Circuit board

A circuit board comprising a substrate, at least one dielectric film formed on the substrate and made of at least one selected from the group consisting of AlN, BN, diamond, diamond-like carbon, BeO and SiC, the dielectric film having pores of a porosity of 5 to 95% by volume, and at least one wiring metal film formed on the dielectric film.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a circuit board on which electronic 
devices such as semiconductor integrated circuit devices are to be mounted 
to constitute a computer system or the like. 
2. Description of the Related Art 
In accordance with an increase in demand for a miniaturized computer system 
which can operate at a high speed, the operation speed and the integration 
density of a semiconductor device to be mounted in the system has been 
increasing in an accelerated manner. Recently, a semiconductor device 
which has a clock frequency of 100 MHz and consumes a power of 30 W or 
more per chip, has been brought into practice. A circuit board on which 
such a semiconductor device is to be mounted must have a high 
heat-radiating property and a high speed signal-transmitting property, so 
that the superior characteristics of the device can reflect on the 
characteristics of the computer system. To improve a heat-radiating 
property, a high thermal conductivity is required, and to increase a 
signal transmitting speed, a low dielectric constant is required. 
Concerning the heat-radiating property of the above two properties required 
for a circuit board, high thermal conductivity materials having a high 
thermal conductivity coefficient of about 30 to 3000 W.multidot.m.sup.-1 
.multidot.K.sup.-1), such as AlN, BN, diamond, diamond-like carbon, BeO 
and SiC, are suitable for improving this property. However, the dielectric 
constant of the high thermal conductivity materials is higher, by 2.5 to 
15 times, than that of low dielectric constant material described below. 
Thus, in the case of using the high thermal conductivity material, the 
signal transmitting speed is inevitably low. those of low dielectric 
constant materials. 
On the other hand, concerning the signal transmitting speed, desirable 
materials for circuit board are the above-mentioned low dielectric 
constant materials, such as SiO.sub.2, polyimide, Teflon, which have low 
dielectric constants of about 3 to 3.8. Those materials are suitable for a 
circuit board, in order to increase the signal transmission speed. 
Further, a demand for lower dielectric constant materials has increased in 
accordance with the increase in signal transmission speed and the increase 
in size of the circuit board. Several materials having a dielectric 
constant of less than 3, which satisfy the demand, are known; however, 
none of them has satisfactory characteristics as a practical dielectric 
film, e.g., the resistivity, the moisture resistance, and the heat 
radiating property. In particular, the thermal conductivity of the low 
dielectric constant material is considerably low, as low as 1/3000 to 1/30 
that of the high thermal conductivity material mentioned above. For 
example, an organic polymer film, such as polyimide or Teflon, has a 
thermal conductivity coefficient of only 1 
W.multidot.-1.multidot.K.sup.-1. Therefore the low dielectric constant 
material is not suitable for a circuit board on which heat-generating 
devices are to be mounted to a high integration density. 
As described above, it is substantially impossible at the present stage to 
achieve, using single material, both requirements for a circuit board, 
i.e., a high heat-radiating property and a high-speed signal transmission. 
Hence, it is proposed that the two requirements be satisfied by forming a 
composite circuit board constituted by a substrate formed of a material 
having a high thermal conductivity and a thin film formed of a low 
dielectric constant material coated thereon. In this case also, however, 
the thin film, on which electronic devices are directly mounted, must have 
not only a low dielectric constant but also a relatively high thermal 
conductivity. In addition, the composite circuit board has the following 
problems: 
In general, a thin film of a dielectric material is formed on the surface 
of a substrate through a thin film forming process, such as vacuum 
deposition, sputtering, a cluster ion beam method, ion plating, ion mixing 
and CVD. The dielectric thin film formed through the thin film process has 
an internal residual stress, such as a tensile stress, depending on 
process conditions. Since the dielectric thin film having such a residual 
stress has low adhesion to the substrate, it is liable to be removed from 
the substrate. Similarly, when a wiring pattern is formed on the 
dielectric thin film having residual stress, as the adhesion between the 
film and the wiring pattern is low, delamination of the wiring pattern may 
arise. Further, when a dielectric film is formed on a substrate using a 
thick film process, a similar internal stress remains in the dielectric 
film due to contraction in a sintering process. 
SUMMARY OF THE INVENTION 
The present invention has been made in consideration of the above problems, 
and its object is to provide a circuit board which satisfies the two 
requirements of a high heat radiating property and a high speed signal 
transmitting property and which also solves the problem of delamination by 
means of a composite circuit board structure. 
The object can be achieved by a circuit board comprising a substrate; at 
least one dielectric film formed on the substrate and made of at least one 
selected from the group consisting of AlN, BN, diamond, diamond-like 
carbon, BeO and SiC, said dielectric film having a porosity of 5 to 95% by 
volume; and at least one wiring metal film formed on the dielectric film. 
Additional objects and advantages of the invention will be set forth in the 
description which follows, and in part will be obvious from the 
description, or may be learned by practice of the invention. The objects 
and advantages of the invention may be realized and obtained by means of 
the instrumentalities and combinations particularly pointed out in the 
appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiments of the present invention will now be described in detail. 
The substrate of the present invention can be formed of an inorganic 
material such as Si, AlN, BN, diamond, BeO, SiC and SiO.sub.2. The wiring 
metal film can be formed of a material used in a conventional circuit 
board, for example, Au, Cu, Al, Ag or TiN. 
The circuit board of the present invention is most obviously characterized 
in that a composite structure, in which a dielectric film and a wiring 
metal film are successively deposited on a substrate, is employed and that 
the dielectric film has porosity of 5 to 95% by volume. 
In the composite structure, adhesion between the substrate and the 
dielectric film as well as adhesion between the dielectric film and the 
wiring metal film is low, as described above, due to the internal residual 
stress such as the tensile stress in the dielectric film. However, the 
present inventors discovered that the residual stress in the dielectric 
film is reduced by providing the porosity of the above-mentioned range in 
the dielectric film, and have achieved the present invention based on that 
discovery. In other words, since the internal residual stress is low in 
the dielectric film of the present invention which has a porosity of 5 to 
95% by volume, the dielectric film adheres with high strength to the 
substrate and the wiring metal film of the circuit board. Therefore, the 
dielectric film is prevented from being removed from the substrate and the 
wiring metal film is prevented from being removed from the dielectric 
film. 
In the present invention, the porosity of the dielectric film is limited to 
5 to 95% by volume for the following reasons: if the porosity is less than 
5%, since an internal stress remains in the dielectric film, the adhesion 
strength of the dielectric film to the substrate and the wiring metal film 
is low, resulting that the dielectric film may be removed from the 
substrate and the wiring metal film may be delaminated; and if the 
porosity exceeds 95%, it becomes difficult to control the shape of pores 
and to form a dielectric film of a uniform thickness. A desirable range of 
the porosity is 5 to 70% by volume and a more desirable range is 9 to 65% 
by volume. 
