JP2008085098A - Wiring substrate, and electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wiring substrate having a high continuity-reliability wherein it can be suppressed that voids are generated in a via conductor 4 for subjecting wiring conductors 3 of the top and bottom surfaces of an insulating substrate 1 to their continuity to each other, and the via conductor 4 and the insulating substrate 1 are peeled from each other, and further, cracks are generated in the insulating substrate 1. <P>SOLUTION: The wiring substrate has a first insulating substrate 1 having first and second surfaces, and has a via conductor 4 which comprises first and second portions positioned respectively on the first- and second-surface sides and passes through the insulating substrate 1. Hereupon, the first portion of the via conductor 4 has a first recessed portion 2a opened to the first surface, and the second portion of the via conductor 4 has a second recessed portion 2b opened to the second surface whose central axis is deviated from the central axis of the first portion. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  Along with the recent remarkable downsizing and high-density mounting of electronic components, a wiring board on which electronic components are mounted is 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 wiring boards whose upper and lower surfaces are electrically connected by via conductors is employed to ensure desired conduction between the layers. As a result, circuit design has been performed to cope with downsizing, high integration, and the like.

  A wiring board having such a three-dimensional high-density wiring is widely put into practical use in the field of a printed wiring board using a resin-made substrate having good workability, but a ceramic substrate having excellent insulating 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. The so-called cofire method and postfire method are known as a method of manufacturing a wiring substrate used in the method of manufacturing a multilayer wiring substrate using such a ceramic substrate.

  The cofire method is a paste-like substance (hereinafter referred to as ceramic green sheet (hereinafter also referred to as green sheet)) in which vias are drilled in a ceramic precursor before sintering and metal powder is dispersed in an organic binder. , 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 vias is filled with a metal paste and refired. As a general-purpose method, a green sheet is processed into a predetermined shape, degreased and fired. Thereafter, the ceramic sintered body is drilled using a laser or sand blast, and a via 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, via conductors for conduction on the upper and lower surfaces are formed.

  In the post-fire method, since vias are formed in the insulating substrate after firing, the via dimensions and position accuracy can be formed with high accuracy, but due to the difference in thermal expansion coefficient when the via conductor is filled with via conductors by plating etc. The long-term reliability of the equipment is reduced by cracks in the insulating substrate, the bonding strength between the insulating substrate and the via conductor is reduced and the bonding reliability is reduced, or the insulating substrate and the via conductor are peeled off. There was a tendency to cause problems.

Post-fire methods that address these problems are also being considered. For example, in Patent Document 1 below, vias that are slanted on the insulating substrate and vias whose upper and lower surfaces are displaced from the central axis of the via are formed, thereby causing a difference in thermal expansion coefficient between the insulating substrate and the via conductor. This is to prevent the occurrence of peeling at the joint.
JP 2000-216514 A

  However, according to the post-fire method as described in Patent Document 1, although the difference in the thermal expansion coefficient in the thickness direction of the substrate can be alleviated, for the difference in the thermal expansion coefficient in the planar direction of the substrate, Since it is the same as the previous filled via, there is no problem if the opening diameter is small, but if the opening diameter of the via opening is increased or the formation density of the via is increased, the thermal expansion coefficient of the insulating substrate and the via conductor Due to this difference, the stress applied to the insulating substrate increases, so that there is a tendency for the insulating substrate to crack and the insulating substrate and via conductors to easily peel off, reducing the connection reliability with the insulating substrate. In addition, there is a problem that heat generated by the elements on the front 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. The object of the present invention is to create a void in the via conductor for conduction between the wiring conductors on the upper and lower surfaces of the insulating substrate, or to connect the via conductor and the insulating substrate. It is an object of the present invention to provide a wiring board with high conduction reliability capable of suppressing the occurrence of peeling and cracks in the insulating board.

  The wiring board of the present invention includes an insulating substrate having first and second surfaces, a first portion located on the first surface side, and a second portion located on the second surface side. A via conductor formed through the insulating substrate, wherein the first portion of the via conductor has a first recess opening in the first surface; The second portion of the via conductor has a second concave portion opened in the second surface, and has a central axis that is shifted from a central axis of the first portion. And

  The wiring board according to the present invention is characterized in that the first concave portion and the second concave portion are filled with a metal material having an electric resistance smaller than that of the via conductor.

  The wiring board of the present invention includes an insulating substrate having first and second surfaces, a first portion located on the first surface side, and a second portion located on the second surface side. A via conductor formed through the insulating substrate, wherein the first portion of the via conductor has a first recess opening in the first surface; The second portion of the via conductor has a second recess opening in the second surface and has a diameter different from the diameter of the first portion.

