JP2001077498A - Ceramic substrate and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a ceramic substrate, by which the effects of electromagnetic waves from the inside of packages can be suppressed, a high flexibility of pattern designing can be ensured, generation of cracks in the ceramic substrate can be suppressed, the connection reliability of metal sleeves and central conductors can be increased, the manufacturing costs can be reduced and the period of manufacture is short. SOLUTION: This ceramic substrate is provided with a via 1 for connecting between a signal wire 3 and an external lead or as transmission line for electrical connection between layers on which wiring patterns are formed and a ground conductor 2 which is disposed coaxially with the via 1 around the via 1 and has notches 9 between the layers of the ceramic substrate. It is preferable that the through-hole containing the via 1 and the through-hole containing the ground conductor 2 be made in the ceramic substrate in one lump using the same mold.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic substrate and a method of manufacturing the same, and more particularly, to a ceramic substrate having vias and ground conductors suitable for a high-frequency signal circuit and a method of manufacturing the same.

[0002]

2. Description of the Related Art Ceramic substrates are used for various electronic devices and the like, and there are many substrates that handle high-frequency signals. In a ceramic substrate that handles a high-frequency signal, impedance matching with a signal line is performed to improve the transmission characteristics of the high-frequency signal.

For example, a first conventional example is disclosed in
In the ceramic substrate described in JP-A-215044, a through-hole is formed in the substrate after the substrate is fired in order to improve the impedance matching and the electromagnetic shielding function of the through-hole metallized wiring of the ceramic substrate. After applying and firing a metal paste inside, filling the through hole with a ceramic paste and further firing, then drilling a through hole in the center of the filled ceramic, filling the metal paste and firing. Thereby, a ground conductor is formed around the through hole.

On the other hand, a second conventional example is disclosed in
In the high-speed IC package described in JP-A-288446,
In order to improve the transmission characteristics by using the through hole part of the high-speed IC package as a coaxial type through hole, this coaxial type through hole is made to pass through the inner conductor through the axis of the metal type sleeve and to the inner cylinder part of the metal type sleeve. It is formed by filling the body and embedded in the substrate before firing the substrate.

Further, as a third conventional example, Japanese Patent Laid-Open No.
Japanese Patent No. 260201 discloses a semiconductor package and a semiconductor device with the object of improving the high-frequency characteristics of FIG.
As shown in FIG. 7, a circuit board 19 forming a package body for matching the impedance of the via 16 by a microstrip structure or a strip structure or the like.
The conductor layer 10 is provided on the outer peripheral side wall of the circuit board 19, and the conductive layer 10 is set to the ground potential. A technique has been disclosed in which a microstrip structure is provided between the conductor layer 10 and the via 16 by disposing.

[0006]

However, in the above-mentioned conventional ceramic substrate and the like, first, when the via for a high-frequency signal has an impedance matching structure, compared with the manufacturing cost of the conventional multilayer ceramic substrate, the equipment is not suitable. There is a problem that the manufacturing cost increases due to the increase in the cost and the number of steps, and the manufacturing period becomes longer.

The reason is that in the first conventional example, a structure is adopted in which impedance matching is performed with a coaxial ground conductor to a via for a high-frequency signal, but in this case, the conventional multi-layer ceramic substrate manufacturing process is not performed. In addition, after firing,
After drilling a through-hole in the substrate, applying a metal paste inside the through-hole and firing it, filling this through-hole with a ceramic paste and firing it further, drilling a through-hole in the center of the filled ceramic. This is because a step of filling and firing the metal paste is required.

In the case where the peripheral conductor is formed by a metal sleeve as in the second conventional example, the inner conductor is made to pass through the axis of the metal sleeve and a dielectric is formed on the inner cylindrical portion of the metal sleeve. This is because the filling requires a step of forming a peripheral conductor and embedding such a coaxial through-hole before firing the substrate.

Further, in the third conventional example, when impedance matching is performed by side metallization, it is necessary to add, as a side metallization step, a step of performing side printing after the laminating step to a normal step.