The pores distributed in the dielectric film contain gas. The gas is not 
limited to a particular one, so long as it does not corrode the dielectric 
film made of the high thermal conductivity materials. For example, the gas 
can be air, nitrogen gas, oxygen gas or hydrogen gas. However, it is 
desirable that the gas contains at least one elements which are members of 
group 0 of the periodic table, i.e., Ar, He, Ne, Kr, Xe and Rn. The group 
0 elements are advantageous because these element are adsorbed to the 
interior surface of the pores to increase the resistivity of the 
dielectric film. To obtain this advantage, it is desirable that the 
partial pressure of the group 0 element be at least 1.times.10.sup.-2 Pa. 
Another advantage of the circuit board according to the present invention 
is that the dielectric film as described above can satisfy the two 
requirements for a circuit board, i.e., a high heat-radiating property and 
a high-speed signal transmission. 
First, the heat-radiating property of the dielectric film of the present 
invention will be described. As mentioned before, the dielectric film is 
formed of AlN, BN, diamond, diamond-like carbon, BeO or SiC. The 
diamond-like carbon means an amorphous diamond in which hydrogen is 
dissolved to form a solid solution. These dielectric materials each have a 
high thermal conductivity of 30 to 3000 W.multidot.m.sup.-1 
.multidot.K.sup.-1. In contrast, conventional low-dielectric constant 
materials, such as SiO.sub.2, polyimide and Al.sub.2 O.sub.3, merely have 
a thermal conductivity of 0.01 to 21 W.multidot.m.sup.-1 
.multidot.K.sup.-1 as mentioned above. Thus, since the dielectric film of 
the present invention has a much higher (30 to 3000 times) thermal 
conductivity than the conventional low dielectric constant materials, the 
dielectric film of the present invention can provide the considerably 
improved heat-radiating property to the circuit board, compared with the 
conventional low dielectric constant film. 
Secondly, with regard to the signal transmission speed, the materials of 
the dielectric film of the present invention, i.e., AlN, BN, diamond, 
diamond-like carbon, BeO and SiC, are disadvantageous, since the 
dielectric constants of these materials are 2.5 to 15 times as high as 
those of the conventional low dielectric constant materials, as described 
above. However, since the dielectric film of the present invention 
contains pores at the level of 5 to 95% by volume, the dielectric constant 
of the thin film is much lower than that of the material itself. By virtue 
of the pores distributed in the dielectric film, it is possible to obtain 
a low dielectric constant property (e.g., a dielectric constant of 2 to 3) 
the same as or more advantageous than that of the conventional low 
dielectric constant materials. 
As described above, the dielectric film of the present invention can 
achieve both requirements for a circuit board: a high thermal conductivity 
and a low dielectric constant, which cannot be achieved by a conventional 
dielectric film formed of a single material. Hence, the heat radiating 
property of the circuit board can be improved and the signal transmission 
speed can be increased. Thus, since the circuit board of the present 
invention is advantageous in having both the heat radiating property and 
the signal transmission speed due to an inherent characteristic of the 
dielectric film, it is possible to apply the circuit board to a 
highly-integrated semiconductor device which is operated at high speed. 
Now, a method for forming the dielectric film of the present invention and 
parameters of the film will be described in detail. 
The dielectric film according to the present invention, having a porosity 
of 5 to 95% by volume, is formed by means of a conventional thin film 
forming process, such as vacuum deposition, sputtering, a cluster ion beam 
method, ion plating, ion mixing and CVD. The thin film process is highly 
advantageous in the formation of a thin film like the dielectric thin film 
of the present invention, in which a number of pores are distributed 
intentionally; because, in the thin film forming method, ambient gas is 
taken into the film during a film forming process, resulting in the 
formation of pores. Therefore, the shape, the size, the range of 
distribution and the content of pores can be easily controlled by changing 
conditions of the thin film process. With the above method, a porosity of 
30% by volume or higher can be easily achieved, and further, even a 
porosity of about 70% by volume can be achieved, depending on the 
conditions. 
There is another method for forming a porous dielectric film. According to 
the method, gas is introduced into a thick film material slurry shaving a 
high viscosity, thereby producing air bubbles therein, and the slurry 
containing the gas bubbles is formed into a thick film, which is sintered 
and set up. However, this method is not suitable for forming the 
dielectric film of the present invention for the following reasons: In 
this method, the ratio of the bubbles formed in the gas introducing 
process is determined by the balance of the viscosity of the slurry and 
the buoyancy of the gas bubbles, i.e., a high viscosity is required to 
obtain a high porosity. However, since the viscosity of the slurry of the 
thick film material has an upper limit, a satisfactorily high porosity 
cannot be obtained. For example, a glass ceramic substrate obtained by the 
method has a volume porosity of 20% at most. In addition, it is very 
difficult to control the shape, size and the distribution range of pores 
in this method. 
The pores distributed in the dielectric thin film during the thin film 
forming step can be either continuous open pores or discontinuous closed 
pores. In the volume porosity range of 5 to 70%, most pores are closed. 
However, when open pores which communicate with the exterior are formed in 
a surface region of the dielectric thin film, the humidity resistance may 
be degraded or the resistivity and the breakdown voltage of the dielectric 
film may be lowered. To avoid these problems, it is desirable that a 
polymer such as polyimide or Teflon be embedded into the open pores formed 
in the surface region of the dielectric thin film. 
When pores in the dielectric film are formed by controlling conditions of 
the thin film method, as described above, it is desirable that the final 
thermal conductivity of the dielectric thin film be 21 W.multidot.m.sup.-1 
.multidot.K.sup.-1 to 1000 W.multidot.m.sup.-1 .multidot.K.sup.-1. If the 
thermal conductivity is less than 21 W.multidot.m.sup.-1 
.multidot.K.sup.-l, the porosity will exceed the upper limit, with the 
result that a satisfactory heat radiating property of the circuit 
substrate cannot be obtained. On the other hand, if the thermal 
conductivity exceeds 1000 W.multidot.m.sup.-1 .multidot.K.sup.-l, the 
porosity will be less than the lower limit of the above-mentioned range, 
with the result that the adhesion between the thin film and the substrate 
and between the thin film and the wiring metal film may be reduced and the 
thin film is liable to be removed from the substrate or the wiring metal 
film. It is also desirable that the thickness of the dielectric thin film 
range from 100 nm to 500 .mu.m. If the thickness is less than 100 nm, it 
is difficult to make the thickness uniform, and if the thickness exceeds 
500 .mu.m, the internal stress may be increased. 
