JP2006319314A - Circuit board and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a circuit board with a high conductive reliability which can suppress a production of a void on a metallic conductor formed from a top face to a bottom surface of an insulating substrate, a peeling of the metallic conductor from the insulating substrate, and a production of a crack on the insulating substrate. <P>SOLUTION: In a circuit board 1 constituted by filling a through-hole 2 formed in an insulating substrate 1 with a metallic conductor 5, while making an inner diameter of a center section in the depth direction of the through-hole 2 smaller than an inner diameter of an opening, an inclination of an inner wall side of the through-hole 2 to the depth direction is changed multiple times toward the opening from the center section of the through-hole 2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a circuit board having a through hole filled with a metal conductor and a method for manufacturing the circuit board.

  Along with the recent remarkable miniaturization and high-density mounting of electronic components, circuit boards on which electronic components are mounted are also required to have high performance. As the method, a method of reducing the size by miniaturizing a patterned circuit conductor, a method of multilayering the circuit conductor three-dimensionally, or the like is adopted.

  As a method of multilayering circuit conductors three-dimensionally, a method of laminating a plurality of circuit boards in which the upper and lower surfaces are electrically connected by metal conductors is adopted, and desired conduction between each layer is ensured. As a result, circuit design has been performed to cope with downsizing, high integration, and the like.

  A circuit board having such a three-dimensional high-density wiring is widely put into practical use in the field of printed wiring boards using a resin-made substrate having good workability, but a ceramic substrate having excellent insulation characteristics and heat dissipation characteristics ( There is also an increasing demand for alumina sintered bodies, aluminum nitride sintered bodies, silicon carbide sintered bodies, and the like. As a circuit board manufacturing method used in the multilayer circuit board manufacturing method using such a ceramic substrate, a so-called cofire method and a postfire method are known.

  The cofire method is a paste-like substance in which a through hole is drilled in a ceramic precursor before sintering called a ceramic green sheet (hereinafter also referred to as a green sheet), and then metal powder is dispersed in the organic binder in the through hole. (Hereinafter, also referred to as a metal paste), followed by degreasing and firing.

  On the other hand, the post-fire method is a method in which a ceramic paste with through holes formed is filled with a metal paste and refired. As a general-purpose method, after punching a green sheet, degreasing, and firing, In this method, a ceramic sintered body is directly processed using a drill, and a metal conductor is formed using an etching method or a copper plating method.

  In any method, after drilling the insulating substrate precursor or the insulating substrate, metal conductors for conduction on the upper and lower surfaces are formed.

  In the post-fire method, through holes are formed in the insulating substrate after firing, so that the through hole dimensions and positional accuracy can be formed with high accuracy, while the through hole is filled with a metal conductor by plating or the like and There was a tendency for the metal conductor bonding reliability and voids to remain in the through-holes to cause problems that deteriorate the long-term reliability of the device.

Post-fire methods that address these problems are also being considered. For example, in Patent Document 1 below, a through hole having a narrowest portion is formed in an insulating substrate, current density is concentrated on the narrowest portion to promote plating growth, and the through hole is blocked from the narrowest portion. This prevents the formation of voids.
JP 2004-311919 A

  However, according to the post-fire method as described in Patent Document 1, although the metal conductor can be formed without generating voids in the through hole, the opening diameter of the through hole is increased. When the through-hole formation density is increased, the stress applied to the insulating substrate increases due to the difference in thermal expansion coefficient between the insulating substrate and the metal conductor. However, there is a problem that the reliability of connection with the insulating substrate is lowered, and heat generated by electronic components mounted on the surface of the substrate cannot be effectively transmitted to the back surface.

  The present invention has been completed in view of the problems of the prior art, and its purpose is that voids are generated in the metal conductor formed from the upper surface to the lower surface of the insulating substrate, or the metal conductor and the insulating substrate are peeled off. An object of the present invention is to provide a circuit board with high conduction reliability capable of suppressing the occurrence of cracks in an insulating substrate.

  The circuit board of the present invention is a circuit board formed by filling a through hole formed in an insulating substrate with a metal conductor, and the inner diameter of the central portion in the depth direction of the through hole is made smaller than the inner diameter of the opening. The inclination angle of the inner wall surface of the through hole with respect to the depth direction is changed a plurality of times from the center of the through hole toward the opening.

  In the circuit board according to the present invention, it is preferable that the inner diameter of the through hole is gradually increased from the central portion of the through hole toward the opening.

