Method for manufacturing ceramic scribe substrate, method for manufacturing ceramic substrate, and method for manufacturing ceramic circuit board

Abstract

A method according to an embodiment of the present invention for manufacturing a ceramic scribe substrate including a ceramic substrate as an element comprises a laser processing step and a removal step. During the laser processing step, a continuous through groove is formed as a scribe line by radiating a laser onto the surface of a ceramic sintered substrate, whereby a removal portion surrounded by a plurality of the scribe lines is formed. During the removal step, the removal portion is removed by injecting an assist gas coaxial to the laser during laser irradiation. The area of the surface of each portion, of the removal portion, that corresponds to one ceramic substrate is preferably 1.0 mm2 to 20.0 mm2.

Description

Manufacturing method of ceramic scribed substrate, manufacturing method of ceramic substrate, and manufacturing method of ceramic circuit substrate

[0001] The embodiments generally relate to a method for manufacturing a ceramic scribed substrate, a method for manufacturing a ceramic substrate, and a method for manufacturing a ceramic circuit substrate.

[0002] With the development of semiconductor elements that require large currents, such as power electronics and next-generation power semiconductors, the demand for ceramic substrates that combine heat dissipation and electrical insulation is increasing year by year. In particular, as elements generate more heat due to miniaturization and higher performance, the thickness of ceramic substrates tends to become thinner in order to dissipate heat more efficiently.

[0003] On the other hand, in order to reduce the manufacturing cost of ceramic substrates, ceramic sintered substrates, which are plate-shaped ceramic sintered bodies containing a plurality of ceramic substrates as elements, are manufactured. As a silicon nitride substrate obtained from a silicon nitride sintered substrate, which has high strength, high toughness, and high heat dissipation properties among ceramic sintered substrates, a silicon nitride substrate having dimensions of 220 mm x 220 mm on both sides and a thickness of 0.32 mm, is disclosed (Patent Document 1).

[0004] As one method for dividing a silicon nitride sintered substrate, which has been manufactured in large size to reduce manufacturing costs, into silicon nitride substrates of the product size to be used, a method for cutting a large number of silicon nitride substrates from a silicon nitride sintered substrate by utilizing scribe lines formed in the silicon nitride sintered substrate by laser processing has been disclosed (Patent Document 2). According to Patent Document 2, after dividing (breaking) the silicon nitride substrate into multiple pieces by laser processing, no more microcracks than necessary are generated, and scribe line processing for cutting multiple pieces can be performed easily and at low cost.

[0005] Also, a method of using air as an assist gas when laser processing a sintered ceramic substrate has been disclosed (Patent Document 3). According to Patent Document 3, chamfered portions can be formed on the ceramic substrate after division by scribe lines formed by through grooves formed by the laser.

[0006] Also, a method for forming chamfers on a sintered ceramic substrate by laser processing has been disclosed (Patent Document 4). According to Patent Document 4, burrs vaporized by the laser can be embrittled and removed by the oxidizing and cooling action of an assist gas.

[0007] Japanese Patent No. 6399252 Japanese Patent Application Laid-Open No. 2002-176119 Japanese Patent Application Laid-Open No. 5-144978 Japanese Patent Application Laid-Open No. 2008-198905

[0008] As the size of the front and back surfaces of sintered ceramic substrates has increased and their thickness has decreased in order to improve productivity, problems have become apparent. For example, when scribe lines are formed using a laser on a sintered ceramic substrate with high strength and toughness, the scribe lines may be made deep in the thickness direction. This is because the high strength of the sintered ceramic substrate requires a large force to separate it along the scribe lines.

[0009] However, when the thickness of a ceramic sintered substrate is thin, the scribe line is at or near the through-groove, increasing the likelihood that the portion formed by the scribe line (i.e., the "removed portion" described below) will unintentionally fall off due to the force applied during processing steps (e.g., the metal joining step) or transportation after the scribe line is formed by the laser. If the unintentional falling off of this portion increases, the portion must be recovered in a later step, increasing the workload. Conversely, if the laser is applied shallowly in the thickness direction, the portion is less likely to fall off during intermediate steps, but a large force must be applied when dividing along the scribe line. This increases the workload, and it has been found that the application of large forces can cause defects (such as chips and cracks) in the ceramic substrate.

[0010] That is, while it is possible to form scribe lines for chamfering the ceramic substrate on a sintered ceramic substrate using laser processing, it is necessary to control the method of removing the scribe lines in order to improve the efficiency of dividing the substrate along the scribe lines and recovering the fallen-off portions, and to prevent defects from occurring in the ceramic substrate.

[0011] One of the problems that the embodiments aim to solve is to efficiently manufacture ceramic scribe substrates, ceramic substrates, and ceramic circuit substrates without defects from a high-strength ceramic sintered substrate that has large, thin front and back surfaces and combines heat dissipation and electrical insulation properties.

