Metal-ceramic bonded substrate

Abstract

This invention provides a technology that can suppress the occurrence of minute defects in nickel plating films. [Solution] A method for manufacturing a metal-ceramic bonded substrate, comprising the steps of: joining a metal plate to at least one main surface of a ceramic substrate via a brazing material containing silver and having a lead concentration of X ppm (X ≤ 50); and forming a nickel plating film on the surfaces of the metal plate and the brazing material using an electroless nickel plating solution having a lead concentration of Y mg / L, wherein in the step of forming the nickel plating film, the lead concentration Y of the electroless nickel plating solution satisfies the relationship 0.05 ≤ Y ≤ -0.002X + 0.5.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a metal-ceramics bonded substrate and a metal-ceramics bonded substrate.

Background Art

[0002] Conventionally, power modules have been used to control large power such as in electric vehicles, trains, and machine tools. As an insulating substrate for such a power module, a metal-ceramics bonded circuit board in which plating is applied to a chip component or a portion where soldering of a terminal is required on a metal circuit board bonded to one surface of a ceramics substrate is used.

[0003] In such a metal-ceramics bonded circuit board, due to the thermal stress caused by the difference in thermal expansion generated between the ceramics substrate and the metal circuit board due to thermal shock after bonding, cracks are likely to occur in the ceramics substrate.

[0004] As a method for relaxing such thermal stress, a method of thinning the surface portion of the metal circuit board, that is, a method of forming a stepped structure or a fillet (the protruding portion of the brazing material for bonding the metal circuit board to the ceramics substrate) at the peripheral edge of the metal circuit board is known (see, for example, Patent Documents 1 to 3).

[0005] However, when a metal-ceramics circuit board in which a fillet (protruding portion) of an active metal-containing brazing material for bonding a metal circuit board (such as a copper circuit board) to a ceramics substrate is formed is incorporated into a power module, migration of a metal (for example, silver or copper when a brazing material composed of an active metal, silver, and copper is used) in the active metal-containing brazing material occurs between circuit patterns of the metal circuit board on the ceramics substrate, etc., which may cause insulation failure. [[ID=2x]]

[0006] As a method for preventing such migration, a method of applying electroless Ni-P plating to the surface of the protruding portion of the brazing material protruding from the end of the metal plate is known (see, for example, Patent Document 4).

[0007] Furthermore, in order to suppress the occurrence of migration, a method for manufacturing a metal-ceramic circuit board is known in which a copper plate is joined to one side of a ceramic substrate via an activated metal-containing brazing material containing silver, then the excess portions of the copper plate and activated metal-containing brazing material are removed, and then the excess portions of the copper plate are removed by chemical polishing so that the activated metal-containing brazing material protrudes from the side of the copper plate, and after removing the silver layer attached to the surface of the copper plate by this chemical polishing, electroless Ni-P plating is applied to the copper plate and the protruding portions of the brazing material (see, for example, Patent Document 5). [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] JP-A-10-125821 (paragraph number 0008) [Patent Document 2] Japanese Patent Publication No. 2001-332854 (paragraph numbers 0014-0019) [Patent Document 3] Japanese Patent Publication No. 2004-307307 (paragraph numbers 0012-0014) [Patent Document 4] Japanese Patent Publication No. 2006-228918 (paragraph numbers 0021-0022) [Patent Document 5] Japanese Patent Publication No. 2018-145047 (paragraph numbers 0030-0034) [Overview of the project] [Problems that the invention aims to solve]

[0009] However, it was found that the method for manufacturing metal-ceramic bonded (circuit) substrates described in the aforementioned patent document could not sufficiently suppress the occurrence of migration. The inventors of this invention diligently investigated the cause and found that when the nickel plating film formed on the surface of the brazing material (excess portion) was observed from the surface, minute defects (minute defects in the nickel plating film) where the brazing material was exposed were observed. It is presumed that these minute defects in the nickel plating film are the cause of migration, and the objective of this invention is to suppress the occurrence of these minute defects in the nickel plating film.

[0010] One embodiment of the present invention aims to provide a technology that can suppress the occurrence of minute defects in a nickel plating film in a method for manufacturing a metal-ceramic bonded substrate. Another embodiment of the present invention aims to provide a technology that can suppress the occurrence of minute defects in a nickel plating film on a metal-ceramic bonded substrate. [Means for solving the problem]

[0011] A first aspect of the present invention is: A step of joining a metal plate to at least one main surface of a ceramic substrate via a brazing material containing silver and having a lead concentration of X ppm (X ≤ 50), The process includes the step of forming a nickel plating film on the surface of the metal plate and the brazing material using an electroless nickel plating solution with a lead concentration of Y mg / L. In the process of forming the nickel plating film, the lead concentration Y of the electroless nickel plating solution is set to satisfy the relationship 0.05 ≤ Y ≤ -0.002X + 0.5, in this method for manufacturing a metal-ceramic bonded substrate.

[0012] A second aspect of the present invention is: The method for manufacturing a metal-ceramic bonded substrate according to the first embodiment is as follows: in the step of forming the nickel plating film, the lead concentration Y of the electroless nickel plating solution is set to satisfy the relationship 0.05 ≤ Y ≤ -0.002X + 0.475.

[0013] The third aspect of the present invention is that in the step of forming the nickel plating film, a nickel-phosphorus plating film is formed using an electroless nickel-phosphorus plating solution, and the method for manufacturing a metal-ceramics joined substrate according to the first or second aspect described above.

[0014] The fourth aspect of the present invention is that after joining the metal plate to the ceramics substrate, the unnecessary portions of the metal plate and the brazing material are removed, and the method for manufacturing a metal-ceramics joined substrate according to any one of the first to third aspects described above, further including a step of forming a predetermined circuit pattern on the metal plate.

[0015] The fifth aspect of the present invention is that after forming a predetermined circuit pattern on the metal plate, the peripheral portion of the metal plate is removed, and the method for manufacturing a metal-ceramics joined substrate according to the fourth aspect described above, further including a step of forming an overhanging portion of the brazing material.

