Two-dimensional image pickup apparatus

[0002] 1. Field of the Invention

[0003] This invention relates to a two-dimensional image pickup apparatus and, more particularly, it relates to a two-dimensional image pickup apparatus adapted to read information originating from radiation such as radiation of X-rays.

[0004] 2. Related Background Art

[0005] FIG. 1 of the accompanying drawings schematically illustrates a known image pickup apparatus adapted to X-ray photography and comprising a fluorescent member (e.g. scintillator) 1 operating as wavelength converter for converting X-rays 101 into rays within the sensible wavelength range of photoelectric converters 2asuch as those of visible light, photoelectric converters 2afor converting the visible light into electric signals, a substrate 2bcarrying the photoelectric converters 2athereon, a base member 7 supporting the substrate 2bthereon, circuit boards 5a,5bfor processing electric signals produced by photoelectric conversion, wires connected to the circuit boards and an apparatus cabinet 8acontaining the above components.

[0006] The substrate 2barranged under the photoelectric converters 2ais typically made of glass because it is required to be free from chemical reactions with the semiconductor devices (such as the photoelectric converters) of the apparatus, resist the high temperature of the semiconductor forming process and maintain dimensional stability. The fluorescent member 1 is prepared by applying a fluorescent material of a metal compound to a resin plate and held in close contact with the substrate 2b.When the photoelectric converters 2aare required to be moisture-impermeable, the fluorescent member 1 and the photoelectric converters 2amay be hermetically sealed by a moisture-impermeable and X-ray transmissive film 6.

[0007] Typically a printed circuit board made of glass epoxy is used for the circuit board 5bon which electronic parts 5care mounted, to meet the requirement of being easily available and hardly inflammable. These and other components are secured to the base member 7 by way of spacers 3aan 3band then to the apparatus cabinet and hermetically closed by means of an X-ray transmissive closure 8b.

[0008] In FIG. 1, reference symbol 3adenotes spacers arranged between the substrate 2bsupporting the photoelectric converters and the base member 7 and reference symbol 3bdenotes spacers arranged between the circuit board 5band the base member 7, whereas reference symbol 5adenotes a flexible circuit board.

[0009] Such an image pickup apparatus is conventionally used for X-ray photography as a stationary apparatus. In recent years, there is an increasing demand for a lightweight, compact and portable image pickup apparatus adapted to rapid image pickup operations for producing fine images. However, with an apparatus having such a configuration, the heat generated by the electronic parts 5cis confined within the apparatus cabinet 8ato raise the internal temperature. Then, the temperature rise can by turn increase the internal noise and reduce the S/N ratio of the apparatus.

[0010] The use of a cooling system comprising one or more cooling fans (not shown) arranged in the apparatus cabinet 8ahas been contemplated to sufficiently prevent such temperature rise from occuring in the inside. However, such an additional system can significantly increase the size and weight of the image pickup apparatus particularly because it requires pillars and a power source for driving the system.

[0011] In view of the above described circumstances, it is therefore an object of the present invention to provide a small, down-sized image pickup apparatus that is free from the above identified problems.

[0012] Another object of the present invention is to provide a two-dimensional image pickup apparatus adapted to stably reading information without significantly increasing the internal noise and reducing the S/N ratio if heat is generated by the electronic parts during the operation of the apparatus.

[0013] Still another object of the present invention is to provide an image pickup apparatus adapted to obtaining transmitted X-ray images for diagnosis and analysis.

[0014] Still another object of the present invention is to provide a low cost cassette-type image pickup apparatus that is small and lightweight and can be carried with ease.

[0015] According to an aspect of the invention, the above objects of the invention are achieved by providing a two-dimensional image pickup apparatus comprising two-dimensional photoelectric converters arranged on a substrate, a base member for supporting the substrate, electronic parts for processing the electric signals of said photoelectric converters and an apparatus cabinet containing the above components, said base member being formed by a metal-based printed circuit board, said electronic parts being mounted on said base member.

