Method for manufacturing metal-ceramic circuit boards

Abstract

This invention provides a method for manufacturing a metal-ceramic circuit board that suppresses non-bonding between the circuit pattern and the ceramic substrate, further suppresses the occurrence of appearance defects due to contamination of the ceramic substrate near the divided grooves, and eliminates the need to form a new resin film when the divided grooves are formed by laser. [Solution] The method comprises the steps of forming a metal-ceramic bond in which a plurality of circuit patterns 30 are formed on at least one surface of a ceramic substrate 5 via a brazing layer 10, forming divided grooves 40 in the ceramic substrate 5 by irradiating the exposed portion of the brazing layer 10 with a laser beam B and performing laser processing, and removing unnecessary portions of the brazing layer 10, wherein the step of forming the metal-ceramic bond is performed before the laser processing.

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 pattern is bonded to a ceramic substrate. [Background technology]

[0002] Conventionally, semiconductor devices such as power modules have been used to control the high power of electric vehicles, trains, machine tools, etc. As metal-ceramic circuit boards for such semiconductor devices, metal-ceramic circuit boards have been used in which a metal circuit pattern made of copper, copper alloys, aluminum, aluminum alloys, etc. is bonded to the surface of an insulating ceramic substrate made of alumina, aluminum nitride, silicon nitride, silicon carbide, etc.

[0003] One known method for manufacturing such metal-ceramic circuit boards involves interposing a brazing material between a ceramic substrate and a metal plate, and then heat-treating the plate in an inert atmosphere or under vacuum to bond the ceramic substrate to the metal plate, thereby forming a desired circuit pattern on the bonded metal plate. Various efforts have been made to mass-produce metal-ceramic circuit boards using this method. One such method is the so-called multi-cavity substrate method, which involves manufacturing multiple metal-ceramic circuit boards from a single ceramic substrate.

[0004] For example, as described in Patent Document 1, a method has been proposed for manufacturing multiple nitride ceramic circuit boards by first creating scribable lines (so-called dividing grooves) composed of discontinuous laser holes in a ceramic substrate, then joining a metal plate and a ceramic substrate using an activated metal brazing method, removing unnecessary parts of the metal plate by etching to form a circuit, removing the brazing material layer exposed in the metal plate removal area, and then separating the ceramic substrate along the scribable lines formed on it.

[0005] Furthermore, as described in Patent Document 2, for example, a method for manufacturing a ceramic substrate has been proposed in which a metal layer and elements are formed on the ceramic substrate, a circuit pattern is formed on the surface of the ceramic substrate, electronic components are mounted on the circuit pattern, a resin film is coated, and then laser scribing slits (so-called dividing grooves) are formed. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2007-324301 [Patent Document 2] Japanese Patent Application Publication No. 03-252384 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, in the method described in Patent Document 1, after forming a divided groove in the ceramic substrate by laser processing, the ceramic substrate and the metal plate are joined by brazing. As a result, there is a possibility that the metal plate and the ceramic substrate may be joined with the ceramic substrate fragments from the laser processing adhering to the surface of the ceramic substrate. When the metal plate and the ceramic substrate are joined with fragments adhering to the surface of the ceramic substrate, there is a problem that unjointed areas will occur at the joint. Furthermore, in order to avoid unjointed areas between the metal and the ceramic substrate, the inventors attempted to form a divided groove in the ceramic substrate by laser processing in the exposed portion of the ceramic substrate after joining the ceramic substrate and the metal plate by removing the unnecessary parts of the metal plate and brazing material. However, when a divided groove is formed by laser processing in the exposed portion of the ceramic substrate, there is a problem that the ceramic substrate fragments from the laser processing adhere to the ceramic substrate, resulting in a defect in appearance near the divided groove of the ceramic substrate.

[0008] In the method described in Patent Document 2, after forming a metal-ceramic circuit board, a new resin film is applied to the areas where the dividing grooves are to be formed, and then the dividing grooves are formed using a laser. After the dividing grooves are formed, the resin film is washed away, thus preventing debris from adhering to the surface of the ceramic substrate. However, the process of forming and washing away the resin film is required, making the manufacturing method complicated. Furthermore, if the resin film is formed, and the washing is insufficient, resin film residue may remain, resulting in a failure to obtain the desired conductivity, or the solder wettability may differ between the areas with and without resin film residue at the soldering points of the circuit pattern, potentially leading to a failure to obtain the desired durability.

[0009] In view of these circumstances, the present invention aims to provide a method for manufacturing a metal-ceramic circuit board in which a divided groove is formed on a ceramic substrate by laser processing, which suppresses non-bonding between the circuit pattern and the ceramic substrate, further suppresses the occurrence of appearance defects due to contamination of the ceramic substrate near the divided groove, and eliminates the need to form a new resin film when forming the divided groove with a laser. [Means for solving the problem]

[0010] As a result of diligent research to solve the above problems, the present inventors have found that a method for manufacturing a metal-ceramic circuit board, comprising the steps of: forming a metal-ceramic bond in which a plurality of circuit patterns are formed on at least one surface of a ceramic substrate via a brazing layer; forming divided grooves in the ceramic substrate by irradiating the exposed portion of the brazing layer with a laser beam and performing laser processing; and removing unnecessary portions of the brazing layer, can suppress unbonded areas between the circuit patterns and the ceramic substrate, further suppress the occurrence of appearance defects, and eliminate the need to form a new resin film when forming divided grooves by laser processing, thus completing the present invention.

