Manufacturing method for metal-ceramic bonded substrate

Abstract

To provide a technique capable of suppressing the occurrence of minute defects in a nickel plating film.SOLUTION: A method for manufacturing a metal-ceramic bonding substrate includes the steps of: bonding a metal plate, on at least one main surface of a ceramic substrate, through a brazing material containing silver and having a lead concentration of X ppm (X≤50); and using an electroless nickel plating solution with a lead concentration of Y mg / L to form a nickel plating film on the surfaces of the metal plate and the brazing material. In the step of forming a nickel plating film, a lead concentration Y in the electroless nickel plating solution is adjusted to satisfy a relationship of 0.05≤Y≤-0.002X+0.5.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a metal-ceramic bonding substrate, and a metal-ceramic bonding substrate. [Background technology]

[0002] Power modules have traditionally been used to control large amounts of power in electric vehicles, trains, machine tools, etc. As an insulating substrate for such power modules, a metal-ceramic bonding circuit board has been used, in which a metal circuit plate bonded to one side of a ceramic substrate is plated on areas that require soldering of chip components and terminals.

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

[0004] Known methods for alleviating such thermal stress include thinning the surface portion of the metal circuit plate, that is, forming a step structure or a fillet (an extended portion of the brazing material for joining the metal circuit plate to the ceramic substrate) on the peripheral edge of the metal circuit plate (see, for example, Patent Documents 1 to 3).

[0005] However, when a metal-ceramic circuit board on which a fillet of active metal-containing brazing filler metal is formed to join a metal circuit plate (such as a copper circuit plate) to a ceramic substrate is incorporated into a power module, migration of the metal in the active metal-containing brazing filler metal (for example, silver or copper when a brazing filler metal made of active metal, silver, and copper is used) can occur between the circuit patterns of the metal circuit plate on the ceramic substrate, which could result in poor insulation.

[0006] As a method for preventing such migration, a method of electrolessly plating the surface of the protruding portion of the brazing filler metal from the edge of the metal plate with Ni-P 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 surface of a ceramic substrate via an active metal-containing brazing filler metal containing silver, unnecessary portions of the copper plate and the active metal-containing brazing filler metal are then removed by chemical polishing so that the unnecessary portions of the copper plate are exposed to the active metal-containing brazing filler metal from the side portions of the copper plate, the silver layer adhering to the surface of the copper plate is removed by this chemical polishing, and then electroless Ni-P plating is applied to the copper plate and the exposed portions of the brazing filler metal (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] JP 2001-332854 A (paragraphs 0014-0019) [Patent Document 3] JP 2004-307307 A (paragraphs 0012-0014) [Patent Document 4] JP 2006-228918 A (paragraphs 0021-0022) [Patent Document 5] JP 2018-145047 A (paragraphs 0030-0034) Summary of the Invention [Problem to be solved by the invention]

[0009] However, it was found that the manufacturing method of metal-ceramic bonded (circuit) substrates described in the aforementioned patent documents cannot sufficiently suppress the occurrence of migration. The present inventors conducted extensive research into the cause of this and found that when the nickel plating film formed on the surface of the brazing filler metal (the protruding portion) was observed from the surface, microscopic defects (microscopic defects in the nickel plating film) where the brazing filler metal was exposed were observed. It is presumed that these microscopic defects in the nickel plating film are the cause of the occurrence of migration, and the object of the present invention is to suppress the occurrence of these microscopic defects in the nickel plating film.

[0010] An object of one embodiment of the present invention is to provide a technique for suppressing the occurrence of minute defects in a nickel plating film in a manufacturing method of a metal-ceramic bonding substrate.An object of another embodiment of the present invention is to provide a technique for suppressing the occurrence of minute defects in a nickel plating film in a metal-ceramic bonding 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 filler metal 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 filler metal using an electroless nickel plating solution having a lead concentration of Y mg / L, In the step of forming the nickel plating film, the lead concentration Y in the electroless nickel plating solution satisfies the relationship 0.05≦Y≦−0.002X+0.5.

[0012] A second aspect of the present invention is In the method for producing a metal / ceramic bonding substrate according to the first aspect, in the step of forming the nickel plating film, a lead concentration Y in the electroless nickel plating solution satisfies the relationship 0.05≦Y≦−0.002X+0.475.

[0013] A third aspect of the present invention is In the method for producing a metal / ceramic bonding substrate according to the first or second aspect, in the step of forming the nickel plating film, the nickel-phosphorus plating film is formed using an electroless nickel-phosphorus plating solution.

[0014] A fourth aspect of the present invention is The method for producing a metal-ceramic bonding substrate according to any one of the first to third aspects further comprises the steps of: after bonding the metal plate to the ceramic substrate, removing unnecessary portions of the metal plate and the brazing filler metal; and forming a predetermined circuit pattern on the metal plate.

