Aluminum nitride plate and its manufacturing method, composite substrate and its manufacturing method, and circuit substrate and its manufacturing method

Abstract

Provided is a method for producing an aluminum nitride plate having a scribe line in the surface thereof, the method having a step for using a laser beam to form a plurality of holes in the surface of a base material containing aluminum nitride so as to provide the scribe line. Each of the plurality of holes is formed by radiating laser light multiple times.

Description

[Technical field]

[0001] The present disclosure relates to an aluminum nitride plate and a manufacturing method thereof, a composite substrate and a manufacturing method thereof, and a circuit substrate and a manufacturing method thereof. [Background technology]

[0002] An insulating ceramic plate may be used for a circuit board mounted on an electronic device. The following technique, as described in Patent Document 1, is known as a method for manufacturing such a circuit board. That is, a carbon dioxide laser, a YAG laser, or the like is used to provide a scribe line on the surface of a ceramic plate, and then a metal layer is bonded to the surface to form a composite substrate. Then, the metal layer on the surface of the composite substrate is processed into a circuit pattern by etching. After that, the composite substrate is divided along the scribe lines to manufacture a plurality of circuit substrates. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-324301 A Summary of the Invention [Problem to be solved by the invention]

[0004] Aluminum nitride sheets are made into products or parts through various processes such as bonding with metal sheets and forming circuits. As electronic devices become more and more sophisticated, the required quality level is also becoming higher and higher. Under these circumstances, there is concern that foreign matter generated during the manufacturing process may not only deteriorate the appearance but also cause a decrease in product performance.

[0005] Therefore, the present disclosure provides an aluminum nitride plate having excellent reliability while maintaining a good appearance, and a method for manufacturing the same. The present disclosure also provides a composite substrate having excellent reliability while maintaining a good appearance, and a method for manufacturing the same. The present disclosure also provides a circuit board having excellent reliability while maintaining a good appearance, and a method for manufacturing the same. [Means for solving the problem]

[0006] The scribe lines on the aluminum nitride plate need to have a certain depth so that the aluminum nitride plate can be divided smoothly in a later process. In order to form scribe lines with a certain depth, it is necessary to irradiate a laser beam with a suitable energy. However, if the energy of the laser beam becomes too high, the aluminum nitride contained in the base material will burn and change in quality, resulting in the generation of foreign matter. The resulting foreign matter will not scatter sufficiently and will adhere to the periphery of the hole. This will cause contamination of the aluminum nitride plate and a decrease in reliability.

[0007] Therefore, in one aspect, the present disclosure provides a method for manufacturing an aluminum nitride plate having a scribe line on its surface, the method comprising a step of forming a plurality of holes on the surface of a substrate containing aluminum nitride with laser light to provide a scribe line, and each of the plurality of holes is formed by irradiating the laser light multiple times.

[0008] In the above manufacturing method, when forming a plurality of holes that become scribe lines, each hole is formed by irradiating the laser light multiple times. Therefore, the energy of the laser light irradiated per time (one shot) can be reduced compared to the case where holes are formed by only one irradiation. This makes it possible to efficiently use the laser light in forming the holes, and suppress the generation of foreign matter due to scorching. Therefore, it is possible to reduce foreign matter adhering to the periphery of the holes and maintain a good appearance of the aluminum nitride plate. Such an aluminum nitride plate has good bondability with members because it can reduce the oxygen-rich layer adhering to the surface, and therefore has excellent reliability. In addition, it is possible to suppress contamination of each manufacturing facility due to peeling and scattering of the oxygen-rich layer in the later process.

[0009] When the laser beam is irradiated in multiple steps, the energy of the laser beam per shot may be less than 70 mJ, which can sufficiently reduce the amount of an oxygen-rich layer formed inside the hole.

[0010] The aluminum nitride plate obtained by the above manufacturing method may have a hole opening diameter of 50 μm or more and a hole depth of 60 μm or more on the surface. An aluminum nitride plate having scribe lines formed by such holes can be smoothly divided.

[0011] The maximum thickness of the oxygen-rich layer at the periphery of the hole may be 4 μm or less, which satisfactorily reduces the oxygen-rich layer as a foreign matter and satisfactorily suppresses the generation of dirt.

[0012] In one aspect, the present disclosure provides an aluminum nitride plate having a scribe line on its surface, in which the thickness of an oxygen-rich layer at the periphery of a plurality of holes constituting the scribe line is 4 μm or less. In this aluminum nitride plate, the oxygen-rich layer, which is a foreign matter, is sufficiently reduced. Therefore, the generation of dirt can be sufficiently suppressed and a good appearance can be maintained. Such an aluminum nitride plate is also excellent in reliability because the amount of peeling oxygen-rich layer can be reduced. In addition, contamination of each manufacturing facility due to peeling and scattering of the oxygen-rich layer can be reduced.

