Abstract:
A workpiece composite includes a preform part and a gel accommodated in a recess in the preform, the recess being enclosed by at least one edge which serves as a creep barrier to prevent the gel from spreading. The at least one edge of the recess defines a termination point of at least one surface which is provided with a coating made of an oleophobic material in an area adjacent to the at least one edge.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a workpiece composite including a preform and a gel. 
         [0003]    2. Description of Related Art 
         [0004]    Workpiece composites containing a preform and a gel, which is accommodated in a recess of the preform, are used as pressure sensors, for example. The preform may contain a pressed screen of a printed circuit board, for example, and may be connected to a pressure sensor chip. The pressure sensor chip is positioned over a recess in the preform. The gel fills the recess and the area underneath the diaphragm of the pressure measuring chip. In general, the pressure measuring chip is bonded to the preform with the aid of an accessory agent. 
         [0005]    Normally the gel is a passivating gel which is used as a barrier against harmful media. These are, for example, corrosive media. 
         [0006]    However, unhardened passivating gels usually tend to creep. It is necessary to select the time period between the application of the gel and hardening to be as short as possible in order to limit areas affected by creeping to a minimum. Another option for preventing creeping is the formation of edges at which creeping stops. However, these edges may stop creeping only temporarily. 
         [0007]    In order to prevent oils from creeping on surfaces, i.e., to prevent a surface from being wetted by an oil, it is known, for example, from published German patent document DE A 196 49 955, to coat a substrate with a fluoroalkyl-functional organopolysiloxane-containing composition. Coatings of this type are offered commercially, for example, by the Dr. Tillwich Company. Published German patent document DE A 198 47 303 describes a sensor element having an anti-adhesive surface coating. The surface coating has a compound selected from the group of the fluoropolymers, fluorormocers, polymeric fluorocarbon resins, fluorine-containing silanes, or partially fluorinated polymers. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    A workpiece composite according to the present invention contains a preform and a gel which is accommodated in a recess of the preform. The recess is enclosed by at least one edge as a creep barrier to prevent the gel from spreading. At least the edge and/or a surface surrounding the recess between the recess and the edge is provided with a coating made of an oleophobic material. 
         [0009]    Surprisingly, it has been found that a surface which is provided with a coating made of oleophobic material also prevents the gel from creeping on this surface. The gel may thus be further prevented from creeping by the workpiece composite designed according to the present invention. 
         [0010]    Another improvement results from providing the surfaces adjacent to the edge with the coating made of the oleophobic material. 
         [0011]    The oleophobic material of the coating is preferably selected from the group composed of fluoropolymers, fluorormocers, polymeric fluorocarbon resins, fluorine-containing silanes, and partially fluorinated polymers. Suitable materials contained in the coating include, for example, silanes of the general formula (1) 
         [0000]      R a —R b —Si(X) 3-n (R c ) n   (1) 
         [0000]    where R a  is a perfluorinated alkyl group having 1 to 16 C atoms, preferably 6 to 12 C atoms, R b  is an alkyl spacer, for example, methyl or ethyl, and R c  is an alkyl group, for example, methyl or ethyl. X is a halogen, an acetoxy or an alkoxy, for example, ethoxy or methoxy, and n has the value of 0 to 2. 
         [0012]    Silanes of the general formulas R a —R b —SiX 3 , R a —R b —Si(X) 2 Me or R a —R b —Si(X)Me 2  and their derivatives are particularly suitable, X denoting fluorine, chlorine, bromine, methoxy, ethoxy, isopropoxy, alkoxy, or acetoxy, Me denoting methyl, and Me 2  dimethyl. R a  denotes perfluoro-butyl, perfluoro-hexyl, perfluoro-octyl, perfluoro-decyl, perfluoro-methyl, and R b  denotes ethyl or methyl. More preferably, R a —R b — denotes 1,1,2,2-tetrahydroperfluorooctyl- or 3,3,3-trifluoropropyl. 