[0012] A method for manufacturing a ceramic scribed substrate including a ceramic substrate as an element according to an embodiment includes a laser processing step and a removal step. In the laser processing step, a laser is irradiated onto the surface of the ceramic sintered substrate to form continuous through grooves as scribe lines, and a removed portion surrounded by a plurality of scribe lines is formed. In the removal step, an assist gas is ejected coaxially with the laser during the laser irradiation to remove the removed portion. The surface area of ​​each removed portion of the ceramic substrate is 1.0 mm. ２ Over 20.0 mm ２ It is preferable that:

[0013] FIG. 1 is a plan view showing an example of a surface of a ceramic scribed substrate manufactured by a method for manufacturing a ceramic substrate according to an embodiment. FIG. 2 is a plan view showing an example of a surface of a ceramic substrate manufactured by a method for manufacturing a ceramic substrate according to an embodiment. FIG. 3 is an enlarged view showing a part of a back surface of a ceramic scribed substrate manufactured by a method for manufacturing a ceramic scribed substrate according to an embodiment. FIG. 4 is an enlarged cross-sectional view showing an example of a ceramic scribed substrate manufactured by a method for manufacturing a ceramic scribed substrate according to an embodiment. FIG. 5 is a side view showing an example of a ceramic circuit substrate manufactured by a method for manufacturing a ceramic circuit substrate according to an embodiment. FIG. 6 is a side view showing an example of a ceramic circuit substrate integrated by a resin mold manufactured by a method for manufacturing a ceramic circuit substrate according to an embodiment. FIG. 7 is a flowchart showing a method for manufacturing a ceramic circuit substrate according to an embodiment. Embodiment

[0014] Hereinafter, embodiments of a method for manufacturing a ceramic scribed substrate, a method for manufacturing a ceramic substrate, and a method for manufacturing a ceramic circuit substrate will be described in detail with reference to the drawings.

[0015] The method for manufacturing a ceramic scribed substrate according to the embodiment includes a laser processing step and a removal step. In the laser processing step, a laser is irradiated onto the surface of the ceramic sintered substrate to form continuous through grooves as scribe lines, and a removed portion surrounded by a plurality of scribe lines is formed. In the removal step, an assist gas is sprayed coaxially with the laser during laser irradiation to remove the removed portion. Of the removed portions, the surface area of ​​each portion of the ceramic substrate (C-face portion 44 cut by C-face 43 described below) is 1.0 mm ２ Over 20.0 mm ２ It is preferable that:

[0016] FIG. 1 is a top view showing an example of the surface of a ceramic scribe substrate (hereinafter abbreviated as "scribe substrate") 1 having rectangular (including square) surfaces on both sides and provided with scribe lines. The scribe substrate 1 is a ceramic sintered substrate, which is a plate-shaped ceramic sintered body, on which scribe lines 3 and 4 are provided. The scribe substrate 1 includes, as elements, a plurality of ceramic substrates 2 that will become products. In the example shown in FIG. 1, the scribe substrate 1 has a total of 16 ceramic substrates 2, four in the vertical direction and four in the horizontal direction. Furthermore, FIG. 7 is a flowchart showing a method for manufacturing the scribe substrate 1 shown in FIG. 1, a method for manufacturing a ceramic substrate based on the scribe substrate 1, and a method for manufacturing a ceramic circuit substrate 8 based on the scribe substrate 1.

[0017] The scribed substrate 1 also includes a peripheral portion 5 around the ceramic substrate 2 that will not become a product. Side scribe lines 3 (shown by two-dot chain lines in FIG. 1 ) are provided at the boundary between the ceramic substrate 2 and the peripheral portion 5 and at the boundary between adjacent ceramic substrates 2. Meanwhile, corner scribe lines 4 are provided at the four corners of each ceramic substrate 2 to form chamfers of the ceramic substrate 2. Of the corner scribe lines 4, outer corner scribe lines 41 (shown by one-dot chain lines in FIG. 1 ), which are corner scribe lines that contact the peripheral portion 5, have one end extending into the interior of the peripheral portion 5. On the other hand, of the corner scribe lines 4, inner corner scribe lines 42 (shown by dashed lines in FIG. 1 ), which are corner scribe lines that contact an adjacent ceramic substrate 2, do not extend into the interior of the adjacent ceramic substrate 2.

[0018] The scribed substrate 1 is also in a state where scribe lines 3 and 4 have been formed. Furthermore, because removal of the removed portions 6, which will be described later, is performed during the laser irradiation for forming the scribe lines 3 and 4, the scribed substrate 1 is in a state where the removed portions 6 have been removed. In FIG. 1 , the removed portions 6 include triangular first removed portions 61 (12 in the example of FIG. 1 ) formed by one side scribe line 3 and two exterior corner scribe lines 41, quadrangular second removed portions 62 (9 in the example of FIG. 1 ) formed by four interior corner scribe lines 42, and triangular third removed portions 63 (4 in the example of FIG. 1 ) formed by two side scribe lines 3 and one exterior corner scribe line 41. The removed portions 6 are regions surrounded by lines of continuous through grooves (which penetrate in the depth direction of the paper in FIG. 1 , i.e., in the thickness direction) formed by the laser.