[0011] The gist of this invention is as follows: [1] A step of forming a metal-ceramic bond in which a plurality of circuit patterns are formed on at least one surface of a ceramic substrate via a brazing layer, A step of forming divided grooves in the ceramic substrate by irradiating the portion of the brazing material layer exposed with a laser beam and performing laser processing, The process includes removing the unnecessary portion of the brazing material layer. A method for manufacturing a metal-ceramic circuit board, characterized in that the step of forming the metal-ceramic bond is performed before the laser processing. [2] The method for manufacturing a metal-ceramic circuit board according to [1], characterized in that the circuit pattern is formed by joining a metal plate to at least one surface of the ceramic substrate via a brazing layer, and etching away the unnecessary portion of the metal plate. [3] The method for manufacturing a metal-ceramic circuit board according to [1] or [2], characterized in that the pulse width of the laser beam used in the laser processing is 10 fs or more and 500 ns or less. [4] The method for manufacturing a metal-ceramic circuit board according to [1] or [2], characterized in that the repetition frequency of the laser beam used in the laser processing is 50 kHz or more and 50,000 kHz or less. [5] The method for manufacturing a metal-ceramic circuit board according to [1] or [2], characterized in that the wavelength of the laser beam used in the laser processing is 12,000 nm or less. [6] The method for manufacturing a metal-ceramic circuit board according to [1] or [2], characterized in that the output of the laser beam used in the laser processing is 1W or more and 500W or less. [7] The method for manufacturing a metal-ceramic circuit board according to [1] or [2], characterized in that the laser processing is performed by scanning the laser beam at a scanning speed of 1 mm / s or more and 5000 mm / s or less. [Effects of the Invention]

[0012] According to the present invention, in a method for manufacturing a metal-ceramic circuit board in which a dividing groove is formed in a ceramic substrate by laser processing, it is possible to suppress the non-bonding between the circuit pattern and the ceramic substrate, and further suppress the occurrence of appearance defects due to the contamination of the ceramic substrate near the dividing groove, and a method for manufacturing a metal-ceramic circuit board can be provided in which a new resin film does not need to be formed when forming the dividing groove by laser.

Brief Description of the Drawings

[0013] [Figure 1] It is a cross-sectional view for explaining a step of applying a brazing material in a method for manufacturing a metal-ceramic circuit board. [Figure 2] It is a cross-sectional view for explaining a step of forming a laminate in a method for manufacturing a metal-ceramic circuit board. [Figure 3] It is a cross-sectional view for explaining a step of forming a resist in a method for manufacturing a metal-ceramic circuit board. [Figure 4] It is a plan view (top view) for explaining a step of forming a resist in a method for manufacturing a metal-ceramic circuit board. [Figure 5] It is a cross-sectional view for explaining after an etching process in a method for manufacturing a metal-ceramic circuit board. [Figure 6] It is a cross-sectional view for explaining a laser processing process in a method for manufacturing a metal-ceramic circuit board. [Figure 7] It is a plan view (top view) for explaining a laser processing process in a method for manufacturing a metal-ceramic circuit board. [Figure 8] It is a cross-sectional view for explaining after a brazing material layer removal process in a method for manufacturing a metal-ceramic circuit board. [Figure 9] It is a plan view (top view) for explaining after a brazing material layer removal process in a method for manufacturing a metal-ceramic circuit board. [Figure 10] It is a plan view for explaining a step of dividing and fragmenting using a dividing groove in a method for manufacturing a metal-ceramic circuit board. [Figure 11]This is a cross-sectional view illustrating the laser processing in Comparative Example 1. [Figure 12] This is a micrograph of the ceramic substrate surface near the dividing groove of the metal-ceramic circuit board of Example 1. [Figure 13] This is a photograph of an ultrasonic flaw detection image of the junction between the copper circuit pattern and the ceramic substrate of the metal-ceramic circuit board in Example 1. [Figure 14] This is a micrograph of the ceramic substrate surface near the dividing groove of the metal-ceramic circuit board of Comparative Example 1. [Figure 15] This is a micrograph of the ceramic substrate surface near the dividing groove of the metal-ceramic circuit board of Comparative Example 2. [Figure 16] This is a photograph of an ultrasonic flaw detection image of the junction between the copper circuit pattern and the ceramic substrate of the metal-ceramic circuit board in Comparative Example 2. [Figure 17] This is a flowchart showing the manufacturing method of the metal-ceramic circuit board of Example 1. [Figure 18] This is a flowchart showing the manufacturing method of the metal-ceramic circuit board of Comparative Example 1. [Figure 19] This is a flowchart showing the manufacturing method of the metal-ceramic circuit board of Comparative Example 2. [Modes for carrying out the invention]

[0014] Hereinafter, embodiments of the method for manufacturing a metal-ceramic circuit board according to the present invention will be described with reference to the drawings. In this specification and the drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant explanations are omitted.

[0015] <Joining process> First, a bonding process is performed to form a metal-ceramic joint 20 in which a metal plate 15 is bonded to at least one surface of a ceramic substrate 5 via a brazing layer 10. In this embodiment, as shown in Figure 1, brazing material is applied to substantially the entire surface of both sides of the ceramic substrate 5 to form a brazing layer 10. Next, as shown in Figure 2, a laminate 18 is formed in which the metal plate 15 is arranged in the order of ceramic substrate 5, brazing layer 10, and metal plate 15. The laminate 18 is heated while a load is applied and bonding is performed to form a metal-ceramic joint 20 in which the metal plate 15 is bonded to the ceramic substrate 5 via the brazing layer 10.

[0016] The ceramic substrate 5 can be made from materials conventionally used for insulating substrates for semiconductor mounting, or from new ceramics with superior strength and thermal conductivity that may be developed in the future. For example, it is preferable to use one or more materials selected from alumina, aluminum nitride, silicon nitride, and silicon carbide. When used as an insulating substrate for power modules, it is preferable to use aluminum nitride or silicon nitride from the viewpoint of reliability and heat dissipation. The size of the ceramic substrate 5 should be such that it can be divided into multiple metal-ceramic circuit boards. For example, a ceramic substrate 5 with a roughly rectangular planar shape can be made with a side length of 30 mm to 150 mm. The side length of the ceramic substrate 5 may also be 50 mm to 130 mm, or 75 mm to 120 mm. The thickness of the ceramic substrate 5 varies depending on the specifications of the semiconductor device such as a power module, but for example, a thickness of 0.25 mm to 2.0 mm can be used. The thickness of the ceramic substrate 5 may be 1.5 mm or less, 1.0 mm or less, or 0.5 mm or less.

