JPH0417392A - Manufacture of multilayer ceramic wiring board - Google Patents

Abstract

PURPOSE:To reduce the warps of a wiring board by printing wiring conductors on ceramic green sheets, and laminating a plurality of them to make a laminate, and then forming ceramic layers without wiring on both top and under surfaces of the laminate, and, after sintering, removing the wiring-free layer by polishing. CONSTITUTION:A hole for through hole is opened in ceramic green sheet, and tungsten paste is filled up in this hole to form a green sheet where a tungsten conductor is wired, and ten green sheets are laminated to make a laminate, and further green sheets 20-250mum in thickness are put on both top and under surfaces of this laminate. This complete laminate is sintered in humidified hydrogen-nitrogen atmosphere to get a mullite ceramic sintered body which includes a tungsten wiring layer. Next, the top and the under surfaces 3 of this sintered body are ground with a diamond stone to remove wiring-free layers, thus a normal circuit board is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention has the following features: Regarding multilayer ceramic wiring boards for child devices,
In particular, the present invention relates to a multilayer ceramic substrate suitable for use in electronic computers.

[Conventional technology]

In recent years, as electronic devices have become smaller, more sophisticated, and more multifunctional,
High density wiring and high reliability are also desired for the electronic circuit boards used for this purpose.

Especially for computer circuit boards, high-density fine wiring,
Since high speed and high reliability are important, ceramics with printed wiring are used as the circuit board material.

Generally, a multilayer ceramic circuit board is composed of ceramics as an insulator and metal as a conductor.
The physical and chemical properties of the two are significantly different.

Therefore, when a composite body containing two types of materials having different properties is heated to a high temperature and sintered, the composite body after sintering inevitably warps because each material exhibits different shrinkage behavior.

The magnitude of this warpage depends on the ratio of ceramic to metal, that is, the wiring density of the board, and the symmetry of the wiring pattern on the top and bottom surfaces of the board, and it is known that the warp increases as the board becomes larger. . The warpage of a normal ceramic substrate is 0.1 mm per 25 m+n of substrate length, 5
This is 0.15+nn per 0 mm, and a normal circuit board can be sufficiently used even with this degree of warpage. However, for electronic computer circuit boards that require high-density, multilayer wiring, it is essential that the length be 0.05 mm or less per 100 fields.

Conventionally, in order to reduce warpage of such ceramic substrates,
The following methods are known.

1) A method of setting sintering conditions to make the temperature distribution as uniform as possible, assuming that the uneven temperature within the ceramic substrate during sintering is the cause of warping.

However, considering the structure of the ceramic substrate, it is fundamentally impossible to significantly reduce the warpage of the substrate using this method.

2) A method in which a sintered substrate is reheated while applying an appropriate amount of load, and the warpage of the substrate is corrected by this load. According to studies conducted by the inventors, this method can reduce the warpage of the substrate to approximately half of that before modification. However, when the original substrate has a large degree of warpage, or when the shape of the warp is irregular, it has not been possible to significantly reduce the warpage even by the above-mentioned load correction method.

3) A method of grinding the warped surface of a sintered ceramic substrate flat using a grinding wheel or the like. This method is very effective in eliminating warpage, but as shown in Figure 3, the amount of grinding varies depending on the location of the board, so the height of the wiring conductor inside the board becomes uneven, and the board There are problems such as the end sealing pattern being removed by grinding or the pattern thickness being insufficient.

[Problem to be solved by the invention]

The above-mentioned conventional technology does not take fundamental measures to reduce warpage of ceramic wiring boards, resulting in poor connections when active elements are mounted on the board and poor airtightness when sealing the periphery of the board. There was a problem in that high-density wiring boards required for computers and the like could not be obtained.

The purpose of the present invention is based on the basic idea that wiring boards are made of different materials such as ceramics and conductive metals, and that the warpage of the board occurs due to the coexistence of these different materials, and that the present invention has an effect of mitigating the effects of the above-mentioned different materials. An object of the present invention is to provide a method for reducing warpage of a wiring board by having such a board configuration.

