JP7588071B2 - Circuit board, manufacturing method thereof, and inspection method thereof - Google Patents

Description

The present disclosure relates to ceramic substrates and manufacturing methods thereof, composite substrates, circuit substrates and manufacturing methods thereof, and methods for inspecting circuit substrates.

Power modules that control large currents are used in fields such as automobiles, electric railways, industrial equipment, and power generation. The circuit board mounted on the power module has an insulating ceramic substrate. The following technology, as described in Patent Document 1, is known as a method for manufacturing a circuit board. That is, a composite substrate is formed by bonding metal layers to both sides of a ceramic substrate having scribe lines formed on its surface. Then, the metal layer on the surface of the composite substrate is processed into a circuit pattern by etching. The composite substrate is then divided along the scribe lines to produce multiple circuit substrates.

As an insulating substrate, a circuit board is required to have voltage resistance characteristics. One method of testing voltage resistance characteristics is to test in a liquid such as insulating oil to avoid discharging into the atmosphere. Patent Document 2 proposes a technology for testing voltage resistance in a fluorine-based inert liquid.

JP 2007-324301 A JP 2016-183923 A

Circuit boards for power modules are required to have excellent insulation properties. Here, if there are defects such as scratches in the ceramic substrate, which is responsible for the insulation of the circuit board, the insulation properties will be impaired, so it is necessary to eliminate defects as much as possible. However, ceramic substrates are more prone to defects than other materials, so it is difficult to completely eliminate defects. For this reason, it is necessary to inspect for defects before forming the circuit board, and to reject ceramic substrates in which defects are found. On the other hand, if a ceramic substrate with even one defect is discarded as a defective product, the yield will decrease. For this reason, it is believed that technology that can eliminate defective parts with high precision, even when using ceramic substrates with defects, can greatly contribute to improving the reliability of circuit boards.

Therefore, the present disclosure provides a ceramic substrate and a manufacturing method thereof that can produce a highly reliable circuit board. It also provides a composite substrate that can produce a highly reliable circuit board. It also provides a highly reliable circuit board and a manufacturing method thereof. It also provides a circuit board inspection method that can improve the reliability of the circuit board.

A ceramic substrate according to one aspect of the present disclosure is a ceramic substrate having a surface divided into multiple sections by partition lines, and at least one of the partition sections defined by the partition lines has a defect and a through hole.

Since such a ceramic substrate has a defect and a through hole in one partition, partitions having defects can be detected with high accuracy even after processing into a circuit board. Therefore, partitions having defects can be removed with high accuracy. Therefore, even if a ceramic substrate having defects is used, a highly reliable circuit board can be obtained. Despite having defects, this ceramic substrate can be used to manufacture circuit boards, so that the circuit boards can be manufactured with a high yield. In other words, the above-mentioned ceramic substrate makes it possible to manufacture highly reliable circuit boards with a high yield.

The opening area of the through hole on the surface of the ceramic substrate may be 1200 μm2 or ^more . This allows the detection of sections having defects with higher accuracy. Therefore, the manufacturing cost of the circuit board and the workload for the insulation inspection can be further reduced.

At least a portion of the through hole may be tapered. This makes it easier for the solder material to be filled from the surface side with the larger opening. This further improves the accuracy of detecting defects.

At least a portion of the through hole may be filled with a brazing material. This can further improve the detection accuracy of the partition having the defect and the through hole. Note that the "through hole" in this disclosure does not necessarily have to be hollow, and may be filled with a material different from the material constituting the ceramic substrate.

A composite substrate according to one aspect of the present disclosure includes a pair of metal substrates arranged to face each other, and a ceramic substrate as described above between the pair of metal substrates. Since the composite substrate includes the ceramic substrate described above, it is possible to manufacture highly reliable circuit substrates with a high yield.

A circuit board according to one aspect of the present disclosure comprises a ceramic substrate as described above and conductor portions arranged to face each other across the ceramic substrate, the conductor portions being provided independently for each partition portion.