As a second problem, in the case of the impedance matching via structure in the third conventional example, the signal is not shielded in the direction inside the substrate with respect to the ground plane at the end of the substrate. From the lines, in particular,
It may be susceptible to electromagnetic waves from inside the package.

Further, as a third problem, in the third conventional example, since impedance matching is constituted by a through hole near the package side wall and a pattern printed on the package side wall, a through hole is required for impedance matching. Must be close to the side wall of the package,
There is a restriction that the via position is concentrated around the outer wall of the package, and the degree of freedom in pattern design is reduced.

As a fourth problem, in the third conventional example, impedance matching is constituted by a through hole near a package side wall and a pattern printed on the package side wall. Is determined by low-precision cutting, the manufacturing tolerance of the distance between the through hole and the outer wall of the package greatly affects the impedance, and the variation in the impedance of the product may be large.

For example, as shown in FIG. 11, as a conventional method of matching the impedance of vias, in the case of a structure in which a strip line is formed by performing metallization on a package side wall and setting it to a ground potential, a conductor on the side surface of the substrate is used. The distance from the layer 10 to the via 16 of the high-frequency signal affects the impedance.

The outer shape of the ceramic substrate portion is cut by a cutter or a snap. The larger the outer shape, the larger the tolerance, which is at least ± 0.07 mm.
The above exists. According to Equation 1, in the case of a 50Ω matching configuration using alumina having a dielectric constant of εr = 9.3, the impedance varies by 4Ω or more due to this tolerance.

[0015]

(Equation 1) Further, as a fifth problem, in the second conventional example, when forming the ground conductor with the metal-type sleeve, the inner conductor is made to penetrate through the axis of the metal-type sleeve, and is inserted into the inner cylindrical portion of the metal-type sleeve. It is formed by filling a dielectric material, and such a coaxial type through hole is buried before firing the ceramic substrate.Therefore, a metal material having a different coefficient of thermal expansion exists inside the ceramic substrate during firing of the ceramic substrate, Cracks are generated in the ceramic substrate portion, and reliability in connection between the metal mold sleeve and the center conductor is reduced.

The present invention has been made in view of the above-mentioned problems in the conventional ceramic substrate and the like, and can suppress the influence of electromagnetic waves from the inside of the package, and has a large degree of freedom in pattern design. It is an object of the present invention to provide a ceramic substrate which suppresses the occurrence of cracks in a substrate portion, increases the connection reliability of a metal mold sleeve and a center conductor, reduces manufacturing costs, and has a short manufacturing period.

[0017]

According to a first aspect of the present invention, there is provided a ceramic substrate, comprising:
A via as a transmission line for connecting a signal line of a ceramic substrate and an external lead, or for making an electrical connection between layers having a wiring pattern formed thereon, and is disposed coaxially with the via around the via. And a ground conductor having a notch between each layer of the ceramic substrate.

According to the first aspect of the present invention, in order to connect the signal lines of the ceramic substrate and the external leads,
Alternatively, by surrounding the via as a transmission line for electrical connection between layers with wiring patterns with a conductor of ground potential, it is a coaxial line structure, so it is hardly affected by electromagnetic waves from the surroundings, and ceramic By adjusting the distance to the surrounding conductor with respect to the dielectric constant, impedance matching can be performed, and high-frequency characteristics can be improved.

Further, since the ground conductor for impedance matching is provided around the via, there is no need to place the via at the end of the substrate, so that the degree of freedom in design is increased and the mounting density of the ceramic substrate is increased. be able to.

Further, since both through holes for the via and the ground conductor can be formed collectively by a mold or the like, the manufacturing cost can be reduced, the manufacturing period can be shortened, and the via and the ground conductor can be connected to each other. Since the distance between them can be set with high accuracy, variations in impedance are reduced.

The invention according to claim 2 is characterized in that the position of the notch of the ground conductor is different between the respective layers. Thereby, the resistance between the ground conductors can be reduced.

