EP2506281B1 - Temperature-dependent circuit with series resistor - Google Patents

Description

The present invention relates to a temperature-dependent switch with a temperature-dependent switching mechanism, a derailleur receiving housing having an upper part with a first outer terminal and an electrically conductive lower part with an outer bottom, with a support plate on top of a heating resistor and two with the Heating resistor connected solder pads are arranged, wherein the bottom of the lower part rests on the heating resistor and the lower part is soldered to the first soldering surface and the second soldering surface serves as a second external connection.

Such a switch is from the DE 43 36 564 C2 known.

The well-known switch is designed as a sealed switch with two-piece metal housing, as he also for example from the DE 21 21 802 A or the DE 196 23 570 C2 is known. The encapsulated switch is arranged on a carrier plate made of ceramic, on which a thick-film resistor is arranged as a heating resistor, which is surrounded by a conductor track in a U-shape. Another trace leads under the thick-film resistor, which rests on both tracks and is thus electrically connected to these. The U-shaped trace is electrically connected to the conductive bottom of the encapsulated switch, while the other trace serves as a solder pad to which a first pigtail is soldered, and the second pigtail is electrically soldered to the conductive lid portion of the encapsulated switch.

The lower part rests with its outer bottom on the heating resistor. The thick-film resistor can be covered by an insulating layer.

The switch should be soldered to the U-shaped track on the support plate, which is not mentioned in this document, as the soldering is to take place. As a result, a line-shaped cohesive contact between the lower part and serving as a soldering surface U-shaped conductor is produced.

This connection is not only problematic to manufacture, but also mechanically not sufficiently stable, which is why the document shows that together on the switch and carrier plate, a shrink tube is shrunk, protrude from the side of the two connecting wires. As a result, the switch and carrier plate are additionally mechanically fixed to one another. Nevertheless, the thermal coupling of the heating resistor to the bottom of the switch for certain applications is unsatisfactory.

Also the DE 41 42 716 A1 describes a switch with a metallic base and a top, in which centrally the first external connection is provided. The second external connection is via the lower part. On this lower part of a supporter ring is clamped from below, which carries a substrate with a thick-film resistor, which is thus arranged electrically in series with the switch and is responsible as a heating resistor for the current sensitivity.

As a second external connection options are provided on the coupling ring or the substrate.

In the known construction is disadvantageous that, although provided for a good mechanical support of the heating resistor to the housing of the switch, the electrical connection, however, is not sufficiently reliable, especially in strong shocks.

These temperature-dependent switches are used in a known manner to protect electrical equipment from overheating. For this purpose, the switch is electrically connected in series with the device to be protected and mechanically arranged on the device so that it is in thermal communication with this.

In the housing, a temperature-dependent switching mechanism of spring washer, bimetallic snap disk and movable contact member is arranged in each case, which is in the closed state of the switch in contact with a stationary contact part inside of the upper part, as is outwardly plated through to a first outer terminal. The second external connection is the conductive lower part.

The operating current of the device to be protected flows through the two contact parts and the spring washer in the lower part.

Below the response temperature of the bimetallic snap disk, the circuit is closed and the device to be protected is powered by the switch with power. If the temperature rises above a permissible value, then deforms the bimetallic snap disk, which opens the switch and the supply of the device to be protected is interrupted.

The now de-energized device can then cool down again. In this case, the thermally coupled to the device switch cools down again, which then automatically closes again. While such switching behavior protects e.g. A hair dryer can be quite useful, this is not desirable anywhere where the device to be protected after switching off may not automatically turn on to avoid damage. This is for example for electric motors, which are used as drive units.

The DE 41 42 716 A1 proposes therefore to provide a so-called self-holding resistor, which is electrically parallel to the external terminals. The self-holding resistor is in the open switch electrically in series with the device to be protected, through which only a harmless residual current now flows because of the resistance value of the self-holding resistor. However, this residual current is sufficient to heat the self-holding resistor so far that it emits a heat that holds the bimetallic snap disk above its switching temperature.