[0013] The opening diameter of the holes on the surface may be 50 μm or more, and the depth of the holes may be 60 μm or more. An aluminum nitride plate having scribe lines formed by such holes can be divided smoothly.

[0014] In one aspect, the present disclosure provides a method for producing a composite substrate, comprising a step of bonding a metal plate to an aluminum nitride plate so as to cover the surface of the aluminum nitride plate obtained by any one of the above-mentioned production methods to obtain a composite substrate. Since this composite substrate includes an aluminum nitride plate obtained by any one of the above-mentioned production methods, the oxygen-rich layer, which is a foreign matter, is reduced, and a good appearance can be maintained. Since the oxygen-rich layer on the surface of the aluminum nitride plate is reduced, such a composite substrate has good bondability with the metal plate. Therefore, it is also excellent in reliability. In addition, it is possible to reduce contamination of each production facility due to peeling and scattering of the oxygen-rich layer.

[0015] In one aspect, the present disclosure provides a method for manufacturing a circuit board, comprising the steps of removing a portion of the metal plate in the composite substrate obtained by the above-mentioned manufacturing method, and forming an independent conductor portion for each partition portion defined by a scribe line to obtain a circuit board. Since this circuit board uses the composite substrate obtained by the above-mentioned manufacturing method, the oxygen-rich layer, which is a foreign matter, is reduced, and a good appearance can be maintained. Since such a circuit board can reduce the oxygen-rich layer peeling off from the holes in the aluminum nitride plate, the bonding between the conductor portion and the aluminum nitride plate is good. Therefore, the reliability is also excellent. In addition, the contamination of each manufacturing facility due to peeling and scattering of the oxygen-rich layer can be reduced.

[0016] In one aspect, the present disclosure provides a composite substrate comprising any one of the aluminum nitride plates described above and a metal plate bonded to the aluminum nitride plate so as to cover the surface of the aluminum nitride plate. Since the composite substrate comprises any one of the aluminum nitride plates described above, the oxygen-rich layer, which is a foreign matter, is reduced, and a good appearance can be maintained. Since the oxygen-rich layer on the surface of the aluminum nitride plate is reduced, such a composite substrate has good bondability with the metal plate. Therefore, the composite substrate is also excellent in reliability. In addition, contamination of each manufacturing facility due to peeling and scattering of the oxygen-rich layer can be reduced.

[0017] In one aspect, the present disclosure provides a circuit board comprising any one of the aluminum nitride plates described above and a conductor portion provided on the surface so as to be independent of each partition portion defined by a scribe line. Since this circuit board comprises any one of the aluminum nitride plates described above, foreign matter is reduced and a good appearance can be maintained. In addition, since the oxygen-rich layer on the surface of the aluminum nitride plate is reduced, bonding with the conductor portion is good. Therefore, reliability is also excellent. In addition, contamination of each manufacturing facility due to peeling and scattering of the oxygen-rich layer can be reduced. Effect of the Invention

[0018] According to the present disclosure, it is possible to provide an aluminum nitride plate having excellent reliability while maintaining a good appearance, and a manufacturing method thereof. It is also possible to provide a composite substrate having excellent reliability while maintaining a good appearance, and a manufacturing method thereof. It is also possible to provide a circuit board having excellent reliability while maintaining a good appearance, and a manufacturing method thereof. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a perspective view of an aluminum nitride plate according to one embodiment. [Diagram 2] FIG. 2 is a cross-sectional view of the aluminum nitride plate shown in FIG. 1 taken along line II-II. [Diagram 3] FIG. 3 is a cross-sectional view of the aluminum nitride plate shown in FIG. 1 taken along line III-III. [Figure 4] FIG. 4 is a partially enlarged view showing a scribe line provided on a portion of the surface of an aluminum nitride plate. [Diagram 5] FIG. 5 is a cross-sectional view of the aluminum nitride plate of FIG. 4 taken along line VV. [Figure 6] FIG. 6 is an enlarged cross-sectional view of a portion of an aluminum nitride plate where a hole is formed. [Figure 7] FIG. 7 is a perspective view showing an example of an aluminum nitride plate to which a brazing material is applied. [Figure 8] FIG. 8 is a perspective view of a composite substrate according to an embodiment. [Figure 9] FIG. 9 is a perspective view showing an example of a composite substrate having a resist pattern formed on the surface thereof. [Figure 10] FIG. 10 is a perspective view of a circuit board according to an embodiment. [Figure 11] FIG. 11 is an SEM photograph of the surface and cross section of the aluminum nitride plate of Example 1 in which a plurality of holes constituting the scribe lines are formed. [Figure 12] FIG. 12 is an SEM photograph of the surface and cross section of the aluminum nitride plate of Example 2 in which a plurality of holes constituting the scribe lines are formed. [Figure 13]FIG. 13 is an SEM photograph of the surface and cross section of the aluminum nitride plate of Comparative Example 1 in which a plurality of holes constituting scribe lines were formed. [Figure 14] FIG. 14 is a SEM photograph taken at 120 and 500 magnifications of the cross section of an aluminum nitride plate with a hole formed therein. [Figure 15] FIG. 15 is an SEM photograph taken at 800 times magnification of the cross section of an aluminum nitride plate with a hole formed therein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings as needed. However, the following embodiment is an example for explaining the present disclosure, and is not intended to limit the present disclosure to the following content. In the description, the same reference numerals are used for the same elements or elements having the same functions, and redundant descriptions are omitted as needed. Furthermore, positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings, unless otherwise specified. Furthermore, the dimensional ratios of each element are not limited to the ratios shown in the drawings.

