High temperature connection

Abstract

 A method and apparatus for producing a permanent connection between a trace (10), such as platinum, of a substrate (2) is provided by placing a silver ring (11) over the trace (10) and placing a current lead (4) over the ring (11). This assembly is then heated, whereby the platinum is dissolved in the silver forming an alloy having a higher melting point than the silver. Preferably, a ceramic housing (6,6',8,) surrounds the interconnection.

Description

[0001] The present invention relates to an electrical connection and a method for producing the connection, for use in high temperature applications, and in particular in applications relating to connection to catalytic converters.

[0002] Automotive catalytic converters include a substrate having printed at the edges thereof, a printed circuit pad is provided, which could be a noble metal, such as platinum printing, and to which, a connection must be made.

[0003] The difficulty in providing this electrical connection, is that a current lead must be interconnected to the circuit pad. Standard electrical connectors are not useable in such applications as the operating temperatures can reach as high as 950°C. Standard metallic materials show rapid stress relaxation in such applications leading to loss of contact force. A permanent connection is needed which can withstand such high temperatures, and a connection such as high temperature soldering can also be considered, but the melting point of the solder is to close to the operating temperature.

[0004] The object of the invention then is to provide an electrical connection for use at higher temperatures.

[0005] It is a further object of the invention to provide an electrical connection between a current lead of a substrate for use at high temperature operating conditions.

[0006] The objects of the invention have been accomplished by a method of providing a permanent interconnection between a substrate trace and a current lead, which method is characterized by the steps of placing a precious metal intermediate the circuit trace and the current lead; heating the precious metal, the circuit trace and current lead to a first temperature where the precious metal melts, whereby the precious metal forms an alloy with the material of the circuit trace having a melting point at a second temperature which is higher than the first temperature.

[0007] Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which:-

Figure 1 is an isometric view of a first embodiment of the invention;

Figure 1A is an isometric view of a precious metal component for incorporation in the first embodiment of Figure 1;

Figure 2 is an isometric view of a ceramic housing half;

Figure 3 is an isometric view of the connector half shown in Figure 2 from the opposite side thereof;

Figure 4 is a cross sectional view through the assembly of Figure 1;

Figure 5 is a top plan view of an alternative embodiment of the invention of Figure 1-4;

Figure 6 is an end view of the current lead strip material shown in Figure 5;

Figure 7 shows a top plan view of an assembly method utilizing the current lead of Figures 5 and 6;

Figure 8 shows a side view of the assembly of Figure 7;

Figure 9 shows a side view similar to that of Figure 8 showing the current lead and substrate in position;

Figure 10 shows an upper plan view of a current lead strip material of a third embodiment of the invention; and

Figure 11 shows an end view of the material shown in Figure 10.

[0008] With reference first to Figure 1, an assembly is shown where the substrate 2 can be sandwiched between two ceramic housing portions, 6 and an intermediate ceramic housing portion 8. The current lead 4 can then be sandwiched between the intermediate ceramic portion 8 and a further ceramic housing portion 6', which is identical to housing portion 6. A silver ring 11 (Figure 1A) can be positioned between the substrate 2 and current lead 4, as will be described further herein.

[0009] With respect now to Figures 2 and 3, the ceramic housing portion 6 will be described in greater detail. The ceramic portion 6 is comprised of upper surface 12 having an alignment peg 14 centrally located therein. The ceramic housing portion 6 further comprises a forward platform portion 16 forming a rearwardly facing edge at 18. With respect now to Figure 3, the lower side of the housing portion 6 comprises a recessed axially extending section at 20 where a central raised section is positioned at 22. The section 22 includes an aperture at 24 which is concentrically positioned relative to the locating pin 14. The raised section 24 is somewhat U-shaped including a flat upper edge 26 and a U-shaped surface 28. As best shown in Figure 4, the lower platform portion 22 includes a lip section 30 surrounding the aperture 24 as will be described in greater detail herein. The housing portion 6 further includes side wall portions 23 which form inner side surfaces 21. The central section 22 upstands from surface 20 higher than the side wall portions 23.

[0010] With respect now to Figure 1, the substrate 2 includes a circuit trace positioned on top of insulative material, and includes a circular portion 10 surrounding an aperture 40. A silver ring 11 can be placed on top of the trace portion 10 or could otherwise be deposited thereon. The trace is comprised of a noble metal, such as a platinum printing, on top of the substrate 2. The substrate 2 has an outwardly projecting section at 42 proximate to a front side edge 44 thereof and it should be appreciated that another such projecting portion 42 as well as trace portion 10 are provided at the opposite side 46.

[0011] The upper ceramic housing half 8 includes an opening 50 having an upper flat surface at 52 and a U-shaped portion at 54. The ceramic housing portion 8 has side edges 55, such that the distance therebetween, is less than the distance between side surfaces 21 of the lower housing portion 6.

[0012] The current lead 4 is provided with a connection section at 60 which is pressed downwardly through the plane of the material forming the lead. This section 60 is formed with a straight portion at 62 and a U-shaped portion at 64, and it should be appreciated that the connection portion 60 can be positioned within the opening 50 in the ceramic housing part 8. A central aperture 66 is provided such that the aperture 66 is positionable over the central pin 14 of the ceramic housing portion 6. An identical housing portion 6' is positioned at the upper region of the assembly as shown in Figure 1 to complete the assembly thereof.