[0016] The sixth aspect of the present invention is that a ceramics substrate, a metal plate joined via a brazing material containing silver and having a lead concentration of X ppm (X ≤ 50) on at least one main surface of the ceramics substrate, and a nickel plating film formed on the surfaces of the metal plate and the brazing material, wherein in the nickel plating film formed on the surface of the brazing material, the maximum length of the exposed portion of the brazing material is 70 μm or less, and it is a metal-ceramics joined substrate.

[0017] The seventh aspect of the present invention is that in the nickel plating film formed on the surface of the brazing material, the maximum length of the exposed portion of the brazing material is 35 μm or less, and it is a metal-ceramics joined substrate according to the sixth aspect described above.

[0018] The eighth aspect of the present invention is that A protruding portion of the brazing material is formed at the peripheral edge of the metal plate. The metal-ceramics bonding substrate according to the sixth or seventh aspect, wherein a nickel plating film is formed on the surface of the protruding portion.

[0019] A ninth aspect of the present invention is The metal-ceramics bonding substrate according to any one of the sixth to eighth aspects, wherein the nickel plating film is a nickel-phosphorus plating film.

Advantages of the Invention

[0020] According to an embodiment of the present invention, in a method for manufacturing a metal-ceramics bonding substrate, generation of fine defects in a nickel plating film can be suppressed. Further, according to an embodiment of the present invention, in a metal-ceramics bonding substrate, generation of fine defects in a nickel plating film can be suppressed.

Brief Description of the Drawings

[0021] [Figure 1] FIG. 1 is a cross-sectional view schematically showing an example of a metal-ceramics bonding substrate 1 according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a flowchart showing an example of a method for manufacturing a metal-ceramics bonding substrate 1 according to a first embodiment of the present invention. [Figure 3] FIG. 3 is an explanatory view showing a brazing material forming step S101 according to a first embodiment of the present invention, and shows a state where a paste-like brazing material 11 is formed on the upper and lower surfaces of a ceramics substrate 10. [Figure 4] FIG. 4 is an explanatory view showing a metal plate bonding step S102 according to a first embodiment of the present invention, and shows a state where a metal plate 12 is bonded to the upper and lower surfaces of a ceramics substrate 10 via a brazing material 11. [Figure 5]Figure 5 is an explanatory diagram showing the circuit pattern formation process S103 according to the first embodiment of the present invention, and shows a state in which a resist 14 having a predetermined circuit pattern and a predetermined shape of the heat dissipation side metal plate is applied to the surface of the metal circuit plate 12a and the heat dissipation side metal plate 12b bonded to the upper surface of the ceramic substrate 10. [Figure 6] Figure 6 is an explanatory diagram showing the circuit pattern formation process S103 according to the first embodiment of the present invention, and shows the state in which unnecessary parts of the metal plate 12 have been etched off. [Figure 7] Figure 7 is an explanatory diagram showing the circuit pattern formation process S103 according to the first embodiment of the present invention, and shows the state after the resist 14 has been removed. [Figure 8] Figure 8 is an explanatory diagram showing the circuit pattern formation process S103 according to the first embodiment of the present invention, and shows the state in which the unnecessary portion of the brazing material 11 has been removed. [Figure 9] Figure 9 is an explanatory diagram showing the overhang formation process S104 according to the first embodiment of the present invention, and shows the state in which the resist 14 has been applied to the surface of the metal plate 12. [Figure 10] Figure 10 is an explanatory diagram showing the overhang formation process S104 according to the first embodiment of the present invention, and shows the state in which the peripheral edge (or side surface) of the metal plate 12 has been etched off. [Figure 11] Figure 11 is an explanatory diagram showing the overhang formation process S104 according to the first embodiment of the present invention, and shows the state after the resist 14 has been removed. [Figure 12] Figure 12 is an explanatory diagram showing the dimensions of the ceramic substrate and the shape of the metal circuit board (circuit pattern dimensions) of the metal-ceramic bonded substrate of sample 1 according to an embodiment of the present invention. [Figure 13] Figure 13 is a scanned electron microscope (SEM) image of a Ni-P alloy plating film formed on the brazing material overflow portion of the metal-ceramic bonded substrate of sample 2 according to an embodiment of the present invention, observed from a direction perpendicular to the metal circuit board. [Figure 14]Figure 14 is a scanned electron microscope (SEM) image of a Ni-P alloy plating film formed on the brazing material overflow portion of the metal-ceramic bonded substrate of sample 11 according to an embodiment of the present invention, observed from a direction perpendicular to the metal circuit board. [Figure 15] Figure 15 is a graph plotting the Pb concentration X in the brazing material and the Pb concentration Y in the electroless Ni plating solution for samples 1 to 11 according to an embodiment of the present invention. [Modes for carrying out the invention]

[0022] <Insights gained by the inventor> First, let me explain the findings the inventors have gained.

[0023] As described above, it has been found that with conventional electroless nickel plating methods, it is difficult to form a nickel plating film without minute defects on the surface of the silver-containing brazing material (especially the excess brazing material). If a large number of minute defects occur in the nickel plating film, it is thought that the migration of the metal-ceramic bond substrate cannot be sufficiently suppressed.

[0024] In the manufacturing method of metal-ceramic bonded substrates, various parameters affect the degree of nickel plating film formation, including phosphorus concentration in the plating solution, pH and temperature of the plating solution, and palladium activation treatment conditions (time, temperature, chemical concentration) as a pretreatment before plating. As a result of the inventor's diligent research, it was found that the lead concentration in the brazing material and the lead concentration in the plating solution affect the occurrence of minute defects in the nickel plating film. Specifically, for example, it was found that if either the lead concentration in the brazing material or the lead concentration in the plating solution exceeds a predetermined value, the deposition of nickel plating on the brazing material surface is inhibited, and relatively large defects in the nickel plating film (sometimes referred to as "exposed brazing material" in this specification) occur in areas where the nickel plating film is not formed on the brazing material surface (unplated areas or cracks in the nickel plating).

