Thermo-siphon and manufacturing method of thermo-siphon and information processing apparatus

The present invention aims to reduce as much as possible the weight of the thermo-siphon being used in spreading heat of the mobile information processing apparatus. The heat spreading board 5 and the thermo-siphon 6 is installed at the lid 51 of the notebook type personal computer, and the heat from the CPU 1 is conducted to the thermo-siphon 6 via the heat pipe 3. The heat spreading board 5 includes the thick part 33 and the thin part 34. The thin part 34 contributes in reducing the weight of the heat spreading board 5.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to thermo-siphon and its manufacturing method 
and an information processing apparatus. Particularly, the present 
invention relates to the information processing apparatus for releasing 
heat generated at a heat generation unit to outside. 
2. Background Art 
Conventionally, a technique relating to this field is disclosed in Japanese 
unexamined patent publication HEI 9-6481. The conventional mobile 
information processing apparatus mentioned in this publication as 
illustrated in FIG. 55 comprises a lid 51 incorporating a heat pipe 3 and 
a heat spreading board 5, and a main body 50 incorporating a heat 
generation unit (central processing unit) 1. The heat generated from the 
heat generation unit 1 is released from the heat spreading board 5 via a 
thermally conductive block 2. 
Another conventional techniques relating to this field are Japanese 
unexamined patent publications HEI 8-87354, HEI 8-204373 and HEI 8-261672. 
FIG. 56 illustrates a side view of disintegrated lid 51. 
Following components are installed in between a front panel 60 and an 
external chassis 12: a liquid crystal display panel 7; a back light 10; a 
back light optical system 62; and a inverter circuit board 95 for the back 
light. 
FIG. 57 illustrates a temperature profile of the lid 51 and the main body 
50. 
In the drawing, curved lines in the temperature profile illustrate 
isotherms. As can be seen from FIG. 57, a lot of heat is being generated 
from the CPU 1, the back light 10 and the inverter circuit board 95. 
FIG. 58 illustrate a conventional manufacturing method of thermo-siphon 
used in heat spreading. 
FIG. 59 illustrate a manufacturing step of roll bond heat pipe disclosed in 
the explanatory note published by Showa Aluminum Kabushiki Kaisha. 
The roll bond is manufactured as follows: cutting aluminum plates (S10); 
printing a path to form a flow channel on top of an aluminum plate by 
using a pressure adhesion preventing agent (S12); place another aluminum 
plate on top of the aluminum plate for rolling them together (S13, S14); 
and inflate the flow channel using high-pressure gas and the thermo-siphon 
is cut into a desired shape (S15, S16). The thermo-siphon is manufactured 
by injecting a working fluid to this inflated flow channel. 
The conventional mobile information processing apparatus has difficulty in 
conducting heat, which is sent from the heat pipe 3, throughout the heat 
spreading board due to an inadequate heat conduction to a direction of 
plane of the heat spreading board 5. As a result of this, from within 
various positions of the heat spreading board 5, only positions that are 
close to the heat pipe 3 were able to contribute in spreading the heat 
such that an effect of heat spreading in the conventional mobile 
information processing apparatus is therefore inadequate. 
The conventional thermo-siphon is manufactured by pressurizing the two 
aluminum plates together, however, since a specific gravity of 
aluminumplate is heavy, a weight of the thermo-siphon will also become 
heavy. This results in a problem of increasing the weight of information 
processing apparatus when attempt to spread the heat using the 
thermo-siphon. 
Also, in the conventional mobile information processing apparatus, from the 
back light which is installed at inner lateral plane of the lid, a heat is 
transferred to the liquid crystal display panel to cause difference in 
temperature at a position close to the back light and at a position far 
from the back light. Due to such a temperature difference, a color 
inconsistency of the back light 10 occurs which is a problem. 
SUMMARY OF THE INVENTION 
The present invention attempts to solve this problem by aiming to reduce a 
weight of the thermo-siphon. 
Also, at the same time as improving the heat generating efficiency of the 
information processing apparatus, the present invention aims to reduce a 
weight of the information processing apparatus. 
Also, the present invention aims to control an effect due to the back 
light. 
According to one aspect of the present invention, a thermo-siphon 
comprises: a heat spreading board; and a flow channel for circulating a 
working fluid. The heat spreading board includes a thick part and a thin 
part. 
According to another aspect of the present invention, the heat spreading 
board of the therno-siphon is arranged to place the thick part closer to 
the flow channel than the thin part. 
According to another aspect of the present invention, the flow channel of 
the thermo-siphon forms a closed loop, and the thick part is formed at an 
inner periphery of the closed loop, and the thin part is formed at an 
inner side of the thick part. 
According to another aspect of the present invention, the heat spreading 
board of the thermo-siphon is a combined plate of a first plate and a 
second plate, wherein the first plate is a flat board and the second plate 
has a lacking part. 
According to another aspect of the present invention, the one of the plate 
of the plates from the first plate and the second plate of the 
thermo-siphon is larger than the other one of the plates, and a protruded 
edge of one of the plates is bent. 
According to another aspect of the present invention, the first plate and 
the second plate of the thermo-siphon have different thickness. 
According to another aspect of the present invention, the thermo-siphon is 
used in spreading heat of an electronic device. 
According to another aspect of the present invention, the electronic device 
of the thermo-siphon comprises a main body having a heat generation unit, 
and a lid covering the main body, and wherein the thermo-siphon is 
installed on the lid. 
According to another aspect of the present invention, a manufacturing 
method of the thermo-siphon comprises the following steps: 
(a) cutting two plates for forming a heat spreading board; 
(b) forming a lacking part on one of the plates; 
(c) printing a flow channel using a pressure adhesion preventing agent on 
one of the plates; 
(d) piling the two plates together; 
(e) adhering the piled two plates by rolling; 
(f) inflating the flow channel formed between the adhered plates; and 
(g) injecting a working fluid in the flow channel. 
According to another aspect of the present invention, the cutting step of 
the manufacturing method of thermo-siphon includes cutting of one plate 
larger in size than the other plate, and further the manufacturing method 
of thermo-siphon comprising a step of bending the protruded part of one of 
the plates after the adhering step. 
According to another aspect of the present invention, an information 
processing apparatus comprises: a main body having the heat generation 
unit; and a lid where a liquid crystal display panel is installed at an 
inner plane. The information processing apparatus includes a heat 
spreading board exposed to and installed at an outer plane of the lid for 
releasing the heat generated at the heat generation unit to outside. 
According to another aspect of the present invention, an exposed plane of 
the heat spreading board of the information processing apparatus is formed 
by a foaming paint layer. 
According to another aspect of the present invention, a thermally 
conductive material for releasing the heat generated at the heat 
generation unit of the main body of the information processing apparatus 
is installed at a rear plane of the main body. 
According to another aspect of the present invention, the foaming paint 
layer of the information processing apparatus is formed at the bottom 
plane of the main body. 
According to another aspect of the present invention, the information 
processing apparatus comprises a frame that is easy to process compared to 
the heat spreading board, which is installed at periphery of the heat 
spreading board. 
