Method for manufacturing an insulated circuit board and an insulated circuit board

Abstract

The present invention provides a method for manufacturing an insulated circuit board and an insulated circuit board that suppresses adhesion between the spacer and the copper plate even when using a Cu-Ti-based brazing material. [Solution] An insulating circuit board 11 is formed by sequentially laminating a brazing layer 2' and a copper plate 3 on at least one surface of an insulating substrate 1, wherein the brazing layer 2' has Cu and Ti as metallic components, and in the cross-section in the thickness direction of the insulating circuit board 11, at a position 5 μm from the interface L1 between the copper plate 3 and the brazing layer 2' toward the brazing layer 2', there is an intermetallic compound IMC containing 50% to 60% by mass of Cu and 30% to 40% by mass of Ti on a straight line L2 drawn perpendicular to the thickness direction of the insulating circuit board 11, and the ratio of the length ΣM occupied by the intermetallic compound IMC to the length of the straight line L2 (100 μm) is 10% to 50%.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing an insulating circuit board and an insulating circuit board.

Background Art

[0002] In a power module that controls power, an insulating circuit board in which a metal plate such as a copper plate or an aluminum plate is joined to a ceramic substrate is often used in order to release the heat of a semiconductor and ensure insulation. Representative manufacturing methods of an insulating circuit board include a metallization method of forming a conductor layer directly on a ceramic substrate, a method of directly joining a ceramic substrate and a metal plate, a method of brazing a metal plate using an active metal, and the like.

[0003] Among these, in a power module that particularly requires high performance, it is mainstream to use an insulating circuit board manufactured by a method of brazing a metal plate and a ceramic substrate using an active metal capable of achieving both heat dissipation and thermal reliability. Further, as a brazing material used in brazing, for example, a brazing material using an Ag-Cu eutectic as in the prior document 1 is known. However, since Ag, which is a noble metal, is used, there is a problem that the cost becomes high, and an insulating circuit board using a brazing material such as the prior document 2 made of Cu and Ti that does not contain Ag has been developed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, the advent of SiC and GaN has made it possible to achieve power control equivalent to that of Si with thinner chips compared to Si. Since thinner chips lead to thinner modules, there is a growing demand for smaller and thinner insulating circuit boards on which the chips are mounted. Therefore, it is desirable to thin the copper plates and brazing materials used to bond the ceramic substrates. However, when the copper plate used to bond the ceramic substrates is made thinner than conventional materials, for example to 0.1 mm, the following problems arise.

[0006] To efficiently perform brazing, multiple laminates, each consisting of brazing material and copper plates placed on a ceramic substrate, are stacked and heated while a load is applied to simultaneously manufacture multiple insulated circuit boards. The heat treatment while applying a load can involve directly applying the load to the stacked ceramic substrates, applying the load via a pressurizing member, or placing spacers between each laminate to facilitate the separation of the multiple insulated circuit boards after the heat treatment and then applying the load. However, when using a Cu-Ti-based brazing material like that described in prior art 2 and heating it to 1000°C, the diffusion of the Ti component into the thin copper plate could not be controlled. During the heating process, the Ti reached the surface of the copper plate, causing it to stick to other ceramic substrates in the stacked laminate, as well as to the heating element and spacers. This resulted in product defects and manufacturing equipment malfunctions, leading to a decrease in the productivity of insulating circuit boards.

[0007] The present invention aims to provide a method for manufacturing an insulating circuit board and an insulating circuit board that suppresses the adhesion of the copper plate to ceramic substrates, pressurizing members, spacers, etc., that come into contact with the copper plate during heat treatment, even when using a Cu-Ti-based brazing material. [Means for solving the problem]

[0008] According to the present invention, a method for manufacturing an insulating circuit board is provided, characterized in that a laminate is formed on at least one surface of an insulating substrate in which a brazing material containing 67% to 81% by mass of Cu and 19% to 33% by mass of Ti as metallic components and a copper plate are arranged in order, and the copper plate is joined to the insulating substrate via the brazing material layer by heating at 890°C to 950°C while applying a load in the thickness direction of the laminate.

[0009] The thickness of the copper plate may be 0.1 mm or less. The laminate may have spacers placed on top of the copper plate. Multiple laminates may be stacked and arranged. The thickness of the brazing layer may be 8 μm or more and 40 μm or less. In the cross-section of the insulating circuit board in the thickness direction, an intermetallic compound containing Cu and Ti is present on a straight line drawn perpendicular to the thickness direction of the insulating circuit board, at a position 5 μm from the interface between the copper plate and the brazing layer toward the brazing layer, and the ratio of the length occupied by the intermetallic compound to the length of the straight line (100 μm) may be 10% or more and 50% or less.

