Circuit Board

Abstract

A circuit board 1 comprising: a ceramic substrate 10; a protruding electrode 20 which is formed on a surface of the ceramic substrate 10; and a protective layer 30 which covers at least part of a side surface 20a of the protruding electrode 20 and which contains a metal oxide, wherein the protective layer 30 is continuously formed so as to straddle the boundary b between the side surface 20a of the protruding electrode 20 and a surface 10a of the ceramic substrate 10.

Description

[Technical field]

[0001] The present invention relates to a circuit board. [Background technology]

[0002] Some substrates have electronic components mounted thereon and protruding electrodes provided around the area where the electronic components are mounted.

[0003] For example, Patent Document 1 discloses a circuit module that includes a substrate having an electrode base and metal posts directly connected onto the electrode base, with a plating layer formed around the periphery of the metal posts. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2018 / 168709 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the circuit module shown in Patent Document 1, the bonding strength between the metal posts (protruding electrodes) and the substrate was insufficient. Specifically, the metal posts sometimes peeled off from the substrate, and cracks sometimes occurred at the bonding portions between the metal posts and the substrate.

[0006] The present invention has been made to solve the above problems, and has an object to provide a circuit board capable of improving the bonding strength between the board and the protruding electrodes. [Means for solving the problem]

[0007] The circuit board of the present invention comprises a ceramic substrate, a protruding electrode formed on a surface of the ceramic substrate, and a protective layer containing a metal oxide covering at least a portion of a side surface of the protruding electrode, wherein the protective layer is formed continuously across the boundary between the side surface of the protruding electrode and the surface of the ceramic substrate. Effect of the Invention

[0008] According to the present invention, it is possible to provide a circuit board capable of improving the bonding strength between the substrate and the protruding electrodes. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view illustrating an example of a circuit board according to a first embodiment. [Diagram 2] FIG. 2 is a top view of the circuit board shown in FIG. [Diagram 3] FIG. 3 is a cross-sectional view taken along line AA in FIG. [Figure 4] FIG. 4 is a schematic diagram showing the thickness and height of the protective layer. [Diagram 5] FIG. 5 is an enlarged cross-sectional view of the vicinity of a protruding electrode of the circuit board of the second embodiment at a reference height. [Figure 6] FIG. 6 is an enlarged cross-sectional view of the vicinity of a protruding electrode of the circuit board of the third embodiment at a reference height. [Figure 7] FIG. 7 is an enlarged cross-sectional view of the vicinity of a protruding electrode of the circuit board of the fourth embodiment at the reference height. [Figure 8] FIG. 8 is an enlarged cross-sectional view of the vicinity of a protruding electrode of the circuit board of the fifth embodiment at the reference height. [Figure 9] FIG. 9 is an enlarged cross-sectional view of the vicinity of a protruding electrode of a circuit board according to the sixth embodiment at a reference height. [Figure 10] FIG. 10 is an enlarged cross-sectional view of the vicinity of a protruding electrode of the circuit board of the seventh embodiment at the reference height. [Figure 11] FIG. 11 is a perspective view illustrating an example of the circuit board according to the eighth embodiment. [Figure 12]FIG. 12 is a cross-sectional view taken along line BB in FIG. [Figure 13] FIG. 13 is a schematic diagram showing an example of a process for laminating constraining layer sheets onto a ceramic green sheet laminate. [Figure 14] FIG. 14 is a schematic diagram showing an example of a process for forming through holes in the constraining layer sheet. [Figure 15] FIG. 15 is a schematic diagram showing an example of a process for filling the through holes with a conductive paste that will become the protruding electrodes. [Figure 16] FIG. 16 is a schematic diagram showing an example of a step of firing the laminate. [Figure 17] FIG. 17 is a schematic diagram showing an example of a step of cleaning the fired laminate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The circuit board of the present invention will be described below. Note that the present invention is not limited to the following configurations, and may be modified as appropriate without departing from the gist of the present invention. In addition, a combination of multiple individual preferred configurations described below also constitutes the present invention.

[0011] [Circuit board] The circuit board of the present invention comprises a ceramic substrate, a protruding electrode formed on a surface of the ceramic substrate, and a protective layer containing a metal oxide covering at least a portion of a side surface of the protruding electrode, wherein the protective layer is formed continuously across the boundary between the side surface of the protruding electrode and the surface of the ceramic substrate.

