Abstract:
An advanced thick film (ATF) pressure transducer can be produced from an advanced thick film stack on a metallic substrate. The metallic substrate has a flexible metallic diaphragm that flexes when there is a pressure differential across its top and bottom surfaces. The conductive and dielectric layers of the ATF stack are patterned into wire networks and bond pads. A strain sensor can be attached to bond pads or can be formed as part of an ATF layer. Flexure of the diaphragm stresses the strain sensor to produce an output proportional to the pressure differential. The ATF pressure transducer can be packaged into a housing that provides easy deployment and electrical interconnectivity.

Description:
TECHNICAL FIELD 
   Embodiments relate to pressure transducers, electrical circuits, thin films, and thin film processing. Embodiments also relate to packaging, chip packaging, and sensor packaging. 
   BACKGROUND OF THE INVENTION 
   Pressure transducers can measure the pressure differential between two adjacent volumes. The volumes can contain a fluid, such as a liquid or gas, with each volume&#39;s fluid having a pressure. The pressure differential is the difference in pressure between the fluids in the adjacent volumes. Current pressure transducers often employ one or more silicon strain sensors in proximity to a silicon diaphragm. The diaphragm separates the two volumes and the pressure differential causes the diaphragm to flex. The flexure can be sensed as strain by the strain sensors and interpreted as a measurement of the pressure differential. The fluid pressure in one of the volumes can be set to a known quantity such that the measurement can be interpreted as an absolute pressure measurement. 
   Many fluids can dissolve, corrode, or otherwise interact with silicon and it&#39;s corresponding die attach adhesive and/or bonding agent. Special precautions must be taken to prevent such fluids from contacting the silicon strain sensors or silicon diaphragm. As such, these systems are limited. Systems and methods sensing pressure in harsh environments are needed. 
   BRIEF SUMMARY 
   The following summary is provided to facilitate an understanding of some of the innovative features unique to the embodiments and is not intended to be a full description. A full appreciation of the various aspects of the embodiments can be gained by taking the entire specification, claims, drawings, and abstract as a whole. 
   It is therefore an aspect of the embodiments that an advanced thick film stack overlies a metal substrate. The metal substrate is a flexible diaphragm. The advanced thick film has a number of layers including an overglaze layer, a component layer, a conductor layer and at least one dielectric layer. The dielectric layer is electrically insulating and thereby can prevent an electrical current from flowing between the metallic substrate and the conductor layer. 
   The conductor layer is made of wire networks. The wire networks conduct electricity between electrical components and bonding pads. Bonding pads provide for external circuits, cabling, or wiring to be attached to the conductor layer. The electrical components can include resistors in the component layer. Resistors can be produced by screen printing, by a deposition and etch process, or by attaching components. The component layer can also contain other components such as transistors. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying figures, in which like reference numerals refer to identical or functionally similar elements throughout the separate views and which are incorporated in and form a part of the specification, further illustrate aspects of the embodiments and, together with the background, brief summary, and detailed description serve to explain the principles of the embodiments. 
       FIG. 1  illustrates a metal substrate in accordance with aspects of the embodiments; 
       FIG. 2  illustrates a dielectric layer in accordance with aspects of the embodiments; 
       FIG. 3  illustrates a conductor layer in accordance with aspects of the embodiments; 
       FIG. 4  illustrates a component layer in accordance with aspects of the embodiments; 
       FIG. 5  illustrates a an overglaze layer in accordance with aspects of the embodiments; 
       FIG. 6  illustrates an advanced thick film (ATF) stack in accordance with aspects of the embodiments; 
       FIG. 7  illustrates a ATF differential pressure transducer package in accordance with aspects of the embodiments; 
       FIG. 8  illustrates an end view of a ATF differential pressure transducer package in accordance with aspects of the embodiments; 
       FIG. 9  illustrates an exploded view of a ATF differential pressure transducer package in accordance with aspects of the embodiments; 
       FIG. 10  illustrates a high level flow diagram of producing an ATF differential pressure transducer in accordance with aspects of the embodiments; 
       FIG. 11  illustrates a ATF differential pressure transducer package with a threaded end cap in accordance with aspects of the embodiments; 
       FIG. 12  illustrates an end view of a ATF differential pressure transducer package with a threaded end cap in accordance with aspects of the embodiments; 
       FIG. 13  illustrates an exploded view of a ATF differential pressure transducer package with a threaded end cap in accordance with aspects of the embodiments; 
       FIG. 14  illustrates the operation of the conversion module  1302  in accordance with aspects of certain embodiments; and 
       FIG. 15 , labeled as prior art, illustrates a Wheatstone bridge in accordance with aspects of the embodiments. 