[0019] The scribe substrate 1 is not limited to the case shown in FIG. 1 . For example, the scribe substrate 1 may include only one ceramic substrate 2 as an element, or may include more than two ceramic substrates 2 in both the vertical and horizontal directions as elements. It is not necessary to form the side scribe lines 3 on all four sides of the ceramic substrate 2; it is sufficient to form the side scribe lines 3 on at least one side. While the ceramic substrate 2 in FIG. 1 has a rectangular shape in plan view, it may also have a substantially polygonal shape. It is not necessary to form chamfered portions on all four corners of the ceramic substrate 2; it is sufficient to form chamfered portions on at least one corner.

[0020] 2 shows one of the plurality of ceramic substrates 2 separated from the scribed substrate 1 shown in FIG. 1. C-faces 43 are formed at the four corners of the ceramic substrate 2 by chamfering along the corner scribe lines 4 in FIG. 1. The chamfered portion is not limited to the C-face 43 in which the line viewed from the surface is linear, but may be an R-face in which the line viewed from the surface is curved. When the chamfered portion is an R-face, the corner scribe line 4 also has a curved line viewed from the surface, and the surface 43 side of the portion 44 constituting the removed portion 6 also has a curved line viewed from the surface.

[0021] In the laser processing step ST1 (shown in FIG. 7 ) in which scribe lines 3 and 4 are formed in the ceramic sintered substrate to form the removed portion 6, it is possible to form a continuous line of through grooves using a laser. Here, a continuous line of through grooves means that, when the scribed substrate 1 is viewed from the surface, each through groove formed intermittently in a line partially overlaps with a portion of the adjacent through groove. The type of laser preferably has a wavelength of 532 nm or more. This is because lasers with wavelengths longer than 532 nm are more likely to be absorbed by the surface of the ceramic substrate. Lasers with wavelengths of 532 nm or more include YAG lasers (fundamental wave or double wave), excimer lasers, fiber lasers, and CO ２Examples of such lasers include lasers. It is preferable that the laser oscillates either continuously or in pulses. In the case of pulsed oscillation, the pulse width is preferably picoseconds or femtoseconds. A short pulse width reduces the thermal effect, allowing for highly accurate micromachining. For this reason, it is even more preferable that the laser be a fiber laser.

[0022] When forming the through grooves, the laser leaves a molten material (dross) in the through grooves. Figure 3 is an example of an enlarged view showing a portion of the back surface of the scribe substrate 1. Figure 3(A) is an enlarged photograph showing a portion of the back surface of the scribe substrate 1. Figure 3(B) is a schematic diagram of Figure 3(A). Reference numeral 7 denotes a molten material. Figure 4 is an example of a cross section of a portion of the ceramic scribe substrate 1. Due to the presence of the molten material 7 in the corner scribe line 4 (e.g., the interior corner scribe line 42), the ceramic substrate 2 and the removed portion 6 (e.g., the second removed portion 62) are partially welded together, and the second removed portion 62 may not be removed in the laser processing step ST1. Because this molten material 7 is present only partially and is brittle, there is a risk that the second removed portion 62 remaining on the scribe substrate in the laser processing step ST1 may unintentionally fall off from the scribe substrate in a step subsequent to the laser processing step ST1.

[0023] For this reason, the manufacturing method of the scribed substrate 1 according to the embodiment includes a removal step ST2 (shown in FIG. 7 ) in which, during laser irradiation in the laser processing step ST1, an assist gas is injected coaxially with the laser to blow off and remove the portion 6 to be removed. Generally, in the laser processing step ST1, an assist gas such as nitrogen or air is injected onto the molten material 7 for the purpose of generating oxidation reaction heat and discharging the molten material 7 from the through groove (i.e., for the purpose of discharging the molten material). In the removal step ST2 using this injection mechanism, the injection of the assist gas coaxially with the laser is also used to remove the portion 6 to be removed, and the assist gas is strongly applied to the edge or surface of the portion 6 to blow off the portion 6 to be removed. This removal step ST2 eliminates the need for a separate mechanism for removing the portion 6 to be removed.

[0024] In the removal step ST2, an assist gas may be sprayed not only during the laser irradiation but also after the laser irradiation to remove the remaining portion to be removed 6. For example, an assist gas is sprayed for the purpose of removing the portion to be removed 6 during the laser irradiation to form each of the adjacent through grooves that make up the continuous through groove, and an assist gas is sprayed for the purpose of removing the previous through groove between the irradiation of the previous through groove and the irradiation of the subsequent through groove (i.e., during the non-laser irradiation period).

[0025] The injection pressure of the assist gas for the purpose of removing the portion 6 to be removed may be intentionally changed between the laser processing step ST1 and the removal step ST2. For example, the injection pressure of the assist gas may be higher in the removal step ST2 than in the laser processing step ST1. If the assist gas is injected at a pressure higher than that in the laser processing step ST1 in order to blow away the portion 6 to be removed with the assist gas in the removal step ST2, the portion 6 to be removed can be removed smoothly. In this case, if changing the injection pressure is complicated or if the amount of change is too large, it is preferable to increase the injection pressure of the assist gas in the laser processing step ST1 and adjust the balance of the injection pressure with the removal step ST2.