[0012] Fig. 1 is a perspective view showing a schematic example of a circuit board according to embodiment 1. Fig. 2 is a top view of the circuit board shown in Fig. 1. Fig. 3 is a cross-sectional view taken along line AA in Fig. 2.

[0013] The circuit board 1 shown in FIG. 1 includes a ceramic substrate 10, protruding electrodes 20, and a protective layer 30. The protruding electrodes 20 are formed on a surface 10 a of the ceramic substrate 10 . The protruding electrodes 20 protrude from the surface 10a of the ceramic substrate 10 in the thickness direction of the ceramic substrate 10 (the direction indicated by the arrow z in FIG. 1). As shown in FIG. 1, at least a part of the side surface 20a of the protruding electrode 20 is covered with a protective layer 30. As shown in FIG.

[0014] As shown in FIG. 2, the bump electrode 20 has a cylindrical shape when viewed from above. The protective layer 30 covers the entire side surface 20a of the bump electrode 20 in top view.

[0015] As shown in FIG. 3, the protective layer 30 is formed continuously across a boundary b between the side surface 20a of the bump electrode 20 and the surface 10a of the ceramic substrate 10. Since the protective layer 30 is continuously formed across the boundary b between the side surface 20a of the protruding electrode 20 and the surface 10a of the ceramic substrate 10, the protective layer 30 can improve the bonding between the protruding electrode 20 and the ceramic substrate 10. Therefore, peeling of the protruding electrode 20 can be prevented.

[0016] As shown in FIG. 3, the ceramic substrate 10 includes a plurality of insulating layers 111, 112, and 113, an internal wiring 120, and a via conductor . The protruding electrodes 20 are electrically connected to the internal wiring 120 through via conductors 130 . The protruding electrodes 20 may be directly connected to the internal wiring 120 .

[0017] (Ceramic substrate) The ceramic substrate includes an insulating layer that includes a ceramic material. The ceramic substrate may include multiple insulating layers.

[0018] The ceramic material constituting the ceramic substrate includes a low-temperature co-fired ceramic material. The low-temperature sintering ceramic material refers to a ceramic material that can be sintered at a sintering temperature of 1000° C. or less and can be co-sintered with silver or copper, which are preferably used as metal materials for internal wiring. The low-temperature sintering ceramic material preferably includes SiO2-CaO-Al2O3-B2O3-based glass ceramic or SiO2-MgO-Al2O3-B2O3-based glass ceramic.

[0019] The ceramic substrate has internal wiring. Examples of materials constituting the internal wiring include Cu, Ag, Al, Fe, Cr, Ni, Au, and alloys containing at least one of these metals. It is preferable that the material be capable of being simultaneously fired with the low-temperature co-fired ceramic material.

[0020] (protruding electrode) The protruding electrodes are formed on the surface of the ceramic substrate. The protruding electrodes may be directly connected to the internal wiring constituting the ceramic substrate, or may be connected through via conductors.

[0021] The shape of the protruding electrodes may be a columnar shape such as a circular cylinder, an elliptical cylinder, or a polygonal cylinder.

[0022] The shape of the protruding electrodes is not particularly limited, but it is preferable that the height is 50 μm or more and 300 μm or less, and the diameter is 100 μm or more and 300 μm or less. The height of the protruding electrode means the height from the surface of the ceramic substrate, and the diameter of the protruding electrode means the diameter (equivalent circle diameter) of a circle having the same area as the area (projected area) of the protruding electrode when viewed from above.

[0023] The aspect ratio (height / circular equivalent diameter) of the protruding electrodes is not particularly limited, but is preferably 0.5 or more and 1.5 or less.

[0024] Examples of materials that can be used to form the bump electrodes include Cu, Ag, Al, Fe, Cr, Ni, Au, and alloys containing at least one of these metals. The bump electrodes may include a sintered metal, which is a sintered body of metal powder made of the above metals.

[0025] The bump electrodes preferably contain at least one metal selected from the group consisting of Cu, Ag, and Ni. If the protruding electrodes contain these metals, they have good electrical conductivity.

[0026] A plurality of protruding electrodes may be formed. The shapes of the plurality of protruding electrodes may be the same or different.