According to another aspect of the present invention, a coefficient of 
thermal expansion of the heat spreading board of the information 
processing apparatus is substantially identical to a coefficient of 
thermal expansion of the frame. 
According to another aspect of the present invention, an additive used in 
the information processing apparatus is mixed into the heat spreading 
board for adjusting the coefficient of thermal expansion. 
According to another aspect of the present invention, the foaming paint 
layer of the information processing apparatus includes a foaming layer 
which is foamed by painting a paint material including a foaming material, 
and a top coating layer having a high degree of hardness than the foaming 
layer on top of the foaming layer. 
According to another aspect of the present invention, the top coating layer 
of the information processing apparatus is formed by a bead-containing 
paint material. 
According to another aspect of the present invention, the paint material of 
the information processing apparatus is one of the paint material and a 
resinous coating material. 
According to another aspect of the present invention, the thickness of the 
foaming layer of the information processing apparatus is ranging from 50 
to 500 .mu.m. 
Further scope of applicability of the present invention will become 
apparent from the detailed description given hereinafter. However, it 
should be understood that the detailed description and specific examples, 
while indicating preferred embodiments of the invention, are given by way 
of illustration only, since various changes and modifications within the 
spirit and scope of the invention will become apparent to those skilled in 
the art from this detailed description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Reference will now be made in detail to the present preferred embodiments 
of the invention, examples of which are illustrated in the accompanying 
drawings, wherein like reference numerals indicate like elements 
throughout the several views. 
Embodiment 1. 
Hereinbelow, a preferred embodiment of the thermo-siphon and the 
information processing apparatus of the present invention are described 
with reference to attached drawings. 
Configuration of the mobile information processing apparatus is described 
with reference to FIG. 1. Description of the numbered components follows: 
the main body 50 of a notebook type personal computer; the lid 51 for 
covering the main body 50; a connecting axis 52 having a hinge structure 
which connects the main body 50 and the lid 51; CPU (Central Processing 
Unit) 1 which is a heat generation unit; and the thermally conductive 
block 2 having a hinge 13 for efficiently collecting heat of CPU and 
conducting this heat to the heat pipe 3. The thermally conductive block 2 
can be made of any material such as metal or carbon, as long as it is 
thermally conductive material. An axis of the hinge 13 of the thermally 
conductive block 2 is same as the connecting axis 52. The heat pipe 
encloses an adequate amount of liquid (hereinafter a working fluid) inside 
an exhausted metallic pipe for vaporizing at a fixed temperature. The heat 
pipe performs highly efficient heat transmission by taking a heat of 
vaporization at a high temperature side and dissipating heat of 
condensation at a low temperature side. Inside the heat pipe, the working 
fluid is circulated by a capillary force of wick having a gutter or a 
porous structure in a vertical direction installed at an inner wall of the 
pipe. A fastening board 4 for fastening the heat pipe 3 to the heat 
spreading board 5 can provide an effective thermal connection. A 
thermo-siphon 6 can perform highly efficient heat transmission under a 
same principal as the heat pipe 3. However, normally, gutter or porous 
structure in the vertical direction is not installed at an inner side of 
the thermo-siphon 6 such that the working fluid is not circulated using 
the capillary force of the wick. The working fluid inside the 
thermo-siphon 6 circulates along flow channel using gravity. An example of 
the thermo-siphon 6 is a roll bond panel 58 manufactured by Showa Aluminum 
Kabushiki Kaisha. As illustrated in FIG. 2, the roll bond panel 58 is 
formed by placing the two aluminum plates together, and has flow channel 
59 that is hollow inside. An advantage of using the roll bond panel is an 
integral manufacturing of the heat spreading board 5 and the thermo-siphon 
6. However, the heat spreading board 5 and the thermo-siphon 6 can be made 
independent of one another, as illustrated in FIG. 3. When a surface area 
of the thermo-siphon 6 is large, there is no need to install the heat 
spreading board 5. FIG. 1 further shows the following elements: the liquid 
crystal display panel 7, the back light 10; and the external chassis 12 of 
the lid 51. 
FIG. 3 is the cross-section cut through B--B of FIG. 2. 
In the drawing of FIG. 3, the heat spreading board 5 includes a first plate 
31 and a second plate 32 that are rolled and adhered together. The first 
plate 31 and the second plate 32, for example, are Al (aluminum) plates 
having thickness of 0.4 mm. The first plate 31 is a flat board. The second 
plate 32 includes openings. The drawing illustrates one example of such 
lacking part. A thick part 33 on the heat spreading board is where the 
first plate 31 and the second plate 32 are overlapping, having thickness 
of 0.8 mm. A thin part 34 on the heat spreading board is where there is 
only the first plate 31, having thickness of 0.4 mm. The thickness of a 
portion where there is the flow channel 59 will be 1.about.2 mm. 
The flow channel 59 forms a closed loop. The thick part 33 is formed at an 
outer periphery of the closed loop. The thin part 34 is formed at an inner 
side of the thick part 33. 
The heat spreading method of the mobile information processing apparatus is 
described with reference to FIG. 4. 
FIG. 5 is a cross-section cut through C--C of FIG. 4. 
The thermo-siphon 6 includes a liquid reservoir 55 for collecting the 
working fluid. The thermo-siphon 6 further includes vapor flow channels 53 
and 54 for circulating the working fluid 9 in the direction of the plane 
of the heat spreading board 5. A case shown in FIG. 4 illustrates a first 
flow channel 53 for circulating around a periphery of the heat spreading 
board 5, and also illustrates second flow channels 54 for extending along 
to a perpendicular direction to the connecting axis 52, which joins to the 
first flow channel 53. The heat generated at the CPU 1 is conducted to the 
heat pipe 3 via the thermally conductive block 2, and is transferred to 
the heat spreading board by means of two-phase flow transfer. At the heat 
spreading board 5 where the thermo-siphon 6 is formed, the heat is 
dissipated efficiently by two-phase flow movement, and finally, the heat 
is dissipated to outer ambient by effects of convection and heat 
radiation. 
Normally, liquid such as fluorinate or water is injected as the working 
fluid 9 to the liquid reservoir and the flow channels. After the 
injection, the liquid reservoir and the flow channels are decompressed and 
air-tightly sealed. The working fluid 9 will be collected at a lower part 
of the liquid reservoir due to an effect of the gravity, however, by 
making a high temperature heat source such as heat pipe attach to the 
lower liquid reservoir, the heat is conducted to the working fluid, which 
turns it into a vapor to cause an ascending vapor flow to a lower 
temperature part. When the heat is transferred accordingly, and the vapor 
flow is condensed to spread the heat inside the vapor flow channel. The 
working fluid is liquefied by the condensation and falls down the vapor 
flow channel under its own weight. That is, inside the thermo-siphon, the 
heat of vaporization is transferred by the circulation and the flow back 
of the working fluid under the effect of gravity. An effective heat 
transfer and the heat equalization occurs by heat transmission processes 
such as condensation and heat spreading. Comparing a use of the 
thermo-siphon to the heat conduction by using a metal only, one can expect 
a large improvement in a cooling capability. 