[0021] Fig. 1 is a perspective view of an aluminum nitride plate according to one embodiment. The aluminum nitride plate 100 in Fig. 1 has a flat plate shape. A surface 100A of the aluminum nitride plate 100 is divided into a plurality of sections by scribe lines. The surface 100A is provided with a plurality of scribe lines L1 extending along a first direction and arranged at equal intervals, and a plurality of scribe lines L2 extending along a second direction perpendicular to the first direction and arranged at equal intervals. The scribe lines L1 and L2 are perpendicular to each other.

[0022] The scribe lines L1, L2 are composed of a plurality of holes formed by laser light. Examples of the laser source include a carbon dioxide laser and a YAG laser. The scribe lines can be provided by forming a plurality of holes along a predetermined direction by intermittently irradiating the laser light from such a laser source. Note that the scribe lines L1, L2 do not have to be arranged at equal intervals, and are not limited to being perpendicular to each other. Moreover, they may be curved or bent instead of straight.

[0023] Fig. 2 is a cross-sectional view taken along line II-II in Fig. 1, and Fig. 3 is a cross-sectional view taken along line III-III in Fig. 1. As shown in Figs. 1, 2, and 3, the partition 10 is composed of a three-dimensional area surrounded by a region on one surface 100A surrounded by scribe lines L1, L2, a region on the other surface 100B corresponding to said region, and virtual lines VL1, VL2 drawn parallel to the thickness direction of the aluminum nitride plate 100 from the scribe lines L1, L2. That is, the aluminum nitride plate 100 has a plurality of partitions 10 (9 in Fig. 1) defined by the scribe lines L1 and L2.

[0024] 1, 2 and 3 show an example in which the scribe lines L1, L2 are formed only on one surface 100A of the aluminum nitride plate 100, but the present invention is not limited to this example. In other words, the scribe lines L1, L2 may also be formed on the surface 100B of the aluminum nitride plate 100 opposite to the surface 100A.

[0025] FIG. 4 is a partially enlarged view showing a scribe line L1 provided on a part of the surface 100A of the aluminum nitride plate 100. The scribe line L1 (L2) is composed of a plurality of holes 20 arranged along the longitudinal direction. The adjacent holes 20 may be connected to each other or may be separated from each other. The opening 20E of the hole 20 on the surface 100A may be circular. The diameter of the opening 20E, i.e., the opening diameter r, may be 50 μm or more, or may be 70 μm or more. The aluminum nitride plate 100 having the scribe line L1 (L2) composed of the holes 20 having such an opening diameter r can be smoothly divided along the scribe line L1 (L2). From the viewpoint of maintaining the mechanical strength of the aluminum nitride plate 100, the opening diameter r may be 400 μm or less, or may be 300 μm or less. In a modified example, the adjacent holes 20 may be separated from each other. In another modified example, the adjacent holes 20 may be partially overlapped with each other.

[0026] 5 is a cross-sectional view of line VV in FIG. 4. That is, FIG. 5 is a cross-sectional view of the aluminum nitride plate 100 cut along a plane that passes through the scribe line L1 (L2) and is perpendicular to the surface 100A. The hole 20 has a cone shape that tapers from the opening 20E toward the inside of the aluminum nitride plate 100. The hole 20 has a depth d from the opening 20E to the bottom 20B on the surface 100A. When the thickness of the aluminum nitride plate 100 is 0.2 to 2 mm, the depth d may be 60 μm or more, or may be 70 μm or more. The aluminum nitride plate 100 having the scribe line L1 (L2) formed by the hole 20 having such a depth d can be smoothly divided along the scribe line L1 (L2). From the viewpoint of maintaining the mechanical strength of the aluminum nitride plate 100, the depth d may be half or less, or may be one-third or less, of the thickness of the aluminum nitride plate 100. The depths d of the multiple holes 20 may be the same or different.

[0027] 6 is a cross-sectional view of the aluminum nitride plate 100 cut along a plane perpendicular to the surface 100A and perpendicular to the longitudinal direction of the scribe lines L1 (L2). As shown in FIG. 6, at least a part of the inner surface of the cone-shaped hole 20 may be covered with an oxygen-rich layer 22. The maximum thickness t of the oxygen-rich layer 22 at the peripheral portion 20a of the hole 20 may be 4 μm or less, less than 3 μm, or less than 2 μm. The oxygen-rich layer 22 is a region in which the oxygen concentration on a mass basis is three times or more higher than that of the surface 100A of the aluminum nitride plate 100 in the portion where the scribe lines L1, L2 are not formed. The oxygen concentration can be measured by an EPMA (electron probe microanalyzer).

