more preferably 4% by mass or more in order to obtain a reduction in bonding temperature and sufficient bonding strength.

  On the other hand, when the active metal is added in excess of 7% by mass, the added bonding strength is increased, but the bonding layer becomes hard and may cause cracks when a thermal cycle is added. The addition amount of the active metal is desirably 7% by mass or less. Furthermore, it is desirable to set it as 5 mass% or less.

  The metal fine particles described above are preferably formed by coating the surface of the metal core fine particles with an organic substance from the viewpoint of improving the handleability. Thereby, the metal fine particles which are easily aggregated can be easily dispersed in the bonding agent 3. Further, even when a solvent or a binder is added to the bonding agent 3, the amount can be reduced, and the solvent or the binder can be easily removed in a step prior to the bonding step.

  Below, the constituent material of the bonding agent 3 used in the method for manufacturing the circuit board 9 of the present invention will be described in more detail.

  In the form described below, in order to explain more specifically, an example in which metal fine particles made of silver and metal fine particles made of copper are mixed and used as the metal fine particles is shown. Needless to say, metal fine particles made of other metals such as palladium may be used alone or in combination.

  Ag metal fine particles and Cu metal fine particles, which are metal fine particles used in the bonding agent 3 used in the present invention, are composed of, for example, a metal nucleus (silver and copper particles) composed of simple silver and copper simple particles of about 5 nm. It has a structure in which the periphery is bound and covered with an organic compound made of, for example, an alkyl chain shell.

  Such silver and Cu fine metal particles bound and covered with alkyl chain shells (organic compounds) are saponified with, for example, myristic acid, stearic acid or oleic acid with sodium hydroxide, and then reacted with silver nitrate. Can be produced at low cost by heating and purifying the linear fatty acid silver salt (for example, the carbon number of the alkyl chain = 14 or 18) in a nitrogen atmosphere at about 250 ° C. for 4 hours.

  In addition, as another production method, for example, silver nitrate (metal salt) is reduced below its decomposition reduction temperature in a naphthenic high boiling point solvent (non-aqueous solvent) and in the presence of oleic acid (ionic organic compound). You may make it manufacture Ag metal microparticles | fine-particles which coat | covered the circumference | surroundings with an ionic organic compound by heating at about 240 degreeC below the decomposition temperature of an ionic organic compound for 3 hours.

  Since the Ag metal fine particles and Cu metal fine particles produced in this way are covered with an alkyl chain shell or an ionic organic compound, when they are dissolved in an organic solvent such as cyclohexane, they do not aggregate with each other. In a stable state, it is uniformly mixed in the solvent and becomes transparent, that is, a solubilized state.

  When the Ag metal fine particles and Cu metal fine particles thus prepared are mixed with a eutectic composition of Cu and Ag (Ag: 72% by mass, Cu: 28% by mass) to produce composite metal fine particles at a lower temperature. It becomes possible to join. The mixing ratio is not limited to this, and it is desirable that the mixing ratio is mainly an eutectic composition of Ag and Cu or a composition in the vicinity thereof.

  Further, an appropriate amount of at least one active metal selected from Ti, Zr, Hf, and Nb is blended with the composite metal fine particles. The active metal is activated at a heat treatment temperature (bonding temperature), reacts with the insulating substrate to become a nitride, contributes to improving the bonding strength, and is uniformly distributed in the bonding layer.

  This active metal can be added to the bonding agent, for example, in the form of a metal powder. The average particle size of the active metal powder does not need to be as fine as the metal fine particles, and a powder of about 1 to 10 μm, particularly a powder of 1 to 3 μm is preferably used. For the purpose of further reducing the bonding temperature, it is desirable to use fine particles of 1 to 100 nm.

  The metal fine particles and the active metal thus produced are mixed and dispersed in a solvent composed of one or a plurality of liquids such as an organic solvent, a liquid polymer material, water, alcohol, etc. A bonding agent is prepared. Here, the metal fine particle has a metal cluster size of about 5 nm and is in a very small cluster shape, and can maintain a state of being uniformly mixed in the medium with good dispersibility.

  Here, the metal fine particles are dispersed in a solvent so that the weight ratio of the metal portion (including both the metal core and aggregate, the same shall apply hereinafter) to the total liquid is preferably 1% or more and 85% or less, and By appropriately adding a dispersant or a gelling agent and liquefying, a liquid bonding agent having desired fluidity in which metal fine particles that can be sintered and bonded at a low temperature are uniformly dispersed can be obtained.

