Thermistor, Varistor Or Capacitor Component With A Fusible Connecting Element Between The Main Body Of The Component

Abstract

The present invention relates to a component which comprises a main body (9) and at least one external electrode (1) which is fastened by a connecting material (4) to the main body (9), wherein the main body (9) and the external electrode (1) have different coefficients of thermal expansion which determine a critical temperature which when exceeded results in a connection between the main body (9) and the external electrode (1) experiencing mechanical stresses which lead to damage to the component, wherein the connecting material (4) has a melting point which is lower than a critical temperature.

Claims

1-16. (canceled)

17. A component comprising: a main body and at least one external electrode that is fastened by a connecting material to the main body, the main body and the external electrode have different coefficients of thermal expansion that determine a critical temperature which, when exceeded, results in a connection between the main body and the external electrode experiencing mechanical stresses that lead to damaging to the component, wherein the connecting material has a melting point that is lower than the critical temperature.

18. The component according to claim 17, wherein the connecting material is a solder material.

19. The component according to claim 18, wherein the solder material comprises tin and bismuth.

20. The component according to claim 18, wherein the solder material comprises tin in a proportion of from 35% by weight to 50% by weight and bismuth in a proportion of from 50% by weight to 65% by weight.

21. The component according to claim 17, wherein the melting point of the connecting material is less than 150° C.

22. The component according to claim 17, wherein the melting point of the connecting material is less than 140° C.

23. The component according to claim 17, wherein the main body comprises a ceramic material.

24. The component according to claim 17, wherein the main body comprises at least one main-body electrode comprising silver.

25. The component according to claim 24, wherein the at least one external electrode is fastened by the connecting material to the at least one main-body electrode of the main body.

26. The component according to claim 17, wherein the main body and the at least one external electrode are pressed against one another by a prestressing unit.

27. The component according to claim 17, wherein the connecting material is arranged on a surface of the main body and encloses a wetting angle with the surface at which the connecting material, when in a liquid state, remains between the main body and the external electrode.

28. The component according to claim 17, wherein the connecting material has a higher specific resistance than the main body and the external electrode.

29. The component according to claim 17, wherein the at least one external electrode comprises copper or Invar.

30. The component according to claim 29, wherein the at least one external electrode has a copper-Invar-copper layer structure.

31. The component according to claim 17, wherein the component comprises a second external electrode that is fastened by the connecting material to the main body.

32. The component according to claim 17, wherein the component is a thermistor, a capacitor or a varistor.

33. The component according to claim 17, wherein the component is a PTC heating element or an inrush current limiter comprising an NTC ceramic.

34. The component according to claim 17, wherein the component is an electronic component or an electric component.

35. A component comprising: a main body having a surface with a main-body electrode thereon, the main body being made of a material having a first coefficient of the thermal expansion; an external electrode positioned away from the main body, the external electrode being made of a material having a second coefficient of the thermal expansion that is different from the first coefficient of thermal expansion; and a connecting material located between and making contract with the main-body electrode and the external electrode, the connecting material having a melting point that is below at least some of the operational temperatures of the component such that the connecting material changes from a solid state to a liquid state to relieve the mechanical stresses from the different coefficients of thermal expansion of the main body and the external electrode, the connecting material maintaining electrical connection between the main-body electrode and the external electrode when in both the liquid state and the solid state.

36. The component according to claim 35, further including a prestressing unit that exerts a force between the main body and the external electrode to assist in maintaining electrical connection between the main-body electrode and the external electrode when the connecting material is in the liquid state.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] A preferred working example of the component is illustrated below with the aid of the figure.

[0027] FIG. 1 shows a schematic view of a component.

DETAILED DESCRIPTION OF THE DRAWINGS

[0028] FIG. 1 shows a component. The component in the working example shown here is a thermistor, in particular an NTC thermistor.

[0029] The component comprises a main body 9 which comprises a disk 3 composed of an NTC material. Furthermore, the main body 9 has two electrodes 2. The electrodes 2 are arranged on opposite sides of the disk 3. The electrodes 2 comprise silver or consist of silver. The electrodes 2 are very thin. The electrodes 2 can, for example, have been applied by means of a screen printing process to the disk 2. The present invention is not restricted to the main body 9 shown in FIG. 1. For example, the main body 9 could also have a multilayer structure.

[0030] For electrical contacting of the component, the component has two external electrodes 1. The external electrodes 1 can comprise copper or consist of copper. A first external electrode 1 is joined by a connecting material 4 to one of the electrodes 2 of the main body 9. A second external electrode 1 is joined by the connecting material 4 to the other electrode 2 of the main body 9.

[0031] The connecting material 4 is a solder material. Accordingly, the external electrodes 1 are joined by a solder connection to the main body 9. The solder material is a tin-bismuth compound. In particular, the solder material can comprise 42% by weight of tin and 58% by weight of bismuth. The solder material can have a melting point of 138° C.

