Abstract:
A pressure sensor assembly configured for use with a catheter. In one illustrative embodiment, the pressure sensor assembly may include a multi-layer co-fired ceramic (MLCC) package. The MLCC package may include two or more ceramic layers that are co-fired together, with a cavity defined by at least some of the ceramic layers. At least one internal bond pad is provided within the cavity, and at least one external connection point is provided on the MLCC package exterior. A sensor, such as a pressure sensor, may be positioned and attached within the cavity. The sensor may be electrically connected to at least one of the internal bond pads. In some cases, a sealant may be used to encapsulate the sensor within the cavity. Once fabricated, the MLCC sensor assembly may be provided in a sensor lumen of a catheter.

Description:
TECHNICAL FIELD 
     Embodiments relate to sensors, pressure sensors, and sensor systems. Embodiments also relate to semiconductor packaging, ceramic packaging, and multi-layer co-fired ceramics. Embodiments additionally relate to catheters and medical instrumentation. 
     BACKGROUND OF THE INVENTION 
     Sensors, such as pressure sensors can be placed near the tip of a catheter. Prior art instrumented catheters include those claimed in U.S. Pat. No. 5,902,248, U.S. Pat. No. 4,274,423, U.S. Pat. No. 6,394,986, U.S. Pat. No. 5,050,297, U.S. Pat. No. 4,809,704, and U.S. Pat. No. 4,722,348 that are herein included by reference in their entirety. 
     The current art catheters, however, can be expensive, lack measurement fidelity, be complex to set-up and/or require cleaning, sterilization &amp; maintenance between uses. For example, reusable catheters cost around $1000 while single use fluid-filled catheters with low enough cost to be disposable can lack performance. Systems and techniques for producing instrumented catheters that are inexpensive are needed. Aspects of the embodiments directly address the shortcomings of current technology by using packaging technologies that can be used in mass production. A further benefit is that the advanced packaging leads to sensors that are more robust than those used in the current art. 
     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 to produce a multilayer co-fired ceramic (MLCC) package with a cavity into which a sensor can be placed. The sensor is electrically connected to internal bond pads within the cavity. Internal interconnects, corresponding to leads, traces, and/or vias, electrically connect the internal bond pads to external connection points on the outside of the MLCC package. 
     MLCC packages can be formed using a variety of different materials. MLCC packages formed with an aluminium oxide substrate (alumina) are often called High Temperature Co-fired Ceramic (HTCC) packages. Low Temperature Co-fired Ceramic (LTCC) packages are MLCCs based upon substrate materials with mixtures of glass and ceramic powders in binders and organic solvents to allow lower firing temperatures. 
     Typically, layers of ceramic material are formed, processed, stacked (laminated), and fired. After forming, a layer of ceramic material is produced. Processing includes operations such as forming holes and printing metal traces. The holes can be metallized to form electrical interconnects that pass through the layer of ceramic materials. Feed through and passages can be produced by processing holes and channels into ceramic layers. Air can pass through a passage. A wire can pass through a feed through. After processing multiple ceramic layers can be stacked and fired to produce a MLCC. Those practiced in the art of ceramic packaging know of these and many other operations that are used in the formation of MLCC packages. 
     It is also an aspect of the embodiments to produce a MLCC sensor assembly by placing a sensor into the cavity, electrically connecting the sensor to the internal bond pads, and sealing the sensor within the cavity. Those practiced in the art of semiconductor packaging or ceramic packaging are familiar with connecting to bond pads and sealing packages. 
     For example, the sensor can be attached, wire bonded, and sealed. A sensor can be attached by dispensing die attach adhesive and then positioning the sensor. Passages for reference air pressure or wiring must be kept open during attachment. Standard wire bonding techniques and equipment can be used to produce the electrical attachments between the sensor and the package. Finally, standard sealants, such as silicones, epoxy or glop top can be used to encapsulate the sensor within the package. 
     It is a further aspect of the embodiments to place the MLCC sensor assembly into one lumen of a catheter having one or more lumen. Many catheters have a single passageway leading from one end of the catheter to the other. Other catheters have multiple passageways. As such, the MLCC sensor assembly can be positioned inside one lumen of a catheter. The lumen containing the MLCC sensor assembly can be called the sensor lumen. An electrical connection can be established with the MLCC sensor assembly by attaching wires, such as those in a ribbon cable, to the MLCC sensor assembly. For example, the wires at one end of a ribbon cable can be connected to a MLCC sensor assembly&#39;s external connection points. The assembly can then be inserted into a lumen and fixed into position. The ribbon cable can then be used to establish electrical connections to the MLCC sensor assembly. 
