JP2881018B2 - Manufacturing method of ceramic substrate - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a ceramic substrate, and more particularly to a method for manufacturing a ceramic multilayer wiring board in which ceramic green sheets are laminated and fired simultaneously.

[Prior art] In recent years, among ceramic sintered bodies, aluminum nitride sintered bodies are particularly excellent in electrical insulation, thermal conductivity, dimensional stability, mechanical strength and the like. Development is active.

Conventionally, an aluminum nitride multilayer wiring board is formed by punching a green sheet made of aluminum nitride to form a hole for forming a through-hole, and filling the hole with a paste mainly composed of tungsten and a dispersing solvent. Are simultaneously fired at normal pressure in a state in which a plurality of sheets are laminated.

[Problems to be Solved by the Invention] Generally, a molded body of aluminum nitride is shrunk during firing, but when the laminated molded body is fired under normal pressure, through holes of a green sheet disposed on the outermost layer of the laminated molded body are required. The paste filled in the forming hole rises from the opening of the hole due to the contraction stress of the aluminum nitride,
There is a problem that the conductive particles are not fixed in the pores in a sufficiently dense state, thereby increasing the through-hole resistance.

In particular, the present inventors have perforated the green sheet,
A multi-layer wiring board is being developed in which pad holes larger in diameter than through holes are filled with tungsten paste and pin pads for fixing external lead pins are integrally formed by simultaneous firing after laminating green sheets. The above problem becomes more serious as the inner diameter of the pad hole filled with is increased.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a ceramic substrate having a low through-hole resistance by densely filling conductive particles into holes of a substrate regardless of shrinkage or the like during firing of the ceramic substrate. An object of the present invention is to provide a method of manufacturing a ceramic substrate, which can easily and reliably manufacture a substrate.

[Means and Actions for Solving the Problems] In order to solve the above problems, the present invention provides a method in which a paste containing conductive particles is filled in the holes of a ceramic green sheet that has been opened in advance, and then the green sheet is filled. A ceramic layer is manufactured by forming a dummy layer having the same composition as that of the green sheet on the side where the paste of the sheet is exposed, baking it at normal pressure, and then grinding and removing the dummy layer.

According to this method, the paste filled in the holes of the green sheet is fired at normal pressure while being sealed in the holes of the green sheet by the dummy layer. Since the dummy layer has the same composition as the green sheet, the paste filled in the holes is compressed in the same manner from all directions as the green sheet and the dummy layer shrink due to normal pressure firing. Therefore, the swelling of the paste or the like that occurs when there is no dummy layer is prevented beforehand, and the conductive particles are fixed in the holes in a dense state. After firing, the ceramic layer having a low through-hole resistance can be obtained by grinding and removing the dummy layer.

It is preferable that a plurality of the green sheets are laminated, and the dummy layer is formed on the green sheet positioned as the outermost layer.

As a result, a ceramic multilayer wiring board having stable quality such as through-hole resistance is formed by normal pressure simultaneous firing.

It is preferable that the dummy layer is formed by laminating green sheets without holes.

As a result, a dummy layer having the same composition as the ceramic green sheet that has been opened in advance is easily formed. The thickness of the dummy layer can be easily adjusted by changing the number of stacked green sheets.

For the dummy layer, a slurry obtained by blending a solvent such as an organic solvent with a raw material composition having the same composition as the green sheet and kneading the mixture was directly applied to the paste exposed surface of the green sheet, and then dried. It may be formed by doing.

Preferably, the thickness of the dummy layer is in the range of 0.2 to 1.5 mm.

When the thickness is less than 0.2 mm, when the green sheet filled with the paste in the hole shrinks by firing, the inner peripheral surface of the hole compresses the paste compared to the force of compressing the paste. Force is small, and the swelling of the paste cannot be sufficiently prevented. On the other hand, if the thickness of the dummy layer exceeds 1.5 mm, the grinding removal amount increases and the workability decreases.

Examples of ceramics to which the present invention can be applied include aluminum nitride, alumina, silicon nitride, and the like, and aluminum nitride is particularly preferable.

As described above, aluminum nitride is excellent in electrical insulation and the like, and is not only suitable as a substrate material, but also has a large shrinkage ratio at the time of normal pressure firing, and the utility value of the present invention is extremely high.

In addition, examples of the conductive particles include tungsten, molybdenum, tantalum, and niobium, and particularly, tungsten is preferable.

Now, the paste containing the conductive particles, the conductive particles, acrylic binder, ether-based solvent, butyral, a dispersion solvent such as glycol, and, if necessary, castor oil, a thixotropic agent such as polyvinyl alcohol and the like Is appropriately blended.

Here, in the case where aluminum nitride is used as the ceramic and tungsten is used as the conductive particles, it is preferable that the paste after drying has a space occupancy of 35 to 45%. By using such a paste, the shrinkage rate due to the firing of the paste is substantially equal to the shrinkage rate due to the normal pressure firing of aluminum nitride, and cracks are prevented from occurring in the fired substrate due to the difference between the two shrinkage rates. Because it is done.

The paste containing the conductive particles is filled in the holes of the green sheet by screen printing using a metal mask or a mesh mask.

Since the hole of this green sheet has a very small inner diameter of about 0.1 mm like a hole for forming a through hole,
The inside diameter may be as large as about 1.0 to 2.0 mm, such as a pad forming hole for directly forming a pin pad integrally with the ceramic substrate. However, if the diameters of these holes are too large, cracks tend to be formed between the holes formed during punching of the green sheet.

Grinding of the dummy layer after firing is performed by surface grinding, lap finishing, or the like.

Hereinafter, Examples and Comparative Examples embodying the present invention will be described.

