NTC SENSOR AND METHOD OF MANUFACTURING AN NTC SENSOR

Abstract

In an embodiment a NTC sensor include a chip, two parallel wires, each wire having contact points, and contact-connections between the chip and the contact points of each of the wires, wherein a maximum lateral dimension of the NTC sensor in any direction perpendicular to a direction of extension of the wires is equal to or less than a sum of the lateral dimensions of the chip and the wires.

Claims

1.-19. (canceled)

20. A NTC sensor comprising: a chip; two parallel wires, each wire having contact points; and contact-connections between the chip and the contact points of each of the wires, wherein a maximum lateral dimension of the NTC sensor in any direction perpendicular to a direction of extension of the wires is equal to or less than a sum of the lateral dimensions of the chip and the wires.

21. The NTC sensor according to claim 20, wherein the maximum lateral dimension of the NTC sensor s not greater than a lateral dimension of the chip in the same direction.

22. The NTC sensor according to claim 20, wherein the lateral dimension of the chip in any direction perpendicular to the direction of extension of the wires is not greater than a total dimension of the two wires in the same direction.

23. The NTC sensor according to claim 20, wherein the chip has a maximum lateral extension of 0.6 mm.

24. The NTC sensor according to claim 20, wherein the chip is a ceramic multilayer component with internal electrodes.

25. The NTC sensor according to claim 20, wherein the chip comprises a monolithic NTC thermistor ceramic.

26. The NTC sensor according to claim 20, wherein the two wires are in direct contact with each other.

27. The NTC sensor according to claim 20, wherein end faces of the wires act as contact points on which the chip is placed.

28. The NTC sensor according to claim 20, wherein contact points of the wires are L-shaped, and wherein the chip is placed on the L-shaped contact points.

29. The NTC sensor according to claim 20, wherein the contact points are formed by exposing the wire from an insulating sheath.

30. The NTC sensor according to claim 20, wherein the contact-connections are formed by a small amount of solder.

31. The NTC sensor according to claim 20, wherein contacts are formed by electrically conductive adhesive.

32. The NTC sensor according to claim 20, further comprising a sensor head encased by a polymer material, wherein the sensor head comprises the chip and the contact-connections.

33. The NTC sensor according to claim 32, wherein a lateral dimension of the sensor head including the encasing polymer material in any direction perpendicular to the direction of extension of the wires is not greater than twice a total dimension of the two wires in the same direction.

34. A method for manufacturing an NTC sensor, the method comprising: providing two wires having contact points; providing a chip comprising an NTC thermistor ceramic; arranging the chip at the contact points of the wires so that a maximum lateral dimension of the NTC sensor in any direction perpendicular to a direction of extension of the wires is less than a sum of the lateral dimensions of the chip and the wires; and forming a mechanical connection and an electrical contact between the chip and the wires by soldering or by applying conductive adhesive.

35. The method according to claim 34, wherein a heat required for soldering is provided by self-heating of the NTC thermistor ceramic when an electrical voltage is applied.

36. The method according to claim 34, wherein the conductive adhesive is cured by self-heating of the NTC thermistor ceramic when an electrical voltage is applied.

37. The method according to claim 34, wherein the conductive adhesive is cured by irradiation with UV light.

38. The method according to claim 34, further comprising: arranging the wires in parallel; forming a plurality of contact points along the wires by exposing the wires from an insulating sheathing; placing a chip on each of the contact points; and subsequently cutting the wires between the chips so that a plurality of NTC sensors are obtained.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0121] FIG. 1 shows a first example of the NTC sensor;

[0122] FIG. 2 shows a first example of the NTC thermistor chip;

[0123] FIG. 3 shows a second example of the NTC sensor;

[0124] FIG. 4 shows a third example of the NTC sensor;

[0125] FIG. 5 shows a fourth example of the NTC sensor; and

[0126] FIG. 6 shows an example of an NTC sensor with a sheath.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0127] FIG. 1 shows a first example of the NTC sensor 100.

[0128] A chip 1 and two wires 2 are provided. Chip 1 comprises an NTC thermistor material. NTC stands for Negative Temperature Coefficient. This means that the thermistor material has a lower electrical resistance at higher temperatures (hot conductor).

[0129] The chip 1 is shown in FIG. 2 and has a cuboid structure. The chip measures a maximum of 0.6 mm in length L, 0.3 mm in width W and 0.33 mm in height H. The chip is electrically contacted at both ends in the longitudinal direction by outer electrodes 3. The outer electrodes 3 are preferably placed on the two ends in the longitudinal direction in the shape of a cap.

[0130] The outer electrodes 3 comprise metallization layers made of silver, for example, which are applied using an immersion process with subsequent baking. NiSn layers can also be applied by electroplating.

[0131] In the embodiment example, the chip 1 is designed as a ceramic multilayer component with internal electrodes. A metallic inner electrode is arranged between every two ceramic layers. The inner electrodes are preferably electrically contacted alternately by the two outer electrodes 3.