[0015] A fifth aspect of the present invention is The method for producing a metal-ceramic bonding substrate according to the fourth aspect further comprises the step of removing a peripheral portion of the metal plate to form an overflowing portion of the brazing filler metal after forming a predetermined circuit pattern on the metal plate.

[0016] A sixth aspect of the present invention is a ceramic substrate; a metal plate joined to at least one main surface of the ceramic substrate via a brazing filler metal containing silver and having a lead concentration of X ppm (X≦50); a nickel plating film formed on the surface of the metal plate and the brazing material, In the metal-ceramic bonding substrate, the maximum length of the exposed portion of the brazing filler metal in the nickel plating film formed on the surface of the brazing filler metal is 70 μm or less.

[0017] A seventh aspect of the present invention is In the metal / ceramic bonding substrate according to the sixth aspect, in the nickel plating film formed on the surface of the brazing filler metal, the maximum length of the exposed portion of the brazing filler metal is 35 μm or less.

[0018] An eighth aspect of the present invention is an overhanging portion of the brazing material is formed on the peripheral edge of the metal plate; In the metal / ceramic bonding substrate according to the sixth or seventh aspect, the nickel plating film is formed on the surface of the protruding portion.

[0019] A ninth aspect of the present invention is a method for manufacturing a semiconductor device comprising: In the metal / ceramic bonding substrate according to any one of the sixth to eighth aspects, the nickel plating film is a nickel-phosphorus plating film. [Effects of the Invention]

[0020] According to one embodiment of the present invention, in a method for manufacturing a metal-ceramic bonding substrate, the occurrence of minute defects in a nickel plating film can be suppressed. Also, according to one embodiment of the present invention, in a metal-ceramic bonding substrate, the occurrence of minute defects in a nickel plating film can be suppressed. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a cross-sectional view schematically showing an example of a metal / ceramic 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-ceramic bonding substrate 1 according to the first embodiment of the present invention. [Figure 3] FIG. 3 is an explanatory diagram showing the brazing material forming step S101 according to the first embodiment of the present invention, and shows a state in which the paste brazing material 11 has been formed on the upper and lower surfaces of the ceramic substrate 10. [Figure 4] FIG. 4 is an explanatory diagram showing the metal plate bonding step S102 according to the first embodiment of the present invention, and shows a state in which metal plates 12 are bonded to the upper and lower surfaces of a ceramic substrate 10 via brazing filler metal 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 the 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] FIG. 6 is an explanatory diagram showing the circuit pattern forming step S103 according to the first embodiment of the present invention, showing a state in which unnecessary portions of the metal plate 12 have been removed by etching. [Figure 7] FIG. 7 is an explanatory diagram showing the circuit pattern forming step S103 according to the first embodiment of the present invention, showing a state in which the resist 14 has been removed. [Figure 8] FIG. 8 is an explanatory diagram showing the circuit pattern forming step S103 according to the first embodiment of the present invention, showing a state in which unnecessary portions of the brazing filler metal 11 have been removed. [Figure 9] FIG. 9 is an explanatory diagram showing the protruding portion forming step S104 according to the first embodiment of the present invention, and shows a state in which the resist 14 is applied to the surface of the metal plate 12. [Figure 10] FIG. 10 is an explanatory diagram showing the protruding portion forming step S104 according to the first embodiment of the present invention, and shows a state in which the peripheral edge portion (or side surface) of the metal plate 12 has been removed by etching. [Figure 11] FIG. 11 is an explanatory diagram showing the protruding portion forming step S104 according to the first embodiment of the present invention, showing a state in which the resist 14 has been removed. [Figure 12] FIG. 12 is an explanatory diagram showing the dimensions of the ceramic substrate and the shape (circuit pattern dimensions) of the metal circuit plate of the metal-ceramic bonding substrate of Sample 1 according to an example of the present invention. [Figure 13] FIG. 13 is a backscattered electron image of a Ni-P alloy plating film formed on the protruding portion of the brazing filler metal of the metal-ceramic bonding substrate of Sample 2 according to an embodiment of the present invention, observed by a scanning electron microscope (SEM) in a direction perpendicular to the metal circuit board. [Figure 14]FIG. 14 is a backscattered electron image of a Ni-P alloy plating film formed on the protruding portion of the brazing filler metal of the metal-ceramic bonding substrate of Sample 11 according to an embodiment of the present invention, taken with a scanning electron microscope (SEM) and observed from a direction perpendicular to the metal circuit board. [Figure 15] FIG. 15 is a graph plotting the Pb concentration X in the brazing filler metal and the Pb concentration Y in the electroless Ni plating solution for Samples 1 to 11 according to an example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] <Insights gained by the inventor> First, the findings of the inventors will be explained.

[0023] It has been found that, using the conventional electroless nickel plating method described above, it is difficult to form a nickel plating film without fine defects on the surface of a silver-containing brazing filler metal (especially the protruding portion of the brazing filler metal). If many fine defects occur in the nickel plating film, it is thought that it is not possible to sufficiently suppress the occurrence of migration in metal-ceramic bonding substrates.

