TEMPERATURE-STABLE COMPOSITE OF A STRANDED WIRE HAVING A CONTACT PAD

Abstract

The invention relates to an electrical element having at least one functional region and a contact surface, wherein a connecting element is arranged on the contact surface, wherein the connecting element comprises a stranded wire coated with sintered material, wherein the stranded wire is connected, in particular sintered, to the contact surface by a sintered material. Furthermore, the invention relates to a method for producing the electrical element according to the invention.

Claims

1. Electrical element having at least one functional region and a contact surface, wherein a connecting element is arranged on the contact surface, wherein the connecting element comprises a stranded wire coated with sintered material, wherein the stranded wire is connected, in particular sintered, to the contact surface by a sintered material, wherein the aspect ratio of the connecting element of height (h) to width (b) is in the range of 0.5 to 3.

2. Electrical element according to claim 1, wherein the electrical element is an electrical or electronic component, preferably a sensor.

3. Electrical element according to claim 1, wherein the sintered material comprises or consists of a precious metal, in particular silver.

4. Electrical element according to claim 1, wherein the stranded wire outside the connecting element is surrounded at least partially by an insulating layer.

5. Electrical element according to claim 1, wherein the stranded wire contains several individual wires, and wherein the individual wires are each at least partially coated with sintered material.

6. Electrical element according to claim 1, wherein the stranded wire contains several individual wires comprising a material selected from the group consisting of copper, silver, gold, nickel, or aluminum, or alloys thereof or combinations thereof.

7. Electrical element according to claim 1, wherein the contact surface in at least one dimension is at most 20% greater than the height of the connecting element.

8. Electrical element according to claim 1, wherein the contact surface comprises an alloy, in particular a silver alloy and very particularly preferably a silver-platinum alloy.

9. Method for producing a connecting element, in particular according to claim 1, on a contact surface, containing the steps of: a. providing a stranded wire, a contact surface, and a sintering agent, b. coating at least a part of the stranded wire with sintering agent to obtain a coated stranded wire, c. positioning the coated stranded wire on the contact surface, d. connecting the coated stranded wire to the contact surface by means of pressure sintering using a heated punch, to produce a connecting element, wherein the punch comprises a depression with an opening, wherein the depression in the punch partially receives the coated stranded wire during the connection process, and wherein the opening of the depression is larger than the diameter of the coated stranded wire so that the coated stranded wire is pressed onto the contact surface into the depression in the punch during pressure sintering.

10. Method according to claim 9, wherein the aspect ratio between the depth (t) of the depression to the width (w) of the opening of the depression is in the range of 0.5 to 3.

11. Method according to claim 9, wherein the stranded wire is at least partially surrounded by an insulating layer.

12. Method according to claim 9, wherein the stranded wire is coated with sintering agent by saturating, in particular by a dip coating.

13. Method according to claim 9, wherein the stranded wire has a cross-section whose aspect ratio is in the range of 0.5 to 2.

14. Method according to claim 9, wherein the individual wires of the stranded wire are stranded or braided.

15. Method according to claim 9, wherein the stranded wire is at least partially saturated with sintering agent so that the individual wires of the stranded wire are coated substantially completely with sintering agent.

Description

[0098] Further features and advantages of the invention become apparent from the following description, in which preferred embodiments of the invention are explained with reference to schematic drawings.

[0099] The Following are Shown:

[0100] FIG. 1 a sketch of the method from the prior art, in which a ribbon cable is fastened to a contact pad;

[0101] FIG. 2 a schematic illustration of the method according to the invention, in which a coated stranded wire is fastened to a contact pad using a heated punch;

[0102] FIG. 3 a cross-section of an embodiment of the connecting element according to the invention;

[0103] FIG. 4 a cross-section of an embodiment of a punch used according to the invention.

[0104] FIG. 1 illustrates the prior art. In FIG. 1a), a stranded wire 50 in the form of a ribbon coated with sintering agent 60 is positioned on a contact pad 20, wherein the contact pad is arranged on a substrate 10. The coated stranded wire is sintered to the contact pad by the heated punch 30. The heated punch 30 has an elevated edge. The circled region 40 represents sintered material and stranded wires that have been squeezed out.

[0105] In FIG. 1b), a stranded wire 50′ in the form of a ribbon coated with sintering agent 60′ is positioned on a contact pad 20′, wherein the contact pad is arranged on a substrate 10′. The coated stranded wire is sintered to the contact pad by means of the heated punch 30′. The heated punch 30′ has a planar pressure surface. The circled region 40′ represents squeezed-out, sintered material and stranded wires.

[0106] FIG. 2 schematically shows the exemplary sequence of the method according to the invention. First, a coated stranded wire 180 having an approximately round shape is positioned on a contact surface 121 of a contact pad 120. The contact pad 120 is fastened to a substrate 110. The stranded wire comprises a stranded wire 181 consisting of individual wires. The stranded wire is coated with sintering agent 182. Pressure is exerted on the coated stranded wire by means of the heated punch 130. The coated stranded wire 180 is thereby deformed and adapts to the depression in the heated punch 130. Since the opening of the depression in the heated punch 130 is greater than the diameter of the coated stranded wire 180, the coated and deformed stranded wire is delimited by the depression. The heated punch 130 exerts pressure on the stranded wire until the sintering agent 171 is sintered to the stranded wire and the contact surface 121. Subsequently, the heated punch 130 is lifted, and the resulting connecting element 170 is thus exposed. The connecting element 170 comprises a stranded wire 171 and sintered material 172.

