Patent Application
20050029463
The present application hereby claims priority under 35 U.S.C. §119 on German patent application number DE 103 35 662.2 filed Aug. 4, 2003, the entire contents of which are hereby incorporated herein by reference.
The invention generally relates to a detector module for a detector for the detection of ionizing radiation. In particular, it is directed to one for use in a computer tomography machine, with a printed circuit board and with an array. The array may be firmly connected to the printed circuit board and may have a plurality of radiation-electrical transducer elements for the conversion of incident electromagnetic radiation into an electrical output signal.
Detectors—constructed in a pixel layout—or detector modules are used in particular for imaging with ionizing radiation, in particular with X-radiation. A comparatively large array for each detector module then needs to be applied to a printed circuit board, which is used for delivering the electrical output signals obtained by the array from the array to an external evaluation instrument. The printed circuit board is also used for fastening the array.
Usually, the arrays are adhesively bonded to their associated printed circuit boards, in which case temperatures of between 80° C. and 150° C. may occur when curing. Undesirable bending or twisting of the printed circuit board may occur after curing, in particular if a standard printed circuit board is being used for this purpose, for example a printed circuit board of the FR-4 type.
One possible remedy might consist in applying a plate made of the same material as the array to the opposite side of the printed circuit board from the array. This would necessitate substantially simultaneous application of both the array and said additional plate, however, which is difficult in terms of production technology. The opposing plate can furthermore lead to undesirable extra costs.
Special thermally stable HTCC printed circuit boards are also known, but these are not viable for many applications owing to their high price.
It is an object of an embodiment of the present invention to provide a detector module in which the array can be applied to the printed circuit board inexpensively but without significant risk of twisting or bending.
In relation to a detector, this object may be achieved according to an embodiment of the invention in that the printed circuit board has a recess in which a plate firmly connected to the printed circuit board is placed, with the plate—indirectly or directly—carrying the array.
In the detector module according to an embodiment of the invention, the plate can be made of a different advantageous material from the printed circuit board, and can thereby be matched to the specific properties of the array which is to be applied in a particular region of the printed circuit board. On the one hand, the opportunity is available to match the plate thermally to the array. On the other hand, by fitting the plate in the printed circuit board, it is possible to locally produce greater planarity, which is advantageous for the application of the array, than could be achieved with a low-cost printed circuit board without a recess.
Preferably, the array is—indirectly or directly—flatly connected, in particular via its entire side that faces away from the incident electromagnetic radiation, to the plate.
According to a particularly preferred configuration, the plate is thermally matched to the array so that the thermal coefficient of longitudinal expansion of the plate is greater or smaller than the corresponding value of the array by less than a factor of 3, preferably less than a factor of 2, in particular less than 50%. This applies in particular to the linear thermal coefficient of longitudinal expansion at room temperature. Bending can be reliably avoided with such a configuration when applying and curing the adhesive used for fastening the array, and increased thermal stability is likewise achieved during operation of the detector module.
The detector module may be used both in a scintillator-photodetector combination and in an array that converts ionizing radiation directly into electrical signals, in particular a semiconductor array. In the former case, the array is preferably a photodetector array, which detects the electromagnetic radiation as light quanta generated by the ionizing radiation in a scintillator layer. In the latter case, the ionizing radiation is identical to the electromagnetic radiation, which the array converts into the electrical output signal.
The array is preferably designed as a photodetector array based on silicon. Both photodiode arrays and CCD arrays may be employed.
The plate and the array are preferably adhesively bonded to each other.
According to a more particularly preferred configuration, the plate is made entirely or predominantly of ceramic, preferably of aluminum oxide, or entirely or predominantly of glass. The further potential advantages of the plate which is to be placed in the recess can be exploited in a particularly straightforward way with such a configuration. This is because plates made of ceramic or glass are particularly inexpensive and easy to produce with high planarity, which greatly facilitates the fastening or adhesive bonding of the array.
The recess is also preferably designed as a groove. As an alternative, it may also be designed as a through-opening in the printed circuit board.
It is particularly advantageous to place the plate in the recess so that it lies flush with the printed circuit board. Like a procedure in which the plate is placed on the printed circuit board without providing a recess and the array is applied on top, this configuration has the advantage that the array has its surface at only a small distance from the upper side of the printed circuit board, which significantly facilitates application of bonding wires.
An exemplary embodiment of a detector module and of a detector will be explained hereafter in more detail, referring to exemplary embodiments thereof with reference to
As viewed from the direction of the ionizing radiation 3, a scintillator structure 11 which is structured in the same way as the array 5 is arranged in front of the array 5. Corresponding scintillator elements 13, 14, 15, . . . are arranged closely and flush over the corresponding transducer elements 7, 8, 9, . . . . In the scintillator layer 11 which consists of an ultrafast gadolinium-doped scintillator ceramic, for example, the incident ionizing radiation 3, in particular X-radiation, is converted into electromagnetic radiation or light which the array 5 in turn converts into a multiplicity of electrical output signals A. The electrical output signals A are sent via a ribbon-type conductor track bundle 17 (indicated only schematically) to a plug 19, from which they can be sent to the downstream signal processing.
The structure made up of the array 5 and the scintillator layer 11 is applied to an approximately 1.6 millimeter thick printed circuit board, which is designed as a standard FR-4 printed circuit board. The thickness of the array 5 is a few 100 μm.
For ease of installation in the detector support (not represented) of the associated computer tomography device, the rigid printed circuit board 21 is connected via a so-called flex strip 23 to another printed circuit board 25, which carries the plug 19. In this way, the entire detector module 1 can be bent in the region 24.
A groove or recess 27, in which a ceramic plate 29 made of aluminum oxide (Al2O3) is adhesively bonded, is machined into the printed circuit board 21 that carries the array 5. In the example of
The printed circuit board 21 thereby provided with a ceramic inlay has the advantage that, by way of the plate 29, the mechanical and thermal properties that are advantageous for coupling the array 5 can be locally adjusted in a controlled way. By using aluminum oxide (alumina), for example, the linear thermal expansion coefficient of the assembly including the plate 29 and the printed circuit board 21 can be locally matched very well to the array 5. A high degree of planarity can furthermore be obtained by way of the plate 29, so that it is even possible to use (and not have to reject) printed circuit boards whose planarity lies outside the tolerance required for this.
Exemplary embodiments 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 present 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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10335662.2 | Aug 2003 | DE | national |
