GB2354484A

GB2354484A - Composite laminate comprising glass and ceramic

Info

Publication number: GB2354484A
Application number: GB0018021A
Authority: GB
Inventors: Shigeyuki Kuroda; Hirokazu Kameda; Shuya Nakao; Kenji Tanaka; Masaru Kojima
Original assignee: Murata Manufacturing Co Ltd
Current assignee: Murata Manufacturing Co Ltd
Priority date: 1999-08-09
Filing date: 2000-07-21
Publication date: 2001-03-28
Anticipated expiration: 2020-07-21
Also published as: JP2001047423A; GB2354484B; CN1179845C; KR100348385B1; KR20010021219A; GB0018021D0; DE10038429A1; DE10038429C2; CN1283549A

Abstract

A composite laminate (2) includes at least one first sheet layer (4) comprising glass, and at least one second sheet layer (6) comprising ceramic particles (5), in contact with the first sheet layer. The second sheet layer constitutes at least one main surface of the composite laminate, the ceramic particles in the second sheet layer are unsintered, and the glass contained in the first sheet layer is melted and partially penetrated into the second sheet layer so that the ceramic particles are bonded to each other. The main surface of the composite laminate has a satisfactory roughness for forming an external conductive film having a fine pattern, and the composite laminate is useful as a multilayered circuit board.

Description

2354484 COMPOSITE LAMINATE AND METHOD FOR MAKING THE SAME

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to composite laminates and methods for making the same. In particular, the present invention relates to a composite laminate which is composed of glass and ceramic materials and which is suitable for use in multilayered circuit boards, and relates to a method for making the same. 2. Description of the Related Art

With reduction in the size and weight of chip components, corresponding reductions in size and weight are also required for circuit boards for mounting the chip components. For example, glass-ceramic multilayered circuit boards effectively satisfy such a requirement, since the glassceramic multilayered circuit boards facilitate high-density wiring and a reduction in thickness and weight of the substrates themselves.

A glass-ceramic multilayered circuit board is generally fon-ned as follows. A plurality of green sheets containing both glass powder and ceramic powder are provided. An internal conductor such as an internal electrode is formed on each of specific green sheets, for example, by printing. These green sheets are laminated, are compressed, and annealed. Finally, external conductive films, such as external electrodes, are formed.

In order to achieve high-density wiring on an outer surface of the glassceramic multilayered circuit board, a fine wiring pattern must be formed on the surface of the substrate. Thus, the surface smoothness of the substrate must be improved.

Such an improvement in surface smoothness requires the use of not only finely pulverized ceramic powder contained in the green sheets constituting outer surfaces but also finely pulverized glass powder contained in other green sheets. Preparation of finely pulverized glass powder, however, is difficult compared to pulverization of ceramic powder and causes increased process costs. As a result, glass-ceramic multilayered circuit boards for high-density wiring are expensive. SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a glassceramic multilayered circuit board which is relatively inexpensive and facilitates high-density wiring and a method for making the glass-ceramic multilayered circuit board.

According to an aspect of the present invention, a composite laminate comprises at least one first sheet layer comprising glass, and at least one second sheet layer comprising ceramic particles, in contact with the first sheet layer, wherein the second sheet layer constitutes at least one main surface of the composite laminate, the ceramic particles in the second sheet layer are unsintered, and the glass contained in the first sheet layer is melted and partially penetrated into the second sheet layer so that the ceramic particles are bonded to each other.

In the composite laminate according to the present invention, the first sheet layer preferably further comprises a ceramic filler.

When the composite laminate according to the present invention is used as a multilayered circuit board, the main surface provided by the second sheet layer may be used as a surface for an external conductive film which constitutes part of the wiring for the multilayered circuit board.

An internal conductor constituting part of the wiring for the multilayered circuit may be provided in the interior of the composite laminate.

According to another aspect of the present invention, a method for making a composite laminate comprises a first step of preparing a green composite laminate comprising at least one first sheet layer comprising glass and at least one second sheet layer comprising ceramic particles, the second sheet layer in contact with the first sheet layer, the second sheet layer constituting at least one main surface of the composite laminate, and a second step of annealing the green composite laminate at a temperature not causing sintering of the ceramic particles but melting of the glass so as to bind the first sheet layer by the melting of the glass in the first sheet layer and to penetrate part of the melted glass into the second sheet layer to bond the ceramic particles to each other.