[0010] Furthermore, the present invention provides an insulating circuit board in which a brazing layer and a copper plate are sequentially laminated on at least one surface of an insulating substrate, wherein the brazing layer has Cu and Ti as metal components, and an intermetallic compound containing Cu and Ti is present on a straight line drawn perpendicular to the thickness direction of the insulating circuit board at a position 5 μm from the interface between the copper plate and the brazing layer toward the brazing layer in the cross-section of the insulating circuit board in the thickness direction, and the ratio of the length occupied by the intermetallic compound to the length of the straight line (100 μm) is 10% or more and 50% or less.

[0011] The thickness of the copper plate may be 0.1 mm or less. Furthermore, the thickness of the brazing material layer may be 8 μm or more and 40 μm or less. [Effects of the Invention]

[0012] According to the present invention, even when a Cu-Ti-based brazing material is used, it is possible to provide a method for manufacturing an insulating circuit board and an insulating circuit board in which sticking of a copper plate to a ceramic substrate, a pressure member, a spacer, etc. that come into contact with the copper plate during heat treatment is suppressed during heat treatment.

Brief Description of Drawings

[0013] [Figure 1] It is a schematic explanatory diagram of a method for manufacturing an insulating circuit board according to an embodiment of the present invention. [Figure 2] In the insulating circuit board according to an embodiment of the present invention, it is a schematic explanatory diagram of a laminated structure in which a brazing material layer and a copper plate are laminated in this order on the other surface of the insulating substrate. [Figure 3] It is a schematic explanatory diagram showing an intermetallic compound existing on a straight line L2 drawn so as to be orthogonal to the thickness direction of the insulating circuit board at a position 5 μm from the interface L1 between the copper plate and the brazing material layer toward the brazing material layer side. [Figure 4] It is a magnified photograph of a cross section in the thickness direction of the insulating circuit board of Example 2. [Figure 5] It is a magnified photograph of a cross section in the thickness direction of the insulating circuit board of Example 5. [Figure 6] It is a magnified photograph of a cross section in the thickness direction of the insulating circuit board of Comparative Example 2. [Figure 7] It is a magnified photograph of a cross section in the thickness direction of the insulating circuit board of Comparative Example 3.

Embodiments for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this specification and the drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

[0015] <Method for Manufacturing Insulating Circuit Board> In the method for manufacturing an insulating circuit board according to an embodiment of the present invention, first, as shown in FIG. 1, on at least one surface of an insulating substrate 1, a brazing material 2 containing 67% by mass or more and 81% by mass or less of Cu and 19% by mass or more and 33% by mass or less of Ti as metal components, a copper plate 3, and a spacer 4 are sequentially arranged to form a laminate 10. In the illustrated example, laminates 10 in which the brazing material 2, the copper plate 3, and the spacer 4 are sequentially arranged are shown on both surfaces (upper and lower surfaces) of the insulating substrate 1. Further, in this example, a state in which a plurality of similar laminates 10 are stacked one above the other is shown. (In the laminates 10 adjacent to each other vertically, the lower spacer 4 of the upper laminate 10 and the upper spacer 4 of the lower laminate 10 are made common.) The laminate 10 does not necessarily require the spacer 4 to be arranged, but when the spacer 4 is used, in a state where a plurality of laminates 10 are stacked one above the other, a plurality of insulating circuit boards (insulating substrates 1) obtained by heat treatment and bonding while applying a load in the thickness direction of the laminate 10 as described later can be easily separated into each insulating circuit board (insulating substrate 1).

[0016] Note that the laminate 10 only needs to have the brazing material 2, the copper plate 3, and the spacer 4 arranged on at least one surface of the insulating substrate 1. For example, the brazing material 2, the copper plate 3, and the spacer 4 may be arranged only on the upper surface (or only on the lower surface) of the insulating substrate 1. Also, it is not necessarily required to stack a plurality of laminates 10. For example, only one laminate 10 may be used.

[0017] The insulating substrate 1 is, for example, a plate-like member made of a ceramic material. As the ceramic material used for the insulating substrate 1, oxide-based ceramics such as alumina, or non-oxide-based ceramics such as aluminum nitride, silicon nitride, silicon carbide, and boron nitride can be used.

