JPH088398B2 - Low dielectric constant substrate - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a low dielectric constant substrate used for, for example, an electronic circuit substrate.

[Conventional technology]

As the operating frequency of electronic circuits increases and the degree of integration increases, a substrate having a low dielectric constant is required.

This is because the propagation delay time τ of the signal traveling in the substrate is
If the speed of light is c, This is because if the permittivity ε is large, the delay time becomes large and the high-speed operation is hindered. Further, if the dielectric constant is large, the stray capacitance between the wirings becomes large, so that the wiring density cannot be increased.

[Problems to be Solved by the Invention]

However, with conventional dense ceramics, SiO ₂
The lower limit of the dielectric constant was ε = 3.8 for the glass ceramics.

Therefore, an object of the present invention is to provide a low dielectric constant substrate which has a smaller dielectric constant than that of the present invention, which enables a reduction in signal propagation delay time and high density wiring.

[Means for solving the problem]

The low dielectric constant substrate of the present invention is made of ceramics 1
All of the upper and lower main surfaces and end surfaces of the porous layer laminated in more than two layers are covered with the dense layer made of ceramics, and the conductor path is formed along the porous layer part and the surface of the dense layer. And the conductor paths are electrically connected to each other through a through hole or a via hole.

[Action]

Since the porous layer contains a large number of pores having a low dielectric constant, the dielectric constant becomes smaller than that of dense ceramics, and the dielectric constant of the whole substrate including such a porous layer having a low dielectric constant also becomes small.

Moreover, since the upper and lower main surfaces and the end surfaces of the porous layer are all covered with the dense layer and the porous layer is not exposed, the weather resistance of the substrate is very high even if the porous layer is included.

〔Example〕

FIG. 1 is a vertical sectional view showing a low dielectric constant substrate according to an embodiment of the present invention.

The low dielectric constant substrate 2 is formed by laminating a plurality of porous layers 4 and a dense layer 6 provided on each of the upper and lower sides of the porous layers 4 one by one. Both the porous layer 4 and the dense layer 6 are made of ceramics.

However, the number of layers of the porous layer 4 is arbitrary as long as it is 1 or more, and the upper and lower dense layers 6 may be plural layers as necessary. It is desirable that the upper and lower dense layers 6 have the same thickness. This is because if they are not equal, the stress due to shrinkage during firing cannot be balanced, and the substrate warps.

Conductor paths 8a are formed between and inside the porous layer 4, and conductor paths 8b are formed on the surface of the dense layer 6 along the layers 4 and 6, respectively, and the conductor paths 8b are formed through the through holes 10. They are electrically connected (i.e. by the conductor filling the through holes 10).

The pattern of the internal conductor path 8a and the surface conductor path 8b, the positions of the through holes, and the like are also arbitrary, and may be determined according to the required circuit configuration and the like.

The porosity of the porous layer 4 is preferably 70% by volume or less. This is because if the porosity exceeds 70% by volume, the conductor path 8a formed in the porous layer 4 may be deformed or broken, and the transmission characteristics may be impaired.

In the low dielectric constant substrate 2, since the porous layer 4 contains many pores having a low dielectric constant, the dielectric constant is smaller than that of dense ceramics.

Further, the dielectric constant of the whole substrate including such a low dielectric constant porous layer 4 is also reduced.

As a result, the inner and outer conductor paths 8a, 8b, especially the inner conductor path 8a
It is possible to reduce the propagation delay time of the signal transmitted through the.

Further, since the stray capacitance can be reduced as much as the dielectric constant is smaller than that of the substrate including only the dense layer, high density wiring can be realized.

Moreover, since the dense layers 6 are provided on both the upper and lower sides of the porous layer 4, the weather resistance (moisture resistance) can be enhanced as compared with the case where the entire porous layer is a porous layer. In addition, the formation of the conductor path 8b on the surface, the soldering of electronic components, and the like are facilitated.

Further, as shown by a chain double-dashed line in FIG. 1, a dense layer 12 is also provided on the end face of the substrate 2, and as a result, the porous layer 4 is formed.
Since the exposure of is completely eliminated, the weather resistance is further improved.

Further, the through-holes 10 exposed on the surface of the dense layer 6 may be covered with a dense insulator, which can further improve weather resistance and reliability.

Next, an example of a method of manufacturing the low dielectric constant substrate having the above structure will be described.