According to the present invention, in order to obtain a dielectric thin 
film of porosity described above, the following improved method is more 
effective than the above-mentioned process condition of the thin film 
process. The improved method comprises the steps of forming a first 
dielectric film on a substrate and forming a number of minute pores having 
predetermined diameters and depths by processing the first dielectric 
film; and depositing a second dielectric film on the first dielectric 
film, thereby closing the openings of the minute pores. 
In this improved method, since the pores are formed in a process different 
from the process adopted for forming the dielectric film, the following 
advantages can be obtained. First, a porosity volume of 90% or higher can 
be easily obtained, Secondly, the size and shape of pores can be 
accurately controlled. Thirdly, it is possible not only to uniformly form 
pores over the entire dielectric film, but also to form pores only in 
limited portions (e.g., a region under the wiring layer) of the dielectric 
film, without forming pores in another portions (e.g., under the capacitor 
electrode). Fourthly, the thermal conductivity of the dielectric film can 
be improved as compared to the case in which the pores in the dielectric 
film are formed by controlling the conditions of the thin film process 
because of the following reasons. The pores formed in the dielectric thin 
film by the process control of the thin film method are very fine, with 
dimensions in the nanometer order. Therefore, if the porosity is 
increased, the crystallinity of the dielectric film will be degraded, 
resulting in a reduction of thermal conductivity. In contrast, according 
to the above improved method, since it is unnecessary that each of the 
dielectric films contains gas bubbles when it is formed, the crystallinity 
of the dielectric film itself is satisfactory and the thermal conductivity 
is not reduced. 
In the above improved method, printing or thermal spraying, as well as the 
thin film method, can be employed as a method for forming first and second 
dielectric films. Further, for processing the first dielectric film to 
form the minute pores, the following methods can be employed. A first 
method is selective etching of a predetermined region of the dielectric 
film by photo-lithography. In this case, either wet etching or dry etching 
can be employed; however, a RIE (reactive ion etching) is desirable. A 
second method is physical or mechanical perforation of the dielectric 
film. Physical perforation can be performed by using a probe of an 
interatomic microscope or a scanning tunneling microscope. In a third 
method, a metal pattern is formed on a region in which minute pores are to 
be formed by using plating or the like, then the dielectric film is formed 
on the metal pattern, followed by selectively etching the metal pattern 
off. 
Irrespective of the method used to form minute pores in the first 
dielectric film, it is necessary that the diameter of minute pores be 10 
.mu.m or less. If the diameter is larger than 10 .mu.m, the openings of 
the pores cannot be completely closed, when the second dielectric film is 
formed on the first dielectric film, resulting in open pores being formed. 
In a case where pores are open, the humidity resistance is degraded. In 
addition, the resistivity and the breakdown voltage of the dielectric thin 
film are reduced. Otherwise, the minute pores may be completely filled 
with the second dielectric film, i.e., no pores are formed. 
The shape of pores may be either circular or polygonal in the plan view. 
However, in order that the second dielectric film completely close the 
openings of minute pores, it is desirable that the aspect ratio 
(depth/diameter) of the minute pores be 0.1 or greater. The greater the 
aspect ratio (i.e., the deeper the minute pores), the easier the pores are 
closed by the second dielectric film. Thus, the upper limit of the aspect 
ratio is determined by a film critical thickness depending on factors of 
the dielectric film, for example, the internal stress. The critical 
thickness is about several millimeters in the case of a film having a 
satisfactory quality, although it varies in accordance with a material of 
a film and a film forming method. 
In the improved method, it is possible to arrange a number of minute pores 
two-dimensionally in a desired fashion. For example, when pores 1 having a 
circular shape in the plan view are to be arranged at regular intervals, 
the pores 1 can be arranged in row and column directions like a matrix as 
shown in FIG. 1A, or the positions of the pores 1 in the adjacent rows can 
be shifted by a half pitch in the row direction, as shown in FIG. 1B. 
However, the arrangement shown in FIG. 1B is preferable for the following 
reasons. First, a higher porosity can be obtained from the arrangement of 
FIG. 1B, according to the closest packing of the pores 1. Secondly, in the 
case of the same porosity, the mechanical strength of the dielectric film 
can be greater in the arrangement of FIG. 1B than that of FIG. 1A, because 
all the paths of the dielectric matrix in the arrangement of FIG. 1A are 
linear, whereas the paths in the column direction are zigzag in the 
arrangement of FIG. 1B. Thirdly, when wiring layers 2.sub.1 and 2.sub.2 
are formed on the dielectric film, the adhesion strength between the 
dielectric film and the wiring layers 2.sub.1,2.sub.2 can be more uniform 
in the arrangement of FIG. 1B. This is evident from the fact that the area 
of the pores under the layer 2.sub.1 is completely different from that of 
the pores under the layer 2.sub.2 in FIG. 1A, whereas the areas of the 
pores under the layers 2.sub.1 and 2.sub.2 are the same in FIG. 1B. These 
effects can be obtained, irrespective of the degree of shift of the pores 
1; however, the greatest effect is obtained, when the shift degree of 
pores 1 is a half pitch in the rows. 
Pores having a rectangular shape in the plan view can be also arranged as 
shown in either FIG. 2A or FIG. 2B. However, the arrangement of FIG. 2B, 
in which the positions of the pores 1 in the adjacent rows are shifted by 
a half pitch in the row direction, is preferable. In this case, both the 
arrangements in FIGS. 2A and 2B are equivalent from the viewpoint of the 
porosity, since pores are arranged in the closest-packing fashion in both 
arrangements. However, from the viewpoint of the mechanical strength of 
the dielectric film and the strength of adhesion of the dielectric film to 
the wiring layers 2.sub.1 and 2.sub.2, the arrangement shown in FIG. 2B is 
more advantageous for the same reasons described above. 
The entire constitution of the circuit board of the present invention will 
now be described. 
The circuit board of the present invention is realized, in general, as a 
composite structure in which a dielectric thin film pattern is formed on a 
substrate and a wiring metal film pattern (circuit pattern) is formed on 
the dielectric thin film. It is possible to form multilayered dielectric 
thin films and multilayered wiring metal films alternately deposited on 
the substrate. In a case of the multilayered wiring structure, the 
lowermost wiring metal film can be deposited directly on the substrate 
without a dielectric thin film interposed therebetween. 