[0013] With respect now to Figures 1 and 4, the assembly of the connection will be described in greater detail. The substrate 2 is first positioned on top of surface 12 such that the aperture 40 overlies the pin 14 on the ceramic porticn 6. The ceramic portion 8 is then placed above the substrate 2 with the aperture 50 overlying the aperture 40 of the substrate 2. The housing portion 8 will move somewhat laterally to allow for perfect alignment of the aperture 50 with the aperture 40. However the lower edge 56 of the ceramic housing portion 8 is positionable against the counter shoulder 18 on the housing portion 6 to longitudinally align the two housing portions 6 and 8.

[0014] The current lead 4 can now be positioned over the housing portion 8 such that the projecting portion 60 is situated within the aperture 50 and such that the aperture 66 is positioned over the pin portion 14. This places the lower surface of the lead portion 4 directly against the silver ring 11 found on the substrate 2. As mentioned above, the side counter ribs 23 upstand from the surface 20 only enough to take up the thickness of the current lead 4, whereas the central portion 22 upstands higher than the counter ribs 23, as measured from the surface 20. Therefore, when the housing portion 6' is positioned above the current lead 4, the projecting portion 22' of the housing portion 6' is positioned within the portion 60 of the current lead 4, and partially into the opening 50 of the ceramic housing portion 8, with the lower aperture 24' being aligned with the pin 14.

[0015] It should be appreciated that as assembled, the substrate 2 and current lead 4 are sandwiched between the lower surface of portion 22' and the surface 12 of portion 6, as best shown in Figure 4. This also positions the silver ring 11 intermediate the trace 10 and a lower surface of the current lead 4. As also shown in Figure 4, as assembled, the housing portion 6' has a lip portion 30' surrounding the lower aperture 24'. The lip portion 30' should be so profiled that, it extends through aperture 66 of the current lead 4, and will contact the upper surface of the substrate 2. This prevents any silver 11 from flowing against the edge 40 of the substrate, thereby shorting it out.

[0016] In the preferred embodiment of the invention the material of the current lead should be resistant to rapid oxidation at the high working temperature. Options for such material are stainless steel, oxidation-resistance steel, or constantan. However in the preferred embodiment, the current lead should be nickel-plated to make the best interconnection.

[0017] It has been found that when a nickel-plated metal has been used as the current lead, and that the silver ring 11 is positioned intermediate the current lead 4 and the platinum trace 10, that when heated in air to 1000°C, the platinum dissolves in the molten silver, changing it into an alloy with a higher melting point, and that this formed a permanent interconnection between the platinum trace 10 and the current lead 4.

[0018] Figures 5-9 show an alternative embodiment of the invention where current leads are stamped at 104 to provide a projecting contact section 160 for placement over the trace portion 134 of the substrate 102. Ceramic housing 106 has an inner cavity 150 which can receive the lead 104, the silver ring 111 and the substrate 102. Heating of the assembly would take place as previously mentioned above.

[0019] Finally a third embodiment of the invention is shown with respect to Figures 10 and 11 where current leads 204 are formed by providing the base material with inlay silver 211 such that the projecting contact portion 260 is formed at the inlay material such that the silver will be placed against the trace on the substrate.

Claims

1. An apparatus for forming a permanent electrical interconnection between a circuit trace (10) and a current lead (4) which is formable upon heating the apparatus to a first temperature, characterized in that the apparatus comprises a housing (6, 8, 6') to position the circuit trace (10) relative to the current lead (4), a precious metal component (11) being meltable at the first temperature, the circuit trace (10) comprising a material that interacts with the precious metal (11) at the first temperature to form an alloy having a melting point at a second temperature, that is higher than the first temperature, whereby this alloy permanently interconnects the circuit trace (10) and the current lead (4).

2. The apparatus of Claim 1, characterized in that the circuit trace (10) includes platinum.

3. The apparatus of Claim 1 or 2, characterized in that the precious metal component (11) is silver.

4. The apparatus of any one of Claims 1-3, characterized in that the circuit trace (10) and the current lead (4), include an alignment feature (40, 66) engageable by a mating feature (14) of the housing to maintain positioning therein.

5. The apparatus of any one of Claims 1-4, characterized in that the housing (6, 8, 6') includes a lip portion (30, 30') extending across the interface between the circuit trace (10) and the current lead (4) to prevent leakage of the precious metal therefrom at the first temperature.

6. The apparatus of any one of Claims 1-5, characterized in that the first (6) and second (6) housings are identical.

7. The apparatus of any one of Claims 1-6, characterized in that the housings (6, 8, 6') are stackable.

8. A method of providing a permanent interconnection between a circuit trace (10) and a current lead (4), characterized by the steps of:
   placing a precious metal (11) intermediate the circuit trace (10) and the current lead (4);
   heating the precious metal (11), the circuit trace (10) and current lead (4) to a first temperature where the precicus metal (11) melts, whereby the precious metal (11) forms an alloy with the material of the circuit trace (11), having a melting point at a second temperature which is higher than the first temperature.

9. A method according to claim 8, characterized in that the conductive trace (10) is platinum printing.

10. A method according to claim 8 or 9, characterized in that the precious metal (10) is silver.

11. A method according to any of claims 8-10, characterized in that the first temperature is approximately 950°C.

12. A method according to any of claims 8-11, further characterized by a ceramic housing (6, 8, 6') surrounding the connection.

Drawing