FIG. 6 is a flow chart showing the heat spreading method. 
In step S0, if the CPU 1 is not generating heat, the heat spreading process 
will not occur at all. If the CPU 1 which is installed on the main body 50 
generates heat, in step S1, the heat from the CPU 1 is transferred to the 
thermo-siphon 6 via the heat pipe 3. Next, in step S2, the heat being 
transferred via the heat pipe 3 heats up the working fluid 9. Step S3 is a 
step to transfer the heat of vaporization. The step S3 includes a step of 
vaporizing the working fluid 9 (S31) and a step of circulating a vapor 
flow inside the vapor flow channel (S32). Next, step S4 is a step for 
spreading heat by the condensation of the vapor flow. The step S4 includes 
a step of liquefying the vaporized working fluid 9 (S41) and a step of 
returning the working fluid 9 through the vapor flow channel back into the 
liquid reservoir (S42). Accordingly, an operation from step S1 to S4 is 
repeated as long as the heat continues to be generated. 
The thermo-siphon 6 has a thickness of 1.about.2 mm, therefore, this is 
made much thinner than a case of installing a fan. Also, the fan will not 
be needed even for CPU which desires a use of the fan, and the 
thermo-siphon 6 can bring about a greater heat spreading effect over the 
fan. 
FIG. 8 illustrates a heat spreading fin 35 having a length L and a 
thickness B, which is attached to a heat generation unit 36. 
FIG. 7 is a graph showing fin efficiency upon changing the length L. 
In the graph of FIG. 7, a black square ".box-solid." indicates the fin 
efficiency of Al plate having thickness B=1 mm. Also, in the graph, a 
white triangle ".DELTA." indicates the fin efficiency of Al plate having 
thickness of B=0.8 mm. Also, a black circle ".circle-solid." in the graph 
indicates the fin efficiency of Al plate having thickness B=1 mm or B=0.4 
mm. Also, an asterisk "*" in the graph indicates the fin efficiency of Al 
plate having thickness B=1 mm. The fin efficiency is the ratio of an 
actual amount of heat spreading from the whole conducting plane of the fin 
and an amount of heat spreading assuming that the whole conducting plane 
of the fin is equivalent to temperature of the heat generation unit. When 
the fin efficiency is 1 (100%), it is a case when the effect of heat 
spreading is maximum. As can be understood from FIG. 7, the longer the 
length L where the heat is conducted, the fin efficiency is poor. In order 
to maintain a sufficient heat spreading efficiency, the fin efficiency 
must ideally be greater than 0.8. Accordingly, when using Al plate having 
thickness B=0.8 mm as the heat spreading board, to make the fin efficiency 
greater than 0.8, the length L of the heat spreading board must be below 9 
cm. Also, when using aluminum plate having a thickness B=0.4 mm as heat 
spreading board, the length L should be below 6 cm. 
FIG. 9 illustrates a thermo-siphon for which a distance between the flow 
channel 59 is 12 cm. 
The flow channel 59 forms a closed loop. The thick part 33 is formed at an 
outer periphery of the closed loop. The thin part 34 is formed at an inner 
side of the thick part 33. 
Provided that a length of the thick part 33 is 3 cm, then a length of the 
thin part 34 will be 6 cm. A central part X of the thin part 34 is located 
at 6 cm from an edge of the flow channel 59. The thermo-siphon is formed 
using the aluminum plates. If a thickness of the thick part 33 is 0.8 mm 
and a thickness of the thin part 34 is 0.4 mm, the fin efficiency is 
indicated by arrow illustrated at a lower part of FIG. 9. That is, the 
thick part 33 having the thickness 0.8 mm shows the fin efficiency as in 
FIG. 7, and the thin part 34 having the thickness 0.4 mm shows the fin 
efficiency as in FIG. 7. If the central part X of the thin part 34 is 
separated by greater than 6 cm from its most closest flow channel 59, then 
there is a possibility of the fin efficiency to be greater than 0.8, such 
that a desirable heat spreading effect cannot be expected. 
FIG. 10 illustrates a thermo-siphon for which the distance between the flow 
channel 59 is 10 cm. 
The central part X is located at 5 cm away from the flow channel 59. 
Accordingly, at the central part X where the fin efficiency is minimum, 
the fin efficiency is 0.85, therefore, the fin efficiency of the central 
part X illustrated in FIG. 9 will be a value higher than 0.8. 
As such, by thinning the thickness of the heat spreading board, the fin 
efficiency declines, however, by shortening the distance from the flow 
channel 59, a pattern of the thick part 33 and the thin part 34 can be 
designed as to maintain the fin efficiency at least greater than 0.7 (70%) 
or preferably to be greater than 0.8 or 0.9. 
As described previously, the disadvantage of installing the thin part 34 to 
the heat spreading board 5 is in the decline in the effect of heat 
spreading. However, an advantage of this is that this can reduce a weight 
of the heat spreading board 5. Particularly, for the mobile information 
processing apparatus, its weight is required to be reduced as much as 
possible. The heat spreading board 5 of the present embodiment installs 
the thin part 34 to reduce its weight. For example, provided that a size, 
a thickness, and a material forming the first plate and the second plate 
are identical, if 30% of the openings (lacking parts) are installed on the 
second plate 32, and given that the weight of the first plate and the 
second plate is 100, the weight of heat spreading board formed will be 
(100+70)/(100+100)=0.85, which means it is 85% of the weight of not 
installing the openings. Alternatively, when installing 50% of openings, 
the weight of heat spreading board 5 will be (100+50)/(100+100)=0.75, and 
comparing this to the case of not installing the openings, the weight is 
75%. 
FIGS. 11 and 12 illustrate manufacturing method of the thermo-siphon for 
the present embodiment. 
First of all in step S10, cut the two aluminum plates. This will be used to 
form the thermo-siphon. Next in step S11, the openings are formed on one 
of the aluminum plates by a punch processing. Next in step S12, the flow 
channel pattern is printed to the other one of the aluminum plates by 
using the pressure adhesion preventing agent. This printing can be done on 
the plate where the openings are being formed. Next in step S13, two 
plates are placed together. Next in step S14, the two plates are adhered 
together by rolling. Next in step S15, high-pressure gas is blown into the 
flow channel of the pressurized plate to cause inflation of the flow 
channel. Next in step S16, the adhered plates is cut into a desired shape. 
Next, in step S17, working fluid is injected into the inflated flow 
channel and a mouth where the working fluid is injected is sealed. The 
thermo-siphon is manufactured this way. 
FIGS. 13 to 17 illustrate various opening patterns installed on the second 
plate 32. 
FIG. 13 illustrates a case of installing one opening at inner side of a 
closed flow channel loop. 
FIG. 14 illustrates a case of installing a plurality of openings at inner 
side of the closed flow channel loop. 
When installing a large opening as the case illustrated in FIG. 13, a 
strength of the second plate 32 is reduced, as a result, the strength of 
the thermo-siphon is also reduced. For the case illustrated in FIG. 14, in 
which a plurality of openings are installed by making them smaller, a 
decline in the strength is reduced as much as possible. 