[0017] The metal plate 15 is preferably made of copper or a copper alloy, which has high thermal and electrical conductivity, but it may also be made of aluminum or an aluminum alloy, which has relatively high thermal conductivity, is light and soft. The metal plate 15, which will form a circuit pattern described later, is bonded to at least one surface of the ceramic substrate 5. The metal plate 15 bonded to the other surface of the ceramic substrate 5 may also serve as a heat sink, described later. Although the metal plate 15 that serves as a heat sink is not required, it is preferable to provide it to dissipate the heat generated by the semiconductor element when the semiconductor element is mounted on the metal-ceramic circuit board.

[0018] A brazing layer 10 for joining the ceramic substrate 5 and the metal plate 15 is placed over substantially the entire surface of at least one side of the ceramic substrate 5. While there are no particular restrictions on the brazing material used in the brazing layer 10 as long as it can join the ceramic substrate 5 and the metal plate 15, a brazing material containing an active metal is preferred, as it chemically reacts with the ceramic substrate 5, improving the wettability of the brazing material and enabling a better joining of the ceramic substrate 5 and the metal plate 15. The active metal-containing brazing material preferably contains at least one metal or its hydrogen compound selected from Ti, Zr, Hf, and Nb as the active metal. The active metal is more preferably Ti or Zr. The active metal-containing brazing material preferably contains one or more of Ag, Cu, and Sn as metal components other than the active metal. For example, in the case of a brazing material containing Ag, Cu, an active metal, and Sn, it is preferable that the metal components consist of 5% to 50% by mass of Cu, 1% to 8% by mass of Sn, 1% to 5% by mass of an active metal, and the remainder being Ag. The brazing material is arranged using, for example, screen printing, so that its thickness is 10 μm to 50 μm. The brazing material layer 10 is formed by heating and joining the laminate 18 described above while applying a load. The thickness of the formed brazing material layer 10 is preferably 5 μm to 50 μm, and more preferably 5 μm to 35 μm. The position (arrangement) of the brazing material layer 10 is arbitrary, and it is preferable to arrange it over substantially the entire surface of at least one side of the ceramic substrate 5, but it does not necessarily have to be arranged over the entire surface.

[0019] The heating temperature of the laminate 18 should be such that the ceramic substrate and the circuit pattern are well bonded, but it can be, for example, 780°C to 890°C. Preferably, it is 800°C to 870°C. From the viewpoint of suppressing the formation of metal oxides, the heat treatment atmosphere should preferably be an inert atmosphere such as helium or argon, or a vacuum atmosphere. For example, a vacuum atmosphere of 8.0 × 10 -2 It is preferable that the procedure be carried out at or below Pa. More preferably, 5.0 × 10 -2 The procedure is carried out in a vacuum of less than Pa. Also, 1.0 × 10⁻⁶ -3 It may be Pa or higher, 1.0 × 10 -2 The pressure may be Pa or higher. The heat treatment time is not particularly limited, but it is preferable to be 30 minutes or longer. From the viewpoint of manufacturing efficiency, it is preferable to keep it to 1 hour or less. The load applied to the laminate 18 in the thickness direction of the laminate 18 should be a load that allows the ceramic substrate and the circuit pattern to bond well, but 0.005 kgf / cm² is preferable. 2 More than 0.5kgf / cm 2 The following is possible. Preferably, 0.01 kgf / cm² 2 More than 0.2kgf / cm 2 The following applies:

[0020] <Metal plate removal process> After fabricating the metal-ceramic bond 20, unnecessary parts of the metal plate 15 are removed, and an etching process is performed as a metal plate removal process to form a circuit pattern 30 and a heat sink 35 of a predetermined shape. The etching process can be carried out, for example, as described below. First, resist ink is printed on substantially the entire surface of each metal plate 15. For example, an ultraviolet-curable alkali peelable resist ink can be used. Next, the printed resist ink is exposed to ultraviolet light to cure the resist ink and form a resist 32. Next, a predetermined part of the resist 32 is removed by irradiating the cured resist 32 with a laser, so that a plurality of circuit pattern forming resists 32a of the desired circuit pattern shape (four in the embodiment shown in Figure 4) are formed on the metal plate 15 on one side of the ceramic substrate 5 as shown in Figures 3 and 4, and a plurality of heat sink forming resists 32b of the desired heat sink pattern shape (four in the embodiment shown in Figure 4) are formed on the metal plate 15 on the other side of the ceramic substrate 5.

[0021] Instead of UV-curing alkaline peel-off resist ink, electrodeposited resist ink may be used. It is preferable to print the resist ink using a positioning jig that uses the side surface of the ceramic substrate 5 as a positioning reference.

[0022] When irradiating the resist 32 with a laser, it is preferable to fix the ceramic substrate 5 with a positioning jig that uses the side surface of the ceramic substrate 5 as a positioning reference, and to perform the irradiation using the center of the ceramic substrate 5 as the reference.

[0023] After forming the circuit pattern resist 32a and the heat sink resist 32b, the unwanted portion of the metal plate 15, which is a predetermined portion from which the resist 32 has been removed, is etched away using an etching solution such as a mixed solution of copper chloride, hydrochloric acid, and water, or an etching solution containing iron chloride. Subsequently, the circuit pattern resist 32a and the heat sink resist 32b are removed using a resist removal solution (an alkaline solution such as an aqueous sodium hydroxide solution in the case of an alkaline peel-type resist), and multiple circuit patterns 30 and heat sinks 35 of a predetermined shape as shown in Figure 5 are formed on a single ceramic substrate 5, thereby forming a metal-ceramic bond 20 including the circuit patterns 30 and heat sinks 35. The brazing material layer 10 is exposed in the metal plate portion removed by the metal plate removal process. The thickness of the remaining brazing material layer 10 is preferably 5 μm to 50 μm, and more preferably 5 μm to 35 μm, as described above. With respect to the exposed brazing layer 10, it is sufficient if the brazing layer 10 is exposed up to a distance of 200 μm or more from the position where the laser processing treatment described later will be performed. Preferably, the brazing layer 10 is exposed up to a distance of 300 μm or more from the position where the laser processing treatment will be performed, or up to a distance of 500 μm or more. It is preferable that the brazing layer 10 covers the entire surface between the circuit patterns 30 or between the heat sinks 35.