[0018] Since the insulating substrate 1 can achieve both high insulating performance and heat dissipation performance, it is preferably made of a ceramic material. Among these, the insulating substrate 1 is preferably formed from a ceramic material of alumina, aluminum nitride, or silicon nitride.

[0019] The brazing material 2 used in the method for manufacturing an insulating circuit board of the present invention preferably contains Cu and Ti as metal components and is in the form of a paste or foil. If the brazing material 2 is a paste, it may further contain the above-mentioned metal components as well as a vehicle consisting of a binder and an organic solvent. The metal components in the brazing material 2 are characterized by containing 67% to 81% by mass of Cu and 19% to 33% by mass of Ti.

[0020] The metal component in the brazing material 2 is preferably Cu at a concentration of 68% to 80.5% by mass, and more preferably 69% to 80.3% by mass.

[0021] The metal component in the brazing material 2 is preferably Ti at a concentration of 19.5% by mass or more and 32% by mass or less, and more preferably 19.7% by mass or more and 31% by mass or less.

[0022] The metal component in the brazing material 2 may be 100% by mass of Cu and Ti, but the metal component in the brazing material 2 may further contain metal element X other than Cu and Ti as the remainder, as long as the effects of the present invention are not impaired. The metal element X may be present in an amount of 3% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less. (The metal component of the brazing material layer 2' after joining will be the same as above.) Examples of metal element X include Ag, Ni, Sn, etc.

[0023] The binder contained in the vehicle of the brazing material 2 is not particularly limited and can be appropriately selected depending on the purpose. Examples include acrylic resin, ethyl cellulose, ethyl hydroxyethyl cellulose, and nitrocellulose. These binders may be used individually or in combination of two or more types.

[0024] Furthermore, when the amount of metal in the brazing material 2 is 100 parts by mass, the amount of binder in the brazing material is 0.4 parts by mass or more and 1.6 parts by mass or less, preferably 0.6 parts by mass or more and 1.4 parts by mass or less, and more preferably 0.8 parts by mass or more and 1.2 parts by mass or less.

[0025] The organic solvent contained in the vehicle in the wax material 2 is not particularly limited and can be appropriately selected depending on the purpose. Examples include toluene, methyl ethyl ketone, methyl isobutyl ketone, tetradecane, tetralin, propyl alcohol, isopropyl alcohol, terpineol, ethyl carbitol, butyl carbitol, ethyl carbitol acetate, butyl carbitol acetate, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, etc. These organic solvents may be used individually or in combination of two or more.

[0026] When the amount of metal in the brazing material 2 is 100 parts by mass, the amount of organic solvent in the brazing material is in the range of 7 parts by mass or more and 19 parts by mass or less, preferably 9 parts by mass or more and 17 parts by mass or less, and more preferably 11 parts by mass or more and 15 parts by mass or less.

[0027] Furthermore, dispersants, viscosity modifiers, plasticizers, etc., may be added to the brazing material 2 as appropriate to adjust the printability of the brazing material 2 and the adhesion of the dried coating film. The brazing material 2 is applied to at least one surface of the insulating substrate 1 and laminated. The coating thickness of the brazing material 2 applied to at least one surface of the insulating substrate 1 is, for example, 10 μm or more and 50 μm or less, and preferably 12 μm or more and 50 μm or less.

[0028] The copper plate 3 is provided by bonding it to one main surface of the insulating substrate 1 for use in circuits on which semiconductor elements are mounted. The copper plate 3 can be a plate-shaped member made of copper or a copper alloy. The thickness of the copper plate 3 is preferably 0.1 mm or less. By making the thickness of the copper plate 3 0.1 mm or less, the power module can be made thinner. The thickness of the copper plate 3 is preferably 0.01 mm or more, and may be 0.03 mm or more.

[0029] Furthermore, spacers 4 are placed on top of the copper plate 3 to form a laminate 10. The method of forming the laminate 10 is not particularly limited. For example, a laminate 10 can be formed by placing the copper plate 3 on top of the spacers 4, then the brazing material 2 on top of the spacers 2, then the insulating substrate 1 on top of the brazing material 2, then the copper plate 3 on top of the spacers 4, and finally the spacers 4 on top of the spacers 4. Multiple layers of such laminates 10 can be stacked. When multiple layers of such laminates 10 are stacked, the spacers 4 below the upper laminate 10 and the spacers 4 above the lower laminate 10 can be the same for stacks of adjacent laminates 10 located vertically. The material of the spacers 4 can be selected as appropriate, and for example, ceramics such as alumina or aluminum nitride are preferred.