FIG. 3 shows an embodiment in which the present invention is applied to a 
circuit board having the multilayered wiring structure. In this 
embodiment, used is a dielectric thin film having a certain porosity 
mentioned above, which is obtained by a thin film process under controlled 
conditions. In FIG. 3, a reference numeral 11 denotes a substrate. Wiring 
metal films 12, 14, 16 and 18 of a predetermined pattern are successively 
deposited on the substrate, with dielectric thin films 13, 15 and 17 
interposed between one wiring metal film and another. Contact holes 19, 20 
and 21 are formed in the dielectric thin films 13, 15 and 17, 
respectively. The wiring metal films 12, 14 and 16 are connected with one 
another through the contact holes. The dielectric thin films 13, 15 and 17 
are formed of at least one of AlN, BN, diamond, diamond-like carbon, BeO 
and SiC, as described above, and the porosity thereof is set within a 
range from 5 to 95% by volume. 
If necessary, a connection layer or a barrier layer may be formed between 
the wiring metal films 12, 14, 16 and 18 and the dielectric thin films 13, 
15 and 17. The connection layer may be formed of a thin film made of, for 
example, Ti, Cr, Nb, Zr, Hf or Ta. The barrier layer may be formed of a 
thin film made of, for example, Ni, Mo, Pt, TiN or W. Further, if 
necessary, metal members such as input/output leads and a seal ring may be 
mounted on the surface of the dielectric thin film 17 or the wiring metal 
film 18. These metal members are mounted thereon by brazing or soldering. 
In this case, Ag-Cu, Ag-Cu-Ti, Au-Sn, or Pb-Sn alloy can be used as a 
brazing or soldering material. 
The circuit board shown in FIG. 3 is advantageous in heat radiating 
property, since the dielectric thin films 13, 15 and 17 have a high 
thermal conductivity. In addition, and a low dielectric constant. It is 
also advantageous in a speed at which a signal is transmitted through the 
wiring metal films 12, 14, 16 and 18, because the dielectric thin films 
have a low dielectric constant. Thus, the circuit board has an efficient 
circuit performance. Furthermore, since, in the circuit board shown in 
FIG. 3, the internal stress of the dielectric thin films 13, 15 and 17 is 
low, the strength of adhesion of the dielectric films to the substrate 11 
or the wiring metal films 12, 14, 16 and 18 is high, thereby preventing 
delamination. 
The circuit board according to the embodiment shown in FIG. 3 can be 
manufactured in the following manner, for example. 
First, a dielectric thin film 13, in which pores are distributed, is formed 
by using the thin film process on a substrate 11 on which a wiring metal 
film 12 is formed. The thin film process can be, for example, vacuum 
deposition, sputtering, a cluster ion beam method, ion plating, ion mixing 
or CVD as previously described. If necessary, the porosity in the 
dielectric thin film 13 can be controlled by changing various conditions 
such as the temperature of the substrate 11, the atmosphere, the degree of 
vacuum and the film forming speed. The material of the dielectric thin 
film 13 is selected from a group consisting of AlN, BN, diamond, 
diamond-like carbon, BeO and SiC, so as to obtain a desired thermal 
conductivity of the circuit board. 
Subsequently, the dielectric thin film is processed into a predetermined 
pattern by, for example, a photolithography method, a lift-off method or a 
printing method. In practice, one of the methods is selected in accordance 
with the wiring pitch, the via dimensions in the multilayered wiring, the 
process accuracy such as dimensions in connecting portions, and the 
requirements for metallization in forming wiring layers, which are 
required in a particular example. Contact holes 19 are formed during the 
above process. 
Then, the processed dielectric thin film 13 is subjected to metallization, 
thereby forming a wiring metal film 14. The wiring metal film 14 may be 
formed of Au, Cu, Al or the like. The wiring metal film 14 is processed in 
the manner as in the process of forming the dielectric film 13, thereby 
forming a predetermined circuit pattern. 
Similarly, dielectric thin films 15 and 17 and wiring metal films 16 and 18 
are alternately formed. Thus, a circuit board of a multilayered wiring 
structure as shown in FIG. 3 can be obtained. If necessary, a connection 
layer or a barrier layer may be successively formed on the wiring layers 
14 and 16. 
In the above embodiment described with reference to FIG. 3, dielectric 
films 13, 15 and 17 having a desired porosity are formed by using a thin 
film process in which the process conditions are controlled for achieving 
the desired porosity. However, it is possible to form the dielectric films 
13, 15 and 17 by using the above-mentioned improved method in which the 
desired porosity is achieved by processing preformed dielectric films. In 
the case of employing the improved method for achieving the desired 
porosity, a circuit board shown in FIG. 3 can be manufactured in the same 
manner as described above, except for the method for forming the 
dielectric films 13, 15 and 17. 
Examples of the present invention will now be described in detail. The 
following examples are presented so that the invention can be easily 
understood, and they does not limit the scope of the invention. 
EXAMPLE 1 (Samples Nos. 1 to 19) 
Dielectric thin films 1 to 19, in which pores are distributed, were formed 
on substrates by a sputtering or CVD method under conditions indicated in 
Tables 1 and 2. The dielectric thin films 1 to 18 are relate to working 
examples of the present invention and the dielectric thin film 19 relates 
to a comparative example. An AlN substrate was used as the substrate, and 
AlN, BN, diamond, diamond-like carbon or SiC was used as a dielectric 
material. The thicknesses of the dielectric thin films 1 to 19 are as 
shown in Tables 1 and 2. 
More specifically, a laminated film consisting of Ti and Pt films, which 
serves as a lower electrode, was formed on an AlN substrate by using a 
sputtering method. The Ti film is 50 nm thick and the Pt film is 150 nm 
thick. A dielectric thin film 1 to 19 were formed on the surface of the 
lower electrode, as described above. Subsequently, a laminated film 
constituted by a Ti film and a Pt film (respectively having thicknesses of 
100 nm and 300 nm) was formed on the dielectric thin film by the 
sputtering method. The laminated film was patterned into a size of 500 
.mu.m square, thereby forming an upper electrode. 
The dielectric characteristic (dielectric constant) and the thermal 
conductivity of each of the dielectric thin films 1 to 19 were measured 
using the upper and lower electrodes as measuring electrodes. To obtain 
the thermal conductivity, the thermal diffusivity was measured first by 
using AC calorimetric method, and the thermal conductivity was calculated 
from the measured value. The cross section of each of the dielectric thin 
films 1 to 19 was observed through a TEM and SEM to measure the area of 
pores distributed in the dielectric thin film, and the porosity (volume 
percentage) was calculated from the measured value. Further, the 10 
warping of the substrate was measured with a film thickness measurer, and 
the internal stress of the dielectric thin film was calculated from the 
measured value. 
The results were shown in the following Table 1. 