[0024] Furthermore, the metal plate removal process for forming the predetermined circuit pattern 30 and heat sink 35 is not limited to etching. For example, unnecessary parts of the metal plate 15 may be mechanically removed by milling. Alternatively, the metal plate 15, which has been pre-formed into a pattern shape, may be bonded to the ceramic substrate 5 using a brazing material or the like. However, mechanical removal by milling has the drawback of being time-consuming. In addition, forming a pattern shape on the metal plate 15 in advance requires, for example, a mold to process copper into the desired pattern, the pattern position is unstable because it is not bonded during lamination, and the pattern width is unstable due to the expansion and contraction of copper during bonding. From this viewpoint, it is preferable to use etching.

[0025] <Laser processing> Next, a laser beam B is irradiated onto the portion of the brazing material layer 10 exposed by the metal plate removal process described above, and a laser processing treatment is performed to form a divided groove 40 at a predetermined location on the ceramic substrate 5. Figure 6 is a cross-sectional view illustrating the laser processing treatment, and Figure 7 is a plan view (top view) illustrating the laser processing treatment, illustrating the structure of the divided groove 40 that is formed. As shown in Figure 6, the laser processing treatment forms through holes 39 that penetrate the brazing material layer 10, and the laser beam B is irradiated onto the surface of the ceramic substrate 5 through the through holes 39 to form the divided groove 40. The divided groove 40 is formed between each circuit pattern 30, for example, as shown in Figure 7 (see dashed line in Figure 7). The groove width, groove depth, and groove angle of the divided groove 40 can be appropriately adjusted according to the distance between each circuit pattern 30 and the thickness and size of the ceramic substrate 5. The distances a and b between each circuit pattern 30 (or between heat sinks 35) are arbitrary and can be designed to be, for example, about 0.5 mm to 3.0 mm.

[0026] For example, the width of the dividing groove 40 can be 5 μm or more and 100 μm or less. Preferably, it is 10 μm or more and 80 μm or less, as this facilitates separation along the dividing groove 40. The depth of the dividing groove 40 can be 40 μm or more and 180 μm or less. Preferably, the depth of the dividing groove 40 is 45 μm or more, and more preferably 50 μm or more, as this facilitates separation along the dividing groove 40. From the viewpoint of shortening the processing time, the depth of the dividing groove 40 is preferably 150 μm or less, and more preferably 100 μm or less. The groove depth / groove width ratio of the dividing groove 40 is preferably 0.7 or more and 11.0 or less, as this facilitates separation along the dividing groove 40. More preferably, it is 0.9 or more and 8.0 or less. The groove angle of the dividing groove 40 is preferably 3° or more and 60° or less, and more preferably 5° or more and 55° or less, as this facilitates separation along the dividing groove 40. The width and depth of the segmented groove 40 can be confirmed using a laser microscope. The groove angle of the segmented groove 40 can be calculated from the obtained groove width and groove depth.

[0027] In the manufacturing method of the metal-ceramic circuit board according to this embodiment, the metal plate 15 and the ceramic substrate 5 are joined before the division grooves 40 are formed by laser processing. This prevents the metal plate 15 and the ceramic substrate 5 from being joined via the brazing layer 10 while scattered material generated during division groove formation is adhering to the surface of the ceramic substrate 5, as described in Patent Document 1. Therefore, it is possible to suppress the non-joining of the circuit pattern 30 and the ceramic substrate 5.

[0028] Furthermore, as shown in Figure 6(a), by irradiating the exposed portion of the brazing material layer 10 with the laser beam B, through holes 39 are formed in the brazing material layer 10, as shown in Figure 6(b). The scattered ceramic substrate 5 generated by the laser beam irradiation adheres to the upper surface of the brazing material layer 10 and to the inner surface of the through holes 39 formed by the laser processing. In this way, adhesion to the surface of the ceramic substrate 5 is prevented, thus preventing appearance defects caused by the adhesion of scattered ceramic substrate 5 to the surface of the ceramic substrate 5. Therefore, as described in Patent Document 2, there is no need for a process to form and wash away a resin film.

[0029] The laser processing process can be performed by setting the irradiation conditions of the laser beam B so that through holes 39 are formed in the brazing material layer 10 and divided grooves 40 of the desired width and depth are formed in the ceramic substrate 5.

[0030] In laser processing, the output of laser beam B is preferably 1W or more in order to shorten the processing time. From the viewpoint of processing time, 2W or more is more preferable. There is no particular upper limit to the output of laser beam B, but it can be, for example, 500W or less, 100W or less, or 60W or less. In laser processing, the irradiation spot diameter of laser beam B can be adjusted as appropriate according to the width of the divided groove to be formed. For example, the irradiation spot diameter of laser beam B may be φ5μm or more and φ200μm or less. The irradiation spot diameter of laser beam B may also be φ150μm or less or φ100μm or less. In laser processing, the power density obtained by dividing the output of the laser beam B by the spot area can be used as an index of the irradiation energy of the laser beam B per unit area. In laser processing, the power density can be 0.1 MW / cm 2 or more and 50 MW / cm 2 or less.

[0031] In laser processing, various laser beams B are applicable. The wavelength of the laser beam B is preferably, for example, 200 nm or more and 12000 nm or less, more preferably 300 nm or more and 1500 nm or less. In laser processing, the irradiation of the laser beam B is preferably performed using a pulsed laser. When using a pulsed laser, the pulse width, which is the irradiation time per pulse of the laser beam B, is preferably 500 ns (nanoseconds) or less, more preferably 300 ns (nanoseconds) or less, because microfabrication is possible and divided grooves can be formed uniformly. There is no particular limitation on the lower limit value of the pulse width, but the pulse width can be, for example, 10 fs (femtoseconds) or more, 100 fs (femtoseconds) or more, or 300 fs (femtoseconds) or more. If the pulse width is less than 1 ns (nanosecond), the peak output is high, the material irradiated with the laser beam B can be sublimated, and the thermal influence on the periphery of the laser beam irradiation location can be reduced, so defects in the ceramic substrate can be suppressed. However, if the pulse width is 1 ns (nanosecond) or more, it becomes possible to use a laser device that is less expensive than the laser device used for laser processing with a pulse width less than 1 ns (nanosecond), and it becomes possible to keep the manufacturing cost low.