[0107] FIG. 3 shows a cross-section of a connecting element 170′ according to the invention on a contact surface 121′ of a contact pad 120′. The connecting element has a width (b) in the contact region with the contact surface 121′. Furthermore, the connecting element has a height (h), which is measured from the contact surface 121′ to the highest point of the connecting element.

[0108] FIG. 4 schematically illustrates an exemplary heated punch 130′. The heated punch has an imaginary plane 132 which runs through the edge regions 133 of the opening. The opening in the heated punch 130′ has a width (w) along the imaginary plane 132 and between the edge regions of the 133. The depression 131 has a depth (t) which extends from the imaginary plane 132 to the lowest point of the depression 131. The volume (v) of the depression 131 is limited by the imaginary plane 132.

LIST OF REFERENCE SIGNS

[0109]

TABLE-US-00001 10, 10′ Substrate 20, 20′ Contact pad 30, 30′ Heated punch 40, 40′ Edge region after the pressure sintering 50, 50′ Stranded wire consisting of individual wires 60, 60′ Sintering agent 110, 110′ Substrate 120, 120′ Contact pad 121, 121′ Contact surface 130, 130′ Heated punch 131 Depression 132 Imaginary plane of the opening of the depression running through the edge regions 133 133 Edge region of the depression 170, 170′ Connecting element 171, 171′ Stranded wire consisting of individual wires 172, 172′ Sintered material 180 Coated stranded wire 181 Stranded wire consisting of individual wires 182 Sintering agent b Width of connecting element h Height of connecting element w Width of the opening of the depression in the heated punch t Depth of the depression

EXAMPLES

Exemplary Embodiment 1

[0110] A Pt thermistor was provided as a temperature sensor, e.g., a PT1000 designated as SMD-FC 0805 (Heraeus Nexensos GmbH, Germany). The size of the sensor was 2.1 mm×1.35 mm (W×L). The thermistor was applied to an aluminum oxide substrate.

[0111] The contact pads consisted of a screen-printed Ag—Pt alloy and contacted the Pt resistor structure at its ends. The contact surface of the contact pads was 0.5 mm×1.35 mm.

[0112] Two stranded wires having a diameter of 0.48 mm were used as the feed line. Each of the two stranded wires consisted of 19 individual copper wires having a diameter of 0.1 mm each. The individual copper wires were coated with a thin silver layer.

[0113] The stranded wires had insulation made of PTFE. At one end of each stranded wire, the insulation was removed by cutting in and pulling off in order to produce a contact region that is approximately 1.5 mm long.

[0114] The free ends of the stranded wire were immersed in a sintering paste (HERAEUS ASP 295-09P9) and then each positioned centrally on the two contact pads. The temperature sensor had a temperature of approximately 250° C. The temperature sensor was on a holder heated from below. The punch for pressure sintering the stranded wire ends, which were impregnated with sintering paste, to the contact pad had a rectangular punch surface which was adapted to the surface of the temperature sensor and was approximately 2 mm×3 mm (W×L) in size. There were two parallel, longitudinal notches in the punch surface. The longitudinal notches had a trapezoidal cross-section. The depth of the longitudinal notch was 0.3 mm, and the width of the opening was 0.5 mm.

[0115] While the sintering paste dried, the punch heated to 350° C. was lowered and pressed at a pressure of approx. 40 N/mm.sup.2 onto the two stranded wire ends impregnated with sintering paste. The stranded wire ends were deformed according to the structure predetermined by the longitudinal notches. The pressure was applied to the sintering paste with the stranded wire for about 10 seconds. The punch was then lifted off the connecting element produced. The punch surface, which consisted of oxidized copper alloy, was free of residues from the sintering paste, even after repeated use.

[0116] In a tensile test in which the temperature sensor was fixed, a rising tensile force was applied in the main axis of the stranded wire, i.e., in parallel to the surface of the sensor surface, using a tensile tester. The tensile strength of the connection was determined at the moment at which the connection detached. The tensile strength determined was 30 N.

[0117] In a permanent storage test, a temperature sensor with the connecting element according to the invention was stored for 140 hours at a temperature of 250° C. After completion of the temperature treatment, the connections had not detached.

[0118] In a change test, a temperature sensor having a connecting element according to the invention was cooled 40 times from 250° C. to 22° C. The connections did not detach.

COMPARATIVE EXAMPLE

[0119] In contrast to exemplary embodiment 1, a punch having a flat surface, i.e., a planar punch surface, was used for pressure sintering the connecting element.

[0120] The stranded wire ends were pressed flat and spread out so that the individual wires projected far beyond the contact pad.