According to a third aspect of the present invention, as a preferred form of the ceramic substrate, a cross section of the through hole for accommodating the via is formed in a circular shape, and a cross section of the through hole for accommodating the ground conductor is provided. The surface is formed in an arc shape.

According to a fourth aspect of the present invention, there is provided a ceramic substrate as a transmission line for connecting a signal line of the ceramic substrate to an external lead or for making an electrical connection between layers having a wiring pattern formed thereon. And a plurality of ground conductors arranged coaxially around the via.

According to the fourth aspect of the present invention, in order to connect the signal lines of the ceramic substrate and the external leads,
Alternatively, since a plurality of ground conductors are arranged coaxially around a via as a transmission line for making an electrical connection between layers having a wiring pattern formed thereon, the structure is a coaxial line, so that electromagnetic waves from the surroundings are It is hardly affected, and impedance adjustment is performed by adjusting the distance to the surrounding conductor with respect to the dielectric constant of the ceramic, so that high-frequency characteristics can be improved.

Further, since the ground conductor for impedance matching is provided around the via, there is no need to place the via at the end of the substrate, which increases the degree of freedom in design and increases the mounting density of the ceramic substrate. be able to.

Furthermore, since both through holes for the via and the ground conductor can be formed collectively by a mold or the like, the manufacturing cost can be reduced, the manufacturing period can be shortened, and the connection between the via and the ground conductor can be reduced. Since the distance between them can be set with high accuracy, variations in impedance are reduced.

Further, since the size of a figure formed by connecting the positions of a plurality of ground conductors can be reduced,
The mounting density of the ceramic substrate can be increased, the stress generated by shrinkage of the ceramic substrate during firing can be reduced, and the occurrence of cracks in the ceramic substrate can be suppressed.

According to a fifth aspect of the present invention, as one of the preferred forms of the ceramic substrate, a plurality of through holes for accommodating the ground conductor are formed in a circular cross section of the through hole for accommodating the via. Are arranged on concentric circles centered on the vias.

According to a sixth aspect of the present invention, there is provided the method of manufacturing a ceramic substrate according to any one of the first to fifth aspects, wherein a through hole for accommodating the via and a through hole for accommodating the ground conductor are formed. It is characterized in that the same mold is used to collectively pierce the ceramic substrate portion.

According to the sixth aspect of the present invention, the through-hole for accommodating the via and the through-hole for accommodating the ground conductor are collectively formed in the substrate by using the same mold. The manufacturing cost of the ceramic substrate can be reduced, the manufacturing period can be shortened, and the distance between the via and the ground conductor can be accurately set, so that the variation in impedance can be reduced.

The invention according to claim 7 is characterized in that the ground conductor is formed by metallizing a side surface of a through hole for accommodating the ground conductor. Accordingly, it is possible to prevent the ceramic substrate portion and the ceramic substrate portion from being broken due to a difference in shrinkage rate during firing of the conductive material.

[0032]

Next, specific examples of embodiments of a ceramic substrate and a method of manufacturing the same according to the present invention will be described with reference to the drawings.

FIG. 1 shows a first embodiment of a ceramic substrate according to the present invention. The ceramic substrate 100 is a four-layer ceramic multilayer substrate for connecting signal lines of the ceramic substrate 100 to external leads. Or a via 1 as a transmission line for making an electrical connection between layers having wiring patterns formed thereon, a ground conductor 2 disposed coaxially with the via 1 around the via 1, a wiring 3, and a ceramic substrate It is composed of a part 4 and the like. In this embodiment, 4
The case of a multi-layer substrate will be described, but there is no particular limitation on the number of layers in the present invention.

Alumina, aluminum nitride, glass ceramic, or the like is used as the material of the ceramic substrate portion 4. The materials of the via 1, the arc-shaped ground conductor 2, and the wiring 3 are as follows.
Tungsten, molybdenum, or the like is used in the case of a ceramic manufactured at a firing temperature of 1500 ° C. or more, such as alumina, in accordance with the firing temperature of the ceramic and the shrinkage rate during firing. On the other hand, 800-100 glass ceramics
In the case of a ceramic manufactured at a firing temperature of 0 ° C., copper, gold and silver are used.