[0026] Furthermore, in the removal step ST2, assist gas may be injected for the purpose of removing the removal portions 6 both when forming the side scribe lines 3 and when forming the corner scribe lines 4, but assist gas may also be injected for the purpose of removing the removal portions 6 only when forming the corner scribe lines 4. This is because the lines that form the removal portions 6 include at least one corner scribe line 4. The first removal portion 61 is formed by two corner scribe lines 4, the second removal portion 62 by four corner scribe lines 4, and the third removal portion 63 by one corner scribe line 4. In the removal step ST2, the removal portions 6 are removed by injecting assist gas coaxially with the laser during laser irradiation when forming the corner scribe line 4 out of the multiple scribe lines 3 and 4.

[0027] The spray pressure of the assist gas in the removal step ST2 is preferably 0.2 MPa or more and 1.0 MPa or less. If the spray pressure is less than 0.2 MPa, the pressure may be too weak and the removal portion 6 may not be sufficiently removed. On the other hand, if the spray pressure is greater than 1.0 MPa, the pressure of the assist gas may cause the scribe substrate 1 to be misaligned. Furthermore, when spraying from the front surface in the removal step ST2, it is preferable to collect dust by suction from the front and back surfaces. By performing suction together with spraying, dust generated during laser processing can be removed.

[0028] The surface area of ​​the C-face portion 44 (shown in FIG. 2) of the removed portion 6, which is a portion of each ceramic substrate 2, is 1.0 mm ２ Over 20.0 mm ２ It is preferable that the surface area of ​​the C-surface portion 44, i.e., the removed portion 6, is too small. If the surface area of ​​the C-surface portion 44, i.e., the removed portion 6, is too small, the space of the through groove will be small, and even if the assist gas is sprayed, the removed portion 6 will be tilted and caught on the inner wall of the through groove, which may result in the removed portion 6 not being released properly or in a poor appearance. On the other hand, if the removed portion 6 is too large, the spray pressure may be insufficient to blow it off, and the removed portion 6 may not be removed. For this reason, a more preferable range for the surface size of the C-surface portion 44 is 2.0 mm ２ Over 10.0 mm ２ The removal of the portion 6 is performed by providing a hole in the table for laser processing, and by directing assist gas downward with the laser processing surface facing upward, causing the portion 6 to drop downward.

[0029] The surface shape of the portion to be removed 6 is preferably simple. Examples of shapes surrounded by a through groove include a circular cutout (through hole) and a rectangular shape such as a square. On the other hand, if the surface of the portion to be removed 6 has a complex shape, it may get caught in the removal step ST2, preventing the portion to be removed 6 from being removed smoothly.

[0030] The ceramic sintered substrate, i.e., the scribe substrate 1 and the ceramic substrate 2, is preferably one of a silicon nitride substrate, an aluminum nitride substrate, and an aluminum oxide substrate. An aridil substrate is also a type of aluminum oxide substrate. Aridil is a sintered body composed of 20 to 80 wt% aluminum oxide and the remainder zirconium oxide. The three-point bending strength of an aluminum nitride substrate or an aluminum oxide substrate is approximately 300 to 450 MPa. The strength of an aridil substrate is also around 550 MPa. The three-point bending strength of a silicon nitride substrate can be increased to 600 MPa or more, or even 700 MPa or more. The thermal conductivity of a silicon nitride substrate can be increased to 50 W / m·K or more, or even 80 W / m·K or more. In recent years, silicon nitride substrates have been developed that combine both high strength and high thermal conductivity.

[0031] Furthermore, the ceramic sintered substrate is preferably a substrate for dividing into a plurality of ceramic substrates 2. When dividing a ceramic sintered substrate into a plurality of ceramic substrates 2, the front and back surfaces of the ceramic sintered substrate are preferably rectangular with short sides of 10 cm or more and long sides of 20 cm or more. As described above, if the front and back surfaces of the ceramic sintered substrate to be processed are large, a larger number of ceramic substrates 2 can be obtained from one scribe substrate 1. Therefore, ceramic substrates 2 can be efficiently divided.

[0032] It is preferable that the assist gas be 70% or more in terms of the sum of the partial pressures of nitrogen or rare gas. However, since nitrogen or rare gas is expensive, it is also possible to add air. If the partial pressure of oxygen contained in the assist gas exceeds 20%, there is a possibility that the surface of the ceramic other than the oxide may be oxidized. For this reason, it is preferable that the partial pressure of oxygen is low, 20% or less.

[0033] Furthermore, the thickness of the ceramic sintered substrate, i.e., the thickness of the ceramic substrate 2, is preferably 0.1 mm or more and 2 mm or less. If it is thicker than 2 mm, it may not be possible to blow it off with the assist gas. On the other hand, if it is thin, less than 0.1 mm, it may not be possible to maintain sufficient strength. A more preferable thickness of the ceramic substrate 2 is 0.2 mm or more and 1 mm or less. A thickness of 0.2 mm or more and 1 mm or less of the ceramic substrate 2 is preferable because it allows for highly efficient processing while maintaining sufficient strength.

[0034] Furthermore, the obtained scribed substrate 1 is preferably cleaned in a cleaning step after the removing step ST2, in which the surface is cleaned by honing, blasting, or the like.

