Wiring board, electronic device, and electronic module

Abstract

A wiring board (1) comprises: an insulation substrate (10) in which a main component is aluminum nitride and a plurality of particles (15) are bonded; a titanium oxide layer (31) which is located on the surface of the insulation substrate; and a conductor layer (32, 33) located above the titanium oxide layer. The insulation substrate has undulations on the surface thereof due to the shape and disposition of the particles. The titanium oxide layer covers the undulations.

Description

Wiring board, electronic device, and electronic module

[0001] The present disclosure relates to a wiring board, an electronic device, and an electronic module.

[0002] 2. Description of the Related Art A wiring board is known in which a conductor layer made of metal is provided on an insulating substrate (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2018-125344

[0004] The wiring board according to the present disclosure comprises an insulating substrate whose main component is aluminum nitride and to which a plurality of particles are bonded, a titanium oxide layer located on the surface of the insulating substrate, and a conductor layer located on the titanium oxide layer, wherein the insulating substrate has undulations on the surface caused by the shape and arrangement of the particles, and the titanium oxide layer covers the undulations.

[0005] An electronic device according to the present disclosure includes the wiring board described above and an electronic component mounted on the wiring board.

[0006] The electronic module of the present disclosure includes the above electronic device and a module substrate on which the electronic device is mounted.

[0007] 1 is a perspective view showing a wiring board according to an embodiment of the present disclosure; FIG. 2 is a cross-sectional view showing a main part of the wiring board of FIG. 1; FIG. 3 is a diagram explaining a method for measuring the size of metal crystal grains; FIG. 4 is a cross-sectional view showing a surface portion of a wiring board; FIG. 5 is a cross-sectional view showing a surface portion of a wiring board; FIG. 6 is a cross-sectional view showing a modified example of a through portion; FIG. 7 is a cross-sectional view showing a modified example of a through portion; FIG. 8 is a diagram showing an electronic device and an electronic module according to an embodiment of the present disclosure.

[0008] The present disclosure aims to reduce the occurrence of defects in wiring boards, and to provide a method for manufacturing wiring boards that includes the steps of: forming a wiring board having a conductor layer with a void or other defect;

[0009] Fig. 1 is a perspective view showing a wiring board 1 according to an embodiment of the present disclosure. Fig. 2 is a cross-sectional view showing a main part of the wiring board 1 of Fig. 1. Fig. 3 shows a cross-section of a part of the wiring board 1 where a wiring conductor is located.

[0010] Hereinafter, "perpendicular" includes not only a state that is strictly perpendicular, but also a state that can be considered substantially perpendicular. The "state that can be considered substantially perpendicular" is not limited to the range of manufacturing tolerances, and may refer, for example, to a state in which the angle formed by two directions is close to 90 degrees; more specifically, it may be less than 90 degrees and 80 degrees or more, less than 90 degrees and 85 degrees or more, or less than 90 degrees and 88 degrees or more. Furthermore, when indicating a numerical range, "numeric value X to numeric value Y" means greater than or equal to numeric value X and less than numeric value Y.

[0011] A wiring board 1 according to one embodiment may include a first surface 11, a second surface 12, an insulating substrate 10, a first wiring conductor 21 located on the first surface 11, a second wiring conductor 23 located on the second surface 12, and a third wiring conductor 25. The second surface 12 may be located on the opposite side of the first surface 11. The insulating substrate 10 may have a through portion 13 extending from the first surface 11 to the second surface 12. The third wiring conductor 25 may be located in the through portion 13. The third wiring conductor 25 may be located from a first opening 13a on the first surface 11 side of the through portion 13 to a second opening 13b on the second surface 12 side. The third wiring conductor 25 may be electrically connected to the first wiring conductor 21 and the second wiring conductor 23. That is, the third wiring conductor 25 may be a through via conductor.

[0012] The insulating substrate 10 may be a ceramic containing aluminum nitride as its main component. The main component is the component with the highest content, and may be a component that is contained at 80 mass % or more. The insulating substrate 10 may also be silicon nitride, aluminum oxide, silicon carbide, or zirconia as its main component. The insulating substrate 10 may also be so-called glass, which is an amorphous solid containing silicate or the like as its main component. The main component of the insulating substrate 10 may be selected depending on the application of the wiring substrate 1. For example, if aluminum nitride is used as the main component, the wiring substrate 1 can have good thermal conductivity. If aluminum oxide is used as the main component, the wiring substrate 1 can be made thinner due to its high rigidity. If silicon nitride is used as the main component, the wiring substrate 1 can have high toughness.