As shown in FIG. 2, the shape of the arc-shaped ground conductor 2 around the via 1 is provided with a notch 9 so that the via 1 and the ceramic substrate 4 (FIG. 1) do not fall off from the periphery. It has become. At least two notches 9 are formed so that the via 1 and the ceramic substrate 4 are not deformed before the laminating step. However, in order to ground the high-frequency signal wiring, it is desirable that the area of the notch 9 for holding the ceramic substrate 4 inside the arc-shaped ground conductor 2 be as small as possible.

The arc-shaped ground conductors 2 are electrically divided in each layer of the ceramic substrate 100. However, if they are laminated, the two ground conductors 2 are electrically connected via the conductors 3 so that the arc-shaped ground conductors 2 are electrically separated. Are all at the same potential (ground). The impedance matching of the via 1 for the high-frequency signal can be adjusted to the target impedance by adjusting the diameter of the via 1, the dielectric constant of the ceramic substrate 4, the distance from the via 1 to the ground conductor 2, and the like.

In manufacturing the ceramic substrate 100, first, a semi-milled ceramic material is printed on a film to manufacture a green sheet having a thickness of 0.2 to 0.5. However, it is not necessary that all sheets have the same thickness. In addition, in consideration of the warpage of the ceramic substrate portion 4 during firing, the ceramic substrate 100 has a symmetric structure with respect to the center in the thickness direction.

Next, a through hole is formed for each green sheet. Here, the diameter of the through hole of the via 1 is 0.
The width of the through hole of the ground conductor 2 is about 0.1 to 0.2 mm, and the distance between the through holes of the ground conductor 2 is about 0.2 to 0.5 mm. When the impedance is set to 50Ω, the distance between the via 1 and the ground conductor 2 is 0.2 mm, and the distance between the via 1 and the ground conductor 2 is 0.2 mm. Is set to 1.27 mm.

A mold is used to form the above-mentioned through-hole, and this mold is provided with both a portion for forming the through-hole of the via 1 and a portion for forming the through-hole of the ground conductor 2. By forming these forming portions in the same mold, both of the through holes can be formed at a time. At this time, since the shape of the mold is different from the conventional one, and no separate process is required, the manufacturing cost does not increase as compared with the conventional one. In addition, about formation of a through hole,
Processing with a puncher is also possible.

Next, using the metal mask shown in FIG.
The through holes for the via 1 and the ground conductor 2 are filled with a conductor by a squeegee or the like. In the figure, the hatched portion is the metal portion 14 and the white portion is the metal opening 7.
Is shown. As for the filling of the conductor, both the through hole of the via 1 and the through hole of the ground conductor 2 may be completely filled with the conductor. When a substrate crack or the like occurs, it is preferable to adopt a method in which the conductor is not filled in the through hole of the ground conductor 2 and the side surface of the through hole on the arc is metallized by wiring printing in the next step.

Wiring printing is performed using a mesh screen mask or the like. As shown in FIG. 4, the printing range 15 (shaded area) of the mesh screen mask for pattern printing overlaps with the through hole 12 (dotted area) of the ground conductor 2 (FIG. 1) opened by the die in the previous step. As the mask contour 13
(Thick line), and printing is performed on the side surface of the substrate by a printing person during printing.

In this case, since the through hole 12 is not completely filled with the conductor, the stress due to the difference in the shrinkage ratio between the ceramic substrate 4 and the ground conductor 2 can be reduced.

Here, as the wiring material, the same material as the ground conductor 2 suitable for the firing temperature or a material adjusted with an additive in consideration of the shrinkage of the ceramic substrate portion 4 is used.
The printing film pressure is about 10 μm. After firing, the wiring is plated with nickel and then plated with gold. Gold plating improves wettability in the subsequent soldering and brazing steps, improves wire bonding in the case of bare chip mounting, and prevents oxidation of the surface conductor.

