Method for manufacturing metal-ceramic circuit board

Abstract

To provide a method for manufacturing a metal-ceramic circuit board that can suppress cloudiness on the surface of a plating film formed on the metal circuit board of a plurality of metal-ceramic circuit boards manufactured by dividing a ceramic substrate along a dividing groove.SOLUTION: A metal-ceramics circuit board is manufactured by a method for manufacturing the metal-ceramics circuit board having a step of forming a plurality of metal circuit boards having a predetermined circuit pattern on one side of a ceramic board; a step of forming division grooves between metal circuit boards on one side of the ceramic board by laser scribing; a step of chemically polishing or ultrasonic cleaning the surface of the metal circuit board; a step of forming a plating film on the surface of the metal circuit board.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a metal-ceramic circuit board, and more particularly to a method for manufacturing a metal-ceramic circuit board in which a metal circuit plate is bonded to a ceramic substrate. [Background technology]

[0002] Conventionally, power modules have been used to control large amounts of power in electric vehicles, trains, machine tools, and the like. Metal-ceramic insulating substrates used for such power modules include metal-ceramic circuit boards in which a metal circuit plate (made of copper, copper alloy, aluminum, or aluminum alloy) is bonded to the surface of an insulating ceramic substrate (made of alumina, aluminum nitride, silicon nitride, silicon carbide, or the like).

[0003] A known method for producing such a metal-ceramic circuit board is to interpose a brazing material between a ceramic substrate and a metal circuit plate, and then heat treat the substrate in an inert atmosphere or under vacuum to bond the metal circuit plate to the ceramic substrate.

[0004] However, when mass-producing metal-ceramic circuit boards using this method, it is necessary to divide one large ceramic substrate into multiple ceramic substrates and then bond a metal circuit plate to each of the individual ceramic substrates, which lengthens the production time and increases the production costs.

[0005] As a method for mass-producing metal-ceramic circuit boards, a manufacturing method for a power module substrate has been proposed, which includes a bonding step of bonding a ceramic substrate and a metal plate, a circuit formation step of etching the metal plate after the bonding step to form a circuit pattern, and a grooving step of forming grooves between the circuit patterns of the ceramic substrate by laser processing after the circuit formation step. This method describes that after the circuit pattern is formed, a plating film such as nickel plating can be formed on the surface of the circuit pattern before the grooves are formed by laser processing (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2010-50164 A (paragraphs 0006 and 0012) Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the method of Patent Document 1, if a plating film is formed on the surface of the circuit pattern after etching a metal plate to form a circuit pattern and before forming grooves between the circuit patterns on the ceramic substrate by laser processing, the plating film on the surface of the circuit pattern may be damaged by debris from the ceramic substrate caused by the laser processing, which may result in poor bonding when an electronic component is joined onto the circuit pattern by soldering or the like.

[0008] Furthermore, in the method of Patent Document 1, when a circuit pattern is formed by etching a metal plate, grooves are formed between the circuit patterns on a ceramic substrate by laser processing, and then a plating film such as a nickel plating film is formed on the surface of the circuit pattern, there is a problem that the surface of the plating film becomes cloudy, resulting in a defective appearance.

[0009] Therefore, in view of the above-mentioned problems in the conventional art, the present invention has an object to provide a method for producing a metal-ceramic circuit board, which can suppress clouding of the surface of a plating film formed on the metal circuit plate of a plurality of metal-ceramic circuit boards produced by joining a ceramic substrate and a metal circuit plate together and then dividing the substrate along division grooves. [Means for solving the problem]

[0010] As a result of intensive research into solving the above-mentioned problems, the inventors have found that if a metal-ceramic circuit board is manufactured by a method for manufacturing a metal-ceramic circuit board comprising the steps of forming a plurality of metal circuit plates having a predetermined circuit pattern on one side of a ceramic substrate, forming dividing grooves between the metal circuit plates on one side of the ceramic substrate by a laser scribing process, chemically polishing or ultrasonically cleaning the surface of the metal circuit plate, and forming a plating film on the surface of the metal circuit plate, it is possible to suppress clouding of the surface of the plating film formed on the metal circuit plates of a plurality of metal-ceramic circuit boards manufactured by dividing a ceramic substrate along the dividing grooves, and have completed the present invention.