         [0013]    Silanes of the general formula (R a —R b ) 2 —SiX 2  and their derivatives are also suitable, X here also denoting fluorine, chlorine, bromine, methoxy, ethoxy, isopropoxy, alkoxy, or acetoxy, R a  denoting perfluoroethyl, perfluorobutyl, perfluoromethyl, and R a  denoting ethyl or methyl. A suitable R a —R b  radical is, for example, 3,3,3-trifluoropropyl 
         [0014]    Suitable silanes include, for example, 1,1,2,2-tetrahydroperfluorodecyltriethoxysilane, 1,1,2,2-perfluorotetrahydrododecyltrichlorosilane, 1,1,2,2-perfluorotetrahydrododecyltrimethoxysilanes, 1,1,2,2-tetrahydroperfluorodecyltrichlorosilane, 1,1,2,2-tetrahydroperfluorodecyltrimethoxysilane, 1,1,2,2-tetrahydroperfluorodecyltriacetoxysilane, 1,1,2,2-tetrahydroperfluorodecyltriethoxysilane, 1,1,2,2-tetrahydroperfluorooctyltrichlorosilane, 1,1,2,2-tetrahydroperfluorooctyltrimethoxysilane, 1,1,2,2-tetrahydroperfluorooctyltriethoxysilane, 1,1,2,2-perfluorotetrahydrohexyltrichlorosilane, 1,1,2,2-perfluorotetrahydrohexyltriethoxysilane, 1,1,2,2-perfluorotetra-hydrohexyltrimethoxysilane, di(3,3,3-trifluoropropyl)dichlorosilane, 3,3,3-trifluoropropyltriacetoxysilane, 3,3,3-trifluoropropyltribromsilane, 3,3,3-trifluoropropyltrichlorosilane, 3,3,3-trifluoropropyltriethoxysilane, 3,3,3-trifluoropropyltrifluorosilane, 3,3,3-trifluoropropyltri-isopropoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, di(pentafluorophenyl)diacetoxysilane, di(pentafluorophenyl)dibromosilane, di(pentafluorophenyl)dichlorosilane, di(pentafluorophenyl)-diethoxysilane, di(pentafluorophenyl)difluorosilane, di(pentafluorophenyl)diisopropoxysilane, di(pentafluorophenyl)dimethoxysilane, perfluorodecyl-1H,1H,2H,2H-dimethylchlorosilane, perfluorodecyl-1H,1H,2H,2H-methyldichlorosilane, perfluorodecyl-1H,1H,2H,2H-triacetoxysilane, perfluorodecyl-1H,1H,2H,2H-trichlorosilane, perfluorodecyl-1H,1H,2H,2H-triethoxysilane, perfluorodecyl-1H,1H,2H,2H-trimethoxysilane, perfluorododecyl-1H,1H,2H,2H-dimethylchlorosilane, perfluorododecyl-1H,1H,2H,2H-methyldichlorosilane, perfluorododecyl-1H,1H,2H,2H-trichlorosilane, perfluorododecyl-1H,1H,2H,2H-triethoxysilane, perfluorododecyl-1H,1H,2H,2H-trimethoxysilane, perfluorohexyl-1H,1H,2H,2H-dimethylchlorosilane, perfluorohexyl-1H,1H,2H,2H-methyldichlorosilane, perfluorohexyl-1H,1H,2H,2H-trichlorosilane, perfluorohexyl-1H,1H,2H,2H-triethoxysilane, perfluorohexyl-1H,1H,2H,2H-trimethoxysilane, perfluorooctyl-1H,1H,2H,2H-dimethylchlorosilane, perfluorooctyl-1H,1H,2H,2H-methyldichlorosilane, perfluorooctyl-1H,1H,2H,2H-triacetoxysilane, perfluorooctyl-1H,1H,2H,2H-trichlorosilane, perfluorooctyl-1H,1H,2H,2H-triethoxysilane, perfluorooctyl-1H,1H,2H,2H-trimethoxysilane, perfluorodecyl-1H,1H-dimethylchlorosilane, perfluorodecyl-1H,1H-methyldichlorosilane, perfluorodecyl-1H,1H-triacetoxysilane, perfluorodecyl-1H,1H-trichlorosilane, perfluorodecyl-1H,1H-triethoxysilane, perfluorodecyl-1H,1H-trimethoxysilane, perfluorododecyl-1H,1H-dimethylchlorosilane, perfluorododecyl-1H,1H-methyldichlorosilane, perfluorododecyl-1H,1H-trichlorosilane, perfluorododecyl-1H,1H-triethoxysilane, perfluorododecyl-1H,1H-trimethoxysilane, perfluorohexyl-1H,1H-dimethylchlorosilane, perfluorohexyl-1H,1H-methyldichlorosilane, perfluorohexyl-1H,1H-trichlorosilane, perfluorohexyl-1H,1H-triethoxysilane, perfluorohexyl-1H,1H-trimethoxysilane, perfluorooctyl-1H,1H-dimethylchlorosilane, perfluorooctyl-1H,1H-methyldichlorosilane, perfluorooctyl-1H,1H-triacetoxysilane, perfluorooctyl-1H,1H-trichlorosilane, perfluorooctyl-1H,1H-triethoxysilane, perfluorooctyl-1H,1H-trimethoxysilane, perfluorodecyl-1H,1H,2H,2H,3H,3H-dimethylchlorosilane, perfluorodecyl-1H,1H,2H,2H,3H,3H-methyldichlorosilane, perfluorodecyl-1H,1H,2H,2H,3H,3H-triacetoxysilane, perfluorodecyl-1H,1H,2H,2H,3H,3H-trichlorosilane, perfluorodecyl-1H,1H,2H,2H,3H,3H-triethoxysilane, perfluorodecyl-1H,1H,2H,2H,3H,3H-trimethoxysilane, perfluorododecyl-1H,1H,2H,2H,3H,3H-dimethylchlorosilane, perfluorododecyl-1H,1H,2H,2H,3H,3H-methyldichlorosilane, perfluorododecyl-1H,1H,2H,2H,3H,3H-trichlorosilane, perfluorododecyl-1H,1H,2H,2H,3H,3H-triethoxysilane, perfluorododecyl-1H,1H,2H,2H,3H,3H-trimethoxysilane, perfluorohexyl-1H,1H,2H,2H,3H,3H-dimethylchlorosilane, perfluorohexyl-1H,1H,2H,2H,3H,3H-methyldichlorosilane, perfluorohexyl-1H,1H,2H,2H,3H,3H-trichlorosilane, perfluorohexyl-1H,1H,2H,2H,3H,3H-triethoxysilane, perfluorohexyl-1H,1H,2H,2H,3H,3H-trimethoxysilane, perfluorooctyl-1H,1H,2H,2H,3H,3H-dimethylchlorosilane, perfluorooctyl-1H,1H,2H,2H,3H,3H-methyldichlorosilane, perfluorooctyl-1H,1H,2H,2H,3H,3H-triacetoxysilane, perfluorooctyl-1H,1H,2H,2H,3H,3H-trichlorosilane, perfluorooctyl-1H,1H,2H,2H,3H,3H-triethoxysilane, perfluorooctyl-1H,1H,2H,2H,3H,3H-trimethoxysilane. 