FIG. 5 and FIG. 6 are pattern diagrams of the surface layer, respectively.
The pattern diagram of the inner layer is shown, and the high-frequency signal wiring 5 forms a ground pattern of the same layer, or a coplanar strip line or a microstrip line with the inner layer ground immediately below, and matches the target impedance. The arc-shaped through-holes 2 are connected to each other via a dotted line (arc-shaped through-hole connection position) 6 on the inner layer and the surface layer at the ground potential.

In the above embodiment, the via 1 can be regarded as a coaxial line, and the ceramic substrate 4
When r9.3 is used, 50Ω is realized when the diameter of the via 1 is set to 0.2 mm and the distance between the via 1 and the ground conductor 2 is set to 1.27 from the approximate expression of FIG. can do.

[0046]

(Equation 2) In the present invention, since a normal circular through-hole and an arc-shaped through-hole are formed in the same mold in the through-hole forming die, the accuracy is ± 10% of the etching accuracy of the mold formation.
It becomes 10 μm or less. As a result, under the same conditions as in the above-described conventional example shown by FIG. 11 and Equation 1, the variation in the impedance of the ceramic substrate according to the present invention is:
Since it is 0.3Ω or less according to FIG. 8 and Equation 2, the variation in impedance can be extremely reduced.

FIG. 8 is a view showing a second embodiment of the ceramic substrate according to the present invention.
Is formed by rotating the arc-shaped ground conductor 2 between the second and third layers by 90 degrees. Thereby, the resistance between the ground conductors 2 can be reduced.

FIG. 9 is a view showing a third embodiment of the ceramic substrate according to the present invention, in which a ground conductor 8 having a circular cross section is arranged around the via 1 of the high-frequency signal transmission line.
In this embodiment, as compared with the ground conductors 2 in the first and second embodiments, the effect of the shield is weakened because the gap between the adjacent ground conductors 8 is large, but by connecting the positions of the plurality of ground conductors 8, Since the diameter of the formed circle 8 'can be reduced, there is an advantage that the mounting density of the ceramic substrate 100 can be increased. Further, since the cross-sectional area of the ground conductor 8 is small, the ceramic substrate 4
Can be alleviated due to shrinkage during firing.

In the first and second embodiments, the via 1 and the ground conductor 2 are arranged concentrically. However, the ground conductor 2 may be arranged on an ellipse centered on the via 1 or the center of the via 1 may be arranged. It is also possible to arrange them in a rectangular shape having the same center as.

In the third embodiment, the via 1 and the plurality of ground conductors 8 are arranged concentrically. However, the plurality of ground conductors 8 may be arranged on an ellipse centered on the via 1, It is also possible to arrange in a rectangular shape having the same center as the center.

[0051]

As described above, according to the first aspect of the present invention, it is hardly affected by electromagnetic waves from the surroundings, and impedance matching is achieved by adjusting the distance to the surrounding conductor with respect to the dielectric constant of the ceramic. To improve the high-frequency characteristics, increase the degree of freedom in design, increase the mounting density of the ceramic substrate, reduce the manufacturing cost, shorten the manufacturing period, and increase the impedance. It is possible to provide a ceramic substrate having a small variation in the thickness.

According to the second aspect of the invention, in addition to the effects of the first aspect, it is possible to provide a ceramic substrate capable of reducing the resistance between the ground conductors.

According to the third aspect of the present invention, as one of the preferred embodiments of the ceramic substrate, the through hole for accommodating the via is formed in a circular cross section and the through hole for accommodating the ground conductor is provided. Can provide a ceramic substrate having a cross section formed in an arc shape.

According to the fourth aspect of the present invention, it is difficult to be affected by electromagnetic waves from the surroundings, and impedance is matched by adjusting the distance to the surrounding conductor with respect to the dielectric constant of the ceramic to improve high-frequency characteristics. The design flexibility is high, the manufacturing cost can be reduced, the manufacturing period can be shortened, the variation in impedance is small, the mounting density of the ceramic substrate can be increased, and cracks in the ceramic substrate part can be reduced. A ceramic substrate capable of suppressing generation can be provided.