[0011] That is, the method for manufacturing a metal-ceramic circuit board according to the present invention is characterized by comprising the steps of: forming a plurality of metal circuit plates having a predetermined circuit pattern on one surface of a ceramic substrate; forming dividing grooves between the metal circuit plates on one surface of the ceramic substrate by laser scribing; chemically polishing or ultrasonically cleaning the surfaces of the metal circuit plates; and forming a plating film on the surfaces of the metal circuit plates.

[0012] In the method for manufacturing a metal-ceramic circuit board, it is preferable to further include a step of forming a plurality of metal heat sinks on the other surface of the ceramic substrate, a step of chemically polishing or ultrasonically cleaning the surface of the metal heat sink, and a step of forming a plating film on the surface of the metal heat sink. It is also preferable to further include a step of manufacturing a plurality of metal-ceramic circuit boards by dividing the ceramic substrate along the dividing grooves.

[0013] The ultrasonic cleaning treatment is preferably a treatment of immersing for 1 to 10 minutes in water generating ultrasonic waves with a frequency of 15 to 40 MHz. The ceramic substrate is preferably mainly composed of aluminum nitride, alumina, silicon nitride, or zirconia-containing alumina. The metal circuit plate and the metal heat sink are preferably made of copper or a copper alloy. In this case, the chemical polishing treatment is preferably a treatment of immersing for 1 to 10 minutes in a chemical polishing solution at 20 to 35°C containing 3 to 10 mass% sulfuric acid and 3 to 10 mass% hydrogen peroxide. Effect of the Invention

[0014] According to the present invention, it is possible to produce a metal-ceramic circuit board that can suppress clouding of the surface of the plating film formed on the metal circuit plate of a plurality of metal-ceramic circuit boards produced by dividing a ceramic substrate along dividing grooves. [Brief description of the drawings]

[0015] [Figure 1] FIG. 2 is a diagram illustrating a step of forming a resist for forming a circuit pattern on a metal-ceramic bonding substrate in the method for producing a metal-ceramic circuit substrate according to the present invention. [Diagram 2] FIG. 2 is a diagram illustrating a step of forming a resist for forming a heat sink on a metal-ceramic bonding substrate in a manufacturing method for a metal-ceramic circuit board according to the present invention. [Diagram 3] 1 is a micrograph of the surface of a plating film on a metal-ceramic circuit board in Example 1. [Figure 4] 2 is a micrograph of the surface of a plating film of a metal-ceramic circuit board of Comparative Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] In an embodiment of the method for manufacturing a metal-ceramic circuit board according to the present invention, an active metal-containing brazing material is applied to substantially the entire surfaces of both sides of a ceramic substrate, a metal plate is placed on the active metal-containing brazing material, and the metal plate is bonded to the ceramic substrate (indicated by reference numeral 10 in FIGS. 1 and 2) to manufacture a metal-ceramic bonded substrate. Then, a resist is formed on substantially the entire surface of each metal plate, and a laser is irradiated onto the resist to remove predetermined portions of the resist, thereby forming a plurality (indicated by reference numeral 12 in the illustrated embodiment, 12 (=3×4)) of resists for forming circuit patterns (indicated by reference numeral 12 in FIG. 1) on the metal plate on one side of the ceramic substrate, and a plurality (indicated by reference numeral 14 in FIG. 2) of resists for forming heat sinks (indicated by reference numeral 15 in FIG. 3) on the other side of the ceramic substrate. A resist is formed, unnecessary parts of the metal plate are etched, and then the resist 12 for forming the circuit pattern and the resist 14 for forming the heat sink are removed to form a plurality of metal circuit plates (having circuit patterns) and a plurality of metal heat sinks (corresponding to the metal circuit plates), and then unnecessary parts of the active metal-containing brazing material are removed, and then scribe lines (division grooves) are formed between adjacent metal circuit plates on one side of the ceramic substrate or between adjacent metal heat sinks on the other side, and then the surfaces of the metal circuit plates and the metal heat sink are chemically polished or ultrasonically cleaned, and then a plating film is formed on the surfaces of the metal circuit plates and the metal heat sink, and then the ceramic substrate is divided along the scribe lines to produce a plurality of metal-ceramic circuit substrates. The resist 12 for forming the circuit pattern and the resist 14 for forming the heat sink may be removed before or after removing the unnecessary parts of the active metal-containing brazing material.