[0030] Then, the laminate is heated and joined while a load is applied in the thickness direction of the laminate. Any method can be used to apply the load in the thickness direction of the laminate, but for example, a weight 5 may be placed on the topmost spacer 4 and the load applied from the topmost spacer 4 towards the bottommost spacer 4. The load applied in the thickness direction of the laminate 10 is 0.005 kgf / cm 2 More than 0.5kgf / cm 2 The following is preferable. More preferably, 0.01 kgf / cm². 2 More than 0.2kgf / cm 2 The following applies:

[0031] By applying a load in the thickness direction of the laminate 10 and heating the laminate 10 at a temperature between 890°C and 950°C, the brazing material 2 is melted. After melting, it solidifies to form a brazing material layer 2', and the copper plate 3 is joined to the insulating substrate 1 via the brazing material layer 2'.

[0032] The heat treatment temperature shall be between 890°C and 950°C. By setting the heat treatment temperature to 890°C or higher, the brazing material 2 can be melted, and the copper plate 3 can be joined to the insulating substrate 1 via the brazing material layer 2' that solidifies after melting.

[0033] The heat treatment temperature is preferably 900°C or higher, as this shortens the time required for the brazing material 2 to melt.

[0034] Furthermore, by setting the heat treatment temperature to 950°C or lower, an intermetallic compound of Cu and Ti is formed in the brazing material layer 2', which suppresses the diffusion of Ti in the brazing material 2 into the copper plate 3.

[0035] The heat treatment temperature is preferably 940°C or lower, and more preferably 930°C or lower.

[0036] From the viewpoint of suppressing the formation of metal oxides, the heat treatment atmosphere should preferably be an inert atmosphere such as nitrogen, helium, or argon, or a vacuum atmosphere. For example, a vacuum atmosphere of 8.0 × 10 -2 It is preferable to carry out the procedure in a vacuum of Pa or less. More preferably, 5.0 × 10 -2 It is below Pa.

[0037] The heat treatment time is not particularly limited, but it is preferably 30 minutes or longer, and preferably 1 hour or less from the viewpoint of manufacturing efficiency.

[0038] <Insulated Circuit Board> Through the above steps, the copper plate 3 is bonded to the insulating substrate 1, and after bonding, the spacer 4 is removed to manufacture an insulating circuit board 11 according to an embodiment of the present invention. As shown in Figure 2, the insulating circuit board 11 according to an embodiment of the present invention has a laminated structure in which a brazing material layer 2' and a copper plate 3 are sequentially laminated on at least one surface of the insulating substrate 1. In the example shown in Figure 2, the brazing material layer 2' and the copper plate 3 are laminated on only one surface of the insulating substrate 1 (only the upper surface of the insulating substrate 1 in Figure 2), but a laminated structure in which the brazing material layer 2' and the copper plate 3 are sequentially laminated on both surfaces (upper and lower surfaces) of the insulating substrate 1 is also possible. In the laminate 10 shown in Figure 1, an insulating circuit board 11 with a laminated structure in which the brazing material layer 2' and the copper plate 3 are sequentially laminated on both surfaces (upper and lower surfaces) of the insulating substrate 1 is manufactured.

[0039] The brazing material layer 2' contains Cu and Ti as metal components, with Cu at 67% to 81% by mass and Ti at 19% to 33% by mass. The thickness of the brazing material layer 2' is preferably 8 μm or more, and preferably 40 μm or less, from the viewpoint of ensuring bonding performance. From the viewpoint of thinning, the thickness of the brazing material layer 2' is preferably 20 μm or less. Furthermore, the binder and vehicle are substantially destroyed by heat treatment.

[0040] The metal component in the brazing layer 2' preferably contains 68% by mass or more of Cu, and more preferably 69% by mass or more. Furthermore, it is preferable that the amount of Cu be 80.5% by mass or less, and more preferably 80.3% by mass or less.

[0041] The metal component of the brazing material layer 2' preferably contains 19.5% by mass or more Ti, and more preferably 19.7% by mass or more. Furthermore, it is preferable that the Ti content be 32% by mass or less, and more preferably 31% by mass or less.

[0042] The metal component of the brazing layer 2' may be 100% by mass of Cu and Ti, but the metal component of the brazing layer 2' may further contain a metal element X other than Cu and Ti as the remainder, as long as the effects of the present invention are not impaired. The metal element X may be present in the metal component of the brazing layer 2' at a rate of 3% by mass or less, more preferably at a rate of 2% by mass or less, and even more preferably at a rate of 1% by mass or less. Examples of metal element X include Ag, Ni, and Sn.