TABLE 1 
__________________________________________________________________________ 
Film forming 
Material of Target, 
Substrate 
No. 
method film Material gas, flow rate 
Power temperature 
__________________________________________________________________________ 
1 Sputtering 
AlN Netrogen gas:Ar gas = 1:1 
Al, 2kW 
200.degree. C. 
2 Sputtering 
AlN Netrogen gas:Ar gas = 1:1 
Al, 3kW 
300.degree. C. 
3 Sputtering 
AlN Netrogen gas:Ar gas = 1:1 
Al, 2kW 
100.degree. C. 
4 CVD AlN Tri-isobutyl aluminum:Ar:NF.sub.4 = 4:20000:3300 
--, 900W 
400.degree. C. 
Microwave 
5 CVD AlN Tri-isobutyl aluminum:Ar:NF.sub.4 = 4:20000:3300 
--, 900W 
250.degree. C. 
Microwave 
6 Ion mixing 
AlN Ar, Oxygen, Nitrogen Al, Leading 
100.degree. C. 
assist voltage 
100 keV, 
Ionization 
current 3mA, 
Deposition 
7 Sputtering 
SiC Ar:C.sub.3 H.sub.8 = 4:3 
Si, 1kW 
150.degree. C. 
8 CVD Diamond 
CH.sub.4 :H.sub.2 = 1:25 
--, 2kW 
600.degree. C. 
Microwave 
9 CVD Diamond 
CH.sub.4 :H.sub.2 = 1:20 
--, 3kW 
300.degree. C. 
Microwave 
10 CVD Diamond 
CH.sub.4 :H.sub.2 = 1:30 
--, 2kW 
250.degree. C. 
Microwave 
11 CVD Diamond 
CH.sub.4 :H.sub.2 = 1:30 
--, 1.5kW 
150.degree. C. 
Microwave 
12 CVD Diamond- 
CH.sub.4 :H.sub.2 = 1:40 
--, 2kW 
100.degree. C. 
like carbon Microwave 
13 CVD Diamond- 
CH.sub.4 :H.sub.2 = 1:45 
--, 2kW 
100.degree. C. 
like carbon Microwave 
14 Sputtering 
BN Netrogen gas:Ar gas = 1:1 
BN, 4kW 
220.degree. C. 
15 Sputtering 
BN Netrogen gas:Ar gas = 1:1 
BN, 3kW 
200.degree. C. 
16 CVD Diamond- 
CH.sub.4 :H.sub.2 = 1:45 
--, 2kW 
100.degree. C. 
like carbon Microwave 
17 CVD Diamond- 
CH.sub.4 :H.sub.2 = 1:45 
--, 2kW 
150.degree. C. 
like carbon Microwave 
18 CVD Diamond- 
CH.sub.4 :H.sub.2 = 1:45 
--, 2kW 
100.degree. C. 
like carbon Microwave 
19 CVD Diamond- 
CH.sub.4 :H.sub.2 = 1:45 
--, 2kW 
200.degree. C. 
like carbon Microwave 
__________________________________________________________________________ 
Pressure Dielectric Porosity 
Internal stress 
No. Pa Film thickness 
constant 
Thermal conductivity 
% MPa 
__________________________________________________________________________ 
1 3 3 .mu.m 4.7 100 40 -2 
2 6 10 .mu.m 2.7 48 70 -3 
3 1.5 20 .mu.m 6.2 195 20 -3 
4 60 100 .mu.m 
7.2 220 10 -6 
5 700 100 .mu.m 
3.3 68 60 -2 
6 1 .times. 10.sup.-3 
1 .mu.m 4.7 120 40 -2 
7 2 3 .mu.m 15 68 60 -2 
8 30k 5 .mu.m 3.0 370 50 -1 
9 80k 10 .mu.m 2.5 280 60 -1 
10 10k 8 .mu.m 4.0 590 30 -1 
11 2k 10 .mu.m 5.1 900 10 -3 
12 1k 10 .mu.m 4.9 500 10 -3 
13 2k 10 .mu.m 4.3 690 20 -2 
14 5 10 .mu.m 4.4 320 30 -1 
15 3 13 .mu.m 5.7 10 10 -3 
16 3.5k 10 .mu.m 3.8 510 30 -1 
17 5k 100 .mu.m 
2.8 300 500 -1 
18 7k 10 .mu.m 2.8 220 60 -1 
19 900 10 .mu.m 5.7 1000 3 35 
__________________________________________________________________________ 
As clear from the tables, the porosities of the dielectric thin films 1 to 
18 are within the range of the present invention (5 to 70% by volume). 
Accordingly, both a high thermal conductivity and a low dielectric 
constant are achieved. In addition, the internal stress is small. Hence, 
it follows that the heat radiating property and the signal transmission 
speed are high, and defects such as delamination do not easily occur in 
the circuit boards having the dielectric thin films 1 to 18 (the working 
examples of the present invention). 
In contrast, the dielectric thin film 19 has a porosity less than the range 
of the present invention, and a particularly great internal stress. 
Therefore, the dielectric thin film is liable to be easily removed from 
the substrate and the wiring metal films, in the circuit board having this 
dielectric thin film (the comparative example). 
EXAMPLE 2 (Samples Nos. 20 to 24) 
In this example, circuit boards having the cross-sectional structure shown 
in FIG. 4 were prepared. In FIG. 4, a reference numeral 31 denotes an Si 
substrate; 32 an SiO.sub.2 film; 33 a Ti connecting film; 34 a Cu 
conductive film; 35 an AlN dielectric film; 36 pores; 37 a Ti connecting 
film; and 38 a Cu conductive film. 
First an SiO.sub.2 film 32 was formed on a surface of an Si substrate 31. 
Then, a sputtering process targeting Ti was performed in an Ar gas 
atmosphere under a pressure of 0.5 Pa, thereby forming a Ti connecting 
film 33 on the SiO.sub.2 film 32. In this process, the sputtering power 
was 2 kW and the substrate temperature was 200.degree. C. Subsequently, a 
sputtering process targeting Cu was performed in an Ar gas atmosphere 
under a pressure of 0.5 Pa, thereby forming a Cu conductive film 34 on the 
Ti connecting film 33. In this process, the sputtering power was 3 kW and 
the substrate temperature was 200.degree. C. 
Thereafter, a sputtering process targeting Al was performed in a gas 
atmosphere containing nitrogen, thereby forming an AlN dielectric film 35 
having a thickness D on the Cu conductive film 34 (the thickness D is 
shown in Table 2 indicated afterward). In this process, the sputtering 
power was 3 kW and the substrate temperature was 200.degree. C. An Ar gas 
and a nitrogen gas were used as the gas atmosphere in the ratio of flow 
rates 5/1 and the sputtering pressure was maintained at 0.3 Pa. 