[0017] The ceramic substrate is preferably composed mainly of aluminum nitride, alumina, silicon nitride or zirconia-containing alumina (preferably containing 85 mass % or more, more preferably 90 mass % or more of aluminum nitride, alumina, silicon nitride or zirconia-containing alumina). The metal plate is preferably made of copper or a copper alloy having high thermal conductivity and electrical conductivity, but may be a metal plate made of aluminum or an aluminum alloy that has a relatively high thermal conductivity and is light and soft. The size of the ceramic substrate is such that it can be divided into multiple metal-ceramic circuit substrates (for example, in the case of a ceramic substrate having a substantially rectangular planar shape, the length (length and width) of one side is 50 mm or more), and an active metal-containing brazing material (preferably a brazing material containing silver, copper, and an active metal, more preferably a brazing material containing silver, copper, tin, and an active metal (for example, a brazing material containing 5 to 50 mass% Cu, 1 to 8 mass% Sn, 1 to 5 mass% active metal, and Ag as metal components)) is applied to substantially the entire surface of at least one side of the ceramic substrate, and a metal plate (preferably a size that protrudes from each side of the ceramic substrate by about 1 to 2 mm, or a size that is smaller than each side of the ceramic substrate by about 1 to 2 mm) is placed on the active metal-containing brazing material, and the metal plate is bonded to the ceramic substrate. The thickness of the ceramic substrate is preferably about 0.25 to 2 mm, and more preferably 0.3 to 1.5 mm. In addition, the ceramic substrate to be used is preferably pre-processed to have an external dimension with high dimensional accuracy by laser processing or scribing. The active metal-containing brazing material preferably contains tin so as to prevent poor bonding (such as cracks or voids) at the end of the ceramic substrate even when a large, approximately rectangular ceramic substrate with a side length (length and width) of 80 mm or more is bonded to a metal plate. The content of the active metal in the active metal-containing brazing material is preferably 1 to 5 mass %, more preferably 1 to 3 mass %. The active metal is preferably titanium or zirconium. The active metal-containing brazing material is preferably applied by fixing the ceramic substrate with a positioning jig that uses the side surface of the ceramic substrate as a reference for positioning.

[0018] By storing large metal-ceramic bonded substrates in this way, in which a metal plate is bonded to a large ceramic substrate, as inventory, it is possible to manufacture metal-ceramic circuit boards in a short period of time after the size of the metal-ceramic circuit board and the shape of the circuit pattern have been determined.

[0019] After the metal-ceramic bonding substrate is manufactured, a UV-curable alkali-peelable resist ink is screen-printed to cover substantially the entire surface of the metal plate, and the resist ink is cured by exposure to UV rays to form a resist. Alternatively, an electrodeposited resist may be used instead of the UV-curable alkali-peelable resist. The printing of the resist ink is preferably performed by fixing the ceramic substrate with a positioning jig that uses the side surface of the ceramic substrate as a reference for positioning.

[0020] After the resist is formed in this way, a laser is irradiated onto the resist to remove predetermined portions of the resist, forming the resist for forming the circuit pattern and the resist for forming the heat sink. In this laser irradiation, the side of the ceramic substrate is fixed with a positioning jig that serves as a reference for positioning, and unnecessary resist is removed with a laser marker using the center of the ceramic substrate as a reference, to draw the shapes of the circuit pattern and the heat sink.