   

   DETAILED DESCRIPTION 
   The particular values and configurations discussed in these non-limiting examples can be varied and are cited merely to illustrate at least one embodiment and are not intended to limit the scope thereof. In general, the figures are not to scale. 
     FIG. 1  illustrates a metallic substrate  100  in accordance with aspects of the embodiments. The metallic substrate is a metallic diaphragm that is thin enough to flex when subjected to a pressure differential. Metallic substrates can be formed from a number of materials such as Hastelloy C22 CW, Hastelloy C22, Haynes-214, Inconel 718, A 286, Kanthal-A, Kanthal-D, or 430 Stainless Steel, many of which are alloys. Those practiced in the arts of metallurgy or advanced thick film processing are familiar with Hastelloy C22 CW, Hastelloy C22, Haynes-214, Inconel 718, A 286, Kanthal-A, Kanthal-D, and 430 Stainless Steel. 
     FIG. 2  illustrates a dielectric layer  200  in accordance with aspects of the embodiments. An ATF stack can have a single dielectric layer or can have many dielectric layers. The dielectric layers can be deposited on the metallic substrate using a number of techniques such as printing, evaporative deposition, chemical deposition, or lamination. Heraeus SD 2000 and Honeywell Z2Zr are examples of dielectric materials that can be used as dielectric layers. Heraeus SD 2000 and Honeywell Z2Zr are known to those practiced in the arts of dielectrics or ATF processing. 
     FIG. 3  illustrates a conductor layer  300  in accordance with aspects of the embodiments. The conductor layer has bond pads  301  and a wire pattern made of a number of wire networks  303 ,  305 . The wire networks  303 , 305  have component pads  302  for components such as resistors, transistors, and capacitors. The wire networks also have sensor pads  304 . 
     FIG. 4  illustrates a component layer in accordance with aspects of the embodiments. The components can include resistors  405 , transistors  401 , capacitors  402 , and sensors  403 ,  404 . Resistors can be printed directly over the conductor layer, can be attached by a conductive adhesive or solder, or can be produced by a lithographic process. Many resistors are sensitive to stress such that the resistor&#39;s conductance changes when the resistor is flexed. Resistors printed directly onto the conductor layer can be particularly sensitive to flex induced stress and can thereby be used as strain sensors. The resistors can be arranged and electrically connected by the wire networks to form a Wheatstone bridge. Those familiar with electric circuits are familiar with using Wheatstone bridges to detect small changes in resistance. 
     FIG. 5  illustrates an overglaze layer  500  in accordance with aspects of the embodiments. The overglaze layer  500  protects the other layers from the environment. Holes  501 ,  502  in the overglaze layer  500  can provide access to the conductor layer or the component layer. For example, external circuits can be attached to the bond pads through holes  501  in the overglaze layer  500 . 
     FIG. 6  illustrates an ATF stack  600  in accordance with aspects of the embodiments. The lowest layer is the metallic substrate  100 . Two dielectric layers  200  are on top of the metallic substrate  100 . Two dielectric layers  200  are shown for illustration purposes only because one or more dielectric layers can be used. A conductor layer  300  is on top of the dielectric layers  200 . A component layer  400  is on top of the conductor layer  300 . Finally, an overglaze layer  500  overlies all the other layers. 
   An ATF stack can be used as an ATF differential pressure transducer because the ATF stack is thin enough to flex when subjected to a pressure differential and because the components, such as printed on resistors, are strain sensors that are sensitive to the flexure. 
     FIG. 7  illustrates a ATF differential pressure transducer package in accordance with aspects of the embodiments. A housing  700  has a cap end  701  and an attachment end  704 . The cap end  701  has a port  705  through which a fluid can reach an ATF differential pressure transducer inside the housing. The attachment end  704  has threads  703  such that the housing can be screwed into a fixture. A wiring cable  702  is shown exiting the housing between the cap end  701  and the attachment end  704 . The wiring cable is a group of wires that can be attached to the bond pads. Many embodiments do not have the wiring cable  702  because, in those embodiments, external circuits access the ATF differential pressure transducer through pins in the attachment end  704 . 
     FIG. 8  illustrates an end view of a ATF differential pressure transducer package in accordance with aspects of the embodiments. The view is from the outside looking directly into the attachment end  704 . Four output pins  801  provide external circuits with access to the enclosed ATF differential pressure transducer. A port  802  allows a fluid to reach one side of the enclosed ATE differential pressure transducer. A different port  705  provides access to the other side. As such, the differential pressure of the two fluids can be measured. 