[0032] The external electrodes 1 are connected via leads 6 to a voltage source 5. A voltage can be applied between the external electrodes 1 by means of the voltage source 5. Accordingly, the voltage source 5 can apply a voltage to the component via the external electrodes 1.

[0033] In such components, there is a risk of damage to the component by mechanical stresses which can arise when the component is heated to above a critical temperature. The external electrode 1 and the main body 9 have different coefficients of thermal expansion. There is therefore a critical temperature for a connection between the external electrodes 1 and the main body 9. If the external electrodes 1 and the main body 9 are heated, they expand to a different extent because of their different coefficients of thermal expansion, so that mechanical stresses arise. The critical temperature is defined as the temperature at which the mechanical stresses occurring at the connection between the external electrode 1 and the main body 9 become so large that damage to the component occurs. The damage can, for example, be in the form of a fracture.

[0034] The connecting material 4 used here is selected so that its melting point is below the critical temperature of the connection between the main body 9 and the external electrode 1. Accordingly, the connecting material 4 melts before damage to the component can occur as a result of excessive heating. Any mechanical stresses are immediately dissipated by melting of the connecting material 4. The component is accordingly constructed so that damage cannot occur as a result of mechanical stresses arising from overheating to above the critical temperature of the component.

[0035] The component additionally comprises a prestressing unit 10. The prestressing unit 10 ensures that the main body 9 and the external electrodes 1 remain in contact with one another when the connecting material 4 melts. The prestressing unit 10 presses the external electrodes 1 against the main body 9.

[0036] The prestressing unit 10 comprises two springs 7 and a support 8. The support 8 surrounds the component or consists of two elements which are arranged on opposite sides of the component.

[0037] Here, a first spring 7 is arranged on the side of the main body 9 on which the first external electrode 1 is arranged. The first spring 7 is clamped between the support 8 and the first external electrode 1. The first spring 7 presses the first external electrode 1 against the main body 9 with a clamping force. The second spring 7 is arranged on the opposite side of the main body 9, i.e. on the side on which the second external electrode 1 is arranged. The second spring 7 is arranged between the support 8 and the second external electrode 1. The second spring 7 presses the second external electrode 1 against the main body 9 with a clamping force. The clamping forces exerted on the main body 9 by the first and second spring 7 act in opposite directions, so that the main body 9 and the two external electrodes 1 are pressed together. When the connecting material 4 melts, electrical contact and a mechanical connection between the external electrodes 1 and the main body 9 remain since the prestressing unit 10 ensures that the external electrodes 1 are pressed against the main body 9.

[0038] The connections between the external electrodes 1 and the main body 9 are such that the connecting material 4 remains in its position between the main body 9 and the respective external electrode 1 even after the connections have melted. In order to achieve this, a connecting material 4 having an appropriate contact angle can be selected. The appropriate contact angle can be present in the liquid state of the connecting material. Appropriate selection of the contact angle ensures that the connecting material 4 does not flow out from the main body 9. A very large contact angle is selected here.

[0039] The component can be configured so that when the component is heated, the connecting material 4 is heated more quickly than the external electrodes 1 and the main body 9. In particular, the connecting material 4 can have a higher specific resistance than the external electrodes 1 and the main body 9. Accordingly, it is ensured that the connecting material 4 is heated to a temperature which is greater than its melting point before the external electrodes 1 and the main body 9 are heated to the critical temperature and can suffer from excessive mechanical stresses due to different coefficients of expansion.

[0040] When the component is cooled, the connecting material 4 becomes solid again when the temperature goes below a solidification temperature. Since the connecting material 4 in the liquid state remains in its position between external electrode 1 and main body 9, the connecting material 4 connects the external electrodes 1 and the main body 9 to one another again after it has solidified.

[0041] Since the state of matter of the connecting material 4 between the main body 9 and the external electrodes 1 changes before heating to the critical temperature and, in particular, the connecting material 4 becomes liquid, destructive mechanical stresses do not occur in the component. Since the connecting material 4 solidifies again and mechanically connects the external electrode 1 and the main body 9 after a cooling phase, a good mechanical and electrical connection is produced, and this will melt again in the next heating cycle.

[0042] If the connecting material 4 is a solder material, aging mechanisms which could otherwise limit the life of a component having solder connections can also be eliminated by the liquefaction of the solder material.

LIST OF REFERENCE NUMERALS

[0043] 1 External electrode

[0044] 2 Electrode

[0045] 3 Disk

[0046] 4 Connecting material

[0047] 5 Voltage source

[0048] 6 Lead

[0049] 7 Spring

[0050] 8 Support

[0051] 9 Main body

[0052] 10 Prestressing unit