In the first step of the method for making the composite laminate, preferably, the glass in the first sheet layer is powdered and the ceramic particles in the second sheet layer have grain sizes which are less than that of the glass powder.

In the first step, the first sheet layer preferably further comprises a ceramic filler.

In the first step, the first sheet layer may be provided as a sheet capable of being handled alone, and the second sheet layer may be formed on the first sheet layer. Alternatively, the first sheet layer and the second sheet layer may be provided as a first sheet and a second sheet, each being capable of being handled alone, and the first sheet and the second sheet may be stacked to form a green composite laminate.

When this method is directed to a method for making a multilayered circuit board, an external conductive film constituting part of the wiring for a multilayered circuit board may be formed on at least one main surface formed by the second sheet layer.

An internal conductor constituting part of the wiring for a multilayered circuit board may be formed in the interior of the green composite laminate.

In accordance with the present invention, the surface roughness of the second sheet layer substantially depends on the size of the ceramic particles contained in the second sheet layer. Thus, the use of small ceramic particles improves the surface smoothness of the second sheet layer, that is, improves the surface smoothness of the main surface of the composite laminate, even when the green sheet for the first sheet layer contains glass powder having a relatively large particle size. Accordingly, the composite laminate in accordance with the present invention can be produced at reduced cost without pulverization of glass powder. Moreover, the mechanical strength of the composite laminate can be further enhanced when the first sheet layer contains a ceramic filler in addition to the glass.

In accordance with the present invention, the surface roughness of the second sheet layer substantially depends on the size of the ceramic particles contained in the second sheet layer. Thus, the use of small ceramic particles improves the surface smoothness of the second sheet layer, that is, improves the surface smoothness of the main surface of the composite laminate, even when the green sheet for the first sheet layer contains glass powder having a relatively large particle size. Accordingly, the composite laminate in accordance with the present invention can be produced at reduced cost without pulverization of glass powder. When the composite laminate is used as a circuit board, an external conductive film having a fine pattern can be formed on the main surface thereof without problem, resulting in high-density wiring on the circuit board. Moreover, the mechanical strength of the composite laminate can be further enhanced when the first sheet layer contains a ceramic filler in addition to the glass.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. I A is a schematic cross-sectional view of a green composite laminate in accordance with an embodiment of the present invention, and Fig. I B is a schematic cross-sectional view of the composite laminate shown in Fig. I A after a heat treatment; Fig. 2A is a schematic cross-sectional view of a green composite laminate in accordance with another embodiment of the present invention, and Fig. 2B is a schematic cross-sectional view of the composite laminate shown in Fig. 2A after a heat treatment; and Fig. 3 is a schematic cross-sectional view of a composite laminate which is applied to a multilayered circuit board.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Fig. I A is a schematic cross-sectional view of a green laminate I in accordance with an embodiment of the present invention, and Fig. I B is a schematic crosssectional view of a composite laminate 2 formed by annealing the green laminate 1.

The green laminate I includes a first sheet layer 4 containing glass powder 3 and second sheet layers 6 containing ceramic particles 5. The second sheet layers 6 are in contact with the first sheet layer 4. Since the second sheet layers 6 sandwich the first sheet layer 4 in this embodiment, the two main surfaces of the green laminate I are provided by the second sheet layers 6.

A preferred glass material for the glass powder 3 in the first sheet layer 4 is anorthite crystallized glass. Examples of other glass materials include borosilicate glass and cordierite crystallized glass. The particle size of the glass powder 3 is not -6necessarily as small as the particle size of the ceramic particles 5 and may be larger than the particle size of the ceramic particles 5.

The first sheet layer 4 is preferably provided as a sheet which can be handled alone, for example, as a green sheet containing the glass powder 3. Such a green sheet is formed by mixing the glass powder 3, a dispersing medium, and a binder to form a slurry, by removing bubbles in the slurry, and by spreading the slurry by a doctor blade process to form a sheet. The binder and the dispersing medium are shown as vehicle 7 in Figs. I A and I B. Examples of useful dispersing media are water, toluene, alcohols, and mixtures thereof. Examples of binders are butyral resins, acrylic resins, urethane resins, vinyl acetate resins, and polyvinyl alcohol. The slurry may contain plasticizers, dispersants, and antifoamers, if necessary. The green sheet may be formed by extruding, rolling, or compression molding.