         [0015]    Particularly suitable are 1,1,2,2-perfluorotetrahydrododecyltrichlorosilane, 1,1,2,2-perfluorotetrahydrododecyltrimethoxysilane, 1,1,2,2-tetrahydroperfluorodecyltrichlorosilane, 1,1,2,2-tetrahydroperfluorodecyltrimethoxysilane, 1,1,2,2-tetrahydroperfluorodecyltriacetoxysilane, 1,1,2,2-tetrahydroperfluorodecyltriethoxysilane, 1,1,2,2-tetrahydroperfluorooctyltrichlorosilane, 1,1,2,2-tetrahydroperfluorooctyltrimethoxysilane, 1,1,2,2-tetrahydroperfluorooctyltriethoxysilane, 1,1,2,2-perfluorotetrahydrohexyltrichlorosilane, 1,1,2,2-perfluorotetrahydrohexyltriethoxysilane, 1,1,2,2-perfluorotetrahydrohexyltrimethoxysilane. 
         [0016]    Furthermore, perfluorodecyl carboxylic acid (PFDA) and perfluorinated plasma polymers are suitable for the coating material. 
         [0017]    The physical and/or chemical bonding of the coating to the material of the preform may be improved by an activating pre-treatment. Oxygen plasma, ozone, steam plasma, or hard UV light at wavelengths &lt;220 nm, for example, is suitable for the activating pre-treatment. 
         [0018]    For applying the coating, the coating material may furthermore contain at least one solvent in which the oleophobic material is dissolved or dispersed. Additives such as antifoam and fluidizing agents may also be added. 
         [0019]    A suitable solution for applying the coating contains, for example, 0.1% to 5% 1,1,2,2-tetrahydroperfluorooctyltrimethoxysilane, 0.5% to 5% water, 0.1% acetic acid, the balance isopropanol. The solution is prepared and homogenized overnight with stirring. The solution is applied at the desired locations and, after drying at 110° C. for 30 minutes, baked in a circulating air oven. 
         [0020]    Many of the above-mentioned silanes are utilizable directly as a solution in hydrocarbons or alcohols without any further additives for the coating. Chlorosilanes are preferably used for the gas phase deposition. In addition to solutions of the pure silanes, these silanes are also suitable for coating in a partially hydrolyzed form or in mixtures with polymers or mixtures of the individual silanes. 
         [0021]    The coating, which is applied to the edge and/or the surface surrounding the recess between the recess and the edge, preferably has a layer thickness in the range of 1 nm to 20 μm; especially preferably the layer thickness of the coating is in the range of 1 nm to 1 μm. 
         [0022]    In another specific embodiment, at least two edges of the preform have a stepped design as creep barriers. The two stepped edges further slow down creeping. In particular, even in the case of long dwelling times, for example, between application and hardening of the gel, creeping on the preform surface may be suppressed. Another improvement results if at least each edge is provided with the oleophobic coating. 
         [0023]    The oleophobic layer may be applied to the preform, for example, as a paint layer or as an epilame layer. The coating may be applied, for example, by pad printing, stamping, dripping, dispensing, immersing, or spraying, as well as by CVD (Chemical Vapor Deposition) methods or PVD (Physical Vapor Deposition) methods. In the pad printing, stamping, dripping, dispensing, immersing, or spraying methods, the coating is applied using a liquid coating material; in the CVD or PVD method, the coating is applied from the gaseous phase. 
         [0024]    After applying the coating, the surfaces that are not provided with the coating may be structured. 
         [0025]    The coating may be applied from a solution or from the gaseous phase. Local application by stamping, spraying, dispensing, etc., is possible from a solution. From the gaseous phase, the entire component is coated; local removal of the coating is possible by applying perforated sheet metal masks and 50 Hz to 40 kHz oxygen plasma or steam plasma, by applying quartz glass masks and UV light, as well as without masking with the help of a laser. 
         [0026]    Since, in general, components are glued to the preform, to which gel is also to adhere, preforms coated on their entire surface have the coating preferably removed again with the exception of the gel stop edges. 
         [0027]    In a particularly preferred specific embodiment of the present invention, the recess, which is enclosed by at least one edge as a creep barrier, is sealed using a diaphragm. The diaphragm which seals the recess is preferably part of a pressure sensor chip. 