[0013] As shown by the dashed lines in Fig. 2 , the through portion 13 has a first opening 13a on the first surface 11 side and a second opening 13b on the second surface 12 side. A third wiring conductor 25 may be located in the through portion 13, the first opening 13a, and the second opening 13b. The inner surface of the through portion 13 may be perpendicular to the first surface 11 and the second surface 12. The end of the inner surface of the through portion 13 located at the first opening 13a may be a first end closer to the first surface 11. Furthermore, the end of the inner surface of the through portion 13 located at the second opening 13b may be a second end farther from the first surface 11. In other words, the third wiring conductor 25 is located continuously from the first end to the second end.

[0014] The wiring board 1 may also have a non-through hole or groove. This non-through hole or groove may have a first opening 13a that opens to the first surface 11. On the inner surface of this non-through hole or groove, an end located at the first opening 13a may be a first end that is closer to the first surface 11. On the inner surface of the non-through hole or groove, an end adjacent to the innermost portion that is the bottom of the hole or groove may be a second end that is farther from the first surface 11. This non-through hole or groove may have a third wiring conductor 25 that has a configuration similar to that of the through portion 13. The third wiring conductor 25 included in the non-through hole or groove that opens to the first surface 11 may be electrically connected to the first wiring conductor 21 located on the first surface 11.

[0015] In the following description, when referring to holes or grooves, the term "holes or grooves" includes not only through-holes 13 that penetrate from the first surface 11 to the second surface 12, but also non-through-holes and grooves that have first openings 13a that open to the first surface 11. Furthermore, when referring to the surface of the insulating substrate 10, the term "surface of the insulating substrate 10" includes all of the surface of the first surface 11, the surface of the second surface 12, the inner surfaces of the through-holes 13, and the inner surfaces and bottom surfaces of the non-through-holes or grooves.

[0016] The first wiring conductor 21, the second wiring conductor 23, and the third wiring conductor 25 may include a titanium oxide layer 31, a first conductor layer 32, and a second conductor layer 33. The titanium oxide layer 31 may be in contact with the surface of the insulating substrate 10. The first conductor layer 32 may be in contact with the titanium oxide layer 31. The second conductor layer 33 may be in contact with the first conductor layer 32.

[0017] The titanium oxide layer 31 is a layer containing titanium oxide. This titanium oxide layer 31 covers the surface of the insulating substrate 10 in the area where the wiring conductor is located. In particular, in the through-hole 13, the titanium oxide layer 31 is continuous from the first end to the second end of the inner surface. The first conductor layer 32 and the second conductor layer 33 are layers made of metal. The first conductor layer 32 may be an electroless plated layer. The second conductor layer 33 may be an electrolytic plated layer. The metal used in the first conductor layer 32 and the second conductor layer 33 may be copper, nickel, cobalt, iron, or the like. The metal used in the first conductor layer 32 and the second conductor layer 33 may be the same type or different types. For example, copper may be used for the first conductor layer 32 and nickel may be used for the second conductor layer 33.

[0018] A first diffusion layer 34 may be present at the interface between the insulating substrate 10 and the titanium oxide layer 31. In one embodiment, elements contained in the insulating substrate 10 and the titanium oxide layer 31 are diffused into the first diffusion layer 34. The presence of the first diffusion layer 34 improves adhesion between the insulating substrate 10 and the titanium oxide layer 31. Furthermore, a second diffusion layer 35 may be present at the interface between the titanium oxide layer 31 and the first conductor layer 32. In one embodiment, elements contained in the titanium oxide layer 31 and the first conductor layer 32 are diffused into the second diffusion layer 35. The presence of the second diffusion layer 35 improves adhesion between the titanium oxide layer 31 and the first conductor layer 32.