  The wiring board according to the present invention is characterized in that the first concave portion and the second concave portion are filled with a metal material having an electric resistance smaller than that of the via conductor.

  The wiring board of the present invention includes an insulating substrate having first and second surfaces, a first portion located on the first surface side, and a second portion located on the second surface side. A via conductor formed through the insulating substrate, wherein the first portion of the via conductor has a first recess opened in the first surface, and the second portion of the via conductor. The portion has a second recess opened in the second surface and has a central axis that is offset from the central axis of the first portion, so that the via conductor embedded in the via and the insulating substrate Since the stress can be reduced by the recess in the via opening where stress due to the difference in thermal expansion coefficient is concentrated, it is possible to effectively suppress the occurrence of cracks in the insulating substrate on which the via is formed. And can be formed at a high density. In addition, when the via conductor is formed by having a central axis that is shifted from the central axis of the first portion and the second portion of the via conductor, even when the via conductor is formed with the same thickness from the wall surface. Since the cross section of the displaced portion is the narrowest, the via is easily blocked at the displaced portion. Also, if it is formed by embedding paste, more paste gathers due to surface tension because the cross section of the boundary that is shifted from the top is suddenly narrowed, so it becomes easier to close the via, Productivity is improved. In addition, air bubbles mixed in the via conductor can be discharged well from the recess, and voids can be effectively prevented from being generated in the via conductor.

  In the wiring board of the present invention, the first recess and the second recess are filled with a metal material having an electric resistance smaller than that of the via conductor, so that the electrical characteristics can be improved by the low resistance metal material. Since stress due to the difference in thermal expansion coefficient between the low-resistance metal material and the insulating substrate can be effectively suppressed by the via conductor, the occurrence of cracks in the insulating substrate and the decrease in the connection reliability between the insulating substrate and the metal material Can be held small.

  The wiring board of the present invention includes an insulating substrate having first and second surfaces, a first portion located on the first surface side, and a second portion located on the second surface side. A via conductor formed through the insulating substrate, wherein the first portion of the via conductor has a first recess opened in the first surface, and the second portion of the via conductor. The portion has a second recess opened in the second surface and has a diameter different from the diameter of the first portion, so that the insulating substrate viewed from the first surface or the second surface can be used. Since the density of vias can be further increased without narrowing the distance between vias, the density of wiring conductors can be increased without the occurrence of cracks in the insulating substrate and the decrease in connection reliability between the insulating substrate and the metal material.

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

  FIG. 1 is a longitudinal sectional view showing an example of an embodiment of a wiring board according to the present invention. FIG. 2 is a longitudinal sectional view showing another example of the embodiment of the wiring board of the present invention. In these drawings, reference numeral 1 denotes an insulating substrate, 2a denotes a first portion via, 2b denotes a second portion via, and 2a and 2b are combined to form a via 2. 3 is a wiring conductor, 4a is a via conductor of the first portion, 4b is a via conductor of the second portion, and 4a and 4b are combined to form a via conductor 4. 5 is a metal material, and 6 is a recess. Note that the longitudinal section of the wiring board refers to a section when the wiring board is cut in the thickness direction of the insulating substrate 1, that is, the direction perpendicular to the main surface of the insulating substrate 1, and therefore the cross section of the via shown in FIG. Indicates a longitudinal section of the via.

  The insulating substrate 1 is made of a ceramic insulating material such as an aluminum oxide (alumina: Al2O3) sintered body, an aluminum nitride (AlN) sintered body, and the insulating substrate 1 is made of, for example, an aluminum oxide sintered body. First, a suitable organic solvent and solvent are added to and mixed with raw material powders such as alumina (Al 2 O 3), silica (SiO 2), calcia (CaO), magnesia (MgO), etc. to form a slurry, which is a conventionally known doctor blade method. A green sheet is obtained by forming into a sheet shape by a calender roll method or the like. 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 wiring 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.

  For the first part via 2a and the second part via 2b, a well-known photolithography method is used so as to penetrate the insulating substrate 1 by using, for example, a resist formed by shifting the positions of the holes on the upper and lower surfaces. The first part via 2a and the second part via 2b are perforated in a state where the central axes of the first part via 2a and the second part via 2b are shifted by a blasting method using etching or an etching method. By adjusting the blasting conditions and the etching conditions, various cross sections such as vias 2a, vias 2b, drums, and mortars having a substantially straight cross section in the first part and the second part. The via 2a and the via 2b can be formed, and an opening portion having a diameter smaller than the diameter of the via 2a and the via 2b is formed in a portion where the via 2a and the via 2b are connected.