         [0028]    The preform is preferably made of a thermoplast or duroplast, usually of LCP, PEEK, or epoxy resin. Other suitable materials for the preform are, however, also ceramics and metals. 
         [0029]    The gel preferably contains silicones, partially fluorinated silicones, or perfluoropolyethers. The gel preferably furthermore contains substances for neutralizing corrosive or poisonous media, for example, anti-corrosion additives. 
         [0030]    In particular when using the workpiece composite as a pressure sensor, the embodiment according to the present invention and the associated increased effectiveness of the creep barrier yield the advantage that the risk of leaks on the boundary surface between the adhesive using which the pressure sensor chip is applied to the preform and the preform is reduced. In addition, the mechanical adhesive strength of the workpiece composite in a plug housing in which it is mounted is improved. 
         [0031]    The gel is held in position by the improved creep barrier. Minor leaks, for example, are prevented by the gel. These leaks, in particular on the adhesive of the pressure sensor chip on the preform, may result in a pressure exchange between the front and back sides of the diaphragm. This prevents the differential pressure from being correctly measured. The measuring accuracy may thus be improved by using the workpiece composite according to the present invention. 
         [0032]    Manufacturability is also enhanced by the workpiece composite according to the present invention. Contamination from handling and manufacturing devices, for example, may thus be prevented. A more reliable protection, which is almost unlimited in time, against gel overflow by creeping also results in this way. This allows substantially longer dwelling times between the introduction of the gel and hardening to be defined, which may increase the flexibility in the manufacturing process. In addition, the workpiece composite according to the present invention also provides protection against gel overflow via mechanical introduction during handling, for example, due to vibrations, shocks, or tipping. Introducing gel into the recess in the preform also offers the advantage that the sensor cannot be damaged by icing. The contained gel prevents water from penetrating. Deposits directly on the diaphragm resulting in a characteristics curve drift are also prevented. In addition, the sensor may be installed in any position, since water is not able to penetrate. Previously, especially in applications in which water might penetrate into the sensor, it was necessary to install the sensor in such a way as to allow penetrating or condensed water to escape. Furthermore, the gel is also used for corrosion protection against basic or acidic media attacking the diaphragm. 
     
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWING 
         [0033]      FIG. 1  shows a section through the workpiece composite for a pressure sensor in a first example embodiment of the invention. 
           [0034]      FIG. 2  shows a section through the workpiece composite for a pressure sensor in a second example embodiment of the invention. 
           [0035]      FIG. 3  shows a pressure sensor according to  FIG. 1 , which is mounted on a connection piece. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0036]    As shown in  FIG. 1 , a workpiece composite  1  for a pressure sensor according to a first example embodiment of the present invention includes a preform  3 , which is connected to a pressure sensor chip  5 . Pressure sensor chip  5  is attached to preform  3  using an adhesive layer  7  for this purpose. 
         [0037]    Preform  3  is a ceramic socket or a PC board, for example. When preform  3  is a ceramic socket, Al 2 O 3  is suitable as a ceramic, for example. When preform  3  is a PC board substrate, epoxy resin materials are typically used. 
         [0038]    Pressure sensor chip  5  is usually a semiconductor chip which has a diaphragm  9 . When there is a pressure difference between the pressures acting on the top and bottom sides of diaphragm  9 , the diaphragm is deformed. Using the deformation of the diaphragm, the pressure difference, and thus, when a pressure on one side of diaphragm  9  is known, the pressure on the other side of diaphragm  9  may be determined. 
         [0039]    For a pressure to be able to act on diaphragm  9  on its side facing preform  3 , a recess  11  is formed in preform  3 . Recess  11  is designed as a borehole, for example. Due to recess  11 , diaphragm  9  is accessible to media also on its side facing preform  3 . 
         [0040]    In the specific embodiment depicted here, a cavity  13  is formed between preform  3  and diaphragm  9 . However, it is also possible as an alternative that the diaphragm lies directly on preform  3 . 