[0019] <Size of Metal Crystal Grains> The first conductor layer 32 and the second conductor layer 33 are polycrystalline metals each consisting of a plurality of metal crystal grains 37. The metal crystal grains 37 are depicted schematically in FIGS. 2 and 3 . Actual metal crystal grains 37 have various shapes, such as granular or columnar, and vary in size. In one embodiment, the size of the metal crystal grains is a cross-sectional dimension measured using a scanning electron microscope (SEM) and is expressed in units of length.

[0020] Because the metal crystal grains 37 have various shapes, such as granular and columnar, the average size of each metal crystal grain 37 is determined as follows. FIG. 3 is a diagram illustrating a method for measuring the size of metal crystal grains. The size of metal crystal grains can be measured using an SEM in a cross section including the first conductor layer 32 and the second conductor layer 33. 1. In an SEM image or SIM image of a cross section including the first conductor layer 32 and the second conductor layer 33, the boundary (grain boundary) lines of each metal crystal grain 37 are extracted. 2. From the image, an area large enough to contain 20 to 100 metal crystal grains 37 is arbitrarily selected as the target region R. Note that, for example, the target region R can be determined by determining the boundary between grains of different grain size from the image. Also, the metal crystal grains 37 are simplified in FIG. 3 , and the number of metal crystal grains 37 in the target region R differs from the actual number. Multiple target regions R are selected from the conductor layer to be measured. 3. The number of metal crystal grains 37 in each target region R is counted, and the area of ​​each region is divided by this number to calculate the average cross-sectional area of ​​each metal crystal grain 37. Furthermore, assuming that the cross-sectional shape of each metal crystal grain 37 is circular, the diameter of the circle is calculated from the area, and this diameter is regarded as the average size of the metal crystal grains 37.

[0021] The average size of the metal crystal grains 37 in the first conductor layer 32 is smaller than the average size of the metal crystal grains 37 in the second conductor layer 33. The difference in the average sizes of the metal crystal grains 37 is a difference that exceeds the level of error. A difference that exceeds the level of error may mean a difference that is 1.5 times or more, or 2 times or more, the standard deviation σ of the sizes of the metal crystal grains 37 measured in any part.

[0022] The average size of the metal crystal grains 37 of the first conductor layer 32 is smaller than the average size of the metal crystal grains 37 of the second conductor layer 33, which has the effect of improving resistance to electromigration.

[0023] 4 and 5 are longitudinal cross-sectional views of the surface vicinity of the wiring substrate 1 in a portion where the first wiring conductor 21, the second wiring conductor 23, and the third wiring conductor 25 are located. The insulating substrate 10 may have a structure in which a plurality of particles 15 are sintered and densified. The particles 15 may have different shapes. Therefore, the surface of the insulating substrate 10 has undulations due to the shapes and arrangement of the particles 15. In other words, the surface of the insulating substrate 10 has irregularities.

[0024] Titanium oxide layer 31 is positioned so as to cover the undulations present on the surface of insulating substrate 10. This means that titanium oxide layer 31 is continuous from the concave portions to the convex portions present on the surface of insulating substrate 10. It can also be said that titanium oxide layer 31 is continuous along the undulations present on the surface of insulating substrate 10. There is no portion on titanium oxide layer 31 where the surface of insulating substrate 10 is exposed, and it can also be said that titanium oxide layer 31 is continuous without interruption.

[0025] Because the titanium oxide layer 31 is positioned in this manner, the first conductor layer 32 that runs along the titanium oxide layer 31 becomes continuous with the wiring conductor. Furthermore, the second conductor layer 33 that runs along the first conductor layer 32 also becomes continuous with the wiring conductor. Therefore, no voids exist in the first wiring conductor 21, the second wiring conductor 23, and the third wiring conductor 25. This reduces the occurrence of defects in the wiring board 1.