[0024] In the manufacturing method of a metal-ceramic bonding substrate, various parameters affect the formation of a nickel plating film, such as the phosphorus concentration in the plating solution, the pH and temperature of the plating solution, and the conditions of the palladium activation treatment (time, temperature, and chemical concentration) that is a pretreatment for plating. As a result of extensive research by the inventors, it was found that the lead concentration in the brazing filler metal and the lead concentration in the plating solution affect the occurrence of minute defects in the nickel plating film. Specifically, it was found that, for example, when either the lead concentration in the brazing filler metal or the lead concentration in the plating solution exceeds a predetermined value, the deposition of nickel plating on the brazing filler metal surface is inhibited, resulting in the occurrence of relatively large defects in the nickel plating film (sometimes referred to in this specification as "exposed brazing filler metal"), which are areas on the brazing filler metal surface where the nickel plating film is not formed (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. A low lead concentration is usually not altered because it can easily lead to precipitation on areas where plating is not desired, such as the surface of a ceramic substrate in a metal-ceramic bonding substrate, the plating tank, or plating jigs. However, after further intensive research, the inventors discovered that controlling the lead concentration in the brazing filler metal below a predetermined value and controlling the lead concentration in the plating solution within a predetermined range corresponding to the lead concentration in the brazing filler metal can suppress the occurrence of minute defects in the nickel plating film. Furthermore, they discovered that the maximum length of the exposed portion of the brazing filler metal (unplated area) in the nickel plating film formed on the surface of the brazing filler metal can be controlled within a predetermined range, leading to the completion of the present invention. According to the present invention, migration can be suppressed.

[0026] [Details of the embodiment of the present invention] Next, an embodiment of the present invention will be described below with reference to the drawings. Note that the present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

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

[0028] <First embodiment of the present invention> (1) Structure of metal-ceramic bonding substrate First, the configuration of the metal-ceramic bonding substrate 1 of this embodiment will be described. Fig. 1 is a cross-sectional view schematically showing an example of the metal-ceramic bonding substrate 1 of this embodiment. As shown in Fig. 1, the metal-ceramic bonding substrate 1 of this embodiment includes, for example, a ceramic substrate 10, a brazing filler metal 11, a metal plate 12, and a nickel plating film 13.

[0029] The ceramic substrate 10 may be, for example, an oxide ceramic substrate containing alumina or the like as a main component, or a non-oxide ceramic substrate containing aluminum nitride, silicon nitride, silicon carbide or the like as a main component. The ceramic substrate 10 may have 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).

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

[0031] The silver content of the brazing filler metal 11 is, for example, preferably 30 to 95 mass %, more preferably 50 to 90 mass %, and even more preferably 60 to 80 mass %, which can lower the melting point (bonding temperature) of the brazing filler metal 11 and improve wettability to the ceramic substrate 10.

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

[0033] The brazing filler metal 11 may further contain at least one metal component selected from tin and indium. The total content of tin and indium contained in the brazing filler metal 11 is, for example, preferably 10 mass % or less, and more preferably 7 mass % or less. This makes it possible to maintain high thermal conductivity of the brazing filler metal 11 and high bondability between the ceramic substrate 10 and the metal plate 12. The total content of tin and indium is, for example, preferably 0.4 mass % or more, and more preferably 3 mass % or more. This makes it possible to lower the melting point (bonding temperature) of the brazing filler metal 11 and improve its wettability to the ceramic substrate 10.

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

[0035] A predetermined circuit pattern is formed on the metal circuit plate 12a, and chip components such as semiconductor elements are mounted on the metal circuit plate 12a. Therefore, the metal circuit plate 12a is preferably made of a material with excellent electrical and thermal conductivity, such as copper, aluminum, or an alloy thereof. In this embodiment, a copper plate or a copper alloy plate is preferably used as the metal circuit plate 12a.

[0036] The heat-dissipating-side metal plate 12b is preferably bonded to the surface of the ceramic substrate 10 opposite to the surface to which the metal circuit plate 12a is bonded in order to dissipate heat generated by chip components such as semiconductor elements mounted on the metal circuit plate 12a. The heat-dissipating-side 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-side metal plate 12b (the surface opposite to the surface bonded to the ceramic substrate 10). The heat-dissipating member can be attached to the heat-dissipating-side metal plate 12b by soldering, bolting, or the like.

[0037] Preferably, a protruding portion 11a of the brazing filler metal 11 is formed at the peripheral edge of the metal plate 12. As shown in FIG. 1, the brazing filler metal 11 is provided at the peripheral edge of the metal plate 12 to be slightly larger than the metal plate 12. Therefore, the protruding portion 11a of the brazing filler metal 11 is exposed before the nickel plating film 13 is formed. The formation of the protruding portion 11a improves the thermal shock resistance of the metal-ceramic bonding substrate 1. The protruding portion 11a preferably has a width of 5 to 500 μm (more preferably 30 to 200 μm, and even more preferably 50 to 150 μm) and a thickness of 3 to 50 μm (more preferably 5 to 20 μm). This further improves the thermal shock resistance of the metal-ceramic bonding substrate 1.