[0025] Nickel plating solutions contain a predetermined amount of lead as a stabilizer to prevent decomposition of the plating solution. The lead concentration is usually not changed because if it is too low, deposition is likely to occur on areas where plating is undesirable, such as the surface of the ceramic substrate in a metal-ceramic bonded substrate, the plating tank, and the plating jig. However, as a result of further diligent research by the inventors, it was discovered that the occurrence of minute defects in the nickel plating film can be suppressed by controlling the lead concentration in the brazing material to below a predetermined value, and by controlling the lead concentration in the plating solution to a predetermined range corresponding to the lead concentration in the brazing material. Furthermore, it was discovered that the maximum length of the exposed portion of the brazing material (unplated area) in the nickel plating film formed on the surface of the brazing material can be controlled to a predetermined range, thus completing the present invention. According to the present invention, the occurrence of migration can be suppressed.

[0026] [Details of the Embodiments of the Invention] Next, one embodiment of the present invention will be described below with reference to the drawings. However, the present invention is not limited to these examples and is intended to include all modifications within the meaning and scope equivalent to the claims as shown in the claims.

[0027] In this specification, "A to B" means a numerical range of "A or greater and B or less".

[0028] <First Embodiment of the Invention> (1) Structure of the metal-ceramic bonded substrate First, the configuration of the metal-ceramic bonded substrate 1 of this embodiment will be described. Figure 1 is a schematic cross-sectional view showing an example of the metal-ceramic bonded substrate 1 of this embodiment. As shown in Figure 1, the metal-ceramic bonded substrate 1 of this embodiment includes, for example, a ceramic substrate 10, a brazing material 11, a metal plate 12, and a nickel plating film 13.

[0029] As the ceramic substrate 10, for example, an oxide-based ceramic substrate mainly composed of alumina, or a non-oxide-based ceramic substrate mainly composed of aluminum nitride, silicon nitride, silicon carbide, etc., can be used. As the ceramic substrate 10, for example, a substrate with a length of 5 to 200 mm (preferably 10 to 100 mm), a width of 5 to 200 mm (preferably 10 to 100 mm), and a thickness of 0.25 to 3.0 mm (preferably 0.3 to 1.0 mm) can be used.

[0030] The brazing material 11 is provided on at least one main surface (preferably both main surfaces) of the ceramic substrate 10 and is configured to join the ceramic substrate 10 and the metal plate 12. To improve versatility and thermal conductivity, the brazing material 11 contains silver. Specifically, for example, a brazing material 11 containing silver and copper as metal components, and further containing an active metal component, can be used. The lead concentration of the brazing material 11 is 50 ppm or less. This suppresses the occurrence of fine defects in the nickel plating film 13. Furthermore, the lead concentration of the brazing material 11 is preferably 40 ppm or less, more preferably 25 ppm or less, and even more preferably 10 ppm or less. This further suppresses the occurrence of fine defects in the nickel plating film 13. In this specification, the content (concentration) of each metal element in the brazing material 11 refers to the ratio of its mass to the total mass of the metal components contained in the brazing material 11.

[0031] The silver content of the brazing material 11 is preferably, for example, 30 to 95% by mass, more preferably 50 to 90% by mass, and even more preferably 60 to 80% by mass. This lowers the melting point (joining temperature) of the brazing material 11 and improves its wettability to the ceramic substrate 10.

[0032] The brazing material 11 preferably contains at least one active metal selected from, for example, titanium or zirconium as an active metal component. The amount of active metal component contained in the brazing material 11 is preferably, for example, 1.0 to 7.0% by mass, and more preferably 1.5 to 6.5% by mass. This improves the bonding between the ceramic substrate 10 and the metal plate 12.

[0033] The brazing material 11 may further contain at least one metal component selected from tin or indium. The total content of tin and indium in the brazing material 11 is preferably, for example, 10% by mass or less, and more preferably 7% by mass or less. This allows for high thermal conductivity of the brazing material 11 and high bonding strength between the ceramic substrate 10 and the metal plate 12. The total content of tin and indium is preferably, for example, 0.4% by mass or more, and more preferably 3% by mass or more. This lowers the melting point (bonding temperature) of the brazing material 11 and improves its wettability to the ceramic substrate 10.

[0034] The metal plate 12 is joined to at least one main surface (preferably both main surfaces) of the ceramic substrate 10 via a brazing material 11. Figure 1 shows a case where two metal circuit boards 12a are joined to the upper surface of the ceramic substrate 10, and one heat dissipation side metal plate 12b is joined to the lower surface of the ceramic substrate 10.

[0035] A predetermined circuit pattern is formed on the metal circuit board 12a, and it is configured to mount chip components such as semiconductor elements. Therefore, it is preferable that the metal circuit board 12a be made of a material with excellent electrical and thermal conductivity, such as copper, aluminum, or an alloy thereof. In this embodiment, it is preferable to use a copper plate or a copper alloy plate as the metal circuit board 12a.

[0036] The heat-dissipating metal plate 12b is preferably bonded to the side of the ceramic substrate 10 opposite to the side to which the metal circuit board 12a is bonded, in order to dissipate heat generated from chip components such as semiconductor elements mounted on the metal circuit board 12a. The heat-dissipating metal plate 12b is preferably made of a material with excellent heat dissipation properties, such as copper, aluminum, or an alloy thereof. A heat-dissipating member (not shown) such as a base plate, heat-dissipating fins, or cooling jacket made of copper, copper alloy, aluminum, aluminum alloy, or an aluminum-silicon carbide composite material may be provided on the surface of the heat-dissipating metal plate 12b (the side opposite to the side bonded to the ceramic substrate 10). The heat-dissipating member can be attached to the heat-dissipating metal plate 12b by soldering, bolting, or the like.