[0028] The oxygen-rich layer 22 is composed of foreign matter other than aluminum nitride. The oxygen-rich layer 22 may contain, for example, an oxide. The oxide may be, for example, aluminum oxide. Such oxide does not scatter sufficiently when a hole is formed by a laser beam, and adheres to the peripheral portion 20a of the hole 20. Therefore, by reducing the maximum thickness t of the oxygen-rich layer 22 at the peripheral portion 20a of the hole 20, it is possible to suppress the generation of dirt and improve the bondability with other members. Such an aluminum nitride plate 100 has an excellent appearance and is also excellent in reliability. In addition, it is possible to reduce contamination of each manufacturing facility by the oxygen-rich layer 22. The maximum thickness t is measured along a direction perpendicular to the surface 100A.

[0029] 6 shows an example in which not only the peripheral portion 20a of the hole 20 but also a part of the inner surface of the hole 20 is covered with the oxygen-rich layer 22, but is not limited to such an example. For example, the entire inner surface of the hole 20 may be covered with the oxygen-rich layer 22, or the inner surface of the hole 20 may not be covered at all with the oxygen-rich layer 22. In addition, the oxygen-rich layer 22 may not be present in the peripheral portion 20a.

[0030] As a manufacturing method of an aluminum nitride plate according to one embodiment, a manufacturing method of an aluminum nitride plate 100 will be described. The manufacturing method of the aluminum nitride plate 100 includes a step of producing a base material containing aluminum nitride, and a step of forming a plurality of holes on the surface of the base material with a laser beam to provide scribe lines, thereby obtaining the aluminum nitride plate 100.

[0031] The substrate containing aluminum nitride can be manufactured by the following procedure. First, a slurry containing aluminum nitride powder, binder resin, sintering aid, plasticizer, dispersant, solvent, etc. is molded to obtain a green sheet. Examples of the sintering aid include rare earth metals, alkaline earth metals, metal oxides, fluorides, chlorides, nitrates, and sulfates. These may be used alone or in combination of two or more. The use of the sintering aid can promote the sintering of the inorganic compound powder. Examples of the binder resin include methyl cellulose, ethyl cellulose, polyvinyl alcohol, polyvinyl butyral, and (meth)acrylic resins.

[0032] Examples of the plasticizer include purified glycerin, glycerin trioleate, diethylene glycol, phthalic acid plasticizers such as di-n-butyl phthalate, and dibasic acid plasticizers such as di-2-ethylhexyl sebacate. Examples of the dispersant include poly(meth)acrylate and (meth)acrylic acid-maleate copolymer. Examples of the solvent include organic solvents such as ethanol and toluene.

[0033] Examples of the method for forming the slurry include the doctor blade method and the extrusion molding method. A green sheet is produced by such a method. The green sheet is degreased and sintered to obtain a base material containing aluminum nitride. The degreasing may be performed, for example, by heating at 400 to 800°C for 0.5 to 20 hours. This makes it possible to reduce the amount of residual organic matter (carbon) while suppressing oxidation and deterioration of the aluminum nitride. The sintering may be performed by heating to 1700 to 1900°C in a non-oxidizing gas atmosphere such as nitrogen, argon, ammonia, or hydrogen.

[0034] The above-mentioned degreasing and sintering may be performed in a state where a plurality of green sheets are laminated. When the green sheets are laminated and degreasing and sintered, a release layer made of a release agent may be provided between the green sheets in order to facilitate separation of the base material after firing. For example, boron nitride (BN) may be used as the release agent. The release layer may be formed by applying a slurry of boron nitride powder by a method such as spraying, brushing, roll coating, or screen printing. The number of green sheets to be laminated may be, for example, 8 to 50 sheets, or may be 10 to 50 sheets, from the viewpoint of efficiently mass-producing the base material while sufficiently proceeding with degreasing.

[0035] A laser beam is irradiated onto the surface of the aluminum nitride-containing substrate thus obtained to form a plurality of holes. As a result, an aluminum nitride plate 100 having scribe lines L1, L2 on the surface 100A is obtained, as shown in Figs. 1 to 3. Examples of the laser beam include a carbon dioxide gas laser and a YAG laser. Each of the plurality of holes 20 shown in Figs. 4 and 5 is formed by irradiating the laser beam multiple times. As a result, the energy of the laser beam irradiated per shot (one shot) can be reduced compared to the case where a hole is formed by irradiating only once. Therefore, it is possible to efficiently use the laser beam to form the holes 20, and deterioration due to scorching of the aluminum nitride can be suppressed. As a result, the generation of the oxygen-rich layer 22, which is a foreign matter, and the adhesion to the peripheral portion 20a of the hole 20 can be suppressed, and the good appearance of the aluminum nitride plate can be maintained. Such an aluminum nitride plate 100 has good bondability with a metal plate, which will be described later, because the oxygen-rich layer 22 on the surface 100A can be reduced. Therefore, it has excellent reliability. Furthermore, contamination of the aluminum nitride plate 100 and each manufacturing facility that uses the aluminum nitride plate 100 can be reduced.