[0038] The nickel plating film 13 is formed on the surfaces of the metal plate 12 and the brazing filler metal 11. When a protruding portion 11a of the brazing filler metal 11 is formed on the peripheral edge of the metal plate 12, it is preferable that the nickel plating film 13 is also formed on the surface of the protruding portion 11a.

[0039] The nickel plating film 13 of this embodiment includes nickel plating films that do not contain any additional elements, as well as nickel alloy plating films that contain 15 mass% or less of the additional elements. Suitable examples of the additional elements include phosphorus and boron. Forming a nickel plating film by electroplating may reduce costs, but when applied to a metal-ceramic bonding substrate having multiple circuit patterns, the electrode arrangement becomes complicated. Considering the variation in plating film thickness, a nickel alloy plating film such as electroless nickel-phosphorus plating or nickel-boron plating is preferred. From the perspective of reducing costs, etc., a nickel-phosphorus plating film is preferred, and from the perspective of improving solderability, etc., a nickel-boron plating film is preferred.

[0040] The nickel plating film 13 formed on the surface of the brazing filler metal 11 may have minute defects, which are exposed portions of the brazing filler metal 11 due to unplated areas (non-adhered areas) or cracks in the plating film. Large areas of exposed brazing filler metal 11 are more likely to cause migration. In the metal-ceramic bonding substrate 1 of this embodiment, the lead concentration of the brazing filler metal 11 is controlled and a method for forming the nickel plating film 13, which will be described later, is devised to prevent 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 filler metal 11, the maximum length L of the exposed portion of the brazing filler metal 11 is 70 μm or less. This makes it possible to prevent migration. The maximum length L of the exposed portion of the brazing filler metal 11 is preferably 35 μm or less, and more preferably 15 μm or less. This makes it possible to more significantly prevent migration. In measuring the maximum length L of the exposed portion of the brazing filler metal 11, for example, the surface of the nickel plating film formed on the surface of the brazing filler metal 11 at the peripheral portion (edge) of the metal circuit plate 12a of the metal-ceramic bonding substrate 1 can be observed using an SEM at a magnification of about 500 times in an area of ​​about 30 mm in length along a randomly selected edge of the metal circuit plate 12a, and the maximum length L can be measured.

[0041] When the metal plate 12 has a protruding portion 11a formed at its peripheral edge, the area on which the nickel plating film 13 is formed is larger than in a metal-ceramic bonding substrate 1 without the protruding portion 11a, increasing the possibility of migration caused by silver (or copper). Therefore, the present invention is particularly suitable for use with a metal-ceramic bonding substrate 1 with the protruding portion 11a.

[0042] (2) Manufacturing method of metal-ceramic bonded substrate Next, a method for manufacturing the metal-ceramic bonding substrate 1 of this embodiment will be described. FIG. 2 is a flowchart showing an example of the method for manufacturing the metal-ceramic bonding substrate 1 of this embodiment. As shown in FIG. 2, the method for manufacturing the metal-ceramic bonding substrate 1 of this embodiment includes, for example, a brazing filler metal forming step S101, a metal plate bonding step S102, a circuit pattern forming step S103, an overhang portion forming step S104, and a nickel plating film forming step S105. Note that this embodiment will be described by taking as an example a method for manufacturing the metal-ceramic bonding substrate 1 shown in FIG. 1, in which two metal circuit plates 12a are bonded to the upper surface of a ceramic substrate 10 via a brazing filler metal 11, one heat-dissipating side metal plate 12b is bonded to the lower surface of the ceramic substrate 10 via the brazing filler metal 11, and an overhang portion 11a of the brazing filler metal 11 is formed around the periphery of the metal plate 12.

[0043] As described above, for example, an oxide ceramic substrate containing alumina or the like as a main component, or a non-oxide ceramic substrate containing aluminum nitride, silicon nitride, silicon carbide or the like as a main component can be used as the ceramic substrate 10. For example, the ceramic substrate 10 can have 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 material forming process S101) As shown in FIG. 3 , in the brazing material forming step S101, for example, a paste-like brazing material 11 is formed on the upper and lower surfaces of a ceramic substrate 10. The brazing material 11 can be formed by a known method such as screen printing, spraying, or using a roll coater. The paste-like brazing material 11 can be produced by a known method of kneading a metal powder containing metal components with a vehicle containing a binder and a solvent. As described above, the brazing material 11 contains, for example, silver and copper as metal components, and preferably contains at least one active metal selected from titanium and zirconium, and may also contain at least one metal component selected from tin and indium.