[0027] (protective layer) The protective layer contains a metal oxide. The protective layer contains a metal oxide and is different from a plating film formed by a plating process.

[0028] The protective layer preferably contains a metal oxide made of at least one metal element selected from the group consisting of Al, Zr, Ti, Si, Zn, and Mg. When the protective layer contains the above-mentioned metal oxide, the bonding strength between the ceramic substrate and the protruding electrodes by the protective layer is increased, and the occurrence of peeling and cracks can be suppressed.

[0029] The protective layer is preferably composed mainly of SiO2. When the main component of the protective layer is SiO2, it has a high affinity with the ceramic material constituting the ceramic substrate, which increases the bonding strength between the ceramic substrate and the protruding electrodes and suppresses the occurrence of peeling and cracks. The main component means the component that is contained in the protective layer in the largest amount (weight percentage).

[0030] The protective layer preferably contains the ceramic material that constitutes the ceramic substrate. When the protective layer contains a ceramic material, the bonding strength between the protective layer and the ceramic substrate is increased, thereby increasing the bonding strength between the protective layer and the ceramic substrate and the protruding electrode, thereby further suppressing peeling and cracking. The protective layer preferably includes a low-temperature sintering ceramic material similar to that of the ceramic substrate, such as SiO2-B2O3-K2O glass ceramic, SiO2-B2O3-K2O-ZrO glass ceramic, SiO2-B2O3-ZnO-Al2O3 glass ceramic, SiO2-B2O3-Al2O3-CaO-SrO glass ceramic, SiO2-BaO-CaO-SrO glass ceramic, SiO2-BaO-Al2O3-TiO2 glass ceramic, SiO2-CaO-Al2O3-B2O3 glass ceramic, SiO2-MgO-Al2O3-B2O3 glass ceramic, or Al2O3-CaO-SiO2-MgO-B2O3 glass ceramic.

[0031] The thickness of the protective layer is not particularly limited, but is preferably 10 μm or more.

[0032] The height of the protective layer from the surface of the ceramic substrate (hereinafter also simply referred to as the height of the protective layer) is not particularly limited, but is preferably 15 μm or more.

[0033] The thickness and height of the protective layer are measured by the following method. First, the circuit board is sealed with a molding resin or the like, and then the circuit board is cut along a plane that passes through the center of gravity of the protruding electrode when viewed from above and that is along the thickness direction of the circuit board (the direction in which the protruding electrode protrudes). The cut surface is observed with a metallurgical microscope, a scanning electron microscope (SEM), a scanning electron microscope-energy dispersive X-ray spectroscopy analysis (SEM-EDX), or the like, and the thickness of the protective layer at a point where the height from the surface of the ceramic substrate is the reference height, and the height of the protective layer from the surface of the ceramic substrate are measured.

[0034] The thickness and height of the protective layer will be described with reference to FIG. FIG. 4 is a schematic diagram showing the thickness and height of the protective layer. The height of the protective layer 30 from the surface 10a of the ceramic substrate 10 is represented by the length indicated by the double-headed arrow h. The thickness of the protective layer 30 is the reference height h rt is the thickness of the protective layer 30 (the length indicated by the double arrow t). Reference height h r is 3 μm. However, when the height of the protective layer is less than 3 μm, half the height of the protective layer is used as the reference height.

[0035] The coverage of the protective layer with respect to the side surfaces of the bump electrodes is preferably 50% or more.

[0036] The coverage rate of the protective layer on the side surface of the protruding electrode is measured by the following method. First, the circuit board is sealed with a molding resin or the like, and then the surface on which the protruding electrode is provided is polished flat to expose a point whose height from the surface of the ceramic substrate is a reference height. In the exposed cross section, the outer periphery of the protruding electrode and the length of the protective layer are determined, and the coverage rate is obtained by dividing the length of the protective layer by the outer periphery of the protruding electrode.

[0037] In the circuit board of the present invention, the protective layer preferably has a thickness of 10 μm or more, a height from the surface of the ceramic substrate of 15 μm or more, and a coverage rate of the side surfaces of the bump electrodes of 50% or more. When all three of the above characteristics are satisfied, peeling and cracking of the protruding electrodes can be further suppressed.