Since such circuit boards are equipped with the above-mentioned ceramic substrate, they have high reliability and can be manufactured with a high yield.

A method for manufacturing a ceramic substrate according to one aspect of the present disclosure includes the steps of irradiating a surface of a substrate made of ceramic with laser light to form partition lines that divide the surface into multiple sections, and providing a through hole in at least one of the partition sections defined by the partition lines, the partition section having a defect, to obtain a ceramic substrate.

In the above manufacturing method, a through hole is provided in at least one partition having a defect, so that partition can be detected with high accuracy. This allows partitions having defects to be removed with high accuracy. Therefore, even if a ceramic substrate having a defect is used to manufacture a circuit substrate, a highly reliable circuit substrate can be obtained. Since the ceramic substrate obtained by this manufacturing method can be used to manufacture a circuit substrate even if it has a defect, the circuit substrate can be manufactured with a high yield. In other words, the above-mentioned manufacturing method for a ceramic substrate makes it possible to manufacture a highly reliable circuit substrate with a high yield.

A method for manufacturing a circuit board according to one aspect of the present disclosure includes the steps of stacking a pair of metal substrates sandwiching the ceramic substrate obtained by the above-described manufacturing method to obtain a composite substrate, removing portions of the metal substrates in the composite substrate to form independent conductor portions for each partition, and applying a voltage between the pair of conductor portions sandwiching the ceramic substrate to measure the current.

In the above manufacturing method, a voltage is applied between a pair of conductors sandwiching a ceramic substrate having a through hole in at least one partition having a defect, and the current is measured. Therefore, the defective portion of the ceramic substrate and the partition having a through hole can be detected with high accuracy. Therefore, the partition having a defective portion can be removed with high accuracy. Therefore, even if a ceramic substrate having a defective portion is used to manufacture a circuit substrate, a highly reliable circuit substrate can be manufactured. In this manufacturing method, since a ceramic substrate having a defective portion can be used to manufacture a circuit substrate, the circuit substrate can be manufactured with a high yield. In other words, this manufacturing method for a circuit substrate makes it possible to manufacture a highly reliable circuit substrate with a high yield.

A method for inspecting a circuit board according to one aspect of the present disclosure is the above-mentioned method for inspecting a circuit board, and includes a step of applying a voltage between at least a pair of conductor portions sandwiching a ceramic substrate and measuring a current. Since the ceramic substrate has a through hole in at least one partition portion having a defect, the partition portion having a defect can be detected with high accuracy. Therefore, a circuit board having high reliability can be obtained. Furthermore, since a ceramic substrate can be used to manufacture a circuit board even if it has a defect, the circuit board can be manufactured with a high yield. In other words, the above-mentioned method for inspecting a circuit board makes it possible to manufacture a circuit board having high reliability with a high yield.

A method for inspecting a circuit board according to another aspect of the present disclosure is a method for inspecting a circuit board comprising a ceramic substrate having a surface divided into a plurality of sections by dividing lines, and conductor portions arranged to face each other across the ceramic substrate and provided independently for each divided section defined by the dividing lines, the method comprising the steps of applying a voltage between a pair of conductor portions sandwiching the ceramic substrate and measuring a current for each divided section.

This inspection method allows for easy and quick inspection of each partition for defects. By performing such inspections, highly reliable circuit boards can be produced with high productivity.

According to the present disclosure, it is possible to provide a ceramic substrate and a manufacturing method thereof that can produce a highly reliable circuit board. It is also possible to provide a composite substrate that can produce a highly reliable circuit board. It is also possible to provide a highly reliable circuit board and a manufacturing method thereof. It is also possible to provide a circuit board inspection method that can improve the reliability of the circuit board.