[0043] Furthermore, in the cross-section of the insulating circuit board 11 in the thickness direction, an intermetallic compound IMC containing Cu and Ti is present at a position 5 μm from the interface L1 between the copper plate 3 and the brazing material layer 2' toward the brazing material layer 2', on a straight line L2 drawn perpendicular to the thickness direction of the insulating circuit board. The intermetallic compound IMC is an intermetallic compound containing 50% to 60% by mass of Cu and 30% to 40% by mass of Ti.

[0044] As shown in Figure 3, the ratio of the length occupied by intermetallic compounds (IMCs) to the length of the straight line L2 (100 μm), that is, the sum of the lengths of each intermetallic compound (IMC) present within the 100 μm length of the straight line L2 (the length of each intermetallic compound (IMC) on the straight line L2) M, ΣM, is between 10% and 50%.

[0045] Such an insulating circuit board 11 can be manufactured by the manufacturing method according to the embodiment of the present invention described above.

[0046] If the amount of Ti in the brazing material 2 used to join the copper plates 3 is too low (less than 19 mass%), the Cu-Ti intermetallic compound IMC will not form, and diffusion into the copper plates 3 will proceed, causing the Ti to reach the surface of the copper plates 3 and adhere to the spacer 4. On the other hand, if the amount of Ti in the brazing material 2 is too high (more than 33 mass%), the Cu-Ti intermetallic compound IMC will form, but the excess Ti will diffuse into the copper plates 3, causing the Ti to reach the surface of the copper plates 3 and adhere to the spacer 4.

[0047] Furthermore, even if the amount of Ti in the brazing material 2 is within an appropriate range (containing 67% to 81% by mass of Cu and 19% to 33% by mass of Ti as metallic components), if the bonding temperature is too high (exceeding 950°C), the intermetallic compound IMC of Cu-Ti will not be formed, and Ti will diffuse into the copper plate 3, reaching the surface layer of the copper plate 3 and sticking to the spacer 4.

[0048] It is important to suppress the solid solution and diffusion of Ti in the brazing material 2 into the copper plate 3, so the amount of Ti in the brazing material 2 and the bonding temperature must be within a predetermined range, and the Cu-Ti intermetallic compound IMC in the brazing material layer 2' must be appropriately controlled. An intermetallic compound IMC containing 50% to 60% by mass of Cu and 30% to 40% by mass of Ti is present on a straight line L2 drawn perpendicular to the thickness direction of the insulating circuit board 11, 5 μm from the interface between the copper plate 3 and the brazing material layer 2' towards the brazing material layer 2', and the ratio of the sum of the lengths M occupied by the Cu-Ti intermetallic compound IMC to a length of 100 μm on the straight line L2 is 10% or more. This ensures that a predetermined amount of Cu-Ti intermetallic compound IMC is formed in the brazing material layer 2', preventing excess Ti from diffusing into the copper plate 3, reaching the surface of the copper plate 3, and sticking to the spacer 4.

[0049] Furthermore, if the ratio of the total length ΣM occupied by the Cu-Ti intermetallic compound IMC to a length of 100 μm on the straight line L2 exceeds 50%, an increase in the ratio of the total length ΣM occupied by the intermetallic compound IMC suppresses the diffusion of Ti into the copper plate 3 and suppresses adhesion between the copper plate 3 and the spacer 4. However, an upper limit on the total ΣM is defined from the viewpoint of the bonding properties between the insulating substrate 1 and the copper plate 3.

[0050] According to the insulating circuit board 11 and its manufacturing method described above in the embodiments of the present invention, an intermetallic compound IMC of Cu and Ti is formed in the brazing layer 2', and the diffusion of Ti into the copper plate 3 is suppressed, thereby preventing the copper plate 3 from sticking to the spacer 4.

[0051] Although an example of an embodiment of the present invention has been described above, the present invention is not limited to the illustrated form. It will be clear to those skilled in the art that various modifications or alterations can be conceived within the scope of the idea described in the claims, and these will naturally also fall within the technical scope of the present invention.

[0052] For example, a copper circuit board is manufactured by joining a copper plate 3 to an insulating substrate 1 via a brazing layer 2', and then forming the copper plate 3 into a predetermined circuit pattern. The copper circuit board may be configured to have a predetermined surface shape through a predetermined chemical polishing treatment. Alternatively, a heat-dissipating metal plate may be manufactured by joining a copper plate 3 to an insulating substrate 1 via a brazing layer 2', and then forming the copper plate 3 into a predetermined heat-dissipating metal pattern. The heat-dissipating metal plate may be subjected to a predetermined chemical polishing treatment, similar to the copper circuit board, and may be configured to have a predetermined surface shape.