[0036] The holes 20 may be formed by a burst pulse mode or a cycle pulse mode. The burst pulse mode is performed according to the following procedure. The first hole 20 is formed by irradiating the same position with a laser beam divided into a number of times. Next, the second hole 20 is formed by irradiating the same position with a laser beam divided into a number of times so as to be adjacent to the first hole 20. In this way, two holes 20 adjacent to each other are formed. This procedure is repeated a number of times to form n holes 20 (n is a positive integer of 2 or more). In this way, a scribe line L1 (L2) consisting of n holes 20 can be formed. When irradiating the laser beam twice to form one hole 20, the laser beam is irradiated divided into 2n times to form n holes 20.

[0037] The cycle pulse mode is performed, for example, in the following manner. The first to n-th holes 20 are each formed by irradiating the laser light once. After that, the first to n-th holes 20 are irradiated with the laser light once again. In this case, the laser light is irradiated 2n times to form n holes 20. The laser light may be irradiated three or more times to form each hole 20. From the viewpoint of work efficiency, the number of times (number of shots) of irradiating the laser light to form each hole 20 may be 10 or less. The method of forming the holes 20 is not limited to the above two methods. For example, the burst pulse mode and the cycle pulse mode may be combined.

[0038] The interval between multiple laser light irradiations to form one hole 20 may be 1200 μsec or more (850 Hz or less) or 1500 μsec or more (670 Hz or less) to ensure cooling time for the aluminum nitride plate 100 heated by the laser light irradiation.

[0039] The energy of the laser light irradiated per time, i.e., the energy per shot, may be less than 70 mJ, may be 50 mJ or less, or may be 30 mJ or less. By reducing the energy irradiated per time in this manner, the maximum thickness t of the oxygen-rich layer 22 formed on the periphery of the hole 20 can be sufficiently reduced. From the viewpoint of efficiently forming the hole 20, the energy of the laser light irradiated per time may be 5 mJ or more, or may be 10 mJ or more.

[0040] From the viewpoint of forming a sufficiently large hole 20 on the surface 100A of the aluminum nitride plate 100 while reducing damage to the aluminum nitride plate 100, the pulse width of the laser light may be 30 to 200 μsec, or may be 50 to 150 μsec.

[0041] By providing the scribe lines L1, L2 in this manner, it is possible to obtain the aluminum nitride plate 100. The scribe lines L1, L2 will become cutting lines when dividing the aluminum nitride plate 100 (circuit board) in a later process.

[0042] In the above-mentioned method for manufacturing an aluminum nitride plate, the holes 20 constituting the scribe lines L1 (L2) are each formed by irradiating the laser light multiple times. Therefore, the energy of the laser light irradiated per time (one shot) can be reduced compared to the case where the holes are formed by irradiating only once. This reduces foreign matter adhering to the periphery of the hole 20, and the aluminum nitride plate 100 can maintain a good appearance. Since such an aluminum nitride plate 100 can reduce the oxygen-rich layer adhering to the surface, it has good bondability with members and is also highly reliable. In addition, it is possible to suppress contamination of each manufacturing facility due to peeling and scattering of the oxygen-rich layer 22 in a later process.

[0043] A manufacturing method for a composite substrate according to one embodiment uses the aluminum nitride plate 100 described above. That is, this manufacturing method includes a step of laminating a pair of metal plates so as to cover the surfaces 100A and 100B of the aluminum nitride plate 100, respectively, and bonding the pair of metal plates to the aluminum nitride plate 100 to obtain a composite substrate. The metal plates may have a flat plate shape similar to that of the aluminum nitride plate 100. The pair of metal plates are bonded to the surfaces 100A and 100B of the aluminum nitride plate 100, respectively, via a brazing material.

[0044] Specifically, first, a paste-like brazing material is applied to a pair of surfaces 100A, 100B of an aluminum nitride plate 100 by a roll coater method, a screen printing method, a transfer method, or the like. The brazing material contains, for example, metal components such as silver and titanium, an organic solvent, and a binder. The viscosity of the brazing material may be, for example, 5 to 20 Pa·s. The content of the organic solvent in the brazing material may be, for example, 5 to 25 mass %, and the content of the binder may be, for example, 2 to 15 mass %.