According to a fifth aspect of the present invention, as one of preferred embodiments of the ceramic substrate, a plurality of through-holes accommodating the ground conductor are formed in a circular cross section of the through-hole accommodating the via. Can provide a ceramic substrate arranged on a concentric circle centered on the via.

According to the sixth aspect of the present invention, there is provided a method of manufacturing a ceramic substrate capable of reducing the manufacturing cost of the ceramic substrate, shortening the manufacturing period, and reducing the variation in impedance. be able to.

According to a seventh aspect of the present invention, in addition to the effect of the sixth aspect of the present invention, the ceramic substrate portion and the ceramic substrate portion which are likely to be caused by a difference in shrinkage during firing of the conductive material are prevented from cracking. It is possible to provide a method of manufacturing a ceramic substrate capable of performing the above.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of a ceramic substrate according to the present invention.

FIG. 2 is a partial perspective view showing vias, a ground conductor, and the like of the ceramic substrate of FIG. 1;

FIG. 3 is a plan view showing a mask for filling through holes in the ceramic substrate of FIG. 1;

FIG. 4 is a plan view showing a pattern printing mask of the ceramic substrate of FIG. 1;

FIG. 5 is a plan view showing a surface pattern of the ceramic substrate of FIG. 1;

FIG. 6 is a plan view showing an inner layer pattern of the ceramic substrate of FIG. 1;

FIG. 7 is a schematic diagram showing a positional relationship between a via and a ground conductor of a ceramic substrate according to the present invention.

FIG. 8 is a perspective view showing a via, a ground conductor, and the like in a second embodiment of the ceramic substrate according to the present invention.

FIG. 9 is a perspective view showing a via and a ground conductor in a third embodiment of the ceramic substrate according to the present invention.

FIG. 10 is a sectional view showing an example of a conventional ceramic substrate.

11 is a schematic diagram showing a positional relationship between a via and a conductor layer of the ceramic substrate of FIG.

[Explanation of symbols]

Reference Signs List 1 via 2 ground conductor 3 wiring 4 ceramic substrate 5 high-frequency signal wiring 6 arc-shaped through-hole connection position 7 metal opening 8 ground conductor 8 'circle (a figure formed by connecting positions of ground conductor 8) 9, 9 'Notch portion 12 Through hole 13 Mask outline 14 Metal portion 15 Printing range of mesh screen mask 100 Ceramic substrate

Claims (7)

[Claims] 1. A via as a transmission line for connecting a signal line of a ceramic substrate to an external lead, or for making an electrical connection between layers on which a wiring pattern is formed, and a via around the via. A ceramic substrate, comprising: a ground conductor that is coaxially arranged and has a notch between each layer of the ceramic substrate. 2. The ceramic substrate according to claim 1, wherein the position of the notch of the ground conductor is different between the respective layers. 3. The cross section of the through hole for accommodating the via is formed in a circular shape, and the cross section of the through hole for accommodating the ground conductor is formed in an arc shape. 2. The ceramic substrate according to 2. 4. A via as a transmission line for connecting a signal line of a ceramic substrate and an external lead, or for making an electrical connection between layers having a wiring pattern formed thereon, and a coaxial line surrounding the via. A ceramic substrate comprising: a plurality of ground conductors arranged. 5. A through hole for accommodating said via is formed in a circular cross section, and a plurality of through holes for accommodating said ground conductor are arranged on a concentric circle centered on said via. Ceramic substrate. 6. The method of manufacturing a ceramic substrate according to claim 1, wherein a through-hole for accommodating the via and a through-hole for accommodating the ground conductor use the same mold. And forming the ceramic substrate at a time. 7. A method for manufacturing a ceramic substrate, comprising: forming a ground conductor by metallizing a side surface of a through hole for accommodating the ground conductor.