[0053] Alternatively, a copper plate 3 may be bonded to one main surface of the insulating substrate 1, and a copper circuit board may be formed on the other main surface of the insulating substrate 1. In this case, a plate-shaped member made of copper or a copper alloy can be used as the copper plate for forming the copper circuit board.

[0054] Alternatively, a copper plate 3 may be bonded to one main surface of the insulating substrate 1, and a heat-dissipating metal plate may be formed on the other main surface of the insulating substrate 1. In this case, a plate-shaped member made of copper or a copper alloy can be used as the copper plate for forming the heat-dissipating metal plate. It is preferable to bond the heat-dissipating metal plate to the other main surface of the insulating substrate 1 because it allows for efficient heat dissipation from the semiconductor elements placed on the insulating circuit board 11. [Examples]

[0055] As embodiments of the present invention, insulated circuit boards of Examples 1 to 5 and Comparative Examples 1 to 4 were prepared.

[0056] [Example 1] A silicon nitride plate measuring 34 mm in length, 34 mm in width, and 0.32 mm in thickness was prepared as an insulating substrate. A paste was prepared as a brazing material by kneading Cu powder, TiH2 powder, an acrylic binder, and an organic solvent into a vehicle. The brazing material contains 80% by mass of Cu and 20% by mass of Ti as metal components. Furthermore, when the total amount of metal components in the brazing material is 100 parts by mass (standard), the mixture is formulated so that there are 13 parts by mass of organic solvent and 1 part by mass of binder. Two oxygen-free copper plates (C1020) measuring 34 mm in length, 34 mm in width, and 0.05 mm in thickness were prepared as copper plates for the copper circuit board and heat dissipation metal plate. Two alumina plates measuring 34 mm in length, 34 mm in width, and 0.4 mm in thickness were prepared as spacers.

[0057] A brazing material was screen-printed onto almost the entire surface of both sides of the insulating substrate to a thickness of 30 μm. Next, an oxygen-free copper plate for the copper circuit board was placed on the brazing material applied to one side of the insulating substrate, and an oxygen-free copper plate (metal plate) for the heat sink was placed on the brazing material applied to the other side of the insulating substrate. These were then placed on one of a pair of spacers (the lower spacer), and the other spacer (the upper spacer) was placed on top of this laminate, thus forming a laminate on both sides (upper and lower) of the insulating substrate, with the brazing material, copper plates, and spacers arranged in that order. A weight was placed on the upper spacer of the formed laminate, applying a load of 0.05 kgf / cm² in the thickness direction of the laminate. 2 An insulated circuit board was fabricated by bonding copper plates to both sides of an insulating substrate by heating it at 920°C for 60 minutes in a nitrogen atmosphere while applying a load, thereby bonding the insulating substrate and copper plates via a brazing layer. The thickness of the brazing layer formed on the insulated circuit board was 10 μm.

[0058] [Example 2] An insulating circuit board was fabricated under the same conditions as in Example 1, except that the metal components of the brazing material were formulated to contain 78% by mass of Cu and 22% by mass of Ti. The thickness of the brazing layer formed on the insulating circuit board was 12 μm.

[0059] [Example 3] An insulating circuit board was fabricated under the same conditions as in Example 1, except that an oxygen-free copper plate measuring 34 mm in length, 34 mm in width, and 0.10 mm in thickness was used as the copper plate for the copper circuit board and the heat dissipation metal plate. The thickness of the brazing material layer formed on the insulating circuit board was 10 μm.

[0060] [Example 4] An insulating circuit board was prepared under the same conditions as in Example 1, except that the metal components of the brazing material were formulated to contain 70% by mass of Cu and 30% by mass of Ti. The thickness of the brazing layer formed on the insulating circuit board was 10 μm.

[0061] [Example 5] An insulating circuit board was fabricated under the same conditions as in Example 1, except that an aluminum nitride plate measuring 34 mm in length, 34 mm in width, and 0.38 mm in thickness was used as the insulating substrate, and an oxygen-free copper plate measuring 34 mm in length, 34 mm in width, and 0.10 mm in thickness was used as the copper plate for the copper circuit board and the heat dissipation metal plate, and the copper plates were bonded to both sides of the insulating substrate by heating at 900°C for 60 minutes in a nitrogen atmosphere. The thickness of the brazing material layer formed on the insulating circuit board was 14 μm.