[Means to solve the problem]

In order to achieve the above object, in the present invention, a wiring conductor is printed on a ceramic green sheet, and a non-wiring ceramic layer is placed on both upper and lower surfaces of a laminate made by laminating a plurality of these sheets using a laminating method or a printing method. After sintering this at high temperature, the non-wiring layer is removed by polishing to obtain a wiring board with less warpage.

[Effect]

As mentioned above, since the ceramic wiring board is composed of two different materials, the wiring pattern within the board may warp due to the difference in shrinkage rate during the sintering process. If the substrate is symmetrical and heated evenly during sintering, the board will not warp, but in a normal wiring board, the wiring patterns on the top and bottom surfaces are the same and are not symmetrical, so warping occurs. It turns out.

Therefore, even if the wiring pattern is substantially different on the upper and lower surfaces of the substrate, the present invention forms a ceramic insulating layer that does not include any wiring pattern on the upper and lower surfaces, so that the ceramic on the upper and lower surfaces of the substrate is equivalently They are designed to have the same wiring pattern.

When a board with such a configuration is sintered, the shrinkage inside the board, including the wiring layer, progresses depending on the symmetry and ratio of the wiring pattern, as in the case of a board with a conventional configuration, and warping is likely to occur. . However, the non-wiring layers existing on the upper and lower surfaces of the substrate act to uniformly shrink against the non-uniform shrinkage inside, and as a result, the warpage of the substrate is reduced. Naturally, there is no wiring pattern on the top and bottom surfaces of the board manufactured in this way, and it does not have the role of a wiring board as it is, so the top and bottom surfaces of the board after sintering are ground to remove only the non-wiring layer. Then, by exposing the wiring pattern, a wiring board is obtained.

〔Example〕

Examples of the present invention will be described below.

[Example 1] Mullite fine powder (purity 99.9%, average particle diameter 2 μm
) 75% by weight, 5in2 (purity 99.9% average particle diameter 1.5 μm) 90% by weight, Al 1.0° (purity 99.
25% by weight of a sintering aid having a composition of 7% by weight, MgO (purity 99.8%, average particle size 0.3μm), Polyvinyl butyral resin as an agent and phthalate as a plasticizer.

Add an appropriate amount of trichlorethylene as a dispersion solvent,
Thoroughly mixed using a ball mill.

The slurry-like mixture thus obtained was formed into a sheet with a thickness of 0.3 mm by a doctor blade method. This sheet is called a green sheet and is the material for the multilayer ceramic substrate.

Next, holes for through holes were made in this green sheet (120 x 120 mm), and tungsten paste was densely filled into the holes to form wiring in the vertical direction of the board. Wiring in the planar direction was performed using tungsten paste.

The tungsten paste used here had an average particle size of 1 μm.
80% by weight of tungsten powder, 17.5% by weight of diethylene glycol mono-n-butyl ether acetate, 2.0% by weight of ethyl cellulose, and 0.5% by weight of polyvinyl butyral.

As described above, ten green sheets 2 each having a tungsten conductor wired thereon were laminated, and further, green sheets 1 having a thickness of 0.3 mm were laminated on both the upper and lower surfaces of this laminate. This laminate was heated to 1630°C.

By sintering in a humidified hydrogen-nitrogen atmosphere for 2 hours, a mullite ceramic sintered body including a tungsten wiring layer as shown in FIG. 1 was obtained.

The warpage of this sintered body is 0.18m per 100m+n of length.
It was m. The reason why the substrate according to the present invention exhibits little warpage is due to the fact that non-wiring layers are formed on the top and bottom surfaces of the laminate during lamination, and the top and bottom surfaces of the substrate shrink evenly during sintering. be. Next, the upper and lower surfaces 3 of this sintered body are ground with a diamond grindstone to form a non-wiring layer (approximately 2
50 μm) was removed to obtain a normal circuit board. The warpage of this polished substrate is 0.008 per 100 nn length.
It had a very small mn, and had sufficient flatness to form a thin film pattern thereon.