[0038] The coverage of the protective layer on the side surface of the bump electrode will be described with reference to FIGS.

[0039] FIG. 5 is an enlarged cross-sectional view of the vicinity of a protruding electrode of the circuit board of the second embodiment at a reference height. The cross-sectional shape of the protruding electrode 21 shown in FIG. 5 is circular. A part of the side surface 21a of the protruding electrode 21 shown in FIG. The length of the region of the side surface 21a of the protruding electrode 21 where the protective layer 31 is provided is 79.2% of the length of the side surface 21a of the protruding electrode 21. Therefore, in the protruding electrode 21 shown in FIG.

[0040] FIG. 6 is an enlarged cross-sectional view of the vicinity of a protruding electrode of the circuit board of the third embodiment at a reference height. The cross-sectional shape of the protruding electrode 22 shown in FIG. 6 is a square. The protective layer 32 covers the entire side surface 22a of the protruding electrode 22. Therefore, the coverage rate of the protruding electrode 22 shown in FIG.

[0041] FIG. 7 is an enlarged cross-sectional view of the vicinity of a protruding electrode of the circuit board of the fourth embodiment at the reference height. The cross-sectional shape of the protruding electrode 23 shown in FIG. 7 is a square. The protective layer 33 is provided so as to cover the corners of the square of the side surface 23a of the protruding electrode 23. The length of one side of the square is l1, and the protective layer 33 covers only a length of l2 from the corner of the one side. Therefore, the coverage rate of the protruding electrode 23 shown in FIG. 7 is expressed as (8×l2) / (4×l1)×100(%).

[0042] FIG. 8 is an enlarged cross-sectional view of the vicinity of a protruding electrode of the circuit board of the fifth embodiment at the reference height. The cross-sectional shape of the protruding electrode 24 shown in FIG. 8 is a square. The protective layer 34 is provided so as to cover a part of the side surface 24a of the protruding electrode 24 that forms the sides of the square. With respect to the length l1 of one side of the square, the protective layer 34 covers each side by a length of l3. Therefore, the coverage rate of the protruding electrodes 24 shown in FIG. 8 is expressed as (4×l3) / (4×l1)×100(%).

[0043] FIG. 9 is an enlarged cross-sectional view of the vicinity of a protruding electrode of a circuit board according to the sixth embodiment at a reference height. The cross-sectional shape of the protruding electrode 25 shown in FIG. 9 is a square. The protective layer 35 is provided so as to cover two corners of the side surface 25a of the protruding electrode 25 that face each other across a diagonal line of the square. With the length of one side of the square being l1, the protective layer 35 covers only a length of l4 from the corner of the side. Therefore, the coverage rate of the protruding electrode 25 shown in FIG. 9 is expressed as (4×l4) / (4×l1)×100(%).

[0044] FIG. 10 is an enlarged cross-sectional view of the vicinity of a protruding electrode of the circuit board of the seventh embodiment at the reference height. The cross-sectional shape of the protruding electrode 26 shown in FIG. 10 is a square. The protective layer 36 is provided so as to cover part of two opposing square sides 26a of the side surface 26a of the protruding electrode 26. With one side of the square having a length of l1, the protective layer 36 covers two sides by a length of l5. Therefore, the coverage of the protruding electrodes 26 shown in FIG. 10 is expressed as (2×l5) / (4×l1)×100(%).

[0045] In the circuit board of the present invention, it is preferable that the protective layer covering the side surfaces of the protruding electrodes has high symmetry. In a cut surface of the circuit board cut at the reference height, a state in which the protective layers are provided at locations facing each other across the center of gravity determined from the outer shape of the protruding electrode is a state of high symmetry. For example, in the protruding electrodes shown in Figures 6, 7, 8, 9 and 10, all of the protective layers face each other across the center of gravity (not shown) of the cross-sectional shape of the protruding electrode, and it can be said that the electrodes are in a highly symmetrical state. On the other hand, in the protruding electrode shown in Figure 5, the protective layer 31a faces the protective layer 31 across the center of gravity C1, but the protective layer 31b does not face the protective layer 31 across the center of gravity C1. Comparing the protruding electrodes 22, 23, 24 and 25 shown in Figures 6, 7, 8, 9 and 10 with the protruding electrode 21 shown in Figure 5, it can be said that the protruding electrodes 22, 23, 24 and 25 shown in Figures 6, 7, 8, 9 and 10 are more symmetrical, as they do not have any parts of the protective layer that are not opposed across the center of gravity.

