Personal computer keyboard

Provided is a personal computer keyboard in which base and reinforcement plates excellent in heat dissipativity and homogeneous in heat dissipation, and with a mechanical strength are incorporated. The keyboard includes a base plate 24 on which key caps K1 to K9 are mounted; and a reinforcement plate 25 disposed on the lower side of the base plate 24, wherein the base plate 24 is constituted of an Al--Mg--Si based alloy plate including 0.2 to 0.8 wt % of Si, 0.3 to 0.9 wt % of Mg, 0.35 wt % or less of Fe and 0.20 wt % or less of Cu with the rest of Al and inevitable impurities and wherein the reinforcement plate 25 is constituted of a heat pipe panel.

TECHNICAL FIELD
 The present invention relates to a personal computer keyboard suitable for
 a personal computer: especially notebook and portable personal computers,
 which are both compact.
 BACKGROUND PRIOR ART
 Since many of heat generating devices such as CPU, a CD-ROM drive and a
 hard disk are incorporated in a personal computer, there is a need to
 dissipate generated heat so as to cool the devices in order to ensure
 normal operations over a long time. For this reason, various kinds of heat
 dissipating plates have been employed. However, especially, in notebook
 and portable personal computers, it is unavoidable that the heat
 generating devices are put inside a small case and a keyboard coexists in
 the case; many of the heat generating devices are resulted in being
 crammed in the narrow space, thereby leading to a desire for high heat
 dissipativity of a heat dissipating plate.
 In the mean time, in the keyboard of a personal computer, since key caps
 with which fingers are put in direct touch are mounted on a base plate
 with a membrane or a pantograph structure interposed therebetween, and it
 is required that when a key is pressed down in typing, the base plate do
 not locally sink due to deformation, therefore a reinforcement plate is
 disposed on the lower side of the base plate to increase stiffness and
 cope with such a deformation. Such base and reinforcement plates each have
 a requirement for having a function as a heat dissipating member to
 prevent overheating inside the personal computer from occurring by
 diffusing heat generated from the devices therein in addition to a
 function as a strength member that supports the key caps and endure shocks
 of key strokes. Further, needless to say that the light weight and
 formability of the base and reinforcement plates are necessary.
 For such reasons as described above, as material of the base and
 reinforcement plates, there have widely been adopted an Al--Mg based alloy
 including aluminum excellent in strength, good in thermal conductivity,
 and with features of light weight and good forming workability, and Mg in
 content of about 2.5 wt % especially to increase a mechanical strength.
 While such an Al--Mg alloy has a sufficient strength and a good
 machinability including an excellent cutting property as compared with
 pure aluminum, the alloy has not been a satisfactory material in terms of
 heat dissipativity since a thermal conductivity thereof is lower by about
 60%. Because of the poor heat dissipativity, the alloy has had a problem
 in a personal computer using the base and reinforcement plates made of the
 same since there arise overheating of CPU and other devices, and some of
 caps with high temperature are locally found in the entire arrangement.
 Under such circumstances, the present inventor has proposed an Al--Si--Mg
 based alloy that seeks a heat dissipativity of pure aluminum, and a
 strength and machinability of the Al--Mg based alloy. Such a proposed
 Al--Si--Mg based alloy actually has a good thermal conductivity whereas
 the alloy is to some extent inferior to the Al--Mg based alloy in regard
 to a strength and thereby, the problems of overheating of CPU and other
 devices and caps of high temperature have almost been solved. However,
 part of the problems have still been left unsolved: Homogeneity in heat
 dissipation is insufficient and there are still locally found some key
 caps with high temperature, though, according to distances from the heat
 generating devices in a personal computer during its operation.
 SUMMARY OF THE INVENTION
 The present invention has been made in light of such technical
 circumstances and it is accordingly an object of the present invention to
 provide a personal computer keyboard with incorporated base and
 reinforcement plates excellent in heat dissipativity, homogeneous in heat
 dissipation and having a mechanical strength.
 A personal computer keyboard of the present invention, which has been
 provided for achieving the object, comprises: a base plate 24 on which key
 caps K1 to K9 are mounted; and a reinforcement plate 25 disposed on the
 lower side of the base plate 24, wherein the base plate 24 is constituted
 of an Al--Mg--Si based alloy plate including 0.2 to 0.8 wt % of Si, 0.3 to
 0.9 wt % of Mg, 0.35 wt % or less of Fe and 0.20 wt % or less of Cu with
 the rest of Al and inevitable impurities and wherein the reinforcement
 plate 25 is constituted of a heat pipe panel.