[Example] (Preparation of green sheet) 100 parts by weight of aluminum nitride powder having a purity of 99% and an average particle diameter of about 1.1 to 1.5 μm, 5 parts by weight of yttrium oxide having an average particle diameter of 2 to 3 μm, and an acrylic binder 8 to 15
Parts by weight, and mixed with toluene, ethanol and ethyl acetate, kneaded in a ball mill for 12 to 60 hours to prepare a raw material slurry, and then a plurality of green sheets (length 80 mm x width 80 mm x thickness) by a sheet casting method. 0.5m
m) was prepared.

Except for the shame green sheet, each green sheet was punched, and a number of holes were formed in each green sheet.
That is, as shown in FIG. 1, a green sheet 2 having a through hole forming hole 1 having an inner diameter of 0.2 mm and an inner diameter of 1.4 m were formed.
A green sheet 4 having a m-shaped pad hole 3 was prepared, and a green sheet 5 having no hole was prepared. Here, the pad hole 3 is a hole for integrally forming a pad for fixing an external lead pin to the multilayer wiring board when the pin grid array is manufactured.

(Filling of tungsten paste) 5 to 10 parts by weight of a mixed solvent composed of an ether solvent in which 10% by weight of an acrylic binder is blended with 100 parts by weight of tungsten fine particles having an average particle size of 0.3 μm, and castor oil 0.1 to 0.5 parts by weight, and the mixture was kneaded for about 1 hour with a three-roll mixer to prepare a tungsten paste. This paste has a density of 7.5 to 8.0 g / cm ³ when the mixed solvent is dried and removed, and the theoretical space occupancy of the tungsten fine particles at that time is about 40%.

The green sheets 2 and 4 were screen-printed to fill the through holes 1 and the pad holes 3 with a tungsten paste 6.

(Preparation of Multilayer Wiring Board) As shown in FIG. 1, a plurality of green sheets 2 having through-hole forming holes 1 were sequentially laminated, and two green sheets 4 having pad holes 3 were laminated thereon. . The uppermost green sheet 4 constitutes the surface layer of the multilayer wiring board. Further, on the green sheet 4,
A plurality of green sheets 5 having no holes were laminated to form a dummy layer (thickness: 1 mm), and a green compact 7 was formed from these green sheets 2, 4, and 5.

Then, the solvent in the laminated molded body 7 was dried by heating and drying, and tungsten fine particles were fixed in the through hole forming holes 1 and the pad holes 3 of the green sheets 2 and 4.

Subsequently, the laminated molded body 7 is placed in a nitrogen gas atmosphere at normal pressure.
After heating at a temperature of 350 to 1650 ° C, the binder in the green sheet is decomposed and removed (degreased), and then heated to 1750 ° C.
For 2 hours at normal pressure. Then, by grinding and removing the dummy layer by surface grinding and lapping,
An aluminum nitride multilayer wiring board as shown in FIG. 2 was obtained.

When the planar dimensions of the multilayer wiring board thus obtained were measured, the overall shrinkage was 14%. The contraction rate of the pad hole was also about 14%, and the contraction rate of the multilayer wiring board as a whole and the contraction rate of the pad hole almost coincided.

The appearance of the multilayer wiring board was visually observed, but no cracks or the like were observed.

[Comparative Example] A multilayer wiring board was produced through exactly the same procedure as in the above-described example. However, without forming a dummy layer of the green sheet 5 on the laminated molded body 7 as described above, normal pressure firing is performed while exposing the paste filling portion of the green sheet 4 in which the pad holes 3 are formed. A multilayer wiring board was obtained.

When the planar dimensions of the multilayer wiring board thus obtained were measured, the overall shrinkage was 14%, while the shrinkage of the pad holes 3 was almost 12%. Of the pad holes and the contraction rate of the pad holes.

When the external appearance of the multilayer wiring board was observed with the naked eye, cracks and the like were not observed at all, but bumps 8 of tungsten were observed on the surface of the pad portion.

[Effects of the Invention] As described above in detail, according to the present invention, regardless of shrinkage or the like during firing of a ceramic substrate, conductive particles are densely filled in holes of the substrate, and ceramics having low through-hole resistance are obtained. There is an excellent effect that the substrate can be easily and reliably manufactured.

[Brief description of the drawings]

FIG. 1 is a partial sectional view showing a laminated molded article having a dummy layer according to an embodiment of the present invention, FIG. 2 is a partial sectional view showing a multilayer wiring board after removing the dummy layer, and FIG. FIG. 4 is a partial cross-sectional view showing a multilayer wiring board in a comparative example. 1 ... through-hole forming holes, 2, 4 ... green sheets, 3 ... pad holes, 5 ... green sheets as dummy layers, 6 ... tungsten paste.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H05K 3/46 B28B 11/02

Claims (5)

(57) [Claims] A paste (6) containing conductive particles is filled in holes (1,3) of a ceramic green sheet (2,4) that has been opened in advance, and then the green sheet (2,4) is filled.
On the side where the paste (6) of (4) is exposed, a dummy layer (5) having the same composition as the green sheet (2, 4) is formed and baked at normal pressure, and then the dummy layer (5) A method for manufacturing a ceramic substrate, comprising: 2. The green sheet according to claim 1, wherein a plurality of said green sheets are laminated, and said dummy layer is formed on a green sheet located at the outermost layer. 3. The method for producing a ceramic substrate according to item 1. 3. The method according to claim 1, wherein the dummy layer is formed by laminating green sheets without holes. 4. The method according to claim 1, wherein a thickness of the dummy layer is in a range of 0.5 to 1.5 mm. 5. The method according to claim 1, wherein said ceramics is aluminum nitride, and said conductive particles are tungsten.