     It is an aspect of certain embodiments to position more than one MLCC sensor assembly in a lumen. Wires can pass under or around one MLCC sensor assembly in order to reach a second MLCC sensor assembly. For example, two MLCC sensor assemblies can be electrically connected to different places on a single ribbon cable. The sensors and cable can then be fixed into position in a lumen. Obviously, each sensor assembly can alternatively have a dedicated cable. 
     It is an aspect of some embodiments that the sensor is a pressure sensor. As such, pressure external to the catheter must reach the sensor. A flexible sealant that transmits pressure can be used or a hole can pass through the catheter wall and sealant to reach the pressure sensor membrane directly. Some pressure sensors require a reference input. A passage through the MLCC package can allow reference media from within the catheter lumen (e.g. vented to atmospheric air) to reach the pressure sensor&#39;s reference input. The passage and the pressure sensor reference input must be aligned within the cavity. For example air can pass through the sensor lumen, through the passage, and to the pressure sensor. 
    
    
     
       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  shows an illustrative ceramic layer with traces, which may be used in some illustrative embodiments of a MLCC package; 
         FIG. 2  shows the illustrative ceramic layer of  FIG. 1  with an additional ceramic layer forming a cavity, which may be used in some illustrative embodiments of a stepped MLCC package; 
         FIG. 3  shows two illustrative ceramic layers similar to that shown in  FIG. 2  with via holes, which may be used in some illustrative embodiments of a MLCC package; 
         FIG. 4  shows a sensor attached in the cavity of an illustrative stepped MLCC package; 
         FIG. 5  shows a sensor encapsulated within the illustrative stepped MLCC package of  FIG. 4 , with an illustrative ribbon cable connection; 
         FIG. 6  shows a sensor attached in the cavity of another illustrative MLCC package; 
         FIG. 7  shows a sensor sealed within the cavity of an illustrative MLCC package that is similar to the MLCC package shown in  FIG. 6 ; 
         FIG. 8  illustrates an illustrative catheter with two lumen and a hole; 
         FIG. 9  illustrates a MLCC sensor assembly, such as that shown in  FIG. 5  or  7 , positioned and attached in a sensor lumen of a catheter, such as the catheter of  FIG. 8 ; 
         FIG. 10  illustrates a cutaway view of an illustrative catheter with two MLCC sensor assemblies; 
         FIG. 11  illustrates a batch of stepped MLCC packages similar to that shown in  FIG. 5 , containing sensors in a single sheet prior to singulation; 
         FIG. 12  illustrates a high level flow diagram of producing a catheter containing a MLCC sensor assembly; 
         FIG. 13  illustrates forming a MLCC package with an air passage into the cavity; 
         FIG. 14  illustrates a three dimensional view of another illustrative MLCC sensor assembly without a sensor yet positioned and attached into the cavity; and 
         FIG. 15  illustrates two cut views of an illustrative MLCC sensor assembly that is similar to that shown in  FIG. 14 . 
     
    
    
     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. 
     A batch fabricated miniature pressure sensor assembly provides a ceramic substrate with cavity to allow sealing and alignment of die to a reference hole/cavity. The assembly offers mechanical protection to wire bonds and die and provides an area for containing protective &amp; isolating encapsulant, such as RTV or silicone, with good control of coating thickness above the pressure membrane. 
     An electronic catheter containing a MLCC sensor assembly in a lumen provides many advantages. The MLCC package can have a reference hole linking to a channel that is buried or on bottom layer of the package to provide venting or a reference input to a pressure sensor. A channel passing completely through the assembly can provide a path for reference air to a second sensor positioned further into the catheter. An ultraminiature assembly is designed to be capable of fitting inside 6 French catheter with two lumen. One lumen is used for the sensor assembly, wires and reference pressure while the second can be used for other purposes such as a fluid fill lumen in Urology. The MLCC package allows forming connections to standard miniature pressure die using standard automated techniques such as wire bonding. Larger external connection points on the MLCC package allow ease of connection to catheter wires or to micro-ribbon cables. 