[0037] It is preferable that an overhang 11a of the brazing material 11 is formed on the peripheral edge of the metal plate 12. As shown in Figure 1, the brazing material 11 is provided slightly larger than the metal plate 12 on the peripheral edge of the metal plate 12, so the overhang 11a of the brazing material 11 is exposed before the nickel plating film 13 is formed. The formation of the overhang 11a improves the thermal shock resistance of the metal-ceramic bonded substrate 1. The overhang 11a is preferably, for example, 5 to 500 μm in width (more preferably 30 to 200 μm, even more preferably 50 to 150 μm) and 3 to 50 μm in thickness (more preferably 5 to 20 μm). This further improves the thermal shock resistance of the metal-ceramic bonded substrate 1.

[0038] The nickel plating film 13 is formed on the surfaces of the metal plate 12 and the brazing material 11. If an overhang 11a of the brazing material 11 is formed on the periphery of the metal plate 12, it is preferable that the nickel plating film 13 is also formed on the surface of the overhang 11a.

[0039] The nickel plating film 13 of this embodiment includes not only a nickel plating film that does not contain additive elements, but also a nickel alloy plating film containing 15% by mass or less of additive elements. Suitable examples of the additive elements include phosphorus and boron. While forming a nickel plating film by electroplating may reduce costs, when applied to a metal-ceramic junction substrate having multiple circuit patterns, the arrangement of electrodes becomes complex, and considering variations in plating film thickness, a nickel alloy plating film such as nickel-phosphorus plating or nickel-boron plating by electroless plating is preferable. From the viewpoint of reducing costs, a nickel-phosphorus plating film is preferable, and from the viewpoint of improving solderability, a nickel-boron plating film is preferable.

[0040] The nickel plating film 13 formed on the surface of the brazing material 11 may have minute defects, such as areas that are not plated (unplated) or cracks in the plating film, which expose the brazing material 11. If the area of ​​exposed brazing material 11 is large, migration is more likely to occur. In the metal-ceramic bonded substrate 1 of this embodiment, the concentration of lead in the brazing material 11 is controlled, and the method of forming the nickel plating film 13, which will be described later, is devised to suppress the occurrence of minute defects in the nickel plating film 13. Therefore, in the nickel plating film 13 formed on the surface of the brazing material 11, the maximum length L of the exposed portion of the brazing material 11 is 70 μm or less. This makes it possible to suppress the occurrence of migration. Preferably, the maximum length L of the exposed portion of the brazing material 11 is 35 μm or less, and more preferably 15 μm or less. This makes it possible to suppress the occurrence of migration more significantly. When measuring the maximum length L of the exposed portion of the brazing material 11, for example, the surface of the nickel plating film formed on the surface of the brazing material 11 at the peripheral edge (end) of the metal circuit board 12a of the metal-ceramic bonded substrate 1 can be observed using a SEM with a magnification of approximately 500x along a randomly selected edge of the metal circuit board 12a, over a length of approximately 30mm, and the maximum length L can be measured.

[0041] When an overhang 11a is formed on the peripheral edge of the metal plate 12, the area on which the nickel plating film 13 is formed becomes larger compared to a metal-ceramic bonded substrate 1 without an overhang 11a, thus increasing the likelihood of migration caused by silver (or copper). Therefore, the present invention is particularly suitable for metal-ceramic bonded substrates 1 with an overhang 11a.

[0042] (2) Method for manufacturing a metal-ceramic bonded substrate Next, the manufacturing method of the metal-ceramic bonded substrate 1 of this embodiment will be described. Figure 2 is a flowchart showing an example of the manufacturing method of the metal-ceramic bonded substrate 1 of this embodiment. As shown in Figure 2, the manufacturing method of the metal-ceramic bonded substrate 1 of this embodiment includes, for example, a brazing material formation step S101, a metal plate joining step S102, a circuit pattern formation step S103, an overhang formation step S104, and a nickel plating film formation step S105. In this embodiment, the manufacturing method of the metal-ceramic bonded substrate 1 will be described as an example, in which two metal circuit boards 12a are joined to the upper surface of a ceramic substrate 10 via brazing material 11, one heat dissipation side metal plate 12b is joined to the lower surface of the ceramic substrate 10 via brazing material 11, and an overhang portion 11a of brazing material 11 is formed on the periphery of the metal plate 12, as shown in Figure 1.

[0043] As described above, the ceramic substrate 10 can be, for example, an oxide-based ceramic substrate mainly composed of alumina, or a non-oxide-based ceramic substrate mainly composed of aluminum nitride, silicon nitride, silicon carbide, etc. The ceramic substrate 10 can be, for example, one with a length of 5 to 200 mm (preferably 10 to 100 mm), a width of 5 to 200 mm (preferably 10 to 100 mm), and a thickness of 0.25 to 3.0 mm (preferably 0.3 to 1.0 mm).

[0044] (Brazing process S101) As shown in Figure 3, in the brazing material formation process S101, for example, a paste-like brazing material 11 is formed on the upper and lower surfaces of the ceramic substrate 10. The brazing material 11 can be formed by known methods such as screen printing, spraying, or a roll coater. The paste-like brazing material 11 can be prepared by a known method of kneading a metal powder consisting of a metal component with a vehicle containing a binder and a solvent. As described above, the brazing material 11 preferably contains, for example, silver and copper, and at least one active metal selected from titanium or zirconium, and may also contain at least one metal component selected from tin or indium.

[0045] In the brazing material formation process S101, a brazing material 11 is formed with a lead concentration of 50 ppm or less (preferably 40 ppm or less, more preferably 25 ppm or less, and even more preferably 10 ppm or less). This suppresses the occurrence of fine defects in the nickel plating film 13. Lead is contained as an impurity in the raw materials of the metal component of the brazing material 11, such as silver, copper, titanium, tin, and indium, or in the raw materials of alloys of these metal components. In this embodiment, the lead concentration in each raw material is analyzed in advance, and the lead concentration in the brazing material 11 is controlled. Specifically, for example, by carefully selecting and using high-purity raw materials for all (or some) of each metal component, a brazing material 11 with a lead concentration of 50 ppm or less can be formed.