[0046] In the circuit board of the present invention, it is preferable that at least a part of the surface of the ceramic substrate on which the protruding electrodes are formed is covered with a molding resin. If the surface of the ceramic substrate on which the protruding electrodes are formed is covered with a molding resin, the protruding electrodes can be protected. It is preferable that the molding resin covers the entire surface of the ceramic substrate on which the protruding electrodes are formed.

[0047] The height of the molding resin is preferably the same as that of the protruding electrodes, and in this case, a plating film is preferably provided on the upper surface of the protruding electrodes. The upper surface of the bump electrode refers to a surface other than the side surface of the bump electrode, that is, the surface opposite to the surface of the bump electrode that is in contact with the ceramic substrate.

[0048] The plating film can be formed, for example, by performing a plating process on the upper surface of the bump electrode. The thickness of the plating film is not particularly limited, but is preferably 5 μm or more and 15 μm or less. Examples of materials that can be used to form the plating film include Cu, Ag, Ni, Sn, Zn, and Au.

[0049] Examples of the molding resin include epoxy resin, acrylic resin, and silicone resin. The molding resin may further contain a filler.

[0050] An example of a circuit board provided with a molding resin will be described with reference to FIGS. Fig. 11 is a perspective view showing a schematic example of a circuit board according to embodiment 8. Fig. 12 is a cross-sectional view taken along line BB in Fig. 11.

[0051] The circuit board 2 shown in FIGS. 11 and 12 includes a ceramic substrate 10, protruding electrodes 20, a protective layer 30, a molding resin 50, and a plating film 60. As shown in FIG.

[0052] The circuit board 2 shown in Figures 11 and 12 has the same configuration as the circuit board 1 shown in Figures 1, 2, and 3, except that the surface 10a of the ceramic substrate 10 is covered with a molded resin 50 and a plating film 60 is formed on the upper surface 20b of the protruding electrode 20.

[0053] As shown in FIG. 12, the height of the molding resin 50 and the height of the protruding electrodes 20 are the same. Since the plating film 60 is formed on the upper surface 20 b of the bump electrode 20 , it can be said that it protrudes from the molding resin 50 . If the plating film 60 protrudes beyond the mold resin 50, the connection between the circuit board 2 and other electronic components is excellent.

[0054] [Circuit board manufacturing method] The circuit board of the present invention can be obtained, for example, by laminating a constraining layer sheet on the surface of a laminate of ceramic green sheets (ceramic green sheet laminate) that will become a ceramic substrate, forming through holes in the laminated constraining layer sheet and filling them with a conductive paste (also called protruding electrode paste) that will become protruding electrodes upon firing, and washing and removing the constraining layer sheet after firing, and adding an additive to the conductive paste.

[0055] An example of a method for producing a circuit board of the present invention will be described with reference to FIGS. Fig. 13 is a schematic diagram showing an example of a process for laminating a constraining layer sheet on a ceramic green sheet laminate. Fig. 14 is a schematic diagram showing an example of a process for forming a through hole in a constraining layer sheet. Fig. 15 is a schematic diagram showing an example of a process for filling a conductive paste that becomes a protruding electrode in the through hole. Fig. 16 is a schematic diagram showing an example of a process for firing the laminate. Fig. 17 is a schematic diagram showing an example of a process for cleaning the laminate after firing.

[0056] First, as shown in FIG. 13, a laminate 300 is prepared by laminating two constraining layer sheets 200 on each side of a ceramic green sheet laminate 210 in which ceramic green sheets 211, 212, and 213 that will become a ceramic substrate are laminated. The ceramic green sheet laminate 210 is provided with conductive paste 220 which will become internal wiring when fired, and conductive paste 230 which will become via conductors. The number of constraining layer sheets 200 constituting the laminate 300 is not particularly limited. However, the height of the protruding electrodes to be formed is determined by the total thickness of the constraining layer sheets 200 laminated on the surface side of the ceramic green sheet laminate 210 where the conductive paste 230 serving as the via conductor is exposed. Therefore, the thickness of the constraining layer sheets and the number of laminated sheets may be appropriately adjusted according to the height of the protruding electrodes to be formed.