Subsequently, the AlN dielectric film 35 was etched by means of ordinary 
photolithography, thereby forming pores 36 having a square shape in the 
plan view. In the etching process, a RIE using Ar, Cl, Br and CF.sub.4 as 
an etchant was employed and the etching power was 250 W. The size of a 
pore 36 was A .mu.m.times.A .mu.m.times.B .mu.m, and the interval between 
pores was C .mu.m (the values of A, B and C are indicated in Table 2). The 
arrangement of the pores 36 is as shown in FIG. 2B. Then, an AlN 
dielectric film was deposited by the sputtering under the same conditions 
as described above, thereby closing the openings of the pores 36. At this 
time, the pores were filled with an Ar-containing gas. Partial pressure of 
Ar in the filled gas is equal to that of sputtering atmosphere 
equilibrated at the sputtering pressure. 
A Ti connecting film 37 and a Cu conductive film 38 were successively 
formed by sputtering. The conditions of the sputtering are the same as 
those in the process 10 for forming the Ti connecting film 33 and the Cu 
conductive film 34. Then, a laminated film constituted by the Ti 
connecting film 37 and the Cu conductive film 38 was patterned into a size 
of 100 .mu.m.times.100 .mu.m, thus forming an upper electrode. 
With respect to Samples Nos. 20 to 24 thus obtained, the dielectric 
constant, the porosity, the resistivity, the crystallinity of the 
dielectric film 35, the moisture resistance and the thermal conductivity 
were evaluated. The results of the evaluation are shown in Table 2. The 
dielectric constant was measured under the condition of 10 MHz and the 
resistivity was measured under the condition of an applied voltage of 10 
V. The cross section of the obtained sample was observed by an SEM, and 
the porosity was calculated. Regarding the crystallinity, the sample, on 
which an upper electrode has not been formed, was first subjected to X-ray 
diffraction, and then a half band width (w.sub.1) of a main peak obtained 
by the diffraction was compared with a half band width (w.sub.2) obtained 
by the X-ray diffraction of bulk solid AlN in the same direction, to 
evaluate the crystallinity. The value of w.sub.1 /w.sub.2 is indicated in 
Table 2. Regarding the moisture resistance, the samples were kept in steam 
of 100.degree. C. for 500 hours, and thereafter the resistivity of each 
sample was measured under the atmosphere. A sample, which has a 
resistivity of 1.times.10.sup.9 .OMEGA..multidot.cm or higher, was 
regarded as acceptable. Regarding the thermal conductivity, a thermal 
diffusivity of the sample was measured by using AC calorimetric method, 
and the thermal conductivity was calculated from the thermal diffusivity. 
As clear from the results indicated in Table 2, each of Samples Nos. 20 to 
24 according to the present invention has a high porosity and a high 
thermal conductivity, satisfactory crystallinity and moisture resistance, 
and a low dielectric constant. 
EXAMPLE 3 (Samples Nos. 25 to 29) 
In this example, circuit boards having the cross-sectional structure shown 
in FIG. 5 were prepared. In FIG. 5, a reference numeral 41 denotes an AlN 
substrate; 42 a W-wiring layer; 43 a Ti connecting film; 44 an Al 
conductive film; 45 an AlN dielectric film; 46 pores; and 47 an Al 
conductive film. 
In this example, an AlN substrate 41, in which a W-wiring layer 42 had been 
preformed, was used. First, a sputtering process targeting Ti was 
performed in an Ar gas atmosphere under a sputtering pressure of 1 Pa, 
thereby forming a Ti connecting film 43 on the AlN substrate 41. In this 
process, the sputtering power was 2 kW and the substrate temperature was 
200.degree. C. Subsequently, a sputtering process targeting Al was 
performed in an Ar gas atmosphere under a sputtering pressure of 1 Pa, 
thereby forming an Al conductive film 44 on the Ti connecting film 43. In 
this process, the sputtering power was 3 kW and the substrate temperature 
was 200.degree. C. 
Thereafter, a sputtering process targeting Al was performed in a gas 
atmosphere containing nitrogen, thereby forming an AlN dielectric film 45 
having a thickness D on the Al conductive film 44 (the thickness D is 
shown in Table 2 indicated later). In this process, the sputtering power 
was 3 kW and the substrate temperature was 200.degree. C. A Ne gas and a 
nitrogen gas were used as the gas atmosphere in a ratio of flow rates 5/1 
and the sputtering pressure was maintained at 0.3 Pa. Subsequently, pores 
46 having a square shape in the plan view were formed in the AlN 
dielectric film 45 in the same manner as in Example 2 (Samples Nos. 20 to 
24). The size of a pore 46 was A .mu.m.times.A .mu.m.times.B .mu.m, and 
the interval between pores was C .mu.m (the values of A, B and C are 
indicated in Table 2). The arrangement of the pores 46 is as shown in FIG. 
2B. Then, an AlN dielectric film was deposited by the sputtering under the 
same conditions as described above, thereby closing the openings of the 
pores 46. At this time, the pores were filled with an Ne-containing gas 
having Ne partial pressure which is equal to that of sputtering atmosphere 
equilibrated at the sputtering pressure. 
Thereafter, an Al conductive film 47 was formed by the sputtering under the 
same conditions as the process for forming the Al conductive film 44. The 
Al conductive film 47 was patterned into a size of 100 .mu.m.times.100 
.mu.m, thus forming an upper electrode. 
With respect to Samples Nos. 25 to 29 thus obtained, the dielectric 
constant, the porosity, the resistivity, the crystallinity of the 
dielectric film, the moisture resistance and the thermal conductivity were 
evaluated in the same manner as in Example 2 (Samples Nos. 20 to 24). The 
results of the evaluation are shown in Table 2. 
As clear from the results indicated in Table 2, each of Samples Nos. 25 to 
29 according to the present invention has a high porosity and a high 
thermal conductivity, satisfactory crystallinity and moisture resistance, 
and a low dielectric constant. 
EXAMPLE 4 (Samples Nos. 30 to 34) 
In this example, circuit boards having the cross-sectional structure shown 
in FIG. 6 were manufactured. In FIG. 6, a reference numeral 51 denotes an 
Si substrate; 52 an SiO.sub.2 film; 53 an Al conductive film; 54 a 
diamond-like carbon dielectric film; 55 pores; and 56 an Al conductive 
film. 
An Si substrate 51, on which an SiO.sub.2 film 52 had been formed, was 
prepared. A sputtering process targeting Al was performed in an Ar gas 
atmosphere under a sputtering pressure of 1 Pa, thereby forming a Al 
conductive film 53 on the SiO.sub.2 film 52. In this process, the 
sputtering power was 2 kw and the substrate temperature was 200.degree. C. 