FIG. 1 is a perspective view of a ceramic substrate according to one embodiment. FIG. 2 is a cross-sectional view taken along line II-II of FIG. FIG. 3 is a cross-sectional view taken along line III-III in FIG. FIG. 4 is a perspective view of a composite substrate according to an embodiment. FIG. 5 is a perspective view of a circuit board according to an embodiment. FIG. 6 is a perspective view showing an example of a ceramic substrate to which a brazing material is applied. FIG. 7 is a perspective view showing an example of a composite substrate having a resist pattern formed on its surface. FIG. 8 is a diagram showing an example of an inspection device for measuring leakage current of a circuit board. FIG. 9 is a photograph of an optical microscope image showing the surface and through holes of the ceramic substrate of Experimental Example 3.

Below, one embodiment of the present disclosure will be described, with reference to the drawings where appropriate. 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 will be used for the same elements or elements having the same functions, and duplicated descriptions will be omitted where appropriate. Furthermore, unless otherwise specified, positional relationships such as up, down, left, right, etc. will be based on the positional relationships shown in the drawings. Furthermore, the dimensional ratios of each element are not limited to those shown in the drawings.

Figure 1 is a perspective view of a ceramic substrate according to one embodiment. The ceramic substrate 100 in Figure 1 has a flat plate shape. The surface 100A of the ceramic substrate 100 is divided into a plurality of sections by partition lines. The surface 100A is provided with a plurality of partition lines L1 extending along a first direction and arranged at equal intervals, and a plurality of partition lines L2 extending along a second direction perpendicular to the first direction and arranged at equal intervals. The partition lines L1 and L2 are perpendicular to each other.

The dividing lines L1, L2 may be, for example, a plurality of depressions arranged in a straight line, or may have linear grooves. Specifically, they may be scribe lines formed with laser light. Examples of laser sources include carbon dioxide lasers and YAG lasers. Scribe lines can be formed by intermittently irradiating laser light from such laser sources. Note that the dividing lines L1, L2 do not have to be arranged at equal intervals, and are not limited to being perpendicular. They may also be curved or bent instead of straight.

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, partition 10 is composed of a three-dimensional area surrounded by an area on front surface 100A surrounded by partition lines L1, L2, an area on back surface 100B corresponding to said area, and imaginary lines VL1, VL2 drawn parallel to the thickness direction of ceramic substrate 100 from partition lines L1, L2. That is, ceramic substrate 100 has a plurality of partitions 10 defined by partition lines L1 and L2. Of the plurality of partitions 10, partition 10a has a defect portion 11 and a through hole 12.

The through hole 12 penetrates the ceramic substrate 100 in the thickness direction, and is formed, for example, by using a laser beam or a drill. The through hole 12 may be formed by hollowing out a cylindrical shape. However, it is not limited to a cylindrical shape. The opening area of the through hole 12 on the front surface 100A and the back surface 100B may be, for example, 1200 μm ² or more, 5000 μm ² or more, or 7000 μm ² or more. By having the opening area on the front surface 100A and the back surface 100B have a predetermined size in this way, the partition portion 10a having the defective portion 11 can be detected with higher accuracy. The opening area of the through hole 12 may be 0.5 mm ² or less from the viewpoint of reducing the time required for forming the through hole 12.

The through hole 12 may be tapered in part so as to be narrowed along the thickness direction of the ceramic substrate 100, for example. That is, the through hole 12 may have a tapered portion whose hole diameter changes along the thickness direction of the ceramic substrate 100. The entire through hole 12 may be tapered. If the opening areas of the through hole 12 on the front surface 100A and the back surface 100B are different, the brazing material can be applied from the side of the through hole 12 with the larger opening area to smoothly fill the brazing material. If the brazing material is filled in the through hole 12, the defective portion 11 can be detected with higher accuracy.