[0046] In the brazing material formation process S101, instead of the paste-like brazing material 11, metal foil of brazing material 11 with a predetermined composition may be placed on the upper and lower surfaces of the ceramic substrate 10.

[0047] In the brazing material formation step S101, it is preferable to form a brazing material 11 having a thickness of, for example, 3 to 50 μm (more preferably 5 to 20 μm). This makes it possible to further improve the thermal shock resistance of the metal-ceramic bonded substrate 1 when the overhang portion 11a is formed in the overhang portion formation step S104, which will be described later.

[0048] (Metal plate joining process S102) As shown in Figure 4, in the metal plate joining process S102, for example, metal plates 12 are joined to the upper and lower surfaces of the ceramic substrate 10 via a brazing material 11. The joining of the metal plates 12 can be performed, for example, by arranging the metal plates 12 so as to be in contact with the brazing material 11, heating them in a vacuum or a non-oxidizing atmosphere, and then cooling them. As described above, the metal circuit board 12a is preferably made of a material with excellent electrical and thermal conductivity, such as copper, aluminum, or an alloy thereof, and the heat dissipation side metal plate 12b is preferably made of a material with excellent heat dissipation, such as copper, aluminum, or an alloy thereof. If the brazing material 11 is in paste form, it is preferable to reduce the amount of solvent components in the vehicle by volatilization, etc., by drying or heating in the air, inert gas, or vacuum, before joining the metal plates 12.

[0049] (Circuit pattern formation process S103) In the circuit pattern formation step S103, for example, after joining the metal plate 12 to the ceramic substrate 10, unnecessary portions of the metal plate 12 and brazing material 11 are removed, and a predetermined circuit pattern is formed on the metal plate 12 (metal circuit board 12a).

[0050] As shown in Figure 5, in the circuit pattern formation step S103, for example, a resist 14 having a predetermined circuit pattern is applied to the surface of a metal circuit board 12a bonded to the upper surface of a ceramic substrate 10. At this time, a resist 14 for forming a heat-dissipating metal board 12b with a predetermined shape (for example, approximately rectangular) may also be applied to the surface of a heat-dissipating metal board 12b bonded to the lower surface of a ceramic substrate 10. Next, as shown in Figure 6, in the circuit pattern formation step S103, unnecessary parts of the metal board 12 are etched away using, for example, an etching solution containing cupric chloride or an etching solution containing iron chloride. After that, as shown in Figure 7, the resist 14 is removed in the circuit pattern formation step S103. Furthermore, as shown in Figure 8, in the circuit pattern formation step S103, unnecessary parts of the brazing material 11 remaining around the metal board 12 are removed using, for example, an aqueous solution containing hydrofluoric acid or an aqueous solution containing a compound that forms a complex with an active metal, such as ethylene-diamine-tetraacetic acid (EDTA). As a result, unnecessary portions of the metal plate 12 and brazing material 11 can be removed, a predetermined circuit pattern can be formed on the metal circuit board 12a, and a heat dissipation side metal plate 12b of a predetermined shape can be formed.

[0051] (Protruding portion formation process S104) In the overhang formation step S104, for example, after forming a predetermined circuit pattern on the metal plate 12 (metal circuit board 12a), the peripheral edge of the metal plate 12 is removed to form the overhang portion 11a of the brazing material 11.

[0052] As shown in Figure 9, in the overhang formation step S104, for example, a resist 14 is applied to the surface of the metal plate 12. Preferably, the resist 14 is applied in the same shape as the surface of the metal plate 12, so that only the sides of the metal plate 12 are exposed, or in a shape slightly smaller than the surface of the metal plate 12, so that the sides and the peripheral edges (for example, about 500 μm wide) of the main surface (top surface) of the metal plate 12 are exposed. Next, as shown in Figure 10, in the overhang formation step S104, for example, the sides (and peripheral edges) of the metal plate 12 are etched off using an etching solution containing cupric chloride or iron chloride, a chemical polishing solution, etc. After that, as shown in Figure 11, in the overhang formation step S104, the resist 14 is removed. As a result, the peripheral edges of the metal plate 12 are removed, and the overhang portion 11a of the brazing material 11 can be formed. This improves the thermal shock resistance of the metal-ceramic bonded substrate 1.

[0053] In the overhang formation step S104, it is preferable to form an overhang 11a having a width of, for example, 5 to 500 μm (more preferably 30 to 200 μm, and even more preferably 50 to 150 μm). This can further improve the thermal shock resistance of the metal-ceramic bonded substrate 1. The width D of the overhang 11a can be controlled by etching conditions (size of the resist 14, type of etching solution, etching temperature and time, etc.).

[0054] (Nickel plating film formation process S105) In the nickel plating film formation step S105, for example, an electroless nickel plating solution is used to form a nickel plating film 13 on the surfaces of the metal plate 12 and the brazing material 11. In this embodiment, if an overhang portion 11a of the brazing material 11 is formed on the periphery of the metal plate 12, it is preferable to also form the nickel plating film 13 on the surface of the overhang portion 11a.

[0055] In the nickel plating film formation step S105, it is preferable to use, for example, an electroless nickel-phosphorus plating solution as the electroless nickel plating solution to form a nickel-phosphorus plating film as the nickel plating film 13. This makes it possible to improve the formation speed of the nickel plating film 13 compared to, for example, a nickel-boron plating film. It also makes it possible to reduce the manufacturing cost of the metal-ceramic bonded substrate 1. Alternatively, in the nickel plating film formation step S105, an electroless nickel-boron plating solution may be used to form a nickel-boron plating film.