[0035] After the removal step ST2, the scribed substrate 1 is divided into ceramic substrates 2 in a pre-bonding division step ST4 (shown in FIG. 7). Then, in a pre-division joining step ST5 (shown in FIG. 7), a metal circuit such as a metal plate can be joined to the divided ceramic substrate 2 to form a ceramic circuit substrate. FIG. 5 shows an example of a ceramic circuit substrate 8 according to this embodiment. In FIG. 5, reference numeral 8 denotes a ceramic circuit substrate, reference numeral 2 denotes a ceramic substrate, reference numeral 9 denotes a metal circuit, and reference numeral 10 denotes a metal heat sink.

[0036] Examples of metal plates used for the metal circuit 9 include Cu (copper), copper-based alloys, and Al (aluminum). The ceramic substrate 2 and the metal circuit 9 are preferably bonded via a bonding layer (not shown). Furthermore, when bonding the metal heat sink 10, it is also preferable to bond it to the ceramic substrate 2 via a bonding layer. Furthermore, it is preferable to provide a bonding layer between the ceramic substrate 2 and the metal circuit 9 using an active metal brazing material containing an active metal such as Ti (titanium). In addition to Ti, examples of active metals include Zr (zirconium). In addition to Ti, examples of active metal brazing materials include a mixture containing either Ag (silver) or Cu as a main component.

[0037] In addition, the active metal brazing material contains 0.1 wt% to 10 wt%, Cu from 10 wt% to 60 wt%, and Ag as the balance. If necessary, the active metal brazing material may contain one or more elements selected from In (indium), Sn (tin), Al, Si (silicon), C (carbon), and Mg (magnesium) in an amount of 1 wt% to 15 wt%. The active metal bonding method using the active metal brazing material involves applying an active metal brazing material paste to the surface of a ceramic substrate 2, placing a metal circuit 9 on top, and heating the substrate to 600°C to 900°C to bond the substrate. The active metal bonding method can achieve a bonding strength of 16 kN / m or more between the ceramic substrate 2 and the metal circuit 9, which is a copper circuit board.

[0038] Furthermore, a metal thin film (not shown) containing one selected from Ni (nickel), Ag (silver), and Au (gold) as a main component may be provided on the surface of the metal circuit 9. Examples of such a metal thin film include a plated film and a sputtered film. By providing a metal thin film on the surface of the metal circuit 9, the corrosion resistance and solder wettability of the metal circuit 9 can be improved.

[0039] Although the method of manufacturing the ceramic circuit substrate 8 by dividing the ceramic substrate 2 before bonding the metal circuit has been described, the present invention is not limited to this. Before dividing the ceramic substrate 2 into individual ceramic substrates 2 in the pre-division bonding step ST6 (shown in FIG. 7 ), a metal circuit 9 may be bonded to the ceramic substrate 2 in the state of the scribed substrate 1 shown in FIG. 1 , and then divided in the post-bonding dividing step ST7 (shown in FIG. 7 ) to obtain the ceramic circuit substrate 8. In this case, the bonded metal circuit 9 is preferably a copper or aluminum member. The bonded metal circuit 9 is preferably a copper or aluminum member because of its excellent thermal conductivity. The copper or aluminum member refers to copper or a copper alloy, aluminum, or an aluminum alloy. Furthermore, when bonding the metal circuit 9 to the ceramic substrate 2, a conductor having a predetermined shape may be bonded in advance. If the pre-division bonding step ST6 for providing the metal circuit 9 involves bonding the metal circuit 9, the metal circuit 9 to be bonded preferably undergoes a process such as etching or chemical polishing after the pre-division bonding step ST6.

[0040] The ceramic circuit substrate 8 obtained in steps ST4, ST5 and steps ST6, ST7 is preferably used in a semiconductor module in which a semiconductor element is mounted on the metal circuit 9 via a bonding layer.

[0041] An example of a semiconductor module (semiconductor device) according to an embodiment is shown in Fig. 6. In Fig. 6, reference numeral 8 denotes a ceramic circuit substrate, reference numeral 11 denotes a semiconductor module, reference numeral 12 denotes bonding wires, reference numeral 13 denotes a semiconductor element, reference numeral 14 denotes a resin mold, and reference numeral 15 denotes a lead frame.

[0042] In FIG. 6 , a semiconductor element 13 is bonded onto a metal circuit 9 of a ceramic circuit board 8 via a bonding layer (not shown). Similarly, a lead frame 15 is bonded onto the metal circuit 9 via a bonding layer (not shown). Adjacent metal circuits 9 are electrically connected to each other via bonding wires 12. In FIG. 6 , in addition to the semiconductor element 13, bonding wires 12 are also bonded to the metal circuit 9. The ceramic circuit board 8 to which the bonding wires 12 are connected is integrated with a resin mold 14 to form a semiconductor module 11. The semiconductor module 11 is not limited to this structure. For example, either the bonding wires 12 or the lead frames 15 may be provided. Furthermore, a plurality of semiconductor elements 13, bonding wires 12, and lead frames 15 may be provided on the metal circuit 9.

[0043] The bonding layer for bonding the semiconductor element 13 and the lead frame 15 may be made of solder, brazing filler metal, or the like. Lead-free solder is preferable. Solder refers to a material with a melting point of 450°C or less. Brazing filler metal refers to a material with a melting point of more than 450°C. A material with a melting point of 500°C or more is called a high-temperature brazing filler metal. An example of a high-temperature brazing filler metal is one containing Ag as its main component.