[0026] The surface condition of the insulating substrate 10 varies depending on the material of the insulating substrate 10 and the pretreatment process performed on the insulating substrate 10 before providing the titanium oxide layer 31. In the surface condition of the insulating substrate 10 shown in FIG. 4 , surface particles have fallen off at the grain boundaries, which are the boundaries between particles 15 after sintering and densification. That is, most of the particles 15 located on the surface of the insulating substrate 10 retain their shape after sintering and densification, and the surfaces that were the grain boundaries are in contact with the titanium oxide layer 31. Furthermore, there are almost no areas 38 where particles 15 located on the surface are separated from adjacent particles 15. Furthermore, the arithmetic mean height Sa, a parameter representing surface roughness, is in the range of 0.3 μm to 1.3 μm. This surface condition is often observed, for example, when a pretreatment process for an insulating substrate 10 primarily composed of aluminum nitride includes a dissolution process for dissolving the surface of the insulating substrate 10.

[0027] In the surface state of the insulating substrate 10 shown in Figure 5, the surface particles 15 have been scraped off to form a smooth surface. Although there are undulations due to the shape and arrangement of the particles 15, the surface is smoother and less undulating than the surface state shown in Figure 4. That is, some of the particles 15 located on the surface of the insulating substrate 10 are smaller than their shape after sintering and densification, and there are areas where surfaces that were not grain boundaries are in contact with the titanium oxide layer 31. Furthermore, there are areas 38 where the surface particles 15 are separated from adjacent particles 15, and the number of separated areas 38 is greater than in the surface state of the insulating substrate 10 shown in Figure 4. This type of surface state is often seen, for example, when a pretreatment process includes a polishing step for polishing the surface of the insulating substrate 10.

[0028] In the wiring board 1 of the present disclosure, the titanium oxide layer 31 continuously covers the surface of the insulating substrate 10 regardless of the difference in the surface condition of the insulating substrate 10 as shown in Figures 4 and 5. That is, the titanium oxide layer 31 continuously covers the surface of the insulating substrate 10 regardless of the surface roughness of the insulating substrate 10. The presence of undulations on the surface of the insulating substrate 10 due to the shape and arrangement of the particles 15 increases the adhesion of the titanium oxide layer 31 due to an anchor effect. In particular, the surface condition shown in Figure 4 is rougher than the surface condition shown in Figure 5, and there are fewer portions 38 separated from adjacent particles 15, resulting in high adhesion of the titanium oxide layer 31.

[0029] Furthermore, the titanium oxide layer 31 may be configured to continuously cover portions of the insulating substrate 10 even if the surface conditions are different. For example, in the structure shown in Fig. 2, even if the surface conditions of the first surface 11, the second surface 12, and the through-hole 13 of the insulating substrate 10 are different, the titanium oxide layer 31 may be configured to continuously cover the surface of the insulating substrate 10. In other words, even if the first surface 11 and the second surface 12 have the surface condition shown in Fig. 5 and the through-hole 13 has the surface condition shown in Fig. 4, the titanium oxide layer 31 may be configured to continuously cover the surface of the insulating substrate 10.

[0030] <Hole or Groove Structure> The relationship between the depth of a hole or groove and the width of the opening can be expressed by the aspect ratio. The aspect ratio of a hole or groove is calculated using the following formula: Aspect ratio = (Depth of hole or groove) / (Width of hole or groove opening) The depth of a non-through hole or groove is the length from the opening to the innermost part, which is the bottom of the hole or groove. The depth of a through hole, such as the through portion 13, is the length from the first opening 13a to the second opening 13b opposite the first opening 13a. If the opening is circular, the width of the hole or groove opening is the diameter of the circle. If the opening is not circular, the width of the hole or groove opening is the length of the shortest straight line passing through the center of the opening and connecting the opposing ends of the opening. In other words, it is the width of the narrowest part of the opening.

[0031] The larger the aspect ratio, the more difficult it is to form the titanium oxide layer 31 on the inner surface of the hole or groove. Therefore, the aspect ratio of the hole or groove provided in the insulating substrate 10 is preferably 1 to 8 in the case of a through hole, and more preferably 2 to 6. In the case of a non-through hole or groove, it is preferably 0.5 to 4, and more preferably 1 to 3.