The defect 11 refers to a cause of leakage current when the circuit board is formed, and examples of the defect include cracks, holes, scratches, and other dents. The defect 11 is different from the through hole 12, and in this embodiment, it appears on the surface 100A. However, it is not limited to such a shape, and may be, for example, a crack that reaches from the surface 100A to the opposite back surface 100B. That is, the defect may be exposed on the surface 100A or the back surface 100B, or may not be exposed. A defect that is not exposed can be detected, for example, by non-destructive testing. From the viewpoint of ease of detection by visual inspection, etc., the defect may be exposed on the surface 100A and/or the back surface 100B of the ceramic substrate 100.

1, 2 and 3 show an example in which the division lines L1 and L2 are formed only on one side, the surface 100A, of the ceramic substrate 100, but this is not limiting. That is, the division lines L1 and L2 may also be formed on the back surface 100B opposite the front surface 100A of the ceramic substrate 100. In addition, the defect portion 11 and the division lines L1 and L2 do not need to coexist on the front surface 100A. For example, the defect portion 11 may be exposed only on the back surface 100B, or may be present inside the ceramic substrate 100.

In this embodiment, among the multiple partitions 10, only partition 10a has a defect 11 and a through hole 12, but this is not limited to this. In some modified examples, the ceramic substrate may have two or more partitions having a defect and a through hole. In addition, it is not necessary to provide a through hole in all partitions having a defect, and for example, a through hole may be provided only in partitions having a defect that is visually detected on the front surface 100A and the back surface 100B.

Since the ceramic substrate 100 has a defect 11 and a through hole 12 in the partition 10a, the partition 10a having the defect 11 can be detected with high accuracy even after processing into a circuit board. Therefore, the partition 10a having the defect 11 can be removed with high accuracy. Therefore, even if the ceramic substrate 100 having the defect 11 is used to manufacture a circuit board, the occurrence of defective products is suppressed, and a circuit board having high reliability can be obtained. In this way, even though the ceramic substrate 100 has a defect, it can be used to manufacture a circuit board, so that a circuit board having high reliability can be manufactured with a high yield. In other words, the ceramic substrate 100 makes it possible to manufacture a circuit board having high reliability with a high yield.

Figure 4 is a perspective view of a composite substrate according to one embodiment. The composite substrate 200 comprises a pair of metal substrates 110 arranged to face each other, and a ceramic substrate 100 between the pair of metal substrates 110. An example of the metal substrate 110 is a copper plate. The ceramic substrate 100 and the metal substrate 110 may have the same shape and size, or may have different shapes and sizes. The metal substrate 110 and the ceramic substrate 100 may be joined by, for example, a brazing material. Since the composite substrate 200 comprises the ceramic substrate 100, it is possible to manufacture a highly reliable circuit substrate with a high yield.

An example of a composite substrate 200 is one in which the ceramic substrate 100 is made of aluminum nitride and the metal substrate 110 is made of aluminum.

Figure 5 is a perspective view of a circuit board according to one embodiment. The circuit board 300 comprises a ceramic substrate 100 and conductor portions 20 arranged opposite each other with the ceramic substrate 100 in between. The conductor portions 20 are provided independently for each partition portion 10 on the front surface 100A and the back surface 100B. That is, a pair of conductor portions 20 arranged opposite each other is provided for each partition portion 10. The defect portions 11 and through holes 12 of the ceramic substrate 100 may be covered by the conductor portions 20.

Since the partition 10a having the defect 11 has a through hole 12, the partition 10a can be detected with high accuracy even if the defect 11 is very small. After dividing the circuit board 300 into divided boards for each partition 10, the divided boards containing the defect 11 can be removed to obtain divided boards that do not contain the defect 11. In this way, the ceramic substrate 100 having the defect 11 can be used to manufacture a circuit board, and high reliability can be ensured. Therefore, a highly reliable circuit board can be obtained with a high yield.

An example of a circuit board 300 is one in which the ceramic substrate 100 is made of aluminum nitride and the conductor portion 20 is made of aluminum.