  The hole diameter of the via 2a and the via 2b is preferably 50 to 500 μm. When the thickness is less than 50 μm, the size of the opening portion tends to become unstable, and the resistance value of heat and electricity tends to increase. When the thickness exceeds 500 μm, cracks tend to occur in the insulating substrate 1. .

  The displacement dimension of the central axis of the via 2a and the via 2b is preferably 20 to 400 μm. When the diameter is less than 20 μm, the diameter of the opening portion where the via 2a and the via 2b are connected is close to the via 2a and the via 2b, and therefore the via 2 is difficult to be filled in the opening portion even if the center axis is shifted. Tend to be difficult to improve. If it exceeds 400 μm, even if the diameter of the via 2 is increased, the ratio of the via conductor that effectively transfers the heat between the front and back through the opening portion is reduced, so that the heat conduction characteristic tends to be lowered.

  The via conductor 4 can be formed of a metal such as silver, palladium, platinum, gold, titanium, zirconium, hafnium, chromium, aluminum, molybdenum, tungsten, copper and nickel-chromium alloy, and preferably an insulating substrate. 1 is made of ceramics, and the via conductor 4 is preferably formed by firing a metal paste. As a result, the via conductor can be firmly joined to the insulating substrate 1 to further improve the conduction reliability. Further, when the metal material 5 is filled in the recess 6 of the via conductor 4 and the electrical resistivity of the filled metal material 5 is made smaller than that of the via conductor 4, the metal material 5 in the recess 6 and the insulating substrate 1 The stress due to the difference in thermal expansion coefficient can be more effectively suppressed by the via conductor 4.

  Here, the electrical resistivity of the metal material 5 filled in the recess 6 is made smaller than that of the via conductor 4, even though the physical electrical resistivity of the metal material 5 is equal to that of the via conductor 4. Even if it is large, when the metal material 5 is filled in the recess 6, it is only necessary that the electrical resistivity of the metal material 5 filled in the recess 6 is smaller than that of the via conductor 4. This can be realized by filling the recess 6 with the metal material 5 by a method different from the method of forming the via conductor 4. For example, when the main component of the via conductor 4 is silver and the metal material 5 is copper having a slightly higher electrical resistivity than silver, the via conductor 4 is formed by a metallization method, while the metal material 5 is plated in the recess 6. In this case, the electrical resistivity of the metal material 5 filled in the recess 6 can be made smaller than the electrical resistivity of the via conductor 4. When the electrical resistivity as a physical property of the metal material 5 is smaller than the via conductor 4, the electrical resistivity of the metal material 5 filled in the recess 6 can be made smaller than that of the via conductor 4 more reliably.

  The metal paste that becomes the via conductor 4 may be applied to the insulating substrate 1 made of fired ceramics and fired, or may be applied to the insulating substrate 1 in the green sheet state before firing and fired simultaneously with the green sheet. May be. Preferably, a metal paste is applied to the insulating substrate 1 made of fired ceramic and fired. Thereby, it can suppress that position shift arises by shrinkage | contraction by baking of the insulated substrate 1, and can form a wiring board with very high position accuracy. Further, the bubbles mixed in the metal paste are discharged well through the recess 6 of the via conductor 4, and it is possible to effectively prevent the void from being generated in the via conductor 4.

  When a metal paste is applied to the insulating substrate 1 made of fired ceramic and fired, the metal paste used is, for example, a metal powder made of silver powder or copper powder, and a binder such as glass powder or metal oxide Can be prepared by, for example, containing 1 to 5% by mass of the metal powder, adding and mixing an appropriate organic solvent and solvent, and kneading.

  Also, when it is applied to the insulating substrate 1 in the green sheet state before firing and fired at the same time as the green sheet, it consists of a high melting point metal such as tungsten, molybdenum, manganese, etc., and these powders are mixed with an organic solvent and solvent. A metal paste may be produced.

  A method of forming a metal layer by depositing these paste-like metal mixtures on ceramics (fired ceramics or green sheets) by screen printing or the like and firing them is generally called a metallization method.

  The via conductor 4 is formed on the inner wall surface of the via 2 by embedding a metal paste mainly composed of silver powder in the via 2 by screen printing or the like, and drying it at an appropriate drying temperature, for example, 120 ° C. 2 can be blocked. Then, the via conductor 4 is formed by baking at about 850 degreeC.