[0045] In the brazing filler metal formation step S101, a brazing filler metal 11 having 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) is formed. This can suppress the occurrence of minute defects in the nickel plating film 13. Lead is contained as an impurity in raw materials for the metal components of the brazing filler metal 11, such as silver, copper, titanium, tin, and indium, or raw materials for alloys of these metal components. In this embodiment, the lead concentration in each raw material is analyzed in advance to control the lead concentration in the brazing filler metal 11. Specifically, for example, by carefully selecting and using high-purity raw materials for all (or some) of the metal components, a brazing filler metal 11 having a lead concentration of 50 ppm or less can be formed.

[0046] In the brazing material forming step S101, instead of the brazing material 11 in paste form, metal foils of the brazing material 11 having a predetermined composition may be placed on the upper and lower surfaces of the ceramic substrate 10.

[0047] In the brazing filler metal forming step S101, it is preferable to form the brazing filler metal 11 with 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 bonding substrate 1 when the protruding portion 11a is formed in the protruding portion forming step S104 described below.

[0048] (Metal plate joining process S102) As shown in FIG. 4 , in the metal plate bonding step S102, for example, metal plates 12 are bonded to the upper and lower surfaces of a ceramic substrate 10 via brazing filler metal 11. The metal plates 12 can be bonded by, for example, placing the metal plates 12 in contact with the brazing filler metal 11, heating them in a vacuum or a non-oxidizing atmosphere, and then cooling them. As described above, the metal circuit plate 12a is preferably made of a material with excellent electrical and thermal conductivity, such as copper, aluminum, or an alloy thereof, and 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. When the brazing filler metal 11 is in paste form, it is preferable to bond the metal plates 12 after reducing the amount of solvent components in the vehicle by volatilization, for example, by drying or heating in the air, an inert gas, or a vacuum.

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

[0050] As shown in FIG. 5, in the circuit pattern forming step S103, for example, a resist 14 having a predetermined circuit pattern is applied to the surface of the metal circuit plate 12a bonded to the upper surface of the ceramic substrate 10. At this time, a resist 14 for forming the heat-dissipating-side metal plate 12b having a predetermined shape (e.g., a substantially rectangular shape) may also be applied to the surface of the heat-dissipating-side metal plate 12b bonded to the lower surface of the ceramic substrate 10. Next, as shown in FIG. 6, in the circuit pattern forming step S103, unnecessary portions of the metal plate 12 are etched and removed using, for example, an etching solution containing cupric chloride or an etching solution containing iron chloride. Thereafter, as shown in FIG. 7, in the circuit pattern forming step S103, the resist 14 is removed. Furthermore, as shown in FIG. 8, in the circuit pattern forming step S103, unnecessary portions of the brazing filler metal 11 remaining around the metal plate 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 ethylenediaminetetraacetic acid (EDTA). As a result of the above, unnecessary portions of the metal plate 12 and the brazing material 11 are removed, and a predetermined circuit pattern can be formed on the metal circuit plate 12a, and the heat-dissipating-side metal plate 12b can be formed in a predetermined shape.

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

[0052] As shown in FIG. 9, in the protruding portion forming step S104, for example, resist 14 is applied to the surface of metal plate 12. The resist 14 is preferably applied in the same shape as the surface of metal plate 12 so that only the side surfaces of metal plate 12 are exposed, or in a shape slightly smaller than the surface of metal plate 12 so that the side surfaces and the peripheral edge portions (e.g., approximately 500 μm wide) of the main surface (upper surface) of metal plate 12 are exposed. Next, as shown in FIG. 10, in the protruding portion forming step S104, the side surfaces (and peripheral edges) of metal plate 12 are etched and removed using, for example, an etching solution or a chemical polishing solution containing cupric chloride or iron chloride. Thereafter, as shown in FIG. 11, in the protruding portion forming step S104, resist 14 is removed. As a result, the peripheral edges of metal plate 12 are removed, and the protruding portions 11a of brazing filler metal 11 are formed. This improves the thermal shock resistance of the metal-ceramic bonding substrate 1.

[0053] In the protruding portion forming step S104, it is preferable to form the protruding portion 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 bonding substrate 1. The width D of the protruding portion 11a can be controlled by the 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 forming 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 filler metal 11. When an overhanging portion 11a of the brazing filler metal 11 is formed on the peripheral edge of the metal plate 12 as in this embodiment, it is preferable to form the nickel plating film 13 also on the surface of the overhanging portion 11a.

[0055] In the nickel plating film forming step S105, it is preferable to form a nickel-phosphorus plating film as the nickel plating film 13 using, for example, an electroless nickel-phosphorus plating solution as the electroless nickel plating solution. This makes it possible to improve the formation rate of the nickel plating film 13 compared to, for example, a nickel-boron plating film. It is also possible to reduce the manufacturing cost of the metal-ceramic bonding substrate 1. Note that in the nickel plating film forming step S105, the nickel-boron plating film may be formed using an electroless nickel-boron plating solution.