  The circuit board according to the present invention is preferably characterized in that an inner surface of the insulating substrate is recessed from the opening toward the center in the longitudinal sectional shape of the through hole.

  In the circuit board of the present invention, it is preferable that an inner surface of the insulating substrate located at a central portion in the depth direction of the through hole is protruded inward to form a protruding portion.

  In the circuit board according to the present invention, preferably, the inner surface of the recessed insulating substrate has a concave curved surface shape.

  In the circuit board of the present invention, preferably, a bonding metal layer made of at least one of titanium, chromium, aluminum, molybdenum, tungsten, copper, and nickel-chromium alloy is deposited on the inner surface of the insulating substrate in the through hole. It is characterized by that.

  In the circuit board of the present invention, preferably, the metal conductor is made of at least one of copper, silver, and titanium.

  In the circuit board of the present invention, preferably, the metal conductor is formed by a plating method.

  The circuit board of the present invention is a circuit board formed by filling a through hole formed in an insulating substrate with a metal conductor, and the inner diameter of the central portion in the depth direction of the through hole is made smaller than the inner diameter of the opening. The inclination angle of the inner wall surface of the through hole with respect to the depth direction is continuously changed from the center of the through hole toward the opening.

  In the method for manufacturing a circuit board according to the present invention, an upper recess is formed on one main surface of an insulating substrate by blasting so that abrasive grains are ejected more at the center than at the periphery, and then the other main surface of the insulating substrate is formed. An inner diameter of the central portion in the depth direction is formed by forming a lower concave portion so that abrasive grains are ejected more in the central portion than in the peripheral portion by a blast method at a position corresponding to the upper concave portion and penetrating the central portion. And forming a through hole in which the inner surface of the insulating substrate is recessed from the opening toward the center in the longitudinal sectional shape.

  According to the circuit board of the present invention, the inner diameter of the center portion in the depth direction of the through hole is made smaller than the inner diameter of the opening portion, and the through hole with respect to the depth direction from the center portion of the through hole toward the opening portion is formed. Since the inclination angle of the inner wall surface is changed several times, the metal conductor can be suppressed very well in the vertical direction, so that peeling between the metal conductor and the insulating substrate may occur. It is possible to provide a circuit board with high conduction reliability that effectively prevents cracks from occurring.

  In addition, the stress generated in the vicinity of the interface between the metal conductor and the insulating substrate due to the thermal expansion in the lateral direction of the metal conductor, the central portion of the through hole located on the inner side in plan view, and the opening of the through hole located on the outer side Since it can be dispersed in the vicinity of the portion, it is possible to effectively prevent the stresses at the respective parts from being combined and become a large stress, and the stress generated in the insulating substrate can be extremely reduced.

  Furthermore, since the inner diameter of the through hole is increased from the center toward the opening, it is effective to disperse the stress due to the difference in thermal expansion between the metal conductor and the insulating substrate and to concentrate the stress locally. Can be prevented.

  Furthermore, since the inner surface of the insulating substrate that forms the inner wall surface of the through hole is in the shape of the metal conductor at the center of the through hole, the metal conductor does not fall off even under mechanical impact. Can be provided.

  According to the circuit board of the present invention, since the inner surface between the projecting portion of the through hole and the opening has a concave curved surface shape, the volume of the metal conductor can be increased, and a circuit board with higher thermal conductivity can be obtained. Can be provided.

  According to the circuit board of the present invention, the joining metal layer made of at least one of titanium, chromium, aluminum, molybdenum, tungsten, copper, and nickel-chromium alloy is deposited on the inner surface of the insulating substrate in the through hole. The inner wall surface of the through hole and the metal conductor can be brought into close contact with each other with high strength, and a highly reliable circuit board can be obtained.

  According to the circuit board of the present invention, since the metal conductor is made of at least one of copper, silver, and titanium, the metal conductor led out from the upper surface to the lower surface of the insulating substrate is used for the thermal conductivity and the electric conductivity. Therefore, it is possible to obtain a highly reliable circuit board having low electrical resistance and excellent heat-drawing characteristics.

  According to the circuit board of the present invention, since the metal conductor is formed by a plating method, the plating is favorably grown from the inside of the protruding portion having a small inner diameter of the through hole, and from the central portion in the depth direction of the through hole. Since metal conductors can be formed in order in the upper and lower openings, it is possible to effectively prevent voids from occurring inside the metal conductor and between the metal conductor and the inner surface of the through hole.