         [0041]    To protect diaphragm  9 , for example, against deposits on diaphragm  9  or condensing water, which may freeze, for example, and even at temperatures below the freezing point of water may permanently damage diaphragm  9 , recess  11  and cavity  13  are filled with a gel  15 . The side of diaphragm  9  facing preform  3  is completely covered by gel  15 . Gel  15  is a passivating gel which, in addition to preventing deposits, also provides corrosion protection against basic or acidic aggressive media. Gel  15  generally contains silicones, partially fluorinated silicones, or perfluoropolyethers. In addition, corrosion protective additives are preferably also contained in the gel. 
         [0042]    When selecting a suitable gel  15 , particular attention must be paid to the fact that, on the one hand, it performs a protective function for diaphragm  9  but, on the other hand, the diaphragm function, i.e., the sensor characteristics and/or the electronic circuit is/are not to be negatively affected. 
         [0043]    Recess  11  and cavity  13  are covered with the gel, for example, as described in German patent document DE-A 10 2005 056 769. For this purpose, the gel is introduced using a soft plastic needle which is inserted through recess  11 , for example. By using a soft plastic, it is ensured that the walls of recess  11  or diaphragm  9  are not damaged. A ring is conveniently used as a stop, so that the plastic needle cannot hit diaphragm  9 , damaging it. A metal ring, for example, is suitable as a ring. It preferably has a diameter that is greater than the diameter of recess  11 . 
         [0044]    As an alternative, it is also possible, for example, to introduce gel  15  into recess  11  and cavity  13  by a vacuum dispensing method. Any other suitable methods known to those skilled in the art may also be used to add the gel. 
         [0045]    To prevent gel  15  from creeping from recess  11  along preform  3 , recess  11  is enclosed by a first edge  17 , which acts as a gel stop edge. A surface  19  adjacent to first edge  17  is coated with an oleophobic coating  21  as a further protection against the creeping of gel  15 . Oleophobic coating  21  preferably contains a compound selected from the group composed of fluoropolymers, fluorormocers, polymeric fluorocarbon resins, fluorine-containing silanes, and partially fluorinated polymers. Polytetrafluoroethylene (PTFE) or perfluoroalkylsilanes are suitable compounds, for example. 
         [0046]    The coating may be applied, for example, from the liquid phase or from the gaseous phase. Methods for applying coating  21  from the liquid phase include, for example, pad printing, stamping, dripping, dispensing, immersing, or spraying. Suitable methods for applying oleophobic coating  21  from the gaseous phase include, for example, CVD methods or PVD methods, but preferably CVD methods. 
         [0047]    In the specific embodiment illustrated here, there is a second edge  23  next to first edge  17 . Second edge  23  is also used as a gel stop edge and prevents creeping, for example, when gel flows out of recess  11  or cavity  13 , for example, due to tipping or jarring, and reaches the area of surface  19 . Both surfaces forming second edge  23  are provided with oleophobic coating  21 . Bottom  25  of preform  3 , adjacent to second edge  23 , is provided with coating  21  only in the area adjacent to edge  23 . 
         [0048]    Another advantage of second edge  23  is that, for example, roughness may occur in the area of first edge  17 , or portions of edge  17  may break off. In this case, creeping of gel  15  occurs in the area of the damage to first edge  17 , which may be further limited by second edge  23 , in addition to oleophobic coating  21 . 
         [0049]    A workpiece composite  1  in a second specific embodiment is illustrated in  FIG. 2 . 
         [0050]    Workpiece composite  1  illustrated in  FIG. 2  differs from the one illustrated in  FIG. 1  by the fact that a third edge  27 , which also acts as a gel stop edge, is situated next to second edge  23 . First edge  17 , second edge  23 , and third edge  27  have a stepped design. An additional creep protection is ensured by third edge  27 , in particular with regard to jarring or tipping of workpiece composite  1 . 