[0062] [Comparative Example 1] An insulating circuit board was fabricated under the same conditions as in Example 1, except that the metal components of the brazing material were formulated to contain 82% by mass of Cu and 18% by mass of Ti. The thickness of the brazing layer formed on the insulating circuit board was 11 μm.

[0063] [Comparative Example 2] An insulating circuit board was fabricated under the same conditions as in Example 1, except that the brazing material was formulated to contain 78% by mass of Cu and 22% by mass of Ti, an aluminum nitride plate measuring 34 mm in length, 34 mm in width, and 0.635 mm in thickness was used as the insulating substrate, and an oxygen-free copper plate measuring 34 mm in length, 34 mm in width, and 0.10 mm in thickness was used as the copper plate for the copper circuit board and the heat dissipation metal plate, and the copper plates were bonded to both sides of the insulating substrate by heating at 970°C for 60 minutes in a nitrogen atmosphere. The thickness of the brazing material layer formed on the insulating circuit board was 15 μm.

[0064] [Comparative Example 3] An insulating circuit board was fabricated under the same conditions as in Example 1, except that the brazing material was formulated to contain 75% by mass of Cu and 25% by mass of Ti, an aluminum nitride plate measuring 34 mm in length, 34 mm in width, and 0.635 mm in thickness was used as the insulating substrate, and an oxygen-free copper plate measuring 34 mm in length, 34 mm in width, and 0.10 mm in thickness was used as the copper plate for the copper circuit board and the heat dissipation metal plate, and the copper plates were bonded to both sides of the insulating substrate by heating at 1040°C for 10 minutes in a nitrogen atmosphere. The thickness of the brazing material layer formed on the insulating circuit board was 13 μm.

[0065] [Comparative Example 4] An insulating circuit board was fabricated under the same conditions as in Example 1, except that the copper plates were bonded to both sides of the insulating substrate by heating at 880°C for 60 minutes in a nitrogen atmosphere. However, under these conditions, the insulating substrate and the copper plates could not be bonded.

[0066] Table 1 shows the composition of the metal components in the brazing material for each insulating circuit board (mass%), for example, in Example 1, Ti is 20 mass%, and the remainder is Cu, the material and thickness of the insulating substrate, the type and thickness of the copper plate (Cu plate), the temperature and time of the heat treatment (bonding temperature, time), the thickness of the brazing material application, the amount of intermetallic compound (the ratio of the total length M occupied by the Cu-Ti intermetallic compound IMC to a length of 100 μm on a straight line L2, ΣM), and whether or not the copper plate and spacer are adhered.

[0067] [Table 1]

[0068] Also, cross-sections in the thickness direction of the insulating circuit boards of Examples 2 and 5 and Comparative Examples 2 and 3. The backscattered electron images were observed by taking 1000x magnified images using a scanning electron microscope (SU3800) manufactured by Hitachi High-Tech Corporation at an acceleration voltage of 15kV. The magnified images are shown in Figures 4 to 7. In the brazing material layer, areas with a different color from copper are intermetallic compounds (IMCs). EDS analysis using an energy-dispersive X-ray analyzer (ULTIM MAX 40) attached to the scanning electron microscope confirmed that the intermetallic compounds in the examples and comparative examples contained 50% to 60% by mass of Cu and 30% to 40% by mass of Ti. Areas with a different color at the interface between the brazing material layer and the insulating substrate are Ti nitride layers. The amount of intermetallic compounds was determined by the ratio of the length of the intermetallic compound to a length of 100 μm on a straight line L2 drawn perpendicular to the thickness direction of the insulating circuit substrate, at a position 5 μm from the interface L1 between the copper plate and the brazing material layer toward the brazing material layer in the cross-section in the thickness direction of the insulating circuit substrate 11. Although intermetallic compounds of Cu and Ti are formed in the brazing material layer, no intermetallic compounds are formed even if Ti is dissolved in the copper plate. Therefore, the interface position between the copper plate and the brazing material was defined as the highest point, which is the upper end of the intermetallic compound (the surface of copper plate 3 (the point closest to the top surface of copper plate 3 in Figures 4 and 5)).