FIG. 15 illustrates a case of installing flow channels to all the openings. 
FIG. 16 illustrates a case of spreading a weakness point in the first plate 
31 by changing the opening pattern. 
FIG. 17 illustrates a case of making the shape of the opening a sawtooth 
shape. Other shapes of the opening can be adopted to the opening patterns 
of FIGS. 13 to 17. 
Besides the lacking part of the thermo-siphon being the openings, FIGS. 18 
and 19 illustrate cases of cutting the lacking part. 
FIG. 18 illustrates a case of thermo-siphon being formed by installing a 
comb-shaped cut-out on the second plate 32. 
FIG. 19 illustrate a case of thermo-siphon being formed by installing a 
hand-shaped cut-out on the second plate 32. 
FIG. 20 illustrate a case of thermo-siphon being formed by installing one 
large opening at a central part. 
Due to this large opening, the thin part 34 is formed at a center, however, 
the size of the thin part 34 is either the same size as the size of liquid 
display panel 7 or greater. In order to make a thickness of the lid 51 
thin, it is desirable to make the thickness of the thermo-siphon thin as 
much as possible especially where there is the liquid crystal display 
panel 7. Accordingly, the thin part 34, which is the thinnest part of the 
thermo-siphon, is placed behind the liquid crystal display panel 7, and 
the thick part 33 and the flow channel 59 are placed to a part where there 
is no liquid crystal display panel 7 to reduce the thickness of the lid 
51. 
FIG. 21 illustrates the side view of the lid 51 from the outer side. 
FIG. 22 illustrates the cross-section cut through C--C of FIG. 21. 
In the drawing of FIG. 21, a chassis 12 is forming the outer cover of the 
lid 51. The heat spreading board 5 is partially exposed to outer chassis 
12 of the lid 51. 
As illustrated in FIGS. 4 and 5, the previously described thermo-siphon is 
used inside the chassis 12. However, as illustrated in FIGS. 21 and 22, 
the heat spreading board 5 itself is exposed as a part of the chassis, 
which enables further improvement in the heat spreading efficiency. 
FIGS. 23 and 24 illustrate another example of the openings. 
As illustrated in FIGS. 23 and 24, the shape, the size, the number of 
openings can be various. 
FIGS. 23 and 24 illustrate cases of making the size of the first plate 31 
greater than the size of the second plate 32. 
The edge of the first plate 31 is bent at a bending line 37 by using 
bending processing or press-out processing, and a strong box-shaped 
thermo-siphon is formed as illustrated in FIG. 25. For the case 
illustrated in FIG. 25, the bent processing or the press-out processing at 
the bending line 37 is bent by a 90 degree angle. Or, the bend processing 
at the bending line 37 can also be bent by a 180 degree angle. 
FIG. 26 illustrate a case of forming a chassis 12 by the press-out 
processing of the first plate 31. That is, FIG. 26 is the case of adopting 
the chassis 12 as the heat spreading board 5. 
The chassis 12 can also be manufactured using an aluminum plate. 
Accordingly, the chassis 12 can be used as the heat spreading board 5. Or, 
the chassis 12 can be used as the thermo-siphon 6. 
FIG. 27 illustrates a case of increasing a thickness W1 of the first plate 
31 more than a thickness W2 of the second plate 32. 
An advantage of FIG. 27 is that even when many openings are installed on 
the second plate 32, the strength of the thermo-siphon is not reduced. 
FIG. 28 illustrates a case of decreasing a thickness W3 of the first plate 
31 less than a thickness W4 of the second plate 32. 
An advantage of FIG. 28 is that the weight the of thermo-siphon is made 
lighter than the weight of the thermo-siphon of FIG. 27. 
FIG. 29 illustrates a case of installing openings on the first plate 31, 
not on the second plate 32. 
FIG. 30 illustrates a case of installing identical openings on the second 
plate 32 as the first plate 31. 
FIG. 31 illustrates a case of installing openings in both the first plate 
31 and the second plate 32, and the openings can have various patterns. 
Accordingly, the openings can be installed at either one of the first plate 
31 or the second plate 32, or, can be installed at both plates. 
Instead of the heat pipe, a metal rod having high thermal conductivity or a 
carbon material which also has high thermal conductivity may be used. 
Similar effects as in the heat pipe are obtained by using the metal rod 
and the carbon material having high thermal conductivity. 
The invention can be applied not only to the notebook type personal 
computers but also can be applied to others such as hand-held information 
processing apparatus, mobile telephones; and mobile facsimile machines. 
As described above, according to embodiment 1 of the present invention, a 
thin part is installed at the heat spreading board of the thermo-siphon, 
therefore, the weight of the thermo-siphon is reduced. 
Also, according to embodiment 1 of the present invention, since the weight 
of the thermo-siphon is reduced, the weight of the information processing 
apparatus using the thermo-siphon is reduced. 
Further, according to embodiment 1 of the present invention, simply by 
adding a simple step of installing a lacking part on the plate to a 
conventional manufacturing method, the weight of the thermo-siphon is 
reduced. 
Embodiment 2. 
Hereinbelow, a preferred embodiment of the information processing apparatus 
is described with reference to the attached drawings. 
Configuration of the mobile information processing apparatus is described 
with reference to FIG. 32. Description of the numbered components follows: 
the main body 50 of a notebook type personal computer; the lid 51 for 
covering the main body 50; a connecting axis 52 having a hinge structure 
which connects the main body 50 and the lid 51; CPU (Central Processing 
Unit) 1 which is a heat generation unit; and the thermally conductive 
block 2 having a hinge 13 for efficiently collecting heat of CPU and 
conducting this heat to the heat pipe 3. The thermally conductive block 2 
can be made of any material such as metal or carbon, as long as it is 
thermally conductive material. An axis of the hinge 13 of the thermally 
conductive block 2 is the same as the connecting axis 52. The heat pipe 
encloses an adequate amount of liquid (hereinafter a working fluid) inside 
an exhausted metallic pipe for vaporizing at a fixed temperature. The heat 
pipe performs highly efficient heat transmission by taking a heat of 
vaporization at a high temperature side and dissipating heat of 
condensation at a low temperature side. Inside the heat pipe, the working 
fluid is circulated by a capillary force of wick having a gutter or a 
porous structure in a vertical direction installed at an inner wall of the 
pipe. FIG. 32 further includes the following components: a fastening board 
4 for fastening the heat pipe 3 to the heat spreading board 5; the liquid 
crystal display panel 7; the back light 10; and the external chassis 12 of 
the lid 51. 
FIG. 33 is the side view of the lid from an outer side. 
FIG. 34 is the cross-section cut through A--A of FIG. 32. 
In the drawing of FIG. 34, a frame 70 forms an outer chassis of the lid 51. 
The heat spreading board 5 is exposed as a part of the outer chassis 12 of 
the lid 51. A foaming paint layer 80 is painted on a surface of the 
chassis 12. A silicon rubber 71 has a high thermally conductive property, 
and in addition, has an insulating property. A circuit board 73 installs a 
thermally conductive hole 76 for conducting a heat of the CPU 1. The 
thermally conductive hole 76 is a via hole or a through hole filled-in by 
a metal such as steel, which is installed at the circuit board 73. 