     FIG. 9  illustrates an exploded view of a ATF differential pressure transducer package in accordance with aspects of the embodiments. The ATF differential pressure transducer  902  can be seen along with a wiring cable  904  that connects it to the pins  801 . The ATF differential pressure transducer  902  can be attached to a port ring  903  through which port  802  passes. An O-ring  901  can help seal the cap end  701  to the attachment end  704 . 
     FIG. 10  illustrates a high level flow diagram of producing an ATF differential pressure transducer in accordance with aspects of the embodiments. After the start  1001  a metallic substrate is provided  1002  onto which dielectric layers are added  1003 . The conductor layer is then formed  1004 . The conductor layer can be formed by printing a conductive pattern, lithography, or in some other manner. Next, the wiring networks of the conductor layer are populated  1005 . Populating the resistors can include the steps of printing the resistors  1006  onto the conductor layer and then firing to fix the resistors  1007 . Those practiced in the art of printed circuitry are familiar with printing and firing resistors, conductors, and other circuit elements. 
   Other populating tasks  1008 , such as attaching transistors or capacitors can also occur. The transistors and capacitors can be discreet circuit elements that can be used to filter or amplify the output of a transducer or sensing circuit. As discussed above, stress sensitive resistors arranged as a Wheatstone bridge are an excellent sensing circuit for detecting flexure and thence differential pressure. Overglazing  1009  provides a protective layer on top of the other layers before the process is done  1010 . 
     FIG. 11  illustrates a ATF differential pressure transducer package  1100  with a threaded end cap  1101  in accordance with aspects of the embodiments. A housing  1103  has a threaded cap end  1101  and an attachment end  704 . The cap end  1101  has a port through which a fluid can reach an ATF differential pressure transducer inside the housing  1103 . The attachment end  704  has threads  703  such that an attachment can be screwed onto the housing  1103 . The cap end  1101  has threads  1102  such that the housing  1103  can be screwed into a fixture. A wiring cable  702  is shown exiting the housing  1103  between the threaded cap end  1101  and the attachment end  704 . The wiring cable is a group of wires that can be attached to the bond pads. Many embodiments do not have the wiring cable  702  because, in those embodiments, external circuits access the ATF differential pressure transducer through pins in the attachment end  704 . 
     FIG. 12  illustrates an end view of a ATF differential pressure transducer package  1100  with a threaded end cap  1101  in accordance with aspects of the embodiments. The view is from the outside looking directly into the threaded cap end  1101 . A port  1201  allows a fluid to reach one side of the enclosed ATF differential pressure transducer. A different port running through the attachment end provides access to the other side. As such, the differential pressure of the two fluids can be measured. 
     FIG. 13  illustrates an exploded view of a ATF differential pressure transducer package  1100  with a threaded end cap  1101  in accordance with aspects of the embodiments. 
   The ATF differential pressure transducer  902  can be seen along with a wiring cable  1303  that connects it to a conversion module  1302 . The ATF differential pressure transducer  902  produces a sensor signal. The conversion module  1302  converts the sensor signal into an output signal. For example, the sensor signal can be a voltage between 0 volts and 1 volt. The output signal can be a voltage ranging between plus and minus 12 volts, an electrical current, a modulated sinusoid, or even a LVDS (low voltage differential signal). The conversion module allows a standard ATF differential pressure transducer  902  to be used in a standard housing while still customizing the package output to a customer&#39;s specifications. In  FIG. 9 , the sensor signal is routed directly to the pins  801 . In  FIG. 13 , the sensor signal is routed to the conversion module  1302  where it is converted into an output signal. The output signal is then routed to the pins  801 . The ATF differential pressure transducer  902  can be attached to a port ring  903  through which port  802  passes. An O-ring  1301  can help seal port  1201  to the ATF differential pressure transducer  902 . 
     FIG. 14  illustrates the operation of the conversion module  1302  in accordance with aspects of certain embodiments. The ATF differential pressure transducer  902  produces a sensor signal  1401  that the conversion module  1302  converts into an output signal  1402  that is then passed to the output pins  801   
     FIG. 15 , labeled as prior art, illustrates a Wheatstone bridge  1500  in accordance with aspects of the embodiments. A voltage can be provided across the power nodes  1501 ,  1502  and an output voltage can be measured across the output nodes  1507 ,  1508 . A change in the resistance of one of the loads  1503 ,  1504 ,  1505 ,  1506  can be easily detected as a change in the output voltage. As discussed above, those practiced in the art of electrical circuitry are familiar with Wheatstone bridges. 
   It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.