Patent Application
20070163355
1. Field of the Invention
The present invention relates generally to sensor housing construction, and more particularly, to preformed sensor housings and methods to produce thin metal diaphragms.
2. Background of the Invention
Diaphragms and membranes are structures that play a critical role in pressure sensors. Diaphragms are used in pressure sensors such that pressure is usually measured by detecting and quantifying the deflection of a diaphragm onto which pressure is applied. Another important application of diaphragms is to isolate two different media but still allow transmission of pressure from one medium to another. This is normally done to protect a pressure-sensing element from an incompatible environment by encapsulating the sensor in a housing that is filled with a neutral fluid such as silicone oil. The external pressure is transmitted to the oil, and therefore to the pressure sensor, through a flexible membrane that is hermetically attached to the housing. In this application, the diaphragm also functions as an isolation membrane to “isolate” one environment from the other. When these diaphragms and isolation membranes are metallic, they may be attached to housings by various methods such as welding, brazing, or with the use of adhesives. These attachment methods, however, are difficult to implement when the application requires very small diaphragms or membranes (i.e., diaphragms and membranes having very small diameters, or sizes). An example of such applications is implantable medical catheters used to measure pressure inside the body.
The present invention is directed to preformed sensor housings and method for creating thin metal diaphragms on a housing. The diaphragm is preferably attached and hermetic sealed to the housing without the need of a separate attachment procedure such as laser welding or brazing. This method is particularly suited for producing miniature diaphragms and isolation membranes that cannot be easily attached to the rest of the mechanical system.
In one preferred embodiment, the method includes inserting a sacrificial element into a housing and then coating (e.g., via electroplating) the sacrificial element/housing combination with a material (e.g., metal) suitable for use as a diaphragm or isolation membrane. The sacrificial element will then be removed, which leaves behind the diaphragm attached to the housing.
In another preferred embodiment, the method described herein for creating a thin film diaphragm on a housing includes inserting a sacrificial element into the housing. Then, depositing a diaphragm material onto the sacrificial element and the housing, and removing the sacrificial element.
A sensor housing formed in accordance with one preferred embodiment of the present invention includes a conduit having an inside; a plug disposed inside the conduit; and a deposit covering at least a portion of the plug and a portion of the conduit.
Other objects, features and advantages will become apparent to those skilled in the art from the following detailed description. It is to be understood, however, that the detailed description and specific examples, while indicating exemplary embodiments, are given by way of illustration and not limitation. Many changes and modifications within the scope of the following description may be made without departing from the spirit thereof, and the description should be understood to include all such variations.
The invention may be more readily understood by referring to the accompanying drawings in which:
Like numerals refer to like parts throughout the several views of the drawings.
The present invention is directed to preformed sensor housings method for creating thin metal diaphragms on a housing. The thin metal diaphragm is attached to the housing and produces a seal (preferably hermetic) without the need of a separate attachment procedure such as laser welding or brazing. This method is particularly suited for producing miniature diaphragms and isolation membranes that cannot be easily attached to the rest of the mechanical system. In one preferred embodiment, the method includes inserting a sacrificial element into a tubular housing and then electroplating the sacrificial element/housing combination with a metal material suitable for use as a diaphragm or separation membrane. The sacrificial element can then be removed, which leaves behind the diaphragm attached to the housing.
In one preferred embodiment of the present invention, after diaphragm 350 has been deposited, sacrificial element 104 is chemically or thermally removed, leaving diaphragm 350 hermetically attached to housing 102.
In another preferred embodiment, the sacrificial element is shaped after it is inserted into the housing. In this embodiment, the sacrificial element may be inserted into the housing without a high degree of precision and a portion of the sacrificial element left out because the portion that protrudes from the housing may be trimmed or shaped after it is inserted. Thus, in this embodiment, the steps of patterning the sacrificial element 702 and the displacement of the sacrificial element 704 are reversed as compared to the first preferred embodiment.
In yet another preferred embodiment, the patterning and displacement of the sacrificial element may occur simultaneously. For example, the tubular housing may have a cap that is shaped in the mirror image of the desired final shape of the sacrificial element and the sacrificial element is in liquid form when it is displaced into the tubular housing. Thus, when the sacrificial element solidifies in the tubular housing, the sacrificial element will take the form of the cap.
In still yet another preferred embodiment, the sacrificial element may be left without a particular patterned surface, such that the diaphragm that is formed will be relatively smooth and without a particular surface pattern.
In step 706, after the sacrificial element is inserted into the tubular housing, the diaphragm is formed onto the sacrificial element and the tubular housing. In one preferred embodiment, the diaphragm is formed by electroplating the sacrificial element/tubular housing combination with a metal material suitable for use as a diaphragm. For example, chromium, nickel, cadmium, platinum, and gold are exemplary preferred materials that may be electroplated onto the combined structure (i.e., the diaphragm material that is electroplated onto the sacrificial element/tubular housing combination). In another preferred embodiment, the diaphragm is formed by deposition of the diaphragm material onto the sacrificial element/tubular housing combination. For example, electroplating, electroless plating, and sputtering (for very thin diaphragms) are various deposition methods that may be used.
In step 708, the sacrificial element is then removed. As the diaphragm is formed onto the sacrificial element/housing combination in a contiguous manner, when the sacrificial element is removed, it leaves behind the diaphragm attached to the housing. In one preferred embodiment, the sacrificial element is removed by an etching process. The removal of the sacrificial element may be effected by such methods as metal etching (e.g., etching using, acids); melting (e.g., where the sacrificial material is lead and/or solder); and/or using solvents (e.g., where the sacrificial material is a conductive polymer and/or plastic). Preferably, after the removal of the sacrificial element, the diaphragm remains attached to the housing, with a hermetic seal between the diaphragm and housing without the need of a separate attachment procedure such as laser welding or brazing. As described herein, this method is particularly suited for producing miniature diaphragms and membranes that normally cannot be easily attached to the rest of the sensor system. This process offers great flexibility in terms of the shape and location of the diaphragm.
Thus, what has been described above is a method to fabricate small metal diaphragms and membranes by depositing a suitable metal or dielectric layer directly onto the surface of a housing. A portion of such housing incorporates a sacrificial element that is chemically or thermally removed after deposition, leaving a freestanding diaphragm attached to the rest of the housing at the perimeter of the membrane. The size and shape of the diaphragm is given by the size and shape of the surface of the sacrificial element. No further steps are required to attach the membrane to the housing.
The embodiments described above are exemplary embodiments. Those skilled in the art may now make numerous uses of, and departures from, the above-described embodiments without departing from the inventive concepts disclosed herein. Various modifications to these embodiments may be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments, without departing from the spirit or scope of the novel aspects described herein. Thus, the scope of the invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. The word “exemplary” is used exclusively herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. Accordingly, the present invention is to be defined solely by the scope of the following claims.