[0069] In Examples 1 to 5, which satisfy the manufacturing method for insulating circuit boards specified in the present invention, when a copper plate with a thickness of 0.05 mm to 0.1 mm is joined to a ceramic substrate using a Cu-Ti-based brazing material, the diffusion of the Ti component in the brazing material into the copper plate can be controlled, and there is no adhesion between the copper plate and the spacer, which can cause product defects and manufacturing equipment defects. In contrast, in Comparative Examples 1 to 3, which do not satisfy the manufacturing method for insulating circuit boards specified in the present invention, the diffusion of the Ti component in the brazing material into the copper plate cannot be controlled, and adhesion between the copper plate and the spacer occurs. Furthermore, in Comparative Example 4, the copper plate could not be joined. By applying the manufacturing method for insulating circuit boards specified in the present invention, when a copper plate is joined to a ceramic substrate using a Cu-Ti-based brazing material, the diffusion of the Ti component in the brazing material into the copper plate can be controlled, the adhesion between the copper plate and the spacer, which can cause product defects and manufacturing equipment defects can be suppressed, and an insulating circuit board with a copper plate joined to a ceramic substrate can be obtained.

[0070] Furthermore, in the insulating circuit boards of Examples 1 to 5 that satisfy the insulating circuit board definition of the present invention, the amount of intermetallic compound, determined from the ratio of the length of the intermetallic compound containing Cu and Ti per 100 μm of length on a straight line L2 drawn perpendicular to the thickness direction of the insulating circuit board at a position 5 μm from the interface L1 between the copper plate and the brazing material layer toward the brazing material layer in the cross-section of the insulating circuit board 11 in the thickness direction, was 20 to 30%, whereas the amount of intermetallic compound in Comparative Examples 1 to 3 was 1 to 5%. It was found that the formation of a predetermined amount of intermetallic compound of Cu and Ti in the brazing material layer suppresses the diffusion of Ti into the copper plate, thereby preventing the copper plate from sticking to the spacer. [Industrial applicability]

[0071] The present invention relates to a method for manufacturing an insulating circuit board and is applicable to an insulating circuit board. [Explanation of Symbols]

[0072] 1. Insulating substrate 2. Brazing material 2' Brazing layer 3 copper plate 4 Spacers 5 weight 10 Laminate 11 Insulated circuit board L1 Interface between copper plate and brazing material layer L2 is a straight line drawn 5 μm from L1 toward the brazing layer, perpendicular to the thickness direction of the insulating circuit board. IMC Intermetallic Compounds

Claims

1. A method for manufacturing an insulated circuit board, A laminate is formed on at least one surface of an insulating substrate, in which a brazing material containing 67% to 81% by mass of Cu and 19% to 33% by mass of Ti as metallic components, and a copper plate are arranged in that order. A method for manufacturing an insulating circuit board, characterized by bonding the copper plate to the insulating substrate via a brazing layer by heating the laminate at 890°C to 950°C while applying a load in the thickness direction of the laminate.

2. A method for manufacturing an insulating circuit board according to claim 1, characterized in that the thickness of the copper plate is 0.1 mm or less.

3. The method for manufacturing an insulating circuit board according to claim 1, characterized in that the laminate is formed by stacking spacers on the copper plate.

4. A method for manufacturing an insulating circuit board according to claim 1, characterized in that a plurality of the aforementioned laminates are stacked and arranged.

5. The method for manufacturing an insulating circuit board according to claim 1, characterized in that the thickness of the brazing material layer is 8 μm or more and 40 μm or less.

6. In the cross-section of the insulating circuit board in the thickness direction, at a position 5 μm from the interface between the copper plate and the brazing layer toward the brazing layer, on a straight line drawn perpendicular to the thickness direction of the insulating circuit board, there is an intermetallic compound containing Cu and Ti, A method for manufacturing an insulating circuit board according to any one of claims 1 to 5, characterized in that the ratio of the length occupied by the intermetallic compound to the length of the straight line (100 μm) is 10% or more and 50% or less.

7. An insulating circuit board in which a brazing material layer and a copper plate are sequentially laminated on at least one surface of an insulating substrate, The brazing layer has Cu and Ti as metal components. In the cross-section of the insulating circuit board in the thickness direction, at a position 5 μm from the interface between the copper plate and the brazing layer toward the brazing layer, on a straight line drawn perpendicular to the thickness direction of the insulating circuit board, there is an intermetallic compound containing Cu and Ti, An insulating circuit board characterized in that the ratio of the length occupied by the intermetallic compound to the length of the straight line (100 μm) is 10% or more and 50% or less.

8. The insulating circuit board according to claim 7, characterized in that the thickness of the copper plate is 0.1 mm or less.

9. The insulating circuit board according to claim 7 or 8, characterized in that the thickness of the brazing material layer is 8 μm or more and 40 μm or less.

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