 Further, a content of Si in the Al--Mg--Si based alloy plate is preferably
 in the range of from 0.32 to 0.60 wt %.
 Still further, a content of Mg in the Al--Mg--Si based alloy plate is
 preferably in the range of from 0.35 to 0.55 wt %.
 Yet further, the base plate is preferably constituted of the Al--Mg--Si
 based alloy plate whose tensile strength is equal to or higher than 200
 N/mm.sup.2.
 Yet further, the reinforcement plate preferably is a heat pipe panel of a
 structure that is formed by bonding two aluminum flat plates and has an
 inflated tubular path serving as a path for a working fluid or a heat pipe
 panel of a structure that has a pipe serving as a path for a working fluid
 attached on an aluminum flat plate.

DESCRIPTION OF THE PREFERRED EMBODIMENT
 The term `aluminum` is herein used in the meanings including aluminum and
 an alloy thereof.
 As shown in FIG. 1, a personal computer keyboard 20 of the present
 invention has a configuration in which key caps K1 to K9 and so on are
 mounted on the upper surface of a base plate 24 constituted of an
 Al--Mg--Si based alloy plate and a reinforcement plate 25 constituted of a
 heat pipe panel is disposed on the lower side of the base plate 24.
 Generally, various kinds of heat generating devices such as CPU are
 arranged below the reinforcement plates 25 and all those are put in a case
 28.
 The base plate 24 has a shape of a flat plate in order to mount the key
 caps K1 to K9 and so on thereon and the Al--Mg--Si based alloy employed as
 a material thereof has a limitation on a chemical composition thereof in
 order to ensure a strength and a heat dissipativity thereof. Significances
 of addition of elements and reasons for limitation on contents of the
 elements will be described below:
 Mg and Si are elements necessary for exerting a strength. If an Mg content
 is less than 0.3 wt % or an Si content is less than 0.2 wt %, a sufficient
 strength cannot be attained. On the other hand, if an Mg content exceeds
 0.9 wt % or an Si content exceeds 0.8 wt %, in the process leading to a
 plate, not only is productivity reduced due to higher load in hot rolling,
 but trimming is also required in the course of the rolling due to
 occurrence of cracks in earrings. Further, if an Mg content is increased
 to 0.9 wt % or higher, Mg is dissolved into aluminum so as to distort the
 lattice structure thereof and thereby heat dissipativity is reduced due to
 hindrance against migration of free electrons. The lower limit of an Mg
 content is preferably 0.35 wt % and the upper limit thereof is 0.55 wt %.
 Further, the lower and upper limits of an Si content are preferably 0.32
 wt % and 0.60 wt %, respectively.
 If Fe and Cu is included a lot, corrosion resistance is reduced and an
 alloy plate has no value in practical use. Hence, Fe and Cu contents are
 respectively controlled to be equal to or less than 0.35 wt % and 0.20 wt
 %, or preferably equal to or less than 0.25 wt % and 0.10 wt %.
 Further, the Al--Mg--Si based alloy is used and processed into a flat plate
 of a predetermined thickness in a normal way including hot rolling and
 cold rolling of an ingot, whereas the following fabrication process can be
 recommended in which rollings are performed in predetermined conditions
 after homogenization in order to not only attain an excellent strength but
 also fabricate a flat plate in a less number of steps: This process is to
 deposit Mg.sub.2 Si in fine sizes in a homogeneous way by performing
 rollings under specific conditions and attain a similar effect to that
 obtained when the alloy is subjected to a solid solution treatment and
 quench hardening.
 That is, after homogenization of an Al--Mg--Si based alloy ingot with the
 above described composition, in any pass of preliminary hot rolling, not
 only is a temperature of the material prior to the pass adjusted to be in
 the range of from 350 to 440.degree. C., but a thickness of a rolled plate
 after the pass is controlled to be equal to or less than 10 mm and
 following the preliminary hot rolling, a finish hot rolling is applied to
 the plate, followed by a cold rolling at a thickness reduction of 30% or
 more and further followed by mechanical processing to attain an alloy
 plate of a desired shape.
 In the preliminary hot rolling, a similar effect to quench hardening is
 obtained in any pass of the rolling by a fall in temperature during the
 pass under a predetermined temperature condition. Therefore, it is
 required that the material prior to a pass is at a temperature at which Mg
 and Si each can be held in a solid solution state in conformity with a
 solid solution treatment: the material is at temperature in the range of
 from 350 to 440.degree. C. If the material is at a temperature lower than
 350.degree. C., Mg.sub.2 Si is deposited in coarse sizes, which makes it
 impossible to obtain a quench hardening effect in a following pass.
