Patent Publication Number: US-7214881-B2

Title: High temperature electrical connection

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present application claims priority to U.S. Provisional Application No. 60/558,793, of Charles Scott Nelson, et al., filed Apr. 1, 2004, entitled “High Temperature Electrical Connection,” which is hereby incorporated by reference herein in its entirety. 

   TECHNICAL FIELD 
   The present invention relates to an electrical connection and more particularly relates to an electrical connection and a method for preparing an electrical connection suitable for use in harsh, high temperature environments such as the exhaust stream of an internal combustion engine. 
   BACKGROUND OF THE INVENTION 
   In high temperature environments, it is often necessary to provide electrical connections in or to equipment or instrumentation that must operate in the environment. For example, sensors are often used to monitor the properties of exhaust gas of internal combustion engines where the exhaust temperature can reach 1000° C. Such sensors generally require electrical connections as an integral part of the sensor and/or to connect the sensor to a lead wire for transmission of the sensor output signal. Electrical connection requirements of such sensors can be complicated by the fact that it is often necessary to make the electrical connection to a ceramic element of the sensor. 
   Mechanical connections are often not sufficiently robust to maintain their performance in the harsh conditions of the high-temperature environment, so wire bonding of a wire to a sensor element is typically employed to provide the electrical connection. Alternatively, brazing techniques may be used to provide the electrical connection. Both of these methods can be expensive and time-consuming to implement. 
   U.S. Pat. No. 5,730,543 to Schonauer et al. entitled “Electrically Conducting Connection” describes an electrically conductive connection made between a metal connector and a metal layer applied and bonded by sintering to a ceramic substrate comprising glass and/or vitreous ceramic in small quantities. An adhesion-promoting layer having a glass and/or vitreous ceramic and metal particles is applied and bonded by fusion to the ceramic substrate. The metal layer with the sintered bond is then applied to the ceramic substrate and the connector is welded to the metal layer by laser welding. 
   U.S. Pat. No. 6,437,681 to Wang et al. entitled “Structure and Fabrication Process for an Improved High Temperature Sensor” describes a temperature sensor including an aluminum oxide substrate and a thin-film resistor having a specific temperature coefficient of resistance (TCR) disposed over the substrate. The temperature sensor further includes an aluminum oxide stress-relief layer covering the thin film resistor. The temperature sensor further includes a passivation layer covering the aluminum oxide stress-relief layer. The aluminum oxide stress-relief layer further has at least one resistor-trimming trench formed by removing a portion of the aluminum oxide stress-relief layer and thin-film resistor therefrom and the resistor-trimming trench is filled with a material of the passivation layer. The temperature sensor may further include a set of dummy pads for resistance-trimming measurement disconnected from the thin film resistor disposed on the substrate near the thin film resistor covered by the passivation layer. The temperature sensor may further include a set of sensor bonding pads disposed on the substrate electrically connected to the thin film resistor covered by the passivation layer. The temperature sensor further includes a set of platinum chip-leads bonded to the sensor bonding pads for temperature measurement connections. 
   The disclosures of the foregoing are incorporated herein by reference in their entireties. 
   A need remains in the art for a simple, inexpensive, and effective way of establishing electrical connections in harsh environmental conditions. 
   SUMMARY OF THE INVENTION 
   The present invention provides an electrical connection comprising a metal element; and a second element to which an electrical connection is to be made; wherein the metal element is connected to the second element by means of a conductive material disposed onto one or both of the metal element and the second element; and wherein the metal element has a configuration such that the conductive material contacts and is dispersed about or about and through at least a portion of the metal element thereby providing both an electrical and a mechanical connection between the metal element and the second element. 
   The invention further provides a method for preparing an electrical connection comprising providing a metal element and a second element to which an electrical connection is to be made; disposing a conductive material onto one or both of the metal element and the second element; contacting the metal element and the second element wherein the metal element has a configuration such that the conductive material contacts and disperses about or about and through at least a portion of the metal element thereby providing both an electrical and a mechanical connection between the metal element and the second element; drying the connected metal element and second element; and firing the connected metal element and second element. 
   These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring now to the drawings, which are meant to be exemplary, not limiting, and wherein like elements are numbered alike in the several Figures: 
       FIG. 1  is a side cross-sectional view of an electrical connection in accordance with the invention including a metal element comprising a metal strip having openings or knurls disposed thereon. 