[0056] In the nickel plating film formation process S105, the electroless nickel plating solution is prepared so as to satisfy the following equation (1), given that the lead concentration of the brazing material 11 is X ppm and the lead concentration of the electroless nickel plating solution is Y mg / L. 0.05≦Y≦-0.002X+0.5 (1)

[0057] If the lead concentration in the electroless nickel plating solution is below the lower limit of equation (1), the stability of the electroless nickel plating solution may decrease, potentially shortening its lifespan. Conversely, by setting the lead concentration of the electroless nickel plating solution to be above the lower limit of equation (1), the stability of the electroless nickel plating solution can be improved, and its lifespan can be extended. On the other hand, if the lead concentration of the electroless nickel plating solution exceeds the upper limit of equation (1), numerous minute defects may occur in the nickel plating film 13, and the length of the exposed portion of the brazing material 11 may increase, potentially making migration more likely. Conversely, by setting the lead concentration of the electroless nickel plating solution to be below the upper limit of equation (1), the occurrence of minute defects in the nickel plating film 13 can be suppressed, and the occurrence of migration can also be suppressed.

[0058] In the nickel plating film formation step S105, it is preferable to adjust the electroless nickel plating solution so that it satisfies the following formula (2), given that the lead concentration of the brazing material 11 is X ppm and the lead concentration of the electroless nickel plating solution is Y mg / L. 0.05≦Y≦-0.002X+0.475 (2) This further suppresses the occurrence of minute defects in the nickel plating film 13 and more significantly suppresses the occurrence of migration.

[0059] Furthermore, the lower limit of the lead concentration in the electroless nickel plating solution may be 0.08 mg / L or 0.1 mg / L. Although bismuth is sometimes used as a stabilizer for the plating solution to suppress the decomposition of the plating solution, similar to lead, it is not used in this embodiment, and the bismuth concentration in the electroless nickel plating solution is below the detection limit (0.001 mg / L or less).

[0060] To adjust the lead concentration in the electroless nickel plating solution, for example, the amount of pH adjusting solution containing lead, which is a component of the plating solution, can be adjusted. Specifically, in the nickel plating film formation step S105, it is preferable to determine the amount of pH adjusting solution by measuring at least one of the nickel concentration or pH of the electroless nickel plating solution, and then adjust the lead concentration of the electroless nickel plating solution.

[0061] By following the above steps, a metal-ceramic bonded substrate 1 as shown in Figure 1 can be manufactured. As mentioned above, heat dissipation members such as a base plate, heat dissipation fins, or cooling jacket made of copper, copper alloy, aluminum, aluminum alloy, or aluminum-silicon carbide composite material may be provided on the surface of the heat dissipation side metal plate 12b. These heat dissipation members can be attached to the heat dissipation side metal plate 12b by soldering, bolting, or the like.

[0062] <Other embodiments of the present invention> Although embodiments of the present invention have been specifically described above, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention.

[0063] For example, in the above embodiment, a case was described in which two metal plates 12 (metal circuit boards 12a) are joined to the upper surface of the ceramic substrate 10 via a brazing material 11. However, the number of metal plates 12 joined to the ceramic substrate 10 is not particularly limited and may be one or three or more.

[0064] Furthermore, although the above embodiment described a case in which the metal plate 12 is bonded to both main surfaces (upper and lower surfaces) of the ceramic substrate 10, in the metal-ceramic bonded substrate 1, it is sufficient that the metal plate 12 is bonded to at least one of the main surfaces of the ceramic substrate 10. [Examples]

[0065] Next, embodiments of the present invention will be described. These embodiments are examples of the present invention, and the present invention is not limited to these embodiments.

[0066] (Sample 1) As the metal component of the brazing material, a metal powder was prepared consisting of 10% by mass of copper (Cu) powder, 5% by mass of tin (Sn) powder, 2% by mass of titanium (Ti) powder (as an active metal component), and the remainder being silver (Ag) powder. Of these metal powders, at least one of the four types of Sn powder (1) to (4) with different lead (Pb) concentrations shown below was selected and mixed with the other metal powders to adjust the Pb concentration in the metal component of the brazing material to 0.5 ppm (0.00005% by mass) by mass ratio. The Pb concentration was calculated by analyzing the Pb concentration of each metal powder using ICP-MS (inductively coupled plasma mass spectrometry). For the metal powders other than Sn powder, it was confirmed that no Pb was present (below the detection limit). Sn powder (1): Sn powder (Pb concentration 0.027% by mass) Sn powder (2): SnPb alloy powder (Pb concentration 38% by mass) Sn powder (3): 3N Sn powder (Pb concentration 0.007% by mass) Sn powder (4): 4N Sn powder (Pb concentration below the detection limit)

[0067] These metal powders were mixed with a vehicle to create a paste-like brazing material containing an activated metal. (It was confirmed that the vehicle did not contain Pb.) This brazing material was screen printed to a thickness of 20 μm onto almost the entire surface of both sides of a ceramic substrate made of aluminum nitride substrate (AlN substrate) measuring 19.8 mm in length, 13.8 mm in width, and 1.0 mm in thickness. After drying, metal plates made of oxygen-free copper plate measuring 20 mm in length, 14 mm in width, and 0.25 mm in thickness were placed in contact with both sides of the brazing material. Next, the copper plates were bonded to both sides of the aluminum nitride substrate by heating to 850°C in a vacuum and then cooling.

[0068] Next, a UV-curable alkali-peelable resist in the shape of a circuit pattern was screen-printed onto the surface of a metal plate bonded to one main surface of the ceramic substrate, and the same resist in the shape of a heat-dissipating metal plate was screen-printed onto the surface of a metal plate bonded to the other main surface. After curing these resists by irradiating them with ultraviolet light, the unwanted parts of the metal plate (copper plate) were etched with an etching solution consisting of copper chloride, hydrochloric acid, and the remainder being water, and the resist was removed with an aqueous sodium hydroxide solution to form a metal circuit board and a heat-dissipating metal plate made of copper plates.