 Further, since a temperature is low, not only rolling workability in the
 pass is greatly degraded, but a temperature after completion of the pass
 is too low, so that a surface quality is worsened. On the other hand, if a
 temperature exceeds 440.degree. C., an after-pass temperature of the
 material does not sufficiently decrease, thus leading to a poor quench
 hardening effect. In order to attain a quench hardening effect, a cooling
 speed during a pass is preferably equal to or higher than 50.degree.
 C./min and a temperature after the pass is preferably in the range of from
 250 to 340.degree. C. It should be noted that in order to control a
 temperature after a pass in the above described range, a high pressure
 wafer shower cooling may be applied directly after the preliminary hot
 rolling. Further, a rolling speed in passes is preferably equal to or
 higher than 50 m/min. In addition, in order to achieve a cooling effect
 equivalent to a quench hardening effect during a pass, there is a
 necessity to control an after-pass thickness of a plate equal to or less
 than 10 mm. This is because if an after-pass thickness exceeds 10 mm, it
 is hard to cool the plate to a temperature which is sufficient for
 attaining the above described quench hardening effect even in a case where
 a water cooling step is incorporated in the process.
 It should be noted that while a preliminary hot rolling is normally
 performed in 10 passes, a pass in the above described conditions in order
 to attain a quench hardening effect may be performed in any stage of the
 process. Because of a condition of an after-pass thickness being equal to
 or less than 10 mm, quench hardening is performed in the last pass in the
 most cases and also in one of passes prior to the last pass in the second
 most cases.
 In cold rolling, it is required to select a thickness reduction to be equal
 to or higher than 30% in order to obtain a predetermined strength by work
 hardening. With the thickness reduction of 30% or higher, a tensile
 strength equal to or higher than 200 N/mm.sup.2 matching to that of an
 Al--Mg based alloy can be attained. A thickness reduction is preferably
 equal to or higher than 50%.
 Further, as the reinforcement plate 25, a heat pipe panel is employed that
 can realize not only stiffness, but also a heat dissipativity and
 homogeneity in heat dissipation more excellent than a flat plate. This is
 because the heat pipe panel is superior to a simple flat panel in heat
 dissipativity and therefore has conspicuously large effect of preventing
 overheating of CPU and other devices, and local presence of some key caps
 with high temperature from occurring. While there is no specific
 limitation on a shape, state and fabrication process of the heat pipe
 panel as far as the heat pipe panel is of a flat plate, the following are
 exemplified: a roll-bond heat pipe panel of a structure in which two flat
 plate of aluminum or the like is bonded and a tubular path is inflated, or
 a panel of a structure in which a heat pipe as a path of a working fluid
 is fixed by squeezing or the like on a surface of a flat plate of aluminum
 or the like. In regard to kinds of material, although a strength that the
 reinforcement plate 25 should have is required, a thermal conductivity as
 high as the base plate as described above is not required since an
 excellent heat dissipativity as a heat pipe panel can be exerted. As
 materials that satisfies such conditions, there can be recommended pure
 aluminum, an Al--Mn based alloy and so on, and needless to say that the
 above described Al--Mg--Si based alloy excellent in thermal conductivity
 may be employed, by which more excellent heat dissipativity can be
 expected.
 A personal computer keyboard of the present invention is provided with not
 only a strength by which key stroke in typing mechanically can be endured,
 but an excellent heat dissipativity that can be exerted so as to remove
 heat generated from a variety of devices by using an Al--Mg--Si based
 alloy including 0.2 to 0.8 wt % of Si, 0.3 to 0.9 wt % of Mg, 0.35 wt % or
 less of Fe and 0.20 wt % or less of Cu with the rest of Al and the
 inevitable impurities as a material of the base plate. Further, with
 restriction on Fe and Cu contents in the base plate, corrosion resistance
 sufficient in practical use can be attained. Furthermore, with the heat
 pipe panel as a reinforcement plate in use, not only are a strength as a
 reinforcement member and a heat dissipativity as a heat dissipating member
 excellent but homogeneity in heat dissipation is also encouraged. For the
 reasons, not only is a long lasting normal operation of a personal
 computer maintained by preventing overheating of CPU and other devices
 therein, but key caps are prevented from being partly heated to high
 temperature and homogeneous heating of all the key caps can realized.
 Further, with such excellent heat dissipativity of the base and
 reinforcement plates, those can preferably employed in not only a notebook
 personal computer but a portable personal computer in each of which many
 of heat generating devices are crammed in a small case.