       FIG. 1  illustrates a ceramic layer  101  with traces  102  in accordance with aspects of the embodiments. In producing a MLCC package, ceramic slurry can be used to form ceramic layers. The layers are then processed. In processing, traces can be printed on the layer. The printed traces become metal traces during firing. 
       FIG. 2  illustrates a stepped MLCC package in accordance with aspects of the embodiments. A first ceramic layer  201  is stacked on ceramic layer  101 . The traces originally printed on the ceramic layer  101  become internal bond pads  202 , internal interconnects  203  and external electrical connection points  204 . The package is called “stepped” because the ceramic layers  101  and  201  do not all have the same dimensions. 
       FIG. 3  illustrates a stepped MLCC package with via holes  301  in accordance with aspects of the embodiments. A hole through the ceramic layer can be metallized to form an internal electrical interconnect connecting an internal bond pad to an external trace or external connection point  302 . 
       FIG. 4  illustrates a sensor  405  in the cavity of a stepped MLCC package in accordance with aspects of the embodiments. For ease of processing the MLCC package  401  is formed from six ceramic layers of equal thickness. The stepped package has the lower layers  402  being longer than other upper layers  403 . The upper layers  403  form a cavity into which a sensor  405  is placed. One or more of the lower layers have been processed to provide internal bond pads, internal interconnects, and external connection points  404 . 
       FIG. 5  illustrates a sensor encapsulated within a stepped MLCC package  401  with a miniature ribbon cable  502  in accordance with aspects of the embodiments.  FIG. 5  is similar to  FIG. 4  with the exceptions that encapsulant  501  now covers the sensor and a ribbon cable  502  is attached by connecting its wires  503  to the external connection points. An adhesive can be used to attach the cable to the MLCC package and thereby provide strain relief. 
       FIG. 6  illustrates a sensor  602  in the cavity of a MLCC package  601  in accordance with aspects of the embodiments. Metallized holes, such as those of  FIG. 3 , connect the internal bond pads to the internal interconnects. The internal interconnects pass between ceramic layers to the external electrical connection points  603  on the base of the package. The sensor  602  can be electrically connected to the interior bond pads using standard semiconductor packaging techniques. 
       FIG. 7  illustrates a sensor sealed within the cavity of a MLCC package  601  in accordance with aspects of the embodiments.  FIG. 7  is similar to  FIG. 6  with the exception that encapsulant  701  is isolating the sensor within the package  601 . 
       FIG. 8  illustrates a catheter  801  with two lumen and holes in accordance with aspects of the embodiments. The catheter  801  has a rounded end  802  and an open end revealing the two lumen. The bottom lumen  804  proceeds through the catheter to a bottom hole  805  such that fluid can flow through the lumen. The top lumen  803  proceeds through the catheter to a top hole  806 . The top hole  806  is shaded grey to indicate MLCC sensor assembly positioning. If the catheter has large enough lumen a MLCC sensor assembly can be positioned by pushing it completely through the top lumen  803  toward the rounded end  802  in which case the top hole  806  need only be the size of the sensing surface. A MLCC sensor assembly can also be positioned by placing it through the top hole  806 . A MLCC sensor assembly can also be located in the top hole  806  by pre-assembling a ribbon cable to the MLCC sensor assembly, threading the ribbon cable through the top hole  806  and top lumen  803 , and using the ribbon cable to locate the MLCC sensor assembly into place in the top hole  806 . The top hole  806  can then be sealed to fasten the MLCC sensor assembly in place and prevent fluid from flowing past the assembly. As such, reference air is allowed to reach the back-side of the sensor from the top lumen  803 , while the top-side is exposed to the external fluid only at the sensing surface. 
       FIG. 9  illustrates a MLCC sensor assembly  903  in a catheter in accordance with aspects of some embodiments. The catheter has a top lumen  901 , holding the MLCC sensor assembly  903 , and a bottom lumen. Notice that the MLCC sensor assembly has removed or rounded edges. The removed or rounded edges can ease the process of positioning of the MLCC assembly  903  within the top lumen  901 . 
