Patent Application
20050217889
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.
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.
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.
Referring now to the drawings, which are meant to be exemplary, not limiting, and wherein like elements are numbered alike in the several Figures:
Referring now to
The metal element 12 of
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 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
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 disposing 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 ink 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 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 poison from attacking the conductive material 16. In the embodiments comprising sandwiched connections, such as illustrated in
The invention contemplates an electrical connection generally, and is particularly suitable for use in harsh, high temperature environments such as internal combustion engine exhaust stream environments, 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 may be disposed so as to cover the meal element 12 only in the area where the electrical and mechanical connection to the second element 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 only where the holes or projections are disposed. In another embodiment, the entire metal strip 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) is disposed such as onto the ceramic pad 16. 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 is typically coated over the bonded area.
While the invention has been described by reference to certain preferred embodiments, it should be understood that numerous changes could be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the disclosed embodiments, but that it have the full scope permitted by the language of the following claims.
The present application claims priority to U.S. Provisional Application No. 60/558,793, (Attorney Docket No. DP-311595), 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.
| Number | Date | Country | |
|---|---|---|---|
| 60558793 | Apr 2004 | US |