[0069] Next, the ceramic substrate was immersed in a chelate aqueous solution containing 1.6% by mass of EDTA·4Na (sodium salt of ethylenediaminetetraacetic acid), 3% by mass of ammonia water, and 5% by mass of hydrogen peroxide. Then, it was immersed in a known brazing solution consisting of 2% by mass of ethylenetriaminepentaacetic acid (DTPA)·5Na and 5% by mass of hydrogen peroxide. This removed unwanted portions of the active metal-containing brazing material remaining between the copper circuit patterns on the surface of the ceramic substrate and around the heat-dissipating copper plate, thereby obtaining an intermediate product.

[0070] Next, the resist described above was applied to the entire surface of the intermediate product's metal circuit board and heat dissipation side metal plate by screen printing. Then, the metal circuit board and heat dissipation side metal plate were etched (chemically polished) by immersion in an etching solution (chemical polishing solution) at a liquid temperature of 45°C, consisting of 14% by mass sulfuric acid, 3.2% by mass hydrogen peroxide, and the remainder water, causing the activated metal-containing brazing material to protrude 100 μm in width from the side surfaces of the circuit side copper plate and heat dissipation side copper plate, forming a brazing material overhang (brazing material fillet). The thickness of the brazing material was approximately 15 μm.

[0071] Next, the intermediate product was degreased, pickled, and then treated with palladium activation as a pretreatment for electroless plating. A 3 μm thick nickel-phosphorus (Ni-P) alloy plating film was then formed on the surfaces of the metal circuit board and the heat dissipation side metal plate, as well as on the surface (overflow portion) of the brazing material, by electroless plating to obtain the metal-ceramic bonded substrate of Sample 1. For the electroless Ni-P alloy plating solution used, a commercially available medium-phosphorus type electroless Ni-P alloy plating solution containing nickel sulfate as a nickel salt and sodium hypophosphite as a reducing agent was used, to which a predetermined amount of pH adjusting solution containing Pb and sodium hydroxide was added to adjust the Pb concentration. The components of this electroless Ni-P alloy plating solution were analyzed by ICP-MS (inductively coupled plasma mass spectrometry), and the results showed that Ni was 5.4 g / L, P was 6.6 g / L, and Pb was 0.47 mg / L. Furthermore, the bismuth concentration was below the detection limit (0.001 mg / L or less) in all electroless nickel plating solutions used to prepare Sample 1 and Samples 2 to 13 described later. The substrate dimensions of the metal-ceramic bonded substrate and the shape of the metal circuit board (circuit pattern dimensions) of Sample 1 are shown in Figure 12.

[0072] A 30 mm long, 100 μm wide area of ​​the Ni-P alloy plating film formed on the surface of the excess brazing material of sample 1 was observed using a scanning electron microscope (SEM: Hitachi High-Tech Corporation TM4000) at 500x magnification to obtain a backscattered electron image. At that time, the underlying brazing material (Ag and / or Cu) could sometimes be observed from areas where the Ni-P plating film was not formed or from cracks in the Ni-P plating film. The length of the largest exposed portion of the brazing material (Ag (and / or Cu), crack in the plating film) was measured. The length of the exposed portion was defined as the diameter of the smallest circle inscribed in the end of the exposed portion. As a result, the maximum length L of the exposed portion of the brazing material was 16 μm, indicating that almost no exposure was observed.

[0073] (Sample 2) The metal-ceramic bonded substrate of Sample 2 was prepared in the same manner as Sample 1, except that Sn powders (1) to (4) were mixed so that the concentration of Pb in the metal component of the brazing material was 5.5 ppm by mass ratio, and the concentration of Pb in the electroless Ni-P alloy plating solution was set to 0.4 mg / L. Similar to Sample 1, the maximum length L of the exposed brazing material in the Ni-P alloy plating film of Sample 2 was measured and found to be 25 μm. Figure 13 shows a backscattered electron image obtained by scanning electron microscope (SEM) observing the Ni-P alloy plating film formed on the brazing material overflow portion of the metal-ceramic bonded substrate of Sample 2 from a direction perpendicular to the metal circuit board.

[0074] (Sample 3) The metal-ceramic bonded substrate of sample 3 was prepared in the same manner as sample 1, except that Sn powders (1) to (4) were mixed so that the concentration of Pb in the metal component of the brazing material was 18.5 ppm by mass ratio, and the concentration of Pb in the electroless Ni-P alloy plating solution was set to 0.4 mg / L. Similar to sample 1, the maximum length L of the exposed brazing material in the Ni-P alloy plating film of sample 3 was measured and found to be 18 μm.

[0075] (Sample 4) The metal-ceramic bonded substrate of sample 4 was prepared in the same manner as sample 1, except that Sn powders (1) to (4) were mixed so that the concentration of Pb in the metal component of the brazing material was 40.0 ppm by mass ratio, and the concentration of Pb in the electroless Ni-P alloy plating solution was set to 0.38 mg / L. Similar to sample 1, the maximum length L of the exposed brazing material in the Ni-P alloy plating film of sample 4 was measured and found to be 11.6 μm.

[0076] (Sample 5) The metal-ceramic bonded substrate of sample 5 was prepared in the same manner as sample 1, except that Sn powders (1) to (4) were mixed so that the concentration of Pb in the metal component of the brazing material was 5.5 ppm by mass ratio. Similar to sample 1, the maximum length L of the exposed brazing material in the Ni-P alloy plating film of sample 5 was measured and found to be 62 μm.

[0077] (Sample 6) The metal-ceramic bonded substrate of sample 6 was prepared in the same manner as sample 1, except that Sn powders (1) to (4) were mixed so that the concentration of Pb in the metal component of the brazing material was 40.0 ppm by mass ratio, and the concentration of Pb in the electroless Ni-P alloy plating solution was set to 0.4 mg / L. Similar to sample 1, the maximum length L of the exposed brazing material in the Ni-P alloy plating film of sample 6 was measured and found to be 64 μm.