  At this time, by including an organic component in the metal paste, the organic component is removed when the metal paste is baked, and the volume shrinks, and the via conductor 4 connects the inner surface of the via 2 and the connection between the via 2a and the via 2b. The recesses 6 can be formed on the surfaces of the vias 2a and 2b which are formed so as to fill the opening to be formed and whose center axes are shifted from each other. The size of the recess 6 can be set to a desired size by adjusting the organic components (resin, solvent, surfactant, etc. as a binder) contained in the metal paste.

  Here, if the volume of the organic resin contained in the metal paste is larger than the volume of the contained metal powder, the resin decomposes during drying and firing and the volume shrinks significantly. 2 can be blocked, and stress due to a difference in thermal expansion coefficient between the insulating substrate 1 and the via conductor 4 can be more effectively prevented.

  As such a metal paste, for example, the volume of the resin as the binder is preferably 50 to 75% with respect to the total volume of the resin and the metal powder (in addition, the volume of the metal powder is in the case of conversion in bulk) Volume). If it is less than 50%, the stress applied to the insulating substrate 1 tends to increase when a metal paste is embedded in the via 2a and via 2b formed on the thin insulating substrate 1 having a thickness of about 0.2 mm or less. When it exceeds%, the via conductor 4 becomes too thin and the resistance value tends to increase.

  The via conductor 4 is formed by depositing a metal made of at least one of titanium, chromium, aluminum, molybdenum, tungsten, copper and nickel-chromium alloy on the inner walls of the via 2a and via 2b in advance by sputtering and vapor deposition. A metal braze paste may then be embedded.

  The thickness of the via inner wall surface of the via conductor 4 is preferably 1 to 50 μm. When the thickness is less than 1 μm, the adhesion to the inner wall surface tends to be lowered, and when it exceeds 50 μm, voids are likely to be generated, and the electrical characteristics and the heat conduction characteristics are likely to be lowered.

  In the wiring board shown in FIG. 1, it is important that the opening portion of the connection portion of the via 2a and the via 2b is suddenly narrowed because the central axes of the via 2a and the via 2b are shifted. . The via 2 may be formed so as to avoid the space where stress due to the difference in thermal expansion coefficient between the via conductor 4 and the insulating substrate 1 is concentrated. For that purpose, the via 2a and the center of the via 2b are formed. The shape of the vias 2a and 2b may be arbitrary as long as the axis is deviated. In addition, any shape of the vias 2a and 2b can discharge bubbles mixed in the via conductor 4 as long as the recess 6 is formed.

  Further, the metal material 5 is filled in the concave portion 6 opened in the first surface of the via conductor 4 by, for example, electrolytic plating. The metal material 5 is preferably made of a material having a lower electrical resistivity than the via conductor 4 such as copper, silver, titanium, and alloys thereof. The metal material 5 filled in the recess 6 is generated in an electronic element mounted on the wiring board while reducing the electrical resistance of the conductor inside the via 2 to improve the electrical characteristics and improving the thermal conductivity. It has a function of favorably conducting heat from the lower surface of the wiring board to the outside through the conductor inside the via 2. Preferably, the metal material 5 is made of a copper alloy containing 90% or more of copper. In this case, the longitudinal elastic modulus is generally larger than that of the silver-based via conductor 4, and electrical conductivity and migration resistance are improved. Best to consider. Therefore, by filling the metal material 5 into the recess 6 by copper plating, a wiring board having a low electrical resistance of the conductor inside the via 2, good migration resistance, and good heat dissipation can be obtained.

  In the wiring board of the present invention, it is preferable to make the longitudinal elastic modulus of the via conductor 4 smaller than the longitudinal elastic modulus of the metal material 5 filled in the recess 6. As a result, the via conductor having a lower longitudinal elastic modulus than the metal material 5 filled in the recess 6 is subjected to a stress in the horizontal direction of the via 2 due to a difference in thermal expansion coefficient between the metal material 5 filled in the recess 6 and the insulating substrate 1. 4 can be suppressed as a cushioning material. Here, the via conductor 4 having a smaller longitudinal elastic modulus than that of the metal material 5 filled in the recess 6 means that the longitudinal elastic modulus as a physical property of the metal material constituting the via conductor 4 is larger than that of the metal material 5. When the metal becomes the via conductor 4 and the metal material 5 is filled in the recess 6, the via conductor 4 is formed as a result due to a large number of minute voids in the via conductor 4. It is sufficient that the longitudinal elastic modulus is smaller than that of the metal material 5 filled in the recess 6. When the recess 6 is filled with the metal material 5 having a larger longitudinal elastic coefficient than the via conductor 4, the longitudinal elastic coefficient of the metal material 5 filled in the recess 6 can be made larger than that of the via conductor 4. .