[0021] After the resist for forming a circuit pattern is formed in this manner, unnecessary portions of the metal plate are etched using an etching solution such as a mixed solution of copper chloride, hydrochloric acid and water, or an etching solution containing iron chloride, and the resist for forming the circuit pattern and the resist for forming the heat sink are removed using a resist removal solution (an alkaline solution such as an aqueous sodium hydroxide solution in the case of an alkali peelable resist), thereby forming a plurality of metal circuit plates and metal heat sinks.

[0022] In this manner, multiple metal circuit plates and metal heat sink plates are formed, and unnecessary portions of the active metal-containing brazing material are removed. After that, a laser scribing device is used to form scribe lines (division grooves) between adjacent metal circuit plates on one side of the ceramic substrate or between adjacent metal heat sink plates on the other side.

[0023] In addition, in order to remove foreign matter adhering to the surfaces of the metal circuit board and the metal heat sink, the surfaces of the metal circuit board and the metal heat sink are subjected to chemical polishing or ultrasonic cleaning, and then a plating film (such as a nickel plating film or a nickel alloy plating film such as Ni-P) is formed on the surfaces of the metal circuit board and the metal heat sink. In the chemical polishing process, foreign matter adhering to the surfaces of the metal circuit board and the metal heat sink is removed. When the metal circuit board and the metal heat sink are made of copper or a copper alloy, a chemical polishing solution containing preferably 3 to 10 mass% sulfuric acid and 3 to 10 mass% hydrogen peroxide (more preferably a chemical polishing solution containing 3 to 10 mass% sulfuric acid and 3 to 10 mass% hydrogen peroxide, with the balance being water) is used, and the polishing is preferably performed by immersing the metal circuit board and the metal heat sink in the chemical polishing solution at 20 to 35°C for 1 to 10 minutes. Note that this chemical polishing solution may contain components other than sulfuric acid, hydrogen peroxide, and water, as long as it can remove foreign matter adhering to the surfaces of the metal circuit board and the metal heat sink made of copper or a copper alloy. When the metal circuit board and the metal heat sink are made of aluminum or an aluminum alloy, a chemical polishing solution containing preferably 1 to 5% by mass of sodium hydroxide (more preferably a chemical polishing solution containing 1 to 5% by mass of sodium hydroxide, the remainder being water) is used, or a chemical polishing solution containing preferably 0.5 to 5% by mass of sulfuric acid and 2 to 10% by mass of phosphoric acid (more preferably a chemical polishing solution containing 0.5 to 5% by mass of sulfuric acid and 2 to 10% by mass of phosphoric acid, the remainder being water) is used, and the chemical polishing is preferably performed by immersing the metal circuit board and the metal heat sink at 20 to 35°C for 1 to 10 minutes. Note that this chemical polishing solution may contain components other than sulfuric acid, phosphoric acid, and water, as long as it can remove foreign matter attached to the surfaces of the metal circuit board and the metal heat sink made of aluminum or an aluminum alloy. In addition, the ultrasonic cleaning treatment is performed to physically shock and remove foreign matter attached to the surfaces of the metal circuit board and the metal heat sink, and is preferably performed by immersing the metal circuit board and the metal heat sink for 1 to 10 minutes in water generating ultrasonic waves with a frequency of 15 to 40 MHz. The chemical polishing or ultrasonic cleaning treatment and the formation of the plating film on the surfaces of the metal circuit plate and the metal heat sink plate may be carried out after removing unnecessary portions of the active metal-containing brazing material and before the formation of the scribe lines (division grooves).

[0024] The ceramic substrate is divided along the scribe lines (division grooves). The ceramic substrate may be divided after the scribe lines are formed, followed by chemical polishing or ultrasonic cleaning of the surfaces of the metal circuit plate and the metal heat sink, and the formation of a plating film.