[0057] The total thickness of the constraining layer sheet 200 provided on the surface of the ceramic green sheet laminate 210 where the conductive paste 230 serving as the via conductor is not exposed is preferably the same as the total thickness of the constraining layer sheet 200 provided on the surface where the conductive paste 230 is exposed, but may be different. In addition, the constraining layer sheet does not have to be provided on the surface of the ceramic green sheet laminate 210 where the conductive paste 230 serving as the via conductor is not exposed.

[0058] 14 and 15, through holes 201 are formed in the upper constraining layer sheet 200, and the formed through holes 201 are filled with the protruding electrode paste 240. When forming the through holes 201, the positions of the through holes 201 are adjusted so that the protruding electrode paste 240 contacts the conductive paste 230 that serves as the via conductor. The formation of the through holes 201 in the constraining layer sheet 200 and the filling of the protruding electrode paste 240 may be performed before laminating the constraining layer sheet 200 on the ceramic green sheet laminate 210.

[0059] 16, the ceramic green sheets 211, 212, and 213 become the insulating layers 111, 112, and 113, respectively, and the conductive paste 220 that becomes the internal wiring and the conductive paste 230 that becomes the via conductor become the internal wiring 120 and the via conductor 130, respectively. Furthermore, the protruding electrode paste 240 becomes the protruding electrodes 20. At this time, the additive components diffuse from the protruding electrode paste 240 into the constraining layer sheet 200, so that a part of the constraining layer sheet 200 becomes the protective layer 30.

[0060] Finally, as shown in FIG. 17, the constraining layer sheet 200 is removed by washing, to obtain the circuit board 1 shown in FIG. The protective layer 30 formed by diffusing the additive component in the constraining layer sheet 200 is more resistant to cleaning than the constraining layer sheet 200 in which the additive component is not diffused. Therefore, it is possible to remove the constraining layer sheet 200 by cleaning and leave the protective layer 30. Here, since the protective layer is more likely to be removed toward the tip of the protruding electrode, the protective layer formed on the side of the part close to the tip of the protruding electrode is easily removed by cleaning. On the other hand, the protective layer formed so as to straddle the boundary between the side of the protruding electrode and the surface of the ceramic substrate is far from the tip of the protruding electrode, and is therefore difficult to remove by cleaning. In addition, the thickness and coverage of the protective layer 30 can be adjusted by controlling the cleaning conditions.

[0061] In this method, the formation of the protruding electrodes and the formation of the protective layer are carried out simultaneously, so that there are no protruding electrodes without a protective layer formed thereon, and therefore there is no need to protect the bare protruding electrodes without a protective layer formed thereon from impacts, which is preferable in terms of process management.

[0062] The constraining layer sheet can be removed, for example, by washing with a washing liquid. The cleaning liquid may be, for example, a cleaning liquid containing ceramic abrasive grains and water. Examples of the ceramic abrasive grains include alumina abrasive grains, zirconia abrasive grains, and glass abrasive grains.

[0063] The bump electrode paste contains at least a conductive powder and a binder. The conductive powder is preferably a metal powder such as Cu, Ag, Al, Fe, Cr, Ni, Au, or a metal or alloy containing at least one of these metals. The binder may be, for example, a terpineol solvent-based binder containing an ethyl cellulose resin.

[0064] The additives added to the bump electrode paste react with the constraining layer sheet during firing to form a protective layer.

[0065] The additive preferably contains, for example, at least one metal element selected from the group consisting of Zr, Ti, Si, Zn, and Mg.

[0066] Examples of additives include SiO2-B2O3-K2O based glass, SiO2-BaO-Al2O3-TiO2 based glass, SiO2-BaO-CaO-SrO based glass, SiO2-B2O3-Al2O3-CaO-SrO based glass, Al2O3-CaO-SiO2-MgO-B2O3 based glass, SiO2-B2O3-K2O-ZrO based glass, and SiO2-B2O3-ZnO-Al2O3 based glass.

[0067] The amount of additive contained in the bump electrode paste is preferably 0.1 to 15% by weight.