[0045] Fig. 7 is a perspective view showing an example of an aluminum nitride plate 100 to which a brazing material 40 is applied. As shown in Fig. 7, the brazing material 40 may be applied independently to each partition 10. Although Fig. 7 shows only the front surface 100A side, the brazing material 40 may be applied to the front surface 100B side as well. In a modified example, the brazing material may be applied to the entire surfaces 100A and 100B.

[0046] In this way, a metal plate is bonded to the surface 100A and the surface 100B of the aluminum nitride plate 100 coated with the brazing material 40 to obtain a bonded body. After that, the aluminum nitride plate 100 and the pair of metal plates are sufficiently bonded to obtain a composite substrate by heating in a heating furnace. The heating temperature may be, for example, 700 to 900°C. The atmosphere in the heating furnace may be an inert gas such as nitrogen, and may be under reduced pressure below atmospheric pressure or under vacuum. The heating furnace may be a continuous type that continuously produces a plurality of bonded bodies, or may be a batch type that produces one or a plurality of bonded bodies. Heating may be performed while pressing the bonded bodies in the stacking direction.

[0047] The aluminum nitride plate 100 has a reduced oxygen-rich layer 22 at the peripheral portion 20a of the hole 20 constituting the scribe lines L1, L2, so that a composite substrate having a good appearance can be obtained. In addition, peeling and scattering of the oxygen-rich layer 22 during firing and the like is suppressed, so that contamination inside the heating furnace can be reduced. In addition, since the oxygen-rich layer 22 at the surface 100A is reduced, the bonding property between the metal plate and the aluminum nitride plate 100 can be improved.

[0048] FIG. 8 is a perspective view of a composite substrate according to one embodiment. The composite substrate 200 includes a pair of metal plates 110 arranged to face each other, and an aluminum nitride plate 100 between the pair of metal plates 110. The pair of metal plates 110 are joined to the aluminum nitride plate 100 so as to cover the surface 100A and the surface 100B of the aluminum nitride plate 100. An example of the metal plate 110 is a copper plate. The aluminum nitride plate 100 and the metal plate 110 may have the same shape and size, or may have different shapes and sizes. The composite substrate 200 can be manufactured by the above-mentioned manufacturing method. Since the thickness of the oxygen-rich layer 22 formed on the peripheral portion 20a of the hole 20 of the aluminum nitride plate 100 is reduced, a good appearance can be maintained. Such a composite substrate 200 has excellent reliability due to good bonding between the aluminum nitride plate 100 and the metal plate 110. In addition, contamination of the composite substrate 200 and each manufacturing facility using the same can be reduced.

[0049] In one embodiment of the method for manufacturing a circuit board, following the above-mentioned method for manufacturing a composite board, a process is performed in which a part of the metal plate in the composite board is removed to form an independent conductor part for each partition part. This process may be performed by, for example, photolithography. Specifically, first, a photosensitive resist is printed on the surface of the composite board. Then, an exposure device is used to form a resist pattern having a predetermined shape. The resist may be negative or positive. Uncured resist is removed by, for example, washing.

[0050] Fig. 9 is a perspective view showing an example of a composite substrate 200 having a resist pattern 30 formed on the front surface 200A. Although Fig. 9 shows only the front surface 200A side, a similar resist pattern may be formed on the front surface 200B side as well. The resist pattern 30 is formed on the front surface 200A and the front surface 200B in regions corresponding to each partition portion 10 of the aluminum nitride plate 100.

[0051] After forming the resist pattern 30, the portions of the metal plate 110 that are not covered by the resist pattern 30 are removed by etching. This exposes the surfaces 100A and 100B of the aluminum nitride plate 100 in those portions. Thereafter, the resist pattern 30 is removed to form independent conductor portions for each partition portion 10. Through the above steps, a circuit board is obtained.

[0052] The aluminum nitride plate 100 has a reduced oxygen-rich layer 22 at the peripheral portion 20a of the hole 20 that constitutes the scribe lines L1, L2, so that a circuit board with a good appearance can be obtained. In addition, the oxygen-rich layer 22 peeling off from the surface 100A can be reduced, so that contamination inside an exposure device or the like can be suppressed. Furthermore, the bonding between the conductor portion and the aluminum nitride plate 100 is good, so that reliability can be improved.

[0053] 10 is a plan view of a circuit board according to one embodiment. The circuit board 300 includes an aluminum nitride plate 100 and conductor parts 50 arranged to face each other with the aluminum nitride plate 100 in between. The conductor parts 50 are provided on the front surface 100A and the front surface 100B independently for each partition part 10. That is, a pair of conductor parts 50 arranged to face each other is provided for each partition part 10.

[0054] The circuit board 300 is cut along the scribe lines L1, L2 and divided into a plurality of divided boards. The divided boards are used as components of a power module, for example. Electronic components, for example, are mounted on the conductor parts 50 in the divided boards. The circuit board 300 can be manufactured by the above-mentioned manufacturing method. In the above-mentioned manufacturing method, since the aluminum nitride plate 100 in which the oxygen-rich layer 22 in the peripheral part 20a of the hole 20 is reduced is used, the circuit board 300 and its divided boards can maintain a good appearance. In addition, it is possible to maintain a good appearance not only of the divided boards but also of the power module on which the divided boards are mounted. In addition, the reliability of the power module can be improved.