  The circuit board of the present invention will be described in detail with reference to FIG.

  FIG. 1 is a sectional view showing an example of an embodiment of a circuit board according to the present invention, and FIG. 2 is a sectional view showing another example of an embodiment of a circuit board according to the present invention. In these drawings, 1 is an insulating substrate, 2 is a through hole, 3 is a protruding portion, 4 is a bonding metal layer, 5 is a metal conductor, and 6 is a wiring conductor layer.

The insulating substrate 1 is made of a ceramic insulating material such as an aluminum oxide (alumina: Al ₂ O ₃ ) sintered body or an aluminum nitride (AlN) sintered body, and the insulating substrate 1 is made of, for example, an aluminum oxide sintered body. In order to form a slurry, first, an appropriate organic solvent or solvent is added to and mixed with raw material powders such as alumina (Al ₂ O ₃ ), silica (SiO ₂ ), calcia (CaO), magnesia (MgO), etc. Is formed into a sheet by a conventionally known doctor blade method, calendar roll method or the like to obtain a ceramic green sheet (hereinafter also referred to as a green sheet). Thereafter, the green sheet is punched into a predetermined shape, and a plurality of sheets are laminated as necessary, and the green sheet is fired at a temperature of about 1600 ° C. Thereafter, the main surface of the insulating substrate 1 may be polished as necessary.

  In particular, when an aluminum oxide sintered body or an aluminum nitride sintered body is used as the material of the insulating substrate 1, the thermal conductivity of these materials is as high as 40 W / m · K or higher, so that high heat dissipation. From the viewpoint of performance, it can be suitably used for a circuit board on which various semiconductor elements having a large calorific value such as LD (laser diode), LED (Light Emitting Diode), and high-speed CPU (Central Processing Unit) are mounted.

  The inner diameter of the through hole 2 gradually decreases from the opening toward the center. Further, in the longitudinal section of the through hole 2, the inner surface of the insulating substrate 1 that forms the inner wall surface of the through hole 2 has a recessed shape between the opening and the center of the through hole 2. In particular, in the circuit board shown in FIG. 1, the inner surface of the insulating substrate 1 protrudes to the inside of the through hole 2 at the center portion of the through hole 2 to form a protruding portion 3. Here, the vertical cross section of the through hole 2 refers to a cross section when the through hole 2 is cut in the axial direction of the through hole 2. As a result, particularly large thermal expansion in the vertical direction of the metal conductor 5 can be suppressed very well by the protrusion 3, so that peeling occurs between the metal conductor 5 and the insulating substrate 1 or cracks are generated in the insulating substrate 1. It is possible to provide a circuit board with high conduction reliability that is effectively prevented from occurring.

  Further, the stress generated in the vicinity of the interface between the metal conductor 5 and the insulating substrate 1 due to the thermal expansion in the lateral direction of the metal conductor 5 is located near the tip of the protruding portion 3 located on the inner side in plan view and on the outer side. Since it can be distributed in the vicinity of the opening, it is possible to effectively prevent the stresses of the respective parts from being combined and become a large stress, and the stress generated in the insulating substrate 1 can be extremely reduced.

  Furthermore, since the inner diameter of the through hole 2 is gradually increased from the protruding portion 3 toward the opening, the stress due to the difference in thermal expansion between the metal conductor 5 and the insulating substrate 1 is dispersed to locally concentrate the stress. Can be effectively prevented.

  Furthermore, since the protruding portion 3 has a shape that bites into the metal conductor 5, it is possible to provide a circuit board having a high connection reliability in which the metal conductor 5 does not fall off even under a mechanical impact.

  The through hole 2 is formed by, for example, forming a recess by a conventionally well-known blast method in each of the portions to be the openings on the upper and lower surfaces of the insulating substrate 1 and then penetrating the bottom surface of the recess by the blast method in the same manner. A shape in which the central portion in the depth direction of the through hole 2 has a protruding portion 3 protruding inward by performing drilling in two stages, and the inner diameter of the through hole 2 gradually increases from the protruding portion 3 toward the opening. It becomes. Here, the depth direction of the through hole refers to a direction parallel to the axial direction of the through hole.