Subsequently, a diamond-like carbon dielectric film 54 having a thickness D 
was formed on the Al conductive film 53 by a plasma CVD using microwaves 
of a power of 2 kW (the thickness D is shown in Table 2). The conditions 
of the CVD were the substrate temperature of 400.degree. C., the pressure 
of 300 Pa, and the ratio of flow rates of Ar gas to CH.sub.4 gas 25/1. 
Then, the diamond-like carbon dielectric film 54 was etched by means of 
ordinary photolithography, thereby forming pores 55 having a square shape 
in the plan view. In the etching process, a RIE method using Ar and O as 
an etchant (the ratio of flow rates is 10) was employed and the etching 
power was 250 W. The size of a pore 55 was A .mu.m.times.A .mu.m.times.B 
.mu.m, and the interval between pores was C .mu.m (the values of A, B and 
C are indicated in Table 2). The arrangement of the pores 55 is as shown 
in FIG. 2B. Thereafter, a diamond-like carbon dielectric film was 
deposited by the CVD under the same conditions as described above, and 
then etched under the above-mentioned etching conditions, thereby forming 
pores 55 of the above-mentioned size. The deposition and etching processes 
were repeated, until the thickness of the dielectric film 54 became 20 
.mu.m. When the thickness of the dielectric film reached 20 .mu.m, a 
diamond-like dielectric film was deposited by the CVD under the same 
conditions as described above, thereby closing the openings of the pores 
55. At this time, the pores were filled with an Ar-containing gas having 
Ar partial pressure equal to that of the sputtering atmosphere 
equilibrated at the sputtering pressure. 
Thereafter, an Al conductive film 56 was formed by the sputtering under the 
same conditions as the process for forming the Al conductive film 53. The 
Al conductive film 56 was patterned into a size of 100 .mu.m.times.100 
.mu.m, thus forming an upper electrode. 
With respect to Samples Nos. 30 to 34 thus obtained, the dielectric 
constant, the porosity, the resistivity, the crystallinity of the 
dielectric film, the moisture resistance and the thermal conductivity were 
evaluated in the same manner as in Example 2 (samples Nos. 20 to 24). The 
results of the evaluation are shown in Table 2. 
As clear from the results indicated in Table 2, each of Samples Nos. 30 to 
34 according to the present invention has a high porosity and a high 
thermal conductivity, satisfactory crystallinity and moisture resistance, 
and a low dielectric constant. 
EXAMPLE 5 (Samples Nos. 35 to 39) 
In this example, circuit boards having the cross-sectional structure shown 
in FIG. 7 were prepared. In FIG. 7, a reference numeral 61 denotes an AlN 
substrate; 62 an internal W-wiring layer; 63 a W conductive film; 64 an 
AlN dielectric film; 65 pores; and 66 a W conductive film. 
In this example, an AlN substrate 61, in which an internal W-wiring layer 
62 had been formed and on which a W conductive film 63 had been formed, 
was used. 
First, an AlN thick film paste was printed on the W conductive film 63 and 
sintered in a nitrogen atmosphere, thereby forming an AlN dielectric film 
64. The AlN thick film paste was prepared by adding AlN, yttrium oxide and 
an acrylic binder into a-Terpineol (CH.sub.3 C.sub.6 H.sub.8 
(CH.sub.3).sub.2 OH) solvent. The conditions of sintering were the 
temperature of 1850.degree. C. and the period of time of 1 hour. 
The surface of the AlN dielectric film was mirror-polished to a surface 
roughness of 30 nm. Subsequently, the AlN dielectric film 64 was etched by 
means of selective wet etching using a 1 wt % solution of 
tetramethylammonium hydroxide as an etchant, thereby forming pores 65, 
having a square shape in the plan view, in the AlN dielectric film 65. The 
size of a pore 65 was A .mu.m.times.A .mu.m.times.B .mu.m, and the 
interval between pores was C .mu.m (the values of A, B and C are indicated 
in Table 2). The arrangement of the pores 65 is as shown in FIG. 2B. Then, 
the above-mentioned AlN thick film paste was printed on the AlN dielectric 
film 64 in a He gas atmosphere, thereby closing the openings of the pores 
65. At this time, the pores were filled with a He gas. Further, a W thick 
film paste was printed on the AlN dielectric film 64, thereby forming a W 
conductive film 66. The W thick film paste was prepared by adding W and an 
acrylic binder into .alpha.-Terpineol (CH.sub.3 C.sub.6 H.sub.8 
(CH.sub.3).sub.2 OH) solvent. The W conductive film 66 was subjected to 
sintering at a temperature of 1850.degree. C. for 1 hour in a nitrogen gas 
atmosphere. 
With respect to Samples Nos. 35 to 39 thus obtained, the dielectric 
constant, the porosity, the resistivity, the crystallinity of the 
dielectric film, the moisture resistance and the thermal conductivity were 
evaluated in the same manner as in Example 2 (Samples Nos. 20 to 24). The 
results of the evaluation are shown in Table 2. 
As clear from the results indicated in Table 2, each of Samples Nos. 35 to 
39 according to the present invention have high porosity and thermal 
conductivity, satisfactory crystallinity and moisture resistance, and a 
low dielectric constant. 
EXAMPLE 6 (Sample No. 40) 
In this example, a circuit board having the cross-sectional structure shown 
in FIG. 8 was prepared. In FIG. 8, a reference numeral 71 denotes an Si 
substrate; 72 an SiO.sub.2 film; 73 an Al conductive film; 74 an AlN 
dielectric film; 75 pores; and 76 an Al conductive film. 
An Si substrate 71, on which an SiO.sub.2 film 72 had been formed, was 
prepared. A sputtering process targeting Al was performed in an Ar gas 
atmosphere under a sputtering pressure of 1 Pa, thereby forming a Al 
conductive film 73 on the SiO.sub.2 film 72. In this process, the 
sputtering power was 2 kW and the substrate temperature was 200.degree. C. 
Then, a sputtering process targeting Al was performed in a gas atmosphere 
containing nitrogen, thereby forming an AlN dielectric film 74 having a 
thickness of 2 .mu.m on the Al conductive film 73. In this process, the 
sputtering power was 6 kW and the substrate temperature was 20.degree. C. 
An Ar gas and a nitrogen gas were used as the gas atmosphere in a ratio of 
flow rates 5/1 and the sputtering pressure was maintained at 15 Pa. At 
this time, the Ar gas of the atmosphere was taken into the AlN dielectric 
film 74, resulting in formation of pores 75. 