[0068] In addition to the method described above, the circuit board of the present invention can also be obtained, for example, by producing a protruding electrode without adding any additives to the protruding electrode paste, and then continuously applying a protective layer-forming paste across the boundary between the side of the protruding electrode and the surface of the ceramic substrate, and then firing the applied paste.

[0069] The protective layer forming paste preferably contains at least one metal element selected from the group consisting of Al, Zr, Ti, Si, Zn, and Mg, and more preferably contains at least one of SiO2 and Al2O3.

[0070] Regardless of the method for forming the protective layer, the preferred composition of the protective layer is the same. EXAMPLES

[0071] Hereinafter, examples will be given that more specifically disclose the circuit board of the present invention, however, the present invention is not limited to these examples.

[0072] Example 1 (Preparation of ceramic green sheets) BaO, Al2O3 and SiO2 were mixed to obtain a predetermined composition and calcined at 800 to 1000° C. The calcined powder obtained was pulverized in a zirconia ball mill for 12 hours to obtain a ceramic powder. Next, an organic solvent containing toluene and ethanol was added to this ceramic powder and mixed, after which a binder and a plasticizer were added and mixed again to obtain a slurry. This slurry was formed by a doctor blade method to prepare a ceramic green sheet having a thickness of 50 μm.

[0073] (Preparation of Constraint Layer Sheet) Alumina powder of 0.5 μm to 5.0 μm was mixed with an acrylic binder to obtain a slurry, which was then formed into a constraining layer sheet having a thickness of 100 μm by a doctor blade method.

[0074] (Preparation of protruding electrode paste) A bump electrode paste was obtained by mixing 86.6 parts of Cu powder, which is a metal powder, 11.0 parts of binder, and 2.4 parts of additive A shown in Table 1, and dispersing them with a triple roll. A terpineol solvent-based binder containing ethyl cellulose resin was used as the binder.

[0075] [Table 1]

[0076] (Forming holes in the constraint layer sheet and filling with protruding electrode paste) Holes having a diameter of 230 μm were formed in the constraining layer sheet by laser processing, and the holes were then filled with the protruding electrode paste to obtain a constraining layer sheet filled with the protruding electrode paste.

[0077] (Lamination and compression) Two constraining layer sheets filled with the above-mentioned protruding electrode paste were laminated on the outermost layer of a ceramic green sheet laminate obtained by laminating ceramic green sheets, and then pressure-bonded to obtain a laminate.

[0078] (Firing) The laminate was fired at a maximum temperature of 930 to 1000° C. to obtain a fired body. During firing, the atmosphere in the firing furnace was controlled using N2 / H2 / H2O so that the oxygen concentration was such that copper would not be oxidized.

[0079] (Removal of the constraining layer sheet) The sintered body was washed for 3 minutes using a cleaning solution containing alumina abrasive grains (average particle size: 20 μm) and water (alumina abrasive grain content: 18% by weight), and the constraint layer sheet was removed to obtain a sintered body with protruding electrodes formed thereon.

[0080] (Sealing with mold resin) The surface (protruding electrode side) of the obtained ceramic substrate was sealed with a mold resin, and the surface of the mold resin was polished to expose the upper surfaces of the protruding electrodes. Thereafter, a plating film was formed on the upper surfaces of the protruding electrodes by a plating process, thereby obtaining the circuit board according to Example 1. A circuit board was also prepared in which the surface of the ceramic substrate was not sealed with molding resin, and the circuit board not sealed with molding resin was used for the peel strength measurement described later.

[0081] (Examples 2 to 14 and Comparative Example 1) Except for changing the composition of the bump electrode paste and the type of additive as shown in Table 2, the circuit boards according to Examples 2 to 14 and Comparative Example 1 were produced in the same manner as in Example 1. The cleaning conditions for removing the constraining layer sheet were the same as in Example 1.

[0082] [Table 2]

[0083] (Measurement of thickness, height and coverage of protective layer) The circuit boards of Examples 1 to 14 and Comparative Example 1 were subjected to surface polishing or cutting to expose predetermined cross sections, and the thickness, height, and coverage of the protective layer were measured. The results are shown in Table 3.