  In addition, since the via axes of the vias 2a and 2b are shifted, the via conductor 4 is suddenly narrowed at the connection portion between the vias 2a and 2b, so that the vias 2 can be efficiently blocked. Further, the length of the via 2a and via 2b in the substrate depth direction is ½ of the thickness of the insulating substrate 1, so that the metal material 5 and the via conductor 4 filled in the recess 6 are thermally expanded with the insulating substrate 1. Since the stress acting in the direction perpendicular to the insulating substrate 1 due to the difference in coefficient is suppressed to ½, peeling occurs between the via conductor 4 and the insulating substrate 1 or cracks occur in the insulating substrate 1. It is possible to provide a wiring board with high conduction reliability in which the above is effectively suppressed.

  Further, as shown in FIG. 3, the first portion of the via conductor has a first recess opened in the first surface, and the second portion of the via conductor opened in the second surface. Via having a second recess and having a diameter different from the diameter of the first portion, the vias of the insulating substrate viewed from the first surface or the second surface are not reduced. Therefore, the density of the wiring conductor can be increased without generating cracks in the insulating substrate and reducing the connection reliability between the insulating substrate and the metal material.

  The longitudinal elastic modulus of the metal material 5 filled in the via conductor 4 and the recess 6 can be measured by, for example, a nanoindentation method. The nanoindentation method calculates hardness and Young's modulus (longitudinal elastic modulus) from the relationship between the load and displacement until the indenter is removed after a diamond indenter is pushed into the measurement sample. Is the method. When the longitudinal elastic modulus of the metal material 5 filled in the recess 6 is measured using this nanoindentation method, the metal material 5 in the recess 6 is cut by cutting the insulating substrate 1 in a direction perpendicular to the main surface thereof. And an indenter may be pushed into the exposed metal material 5. Further, when measuring the longitudinal elastic modulus of the via conductor 4, the via conductor 4 is exposed by cutting the insulating substrate 1 in a direction parallel to the main surface, and an indenter is pushed into the exposed via conductor 4. .

  Further, after polishing both main surfaces of the insulating substrate 1, a via conductor 4 or a metal material 5 in which a wiring conductor 3 formed on the upper and lower surfaces of the insulating substrate 1 by a conventionally known thin film forming technique is embedded in the via 2. Are electrically connected.

  An electronic device in which an electronic component is mounted on the wiring conductor 3 formed on the upper surface of the wiring board described above and electrically connected to the wiring conductor 3 formed on the lower surface of the wiring board via the via conductor 4 is provided. It becomes an electronic device with very high operation reliability.

  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 a longitudinal cross-sectional view which shows an example of embodiment of the wiring board of this invention. It is a longitudinal cross-sectional view which shows the other example of embodiment of the wiring board of this invention. It is a longitudinal cross-sectional view which shows the other example of embodiment of the wiring board of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1: Insulation board | substrate 2: Via 2a: Via of the 1st part 2b: Via of the 2nd part 3: Wiring conductor 4: Via conductor 5: Metal material 6: Concave part

Claims (6)

An insulating substrate having first and second surfaces;
A via conductor formed of a first portion located on the first surface side and a second portion located on the second surface side, and penetrating through the insulating substrate; ,
The first portion of the via conductor has a first recess opening in the first surface;
The second portion of the via conductor has a second concave portion opened in the second surface, and has a central axis that is shifted from a central axis of the first portion. Wiring board.   The wiring board according to claim 1, wherein the first concave portion and the second concave portion are filled with a metal material having an electric resistance smaller than that of the via conductor. An insulating substrate having first and second surfaces;
A via conductor formed of a first portion located on the first surface side and a second portion located on the second surface side, and penetrating through the insulating substrate; ,
The first portion of the via conductor has a first recess opening in the first surface;
The wiring board, wherein the second portion of the via conductor has a second recess opening in the second surface and has a diameter different from the diameter of the first portion.   4. The wiring board according to claim 3, wherein the first concave portion and the second concave portion are filled with a metal material having an electric resistance smaller than that of the via conductor.   The wiring board according to claim 1, further comprising a wiring conductor that is electrically connected to the via conductor and formed on the first surface of the insulating board. . The wiring board according to claim 5;
And an electronic component electrically connected to the wiring conductor of the wiring board and mounted on the first surface of the wiring board.

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