  At this time, if the weight ratio with respect to the whole metal portion in the bonding agent using the metal fine particles as the bonding material exceeds 85%, the fluidity as the liquid bonding agent is remarkably lowered. When filling with, incomplete filling portion is likely to occur.

  Furthermore, when the weight ratio with respect to the whole metal part in the bonding agent is 1% or less, as a result of excessive organic components contained in the bonding agent, degassing at the time of firing becomes insufficient, and defects are likely to occur in the bonding portion. Therefore, this ratio is limited to the above range.

  The paste containing the metal fine particles and the active metal, which is the bonding agent 3 obtained in this way, is formed on the surface of the insulating substrate 1 by a screen printing method or the like as shown in FIG. The circuit board 9 of the present invention as shown in FIG.

  The insulating substrate 1 used for the circuit board 9 is preferably a ceramic made of a material selected from aluminum nitride, silicon nitride, and aluminum oxide.

  Thus, by making the insulating substrate 1 a ceramic made of a material selected from aluminum nitride, silicon nitride, and aluminum oxide, it is possible to increase the thermal conductivity of the insulating substrate 1, and an excellent circuit with high heat dissipation. The substrate 9 can be obtained, the strength of the insulating substrate 1 can be increased, and the insulating substrate 1 can be prevented from being damaged by thermal stress.

  At this time, as the material of the insulating substrate 1, for example, it is preferable to use aluminum nitride in terms of high thermal conductivity and high cooling efficiency, and in terms of high strength, it is preferable to use silicon nitride. Aluminum oxide is preferably used in terms of high strength and low cost.

  In particular, when aluminum oxide is used, the thermal conductivity tends to be lower than that of aluminum nitride or silicon nitride, but the amount of sintering aid should be 10% by mass or less, particularly 7.5% by mass or less. The thermal conductivity can be improved. Moreover, in aluminum oxide, it is preferable that the content rate of the amorphous phase which reduces heat conductivity is low, and it is preferable to set it as 7 mass% or less, and also 5 mass% or less.

  At this time, in order to improve the heat dissipation of the circuit board 9, the insulating substrate 1 should have a thermal conductivity of 10 W / (m · k) or more, more preferably 20 W / (m · k) or more.

  Moreover, it is preferable that the metal which comprises the metal plate 5 consists of at least 1 sort (s) of copper, aluminum, tungsten, molybdenum, and those alloys.

  In particular, it is more preferable that copper is a main component from the viewpoint of thermal conductivity, raw material cost, and conductivity. Moreover, although an alloy or a mixture of copper and other metals or metal oxides may be used, the amount of copper is preferably 90 mol% or more from the viewpoint of thermal conductivity.

Further, by using an alloy made of copper and tungsten or molybdenum, the thermal expansion coefficient at 20 to 300 ° C. can be made 6.5 to 13.0 × 10 ⁻⁶ / ° C., but the addition of tungsten or molybdenum When the amount is 50% or more, the thermal conductivity is reduced to 200 W / (m · k) or less, so the addition amount is 50% or less, preferably 30% or less.

  When the insulating substrate 1 formed by printing the bonding agent 3 and the metal plate 5 are bonded, the metal plate 5 is heated and baked under a predetermined pressure while the metal plate 5 is held at a predetermined position. It becomes possible to join both more firmly by joining.

At this time, the pressurizing pressure is preferably in the range of 10 to 100 g / cm ² with respect to the area of the joint. More preferably, it is in the range of 30 to 70 g / cm ² .

This is because when the pressurizing pressure is low, the adhesiveness between the two decreases, and a defect due to the presence of fine voids between the two is generated. Moreover, when the pressurizing pressure is too large, when the bonding material is melted, the bonding layer is extremely thin by being discharged outside the gap between the two. From this, it is desirable that the pressure applied at the time of bonding is in the range of 10 to 100 g / cm ² .

  The bonding temperature is preferably 500 ° C. or lower, particularly 400 ° C. or lower, and more preferably 300 ° C. or lower.

  Thus, by lowering the bonding temperature, it is possible to reduce thermal stress due to the difference in thermal expansion coefficient between the insulating substrate 1 and the metal plate 5, and to prevent cracks generated in the ceramic. The circuit board 9 having excellent strength and high reliability can be obtained.

Further, it is desirable that the bonding atmosphere at the time of bonding is in an inert gas atmosphere containing nitrogen, argon or the like, or in a vacuum of 10 ⁻⁵ torr or less.

  As a result, oxygen in the bonding atmosphere can be reduced, oxidation of the metal plate 5 and the bonding agent 3 can be prevented, and a good bonding state can be maintained.