[0025] In the embodiment of the manufacturing method of the metal-ceramic circuit board described above, the metal plate is bonded to the ceramic substrate using an active metal-containing brazing material, but the metal plate may be bonded to the ceramic substrate using other brazing materials such as an aluminum-based brazing material. In addition, when the metal plate is a copper plate and the ceramic substrate is an oxide-based ceramic substrate, the metal plate may be bonded to the ceramic substrate by a so-called direct bonding method, in which a eutectic melt of copper and oxygen is generated by heating the copper plate and the ceramic substrate in an inert gas. Furthermore, when the metal plate is made of aluminum or an aluminum alloy, the metal plate may be bonded to the ceramic substrate by a so-called molten metal bonding method, in which molten aluminum or aluminum alloy is brought into contact with the ceramic substrate and solidified to bond the metal plate to the ceramic substrate. EXAMPLES

[0026] Hereinafter, examples of the method for producing a metal-ceramic circuit board according to the present invention will be described in detail.

[0027] [Example 1] A paste-like active metal-containing brazing material (Ag:Cu:Sn:Ti=83:10:5:2) containing 83% by mass silver, 10% by mass copper, 5% by mass tin, and 2% by mass titanium (as an active metal component) as metal components was screen-printed to a thickness of 20 μm on almost the entire surface of both sides of a ceramic substrate made mainly of aluminum nitride and having a planar shape of approximately 102 mm long x 102 mm wide x 0.32 mm thick. An oxygen-free copper plate having a planar shape of approximately 70 mm long x 70 mm wide x 0.25 mm thick and a planar shape of approximately 105 mm long x 105 mm wide x 0.25 mm thick was placed on the brazing material on one side of the ceramic substrate, and an oxygen-free copper plate having a planar shape of approximately 105 mm long x 105 mm wide x 0.25 mm thick and a planar shape of approximately 105 mm long x 105 mm wide x 0.25 mm thick was placed on the brazing material on the other side of the ceramic substrate. The copper plates were then bonded to both sides of the ceramic substrate by heating to 850° C. in a vacuum, thereby producing a metal-ceramic bonded substrate.

[0028] Next, an ultraviolet-curing alkaline peelable resist was applied by screen printing to substantially the entire surface of the copper plates bonded to both sides of the ceramic substrate, and the resist was irradiated with ultraviolet light to be cured.

[0029] Next, the resist coated on almost the entire surface of the copper plate (copper plate for circuit) bonded to one side of the ceramic substrate was irradiated with a 30W Yb laser (F300FAYb manufactured by Keyence Corporation) to remove predetermined parts of the resist, forming 9 (=3×3) resists for forming circuit patterns. Also, the resist coated on almost the entire surface of the copper plate (copper plate for heat dissipation) bonded to the other side of the ceramic substrate was irradiated with the same laser to remove predetermined parts of the resist, forming 9 (=3×3) resists for forming heat dissipation plates. Next, unnecessary portions of the copper plate for the circuit and the copper plate for the heat sink were etched using an etching solution consisting of copper chloride, hydrochloric acid, and water, and the resist was removed using an aqueous sodium hydroxide solution to form nine copper circuit plates with copper circuit patterns, and nine copper heat sink plates were formed in positions corresponding to these copper circuit plates.

[0030] Next, the specimen was immersed in dilute sulfuric acid for 20 seconds for pickling, and then immersed in an aqueous chelating solution containing EDTA, ammonia water, and hydrogen peroxide water to remove unnecessary portions of the active metal-containing brazing material.

[0031] Next, a scribe line (division groove) was formed on the surface of the ceramic substrate by a laser scribing device along approximately the center line between adjacent copper circuit patterns.

[0032] Next, the copper circuit board and the copper heat sink were immersed for 3 minutes in a chemical polishing solution at 25°C containing 5% by mass sulfuric acid, 20% by mass hydrogen peroxide (containing 35% by mass hydrogen peroxide), and the remainder water, to perform a chemical polishing treatment, followed by rinsing with water and drying.

[0033] Next, a 4 μm-thick electroless Ni-P plating film was formed on the copper plates (copper circuit plate and copper heat sink) bonded to both sides of the ceramic substrate.

[0034] Next, the ceramic substrate was divided along the scribe lines (division grooves) to obtain nine metal-ceramic circuit substrates each measuring 34 mm×34 mm.