[0132] The electrical resistance of such a multilayer component can be set very precisely. The resistance tolerance, i.e. the possible deviation of the resistance from a specified, desired electrical resistance at a nominal temperature, is less than 1%.

[0133] Alternatively, in an embodiment not shown here, the chip 1 can comprise a monolithic NTC ceramic block. The NTC ceramic block has no internal electrodes and is easy to manufacture. Outer electrodes 3 are applied to two opposite sides of the NTC ceramic block, which preferably cover the entire side surface of the ceramic block and via which the NTC ceramic block can be electrically contacted.

[0134] The wires 2 are, for example, silver-plated nickel wires, copper wires, stranded copper wires, NiFe or CrNi wires with Cu, Ag or Pt sheathing.

[0135] The wires 2 are preferably wrapped in an electrically insulating sheath 4. The sheath 4 consists of an electrically non-conductive polymer material such as perfluoroalkoxy alkane (PFA), Teflon, polyurethane (PU), polyamide (PA), polyimide (PI), silicone, polyester, polyacrylate, epoxy polymers, resins, or epoxy resins.

[0136] The two wires 2 have blunt ends 5 at their end faces, at which the electrically conductive wires are exposed. The blunt ends 5 thus represent contact points to which the chip 1 is attached.

[0137] There are several possible procedures for this.

[0138] According to a first exemplary process, the blunt ends 5 of the wires 2 are dipped into a solder paste and thus small amounts of solder paste are applied to the blunt ends 5 of the wires 2. The blunt ends 5 of the wires 2 are then arranged with the applied solder paste on the two opposing outer electrodes 3 of the chip 1.

[0139] An electrical voltage is then applied to chip 1 via the wires. When the electrical voltage is applied, chip 1 heats up and the solder paste melts. The flux in the solder paste is volatilized and the solder is hardened by subsequent cooling. Thus, a solder connection between the outer electrodes 3 and the contact points of the wires 2 is obtained exclusively by the self-heating of the chip 1 when an electrical voltage is applied.

[0140] The method described enables the application of the minimum amount of solder paste required to obtain a reliable connection between the chip 1 and the wires 2. The dimensions of the sensor head, which comprises the chip 1 and the connecting wires 2, can thus be minimized.

[0141] In an alternative method, the chip 1 is glued onto the contact points of the wires 2. To do this, the blunt ends 5 of the wires 2 are dipped into a thermosetting adhesive. The blunt ends 5 of the wires are then applied to the outer electrodes 3 of the chip 1. By applying an electrical voltage to the wires, the chip 1 is heated and the thermosetting adhesive is hardened.

[0142] In an alternative method, the chip 1 is also glued to the contact points of the wires 2. For this purpose, the blunt ends 5 of the wires 2 are dipped into a UV-curable adhesive. The blunt ends 5 of the wires 2 are then applied to the outer electrodes 3 of the chip 1. The adhesive is then hardened by irradiation with UV light.

[0143] The adhesive is electrically conductive. Examples of such adhesives are polymer-based adhesives that contain electrically conductive metallic particles such as silver particles. The method described enables the application of minimal amounts of adhesive to create the connection between chip 1 and wires 3, so that the dimensions of the sensor head can be minimized.

[0144] Furthermore, the geometry of the sensor head is optimized by a suitable dimension of the chip 1 and by an advantageous arrangement of the chip 1 on the wires 2.

[0145] Thus, in the present method, a chip 1 is used which is no longer than the sum of the two diameters of the two adjacent wires 2 and no wider than the diameter of one wire 2.

[0146] The length L is understood here and in the following as the dimension of the chip 1 between the two outer electrodes 3. This direction of expansion corresponds to the direction in which the two wires 2 lie next to each other.

[0147] The width W of chip 1 is referred to here and in the following as the perpendicular direction of expansion of the contact surfaces between chip 1 and wire 2. Height H here and in the following refers to the direction perpendicular to the contact surface.

[0148] Chip 1 is positioned here on the blunt ends 5 of the two adjacent wires 2. Due to the dimensions of the chip 1, it does not protrude beyond the wires 2 in either length or width. The sensor head is therefore no longer or wider than the remaining double wire 2.

[0149] FIG. 3 and FIG. 4 show a second and third embodiment example of the NTC sensor 100. Features of the second and third embodiment examples, which correspond to the first embodiment example, are not explicitly described.

[0150] In contrast to the first embodiment example, the wires 2 in the second and third embodiment examples have L-shaped ends 6. The end faces of the wires are therefore not blunt but are shaped into a blade.

[0151] L-shaped here means that the wires 2 are flattened at their ends. The flat sections of the wires 2 therefore have a geometry that is similar to a shovel blade. The L-shaped ends 6 of the wires 2 can be applied laterally to the outer electrodes 3 of the chip 1. The L-shaped ends 6 have the advantage over the blunt ends 5 of the wires 2 that the contact surfaces between the wires 2 and the chip 1 are larger.