[0032] In order to shorten the processing time of laser processing, the scanning speed of the laser beam B is preferably 1 mm / s or more. From the viewpoint of the processing time, 5 mm / s or more is more preferable. There is no particular limitation on the upper limit value of the scanning speed, but it can be, for example, 5000 mm / s or less. The scanning speed can also be 4000 mm / s or less, or 2500 mm / s or less.

[0033] The number of times laser beam B is irradiated can be adjusted as appropriate according to the width and depth of the divided groove to be formed and the scanning speed of laser beam B. There is no particular limit to the number of times laser beam B is irradiated, but for example, it can be 100 times or less, or 80 times or less.

[0034] In this embodiment, the processing speed for obtaining the desired divided grooves in the laser processing process can be calculated by dividing the scanning speed of the laser beam B by the number of repetitions of irradiation with the laser beam B, i.e., the scanning speed of the laser beam B divided by the number of repetitions of irradiation with the laser beam B. The processing speed varies depending on the width and depth of the divided grooves to be formed. From the viewpoint of processing time, the processing speed is preferably 1 mm / s or more, and more preferably 5 mm / s or more. There is no particular upper limit to the processing speed, but from the viewpoint of processing accuracy, it is preferably 60 mm / s or less.

[0035] In laser processing, the repetition frequency of laser beam B is preferably 50 kHz or higher, more preferably 75 kHz or higher, and even more preferably 100 kHz or higher, because it enables fine processing and uniform formation of divided grooves. There is no particular upper limit to the repetition frequency of laser beam B, but it can be, for example, 50,000 kHz or lower. The repetition frequency of laser beam B may also be 10,000 kHz or lower, 5,000 kHz or lower, or 1,500 kHz or lower. The repetition frequency is the number of pulses generated per second at a constant period. The repetition frequency f can be calculated from the pulse interval T (seconds) using the following formula. The repetition frequency is f = 1 / T (Hz).

[0036] <Removal of brazing layer> Next, a brazing layer removal process is performed to remove unnecessary portions of the brazing layer 10 remaining on the surface of the ceramic substrate 5, such as between the circuit patterns 30 and around the heat sink 35. Figures 8 and 9 are explanatory diagrams illustrating the state after the brazing layer removal process; Figure 8 is a cross-sectional view, and Figure 9 is a plan view (top view). Here, unnecessary portions of the brazing layer 10 refer, for example, to the exposed portions of the brazing layer 10 on the ceramic substrate 5, excluding those directly beneath the circuit patterns 30 and heat sink 35. In this embodiment, as shown in Figure 9, it refers to the exposed brazing layer 10 other than the portion where the circuit patterns 30 are joined in a plan view.

[0037] As shown in Figures 8 and 9, by removing the brazing material layer, a metal-ceramic circuit board can be obtained in which multiple circuit patterns 30 and a heat sink 35 are bonded to a ceramic substrate 5 on which segmented grooves 40 (dashed lines in Figure 9) are formed. As described above, scattered material from the ceramic substrate 5, generated by the laser processing process in which a laser beam is irradiated onto the portion of the brazing material layer 10 exposed by the metal plate removal process, adheres to the brazing material layer. Therefore, by removing the brazing material layer 10 to which the scattered material has adhered, it is possible to suppress the adhesion of scattered material from the ceramic substrate 5 to the surface of the ceramic substrate 5, thereby suppressing defects in appearance.

[0038] The brazing layer removal treatment may be carried out using a chemical solution. The chemical solution used to remove the brazing layer 10 can be an aqueous solution containing hydrofluoric acid or ethylenediaminetetraacetic acid (EDTA). The brazing layer removal treatment may be carried out by immersing the metal-ceramic joint 20 in the chemical solution, or by spraying the chemical solution onto the unwanted parts of the brazing layer 10. In addition, before removing the brazing layer 10 with the chemical solution, pickling may be performed to remove the oxide layer formed on the surface of the brazing layer 10. Pickling may be carried out, for example, by immersing the metal-ceramic joint 20 in dilute sulfuric acid or by spraying dilute sulfuric acid onto the metal-ceramic joint 20.

[0039] <Chemical polishing treatment> Next, a chemical polishing treatment may be performed to remove foreign matter adhering to the surfaces of the circuit pattern 30 and the heat sink 35. If the circuit pattern 30 and the heat sink 35 are made of copper or a copper alloy, this is preferably performed by immersing them in a chemical polishing solution containing 3% to 10% by mass of sulfuric acid and 3% to 10% by mass of hydrogen peroxide (more preferably a chemical polishing solution containing 3% to 10% by mass of sulfuric acid and 3% to 10% by mass of hydrogen peroxide, with the remainder being water) at a temperature of 20°C to 35°C for 1 minute 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 circuit pattern 30 and the heat sink 35 made of copper or a copper alloy. If the circuit pattern 30 and heat sink 35 are made of aluminum or an aluminum alloy, the polishing is preferably carried out by immersing them in a chemical polishing solution preferably at a temperature of 20°C to 35°C for 1 minute to 10 minutes, using a chemical polishing solution preferably containing 1% to 5% by mass of sodium hydroxide (more preferably containing 1% to 5% by mass of sodium hydroxide with the remainder being water), or preferably containing 0.5% to 5% by mass of sulfuric acid and 2% to 10% by mass of phosphoric acid (more preferably containing 0.5% to 5% by mass of sulfuric acid and 2% to 10% by mass of phosphoric acid with the remainder being water). 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 adhering to the surface of the circuit pattern 30 and heat sink 35 made of aluminum or an aluminum alloy.

[0040] <Individuation> Next, the ceramic substrate 5 is divided by bending it along the dividing groove 40 by the worker's hand, and as shown in Figure 10, it is separated into individual metal-ceramic circuit boards.

[0041] Although an example of an embodiment of the present invention has been described above, the present invention is not limited to the illustrated form. It will be clear to those skilled in the art that various modifications or alterations can be conceived within the scope of the idea described in the claims, and these will naturally also fall within the technical scope of the present invention. It is preferable to manufacture the metal-ceramic circuit board by performing each step described in the above embodiment in order, but other steps may be included in addition to the above steps. For example, a cleaning step may be included between each step, such as after the bonding process that forms the metal-ceramic bond 20. [Examples]

[0042] Below, we evaluated the appearance and bonding properties of a metal-ceramic bonded body produced using the metal-ceramic circuit board manufacturing method according to the present invention (Example) and a metal-ceramic bonded body produced using a conventional method (Comparative Example).