A thermally conductive plate 72 conducts heat transferred to the chassis 12 
via the silicon rubber 71. A material quality of the thermally conductive 
plate 72 can be of any type as long as it has high thermally conductive 
property. Also, those that has a spring property is desirable. 
Heat spreading processing of the mobile information processing apparatus is 
described with reference to FIGS. 33 and 34. 
The heat generated at the CPU 1 is transferred to the heat pipe 3 via the 
thermally conductive block 2, and is conducted to the heat spreading board 
5 by means of two-phase flow transfer. The heat spreading board 5 is 
exposed to outside such that the heat dissipation is extremely efficient, 
and at last the heat spreads to ambient by effect of heat radiation. 
In the previously described example, the heat pipe 3 is being used. Instead 
of the heat pipe, the flexible sheet 8 having a high thermally conductive 
property such as graphite or carbon fiber may be used. Or, a wire rod 
having a high thermally conductive property may be used. Similar effect as 
in the heat pipe is obtained by using the wire rod. 
A preferred example of the material of the heat spreading board 5 as 
illustrated in FIG. 34 is aluminum. Also, a preferred example of the 
material of the frame 70 is magnesium. Compared to aluminum, magnesium is 
a material that is easily processed for the bending processing and the 
press-out processing, as well for other mechanical processing. 
Accordingly, as illustrated in FIG. 34, the heat spreading board 5 uses a 
flat aluminum board, and the frame 70 uses a mechanical processing molded 
products made of magnesium. 
Instead of magnesium, other material that is easily processed may be used. 
For example, a plastic processing product or a resinous processing product 
may be used. Also, instead of aluminum, a graphite or steel may be used as 
the material forming the heat spreading board 5. 
For the liquid crystal display panel adopting a thin film transistor (TFT), 
a temperature difference inside the liquid crystal display panel needs to 
be controlled, because, due to a temperature dependency of a liquid 
crystal, the temperature difference can cause a color variation and a 
display inconsistency of the panel. In the drawing of FIG. 34, the heat 
spreading board 5 and the liquid crystal display panel 7 are closely 
attached together, therefore, the heat of the liquid crystal display panel 
7 is conducted to the heat spreading board 5, which gives an effect of 
preventing addition of heat or increased temperature partially or 
throughout the liquid crystal display panel 7. If the temperature of the 
heat spreading board is not so high, or, if there is a large temperature 
difference in the liquid crystal display panel 7 due to the heat being 
generated by the back light, by closely attaching the liquid crystal 
display panel 7 and the heat spreading board 5, the heat spreading board 5 
is cooled together with the liquid crystal display panel 7. Accordingly, 
the display inconsistency is removed by equalizing the temperature profile 
of the liquid crystal display panel 7, and this improves the display 
quality. 
With reference to FIG. 35, a configuration to assemble the heat spreading 
board is described. 
FIG. 36 is the cross-section of FIG. 35. 
In the drawing of FIG. 36, the frame 70 and the heat spreading board 5 is 
attached together at "B" by using an adhesive. 
As a material of the heat spreading board 5, for example, aluminum is used. 
Or, as a material of the frame 70, for example, magnesium is used. The 
cases illustrated in FIGS. 35 and 36 shows the adhesive being applied to 
the surrounding edge of the heat spreading board 5, and the heat spreading 
board is pasted at inner side of the frame 70. Since a coefficient of 
thermal expansion of aluminum is greater than a coefficient of thermal 
expansion of magnesium, it is preferable to make both coefficients equal. 
For example, in order to reduce the coefficient of thermal expansion of 
aluminum, mix an additive having a smaller coefficient of thermal 
expansion than the aluminum. As one example of such an additive, a carbon 
fiber can be mixed with the aluminum. By mixing-in the carbon fiber, the 
coefficient of thermal expansion of aluminum decreases. As such, the 
coefficient of thermal expansion for both aluminum with carbon fiber being 
mixed-in and magnesium can be made equal. 
Instead, an additive having a larger coefficient of thermal expansion than 
magnesium may be mixed with the magnesium. 
With reference to the drawing of FIG. 37, another configuration for 
assembling the heat spreading board is described. 
FIG. 38 is the cross-section of FIG. 37. 
As illustrated in FIG. 38, a frame 70 and the heat spreading board 5 are 
attached together at "C" using the adhesive. Also, as illustrated in FIG. 
38, a gap E is installed in between the frame 70 and the heat spreading 
board 5, and even if the coefficient of thermal expansion of the frame 70 
and the coefficient of thermal expansion of the heat spreading 5 varies, a 
damage from the thermal expansion will not occur. As illustrated in FIG. 
38, when installing the gap E, the coefficient of thermal expansion of the 
frame 70 can be larger. Or, the coefficient of thermal expansion of the 
heat spreading board 5 can be larger. 
With reference to the drawing of FIG. 39, another configuration for 
assembling the heat spreading board is described. 
FIG. 40 is the cross-section of FIG. 39. 
In the drawing of FIG. 40, the frame 70 and the heat spreading board 5 is 
attached together at "D" by using the adhesive. For the case illustrated 
in FIG. 40, there will be no problem even if the coefficient of thermal 
expansion of the frame 70 and the heat spreading board 5 are not 
identical. 
In recent years, particularly for mobile electronic devices represented in 
the mobile computing, a technique to implement a product with small-sized, 
high-performance and lightweight are the key points. From such background, 
in mobile computing, the use of metallic substrate formed by die-casting 
is on an increase, from its excellence in terms of strength against 
weight. Comparing the metallic substrate with the conventional resinous 
substrate, the thermal conductivity is 100.about.1000 times greater than 
that of the metallic substrate. Therefore, the metallic substrate is 
advantageous for spreading heat. 
The present invention attempts to implement a method to deal with the 
touching warmth, by devising the surface processing method based on the 
coating method, maintaining advantages such as designs, surface 
applicability, productivity and low manufacturing cost. 
Particularly, the present invention aims to soften the touching warmth at 
the surface of metallic mobile electronic devices, improve 
design/appearance of the product, and supply coating that is resistant to 
abrasions. 
The concepts of "insulating heat" and "softening the touching warmth" 
according to the present invention are two different concepts. What is 
meant by "insulating heat" is to isolate the heat and the heat is not 
transmitted. For example, consider a case when the heat is generated 
inside the mobile electronic device. In this regard, the meaning of 
"insulating heat" is to shut the heat being generated in the mobile 
electronic device and this will result in a damage of the device. On the 
other hand, the meaning of "softening the touching warmth" is to reduce 
the heat flow to the hand. When the heat being generated from inside the 
device spreads to outside of the substrate surface, the amount of heat 
flow to hand has to be reduced. That is, the technique of "softening the 
touching warmth" for the present invention must satisfy the following two 
contradicting requirements, namely: spreading the heat generated inside 
the mobile electronic device through the substrate surface; and removing 
an unpleasant sensation perceived by the human body from the spreading 
heat. Thus, the present invention aims to provide a coating technique to 
ease the heat influence on the human body as well as maintaining the heat 
spreading property. 