  The through hole 2 may have a shape having a bent portion at the base of the protruding portion 3 as shown in FIG. 1, and the inner wall surface of the through hole 2 extends from the tip of the protruding portion 3 to the opening of the through hole 2 as shown in FIG. A gently continuous shape may be used. Preferably, in the longitudinal sectional view, the inner wall surface of the through hole 2 is located on the outer peripheral side of the insulating substrate 1 with respect to the straight line connecting the tip of the protruding portion 3 and the opening edge of the through hole 2, that is, the protruding portion 3. The inner wall surface of the through hole 2 between the front end of the through hole 2 and the opening edge of the through hole 2 is preferably recessed. Thereby, the tangent line of the upper and lower surfaces of the projecting portion 3 and the upper and lower surfaces of the insulating substrate 1 can be made parallel to each other, and the projecting portion 3 is made substantially orthogonal to the vertical direction of the metal conductor 5 Can be suppressed very effectively.

  Moreover, the protrusion part 3 may be formed over the perimeter of the through hole 2, and may be formed partially. From the viewpoint of more effectively suppressing the thermal expansion in the vertical direction of the metal conductor 5, the metal conductor 5 is preferably formed over the entire circumference of the through hole 2.

  It is preferable that the hole diameter inside the protrusion part 3 shall be within 20-100 micrometers. When the thickness is less than 20 μm, the resistance value of heat and electricity tends to increase, and when it exceeds 100 μm, the insulating substrate 1 tends to be cracked.

  Preferably, the inner surface between the projecting portion 3 of the through hole 2 and the opening has a concave curved surface shape. Thereby, the volume of the metal conductor 5 can be enlarged and a circuit board with higher thermal conductivity can be provided.

  Further, in order to make the inner wall surface of the through hole 2 between the protruding portion 3 and the opening have a concave curved surface shape, the nozzle shape is adjusted when the concave portions are formed on the upper and lower surfaces of the insulating substrate 1 by blasting. Thus, the abrasive grains may be ejected slightly more at the center than at the periphery. Specifically, an upper concave portion is formed on one upper surface of the insulating substrate 1 such that abrasive grains are ejected more in the center than in the peripheral portion by blasting, and then corresponds to the upper concave portion on the lower surface of the insulating substrate 1. A lower recess may be formed at a position so that abrasive grains are ejected more at the center than at the periphery by blasting, and the center may be penetrated. This is effective for a circuit board for mounting high-power elements such as a board for mounting LED elements, and particularly a circuit for mounting a power system LED element for general lighting or the like that needs to apply a high current to obtain high brightness. Effective for substrates.

  In addition, until now, the structure which formed the protrusion part 3 in the center part of the through-hole 2, and the structure which makes the inner wall surface of the through-hole 2 between the protrusion part 3 and the opening part of the through-hole 2 into a concave curved surface shape As described above by way of example, the inner diameter of the through hole 2 in the center in the depth direction is made smaller than the inner diameter of the opening, and the through hole in the depth direction from the center of the through hole 2 toward the opening If the inclination angle of the inner wall surface of 2 is changed a plurality of times, voids are generated in the metal conductor formed from the upper surface to the lower surface of the insulating substrate, the metal conductor and the insulating substrate are peeled off, or the insulating substrate is cracked. Thus, it is possible to realize a circuit board with high conduction reliability capable of suppressing the occurrence of the above.

  Here, when the inclination angle of the inner wall surface of the through hole 2 with respect to the depth direction of the through hole 2 is continuously changed a plurality of times, the inner wall surface becomes a curved surface in the changed region. For example, the shape of the inner wall surface of the through hole 2 shown in FIG. 2 is from the opening of the through hole 2 to the center so that the inclination angle is maximum at the center of the through hole 2, preferably 90 degrees. This is a shape when the inclination angle is continuously increased.

  Further, if the inclination angle of the inner wall surface is changed, dropout of the metal conductor 5 under a mechanical impact can be suppressed more than when the inner wall surface of the through hole 2 is flattened. A circuit board having connection reliability can be realized.

  Further, the metal conductor 5 is filled in the through hole 2 by embedding the metal paste, for example, by embedding the metal paste by an electrolytic plating method or an electroless plating method. In this case, the metal conductor 5 may be made of at least one of copper, silver, and titanium. Of these, copper is the best, and the metal conductor 5 is filled in the through hole 2 by copper plating, whereby a circuit board with low electrical resistance on the front and back surfaces and excellent heat dissipation can be obtained.