[0056] In the nickel plating film forming step S105, when the lead concentration of the brazing filler metal 11 is X ppm and the lead concentration of the electroless nickel plating solution is Y mg / L, the electroless nickel plating solution is adjusted to satisfy the following formula (1). 0.05≦Y≦-0.002X+0.5 (1)

[0057] If the lead concentration in the electroless nickel plating solution is less than the lower limit of formula (1), the stability of the electroless nickel plating solution may decrease, potentially shortening its lifespan. By adjusting the lead concentration in the electroless nickel plating solution to equal to or greater than the lower limit of formula (1), the stability of the electroless nickel plating solution can be improved and its lifespan extended. On the other hand, if the lead concentration in the electroless nickel plating solution exceeds the upper limit of formula (1), numerous fine defects may occur in the nickel plating film 13, and the exposed portion of the brazing filler metal 11 may become longer, potentially increasing the likelihood of migration. By adjusting the lead concentration in the electroless nickel plating solution to equal to or less than the upper limit of formula (1), the occurrence of fine defects in the nickel plating film 13 and migration may be suppressed.

[0058] In the nickel plating film forming step S105, when the lead concentration of the brazing filler metal 11 is X ppm and the lead concentration of the electroless nickel plating solution is Y mg / L, it is preferable to adjust the electroless nickel plating solution so as to satisfy the following formula (2): 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. The upper limit of the lead concentration in the electroless nickel plating solution may be set to 0.42 mg / L.

[0059] 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 plating solution stabilizer to suppress 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] The lead concentration in the electroless nickel plating solution can be adjusted, for example, by adjusting the amount of a pH adjusting solution containing lead, which is a component of the plating solution. Specifically, in the nickel plating film forming step S105, it is preferable to determine the amount of pH adjusting solution by measuring at least one of the nickel concentration and pH of the electroless nickel plating solution, and adjust the lead concentration in the electroless nickel plating solution.

[0061] The above steps allow the production of a metal-ceramic bonding substrate 1 as shown in Fig. 1. As mentioned above, a heat dissipation member 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. The heat dissipation member 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 the embodiments of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments and can be modified in various ways without departing from the spirit of the present invention.

[0063] For example, in the above embodiment, a case has been described in which two metal plates 12 (metal circuit plates 12a) are joined to the upper surface of the ceramic substrate 10 via a brazing material 11, but 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, for example, in the above-described embodiment, the case where the metal plate 12 is bonded to both main surfaces (upper and lower surfaces) of the ceramic substrate 10 has been described, but in the metal-ceramic bonding substrate 1, it is sufficient that the metal plate 12 is bonded to at least one main surface of the ceramic substrate 10. [Example]

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

[0066] (Sample 1) The metal components of the brazing filler metal were prepared as follows: 10% by mass copper (Cu) powder, 5% by mass tin (Sn) powder, 2% by mass titanium (Ti) powder (as the active metal component), and the remainder silver (Ag) powder. Among these metal powders, at least one of the four Sn powders (1) to (4) with different lead (Pb) concentrations was selected and mixed with the other metal powders to adjust the Pb concentration in the brazing filler metal to 0.5 ppm (0.00005% by mass). The Pb concentration was calculated by analyzing the Pb concentration of each metal powder using inductively coupled plasma mass spectrometry (ICP-MS). It was confirmed that the metal powders other than the Sn powder contained no Pb (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 detection limit)

[0067] A vehicle was added to these metal powders and kneaded to prepare a paste-like brazing filler metal containing active metal. (Note: It was confirmed that the vehicle did not contain Pb.) This brazing filler metal was screen-printed to a thickness of 20 μm on almost the entire surface of both sides of a ceramic substrate made of an aluminum nitride (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 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 filler metal. The substrate was then heated to 850°C in a vacuum and cooled, thereby bonding the copper plates to both sides of the aluminum nitride substrate.

[0068] Next, an ultraviolet-curable alkali-peelable resist in the shape of a circuit pattern was applied by screen printing to 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 applied to the surface of a metal plate bonded to the other main surface. After these resists were hardened by irradiation with ultraviolet light, unnecessary portions of the metal plate (copper plate) were etched with an etching solution consisting of copper chloride, hydrochloric acid, and the remainder water, and the resist was removed with an aqueous sodium hydroxide solution to form a metal circuit plate and a heat-dissipating metal plate made of copper plate.

[0069] Next, the substrate was immersed in a chelating aqueous solution containing 1.6 mass% EDTA·4Na (sodium salt of ethylene diamine tetraacetic acid), 3 mass% ammonia water, and 5 mass% hydrogen peroxide water, and then in a known brazing filler metal etching solution consisting of a chelating aqueous solution containing 2 mass% ethylene triamine pentaacetic acid (DTPA)·5Na and 5 mass% hydrogen peroxide water, thereby removing unnecessary portions of the active metal-containing brazing filler metal remaining between the copper circuit patterns on the surface of the ceramic substrate and around the copper plate on the heat dissipation side, and obtaining an intermediate product.