[0016] According to another aspect of the invention, in an image pickup apparatus according to the invention, said base member and part or all of said apparatus cabinet are formed by a metal-based printed circuit board and said electronic parts are mounted on said printed circuit board.

[0017] FIG. 1 is a schematic cross sectional view of a typical two-dimensional image pickup apparatus.

[0018] FIGS. 2A and 2B are respectively a schematic cross sectional view and a schematic perspective view of a two-dimensional image pickup apparatus comprising a metal-based board.

[0019] FIG. 3 is a schematic cross sectional view of a metal-based board.

[0020] FIG. 4 is a schematic cross sectional view of another two-dimensional image pickup apparatus comprising a metal-based board.

[0021] (First Embodiment)

[0022] Now, the present invention will be described in greater detail by referring to FIGS. 2A, 2B and 3 of the accompanying drawings that illustrate a first preferred embodiment of the invention. The components of the embodiment which are the same as those of the image pickup apparatus of FIG. 1 are denoted respectively by the same reference symbols and will not be described any further. Reference symbol 9 denotes a metal-based printed circuit board (hereinafter referred to as metal-based board) that operates as support structure for the substrate 2b.Reference symbol 5adenotes a flexible circuit board adapted to taking out electric signal from the photoelectric converters 2aand connected electrically to both the substrate 2band the metal-based board 9.

[0023] FIG. 3 schematically illustrates the configuration of a typical metal-based board 9 that can be used for this embodiment. The metal base 9aof this board is a plate of iron, aluminum or copper. The actual material of the metal base 9awill be selected by taking the strength, the heat emitting performance, the weight and the manufacturing cost into consideration. An insulation layer 9aof an insulator material is formed on the surface of the metal base 9aand then a conductor circuit 9bis formed thereon by patterning an electrically conductive material such as copper foil.

[0024] The upper surface of the conductor circuit 9dis surface-treated by a layer 9eto protect it against oxidation and other possible adverse effects. The portions of the circuit that require insulation are covered by insulating solder resist 9c.The insulation layer 9bis typically made of resin such as polyimide, although a filler substance such as silica or aluminum powder may be mixed with it to raise its thermal conductivity.

[0025] With this embodiment, the apparatus is down-sized and its thermal conductivity is improved by using the base member 7 itself of FIG. 1 as printed circuit board.

[0026] The heat generated by the electronic parts 5cis transmitted to the metal-based board 9 and then to the apparatus cabinet 8auntil it is finally transmitted to the ambient air surrounding the apparatus cabinet 8a,which dissipates the heat with ease. The heat emitting surface of the apparatus can be made sufficiently large to prevent any of the electronic parts 5cfrom operating erroneously due to heat by using an apparatus cabinet 8athat is made of a metal plate. With this arrangement, the apparatus cabinet does not require the use of any internal cooling system so that the image pickup apparatus can be further down-sized to reduce its weight.

[0027] (Second Embodiment)

[0028] FIG. 4 schematically illustrates a second embodiment of the invention. This embodiment may be useful when the heat emitting performance of the electronic parts 5cof the first embodiment is not satisfactory because, in addition to the metal-based board 9 per se, the apparatus cabinet 8ais partly or entirely made of metal-based board. As seen from FIG. 4, the cooling effect of the apparatus can be improved by rigidly fitting radiator fins 8cto the apparatus cabinet 8a.

[0029] As described above, according to the invention, there is provided a two-dimensional image pickup apparatus that is compact, lightweight and conveniently portable and adapted to X-ray photography.

[0030] Additionally, an image pickup apparatus according to the invention is free from the above identified problem of an increased noise level due to the heat generated by the electronic parts thereof so that it can read information more accurately and more reliably than ever.

[0031] Still additionally, an image pickup apparatus according to the invention can be made very compact, lightweight and conveniently portable at low cost because it can eliminate or minimize the cooling system typically comprising one or more cooling fans.