 EXAMPLE
 Then, detailed description will be made of a concrete example of a personal
 computer keyboard of the present invention with reference to the
 accompanying drawings:
 In this example, various kinds of base and reinforcement plates were
 compared with one another in terms of heat dissipativity in a notebook
 personal computer that requires a high heat removal performance since many
 of heat generating devices are put in a narrow space thereof.
 In the examples, an experimental keyboard 20, as shown in FIG. 1, imitating
 a notebook personal computer was employed. In the keyboard 20, many key
 caps K1 to K9 and so on are mounted on the upper surface of a base plate
 24 with a membrane or a pantograph structure (not shown) interposed
 therebetween and CPU 27 is mounted on the rear surface of a reinforcement
 plate 25 in pantograph structure (not shown) interposed therebetween and
 CPU 27 is mounted on the rear surface of a reinforcement plate 25 in the
 middle thereof with a heat spreader 26 interposed therebetween. A
 clearance of 0.5 mm in width is provided between the base plate 24 and
 reinforcement plate 25, and the base plate 24 and reinforcement plate 25
 are put in a case 28 while superimposing on each other. Further, a fan 29
 is disposed in one corner of the case 28 for acceleration of removal of
 heat. It should be noted that in FIG. 1, key names on the key caps K1 to
 K9 and so on and locations thereof correspond to the Japanese key
 arrangement.
 In the keyboard 20, two kinds of base plates 24 were prepared: one was an
 Al--Mg--Si based alloy flat plate of a thickness of 0.6 mm and the other
 was an Al--Mg--Cr alloy flat plate including 2.5 wt % of Mg and 0.25 wt %
 of Cr (heat-refined H38) of a thickness of 0.6 mm. Further, two kinds of
 heat pipe panels 30 shown in FIG. 2 as the reinforcement plate 25 were
 prepared: one was an Al--Mg--Si based alloy flat plate of a thickness of
 0.6 mm and the other was an Al--Mg--Cr alloy flat plate including 2.5 wt %
 of Mg and 0.25 wt % of Cr of a thickness of 0.6 mm.
 The Al--Mg--Si based alloy flat plate had a composition including 0.5 wt %
 of Si, 0.5 wt % of Mg, 0.15 wt % of Fe and 0.05 wt % of Cu with the rest
 of Al and the inevitable impurities. An ingot with the composition was
 surface ground, thereafter subjected to homogenization at 580.degree. C.
 for 10 hr, after the homogenization hot and cold rolled under
 predetermined conditions, further annealed as the final step at
 140.degree. C. for 5 hr. A plate thus processed was cut to a desired
 shape. Rolling conditions were a starting temperature of the last pass in
 the preliminary hot rolling was 395.degree. C., an after-pass temperature
 was 282.degree. C., an after-pass thickness was 7 mm and further a
 thickness reduction in the cold rolling after the finish hot rolling was
 85%.
 Measurements of a tensile strength of the Al--Mg--Si based alloy flat plate
 and the Al--Mg--Cr alloy flat plate including 2.5 wt % of Mg and 0.25 wt %
 of Cr were conducted on JIS No. 5 test pieces according to the normal
 method with the respective results of 281 N/mm.sup.2 and 295 N/mm.sup.2.
 It was confirmed that the Al--Mg--Si based alloy flat plate and the
 Al--Mg--Cr alloy flat plate including 2.5 wt % of Mg and 0.25 wt % of Cr
 showed almost the same strength as each other.
 The heat pipe panel 30 was a roll-bond heat pipe panel and was fabricated
 in such a way that two aluminum plates 31 and 32 were press-bonded with
 each other so as to superimpose one on the other, non-bonded parts in the
 composite plate were inflated toward the upper surface side thereof by
 applying a pressure through an opening 34 so as to create a path 33
 extended longitudinally and laterally over almost the entire surface of
 the panel, and the opening 34 was closed by welding after a working fluid
 is filled into the path 33. In the examples of this experiment, the
 aluminum plates 31 and 32 were made of an Al--Mg--Si based alloy with the
 same composition as the base plate fan 29 in use was one made by
 Matsushita Electric Industrial Co., Ltd. with the maximum air volume of
 1.4 CFM (Model No. UDQFC3E04), and a heat spreader 26 in use was a pure
 aluminum plate of a surface area of 31 square mm and a thickness of 1 mm.
 The members were used to fabricate 5 kinds of experimental keyboards 20 in
 combinations shown in Table 1.

Keyboard temperature