Thereafter, an Al conductive film 76 was formed by the sputtering under the 
same conditions as the process for forming the Al conductive film 73. The 
Al conductive film 76 was patterned into a size of 100 .mu.m.times.100 
.mu.m, thus forming an upper electrode. 
In Sample No. 40 thus obtained, the pores 75 were formed in the process 
control of the sputtering. Thus, Sample No. 40 is equivalent to Samples 
Nos. 1 to 18 obtained in Example 1. With respect to Sample No. 40, the 
dielectric constant, the porosity, the resistivity, the crystallinity of 
the dielectric film, the moisture resistance and the thermal conductivity 
were evaluated in the same manner as in Example 2 (Samples Nos. 20 to 24). 
The results of the evaluation are shown in Table 2. 
As clear from the results indicated in Table 2, Sample No. 40 according to 
the present invention has a satisfactory moisture resistance; however, it 
has a lower porosity than in Examples 2 to 5 (Samples Nos. 20 to 39). 
Further, it has lower coefficient of thermal conductivity and 
crystallinity and higher dielectric constant as compared to Examples 2 to 
5. 
COMATIVE EXAMPLE 
In this comparative example, a circuit board having the cross-sectional 
structure shown in FIG. 9 was prepared. In FIG. 9, a reference numeral 81 
denotes an Si substrate; 82 an SiO.sub.2 film; 83 an Al conductive film; 
84 an SiO.sub.2 dielectric film; 85 pores; and 86 an Al conductive film. 
An Si substrate 81, on which an SiO.sub.2 film 82 had been formed, was 
prepared. A sputtering process targeting Al was performed in an Ar gas 
atmosphere under a sputtering pressure of 1 Pa, thereby forming a Al 
conductive film 83 on the SiO.sub.2 film 82. In this process, the 
sputtering power was 3 kW and the substrate temperature was 100.degree. C. 
Then, a sputtering process targeting Si was performed in a gas atmosphere 
containing oxygen, thereby forming an SiO.sub.2 dielectric film 84 having 
a thickness of 5 .mu.m on the Al conductive film 83. In this process, the 
sputtering power was 6 kW and the substrate temperature was 20.degree. C. 
An Ar gas and a oxygen gas were used as the gas atmosphere in a ratio of 
flow rates 5/1 and the sputtering pressure was maintained at 15 Pa. At 
this time, the Ar gas of the atmosphere was taken into the SiO.sub.2 
dielectric film 84, resulting in formation of random pores 85. Some of the 
pores 85 were opened through the side walls of the SiO.sub.2 dielectric 
film 74. 
Thereafter, an Al conductive film 86 was formed by the sputtering under the 
same conditions as the process for forming the Al conductive film 83. The 
Al conductive film 86 was patterned into a size of 100 .mu.m.times.100 
.mu.m, thus forming an upper electrode. 
With respect to Sample No. 41, the dielectric constant, the porosity, the 
resistivity, the crystallinity of the dielectric film, the moisture 
resistance and the thermal conductivity were evaluated in the same manner 
as in Example 2 (Samples Nos. 20 to 24). The results of the evaluation are 
shown in Table 2. 
As clear from the results indicated in Table 2, since the SiO.sub.2 
dielectric film 84 of Sample No. 41 is made of a material different from 
those of the present invention, it has a lower thermal conductivity. 
Further, it has a lower resistivity and an inferior moisture resistance, 
since the pores 85 are not completely closed. 
TABLE 2 
______________________________________ 
Relative 
dielectric 
Resistivity 
No. A (.mu.m square 
B (.mu.m) 
C (.mu.m) 
constant 
(.OMEGA..cm) 
______________________________________ 
20 2 2 0.1 1.4 2 .times. 10.sup.14 
21 3 3 0.15 1.4 2 .times. 10.sup.14 
22 1 1.1 0.025 1.2 2 .times. 10.sup.14 
23 1 1 1 6.6 2 .times. 10.sup.14 
24 2 2 0.25 4.5 3 .times. 10.sup.14 
25 5 5 1.25 2.9 2 .times. 10.sup.14 
26 1 2 0.025 1.2 3 .times. 10.sup.14 
27 1 4 0.025 1.2 3 .times. 10.sup.14 
28 1 1 0.5 5.0 2 .times. 10.sup.14 
29 1 1 0.4 4.0 4 .times. 10.sup.14 
30 1 10 1 3.7 3 .times. 10.sup.13 
31 1 15 1 3.4 2 .times. 10.sup.13 
32 2 15 1 2.8 3 .times. 10.sup.13 
33 4 15 1 2.1 3 .times. 10.sup.13 
34 2 15 0.6 2.1 2 .times. 10.sup.13 
35 5 30 2 2.4 3 .times. 10.sup.14 
36 2 30 0.6 2.3 3 .times. 10.sup.14 
37 4 30 0.7 1.6 2 .times. 10.sup.14 
38 1 20 1 3.6 3 .times. 10.sup.14 
39 5 20 1 2.3 3 .times. 10.sup.14 
40 7.0 3 .times. 10.sup.14 
41 2.0 1 .times. 10.sup.11 
______________________________________ 
Thermal 
conducti- 
Crystalli- Moisture 
No. vity nity Porosity 
resistance 
D 
______________________________________ 
20 23 0.99 86 Acceptable 
2.2 
21 23 0.98 86 " 3.3 
22 11 0.97 93 " 1.2 
23 221 0.99 10 " 2.0 
24 48 0.98 69 " 2.5 
25 90 0.99 49 " 6.3 
26 5 0.97 95 " 2.1 
27 5 0.97 96 " 4.0 
28 160 0.97 26 " 2.0 
29 123 0.98 34 " 1.8 
30 520 36 " 12 
31 470 39 " 17 
32 300 56 " 17 
33 190 69 " 17 
34 190 70 " 16 
35 68 1.0 60 " 34 
36 44 1.0 73 " 31 
37 30 1.0 81 " 31 
38 116 1.0 42 " 22 
39 44 1.0 74 " 22 
40 0.6 0.3 15 " 2 
41 1.0 0.6 50 Rejected 
5 
______________________________________ 
As has been described in detail, according to the present invention, there 
is provided a circuit board which satisfies the two requirements of a high 
heat radiating property and a high speed signal transmitting property and 
in which defects such as delamination do not easily occur. Therefore, the 
circuit board of the present invention can be applied to mount a 
highly-integrated semiconductor devices which is operated at high speed, 
and is significantly valuable for industry. 
Additional advantages and modifications will readily occur to those skilled 
in the art. Therefore, the invention in its broader aspects is not limited 
to the specific details, representative devices, and illustrated examples 
shown and described herein. Accordingly, various modifications may be made 
without departing from the spirit or scope of the general inventive 
concept as defined by the appended claims and their equivalents.