[0032] The inner surface of the hole or groove is not limited to being perpendicular to the first surface 11 and the second surface 12 as shown in FIG. 1 , and may have other shapes. FIGS. 6 to 8 show examples of the cross-sectional shape of the through portion 13. The internal width of the through portion 13 may be narrower than the widths of the first opening 13a and the second opening 13b. The through portion 13 shown in FIG. 6 has a shape in which the width gradually narrows from the first opening 13a and the second opening 13b toward the center of the through portion 13. That is, the through portion 13 has a portion with a diameter d3 narrower than the diameter d1 of the first opening 13a and the diameter d2 of the second opening 13b. The through portion 13 shown in FIG. 7 gradually narrows from the first opening 13a to the second opening 13b. That is, the diameter d3 of each portion of the through portion 13 is narrower than the diameter d1 of the first opening 13a and wider than the diameter d2 of the second opening 13b. 6 and 7 are shapes in which the inner diameter of the hole is narrower than the diameter of at least one of the openings. The shape shown in Fig. 6 is often seen when the through-hole 13 is formed by blasting from both the first surface 11 side and the second surface 12 side of the insulating substrate 10. The shape shown in Fig. 7 is often seen when the through-hole 13 is formed by laser processing from the first surface 11 side of the insulating substrate 10.

[0033] The internal width of the through-hole 13 may be wider than the width of the opening. The through-hole 13 shown in FIG. 8 has an expanded diameter portion having a diameter d3 wider than the diameter d1 of the first opening 13a and the diameter d2 of the second opening 13b. While the expanded diameter portion is located near the first opening 13a, this is not limitative and it may be located in the center of the through-hole 13 or near the second opening 13b. The width of the through-hole 13 gradually increases from the center toward the second opening 13b. That is, the through-hole 13 has a reduced diameter portion having a diameter d4 narrower than the diameter d2 of the second opening 13b. The diameter d4 of the reduced diameter portion and the diameter d1 of the first opening 13a may be the same or different.

[0034] That is, the shape shown in Figure 8 has a portion where the inner diameter of the hole is wider than the diameters of both openings. The shapes shown in Figures 1 and 8 can also be said to have a region that passes through the first opening 13a or the second opening 13b and does not intersect with a line along the depth direction of the hole or groove. The shapes shown in Figures 1 and 8 can also be said to have a region that passes through the first opening 13a or the second opening 13b and does not intersect with a line perpendicular to the first surface 11 or the second surface 12. The shapes shown in Figures 1 and 8 are often seen when the through-hole 13 is formed by punching from the first surface 11 side of a green sheet in an unsintered state.

[0035] The present disclosure is applicable to through-holes 13 having any shape. That is, even for through-holes 13 having these shapes, the titanium oxide layer 31 continuously covers the inner surface, which becomes the surface of the insulating substrate 10, from the first opening 13a to the second opening 13b. Furthermore, for non-through holes and grooves, the internal width may be narrower or wider than the width of the opening. For example, the titanium oxide layer 31 may have a cross section as shown in FIGS. 1, 6, 7, and 8, with one opening closed. The titanium oxide layer 31 continuously covers the inner surface and bottom surface, which become the surface of the insulating substrate 10, even for non-through holes and grooves having these shapes. This allows the first conductor layer 32 and the second conductor layer 33 to be arranged so that they are continuous in the wiring conductor, regardless of the shape of the hole or groove.

[0036] <Thickness of Titanium Oxide Layer> The thickness of the titanium oxide layer 31 is preferably 10 nm or more and 80 nm or less, and more preferably 20 nm or more and 60 nm or less. If the thickness of the titanium oxide layer 31 is thin, it can be applied to fine structures. When the thickness is within the above range, the titanium oxide layer 31 is positioned uniformly in the holes or grooves, and a wiring conductor can be obtained in which there are no portions where the titanium oxide layer 31 is thicker than necessary.

[0037] The thickness of the titanium oxide layer 31 on the first surface 11 or the second surface 12 is preferably in the range of 20 nm to 60 nm. When the thickness of the titanium oxide layer 31 on the first surface 11 or the second surface 12 is within the above range, it can be easily removed by etching.