After the first sheet layer 4 is provided as the sheet which can be handled alone, as described above, the second sheet layers 6 may be formed on this sheet. In this case, a slurry containing the ceramic particles 5, a dispersant, and a binder is provided, and the sheet for the first sheet layer 4 is dipped into the slurry. The dipping process can efficiently produce the green laminate I including the second sheet layers 6 provided on both surfaces of the first sheet layer 4. The thickness of the second sheet layers 6 can be controlled by the content of the ceramic particles 5 in the slurry and the dipping time.

The binder and the di spersant, shown as vehicle 8 in Figs. I A and I B, in the slurry for the second sheet layers 6, may be the same as or different from the binder and the dispersant in the slurry for the first sheet layer 4.

Instead of the dipping process, the second sheet layers 6 may be formed by spraying, roll-coating, or printing the slurry containing the ceramic particles 5. Alternatively, the green laminate I may be formed by providing the second sheet layers 6 as sheets which can be handled alone, as in the first sheet layer 4, and overlaying the second sheet layers 6 on the first sheet layer 4.

It is preferable that the ceramic particles 5 in the second sheet layers 6 exhibit high wettability for the glass powder 3 in the first sheet layer 4. A preferred ceramic material for the ceramic particles 5 is alumina. Examples of other useful ceramic materials include MgO, Zr02, Si02, and Ti02.

The green laminate I is preferably compressed in the laminated direction before annealing. In the annealing process, a temperature not causing sintering of the ceramic particles 5 but causing melting of the glass powder 3 is applied. During the annealing process, the vehicle 7 in the first sheet layer 4 and the vehicle 8 in the second sheet layers 6 are removed, while the glass powder 3 in the first sheet layer 4 is melted as melt glass 9 to bind the first sheet layer 4, as shown in Fig. I B. Moreover, part of the melt glass 9 is penetrated into the second sheet layers 6 by capillary force, enters the gaps between ceramic particles 5, and bonds the ceramic particles 5 to each other.

The surface roughness of the two main surfaces of the resulting composite laminate 2 depends on the size of the ceramic particles 5 in the second sheet layers 6. Thus, using ceramic particles 5 having small sizes can reduce the surface roughness of the composite laminate 2, even when the glass powder 3 has a relatively large particle size.

The size of the ceramic particles 5 in the second sheet layers 6 smaller, the second sheet layers 6 more dense. In this case, the capillary force inducing a viscous flow of the melt glass 9 is enhanced, and the melt glass 9 is more densely packed.

Moreover, the melt glass 9 reaches the outer surfaces of the second sheet layers 6 and the surface tension of the melt glass 9 smoothes these surfaces. Accordingly, the melt glass 9 also contributes to an improved smoothness of the two main surfaces of the composite laminate 2.

Figs. 2A and 2B show another embodiment of the present invention and correspond to Figs. I A and I B. In Figs. 2A and 213, the same components shown in Figs. I A and I B are referred to by the same reference numerals, and the description thereof is omitted.

In the embodiment shown in Figs. 2A and 213, a first sheet layer 4a of a green laminate I a shown in Fig. 2A contains not only the glass powder 3 but also a ceramic filler 10. Thus, the first sheet layer 4a of the composite laminate 2a shown in Fig. 2B contains the ceramic filler 10, in addition to the melt glass 9.

The ceramic filler 10 may be different from or the same as the ceramic particles 5 contained in the second sheet layers 6 with regard to the particle size and the material.

Other configurations and the production method in the second embodiment shown in Figs. 2A and 2B are substantially the same as those in the embodiment shown in Figs. I A and I B. Since the first sheet layer 4a contains the ceramic filler 10, the resulting composite laminate 2a has enhanced mechanical strength.

In both the composite laminate 2 shown in Figs. I A and I B and the composite laminate 2a shown in Figs. 2A and 213, the second sheet layers 6, which can produce smooth surfaces by using fine ceramic particles 5, are arranged at outer sides. When the composite laminate 2 or 2a is used as a circuit board, an external conductive film having a fine pattern can be fori-ned on the main surface thereof without problem, resulting in high-density wiring on the circuit board.