[0055] Although several embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-mentioned embodiments. For example, the shapes of the conductors 50 provided in each partition 10 do not need to be the same, and each partition 10 may have a different shape. In addition, the aluminum nitride plate and the composite substrate may have a shape other than a rectangular prism shape.

[0056] Any surface treatment may be applied to the conductor portion 50 of the circuit board 300. For example, a part of the surface of the conductor portion 50 may be covered with a protective layer such as a solder resist, and the other part of the surface of the conductor portion 50 may be plated. EXAMPLES

[0057] [Preparation of aluminum nitride plate with scribe lines] Example 1 A flat aluminum nitride plate (length x width x thickness = 127.0 mm x 177.8 mm x 0.64 mm) was prepared. A carbon dioxide gas laser processing machine was used to form multiple holes in a line along one direction on the surface of this aluminum nitride plate, creating scribe lines. The multiple holes were formed by irradiating the same position with laser light seven times in burst pulse mode (number of shots: 7). The energy and pulse width of the laser light per shot were as shown in Table 1.

[0058] Example 2 A flat aluminum nitride plate (length x width x thickness = 127.0 mm x 177.8 mm x 0.64 mm) was prepared. A carbon dioxide gas laser processing machine was used to form a series of holes in one direction on the surface of this aluminum nitride plate, providing a scribe line. The holes were formed in the same manner as in Example 1, except that the holes were formed in cycle pulse mode and the laser light was irradiated in four cycles (number of shots: 4). The energy and pulse width of the laser light per shot were as shown in Table 1.

[0059] Comparative Example 1 An aluminum nitride plate of the same shape and material as in Example 1 was prepared. A carbon dioxide gas laser processing machine was used to form a plurality of holes aligned in one direction on the surface of this aluminum nitride plate, providing scribe lines. Each hole was formed by irradiating the laser light only once (number of shots: 1). The energy and pulse width of the laser light per shot were as shown in Table 1.

[0060] [Evaluation of holes that make up scribe lines 1] Fig. 11 shows SEM photographs of the surface and cross section of the aluminum nitride plate of Example 1 in which a plurality of holes constituting scribe lines are formed. SEM photograph A in Fig. 11 shows the surface of the aluminum nitride plate of Example 1 in which a plurality of holes 20 are formed. SEM photograph B in Fig. 11 shows the cross section of the aluminum nitride plate of Example 1 in which a plurality of holes 20 are formed. That is, SEM photograph B shows a cross section when the aluminum nitride plate is cut along a plane perpendicular to the surface on which the scribe lines are formed and passing through the scribe lines.

[0061] Fig. 12 shows SEM photographs of the surface and cross section of an aluminum nitride plate of Example 2 in which a plurality of holes constituting a scribe line are formed. SEM photograph A in Fig. 12 shows the surface of an aluminum nitride plate of Example 2 in which a plurality of holes 20 are formed. SEM photograph B in Fig. 12 shows a cross section of an aluminum nitride plate of Example 2 in which a plurality of holes 20 are formed. That is, SEM photograph B shows a cross section when the aluminum nitride plate is cut along a plane perpendicular to the surface on which the scribe line is formed and passing through the scribe line.

[0062] Fig. 13 shows SEM photographs of the surface and cross section of the aluminum nitride plate of Comparative Example 1 in which a plurality of holes constituting scribe lines are formed. SEM photograph A in Fig. 13 shows the surface of the aluminum nitride plate of Comparative Example 1 in which a plurality of holes 120 are formed. SEM photograph B in Fig. 13 shows the cross section of the aluminum nitride plate of Comparative Example 1 in which a plurality of holes 120 are formed. That is, SEM photograph B shows a cross section when the aluminum nitride plate is cut perpendicular to the surface along the longitudinal direction of the scribe lines.

[0063] Fig. 14 is an SEM photograph taken at 120x and 500x magnification of the cross sections of the aluminum nitride plates in which holes are formed of Example 1, Example 2, and Comparative Example 1. Fig. 15 is an SEM photograph taken at 800x magnification of the cross sections of the aluminum nitride plates in which holes are formed of Example 1, Example 2, and Comparative Example 1. Figs. 14 and 15 show cross sections of the aluminum nitride plates cut along a plane perpendicular to the surface on which the scribe lines are formed and perpendicular to the longitudinal direction of the scribe lines.

[0064] As shown in Fig. 14 and Fig. 15, in Comparative Example 1, it was confirmed that the peripheral portion of the hole was covered with a layer that was whiter than the color of the aluminum nitride. When this white layer was subjected to EPMA analysis, it was confirmed that it contained oxygen. In other words, it was confirmed that the white layer was an oxygen-rich layer that contained more oxygen than the inside of the aluminum nitride plate. When the maximum thickness t of the oxygen-rich layer at the peripheral portion of the hole was measured, it was 6 μm.