As a method for manufacturing a ceramic substrate according to one embodiment, a method for manufacturing a ceramic substrate 100 will be described. The method for manufacturing the ceramic substrate 100 includes a step of irradiating a surface of a base material made of ceramic with laser light to form partition lines L1, L2 that partition the surface into multiple sections, and a step of providing a through hole 12 in a partition section 10a having a defect section 11 among partition sections 10 defined by the partition lines L1, L2 to obtain the ceramic substrate 100.

As the substrate made of ceramics, a flat ceramic substrate having an external shape as shown in Figure 1 is used. There are no particular limitations on the type of ceramic, and examples include carbides, oxides, and nitrides. Specific examples include silicon carbide, alumina, silicon nitride, aluminum nitride, and boron nitride.

Examples of the laser light irradiated onto the surface of the substrate include a carbon dioxide laser and a YAG laser. By intermittently irradiating the laser light from such a laser source, scribe lines that become the division lines L1 and L2 are formed. The division lines L1 and L2 become the cutting lines when dividing the circuit board 300 in a later process.

Next, of the partitions 10 defined by the partition lines L1 and L2, a through hole 12 is provided in the partition 10a having the defect 11. The through hole 12 is formed using a laser or a drill or the like. The size and shape of the through hole 12 are as described above. The defect 11 in the ceramic substrate 100 may be detected visually or by non-destructive testing such as ultrasonic flaw detection and infrared testing. If the defect 11 is not detected, the through hole 12 does not need to be provided. In this manner, the ceramic substrate 100 shown in Figures 1, 2 and 3 is obtained.

The manufacturing method for a composite substrate according to one embodiment uses the ceramic substrate 100 described above. That is, this manufacturing method includes a step of stacking a pair of metal substrates 110 so as to sandwich the ceramic substrate 100 to obtain a composite substrate. The metal substrate 110 may have a flat plate shape similar to the ceramic substrate 100. The pair of metal substrates 110 are joined to the front surface 100A and the back surface 100B of the ceramic substrate 100, respectively, via a brazing material.

Specifically, first, a paste-like brazing material is applied to the front surface 100A and rear surface 100B of the ceramic substrate 100 by a method such as a roll coater method, a screen printing method, or a transfer method. 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 organic solvent content in the brazing material may be, for example, 5 to 25 mass %, and the binder content may be, for example, 2 to 15 mass %.

Figure 6 is a perspective view showing a ceramic substrate 100 coated with brazing material 40. Although only the front surface 100A side is shown in Figure 6, the brazing material 40 may also be coated on the back surface 100B side. A metal substrate 110 is bonded to the front surface 100A and the back surface 100B of the ceramic substrate 100 coated with the brazing material 40 in this manner to obtain a bonded body. The bonded body is then heated in a heating furnace to sufficiently bond the ceramic substrate 100 and the metal substrate 110 to obtain the composite substrate 200 shown in Figure 4. The heating temperature may be, for example, 700 to 900°C. The atmosphere in the furnace may be an inert gas such as nitrogen. The bonded body may be heated under reduced pressure below atmospheric pressure or in vacuum. The heating furnace may be a continuous type that continuously supplies and heats a plurality of bonded bodies, or may be a type that heats one or a plurality of bonded bodies in a batch manner. The bonded body may be heated while pressing the bonded body in the stacking direction.

In one embodiment of the method for manufacturing a circuit board, following the above-mentioned method for manufacturing a composite board, a process is carried out in which a portion of the metal substrate 110 in the composite board 200 is removed to form an independent conductor portion 20 for each partition portion 10. This process may be carried out, for example, by photolithography. Specifically, first, as shown in FIG. 7, a photosensitive resist is printed on the surface 200A of the composite board 200. 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, for example, by cleaning.

Figure 7 is an oblique view showing a composite substrate 200 with a resist pattern 30 formed on the front surface 200A. Although only the front surface 200A side is shown in Figure 7, a similar resist pattern is also formed on the back surface 200B side. The resist pattern 30 is formed in areas on the front surface 200A and back surface 200B that correspond to each partition portion 10 of the ceramic substrate 100.