[0043] <Example 1> The metal-ceramic circuit board according to Example 1 was fabricated in the order shown in the manufacturing method flow chart in Figure 17. Each processing step will be described below.

[0044] (Joining process) First, a ceramic substrate mainly composed of aluminum nitride was prepared, with a roughly rectangular planar shape measuring 102 mm in length, 102 mm in width, and 0.32 mm in thickness. An activated metal-containing brazing material was also prepared by kneading a vehicle consisting of Ag powder, Cu powder, Sn powder, Ti powder, an acrylic binder, and an organic solvent. The activated metal-containing brazing material contained 83% by mass of Ag, 10% by mass of Cu, 5% by mass of Sn, and 2% by mass of Ti as its metal components. The mixture was formulated so that, when the total amount of Ag, Cu, Sn, and Ti in the brazing material was 100 parts by mass (standard), the organic solvent was 6.5 parts by mass and the binder was 7.2 parts by mass.

[0045] Next, an activated metal-containing brazing material was screen-printed to a thickness of 20 μm onto almost the entire surface of both sides of the ceramic substrate (see Figure 1). Then, a laminate was formed by placing an oxygen-free copper plate (metal plate) with a roughly rectangular plan shape measuring 105 mm in length, 105 mm in width, and 0.25 mm in thickness on the brazing material applied to one side of the ceramic substrate for the circuit pattern, and placing an oxygen-free copper plate (metal plate) with a roughly rectangular plan shape measuring 105 mm in length, 105 mm in width, and 0.25 mm in thickness on the brazing material applied to the other side of the ceramic substrate (see Figure 2). A pressure of 0.05 kgf / cm² was applied to the formed laminate in the thickness direction of the laminate. 2 While applying the load 4.0 × 10 -2 A metal-ceramic bond was fabricated by bonding copper plates to both sides of a ceramic substrate by heating it at 850°C for 45 minutes in a vacuum of Pa, thereby forming a brazing layer, and bonding the ceramic substrate and the metal plate via a 10 μm thick brazing layer (see Figure 2).

[0046] (Metal plate removal process) Next, an ultraviolet-curable alkaline peel-off resist was screen-printed onto the surface of a copper plate bonded to one side of the ceramic substrate of the metal-ceramic bond, and onto the surface of a copper plate bonded to the other side of the ceramic substrate. Then, the applied resist was cured by irradiating it with ultraviolet light.

[0047] Next, a 30W Yb laser (F300FAYb manufactured by Keyence Corporation) was irradiated onto predetermined locations on the hardened resist on the surface of the copper plate bonded to one side of the ceramic substrate of the metal-ceramic bond, and on the hardened resist on the surface of the copper plate bonded to the other side of the ceramic substrate, to remove the resist from predetermined parts of the resist and form circuit pattern resist and heat sink resist of predetermined shapes (see Figures 3 and 4). In this embodiment 1, four circuit pattern resists and heat sink resists were formed on the surface of the copper plate bonded to one side of the ceramic substrate of the metal-ceramic bond (see Figure 4).

[0048] Then, unwanted parts of the copper plate were etched using an etching solution consisting of copper chloride, hydrochloric acid, and water, and the resist was removed with an aqueous sodium hydroxide solution to form four copper circuit patterns measuring 31 mm in length and 31 mm in width on one side of the ceramic substrate of the metal-ceramic bond, and four copper heat sinks measuring 31 mm in length and 31 mm in width on the other side of the ceramic substrate (see Figure 5). Note that the brazing material layer is exposed where the copper was etched. Therefore, in the brazing material applied to almost the entire surface of both sides of the ceramic substrate as described above, the brazing material is exposed in all areas except directly beneath the four copper circuit patterns and the four copper heat sinks. The thickness of the brazing material layer was 10 μm. The distance between the four copper circuit patterns and the distance between the four copper heat sinks (distances a and b in Figure 7) were 2 mm.

[0049] (Laser processing) Next, using a laser processing device (MD-X2520A manufactured by Keyence), a laser beam was irradiated onto the portion of the brazing material layer exposed by the etching process along approximately the center line between adjacent copper circuit patterns, under the following laser irradiation conditions, to form six dividing grooves on the surface of the ceramic substrate so that the four sets of circuit patterns of the metal-ceramic bond were divided into predetermined sizes for the ceramic substrate (see Figures 6 and 7). Specifically, the dividing grooves were formed so as to coincide with approximately the center line between adjacent copper circuit patterns (or copper heat sinks) on the ceramic substrate.

[0050] The laser irradiation conditions are as follows: Output: 20W Wavelength: 1064nm Pulse width: 8 ns (nanoseconds) Spot diameter: 80 μm Laser scanning speed: 200 mm / s Number of repetitions: 20 Machining speed: 10mm / s Power density: 0.4 MW / cm² 2 Frequency: 120kHz

[0051] For one of the divided grooves in the metal-ceramic joint obtained in this way, three arbitrary locations were extracted from the irradiated surface (top surface), and the width of the divided groove was measured by observing it at 500x magnification using a Keyence laser microscope (VHX-6000). Similarly, three arbitrary locations were extracted from the cross-section of the divided groove, and the depth of the divided groove was measured by observing it at 500x magnification. In this example, the width and depth of the divided groove were measured before the brazing material was removed, and the measurement was taken as the dimension of the divided groove + through hole. That is, the measurement was taken as the groove dimension including the through hole 39 and the divided groove 40 shown in Figure 6(b) of the above embodiment. The median values ​​obtained from the measurements are taken as the width and depth of the segmented groove + through hole. The angle of the segmented groove is calculated from these width and depth values ​​using the following formula (1), and this is taken as the groove angle value. Groove angle = 2 × atan(width / (2 × depth)) ... (1) In equation (1), "atan" means arctangent.