[0152] The L-shaped ends 6 of the wires 2 can either be placed on the cap-shaped outer electrodes 3 at two opposite ends, as shown in FIG. 3, or contact them from the same side, as shown in FIG. 4.

[0153] If both outer electrodes 3 are contacted from the same side, both outer electrodes 3 must be present on one side surface of the chip 1.

[0154] The exact arrangement depends primarily on practicability during production. The L-shaped ends 6 of the wires 2 have very small dimensions, which are negligible compared to the diameter of the non-flattened sections of the wires 2. Thus, even in the described arrangement of the second and third embodiment example, the sensor head has hardly any larger dimensions than the dimensions along the remaining double wire 2.

[0155] In the current design example, the contact surfaces between the wires and the chip can be made sufficiently large to achieve reliable contacting with low connection resistance.

[0156] The large contact surfaces also increase the mechanical stability of the sensor. If the chip is arranged between the wires as shown in FIG. 4, the mechanical stability of the sensor can be further improved.

[0157] FIG. 5 shows a fourth embodiment example of the NTC sensor 100. Features of the fourth embodiment example, which correspond to the first embodiment example, are not explicitly described.

[0158] In contrast to the first embodiment example, the wires 2 in the fourth embodiment example are not yet cut to their final size but are present as a complete wire spool 200. Before the manufacturing process, a section of a defined length is unwound from the wire spool 200.

[0159] Contact points 7 are then exposed on the sides of the wires 2 by removing the insulating sheathing 4 at the contact points 7 up to the electrically conductive wire 2. Two adjacent contact points 7 are always exposed on both wires 2. In the embodiment example, the sheath 4 is preferably removed in such a way that the entire chip 1 can be applied directly to the wires 2 and the sensor head comprising the wires 2 and the chip 1 does not have unnecessarily large dimensions.

[0160] As in the previous embodiment examples, the chip 1 can be attached to the wires 2 both by gluing and soldering. For this purpose, small amounts of solder paste or adhesive are preferably applied to the exposed contact points 7 using a dispensing device. The chips 1 can then be applied to the contact points 7. By applying an electrical voltage, the connections to all the chips 1 applied to the wires 2 can then be soldered simultaneously or the adhesive can be cured simultaneously.

[0161] After the chips 1 have been completely applied, the double wires 2 with chips 1 are each cut between the chips 1 in order to obtain the desired individual sensors 100.

[0162] The process described can save work steps and simplify the mass production of chips 1.

[0163] Regardless of the embodiments described above, the sensor head is encased in a polymer material for protection against external mechanical influences, for protection against contamination, for protection against moisture and for electrical insulation.

[0164] FIG. 6 shows an exemplary NTC sensor with sheath 8. The dimensions of the sensor shown in FIG. 6 in the direction in which the wires HL and CL extend and the dimensions perpendicular to them are to be understood as examples only and do not necessarily correspond to the dimensions of the NTC sensor according to the invention.

[0165] The dimension HL here is the dimension of the sensor head from the wire ends in the direction in which the wires extend. The dimension CL is the dimension of the entire encasing coating 8 around the sensor head and the wires in the direction in which the wires extend. The dimension HD is the diameter of the rotationally symmetrical sheath in a direction perpendicular to the direction in which the wires extend.

[0166] The coating is carried out after the chip 1 is connected to the wires 2. The polymer material can be applied using various methods.

[0167] For example, the sensor head can be immersed in a reservoir of polymer powder and then heated by applying an electrical voltage. This melts the polymer powder and forms a thin encasing polymer coating around the sensor head. This process allows a very thin coating 8 to be formed and the dimensions of the sensor head can thus be further minimized.

[0168] Preferably, the lateral dimension of the sensor head HD including the encasing polymer coating 8 in any direction perpendicular to the direction of extension of the wires is not more than twice the total dimension of the two wires in the same direction and even more preferably not more than the total dimension of the two wires in the same direction.

[0169] In addition, thermal post-treatment in an oven can be carried out to increase the degree of hardening.

[0170] In an alternative process, the sensor heads are immersed in already liquefied polymer material to form the encasing coating 8. After immersion, the encasing coating 8 must be cured.

[0171] According to a third possible method, a shrink tube is placed over the sensor head and shrunk in the oven by applying heat. By selecting the shrink parameters, the shrinkage can be adjusted so that the sensor heads are completely and tightly encased.

[0172] In another process, a polymer powder is electrostatically charged and fluidized in a fluid bed by supplying a gas stream. The electrostatically charged powder particles adhere to the sensor head immersed in the fluid bed and can then be heated, melted, and subsequently cured in the oven.

[0173] All four methods described above enable the application of an advantageous thin polymer coating 8 to protect the sensor head.

[0174] In a mass production process, the encasing polymer coating can be applied around the sensor head before the individual NTC sensors 100 are separated by cutting the wires 2 from a wire spool 200.