[0044] While semiconductor elements 13 continue to become smaller, the amount of heat generated from the chip continues to increase. Therefore, improving the heat dissipation properties of the ceramic circuit board 8 on which the semiconductor elements 13 are mounted is becoming increasingly important. Furthermore, to improve the performance of the semiconductor module 11, multiple semiconductor elements 13 are now mounted on the ceramic circuit board 8. If even one of the semiconductor elements 13 exceeds its intrinsic temperature, the resistance changes to a negative temperature coefficient. This can lead to thermal runaway, where power flows intensively, resulting in instantaneous destruction. Therefore, improving heat dissipation properties is effective.

[0045] The semiconductor module 11 can also be used in modules such as PCUs (Power Control Units), IGBTs (Insulated Gate Bipolar Transistors), and IPMs (Intelligent Power Modules) used in inverters for automobiles (including electric vehicles), electric railcars, industrial machinery, and air conditioners. The automotive industry is moving toward electric vehicles. Improving the reliability of the semiconductor module 11 directly leads to improved automobile safety. The same can be said for electric railcars, industrial machinery, and air conditioners.

[0046] (Silicon nitride sintered substrate) Next, a laser scribing method for a silicon nitride sintered substrate among ceramic sintered substrates will be described. The laser scribing method for a silicon nitride sintered substrate is not particularly limited, but the following method may be used to obtain a silicon nitride scribed substrate as the scribed substrate 1 with a good yield.

[0047] First, a silicon nitride sintered substrate is prepared. In particular, considering the heat dissipation properties of the entire ceramic circuit substrate 8 produced from the silicon nitride sintered substrate, it is preferable that the silicon nitride sintered substrate have a thermal conductivity of 50 W / m·K or more and a three-point bending strength of 600 MPa or more.

[0048] Furthermore, when conducting electrical connection between the metal circuit 9 and the metal heat sink 10, a silicon nitride scribed substrate having through holes is prepared. The silicon nitride scribed substrate having through holes may be obtained by sintering a molded body having through holes, or by providing through holes in a silicon nitride sintered substrate. In the latter case, the step of providing through holes in the silicon nitride sintered substrate is carried out by cutting or laser processing similar to laser scribing. Cutting is carried out by drilling or the like.

[0049] The silicon nitride sintered substrate is set on the precision processing table of a laser processing machine. The silicon nitride sintered substrate is irradiated with a laser to form side scribe lines 3 and corner scribe lines 4, thereby obtaining a silicon nitride scribed substrate as a scribed substrate 1. At this time, dots of a predetermined size are formed according to the conditions of the laser processing machine.

[0050] Next, in the pre-bonding division process ST4, stress is applied to the silicon nitride scribe substrate 1 as the scribe substrate 1 to divide the silicon nitride scribe substrate 1 along the scribe lines, thereby producing silicon nitride substrates as one or more ceramic substrates 2.

[0051] Next, in the post-division bonding step ST5, the metal circuit 9 is bonded to the silicon nitride substrate serving as the ceramic substrate 2. The bonding of the silicon nitride substrate and the metal circuit 9 is preferably performed by an active metal bonding method. The active metal bonding method uses an active metal brazing material containing an active metal such as Ti. Examples of the active metal brazing material include a mixture of Ti, Ag, and Cu. For example, the active metal brazing material contains 0.1 wt% to 10 wt% of Ti, 10 wt% to 60 wt% of Cu, and the remainder is Ag. If necessary, the active metal brazing material may contain 1 wt% to 15 wt% of one or more selected from In, Sn, Al, Si, C, and Mg.

[0052] The active metal brazing filler metal is made into a paste. The paste is a mixture of brazing filler metal components and organic matter, but the brazing filler metal components must be mixed evenly. This is because uneven distribution of the brazing filler metal components results in unstable brazing and poor joint performance.

[0053] The active metal brazing paste is applied to a silicon nitride substrate as the ceramic substrate 2. A copper plate as the metal circuit 9 is placed on top of the applied paste. Next, the process of heating and bonding is performed at a temperature of 600°C to 900°C. The heating process is performed in a vacuum or a non-oxidizing atmosphere as required. When the heating process is performed in a vacuum, the temperature is set to 1×10 －２ The pressure is preferably 0.1 Pa or less. Examples of the non-oxidizing atmosphere include a nitrogen atmosphere and an argon atmosphere. By using a vacuum or a non-oxidizing atmosphere, the bonding layer can be prevented from being oxidized, thereby improving the bonding strength.

[0054] The metal circuit 9 to be bonded may be either one that has been pre-patterned for circuit formation, or a single plate that has not been patterned. If a single plate is used, it is etched after bonding to form the pattern. This process allows for the production of a silicon nitride metal circuit board as the ceramic circuit substrate 8.