       FIG. 10  illustrates a cutaway view of a catheter  1001  with two MLCC sensor assemblies in accordance with aspects of some embodiments. The catheter  1001  has a bottom lumen  1003  and a top lumen  1002 . The top lumen  1002  is used as the sensor lumen. A first MLCC sensor assembly  1004  is attached to a ribbon cable  1005  that passes under a second MLCC sensor assembly  1006 . The second MLCC sensor assembly can also be attached to the ribbon cable  1005  to form electrical connections or have its own ribbon cable or other such miniature wires. The MLCC sensor assemblies can sense the outside environment through holes  1007  in the catheter. 
       FIG. 11  illustrates a sheet  1101  of stepped MLCC packages  1102  in a batch containing sensors  1103  prior to singulation in accordance with aspects of the embodiments. Those practiced in the art of semiconductor packaging know that ceramic packages can be produced in bulk in the form of sheets. The sheets can be split into individual packages by breaking, cutting, or otherwise separating the sheets along horizontal cut lines  1104  and vertical cut lines  1105 . Rounded edges shown in  FIG. 9  can be produced by pre-scoring of the ceramic sheet before firing or making additional cuts (e.g. v-shape) prior to singulation, or also by mechanical processing after singulation. 
       FIG. 12  illustrates a high level flow diagram of producing a catheter containing a MLCC sensor assembly in accordance with aspects of the embodiments. After the start  1202  the process path branches. On one branch, a catheter is obtained  1206  and holes formed  1211  if required. On the other branch a batch of MLCC packages are produced  1202 , die attach adhesive is dispensed  1203 , and sensors bonded into the package  1209 . Wire bonding  1210  electrically attaches the sensor to the internal bond pads and then the sensor is encapsulated in the package cavity  1204 . Singulation from the batch MLCC sheet  1213  creates individual sensor assemblies. A ribbon cable is attached  1205  to the packages external connection points. Optionally at step  1213  the batch sheet could be only partially singulated forming horizontal strips so that ribbon cable can be attached in strips along one edge prior complete singulation. Finally the individual sensor assembly is positioned into a catheter lumen  1207  before the assembly is sealed into place  1208  and the process is complete  1212 . 
       FIG. 13  illustrates a forming a MLCC package with a passage in accordance with aspects of the embodiments. For illustrative purposes, the MLCC package has 5 layers although any number can be used. The first layer  1301  and the second layer  1302  will form a cavity. The third layer  1303  has a hole that can be aligned with the reference port of a pressure sensor. The fourth layer  1304  has a cut that will form an air passage. The fifth layer  1305  is blank. The five layers can be stacked and fired to form a MLCC package  1306  having a passage to the sensor lumen through which air can reach from the exterior. A pressure sensor die can be placed in the cavity such that the reference input and the hole align to thereby provide a reference to the backside of the sensor. The internal bond pads, internal interconnects, and exterior connection points are not shown. Also not shown is continuation of the channel  1304  to allow air or other reference media to pass through the sensor package to another sensor as shown in  FIG. 10 . 
       FIG. 14  illustrates a three dimensional view of an MLCC sensor assembly  1401  in accordance with aspects of the embodiments. The cavity  1402  is illustrated as a stepped cavity that has a lower cavity  1403  in which to locate and seal the sensor die. A hole  1407  can be seen in the base of the lower cavity  1403 . The hole  1407  connects to a channel in a lower layer, with another hole  1404  being at the other end of this channel. The internal bond pads  1405  are electrically connected to the external connection points  1406 . 
       FIG. 15  illustrates two cut views of an MLCC sensor assembly  1501  in accordance with aspects of the embodiments. The cavity  1507  is illustrated as a stepped cavity that has a lower cavity. A channel  1506  passes completely through the MLCC sensor assembly  1501  as well as connecting to a hole in the cavity  1507  base. A sensor  1502  is sealed in the cavity  1507  using a die attach adhesive  1504  that bonds and seals the sensor  1502  to the MLCC. The amount and placement of sealant must be controlled so that the hole under the sensor  1502  remains open. The sensor  1502  has wire leads  1505  that electrically connect the sensor  1502  to internal bond pads. The sensor  1502  has a reference chamber  1503  that is positioned over the hole. A fluid, such as air, should be free to pass through the channel  1506  and into the reference chamber  1503 . 
     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.