[0035] The metal-ceramic circuit board thus obtained was observed with an optical microscope (visual inspection), and as shown in FIG. 3, no cloudiness was observed on the surface of the plating film.

[0036] [Example 2] A metal-ceramic circuit board was produced in the same manner as in Example 1, except that, instead of chemical polishing, an ultrasonic cleaning process was performed by immersing the copper circuit board and the copper heat sink in water generating ultrasonic waves of 25 MHz using an ultrasonic cleaner for 3 minutes. When the board was observed with an optical microscope (appearance inspection), no cloudiness was observed on the surface of the plating film.

[0037] [Comparative Example 1] A metal-ceramic circuit board was produced in the same manner as in Example 1, except that the copper circuit board and the copper heat sink were immersed in water for 3 minutes instead of the chemical polishing treatment. When the board was observed with an optical microscope (appearance inspection), cloudiness was found on the surface of the plating film, as shown in FIG. 4.

[0038] [Comparative Example 2] A metal-ceramic circuit board was produced in the same manner as in Example 1, except that instead of chemical polishing, the copper circuit board and the copper heat sink were immersed in an acidic degreasing solution containing a commercially available surfactant at 40°C for 10 minutes. When the board was observed with an optical microscope (appearance inspection), cloudiness was found on the surface of the plating film.

[0039] [Comparative Example 3] A metal-ceramic circuit board was produced in the same manner as in Example 1, except that instead of chemical polishing, the copper circuit board and the copper heat sink were immersed in 10 mass % sulfuric acid at room temperature for 3 minutes for pickling. When observed with an optical microscope (appearance inspection), cloudiness was found on the surface of the plating film. [Explanation of symbols]

[0040] 10 Metal-ceramic bonded substrate 12 Resist for forming circuit patterns 14 Resist for forming heat sink

Claims

1. A method for producing a metal-ceramic circuit board, comprising the steps of: forming a plurality of metal circuit plates having a predetermined circuit pattern on one surface of a ceramic substrate; forming dividing grooves between the metal circuit plates on one surface of the ceramic substrate by laser scribing; chemically polishing or ultrasonically cleaning the surfaces of the metal circuit plates; and forming a plating film on the surfaces of the metal circuit plates.

2. The method for manufacturing a metal-ceramic circuit board according to claim 1, further comprising the steps of: forming a plurality of metal heat sinks on the other surface of the ceramic substrate; subjecting the surfaces of the metal heat sinks to a chemical polishing treatment or ultrasonic cleaning treatment; and forming a plating film on the surfaces of the metal heat sinks.

3. 3. The method for producing a metal-ceramic circuit board according to claim 1, further comprising the step of producing a plurality of metal-ceramic circuit boards by dividing the ceramic substrate along the dividing grooves.

4. 3. The method for producing a metal-ceramic circuit board according to claim 1, wherein the ultrasonic cleaning treatment is a treatment of immersing the substrate in water in which ultrasonic waves having a frequency of 15 to 40 MHz are generated for 1 to 10 minutes.

5. 3. The method for producing a metal-ceramic circuit board according to claim 1, wherein the ceramic substrate is mainly composed of aluminum nitride, alumina, silicon nitride or zirconia-containing alumina.

6. 3. The method for producing a metal-ceramic circuit board according to claim 1, wherein the metal circuit plate is made of copper or a copper alloy.

7. 3. The method for producing a metal-ceramic circuit board according to claim 2, wherein the metal heat sink plate is made of copper or a copper alloy.

8. 7. The method for producing a metal-ceramic circuit board according to claim 6, wherein the chemical polishing treatment is a treatment of immersing the substrate in a chemical polishing solution containing 3 to 10 mass % of sulfuric acid and 3 to 10 mass % of hydrogen peroxide at 20 to 35° C. for 1 to 10 minutes.

9. 8. The method for producing a metal-ceramic circuit board according to claim 7, wherein the chemical polishing treatment is a treatment of immersing the substrate in a chemical polishing solution containing 3 to 10 mass % of sulfuric acid and 3 to 10 mass % of hydrogen peroxide at 20 to 35° C. for 1 to 10 minutes.

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