[0070] Next, the above-mentioned resist was applied to the entire surfaces of the intermediate product's metal circuit board and heat-dissipating metal plate by screen printing, and then immersed in an etching solution (chemical polishing solution) consisting of 14 mass% sulfuric acid, 3.2 mass% hydrogen peroxide, and the remainder water at a liquid temperature of 45°C to etch (chemically polish) the sides of the metal circuit board and heat-dissipating metal plate, causing the active metal-containing brazing filler metal to protrude 100 μm wide from the side portions of the circuit-side copper plate and heat-dissipating copper plate, forming protruding portions of the brazing filler metal (brazing fillet). The brazing filler metal had a thickness of approximately 15 μm.

[0071] Next, the intermediate product was degreased, pickled, and then subjected to a palladium activation treatment as pretreatment for electroless plating. After that, a 3 μm-thick nickel-phosphorus (Ni-P) alloy coating was formed by electroless plating on the surfaces of the metal circuit board, the heat-dissipating metal plate, and the surface (extrusion area) of the brazing filler metal, resulting in the metal-ceramic bonding substrate (Sample 1). The electroless Ni-P alloy plating solution used was a commercially available medium-phosphorus electroless Ni-P alloy plating solution containing nickel sulfate as the nickel salt and sodium hypophosphite as the reducing agent, with a Pb-containing pH adjuster containing sodium hydroxide added to adjust the Pb concentration. Analysis of the electroless Ni-P alloy plating solution by inductively coupled plasma mass spectrometry (ICP-MS) revealed Ni at 5.4 g / L, P at 6.6 g / L, and P at 0.47 mg / L. The bismuth concentration was below the detection limit (0.001 mg / L or less) in all of the electroless nickel plating solutions used to prepare Sample 1 and Samples 2 to 13 described below. The substrate dimensions of the metal-ceramic bonding substrate of Sample 1 and the shape of the metal circuit board (circuit pattern dimensions) are shown in Figure 12.

[0072] A 30 mm long, 100 μm wide area of ​​the Ni-P alloy plating coating formed on the surface of the protruding brazing filler metal of Sample 1 was observed at 500x backscattered electron images using a scanning electron microscope (SEM: TM4000, manufactured by Hitachi High-Technologies Corporation). In some cases, the underlying brazing filler metal (Ag and / or Cu) was observed in areas where the Ni-P plating coating was not formed or in cracks in the Ni-P plating coating. The maximum length of the exposed brazing filler metal (Ag (and / or Cu), cracks in the plating coating) was measured. The exposed length was defined as the diameter of the smallest circle inscribed by the edge of the exposed portion. The maximum length L of the exposed brazing filler metal was 16 μm, with almost no exposure observed.

[0073] (Sample 2) The metal-ceramic bonding 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 Pb concentration in the metal components of the brazing filler metal was 5.5 ppm by mass, and the Pb concentration in the electroless Ni-P alloy plating solution was 0.4 mg / L. As with Sample 1, the maximum length L of the exposed portion of the brazing filler metal in the Ni-P alloy plating film of Sample 2 was measured and found to be 25 μm. Furthermore, Figure 13 shows a backscattered electron image of the Ni-P alloy plating film formed on the protruding portion of the brazing filler metal in the metal-ceramic bonding substrate of Sample 2, observed with a scanning electron microscope (SEM) in a direction perpendicular to the metal circuit board.

[0074] (Sample 3) The metal-ceramic bonding 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 Pb concentration in the metal components of the brazing filler metal was 18.5 ppm by mass, and the Pb concentration in the electroless Ni-P alloy plating solution was 0.4 mg / L. As with Sample 1, the maximum length L of the exposed portion of the brazing filler metal in the Ni-P alloy plating film of Sample 3 was measured and found to be 18 μm.

[0075] (Sample 4) The metal-ceramic bonding 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 Pb concentration in the metal components of the brazing filler metal was 40.0 ppm by mass, and the Pb concentration in the electroless Ni-P alloy plating solution was 0.38 mg / L. As with Sample 1, the maximum length L of the exposed portion of the brazing filler metal 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 bonding 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 Pb concentration in the metal components of the brazing filler metal was 5.5 ppm by mass. As in Sample 1, the maximum length L of the exposed portion of the brazing filler metal in the Ni-P alloy plating coating of Sample 5 was measured and found to be 62 μm.

[0077] (Sample 6) The metal-ceramic bonding 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 Pb concentration in the metal components of the brazing filler metal was 40.0 ppm by mass, and the Pb concentration in the electroless Ni-P alloy plating solution was 0.4 mg / L. As with Sample 1, the maximum length L of the exposed portion of the brazing filler metal in the Ni-P alloy plating film of Sample 6 was measured and found to be 64 μm.