The composite laminate 2 or 2a may include internal conductors, such as an internal conductive film and a via hole contact, therein.

Fig. 3 is a schematic cross-sectional view of a composite laminate I I provided with the above-mentioned external conductive films and internal conductors. The composite laminate I I includes a first sheet layer 12, which corresponds to the first sheet layer 4 or 4a in the above embodiments, and second sheet layers 13, which correspond to the second sheet layers 6 in the above embodiment. These second sheet layers 13 constitute two outer surfaces, that is, main surfaces of the composite laminate 11.

The composite laminate I I has external conductive films 14, 15, 16, 17, and 18 formed on these main surfaces, and internal conductors formed therein, such as internal conductive films 19, 20, 21, 22, 23, and 24 and via hole contacts 25, 26, 27, 28, 29, and 30. The internal conductive films 19 and 20 are formed along the interface between the first sheet layer 12 and the upper second sheet layer 13. As shown by the geometric arrangement of the internal conductive films 21 to 24 and the via hole contacts 27 to 30, the first sheet layer 12 is formed by laminating a plurality of green sheets, each having a predetermined pattern for the internal conductive films 19 to 24 and the via hole contacts 25 to 30.

Moreover, each second sheet layer 13 may be formed by laminating a plurality of green sheets. In this case, internal conductive films can be readily fon-ned in the interior of the second sheet layer 13.

- 10Examples I to 4 and Comparative Examples I to 5 Composite plates of Examples I to 4 in accordance with the present invention and of Comparative Examples I to 5 were prepared as shown in Table I to evaluate the surface roughness.

The glass powder contained in the first sheet layer was of anorthite crystallized glass, and had a particle size of approximately 6.50 Lrn in Examples I to 4, or a particle size ranging from approximately 3.6-3) [tm to approximately 7.47 tm in Comparative Examples I to 4. The first sheet layer in Comparative Example 5 did not contain the glass powder.

The first sheet layer contained powdered alumina having a particle size of approximately 0.35 tm as a ceramic filler, in all composite plates.

The glass powder and the ceramic filler were mixed at a ratio by weight of 60:40. Water as a dispersant and a butyral resin as a binder were added to the mixture in Examples I to 4 and Comparative Examples I to 4 or were added to the ceramic filler in Comparative Example 5 to form slurry. Bubbles in the slurry were removed, and a green sheet was formed by a doctor blade process so that the dried thickness was 500 Lrn.

Using powdered alumina having a particle size ranging from approximately 0.35 tm to 0.60 gm as ceramic powder, aqueous slurry was prepared for forming second sheet layers of Examples I to 4 so that the solid content was 10 percent by volume.

The green sheet for the first sheet layer was dipped into the slurry and was dried to form ceramic layers with a thickness of approximately 10 Lrn as second sheet layers on the two surfaces of the green sheet.

- I I - Each green laminate or sheet was compressed under a pressure of 100 kg/cm 2 using a rigid press, and was heated in air for 2 hours at 850'C for Examples I to 4 and Comparative Examples I to 4, or at 1,500'C for Comparative Example 5, to form a plate. The surface roughness Ra of each plate is shown in Table 1.

/a First Sheet Layer Second Sheet Layer Heating Surface Glass Filler Temperature roughness Particle Particle Ceramic Particle (OC) (Ra) Size Size Size (AM) (AM) (AM) (AM) 1 6.50 0.35 0.35 850 0.17 Example 2 6.50 0.35 0.38 850 0.26 3 6.50 0.35 0.45 850 0.34 4 6.50 0.35 0.60 850 0.48 1 3.63 0.35 850 0.30 2 6.40 0.35 850 0.71 Comparative 3 6.50 0.35 850 0.80 Example 4 7.47 0.35 850 0.90 - 0.35 1500 0.20 Table I shows that the surface roughness Ra of each plate having the second sheet layers lies in a range of 0. 17 gm to 0.48 tm. The surface roughness Ra depends on the particle size of the ceramic powder contained in the second sheet layers. That is, the surface smoothness is improved as the particle size of the ceramic powder decreases.

The surface roughness Ra is significantly decreased in Examples I to 4 compared to the surface roughness Ra, 0.80 tm, of Comparative Example 3 prepared under the same conditions except that the second sheet layers are not formed.