On the other hand, the warpage of the substrate produced by the conventional method without providing a non-wiring layer on the upper and lower surfaces of the laminate during lamination was as large as 0.32 no per 10011111 of the length. Furthermore, as a result of smooth grinding of this board using the conventional method, it became clear that the conductors in the inner layer of the board were also ground and lost, as shown in FIG. 3, and the performance as a single circuit board could not be maintained.

[Example 2] In the same manner as in Example 1, 55 sheets with printed wiring of tungsten conductors were laminated on green sheets of mullite-based ceramics, and green sheets without conductor wiring were placed on both the top and bottom surfaces of the laminate. (thickness: 70 μm) were laminated one by one, and this was sintered at 1630° C. for 3 hours in a humidified hydrogen-nitrogen atmosphere. The warpage of the obtained substrate is 10100 mm in length.
It was 0.006 mb per liter. Next, both the upper and lower surfaces of this substrate were smooth-ground using a diamond grindstone to remove only the conductor-free layer (thickness: 70 μm). The warpage of this polished substrate was 0.004 mm per 100 m length, which was very flat.

On the other hand, when we sintered a 45-layer stack made by the conventional method, the warpage of the substrate was 10010111
It was large at 0.25mm per hit. As a result of polishing the upper and lower surfaces of this substrate, the thickness of the inner layer near the surface of the substrate became uneven, making it unsuitable for use as a 5-wiring substrate.

[Example 3] Alumina fine powder (purity 99.5%, average particle size 3 μm
) 92% by weight, 6% by weight of 5in2 powder (purity 99.7%, average particle size 1.0 μm), 2% by weight MgO powder (purity 99.5%, average particle size 0.5 μm), and Examples After adding the same organic binder and plasticizer 2 dispersion solvent as in 1 and mixing thoroughly, use the doctor blade method to reduce the thickness to 0.
．． A 25nn+ alumina green sheet was produced.

Next, tungsten conductor wiring was applied to this green sheet in the same manner as in Example 1, and after laminating 30 such sheets, unwired alumina green sheets (thickness 120 μm ) were laminated one by one. The laminate was then sintered at 1590'C for 2 hours in a humidified hydrogen-nitrogen atmosphere.

The warpage of the obtained substrate was 0.11I per 100mm of length.
When this was polished smooth (polishing thickness: about 110 μm) in the same manner as in Example 1, a very flat substrate with a warp of 0.007 nn per 100 I of length was obtained, and the wiring on the surface of the substrate There was no problem with the layer thickness.

[Example 4] Alumina fine powder (purity 99.5%, average particle size 5 μm)
55% by weight, silicate glass fine powder (average particle size 3
A green sheet with a thickness of 0.25 M was obtained in the same manner as in Example 1 by adding an appropriate amount of an organic binder and a plasticizer 2 dispersion solvent to the green sheet. On this green sheet, wiring similar to that in Example 1 was provided using a conductive paste containing Cu as a main component. Fifteen sheets prepared in this way were stacked, and non-wired green sheets (thickness 250 μm) were layered on both the upper and lower surfaces of the stack, and the mixture was placed in a weakly oxidizing nitrogen atmosphere at 950°C for 4 hours. Sintered with

The warpage of the obtained substrate was 0.16 per 10100a of length.
When this was polished smooth (polishing piece 200 μm thick) in the same manner as in Example 1, good results were obtained with a warpage of 0.005 μm per 100 m length.

On the other hand, the warpage of a board manufactured by a conventional method that does not form a non-wiring layer on the upper and lower surfaces of the laminate is as follows per 100 mm in length.
The thickness was very large at 0.35 mm, and even if it was polished smooth, there was a problem in that there would be large variations in the thickness of the conductor layer on the surface of the substrate.