[0055] Following the post-division bonding step ST5, a step of bonding the semiconductor element 13 and other components is performed. A bonding layer is provided at the location where the semiconductor element 13 is to be bonded. The bonding layer is preferably made of solder or brazing material. The bonding layer is provided, and the semiconductor element 13 is provided on top of it. If necessary, the lead frame 15 is bonded via the bonding layer. If necessary, bonding wires 12 are also provided. The required number of semiconductor elements 13, lead frames 15, and bonding wires 12 are also provided. The silicon nitride circuit board 8 with the semiconductor elements 13, lead frames 15, and bonding wires 12 attached is integrated with a resin mold 14 to seal the interior.

[0056] In the above, it has been explained that the ceramic circuit substrate 8 is manufactured by bonding the metal circuit 9 and the like to the ceramic substrate 2 after separation from the scribe substrate 1 (steps ST4 and ST5), but this is not limited to this case. For example, the ceramic circuit substrate 8 may be manufactured by bonding the metal circuit 9 and the like to the ceramic substrate 2 before separation in the scribe substrate 1, and then applying stress to the scribe substrate 1 with the bonded metal circuit 9 and the like to separate it along the scribe line (steps ST4 and ST5). In other words, the order of the step of separating the scribe substrate 1 and the step of bonding the metal circuit 9 and the like does not matter.

[0057] (Aluminum Nitride Sintered Substrate) Next, a laser scribing method for an aluminum nitride sintered substrate, which is one of the ceramic sintered substrates, will be described. First, an aluminum nitride sintered substrate is prepared. In particular, considering the heat dissipation properties of the entire ceramic circuit board 8, it is preferable that the aluminum nitride sintered substrate have a thermal conductivity of 170 W / m·K or more and a three-point bending strength of 350 MPa or more. The laser scribing method for an aluminum nitride sintered substrate is not particularly limited, but in order to obtain an aluminum nitride scribed substrate as the scribed substrate 1 with a good yield, the same method as that for the silicon nitride scribed substrate described above is used.

[0058] (Examples 1 to 18, Comparative Examples 1 and 2) For each of the Examples and Comparative Examples shown in Table 1, 100 ceramic sintered substrates were prepared. The ceramic sintered substrates were silicon nitride sintered substrates, aluminum nitride sintered substrates, aluminum oxide (alumina) sintered substrates, and aluzirconia (alumina zirconia) sintered substrates. ３ N ４ The thermal conductivity of the aluminum nitride (AlN) sintered substrate is 90 W / m·K and the three-point bending strength is 650 MPa. The thermal conductivity of the aluminum nitride (AlN) sintered substrate is 170 W / m·K and the three-point bending strength is 300 MPa. The aluminum oxide (Al ２ O ３The thermal conductivity of the sintered substrate is 25 W / m·K and the three-point bending strength is 400 MPa. The thermal conductivity of the aridil-sintered substrate is 25 W / m·K and the three-point bending strength is 650 MPa. The front and back surfaces of the ceramic sintered substrates in the examples and comparative examples are 14 cm x 27 cm. The thickness of the ceramic sintered substrates in the examples and comparative examples is 0.32 mm for the silicon nitride sintered substrate and 0.64 mm for the aluminum nitride sintered substrate, aluminum oxide sintered substrate, and aridil-sintered substrate.

[0059] In the example, side scribe lines 3 (shown in FIG. 1 ) are formed on the sintered ceramic substrate by laser processing in the laser processing step ST1. The injection pressure of the assist gas injected during laser irradiation to remove the molten material when forming the side scribe lines 3 is 0.1 MPa (oxygen partial pressure 0%). Then, corner scribe lines 4 of the same shape and area were formed on the four corners of each ceramic substrate 2. The surface area of ​​the C-face portion 44 cut by one C-face 43 of one ceramic substrate 2 shown in FIG. 2 (average value for 100 scribed substrates 1) is shown in Table 1.

[0060] The C-plane portions 44 refer to portions of the removed portion 6 that correspond to the respective ceramic substrates 2. For example, in the first removed portion 61, the surface area of ​​each of the two C-plane portions 44 is half the surface area of ​​the first removed portion 61. In the second removed portion 62, the surface area of ​​each of the four C-plane portions 44 is one-fourth the surface area of ​​the second removed portion 62. In the third removed portion 63, the surface area of ​​the single C-plane portion 44 is the same as the surface area of ​​the third removed portion 63.

[0061] Furthermore, the injection pressure of the assist gas during laser irradiation when forming the angular scribe line 4 is shown as the injection pressure in Table 1. In Comparative Examples 1 and 5 to 7, during laser irradiation when forming the angular scribe line 4, no assist gas was even injected for the purpose of discharging the molten material. Furthermore, a nitrogen-based assist gas was used, and the oxygen partial pressure in the assist gas is shown as the oxygen partial pressure in Table 1. Laser processing was also performed on a ceramic sintered substrate under the conditions related to the comparative examples in Table 1 to produce a scribed substrate.