       FIG. 2  is a side cross-sectional view of an electrical connection in accordance with another embodiment of the invention including a metal element comprising a flattened, knurled wire. 
       FIG. 3  is a perspective view of an electrical connection in accordance with yet another embodiment of the invention. 
       FIG. 4  is a perspective view of the electrical connection of  FIG. 3  having a glass seal disposed thereon. 
       FIG. 5  is a perspective view of a clipped electrical connection in accordance with another embodiment of the invention. 
       FIG. 6  is a perspective view of the clipped electrical connection of  FIG. 5  having a glass seal disposed thereon. 
       FIG. 7  is a perspective view of a clipped electrical connection in accordance with another embodiment of the invention. 
       FIG. 8  is a perspective view of the clipped electrical connection of  FIG. 7  having a glass seal disposed thereon. 
       FIG. 9  is a perspective view of a sandwiched electrical connection in accordance with another embodiment of the invention. 
       FIG. 10  is a perspective view of a sandwiched electrical connection in accordance with another embodiment of the invention. 
       FIG. 11  is a perspective view of a sandwiched electrical connection in accordance with another embodiment of the invention. 
       FIG. 12  is a side cross-sectional view of the electrical connection of  FIG. 1 , but with the metal element completely covered by conductive material. 
       FIG. 13  is a side cross-sectional view of the electrical connection of  FIG. 1 , but with only the surface area of the metal element connected to the second element covered by conductive material. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to  FIG. 1 , one possible embodiment of the present electrical connection  10  and method for preparing the electrical connection  10  is illustrated. The electrical connection  10  includes a metal element  12  connected to a second element  14  via a conductive material  16  disposed onto one or both of the metal element  12  and the second element  14  such that the conductive material  16  contacts and disperses about or about and through the metal element  12  thereby providing both an electrical and a mechanical connection between the metal element  12  and the second element  14 . A cover plate  18  is disposed over the second element  14 . A protective glass seal  24  is disposed over the electrical connection area. A resistance or laser weld  20  or other suitable weld means is used to connect the electrical connection  10  to a wire or cable  22 . 
   The metal element  12  of  FIG. 1  may be a metal strip or pad having a plurality of openings disposed thereon such as by stamping, although any suitable means may be employed to dispose the openings onto the metal strip or pad. The invention contemplates any number of stamping patterns, such as, but not limited to, a pattern forming a “Swiss cheese-like” effect. Alternatively, the metal strip or pad  12  of  FIG. 1  may be configured with a plurality of knurls, knots, protuberances, nodules, bosses, or other type of projection collectively referred to herein as “knurls.” The knurls may be formed on the metal strip by any suitable means such as stamping or knurling. 
   The metal element  12  preferably comprises a metal that is capable of withstanding a harsh, high temperature environment, such as a noble metal including, but not limited to, platinum. Alternately, the metal element  12  comprises a material coated with a metal, preferably a noble metal, most preferably platinum, that is capable of withstanding a high temperature environment. 
   In a preferred embodiment, the second element  14  is a ceramic element, preferably with a conductive pad, most preferably a noble metal conductive pad (for example, platinum),  15  disposed thereon, to which the metal element  12  is attached. 
   In yet another embodiment, as shown in  FIG. 2 , the metal element  12  comprises a round wire that is flattened and patterned with a plurality of knurls. The flattening and knurling may be accomplished in one step or in two separate steps. The metal element  12  of  FIG. 2  may alternately represent a wire mesh. As in the connection of  FIG. 1 , the flattened, knurled wire or wire mesh  12  is welded to the cable  22 . 
     FIGS. 3–11  illustrate a variety of electrical connections  10  in accordance with alternate embodiments of the invention. 
     FIG. 3  is a perspective view of an electrical connection  10  in accordance with another embodiment of the invention wherein the metal element  12  includes a crimp portion  17  and a strain relief  13  providing minimization of deleterious effects from thermal expansion mismatches between materials.  FIG. 4  shows in perspective view the electrical connection of  FIG. 3  after drying, firing, and disposing a glass potting seal  24  thereon. 
     FIG. 5  is perspective view of an electrical connection  10  in accordance with another embodiment of the invention wherein the metal element  12  includes a crimp portion  17 , a strain relief portion  13 , and a clip portion  19  for securing the electrical connection  10  until the conductive material  16  is dried. Thereafter, the clip configuration of this embodiment provides increased mechanical strength to the overall electrical connection  10 .  FIG. 6  is a perspective view of the electrical connection  10  of  FIG. 5  after drying, firing, and disposing a glass potting seal  24  thereon. 