After forming the resist pattern 30, the portions of the metal substrate 110 that are not covered by the resist pattern 30 are removed by etching. This exposes the front surface 100A and rear surface 100B of the ceramic substrate 100 in those portions. The resist pattern 30 is then removed to form independent conductor portions 20 for each partition portion 10. The conductor portions 20 are formed in pairs for each partition portion 10, sandwiching the ceramic substrate 100 therebetween, as shown in FIG. 5.

Through the above steps, a circuit board 300 as shown in Figure 5 is obtained. Next, a step (inspection step) is performed in which a voltage is applied between a pair of conductor parts 20 that sandwich the ceramic substrate 100 and the current is measured. Specifically, a voltage is applied between the pair of conductor parts 20 that sandwich the ceramic substrate 100 and the current is measured. This measurement may be performed for each partition part 10. This allows the partition part 10a having the defective part 11 and the through hole 12 to be detected.

Figure 8 is a schematic diagram showing an example of an inspection device that measures leakage current of a circuit board 300 to inspect for dielectric breakdown. The inspection device 400 includes an AC power source 60 and a voltage resistance tester 50 connected to the AC power source 60. One terminal of the voltage resistance tester 50 is electrically connected to a conductive support 72a that contacts one of a pair of conductors 20 formed in the partition 10. The other terminal of the voltage resistance tester 50 is electrically connected to a conductive support 72b that contacts the other of the pair of conductors 20 through an electrode 70 arranged in an insulating solvent tank 77 that stores a solvent 76. That is, the pair of conductors 20 that face each other across the ceramic substrate 100 in the partition 10 where the current is measured are in contact with the conductive support 72a and the conductive support 72b, respectively.

The electrode 70 is arranged along the bottom surface and one side surface of the insulating solvent tank 77. As shown in FIG. 8, the electrode 70 has an L-shape when viewed in vertical cross section. Two insulating support parts 74 are provided adjacent to the conductive support part 72b on the electrode 70. The two insulating support parts 74 are in contact with two conductor parts 20 arranged adjacent to the conductor part 20 electrically connected to the conductive support part 72b, respectively, and support the circuit board 300 in the solvent 76.

The electrode 70 and the conductive support parts 72a, 72b may be made of, for example, oxygen-free copper. The solvent 76 may be, for example, a fluorine-based inert liquid. The voltage endurance tester 50 may be a commercially available one. The positions of the insulating support part 74 and the conductive support part 72b are configured to be interchangeable depending on the position of the partition part 10 to be measured. The position of the conductive support part 72a is also configured to be movable to match the position of the conductive support part 72b. By using such an inspection device 400, a voltage can be applied to a pair of conductor parts 20 for each partition part 10 to measure the leakage current.

The inspection device 400 applies a voltage of, for example, 1500 to 6000 V between a pair of conductor parts 20 that sandwich the ceramic substrate 100, and the presence or absence of leakage current is measured using a voltage resistance tester 50. The partition part 10a having the defect part 11 has a through hole 12, so leakage current occurs even at a low voltage. Therefore, the partition part 10a can be detected with high accuracy by an inspection method that detects the presence or absence of leakage current at a specified voltage.

Using such an inspection device 400, an inspection method can be performed that includes a step of applying a voltage between a pair of conductors 20 that sandwich the ceramic substrate 100 and measuring the current for each partition 10. The inspection device is not limited to the configuration shown in FIG. 8, and any inspection device can be used without particular restrictions as long as it is capable of measuring the current flowing between a pair of conductors arranged opposite each other in at least one partition when a voltage is applied between the conductors.

