Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1994-10-28
2001-12-11
Ball, Michael W. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S214000, C156S286000, C264S511000
Reexamination Certificate
active
06328838
ABSTRACT:
BACKGROUND OF THE INVENTION
In a number of devices, such as radiation imagers, it is desirable to apply a thin membrane to an irregularly shaped surface. For example, in a radiation imager in which a scintillator is optically coupled to a photosensor, it is desirable to apply a layer of reflective material to the surface of the scintillator opposite the surface adjoining the photodetector so that optical photons generated in the scintillator are reflected towards the photosensor. Commonly, one surface of the scintillator is irregularly shaped, that is, protrusions extend from the surface so that the surface is not flat. Such protrusions are needle or pyramid-like structures that result from the deposition process and serve to localize detection of photons generated in the array to the area in which the incident radiation was absorbed in the scintillator.
Application of reflective coatings to the irregular surface of the scintillator poses a number of difficulties. Many scintillator materials, such as cesium iodide, have large thermal expansion coefficients and thus are extremely sensitive to processes in which a reflective coating is deposited onto the surface, such as by sputtering. The relatively high temperatures associated with such deposition processes (e.g., above about 300°-400° C.) cause degradation of the scintillator material that and the overlying reflective material, resulting in much degraded performance of the scintillator. Traditional techniques of mechanically applying a coating, such as pulling a coating sheet across the surface to be covered, or mechanically pressing a coating onto the surface from above, cannot be used because of the malleable nature of cesium iodide. Specifically, the cesium iodide needle structure (on the light-receiving side of the scintillator) is deformed by such conventional processes, resulting in a distortion of the needle structure, causing light traveling through the structure to strike the interior surface boundaries of the needle many thousand more times before the right emerges from the scintillator into the detector array. Deformation of the needle structure as results from conventional cover application processes result in degraded imager performance (as measured, for example, by the imager's modulation transfer function (MTF)). Further, most conventional mechanical cover application processes do not provide for the evacuation of air that may be trapped between the scintillator surface and the cover material; such trapped air further degrades the optical performance of the scintillator.
A reflective coating on a scintillator surface desirably conforms to the irregular shape of the scintillator so that optical photons are directly coupled between the reflective layer and the scintillator material, with few it any interstitial voids between the scintillator material and the reflective material. Additionally, the application of the reflective material should not degrade the scintillator structure, either by thermally degrading the material or mechanically deforming the needle or pyramid-like structure of the scintillator. Reflective materials having the desired optical and physical characteristics are available in monolithic thin membranes (as used herein, “monolithic” refers to a substantially uniform material in a sheet-like form), however application of such thin membranes to the irregular shaped surfaces of a scintillator without damaging the scintillator or the thin membrane has been problematic.
One object of this invention is to provide a method for applying a thin membrane over a scintillator on a radiation imager, including precisely aligning the membrane with the surface and causing the membrane to be conformingly disposed over the needle-like structures of the scintillator without causing deformation or lateral movement of the needle-like structures.
SUMMARY OF THE INVENTION
In accordance with this invention, a method of depositing a thin pliant membrane to be in conformal contact with light-receiving surface of a scintillator having a plurality of needle-like protrusions (comprising a malleable scintillator material) includes the steps of precisely positioning a coupling surface of the membrane with respect to the scintillator light-receiving surface so that the coupling surface is in contact with at least some of the needle-like protrusions without causing deformation of the protrusions and then drawing the membrane down over the light receiving surface so that the membrane is conformingly-disposed over around substantially all of the protrusions from the scintillator light-receiving surface without distorting the shape of the protrusions. The step of drawing the membrane down around the light receiving surface includes the step of applying a substantially uniform differential pressure across the pliant membrane so as to urge the membrane in to conformal contact with the light receiving surface, such as by placing the scintillator assembly on a vacuum bed, disposing a vacuum blanket over the pliant membrane and the scintillator to form a sealed area between the blanket and the vacuum bed, and drawing a vacuum in the sealed area so as to evacuate air between the membrane and the scintillator surface and to cause the blanket to urge the membrane into conformal contact with the scintillator surface.
The step of precisely positioning the thin membrane in the desired position with respect to the scintillator surface includes the steps of retaining the pliant membrane on an applicator by means of a differential pressure which keeps the thin membrane seated against a mating surface of the applicator such that the membrane is maintained in a relatively flat condition; positioning the applicator with respect to the workpiece so as to dispose the membrane in the desired position; and then releasing the thin membrane from the applicator.
REFERENCES:
patent: 3398811 (1968-08-01), Muller
patent: 4398118 (1983-08-01), Galves et al.
Lubowski Stanley Joseph
Wirth Reinhold Franz
Ball Michael W.
Cabou Christian G.
General Electric Company
Ingraham Donald S.
Piazza Gladys
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