         [0051]    Also in the case of third edge  27 , as in the case of second edge  23 , both adjacent surfaces are provided with oleophobic coating  21 . Also in  FIG. 2 , in the area of bottom  25  of preform  3  only the area adjacent to third edge  27  is coated with oleophobic coating  21 . After oleophobic coating  21  has been applied, it is possible that exposed surfaces, for example, bottom  25  of preform  3 , the top of preform  3  or exposed surfaces of pressure sensor chip  5  are structured. Structuring may be performed, for example, using UV light, laser, or a plasma method. When coating is removed using a plasma method, the areas containing oleophobic coating  21  preferably remain covered. A loosely placed screen may be used for covering, for example. A PC-board structure, for example, may be applied to preform  3  using structuring. 
         [0052]      FIG. 3  shows a pressure sensor, which is mounted on a connection piece. 
         [0053]    The pressure sensor illustrated in  FIG. 3  differs from the pressure sensor illustrated in  FIG. 1  by the fact that only surface  19  adjacent to first edge  17  is provided with oleophobic coating  21 . The surfaces adjacent to second edge  23  have no oleophobic coating. 
         [0054]    Workpiece composite  1  containing pressure sensor chip  5  is mounted on a connection piece  29 . Connection piece  29  is installed, for example, on a housing containing a gas or a liquid. Such a housing may be a gas or liquid tank, for example. Workpiece composite  1  is mounted on connection piece  29  as a cover. A flange  31 , for example, is formed on connection piece  29  for this purpose. Workpiece composite  1  is attached to preform  3  via flange  31 . It may be attached using an adhesive, for example. For this purpose, an adhesive layer  33  is applied between flange  31  and bottom  25  of preform  3 . Alternatively, however, a detachable connection of workpiece composite  1  with connection piece  29  is also possible. For this purpose, workpiece composite  1  and connection piece  29  may be screwed together, for example. Clamping is also conceivable. In the case of a detachable, connection, a sealing element is preferably introduced between flange  31  of connection piece  29  and bottom  25  of preform  3  to prevent the medium, i.e., the liquid or gas contained, from flowing out from the housing or the piping on which connection piece  29  is mounted. Alternatively, gases or liquids from the environment are also prevented from penetrating into the tank or the piping, for example. 
         [0055]    In particular if there is a positive pressure in the tank or the piping and corrosive or poisonous media are possibly contained, it is necessary to achieve a sufficient seal between preform  3  and connection piece  29  to prevent the medium from escaping. 
         [0056]    To measure the pressure, the pressure of the medium contained in the tank or the piping acts initially on gel  15  and thus on diaphragm  9  through connection piece  29 . This pressure causes diaphragm  9  to deform, the deformation being a function of the pressure difference between the pressure in connection piece  29  and the pressure in the environment. The greater the pressure difference, the greater is the degree of deformation of diaphragm  9 . The pressure difference and thus, if the pressure in the environment is known, the pressure in connection piece  29  may be ascertained using the deformation of diaphragm  9 . 
         [0057]    In addition to the specific embodiments illustrated in  FIGS. 1 through 3 , it is also possible, for example, to position a glass plate between preform  3  and pressure sensor chip  5 . The glass plate has preferably the same peripheral geometry as pressure sensor chip  5 . A through opening is formed in the glass plate, which may also be filled with gel  15  with the glass plate installed. 
         [0058]    In addition to its use as a pressure sensor, the embodiment according to the present invention having a gel stop edge and oleophobic coating is also suitable for any other workpiece composite in which a gel is used and creeping of the gel is to be prevented. Thus, for example, instead of a pressure sensor chip  5 , alternatively other capacitive or other sensor structures may also be used in which diaphragms are applied. Sensor structures of this type include, for example, mass flow rate sensors or microphones (dynamic pressure sensors).