[0078] (Sample 7) The metal-ceramic bonded substrate of sample 7 was prepared in the same manner as sample 1, except that the Pb concentration in the electroless Ni-P alloy plating solution was set to 0.4 mg / L. Similar to sample 1, the maximum length L of the exposed brazing material in the Ni-P alloy plating film of sample 7 was measured and found to be 10 μm.

[0079] (Sample 8) The metal-ceramic bonded substrate of sample 8 was prepared in the same manner as sample 1, except that the concentration of Pb in the electroless Ni-P alloy plating solution was set to 0.38 mg / L. Similar to sample 1, the maximum length L of the exposed brazing material in the Ni-P alloy plating film of sample 8 was measured and found to be 5 μm.

[0080] (Sample 9) The metal-ceramic bonded substrate of sample 9 was prepared in the same manner as sample 1, except that the concentration of Pb in the electroless Ni-P alloy plating solution was set to 0.33 mg / L. Similar to sample 1, the maximum length L of the exposed brazing material in the Ni-P alloy plating film of sample 9 was measured and found to be 5 μm.

[0081] (Sample 10) The metal-ceramic bonded substrate of sample 10 was prepared in the same manner as sample 1, except that Sn powders (1) to (4) were mixed so that the concentration of Pb in the metal component of the brazing material was 18.5 ppm by mass ratio. Similar to sample 1, the maximum length L of the exposed brazing material in the Ni-P alloy plating film of sample 10 was measured and found to be 80 μm.

[0082] (Sample 11) The metal-ceramic bonded substrate of sample 11 was prepared in the same manner as sample 1, except that Sn powders (1) to (4) were mixed so that the concentration of Pb in the metal component of the brazing material was 40.0 ppm by mass ratio. Similar to sample 1, the maximum length L of the exposed brazing material in the Ni-P alloy plating film of sample 11 was measured to be 122 μm. Figure 14 shows a backscattered electron image obtained by scanning electron microscope (SEM) from a direction perpendicular to the metal circuit board, of the Ni-P alloy plating film formed on the brazing material overflow portion of the metal-ceramic bonded substrate of sample 11.

[0083] (Sample 12) The metal-ceramic bonded substrate of sample 12 was prepared in the same manner as sample 3, except that the concentration of Pb in the electroless Ni-P alloy plating solution was set to 0.54 mg / L. Similar to sample 1, the maximum length L of the exposed brazing material in the Ni-P alloy plating film of sample 12 was measured and found to be 163 μm.

[0084] (Sample 13) The metal-ceramic bonded substrate of sample 13 was prepared in the same manner as sample 3, except that an electroless Ni-P alloy plating solution without Pb was used. As a result, Ni plating was deposited on the surface of the ceramic substrate, resulting in a defective product in which insulation between circuits and between surfaces of the metal-ceramic bonded substrate could not be ensured.

[0085] Table 1 shows the maximum length L of the exposed brazing material for samples 1 to 13, along with the Pb concentration X in the brazing material, the Pb concentration Y in the electroless Ni plating solution, the upper limit of equation (1), and the upper limit of equation (2). Figure 15 shows a graph plotting the Pb concentration X in the brazing material and the Pb concentration Y in the electroless Ni plating solution for samples 1 to 11.

[0086] [Table 1]

[0087] As shown in Table 1 and Figure 15, for samples 1-9, where the Pb concentration Y in the electroless Ni plating solution was below the upper limit of equation (1), the maximum length L of the exposed brazing material was 70 μm or less (5-64 μm). For samples 1-4 and 7-9, where the Pb concentration Y in the electroless Ni plating solution was below the upper limit of equation (2), the maximum length L of the exposed brazing material was 35 μm or less (5-25 μm). On the other hand, for samples 10-12, where the Pb concentration Y in the electroless Ni plating solution exceeded the upper limit of equation (1), the maximum length L of the exposed brazing material was greater than 70 μm (80-163 μm). Furthermore, for sample 13, where the Pb concentration Y in the electroless Ni plating solution was below the lower limit (0.05) of equation (1), it was a defective product where insulation between circuits and between surfaces of the metal-ceramic bonded substrate could not be ensured. Based on the above, it was confirmed that in a metal-ceramic bonded substrate, the occurrence of fine defects in the nickel plating film can be suppressed by controlling the lead concentration X in the brazing material to a predetermined value or less, and by controlling the lead concentration Y in the electroless Ni plating solution to a predetermined range corresponding to the lead concentration X in the brazing material. [Explanation of Symbols]

[0088] 1. Metal-ceramic bonded substrate 10 Ceramic substrates 11 Brazing material 11a Overhang 12 metal plate 12a metal circuit board 12b Heat radiation side metal plate 13 Nickel plating film 14 Resist S101 Brazing material formation process S102 Metal plate joining process S103 Circuit pattern formation process S104 Process for forming protruding portion S105 Nickel plating film formation process

Claims

1. Ceramic substrate and A metal plate is bonded to at least one main surface of the ceramic substrate via a brazing material containing silver and having a lead concentration of X ppm (X ≤ 50), The metal plate and the brazing material have an electroless nickel plating film formed on their surfaces, A metal-ceramic bonded substrate in which the electroless nickel plating film formed on the surface of the brazing material has a maximum length of 70 μm or less for the exposed portion of the brazing material.

2. The metal-ceramic bonded substrate according to claim 1, wherein the electroless nickel plating film formed on the surface of the brazing material has a maximum length of 35 μm or less of the exposed portion of the brazing material.

3. An excess portion of the brazing material is formed on the peripheral edge of the metal plate. The metal-ceramic bonded substrate according to claim 1, wherein the electroless nickel plating film is formed on the surface of the protruding portion.

4. The metal-ceramic bonded substrate according to any one of claims 1 to 3, wherein the electroless nickel plating film is a nickel-phosphorus plating film.

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