[0052] Table 1 shows the width and depth values ​​of the segmented grooves and through holes obtained by measurement, and the groove angles obtained by calculation. In addition to Example 1, Table 1 also describes the laser irradiation conditions and evaluations for Examples 2 to 4 and Comparative Examples 1 and 2, which will be described later. [Table 1]

[0053] (Removal of brazing layer) Next, the brazing layer was removed by immersion in a chelate aqueous solution containing 1.6% by mass of EDTA·4Na (sodium salt of ethylene diamine tetraacetic acid), 3% by mass of ammonia water, and 5% by mass of hydrogen peroxide water (see Figures 8 and 9). The unwanted parts of the brazing layer are the areas on the ceramic substrate where the brazing layer is exposed, excluding those directly beneath the copper circuit patterns and copper heat sinks.

[0054] (Chemical polishing treatment) Next, the copper circuit patterns and copper heat sinks were chemically polished by immersion for 3 minutes in a 25°C chemical polishing solution containing 5% by mass sulfuric acid and 7% by mass hydrogen peroxide, with the remainder being water. After that, they were rinsed with water and dried.

[0055] When the metal-ceramic circuit board obtained in this manner was observed (visual inspection) using an optical microscope, no contamination was found on the surface of the ceramic substrate near the divided grooves formed on the ceramic substrate, as shown in Figure 12. Furthermore, the joint between the copper circuit pattern and the ceramic substrate of the obtained metal-ceramic circuit board was examined using an ultrasonic flaw detector (Fine Ultrasonic flaw detection was performed using a SAT FS100II (manufactured by Hitachi Power Solutions, Ltd.), and ultrasonic flaw detection images were acquired. The acquired ultrasonic flaw detection images were binarized using the analysis software included with the ultrasonic flaw detector, and the presence or absence of unjointed areas was checked. As shown in Figure 13, there were no unjointed areas, and the bonding was good. Furthermore, it is possible to separate the ceramic substrate along the formed dividing groove to create individual metal-ceramic circuit boards.

[0056] <Example 2> A metal-ceramic circuit board according to Example 2 was fabricated in the same manner as in Example 1, except that a laser processing treatment was performed using a laser processing device (MD-F5220 manufactured by Keyence Corporation) to irradiate the portion of the brazing material layer exposed by etching along approximately the center line between adjacent copper circuit patterns under the following laser irradiation conditions, thereby forming segmented grooves on the surface of the ceramic substrate.

[0057] The laser irradiation conditions are as follows: Output: 40W Wavelength: 1090nm Pulse width: 220 ns (nanoseconds) Spot diameter: 90 μm Laser scanning speed: 1000 mm / s Number of repetitions: 24 Machining speed: 42mm / s Power density: 0.6 MW / cm² 2 Frequency: 100kHz

[0058] The width and depth of the divided grooves were measured and the groove angles were calculated for the metal-ceramic circuit board obtained in Example 2, in the same manner as in Example 1. The results are shown in Table 1. The metal-ceramic circuit board obtained in Example 2 was also observed using an optical microscope (visual inspection) and checked for any unbonded areas using an ultrasonic flaw detector. As a result, no contamination was found on the ceramic substrate near the divided grooves formed on the ceramic substrate. Furthermore, there were no unbonded areas at the joint between the copper circuit board and the ceramic substrate of the obtained metal-ceramic circuit board, and the joint was good.

[0059] The metal-ceramic circuit board obtained in Example 2 was observed using an optical microscope (visual inspection) in the same manner as in Example 1, and the presence or absence of unbonded areas was checked using an ultrasonic flaw detector. As a result, no contamination was found on the ceramic substrate near the divided grooves formed on the ceramic substrate. Furthermore, there were no unbonded areas at the joint between the copper circuit board and the ceramic substrate of the obtained metal-ceramic circuit board, and the joint was good.

[0060] <Example 3> A metal-ceramic circuit board according to Example 3 was fabricated in the same manner as in Example 1, except that a laser processing treatment was performed using a laser processing device (Tangor 100 manufactured by Amplitude) to irradiate the portion of the brazing material layer exposed by etching along approximately the center line between adjacent copper circuit patterns under the following laser irradiation conditions, thereby forming segmented grooves on the surface of the ceramic substrate.

[0061] The laser irradiation conditions are as follows: Output: 27W Wavelength: 345nm Pulse width: 450 fs (femtoseconds) Spot diameter: 9.4 μm Laser scanning speed: 2000 mm / s Number of repetitions: 68 Machining speed: 29mm / s Power density: 38.9 MW / cm² 2 Frequency: 1000kHz

[0062] The width and depth of the divided grooves were measured and the groove angles were calculated for the metal-ceramic circuit board obtained in Example 3, in the same manner as in Example 1. The results are shown in Table 1. The metal-ceramic circuit board obtained in Example 2 was observed using an optical microscope (visual inspection) and checked for the presence of unbonded areas using an ultrasonic flaw detector. As a result, no contamination was found on the ceramic substrate near the divided grooves formed on the ceramic substrate. Furthermore, there were no unbonded areas at the joint between the copper circuit board and the ceramic substrate of the obtained metal-ceramic circuit board, and the joint was good.

[0063] <Example 4> A metal-ceramic circuit board according to Example 4 was fabricated in the same manner as in Example 1, except that a laser processing treatment was performed using a laser processing device (Pharos manufactured by Light Conversion Inc.) to irradiate the portion of the brazing material layer exposed by etching along approximately the center line between adjacent copper circuit patterns under the following laser irradiation conditions, thereby forming segmented grooves on the surface of the ceramic substrate.

[0064] The laser irradiation conditions are as follows: Output: 3W Wavelength: 1026nm Pulse width: 500 fs (femtoseconds) Spot diameter: 7.8 μm Laser scanning speed: 10 mm / s Number of repetitions: 1 Machining speed: 10mm / s Power density: 6.3 MW / cm² 2 Frequency: 1000kHz

[0065] The width and depth of the divided grooves were measured and the groove angles were calculated for the metal-ceramic circuit board obtained in Example 4, in the same manner as in Example 1. The results are shown in Table 1. The metal-ceramic circuit board obtained in Example 2 was observed using an optical microscope (visual inspection) and checked for the presence of unbonded areas using an ultrasonic flaw detector. As a result, no contamination was found on the ceramic substrate near the divided grooves formed on the ceramic substrate. Furthermore, there were no unbonded areas at the joint between the copper circuit board and the ceramic substrate of the obtained metal-ceramic circuit board, and the joint was good.