FIG. 41 is a side view of the surface coated substrate for part indicated 
in A in FIG. 34. 
As a metal chassis 12, for example, pure magnesium or a magnesium alloy is 
used. Or, pure aluminum or an aluminum alloy may also be used. 
Alternatively, other light metals with a density less than 4.0 g/cm.sup.3 
or 5.0 g/cm.sup.3 may be used. 
Generally, it is difficult to apply a thick coating, therefore, a resinous 
coating material 87 is applied first to form a base to increase a 
thickness of thermally insulating coating, so as to increase a thickness 
of the surface processed layers, and this will reduce the touching warmth 
at the surface. For use as the base material, vinyl chloride resin is 
suitable, where a thickness greater than 100 microns has proved to be 
effective as the base material. In the present embodiment, different types 
of paint materials (paint 86 and resinous coating material 87) are 
arranged to form a multi-layered films to increase the thickness of 
surface processed layers, thereby improving the touching warmth property. 
The following macromolecular compounds (polymers) are examples that can be 
applied other than vinyl chloride resin: acrylic resin, fluorocarbon 
polymers, vinyl resin, phenol resin, polyester, epoxy resin, polyethylene, 
rubber, urea resin, meramine resin, polyurethane, silicone resin, and 
polyamide. These polymers can either be used alone or in combination. 
FIG. 42 is the cross-section for a case of incorporating the thermally 
insulating layer, prepared by applying a paint made from mixing a fibrous 
insulating filler material 88 with the paint 86. The touching warmth is 
reduced by using the paint made from the mixing of insulating filler 
material 88 with the paint 86 because it lowers the thermal conductivity 
of the film layer. 
Specific examples of the insulating filler materials 88 are the materials 
with a low value of thermal conductivity and effective insulation, such as 
mica or pearlite. Other than mica or pearlite, inorganic particles such as 
diatomaceous earth (SiO.sub.2 +H.sub.2 O), alumina powder (Al.sub.2 
O.sub.3 +nH.sub.2 O), calcium carbonate (CaCO.sub.3), and titanium oxide 
(TiO.sub.3) can be used. Fibrous materials of cattle leather and mixed 
leathers can also be used. The insulating filler material 88 also acts as 
a weight increaser, thereby increasing the thickness of film layer. The 
paint can also be made from mixing the insulating filler material 88 with 
the resinous coating material 87. 
FIG. 43 is the cross-section of an embodiment of the surface coated 
substrate that incorporates a plurality of granulated insulating materials 
89 in the film layer. 
The specific examples of the granulated insulating materials 9 are 
materials with a low value of thermal conductivity and effective 
insulation, such as cork powder or hollow beads to make gaseous 
entrapments, for example, air entrapments and hydrocarbon entrapments, 
inside the film. The thermal conductivity of the film layer will be 
effectively lowered to reduced the touching warmth. The granulated 
insulating materials can also become a weight increaser, therefore, it is 
able to increase the thickness of film layer. The granulated insulating 
material 89 can also be mixed with the resinous coating material 87. Other 
than the hollow beads, following can be used: carbon balloon, acrylic and 
styrene, silicate mineral, silica-alumina fiber, and glass. The hollow 
beads and other materials such as carbon balloon can either be used alone 
or in combination. 
FIG. 44 is the cross-section of a surface processed substrate that includes 
gaseous entrapments by pre-mixing a foaming material 90 with the paint, 
followed by foaming the mixed material at a high temperature. 
A specific example of the foaming material 90, the thermally expandable 
micro-capsules such as hydrocarbons having a low boiling point are mixed 
in a normal paint. By heating and foaming the mixed materials, a porous 
structure is formed in the painted film, thereby reducing the thermal 
conductivity of the film layer and reducing the touching warmth. The 
foaming material can also increase the weight and thickness of the film 
layer. The foaming material 90 can also be mixed with the resinous coating 
material 87. 
Here are some examples of the foaming material 90: foaming glass, foaming 
concrete, foaming urethane, foaming styrene, foaming polypropylene, and 
foaming PET (polyethylene terephthalate) can either be used alone or in 
combination. 
Instead of the foaming material 90 the following materials may be included 
in the paint 86 or resinous coating material 87: alumina powder (Al.sub.2 
O.sub.3 +nH.sub.2 O), calcium carbonate (CaCO.sub.3), and titanium oxide 
(TiO.sub.3), silicate mineral, glass, acrylic and styrene beads. These 
materials will become a spacer to form gaseous entrapments. When painting 
the paint 86 and resinous coating material 87, the gaseous entrapments can 
be formed at the sides of the spacer. In addition, as foaming material 90, 
monomers having a vapor pressure different from the paint 86 or the 
resinous coating material 87 can either be used alone or in combination. 
The gaseous entrapments are formed by volatization of the monomers at the 
time of painting. 
There are two effects from incorporating the minute gaseous entrapments 
upon painting the foaming paint. As the first, the combined thermal 
conductivity is decreased by a presence of numerous number of small 
gaseous entrapments that will be contained in the normal coating. As the 
second, the thickness of film is increased by a presence of the foamed 
layer. Compared to the thermal conductivity for the case of normal 
coating, the thermal conductivity of the layer for the case of using the 
foaming material is lower by about 1/10 of the normal coating. This effect 
of decreasing the amount of heat flow from the aluminum chassis to the 
hand appears as difference in characteristics for both cases of the normal 
coating and the coating using the foaming material. Looking from a side of 
the hand, the heat transfer rate between the finger and the aluminum 
surface is the dominant heat transmitting parameter. However, with the 
presence of the foamed layer, the amount of heat flow to hand is eased by 
controlling the heat transfer rate by the foaming layer. By applying the 
foaming paint, the heat transfer rate of the painted film will be 440 
(W/m.sup.2 K), and compare this to the heat transfer rate with those that 
have applied the normal paint, which is 3750 (W/m.sup.2 K), the heat 
transfer inside the chassis will be difficult, and this results in a heat 
accumulation inside the mobile electronic devices. However, the heat 
transfer rate from the surface of chassis upon natural cooling of the 
mobile electronic device is small of about 10 (W/m.sup.2 K) such that even 
if the heat transfer rate of the painted film has declined to 440 
(W/m.sup.2 K), the natural cooling of the chassis surface 10 (W/m.sup.2 K) 
has apparently a larger insulating effect in the whole heat spreading 
system. Therefore, increase in the temperature inside the chassis due to 
an increase in the thickness of film can be ignored. 
FIG. 45 shows a repeatedly applied layers of bead-containing paint 91, 
increasing the layer thickness, and incorporated a porous structure with a 
large amount of gas incorporated in the film layers. Instead of the 
bead-containing paint 91, a bead-containing resinous coating material and 
multiple-layered glass are similarly used. 
FIG. 46 is the example that combined FIGS. 43 and 44. 