  In the example described above, the example in which the metal plate 5 is bonded only to one main surface of the insulating substrate 1 has been described. However, the metal plate 5 may be formed on both main surfaces of the insulating substrate 1. Not too long.

  A wiring layer may be formed inside the insulating substrate 1.

  Needless to say, the metal plate 5 can have a function as a wiring circuit and a function as a heat sink.

  First, Ag metal fine particles and Cu metal fine particles having an average particle size shown in Table 1 are blended in a ratio of Ag: 72% by mass and Cu 28% by mass, and the active metal shown in Table 1 having an average particle size of 1.8 μm. An amount of the powder shown in Table 1 and 100% by mass of the internally added metal component was added with 23% by mass of an acrylic binder and 74% by mass of terpineol as a solvent to prepare a bonding paste as a bonding agent.

  Next, a bonding paste was applied to both sides of an aluminum nitride substrate having an outer dimension of 40 mm square and a thickness of 0.3 mm so as to have a thickness of 30 μm by screen printing, and then a length of 40 mm made of copper on both sides of the aluminum nitride substrate. Then, a metal plate having a width of 10 mm and a thickness of 0.5 mm was brought into contact, a load shown in Table 1 was applied from above the copper plate, and the laminate was bonded in a vacuum.

  Next, the end surface of the copper plate of the obtained laminate was pulled vertically upward with respect to the substrate, and the load when the copper plate peeled was measured to obtain the peel strength.

  Moreover, the obtained laminated body was thrown into the temperature cycle test of -40-125 degreeC in the gaseous phase, the peeling condition of the interface was confirmed visually, and the cycle number until a crack generate | occur | produced was measured.

Table 1 shows the particle size, stacking load condition, bonding temperature condition, and measurement result of the above metal fine particles.

  From Table 1, the sample Nos. With the average particle size of the metal particles exceeding the range of the present invention exceeding 100 nm are shown. In No. 1, sufficient bonding force could not be obtained at a bonding temperature of 400 ° C. Sample No. which does not use an active metal that is outside the scope of the present invention. 2 uses metal fine particles having an average particle diameter of 50 nm. As in the case of 1, a sufficient bonding force could not be obtained at a bonding temperature of 400 ° C. Moreover, although the active metal which is outside the scope of the present invention is used, Sample No. 3 also sample No. Similar to 1 and 2, a sufficient bonding force could not be obtained at a bonding temperature of 400 ° C.

  On the other hand, sample No. using the metal fine particles and the active metal of the present invention. In 4-17, the remarkably high joining force was obtained and the circuit board excellent in reliability was obtained.

It is process drawing which shows the manufacturing method of the circuit board of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Insulating substrate 3 ... Bonding agent 5 ... Metal plate 7 ... Laminated body 9 ... Circuit board

Claims (11)

An insulating substrate and a metal plate are interposed with a bonding agent containing metal fine particles having an average particle diameter of 1 to 100 nm and at least one active metal selected from Ti, Zr, Hf, and Nb, A method for producing a circuit board, comprising: a step of joining the insulating substrate and the metal plate by heating the laminated body to a joining temperature lower than the melting point of the metal fine particles. The method for manufacturing a circuit board according to claim 1, wherein the active metal is 2 to 7 mass% of a metal component contained in the binder. The method for manufacturing a circuit board according to claim 1, wherein the metal fine particles contain one or more elements selected from the group consisting of iron, silver, copper, nickel, and indium. 4. The method for manufacturing a circuit board according to claim 1, wherein the metal fine particles are formed by coating the periphery of the metal core particles with an organic substance. 5. The method for manufacturing a circuit board according to claim 1, wherein the insulating substrate is at least one ceramic selected from aluminum nitride, silicon nitride, and aluminum oxide. 6. The method of manufacturing a circuit board according to claim 1, wherein the metal plate is made of at least one metal selected from copper, aluminum, tungsten, molybdenum, and alloys thereof. The method of manufacturing a circuit board according to any one of claims 1 to 6, wherein the laminate is heated while being pressed in a laminating direction to be joined. The method of manufacturing a circuit board according to any one of claims 1 to 7, wherein the laminated body is pressurized at a pressure of 10 to 100 g / cm ² with respect to an area of the joint portion. The method for manufacturing a circuit board according to claim 1, wherein the bonding is performed at 500 ° C. or lower. The circuit board manufacturing method according to claim 1, wherein the bonding step is performed in an inert gas atmosphere or in a vacuum. A circuit board manufactured by the method for manufacturing a circuit board according to claim 1.

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