     FIG. 7  is a perspective view of an electrical connection  10  in accordance with yet another embodiment of the invention wherein the metal element  12  includes a crimp portion  17 , a strain relief portion  13 , and a clip portion  19  for securing the electrical connection  10  until the conductive material  16  is dried.  FIG. 8  is a perspective view of the electrical connection of  FIG. 7  after drying, firing, and disposing a glass potting seal  24  thereon. 
     FIG. 9  is a perspective view of a sandwiched electrical connection  10  in accordance with another embodiment of the invention. In this embodiment, the metal element  12  is sandwiched between the cover plate  18  and second element  14  eliminating the need for a glass potting seal. The connection is protected by the cover plate  18  and element  14 . 
     FIG. 10  is a perspective view of a sandwiched electrical connection  10  in accordance with another embodiment of the invention. As in 
     FIG. 9 , the metal element  12  is sandwiched between the cover plate  18  and the second element  14  eliminating the need for a glass potting seal. 
     FIG. 11  is a perspective view of a sandwiched electrical connection  10  in accordance with yet another embodiment of the invention. Again, the metal element  12  is sandwiched between the cover plate  18  and the second element  14  eliminating the need for a glass potting seal. 
   In a particularly advantageous feature of the present electrical connection, the metal element  12  configured with a plurality of openings or knurls provides increased surface area for the conductive material  16  to contact thereby forming in combination an electrical and a mechanical connection. 
   After the conductive material  16  onto one or both of the metal element  12  and second element  14 , the metal element  12  and the second element  14  are brought into contact so that the conductive material  16  seeps through the holes or mesh of the metal element  12  or around and about the knurls of the metal element  12 . The thus formed electrical and mechanical connection  10  is then dried in an oven, typically at a temperature of about 120° C., and fired in an oven, typically at a temperature of about 1300° C., although drying and firing temperatures are selected in accordance with the particular materials. 
   Preferably, the connection  10  is covered with a high temperature-resistant protective seal such as a glass seal  24  that is disposed upon the electrical and mechanical connection. For example, the connection  10  may be covered with a protective seal such as glass potting  24  providing additional mechanical strength and preventing corrosion from attacking the conductive material  16 . In the embodiments comprising sandwiched connections, such as illustrated in  FIGS. 9–11 , the need for a glass  24  potting is eliminated. 
   The invention contemplates an electrical connection  10  generally, and is particularly suitable for use in harsh, high temperature environments such as internal combustion engine exhaust streams, for example. The second element  14 , to which the metal element  12  is attached may be, for example, but is not limited to, a gas sensor such as a NOx sensor, etc., a temperature sensor, a plasma reactor connection, among others. 
   The conductive material  16  may be disposed so as to completely cover the metal element  12 . Alternately, the conductive material  16  may be disposed so as to cover the metal element  12  only in the area where the electrical and mechanical connection to the second element  14  is to be made. For example, in one embodiment, the metal strip  12  is plated (e.g., coated) with a precious metal at the top and bottom portions of the metal strip  12  only where the holes or projections are disposed. In another embodiment, the entire metal strip  12  is plated with a precious metal. 
   The conductive material  16  may be any suitable conductive material as known in the art, including, but not limited to, conductive ink pastes generally containing a metal such as a noble metal in a binder-adhesion system such as a spinel, glass frit, or alumina frit. The precious metal may be any metal and is preferably a metal that can withstand high temperature environments. Preferably, the precious metal is the same type of metal that occupies the pad or portion of the ceramic to which the electrical connection is being attached. 
   In a preferred embodiment, an excess amount of ink paste (i.e., conductive material  16 ) is disposed such as onto the ceramic pad  15 . The horizontal portion of the metal strip  12  is set down onto the excess ink. The ink will seep into the openings and/or around the knurls and overfill the top by some amount, depending on how much ink is used. The metal strip  12  is held in place by capillary action. 
   The electrical connection assembly is then dried and fired. After firing, the metal strip  12  is bonded to the sensor output wire  22  such as by any type of metal weld, including, but not limited to, a diffusion weld, a resistance weld, or a laser weld. The protective glass seal  24  is typically coated over the bonded area.