[0066] <Comparative Example 1> The metal-ceramic circuit board according to Comparative Example 1 was fabricated in the order shown in the manufacturing method flow chart in Figure 18. Specifically, up to the etching process, four copper circuit patterns were formed on one side of the ceramic substrate of the metal-ceramic bond, and four copper heat sinks were formed on the other side of the ceramic substrate using the same method as in Example 1. Next, a brazing layer removal process and chemical polishing were performed using the same method as in Example 1 to remove unnecessary portions of the brazing layer. As shown in Figure 11, after chemical polishing, a divided groove was formed on the surface of the ceramic substrate of the metal-ceramic bond under the same laser irradiation conditions as in Example 1, thereby obtaining the metal-ceramic circuit board according to Comparative Example 1.

[0067] The metal-ceramic circuit board obtained in Comparative Example 1 was observed (visual inspection) using an optical microscope in the same manner as in Example 1. As shown in Figure 14, a band-shaped stain approximately parallel to the dividing groove was observed near the dividing groove formed on the ceramic substrate (specifically, at a position of about 0.24 mm from the center line of the dividing groove). Because stain was observed near the dividing groove formed on the ceramic substrate, the unbonded portion at the joint between the copper circuit board and the ceramic substrate of the obtained metal-ceramic circuit board was not checked.

[0068] <Comparative Example 2> A metal-ceramic circuit board according to Comparative Example 2 was fabricated in the order shown in the manufacturing method flow chart in Figure 19. Specifically, a divided groove was formed on the prepared ceramic substrate under the same laser irradiation conditions as in Example 1, and then bonding, etching, brazing layer removal, and chemical polishing were performed in the same manner as in Example 1.

[0069] The metal-ceramic circuit board obtained in Comparative Example 2 was observed (visual inspection) using an optical microscope in the same manner as in Example 1. As shown in Figure 15, no dirt was found near the divided grooves formed on the ceramic substrate. When the presence or absence of unbonded areas was checked at the junction between the copper circuit pattern and the ceramic substrate of the obtained metal-ceramic circuit board, unbonded areas (gray areas) were found as shown in Figure 16, indicating that a good bond had not been achieved.

[0070] Furthermore, the following configuration examples also fall within the technical scope of the present invention. (1) A step of forming a metal-ceramic bond in which a plurality of circuit patterns are formed on at least one surface of a ceramic substrate via a brazing layer, A step of forming divided grooves in the ceramic substrate by irradiating the portion of the brazing material layer exposed with a laser beam and performing laser processing, The process includes removing the unnecessary portion of the brazing material layer. A method for manufacturing a metal-ceramic circuit board, characterized in that the step of forming the metal-ceramic bond is performed before the laser processing. (2) The method for manufacturing a metal-ceramic circuit board according to (1), characterized in that the circuit pattern is formed by joining a metal plate to at least one surface of the ceramic substrate via a brazing layer, and etching away the unnecessary portion of the metal plate. (3) The method for manufacturing a metal-ceramic circuit board according to (1) or (2), characterized in that the pulse width of the laser beam used in the laser processing is 10 fs or more and 500 ns or less. (4) The method for manufacturing a metal-ceramic circuit board according to any one of (1) to (3), characterized in that the repetition frequency of the laser beam used in the laser processing is 50 kHz or more and 50,000 kHz or less. (5) A method for manufacturing a metal-ceramic circuit board according to any one of (1) to (4), characterized in that the wavelength of the laser beam used in the laser processing is 12,000 nm or less. (6) The method for manufacturing a metal-ceramic circuit board according to any one of (1) to (5), characterized in that the output of the laser beam used in the laser processing is 1W or more and 500W or less. (7) The method for manufacturing a metal-ceramic circuit board according to any one of (1) to (6), characterized in that the laser processing is performed by scanning the laser beam at a scanning speed of 1 mm / s or more and 5000 mm / s or less. [Industrial applicability]

[0071] The present invention relates to a method for manufacturing a metal-ceramic circuit board, and is particularly applicable to a method for manufacturing a metal-ceramic circuit board in which a metal circuit pattern is bonded to a ceramic substrate. [Explanation of Symbols]

[0072] 5…Ceramic substrate 10...Waxing layer 15...Metal plate 18…Laminate 20…Metal-ceramic joint 30... Circuit Pattern 32…Resist 35...Heat sink 40...Dividing groove B... Laser beam

Claims

1. A process for forming a metal-ceramic bond in which multiple circuit patterns are formed on at least one surface of a ceramic substrate via a brazing layer, A step of forming divided grooves in the ceramic substrate by irradiating the portion of the brazing material layer exposed with a laser beam and performing laser processing, The process includes removing the unnecessary portion of the brazing material layer. A method for manufacturing a metal-ceramic circuit board, characterized in that the step of forming the metal-ceramic bond is performed before the laser processing.

2. The method for manufacturing a metal-ceramic circuit board according to claim 1, characterized in that the circuit pattern is formed by joining a metal plate to at least one surface of the ceramic substrate via a brazing layer, and etching away the unnecessary portion of the metal plate.

3. A method for manufacturing a metal-ceramic circuit board according to claim 1 or 2, characterized in that the pulse width of the laser beam used in the laser processing is 10 fs or more and 500 ns or less.

4. A method for manufacturing a metal-ceramic circuit board according to claim 1 or 2, characterized in that the repetition frequency of the laser beam used in the laser processing is 50 kHz or more and 50,000 kHz or less.

5. A method for manufacturing a metal-ceramic circuit board according to claim 1 or 2, characterized in that the wavelength of the laser beam used in the laser processing is 12,000 nm or less.

6. A method for manufacturing a metal-ceramic circuit board according to claim 1 or 2, characterized in that the output of the laser beam used in the laser processing is 1W or more and 500W or less.

7. The method for manufacturing a metal-ceramic circuit board according to claim 1 or 2, characterized in that the laser processing is performed by scanning the laser beam at a scanning speed of 1 mm / s or more and 5000 mm / s or less.

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