[0038] In one embodiment, the titanium oxide layer may be formed by coating the surface of the insulating substrate 10 with organic titanium and then oxidizing the coated organic titanium. This method allows for more efficient production of the wiring substrate 1 of the present disclosure than by forming a titanium-containing layer by other means, such as sputtering. For example, this method of forming a titanium oxide layer allows for a uniform titanium film to be formed on the surface of the insulating substrate 10, including the inner surfaces and bottom surfaces of holes and grooves. This allows for the titanium oxide layer 31 to cover undulations caused by the shape and arrangement of particles located on the surface of the insulating substrate 10. Furthermore, the titanium oxide layer 31 is positioned continuously on the inner surface of the hole or groove, from a first end portion closer to the first surface 11 to a second end portion farther from the first surface 11. This allows the first conductor layer 32 and the second conductor layer 33 to be continuous from the first end portion to the second end portion, resulting in a void-free third wiring conductor 25. 1 and 8, the titanium oxide layer 31 can be easily formed by the above-described formation method. Furthermore, because titanium exists as titanium oxide, which is not conductive, it is easier to prevent the risk of short circuits than when titanium exists in a conductive state.

[0039] 9 is a cross-sectional view showing an electronic device and an electronic module according to an embodiment of the present disclosure. An electronic device 60 according to one embodiment is configured by mounting an electronic component 50 on a wiring substrate 1. The electronic component 50 has a terminal connected to a first wiring conductor 21, and the terminal may be electrically connected to a second wiring conductor 23 on the second surface 12 via the first wiring conductor 21 and a third wiring conductor 25. A Ni film may be provided on the surfaces of the first wiring conductor 21 and the second wiring conductor 23.

[0040] Various electronic components can be used as the electronic component 50, such as optical elements such as laser diodes (LDs), photodiodes (PDs), and light-emitting diodes (LEDs), imaging elements such as charge-coupled devices (CCDs) and complementary metal oxide semiconductors (CMOSs), piezoelectric vibrators such as quartz crystal vibrators, surface acoustic wave elements, semiconductor elements such as integrated circuits (ICs), capacitance elements, inductors, and resistors. In particular, when the insulating substrate 10 is primarily composed of aluminum nitride, the wiring board 1 can have good thermal conductivity, making it suitable for use as a wiring board for automotive headlight LEDs, industrial lasers, and the like.

[0041] An electronic module 100 according to one embodiment is configured by mounting an electronic device 60 on a module substrate 110. In addition to the electronic device 60, other electronic devices, electronic elements, electric elements, etc. may be mounted on the module substrate 110. Electrode pads 111 may be provided on the module substrate 110, and wiring conductors 23 of the electronic device 60 may be joined to the electrode pads 111 via a joining material 113 such as solder.

[0042] The above describes the embodiments of the present disclosure. However, the wiring board 1, electronic device 60, and electronic module 100 of the present disclosure are not limited to the above embodiments. For example, in the above embodiments, the first wiring conductor 21 and the second wiring conductor 23 are exposed on the outer surface of the wiring board 1, and the third wiring conductor 25 is located between the two wiring conductors exposed on the outer surface of the wiring board 1. However, the wiring conductors may be wiring layers located inside the multilayer wiring board, and the third wiring conductor 25 may be an interlayer via of the multilayer wiring board. Furthermore, the third wiring conductor 25 may be a conductor forming a through hole or a conductor forming a castellation. The wiring board of the present disclosure can reduce the occurrence of defects in the wiring board 1 and the electronic device 60 and electronic module 100 including the wiring board 1.

[0043] In one embodiment, (1) a wiring board comprises: an insulating substrate having a first surface and a hole or groove opening on the first surface; a titanium oxide layer located in the hole or groove of the insulating substrate; and a conductor layer located on the titanium oxide layer, wherein the hole or groove has an inner surface, the inner surface having a first end closer to the first surface and a second end farther from the first surface, and the titanium oxide layer is located continuously from the first end to the second end on the inner surface.

[0044] (2) A wiring board comprises an insulating substrate whose main component is aluminum nitride and to which a plurality of particles are bonded; a titanium oxide layer located on the surface of the insulating substrate; and a conductor layer located on the titanium oxide layer, wherein the insulating substrate has undulations on the surface due to the shape and arrangement of the particles, and the titanium oxide layer covers the undulations.

[0045] (3) The wiring board of (2) above may further include: the insulating substrate has a first surface and a hole or groove opening in the first surface; the hole or groove has an inner surface that is part of the surface; the inner surface has a first end closer to the first surface and a second end farther from the first surface; and the titanium oxide layer may be positioned continuously from the first end to the second end on the inner surface.