[0084] (Measuring the bonding strength) The bonding strength was measured by the following method using the circuit board in which the surface of the ceramic substrate was not covered with the molding resin. The bonding strength between the protruding electrodes and the substrate was measured using a universal bond tester 4000Plus (manufactured by Nordson Advanced Technology). The tip of the tool was moved toward the protruding electrodes at a constant speed, and the force at which the protruding electrodes peeled off from the ceramic substrate was measured as the bonding strength. The load cell was BS5kg, the tool size was 300μm, the tool speed was 50μm / s, and the height was 50μm. The protruding electrodes used to measure the bonding strength were all cylindrical, with a height of 200μm and a diameter of 230μm. The measured bonding strength was evaluated according to the following criteria. ⊚: The bonding strength is greater than 3.5 N, and is particularly effective in preventing peeling and cracking. ◯: The bonding strength is greater than 2.5 N and equal to or less than 3.5 N, and the effect of suppressing peeling and cracks is excellent. △: The bonding strength is greater than 2.0 N and less than 2.5 N, and peeling and cracks are suppressed. ×: The bonding strength is 2.0 N or less, and the occurrence of peeling or cracks cannot be prevented.

[0085] [Table 3]

[0086] The results in Table 3 show that in the circuit boards of each embodiment, the bonding strength of the protruding electrodes was high and cracks and peeling were unlikely to occur. Furthermore, by comparing Examples 1 to 11 with Examples 12 to 14, it was found that the bonding strength was increased when all three conditions were met: the thickness of the protective layer was 10 μm or more, the height of the protective layer was 15 μm or more, and the coverage rate was 50% or more. [Explanation of symbols]

[0087] 1, 2 Circuit Board 10 Ceramic Substrate 10a Surface of ceramic substrate 20, 21, 22, 23, 24, 25, 26 protruding electrode 20a, 21a, 22a, 23a, 24a, 25a, 26a Sides of protruding electrodes 20b Upper surface of protruding electrode 30, 31, 31a, 31b, 32, 33, 34, 35, 36 protective layer 50 Molding resin 60 Plating Film 111, 112, 113 Insulating layer 120 Internal wiring 130 Via conductor 200 Constraint layer sheet 201 Through hole 210 Ceramic green sheet laminate 211, 212, 213 Ceramic green sheet 220 Conductive paste for internal wiring 230 Conductive paste for via conductor 240 Protruding electrode paste 300 Laminate b The boundary between the side of the protruding electrode and the surface of the ceramic substrate C1 Center of gravity of protruding electrode h Height of the protective layer h r Reference Height l1 length of one side of a square l2, l3, l4, l5 protective layer lengths t Thickness of protective layer

Claims

1. A ceramic substrate, a protruding electrode formed on a surface of the ceramic substrate, and a protective layer containing a metal oxide, the protective layer covering at least a part of a side surface of the protruding electrode, the protective layer is formed continuously across a boundary between a side surface of the bump electrode and a surface of the ceramic substrate, The protruding electrodes have a height of 50 μm or more and 300 μm or less and a diameter of 100 μm or more and 300 μm or less, the protective layer has a thickness of 10 μm or more, a height from the surface of the ceramic substrate of 15 μm or more, and a coverage rate of the side surface of the bump electrode of 50% or more; When a position of 3 μm from the surface of the ceramic substrate is set as a reference height, a protective layer provided discontinuously at a plurality of locations when the protruding electrode is viewed in cross section at the reference height, the protective layer being provided discontinuously at a plurality of locations.

2. The protective layer is made of SiO ２ The circuit board according to claim 1 ,

3. 3. The circuit board according to claim 1, wherein the protective layer contains a metal oxide made of at least one metal element selected from the group consisting of Al, Zr, Ti, Si, Zn, and Mg.

4. 4. The circuit board according to claim 1, wherein the protective layer contains a ceramic material that constitutes the ceramic board.

5. 5. The circuit board according to claim 1, wherein the protruding electrodes contain at least one metal selected from the group consisting of Cu, Ag, and Ni.

6. 6. The circuit board according to claim 1, wherein the protruding electrodes include a sintered metal.

7. 7. The circuit board according to claim 1, wherein at least a part of the surface of said ceramic substrate on which said protruding electrodes are formed is covered with a molding resin.

8. 8. The circuit board according to claim 1, wherein, when said protruding electrode is viewed in cross section at said reference height, said protective layer is provided at a plurality of discontinuous and symmetrical positions.

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