[0065] On the other hand, in Examples 1 and 2, the oxygen-rich layer (oxygen concentration was the same as in Comparative Example 1) at the periphery of the hole was thinner than in Comparative Example 1. The maximum thickness t of the oxygen-rich layer at the periphery of the hole in Examples 1 and 2 was less than 1 μm and 4 μm, respectively. This confirmed that the oxygen-rich layer formed on the surface of the aluminum nitride plate could be reduced by irradiating the laser light multiple times when forming the hole.

[0066] [Evaluation of holes that make up scribe lines 2] The surfaces of the aluminum nitride plates of Example 1 and Comparative Example 1 were observed with an optical microscope (magnification: 250 times) in the areas where the scribe lines were formed, and the opening diameter r of the holes 20 (holes 120) was measured. The results are shown in Table 1. The aluminum nitride plates of Example 1 and Comparative Example 1 were also folded along the scribe lines to obtain cross sections as shown in SEM photographs B of Figs. 11 and 12. The cross sections were observed with an optical microscope (magnification: 250 times) and the depth d of the holes 20 (holes 120) was measured. The results are shown in Table 1.

[0067] [Table 1]

[0068] In the aluminum nitride plates of Examples 1 and 2, the thickness of the oxygen-rich layer formed on the periphery of the hole constituting the scribe line was smaller than that of Comparative Example 1. With such an aluminum nitride plate, contamination due to peeling of the oxygen-rich layer is suppressed, and a good appearance can be maintained. In addition, a decrease in reliability due to peeling of the oxygen-rich layer is suppressed, and contamination of each manufacturing facility can be reduced. [Industrial Applicability]

[0069] According to the present disclosure, it is possible to provide an aluminum nitride plate having excellent reliability while maintaining a good appearance, and a manufacturing method thereof. It is also possible to provide a composite substrate having excellent reliability while maintaining a good appearance, and a manufacturing method thereof. It is also possible to provide a circuit board having excellent reliability while maintaining a good appearance, and a manufacturing method thereof. [Explanation of symbols]

[0070] 10...partition portion, 20...hole, 20a...periphery, 20B...bottom, 20E...opening, 22...oxygen-rich layer, 30...resist pattern, 40...soldering material, 100...aluminum nitride plate, 100A, 100B...surface, 110...metal plate, 200...composite substrate, 200A, 200B...surface, 300...circuit board, L1, L2...scribe line, VL1, VL2...virtual line.

Claims

1. A method for manufacturing an aluminum nitride plate having a scribe line on a surface thereof, comprising the steps of: The method includes a step of forming a plurality of holes having bottoms on a surface of a sintered base material containing aluminum nitride by using a laser beam to provide the scribe lines; A method for manufacturing an aluminum nitride plate, wherein each of the plurality of holes is formed by irradiating the laser light multiple times, and a maximum thickness of an oxygen-rich layer at the periphery of the hole is 4 μm or less.

2. The method for producing an aluminum nitride plate according to claim 1 , wherein the energy of the laser light per irradiation is less than 70 mJ when the laser light is irradiated in a plurality of times.

3. The method for manufacturing an aluminum nitride plate according to claim 1 or 2, wherein the opening diameter of the holes on the surface is 50 μm or more, and the depth of the holes is 60 μm or more.

4. The method for manufacturing an aluminum nitride plate according to any one of claims 1 to 3, wherein at least one of peripheral portions of the plurality of holes and inner surfaces of the plurality of holes is covered with the oxygen-rich layer.

5. An aluminum nitride plate having a scribe line on a surface thereof, An aluminum nitride plate, wherein at least one of the peripheral portions of a plurality of holes having bottoms that form the scribe line and the inner surfaces of the plurality of holes is covered with an oxygen-rich layer, and the thickness of the oxygen-rich layer in the peripheral portion is 4 μm or less.

6. 6. The aluminum nitride plate according to claim 5, wherein the opening diameter of the holes on the surface is 50 μm or more, and the depth of the holes is 60 μm or more.

7. A method for producing a composite substrate, comprising a step of bonding a metal plate to an aluminum nitride plate so as to cover the surface of the aluminum nitride plate obtained by the production method according to any one of claims 1 to 4, to obtain a composite substrate.

8. 8. A method for manufacturing a circuit board, comprising the steps of removing a portion of the metal plate in a composite substrate obtained by the manufacturing method according to claim 7, and forming an independent conductor portion for each partition portion defined by the scribe lines to obtain a circuit board.

9. The aluminum nitride plate according to claim 5 or 6, a metal plate joined to the aluminum nitride plate so as to cover the surface.

10. The aluminum nitride plate according to claim 5 or 6, a conductor portion provided on the surface so as to be independent for each partition portion defined by the scribe lines.

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