  Preferably, the metal conductor is formed by a plating method. Thereby, since plating can be favorably grown from the inside of the protruding portion 3 having a small inner diameter of the through hole 2 and the metal conductor 5 can be formed in order from the center in the depth direction of the through hole 2 to the upper and lower openings, It is possible to effectively prevent voids from being formed inside the metal conductor 5 or between the metal conductor 5 and the inner surface of the through hole 2.

  Preferably, the bonding metal layer 2 made of at least one of titanium, chromium, aluminum, molybdenum, tungsten, copper and nickel-chromium alloy is deposited on the inner surface of the through hole 2 by sputtering or vapor deposition. Is good. Thereby, the inner wall surface of the through hole and the metal conductor 5 can be adhered with high strength, and a highly reliable circuit board can be obtained.

  The connection metal layer 4 is formed, for example, by successively depositing titanium and copper sequentially by sputtering, and the connection metal layer 4 formed on the inner wall surface of the through hole 2 by these metals is formed between the metal conductor 5 and the insulating substrate 1. It is used as a close contact metal and as a conductive film when the metal conductor 5 is filled by plating. In this case, the thickness of titanium of the connection metal layer 4 is preferably 0.05 to 0.15 μm. If the thickness is less than this, the adhesion to the insulating substrate 1 is likely to be lowered, and if it is greater, titanium or the like that is the connection metal layer 4 diffuses into the metal conductor 5 and the conduction resistance is likely to vary.

  Further, after embedding the metal conductor 5 in the through hole 2, both the main surfaces of the insulating substrate 1 are polished if necessary, and the wiring conductor layer 6 is formed on the upper and lower surfaces of the insulating substrate 1 by a conventionally well-known thin film forming technique. You may form so that it may electrically connect with the conductor 5. FIG. Thereby, the electrode for mounting an electronic component can be formed in the upper and lower surfaces of the insulated substrate 1, and electrical connection with an electronic component can be made favorable.

  Note that the present invention is not limited to the above-described embodiment, and various modifications may be made without departing from the scope of the present invention.

It is sectional drawing which shows an example of embodiment of the circuit board of this invention. It is sectional drawing which shows the other example of embodiment of the circuit board of this invention.

Explanation of symbols

1: Insulating substrate
2: Through hole 3: Projection 4: Connection metal layer 5: Metal conductor

Claims (10)

In a circuit board formed by filling a through hole formed in an insulating substrate with a metal conductor, the inner diameter of the central portion in the depth direction of the through hole is made smaller than the inner diameter of the opening, and the opening is opened from the central portion of the through hole. A circuit board, wherein the inclination angle of the inner wall surface of the through hole with respect to the depth direction is changed a plurality of times toward the portion. The circuit board according to claim 1, wherein an inner diameter of the through hole is gradually increased from a central portion of the through hole toward an opening. 3. The circuit board according to claim 1, wherein an inner surface of the insulating substrate is recessed from the opening toward the center in the longitudinal sectional shape of the through hole. 4. The protruding portion is formed by projecting an inner surface of the insulating substrate located at a center portion in a depth direction of the through hole to the inside of the through hole. 5. Circuit board. 5. The circuit board according to claim 3, wherein an inner surface of the recessed insulating substrate has a concave curved surface shape. 2. A bonding metal layer made of at least one of titanium, chromium, aluminum, molybdenum, tungsten, copper, and nickel-chromium alloy is deposited on the inner surface of the insulating substrate in the through hole. The circuit board according to claim 5. The circuit board according to claim 1, wherein the metal conductor is made of at least one of copper, silver, and titanium. The circuit board according to claim 1, wherein the metal conductor is formed by a plating method. In a circuit board formed by filling a through hole formed in an insulating substrate with a metal conductor, the inner diameter of the central portion in the depth direction of the through hole is made smaller than the inner diameter of the opening, and the opening is opened from the central portion of the through hole. A circuit board, wherein the inclination angle of the inner wall surface of the through hole with respect to the depth direction is continuously changed toward the portion. After forming an upper concave portion on one main surface of the insulating substrate by blasting so that abrasive grains are ejected more in the center than on the peripheral portion, blasting is performed at a position corresponding to the upper concave portion on the other main surface of the insulating substrate. By forming a lower concave portion so that abrasive grains are ejected more in the central portion than in the peripheral portion and penetrating the central portion, the inner diameter of the central portion in the depth direction is made smaller than the inner diameter of the opening portion. A method of manufacturing a circuit board, comprising the step of forming a through hole in which the inner surface of the insulating substrate is recessed from the opening toward the center in the longitudinal sectional shape.

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