[0062]

[0063] After the laser processing step ST1 and the removal step ST2, the appearance of 100 scribed substrates 1 for each example was inspected, and those in which the removed portion 6 remained on the scribed substrate 1 were deemed to have been defective. The removal defect rate [%] was calculated as the percentage of scribed substrates with removal defects out of the 100 scribed substrates 1 for each example. For each example, those in which discoloration was observed around the scribe lines 3 and 4 of the scribed substrate 1 were deemed to have been defective in discoloration, and the discoloration defect rate [%] was calculated similarly. For each example, those in which the scribe lines 3 and 4 of the scribed substrate 1 deviated from the design tolerance were deemed to have been defective in dimensional accuracy, and the dimensional accuracy defect rate [%] was calculated similarly. The respective defect rates are shown in Table 2. Similarly, the removal defect rate [%], discoloration defect rate [%], and dimensional accuracy defect rate [%] were calculated for cases in which laser processing was performed on a ceramic sintered substrate under the conditions of the comparative example in Table 1.

[0064]

[0065] As can be seen from Table 2, in the scribed substrate 1 manufactured under the conditions of the examples in Table 1, either no removal defects occurred or the removal defect rate was small, at 2% or less. This is because the removal portion 6 was properly removed by the ejection of assist gas. In contrast, in the scribed substrate manufactured under the conditions of the comparative examples in Table 1, there were many removal defects, and the removal defect rate was high, at 9% or more. This is because, under the conditions of comparative examples 1 and 5 to 7, no assist gas was used, so the assist gas did not hit the removal portion 6, and therefore the removal portion 6 could not be completed. Under the conditions of comparative examples 2 and 3, the pressure of the assist gas injected during laser irradiation was low, so sufficient pressure was not applied to the removal portion 6, and therefore the removal portion 6 could not be completed. Under the conditions of comparative example 4, the pressure of the assist gas injected during laser irradiation was too high, so the position of the scribed substrate was shifted, and the assist gas did not hit the necessary location, and therefore the removal portion 6 could not be completed.

[0066] Furthermore, the scribed substrates 1 manufactured under the conditions of the Example did not suffer from discoloration defects or had a small discoloration defect rate of 1% or less. This is because oxidation of the surface of the scribed substrate 1 was prevented by keeping the oxygen partial pressure low. In contrast, the scribed substrates manufactured under the conditions of Comparative Examples 1 to 5 suffered from many discoloration defects, with a high discoloration defect rate of 16% or more. This is because Comparative Examples 1 to 5 are scribed substrates using nitride-based ceramic sintered substrates, and no assist gas was used or the oxygen partial pressure was high, causing oxidation of the surface of the scribed substrate.

[0067] According to at least one of the embodiments described above, the scribe substrate 1, the ceramic substrate 2, and the ceramic circuit substrate 8 can be efficiently manufactured without defects from a high-strength, thin ceramic sintered substrate with large front and back surfaces that combines heat dissipation and electrical insulation properties.

[0068] Although several embodiments of the present invention have been described above, these embodiments are presented by way of example only and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. Modifications of these embodiments are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims. Furthermore, the above-described embodiments can be implemented in combination with each other.

Claims

1. A method for manufacturing a ceramic scribed substrate that includes a ceramic substrate as an element, comprising: a laser processing step of irradiating a surface of a sintered ceramic substrate with a laser to form continuous through grooves as scribe lines and form removed portions surrounded by a plurality of said scribe lines; and a removal step of removing said removed portions by injecting an assist gas coaxially with the laser during the laser irradiation.

2. A method for producing a ceramic scribed substrate according to claim 1, wherein the ejection pressure of the assist gas is 0.2 MPa or more and 1.0 MPa or less.

3. A method for manufacturing a ceramic scribed substrate according to claim 1 or 2, wherein the surface area of ​​the C-face portion of each of the removed portions of the ceramic substrate is 1.0 mm ２ More than 20.0 mm ２ A method for producing a ceramic scribed substrate, comprising:

4. A method for manufacturing a ceramic scribe substrate according to claim 1 or 2, wherein the ceramic sintered substrate is an aluminum nitride substrate or a silicon nitride substrate, and the oxygen partial pressure contained in the assist gas is 20% or less.

5. A method for manufacturing a ceramic scribed substrate as described in claim 1 or 2, wherein the removal step is performed during the laser irradiation, and the removal portion is removed by spraying the assist gas after the laser irradiation.

6. A method for manufacturing a ceramic scribed substrate as described in claim 1 or 2, wherein the removal step removes the portion to be removed by injecting an assist gas coaxially with the laser during irradiation of the laser when forming a corner scribe line among the plurality of scribe lines.

7. A method for manufacturing a ceramic substrate comprising: a laser processing step and a removal step included in the method for manufacturing a ceramic scribed substrate as described in claim 1; and a pre-bonding division step of manufacturing a ceramic substrate by applying stress to the ceramic scribed substrate after the removal step to divide it along the multiple scribe lines.

8. A method for producing a ceramic circuit board, comprising the laser processing step, the removing step, and the pre-joining dividing step of the method for producing a ceramic circuit board as set forth in claim 7, and a post-division joining step of manufacturing a ceramic circuit board by joining a metal circuit to the ceramic board.

9. A method for manufacturing a ceramic circuit board, comprising: a laser processing step and a removal step of the method for manufacturing a ceramic scribed substrate as described in claim 1; a pre-division joining step of joining a metal circuit to the ceramic scribed substrate after the removal step; and a post-division step of applying stress to the ceramic scribed substrate to which the metal circuit is joined, thereby dividing it along the scribe line to manufacture a ceramic circuit board.

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