The inspection device 400 is not limited to the inspection of the circuit board 300 having the ceramic substrate 100 with the through hole 12 formed therein, but can be used to inspect various circuit boards having independent conductors for each partition. With an inspection method using such an inspection device 400, partitions containing defective parts in a ceramic substrate can be easily detected with high accuracy. This improves the reliability and productivity of the circuit board 300.

The inspected circuit board 300 is cut along the dividing lines L1 and L2 and divided into a number of divided boards. By eliminating the divided boards with through holes and manufacturing or semi-manufacturing the divided boards without through holes as components for use in, for example, a power module, it is possible to avoid using divided boards with defects as components and to increase the reliability of the components. For example, electronic components are mounted on the conductor portions 20 of the divided boards.

Although several embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments. For example, the shapes of the conductor portions 20 provided in each partition portion 10 do not need to be the same, and each partition portion 10 may have a different shape. Also, for example, the application of voltage to and measurement of current between pairs of conductor portions 20 sandwiching the ceramic substrate 100 may be performed simultaneously for multiple pairs, rather than performing the application of voltage to and measurement of current between pairs of conductor portions 20 one by one.

The conductor portion 20 in the circuit board 300 may be subjected to any surface treatment. For example, a part of the surface of the conductor portion 20 may be covered with a protective layer such as solder resist, and the other part of the surface of the conductor portion 20 may be subjected to plating treatment. Such surface treatment may be performed before or after inspection using the inspection device 400.

(Experimental Examples 1 to 3)
A laser beam was irradiated onto the surface of a silicon nitride ceramic substrate to form a partition line, which was then partitioned into three sections along the vertical and horizontal directions. Thus, a ceramic substrate having a total of nine partitions was prepared. This ceramic substrate had an outer periphery with a width of 5 mm outside the nine partitions. The size of each partition was length x width x thickness = 41 mm x 41 mm x 0.32 mm. A through hole was formed in the partition in the center of the ceramic substrate using a fiber laser (wavelength: 1064 nm). By changing the area to which the laser beam was irradiated, five ceramic substrates each having through holes of different sizes were produced. The opening shape of the through hole on the front and back surfaces of each ceramic substrate was circular, and the size (diameter) was as shown in Table 1. FIG. 9 is a photograph of an optical microscope image showing the surface and through hole of the ceramic substrate of Experimental Example 3.

A brazing filler material containing Ag as a main component was applied to the front and back surfaces of the ceramic substrate by screen printing. The copper plate and ceramic substrate were laminated so that each ceramic substrate was sandwiched between two copper plates (thickness 0.8 mm). In this way, a joint was produced that had a copper plate, a ceramic substrate, and a copper plate in that order.

Five sets of bonded bodies were stacked in a vacuum bonding furnace and arranged as a laminate. A copper plate was placed on this laminate, and heated at a heating temperature of 810°C for 20 minutes while applying a pressure of 5 g/cm2 ^to sufficiently bond the copper plate and the ceramic substrate. At this time, heating was performed in a state where the pressure inside the furnace was reduced to 1 x ^10-3 Pa or less. In this way, a composite substrate including a pair of copper plates and a ceramic substrate between them was produced.

Using an inspection device as shown in FIG. 8, a voltage resistance test was performed on each composite substrate manufactured in accordance with JIS C2110-1:2010 (n=5). For this test, an AC 20 kV voltage resistance tester (model: 7473) manufactured by Keisoku Gijutsu Kenkyusho Co., Ltd. was used. Perfluorocarbon (manufactured by 3M Japan Ltd., product name: Fluorinert, model number: FC-3283) was used as the solvent. Inspection jigs manufactured by Onishi Electronics Co., Ltd. were used as the insulating solvent tank 77, the electrode 70, the conductive support parts 72a, 72b, and the insulating support part 74. The electrode 70 was made of oxygen-free copper, and the conductive support parts 72a, 72b were made of carbon tool steel (SK material) plated with rhodium.