In this embodiment, a decline in the restoring strength of the foaming 
material is supplemented by the top coating with the bead-containing paint 
91 because this can increase a hardness at the film surface. The foamed 
layer is prone to damage due to formations of porous structure and gas 
layers inside. Such surface of the foamed layer is top coated using a 
paint with high degree of hardness so that the strength of the film is 
intensified. 
A large difference between the conventional paint and the bead-containing 
paint is the way in which a pigment component is blended in the paint. 
The pigment is dispersed inside the conventional paint as it is. On the 
other hand, a large amount of "pigment enclosed using special resin to 
form minute bead-containing paint" or in other words, "pigmented beads" 
are contained in the bead-containing paint. These beads can give various 
colors to the paint. 
A scope of application is large for a well-balanced combination of the 
pigmented beads having varied radius. For instance, a suede-like film 
needs raised naps and knobby feels. In addition to a velvet or back skin 
and melange-like film that need a minor knobby feels, there is also a 
paint containing grounded natural collagen fibers with a flat painted 
surface. 
Such processing methods in previously described embodiments are 
individually effective as well as in combinations, in accordance with 
various objectives. 
Following are examples of combinations, in order, from top to bottom 
layers. 
(1) paint 86 of type number one paint 86 of type number two (same or 
different from paint type number one) metal chassis plate 12 
(2) resinous coating material 87 of type number one resinous coating 
material 87 of type number two (same or different from resinous coating 
material of type number one) metal chassis plate 12 
(3) paint 86 (or paint 86 mixed with insulating filler material 88, 
granulated insulating material 89, or foaming material 90) 
resinous coating material 87 (or resinous coating material 87 that is mixed 
with heat insulating filler material 88, powdery insulating material 9 or 
foaming material 90) 
paint 86 (or paint 86 that is mixed with insulating filler material 88 or 
granulated insulating material 89 or foaming material 90) 
metal chassis plate 12 
(4) resinous coating material 87 (or resinous coating material 87 that is 
mixed with insulating filler material 88 or granulated insulating material 
89 or foaming material 90) 
paint 86 (or paint 86 that is mixed with insulating filler material 88 or 
granulated insulating material 89 or foaming material 90) 
resinous coating material 87 (or resinous coating material 87 that is mixed 
with insulating filler material 88 or granulated insulating material 89 or 
foaming material 90) 
metal chassis plate 12 
(5) bead-containing paint 91 
resinous coating material 87 that is mixed with insulating filler material 
88, granulated insulating material 89, or foaming material 90) 
paint 86 
metal chassis plate 12 
(6) resinous coating material 87 that is mixed with insulating filler 
material 88, granulated insulating material 89 or foaming material 90) 
bead-containing paint 91 
paint 86 
bead-containing paint 91 
metal chassis plate 12 
(7) paint 86 
bead-containing paint 91 
metal chassis plate 12 
(8) resinous coating material 87 
bead-containing paint 91 
metal chassis plate 12 
Various other combinations are also possible. 
Using any of the processing methods mentioned previously, the hand contact 
area will be reduced by intentionally incorporating the rough surface, and 
reducing the thermal conductivity to the hand, so that excessive rise in 
touching warmth is prevented. 
FIG. 47 shows an embodiment that appropriately combines the surface 
processing methods mentioned previously, as well as aiming to fill a dent, 
wrinkle or scar at a surface formed during molding in die-casting. In the 
die-casting of metal chassis made of magnesium or aluminum, small dents or 
wrinkles 92 occur on its surface at an ejection stage, and repairs are 
generally made by puttying. A dent on the surface is a detriment that 
occurs during casting. A surface wrinkle is formed during casting when 
molten metal flows into a void casting frame. In practice, the method 
thick layer coating as described previously has a filling effect and 
conceals dents or wrinkles 92. Thus, for those small detriments, there is 
no requirement to repairs with puttying, thereby reducing costs, 
decreasing the number of processing steps, and improving quality. 
Generally, for electronic devices, the metal chassis plate 21 becomes hot 
due to a heat generated from the heating device. By applying paint and 
resinous coating material in multiple layers, or by applying paint and/or 
resinous coating material that are mixed with a high proportion of 
insulating material, the insulating layer structure is incorporated in the 
film layer. Also, the mixing of insulating material is effective in 
reducing the amount of heat flow to a hand. Also, mixing of the foaming 
material to form a foamed structure can create a rough structure at the 
surface of film which can reduce the touching warmth and effective in 
reducing the amount of heat flow to a hand. Also for a metal chassis that 
became too hot, painting the paint or resinous coating material including 
the insulating material and gaseous entrapments can lower the thermal 
conductivity, so, the touching warmth reduction is improved significantly. 
Also, by intentionally forming a rough surface of a substrate, the contact 
area upon handling is reduced and effectively lowering the thermal 
conductivity to a hand. That is, the amount of heat flow to a hand is 
reduced by reducing the heat flow from the moment of handling the metal as 
well as afterward, reducing the touching warmth. 
The surface processing is done on various portions: throughout the external 
cover; to apart subjected to a change in temperature (e.g., the elliptical 
region of FIG. 1); and to a part where there is a possibility of handling. 
FIG. 48 illustrate another configuration of the mobile information 
processing apparatus. 
In the drawing of FIG. 48, the numbered components are same as those 
indicated in FIG. 32. Hereinbelow, particularly, different points are 
described. 
The thermo-siphon 6 is formed on the heat spreading board 5. Both the 
thermo-siphon 6 and the heat pipe 3 performs highly efficient heat 
conduction under the same principal. However, normally in the 
thermo-siphon 6, there is no porous structure or gutter in a vertical 
direction installed at inner wall of the pipe, and therefore, the working 
fluid is not circulated by using the capillary force of the wick. 
Accordingly, the thermo-siphon 6 circulates the working fluid along the 
flow channel by using the gravity. For example, the roll bond panel 58 
made by Showa Aluminum Kabushiki Kaisha can be used as the thermo-siphon 
6. As illustrated in the drawing of FIG. 49, the roll bond panel is a 
component having a hollow flow channel 59 inside the aluminum plate. By 
using the roll bond panel, the heat spreading board 5 and the 
thermo-siphon 6 is formed as one. Alternatively, the heat spreading board 
5 and the thermo-siphon 6 can be made independently, as illustrated in 
FIG. 50. 
The heat spreading processing of the mobile information processing 
apparatus is described with reference to drawing of FIG. 51. 
FIG. 52 is a cross-section cut through C--C of FIG. 51. 
The thermo-siphon 6 has the liquid reservoir 55 for collecting the working 
fluid 9. Also, the thermo-siphon 6 has the vapor flow channels 53 and 54 
for circulating the working fluid 9 in the plane direction of the plane of 
the heat spreading board 5. A case shown in FIG. 51 illustrates a first 
flow channel 53 for circulating around a periphery of the heat spreading 
board 5, and also illustrates second flow channels 54 for extending along 
to a perpendicular direction to the connecting axis 52, which joins to the 
first flow channel 53. 