[0046] (4) The wiring board according to any one of (1) to (3) above may further include the titanium oxide layer on the entire inner surface.

[0047] (5) In any of the wiring boards (1) to (4) above, the insulating substrate may further include a second surface opposite to the first surface, and the hole may be a through hole extending from the first surface to the second surface.

[0048] (6) The wiring board of any one of (1) to (5) above may further include a first diffusion layer at the interface between the titanium oxide layer and the insulating substrate, and the first diffusion layer may contain diffused elements contained in the titanium oxide layer and the insulating substrate.

[0049] (7) The wiring board according to any one of (1) to (6) above may further include a second diffusion layer at the interface between the titanium oxide layer and the conductor layer, and the second diffusion layer may have elements contained in the titanium oxide layer and the conductor layer diffused therein.

[0050] (8) In any of the wiring boards (1) to (7) above, the conductor layer is made of metal and includes a first conductor layer in contact with the titanium oxide layer and a second conductor layer located on the side opposite the titanium oxide layer with the first conductor layer in between, and the average size of the metal crystal grains in the first conductor layer can be smaller than the average size of the metal crystal grains in the second conductor layer.

[0051] (9) In the wiring board of any one of (1) to (8) above, the first conductor layer may be an electroless plated layer, and the second conductor layer may be an electrolytic plated layer.

[0052] (10) An electronic device may include the wiring board according to any one of (1) to (9) above, and an electronic component mounted on the wiring board.

[0053] (11) An electronic module may include the electronic device of (10) above, and a module substrate on which the electronic device is mounted.

[0054] The present disclosure can be used as a wiring board, an electronic device, and an electronic module.

[0055] REFERENCE SIGNS LIST 1 wiring substrate 10 insulating substrate 11 first surface 12 second surface 13 through portion 13a first opening 13b second opening 15 particles 31 titanium oxide layer 32 first conductor layer 33 second conductor layer 34 first diffusion layer 35 second diffusion layer 50 electronic component 60 electronic device 100 electronic module

Claims

1. A wiring board comprising: an insulating substrate whose main component is aluminum nitride and to which a plurality of particles are bonded; a titanium oxide layer located on a surface of the insulating substrate; and a conductor layer located on the titanium oxide layer, wherein the insulating substrate has undulations on its surface due to the shape and arrangement of the particles, and the titanium oxide layer covers the undulations.

2. The wiring board described in claim 1, wherein the insulating substrate comprises a first surface and a hole or groove opening into the first surface, the hole or groove having an inner surface which is a part of the surface, the inner surface having a first end closer to the first surface and a second end farther from the first surface, and the titanium oxide layer is positioned continuously from the first end to the second end of the inner surface.

3. The wiring board according to claim 2, wherein the titanium oxide layer is provided on the entire inner surface.

4. A wiring board as described in claim 2 or 3, wherein the insulating substrate has a second surface opposite to the first surface, and the hole is a through hole extending from the first surface to the second surface.

5. A wiring board as claimed in any one of claims 1 to 4, further comprising a first diffusion layer at the interface between the titanium oxide layer and the insulating substrate, the first diffusion layer having elements diffused therein from the titanium oxide layer and the insulating substrate.

6. A wiring board according to any one of claims 1 to 5, further comprising a second diffusion layer at the interface between the titanium oxide layer and the conductor layer, the second diffusion layer having elements diffused therein from the titanium oxide layer and the conductor layer.

7. A wiring board as claimed in any one of claims 1 to 6, wherein the conductor layer is made of metal and comprises a first conductor layer in contact with the titanium oxide layer, and a second conductor layer located on the side opposite the titanium oxide layer with the first conductor layer in between, and wherein the average size of the metal crystal grains in the first conductor layer is smaller than the average size of the metal crystal grains in the second conductor layer.

8. The wiring board according to claim 7, wherein the first conductor layer is an electroless plated layer, and the second conductor layer is an electrolytic plated layer.

9. An electronic device comprising: a wiring board according to any one of claims 1 to 8; and an electronic component mounted on the wiring board.

10. An electronic module comprising: the electronic device according to claim 9; and a module substrate on which the electronic device is mounted.

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