In comparison between Comparative Examples I to 4, the surface roughness is decreased as the particle size of the glass powder decreases. As shown in Comparative Example 1, however, the particle size of the glass powder must be decreased to approximately 3.63 tm in order to achieve a surface roughness which is comparable to that in Examples I to 4. Such a small particle size is impractical due to high production costs for preparing the glass powder.

When the second sheet layers are not formed on the first sheet layer, which contains only the ceramic filler, as shown in Comparative Example 5, the surface roughness Ra is 0.20 gm and is at a satisfactory level. In such a case, however, the heating temperature must be increased to 1, 500'C. Thus, metals which can be used as the internal conductive films 19 to 24 and the via hole contacts 25 to 30 are limited. Such a small surface roughness is readily achieved by, for example, decreasing the particle size of the ceramic powder in the second sheet layers to 0.35 tm, as shown in Example 1.

The present invention may include various modifications of the abovedescribed embodiments with reference to the drawings and Examples shown in Table 1.

The numbers of the first sheet layers and the second sheet layers and the order of lamination thereof may be changed according to required designs, as long as each second sheet layer is in contact with each first sheet layer and the second sheet layers constitutes at least one main surface of the composite laminate.

The first sheet layer may be of any thickness. Also, the second sheet layers may be of any thickness, as long as the melted glass in the first sheet layer is partly penetrated into the second sheet layers and the ceramic powder particles in the second sheet layers are bonded to each other.

The green sheet for the first sheet layer may contain glass fibers, glass whiskers, glass flakes, or glass platelets, instead of the glass powder.

The present invention is also applicable to a composite laminate provided with cavities having openings along outer surfaces. Such cavities are formed in the green composite laminate and are used for holding electronic components when the composite laminate is used as a multilayered circuit board.

Claims

CLAIMS:

1. A composite laminate comprising: at least one first sheet layer comprising glass; and at least one second sheet layer comprising ceramic particles, in contact with the first sheet layer; wherein the second sheet layer constitutes at least one main surface of the composite laminate, the ceramic particles in the second sheet layer are unsintered, and the glass contained in the first sheet layer is melted and partially penetrated into the second sheet layer so that the ceramic particles are bonded to each other.

2. A composite laminate according to claim 1, wherein the first sheet layer further comprises a ceramic filler.

3. A composite laminate according to either claim I or 2, further comprising an external conductive film formed on the main surface provided by the second sheet layer.

4. A composite laminate according to any one of claims I to 3, further comprising an internal conductor provided therein.

5. A method for making a composite laminate comprising: a first step of preparing a green composite laminate comprising at least one first sheet layer comprising glass and at least one second sheet layer comprising ceramic particles, the second sheet layer in contact with the first sheet layer, the - 16second sheet layer constituting at least one main surface of the composite larninate; and a second step of annealing the green composite laminate at a temperature not causing sintering of the ceramic particles but melting of the glass so as to bind the first sheet layer by the melting of the glass in the first sheet layer and to penetrate part of the melted glass into the second sheet layer to bond the ceramic particles to each other.

6. A method for making a composite laminate according to claim 5, wherein, in the first step, the glass in the first sheet layer is powdered and the ceramic particles in the second sheet layer have grain sizes which are less than that of the glass powder.

7. A method for making a composite laminate according to either 5 or 6, wherein, in the first step, the first sheet layer further comprises a ceramic filler.

8. A method for making a composite laminate according to any one of claims 5 to 7, where, in the first step, the first sheet layer is provided as a sheet capable of being handled alone, and the second sheet layer is formed on the sheet for the first sheet layer.

9. A method for making a composite laminate according to any one of claims 5 to 7, wherein, in the first step, the first sheet layer and the second sheet layer are provided as a first sheet and a second sheet, each being capable of being handled alone, and the first sheet and the second sheet are stacked to form a green composite laminate.

10. A method for making a composite laminate according to any one of claims 5 to 9, further comprising a step of forming an external conductive film on said at least one main surface constituted by the second sheet layer.

11. A method for making a composite laminate according to any one of claims 5 to 10, wherein the first step comprises forming an internal conductor in the interior of the green composite laminate.

12. A composite laminate substantially as hereinbefore, described with reference to the accompanying drawings.

13. A method for making a composite laminate substantially as hereinbefore described with reference to the accompanying drawings.