[0078] (Sample 7) The metal-ceramic bonding 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. As in Sample 1, the maximum length L of the exposed portion of the brazing filler metal in the Ni-P alloy plating film of Sample 7 was measured and found to be 10 μm.

[0079] (Sample 8) The metal-ceramic bonding substrate of Sample 8 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 0.38 mg / L. As in Sample 1, the maximum length L of the exposed portion of the brazing filler metal in the Ni-P alloy plating film of Sample 8 was measured and found to be 5 μm.

[0080] (Sample 9) The metal-ceramic bonding substrate of Sample 9 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 0.33 mg / L. As in Sample 1, the maximum length L of the exposed portion of the brazing filler metal in the Ni-P alloy plating film of Sample 9 was measured and found to be 5 μm.

[0081] (Sample 10) The metal-ceramic bonding 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 Pb concentration in the metal components of the brazing filler metal was 18.5 ppm by mass. As in Sample 1, the maximum length L of the exposed portion of the brazing filler metal in the Ni-P alloy plating coating of Sample 10 was measured and found to be 80 μm.

[0082] (Sample 11) The metal-ceramic bonding 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 Pb concentration in the metal components of the brazing filler metal was 40.0 ppm by mass. As with Sample 1, the maximum length L of the exposed portion of the brazing filler metal in the Ni-P alloy plating film of Sample 11 was measured and found to be 122 μm. Fig. 14 shows a backscattered electron image of the Ni-P alloy plating film formed on the protruding portion of the brazing filler metal in the metal-ceramic bonding substrate of Sample 11, observed with a scanning electron microscope (SEM) in a direction perpendicular to the metal circuit board.

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

[0084] (Sample 13) Sample 13, a metal-ceramic bonding substrate, was fabricated in the same manner as Sample 3, except that an electroless Ni-P alloy plating solution containing no Pb was used. As a result, Ni plating was also 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 bonding substrate could not be ensured.

[0085] The maximum length L of the exposed portion of the brazing filler metal in Samples 1 to 13 is shown in Table 1, along with the Pb concentration X in the brazing filler metal, the Pb concentration Y in the electroless Ni plating solution, the upper limit value of formula (1), and the upper limit value of formula (2). Fig. 15 shows a graph plotting the Pb concentration X in the brazing filler metal 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 FIG. 15, in samples 1 to 9, in which the Pb concentration Y in the electroless Ni plating solution was equal to or less than the upper limit of formula (1), the maximum length L of the exposed portion of the brazing filler metal was 70 μm or less (5 to 64 μm). In samples 1 to 4 and 7 to 9, in which the Pb concentration Y in the electroless Ni plating solution was equal to or less than the upper limit of formula (2), the maximum length L of the exposed portion of the brazing filler metal was 35 μm or less (5 to 25 μm). On the other hand, in samples 10 to 12, in which the Pb concentration Y in the electroless Ni plating solution exceeded the upper limit of formula (1), the maximum length L of the exposed portion of the brazing filler metal was greater than 70 μm (80 to 163 μm). In sample 13, in which the Pb concentration Y in the electroless Ni plating solution was below the lower limit (0.05) of formula (1), the metal-ceramic bonding substrate was found to be defective, as it was unable to ensure insulation between the circuits and between the surfaces. From the above, it was confirmed that in a metal-ceramic bonding substrate, the occurrence of minute defects in the nickel plating film can be suppressed by controlling the lead concentration X in the brazing filler metal to a predetermined value or less and controlling the lead concentration Y in the electroless Ni plating solution to within a predetermined range corresponding to the lead concentration X in the brazing filler metal. [Explanation of symbols]

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

Claims

1. a step of joining a metal plate to at least one main surface of a ceramic substrate via a brazing filler metal 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 filler metal using an electroless nickel plating solution having a lead concentration of Y mg / L, In the step of forming the nickel plating film, a lead concentration Y in the electroless nickel plating solution satisfies the relationship 0.05≦Y≦−0.002X+0.

5.

2. 2. The method for manufacturing a metal-ceramic bonding substrate according to claim 1, wherein in the step of forming the nickel plating film, a lead concentration Y in the electroless nickel plating solution satisfies a relationship of 0.05≦Y≦−0.002X+0.

475.

3. 3. The method for producing a metal / ceramic bonding substrate according to claim 1, wherein in the step of forming the nickel plating film, the nickel-phosphorus plating film is formed using an electroless nickel-phosphorus plating solution.

4. 4. The method for producing a metal-ceramic bonding substrate according to claim 1, further comprising the steps of: after bonding the metal plate to the ceramic substrate, removing unnecessary portions of the metal plate and the brazing filler metal; and forming a predetermined circuit pattern on the metal plate.

5. 5. The method for producing a metal / ceramic bonding substrate according to claim 4, further comprising the step of removing a peripheral portion of said metal plate to form an overhanging portion of said brazing material after forming a predetermined circuit pattern on said metal plate.

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