With the composite board set in the testing device, the voltage was increased to 4.2 kV at a rate of 0.12 kV/sec. The contact current threshold was set to 9.99 mA, and a current above this threshold was judged to have been a dielectric breakdown. The voltage at which a dielectric breakdown was judged to have occurred is shown in the "Voltage Withstand Test Results" column in Table 1.

The through-hole in Experimental Example 1 had a cylindrical shape. On the other hand, the through-holes in Experimental Examples 2 and 3 had a tapered portion inside the ceramic substrate, in which the hole diameter changed along the thickness direction of the ceramic substrate. In Table 1, "<0 kV" indicates that the leakage current value became equal to or greater than the above-mentioned predetermined value immediately after the start of voltage application. In Experimental Example 1 No. 3, the ceramic substrate underwent dielectric breakdown at the voltage listed in Table 1. In all of the experimental examples, the leakage current value became equal to or greater than the above-mentioned predetermined value before the voltage reached 4.2 kV. From these results, it was confirmed that by forming a through-hole, a substrate (partition portion) having a defect can be detected with high accuracy.

According to the present disclosure, a ceramic substrate and a manufacturing method thereof capable of producing a highly reliable circuit board are provided. A composite substrate is also provided from which a highly reliable circuit board is produced. A highly reliable circuit board and a manufacturing method thereof are also provided. A circuit board inspection method capable of improving the reliability of the circuit board is also provided.

10, 10a...partition portion, 11...defective portion, 12...through hole, 20...conductor portion, 30...resist pattern, 50...voltage resistance tester, 60...AC power source, 70...electrode, 72a, 72b...conductive support portion, 74...insulating support portion, 76...solvent, 77...insulating solvent tank, 100...ceramic substrate, 110...metal substrate, 100A...surface, 100B...rear surface, 110...metal substrate, 200...composite substrate, 200A...surface, 200B...rear surface, 300...circuit substrate, 400...inspection device.

Claims (8)

A ceramic substrate having a surface divided into a plurality of sections by dividing lines ;
and conductor portions arranged to face each other across the ceramic substrate,
the ceramic substrate has a through hole covered by the conductor portion only in at least one partition portion having a defect portion among a plurality of partition portions defined by the partition lines;
The conductor portion is a circuit board provided independently for each of the partition portions. The opening area of the through hole on the surface is 1200 μm ² The circuit board according to claim 1 . The circuit board according to claim 1 , wherein at least a portion of the through hole is tapered. The circuit board according to any one of claims 1 to 3, wherein at least a portion of the through hole is filled with a brazing material. 5. The circuit board according to claim 1, wherein all partitions having the defective portion have a through hole. A step of irradiating a surface of a substrate made of ceramic with laser light to form partition lines that partition the surface into a plurality of sections;
providing a through hole only in at least one of the partitions, which has a defect in the base material made of the ceramic, among the plurality of partitions defined by the partition lines, to obtain a ceramic substrate;
laminating a pair of metal substrates so as to sandwich the ceramic substrate therebetween to obtain a composite substrate;
removing a portion of the metal substrate in the composite substrate to form an independent conductor portion for each partition portion;
and applying a voltage between the pair of conductors that sandwich the ceramic substrate and measuring a current. A step of irradiating a surface of a substrate made of ceramic with laser light to form partition lines that partition the surface into a plurality of sections;
providing a through hole in at least one of the partitions defined by the partition lines, the through hole having a defect, to obtain a ceramic substrate;
laminating a pair of metal substrates so as to sandwich the ceramic substrate therebetween to obtain a composite substrate;
removing a portion of the metal substrate in the composite substrate to form an independent conductor portion for each partition portion;
and applying a voltage between the pair of conductors that sandwich the ceramic substrate and measuring a current. The method for inspecting a circuit board according to any one of claims 1 to 5 ,
The method for inspecting a circuit board includes a step of applying a voltage between at least a pair of the conductor portions sandwiching the ceramic substrate therebetween and measuring a current.

Images