As the ceramic material, as an example, a low temperature sinterable material which was separately proposed by the same applicant was used. That is, cordierite (see, for example, JP-A-61-234128) has a 50
~ 95 wt%, B ₂ O ₃ 5 ~ 20 wt% and SiO _{2 1} ~ 46 wt% to the main component, at least one of NiO and CuO was added by 15 wt% or less, and mixed raw material Prepare,
This was calcined and pulverized to obtain a powder ceramic.

Then, an acrylic binder was added to and mixed with the obtained powder ceramic, and a first ceramic green sheet was produced by the doctor blade method. This green sheet becomes a dense layer after firing.

Further, fine powder cellulose was added to the above powder ceramic in a volume ratio of 2.5 times, an acrylic binder was also added thereto, and a second ceramic green sheet was prepared by a doctor blade method. This green sheet becomes a porous layer after firing.

Then, after forming through holes at the required positions of the required number of the first and second ceramic green sheets obtained as described above, Ag as a conductor paste is formed on the surfaces of the required ceramic green sheets and the through holes. -Printed Pd paste.

Then, as described above, the second ceramic green sheets are laminated between them so that the first ceramic green sheets are located above and below (that is, arranged as shown in FIG. 1) and pressure-bonded. Then, firing was performed in the atmosphere at a temperature of around 980 ° C. As a result, a low dielectric constant substrate having the structure shown in FIG. 1 was obtained. By the way, the reason why the porous layer is obtained by firing the second ceramic green sheet is that the finely powdered cellulose or the like in the green sheet is burned and the pores remain after that.

Further, in this example, an insulating paste was printed and baked on the end surface of the substrate obtained as described above to completely prevent the porous layer from being exposed. This insulator paste was prepared by adding and mixing an acrylic binder to the same powder ceramic as above and adjusting the viscosity with a solvent. The baking temperature is almost the same as the baking temperature of the substrate.

The porosity of the porous layer obtained as described above is 70% by volume, and the dielectric constant of the circuit (capacitor part) formed in the porous layer part is ε = 2.0, which is It was less than half that of quality. In addition, the value is almost half that of the conventional SiO ₂ glass ceramics.

As described above, the insulating paste as described above may be applied and baked on the through-hole portion on the surface of the dense layer in order to further enhance the reliability.

A Cu paste can also be used as the conductor paste, but in this case, the firing is performed in an atmosphere of H ₂ O / N ₂ (that is, water vapor is contained in nitrogen).

Further, for the end face sealing, glass paste may be used as long as it has a thermal expansion coefficient close to that of each substrate and a baking temperature is equal to or lower than the baking temperature of the substrate.

〔The invention's effect〕

As described above, according to the present invention, the dielectric constant of the porous layer portion is smaller than that of the dense ceramics, and the dielectric constant of the entire substrate including such a low dielectric constant porous layer is also reduced. .

As a result, it is possible to reduce the propagation delay time of a signal transmitted through the inner and outer conductor paths, particularly the inner conductor path.

In addition, since the dielectric constant is small and the stray capacitance can be reduced as compared with the substrate including only the dense layer, high density wiring can be realized. In particular, since the effect of reducing the stray capacitance in the internal porous layer portion is great, it is possible to further increase the internal wiring density.

Moreover, since the upper and lower main surfaces and the end surfaces of the porous layer are all covered with the dense layer and the porous layer is not exposed, the weather resistance of the substrate is very high even if the porous layer is included.

Further, since the surface of the porous layer is covered with a dense layer and the surface is dense, it is easy to form the conductor path on the surface,
When an electronic component is placed on the surface and soldered, the melted solder can be prevented from penetrating into the substrate, and the electronic component can be easily mounted by soldering.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing a low dielectric constant substrate according to an embodiment of the present invention. 2 ... Low dielectric constant substrate according to example, 4 ... Porous layer, 6
...... Dense layers, 8a, 8b …… Conductor paths, 10 …… Through holes.

Claims (1)

[Claims] 1. A porous layer, which is made of ceramics and is laminated in one or more layers, has upper and lower main surfaces and end faces all covered with a dense layer made of ceramics, and the porous layer portion and the dense layer are A low dielectric constant substrate in which conductor tracks are formed on the surface along the respective layers, and the conductor tracks are electrically connected to each other through through holes or via holes.