Normally, liquid such as fluorinate or water is injected as the working 
fluid 9 to the liquid reservoir and the flow channels. After the 
injection, the liquid reservoir and the flow channels are decompressed and 
air-tightly sealed. The working fluid 9 will be collected at a lower part 
of the liquid reservoir due to an effect of the gravity, however, by 
making a high temperature heat source such as heat pipe to attach to the 
lower liquid reservoir, the heat is conducted to the working fluid, which 
turns it into a vapor to cause an ascending vapor flow to a lower 
temperature part. When the heat is transferred accordingly, and the vapor 
flow is condensed to spread the heat inside the vapor flow channel. The 
working fluid is liquefied by the condensation and falls down the vapor 
flow channel under its own weight. That is, inside the thermo-siphon, the 
heat of vaporization is transferred by the circulation and the flow back 
of the working fluid under the effect of gravity. An effective heat 
transfer and the heat equalization occurs by heat transmission processes 
such as condensation and heat spreading. Comparing a use of the 
thermo-siphon to the heat conduction by using a metal only, one can expect 
a large improvement in a cooling capability. 
The heat spreading method is same as the flow chart illustrated in FIG. 6. 
The thermo-siphon 6 has a thickness of 1.about.2 mm, therefore, this is 
made much thinner than a case of installing a fan. Also, the fan will not 
be needed even for CPU which desires a use of the fan, and the 
thermo-siphon 6 can bring about a greater heat spreading effect over the 
fan. 
FIG. 53 illustrates a case of using the chassis 12 as the heat spreading 
board 5. The chassis 12 is also possible to be made by the aluminum 
plates. Therefore, the chassis 12 can be used as the heat spreading board 
5 itself. Alternatively, it is possible to use the chassis 12 as the 
thermo-siphon 6. 
A configuration to sandwich a thermally conductive sheet in between the 
heat spreading board and the liquid crystal display panel is described, 
along with its advantage, with reference to FIG. 54. 
It is desirable to use an elastic material with a good thermal conductivity 
as the thermally conductive sheet 11 such as silicon and rubber. By using 
the elastic material, for components such as the liquid crystal display 
panel 7 and the heat spreading board 5, as well as the liquid crystal 
display panel 7 and the thermo-siphon 6 will be adhered together without 
allowing a gap in between them. The reason for using the elastic material 
is because the elastic material absorbs and fills-in the dents on a 
surface of the thermo-siphon which is formed by the vapor flow channels, 
so that the components will be adhered together without allowing any gap 
in between them. 
Also, on one side of the liquid crystal display panel 7, a high frequency 
inverter circuit board 95 is placed. The high frequency inverter circuit 
board 95 has a circuit for turning on the back light. The thermally 
conductive sheet is used as an insulating sheet, which prevents the 
leakage current to flow from the high frequency inverter circuit board 95 
to the chassis 12 or to the heat spreading board 5. That is, the leakage 
current is insulated by the insulating sheet, and the current will not 
flow to the chassis 12 or to the heat spreading board 5. 
In the previously described example, the thermally conductive and 
insulating sheet is used, however, only the thermally conductive sheet may 
be used. Or, the insulating sheet only may be used. 
The invention can be applied not only to the notebook type personal 
computer but also can be applied to others such as hand-held information 
processing apparatus, mobile telephones and mobile facsimile machines. 
As described above, according to embodiment 2 of the present invention, 
since the heat spreading board is exposed at outer plane of the lid, 
therefore, the heat generated at the heat generation unit can effectively 
be released outside. As a result of this, even if an amount of heat 
generation from the heat generation unit is large, temperature inside the 
main body can be maintained at a low temperature. Also, with the thinning 
of the main body, even if there is almost no space at all inside the main 
body to let go of the heat, the heat is released to the outside, through 
the heat spreading board, and the temperature inside the main body is 
maintained low. 
Also, according to embodiment 2 of the present invention, since an exposed 
plane of the heat spreading board is painted to form the foaming paint 
layer, the exposed plane of the heat spreading board will be rough such 
that an area where a hand touches this exposed surface declines. As a 
result of this, an amount of heat from the heat spreading board 
transferred to hand decreases, and the touching warmth at the exposed 
plane of the heat spreading board improves. 
Further, according to embodiment 2 of the present invention, since the 
thermally conductive material is installed at the main body, the heat 
generated at the heat generation unit is released from both the exposed 
plane of the heat spreading board and a rear plane of the main body. As 
such, compared to the conventional heat spreading, an area of plane for 
releasing heat is twice as much, therefore, the heat generated at the heat 
generation unit is effectively released to outside. 
Furthermore, according to embodiment 2 of the present invention, since a 
rear plane of the main body is painted to form the foaming paint layer, 
the rear plane of the main body will be rough such that the area of the 
rear plane surface touched by a hand decreases. As a result of this, an 
amount of heat from the main body transferred to the hand decreases, and 
the touching warmth at the rear plane of the heat spreading board 
increases. 
Furthermore, according to embodiment 2 of the present invention, since a 
frame is installed at a periphery of the heat spreading board, which is 
easily processed compared to the heat spreading board, the processing at 
the lid becomes easy. As a result of this, an outline of the lid can have 
a designing property, in addition, it becomes easy to take corners of the 
lid. 
Furthermore, according to embodiment 2 of the present invention, since the 
coefficient of thermal expansion for the heat spreading board and the 
frame is identical, even if the temperature of the heat spreading board 
and the frame by the heat spreading process increases, the heat spreading 
board or the frame will not bend backward or shrink. 
Furthermore, according to embodiment 2 of the present invention, since an 
additive is being mixed into the heat spreading board, in accordance to 
the coefficient of thermal expansion of the frame, the coefficient of 
thermal expansion of the heat spreading board is adjusted. As a result of 
this, the coefficient of thermal expansion of the heat spreading board and 
the lid is identical, and even if the temperature of the heat spreading 
board or the lid increased by the heat spreading process, the heat 
spreading board or the frame will not bend backward or shrink. 
Furthermore, according to embodiment 2 of the present invention, since 
aluminum having a good conductivity is being used as a material to form 
the heat spreading board, the heat generated at the heat generation unit 
is efficiently released to the outside. Also, since magnesium which is 
easily processed is being used as a material to form the frame, an outline 
of the lid can have a designing property, in addition, it becomes easy to 
take corners of the lid. 
Furthermore, according to embodiment 2 of the present invention, since the 
heat spreading board and the liquid crystal display panel are attached 
together, the heat from the liquid crystal display panel is conducted to 
the heat spreading board, and the temperature at various positions of the 
liquid crystal display panel is equalized. As a result of this, a color 
inconsistency due to temperature variation at various positions of the 
liquid crystal display panel is prevented, and a visibility of the liquid 
crystal display panel improves. Particularly, due to the heat of back 
light which is placed at a side of the liquid crystal display panel, the 
temperature at various positions of the liquid crystal display panel is 
variable, however, because the heat spreading board equalizes temperature 
of the liquid crystal display panel, the color inconsistency of the liquid 
crystal display panel is effectively prevented. 
The invention being thus described, it will be obvious that the same may be 
varied in many ways. Such variations are not to be regarded as a departure 
from the spirit and scope of the invention, and all such modifications as 
would be obvious to one skilled in the art are intended to be included 
within the scope of the following claims.