[Example 5] A 40-layer wiring laminate using alumina green sheets was made in the same manner as in Example 3, and a paste of the same composition as the alumina green sheets was applied to the top and bottom surfaces of the laminate to a thickness of 80 μm by screen printing. A non-wiring layer was formed. Thereafter, sintering was carried out under the same conditions as in Example 3. The warpage of the obtained substrate was 0.07 mm, which was extremely small. As a result of polishing this sintered substrate to a thickness of 80 m with a diamond grindstone, the warpage per 10011111 of the substrate was 0,0 O5nwo.
Met.

On the other hand, the warpage of the substrate produced by the conventional method is 10
It was large at 0.27 mm per 0 mm, and even if it was smoothed and polished, a practical circuit board could not be obtained. [Example 6] A glass-ceramic green sheet was used in the same manner as in Example 4. A 70-layer wiring laminate was made, and an insulating paste of the same composition as a glass-ceramic green sheet was printed on the top and bottom surfaces of the laminate to a thickness of 15μ by screen printing.
m non-wiring layers were formed. Thereafter, this laminate was sintered under the same sintering conditions as in Example 4. The warpage of the obtained substrate was 14 μm per 100 1/1 length. The reason why the warpage of this substrate is smaller than that of the other embodiments is because the number of laminated layers is large.

Next, the top and bottom surfaces of the sintered substrate are polished with a diamond grindstone (
When the polishing piece was 20 μm thick), the length of the substrate was 100 μm.
The warpage per mm was 0.004 μm, and a substrate suitable for high-density wiring was obtained.

On the other hand, the warpage of a substrate produced by the conventional method without providing a non-wiring layer on both the upper and lower surfaces of the laminate was as large as 0.23 mm per 100 nn of length, and a practical substrate could not be obtained.

〔Effect of the invention〕

As explained above, according to the present invention, since the warpage of the ceramic circuit board is extremely small, a high-density circuit wiring board suitable for use in electronic computers is possible. In other words, since the height of the wiring conductor on the board surface is uniform, problems such as poor connection when mounting active elements and poor airtightness in the sealing area around the board are eliminated, allowing for highly reliable high-density wiring. A substrate is obtained.

Furthermore, when forming a circuit pattern on the top surface of a sintered substrate using an organic thin film method, etc., there is a significant effect of eliminating problems such as breakage and blistering of the thin film layer, improving the performance of ultra-high density wiring circuit boards. At the same time, it greatly contributes to improving the yield in manufacturing substrates.

[Brief explanation of drawings]

1 and 2 are schematic cross-sectional views of a ceramic circuit board according to the present invention, and FIG. 3 is a schematic cross-sectional view of a circuit board according to a conventional method.

Claims (7)

[Claims] 1. In a method of manufacturing a multilayer ceramic wiring board by laminating and pressing a plurality of ceramic green sheets and sintering the laminate, after forming a wiring-free insulating layer on both upper and lower surfaces of the laminate and sintering. . A method for producing a multilayer ceramic wiring board, characterized in that the non-wiring layer is removed by polishing. 2. 2. The method for manufacturing a multilayer ceramic wiring board according to claim 1, wherein the thickness of the non-wiring layer to be removed by polishing is 20 to 25 mm.
A method for manufacturing a multilayer ceramic wiring board characterized by a thickness of 0 μm. 3. 2. The method of manufacturing a multilayer ceramic wiring board according to claim 1, wherein a ceramic green sheet is used as the non-wiring insulating layer. 4. 2. The method of manufacturing a multilayer ceramic wiring board according to claim 1, wherein the wiring-free insulating layer is formed by a screen printing method using an insulating paste. 5. 4. The method of manufacturing a multilayer ceramic wiring board according to claim 3, wherein a green sheet having a thickness of 70 to 300 μm is used as the non-wiring insulating layer. 6. 5. The method for manufacturing a multilayer ceramic wiring board according to claim 4, wherein the printing thickness is 15 to 80 μm. 7. 2. The method of manufacturing a multilayer ceramic wiring board according to claim 1, wherein the ceramic green sheet is made of an alumina-based, mullite-based, or glass-ceramic material.