The from the DE 41 42 716 A1 and DE 43 36 564 C2 Known switches are also still equipped with a current-dependent switching function, including the heating resistor is provided, which is permanently connected in series with the external terminals. The operating current of the device to be protected thus flows constantly through this heating resistor, which can be dimensioned so that it ensures that when exceeding a certain operating current that the bimetallic snap disk is heated to a temperature above its response temperature, so that the switch at an increased Operating current already opens before the device to be protected has warmed up inadmissible.

The DE 44 28 226 C1 as well as the DE 195 07 105 C1 describe each temperature-dependent switch with a housing having a lower part, which is closed by a shell. In the housing, a temperature-dependent switching mechanism is arranged with a movable contact part, which cooperates with a stationary contact part, which is arranged centrally in the upper part.

The temperature-dependent switches each have a self-holding resistor, which is connected in parallel to the switching mechanism, and a further heating resistor, which is connected in series with the switching mechanism, as this already in principle for the switch from the DE 41 42 716 A1 and the DE 43 36 564 C2 is known.

In particular, when the known switches are used for the protection of high-performance engines, they must because of the operation and especially when starting the engines occurring strong shocks to be mechanically very resilient.

Furthermore, the switches must be able to reliably protect the motors both in the limit mode with maximum allowable power and with a blocking rotor. To test whether the switch does this, usually two tests are performed.

In the so-called heating test , the motor is operated at maximum power, wherein neither the flow of current through the switch nor the case thereby transferred from the engine to the switch heat may open the switch.

In contrast, in the so-called locked rotor test , the motor is connected to the operating voltage with the rotor locked , which results in an operating current flowing through the motor which is three to five times greater than the usual operating current.

Of course, this high current also leads to a heating of the motor and thus to an increase in temperature at the switch.

However, this heating takes place so slowly that the engine may already irreversibly destroyed before the switch starts due to the increase in engine temperature. Therefore, in this test, a heater resistor must cause the switch to open very quickly.

Even with a suitable coordination between the response temperature of the bimetallic snap disk and the resistance of the heating resistor alone, however, these two conflicting conditions in the known switches described above can not be met.

Although these values could be adjusted so that the maximum allowable operating current does not cause the heating resistor heats the bimetallic snap disk to a temperature above its switching temperature, but that this is done only by the much higher current at locked rotor.

On the other hand, the response temperature of the bimetallic snap disk could be chosen to be above the temperature that the engine assumes at maximum allowable power during operation and transmits to the switch, but below the temperature to which the bimetallic snap disk is subjected by the heating resistor is heated when it is traversed by the current with blocked rotor.

However, the so set switching behavior is only achieved in static operation, so if enough time has elapsed, so that either opens at too high a temperature of the motor or too high current, the switch. To protect a powerful engine, it is also necessary that the switch starts extremely fast, especially with a blocking rotor.

This requires a very good thermal coupling of the heating resistor to the switch, so that a change in the temperature of the heating resistor is transmitted to the bimetallic snap disk in no time.

Based on this prior art, it is therefore an object of the present invention to develop the aforementioned switch such that at low cost and reliable construction a good thermal coupling of the heating resistor to the switch and at the same time a good mechanical hold between the switch and heating resistor is realized.

According to the invention this object is achieved in the switch mentioned above in that lying on the floor next to each other an electric Contact surface to the first soldering surface and a thermal contact surface are formed to the heating resistor, the bottom is soldered flat on the first soldering surface, and the first soldering surface is formed by at least two adjacent to the heating resistor tin sheets.

In contrast to the construction of the DE 43 36 564 C2 According to the invention, the bottom of the switch and not only the lateral transition between the bottom and side wall is soldered. The bottom of the switch is now used for two purposes, for one, it lies on the entire surface of the heating resistor, on the other hand, it is held flat by material bond on the soldering surface. As a result of this laminar material connection in addition to the heating resistor, according to the inventor, a very good thermal connection of the switch to the heating resistor results.

The switch is set not only mechanically very stable on the support plate in this way, this type of fixing also leads to the desired thermal coupling.

Now, when the new switch is used in the Locked Rotor Test , the heating resistor now heats up very quickly due to the very high operating current and, due to the good and firm contact to the bottom of the switch, introduces this heat into the switching mechanism, thus rapidly increasing the operating current interrupts.

Because the first soldering surface is formed by at least two tin tracks arranged next to the heating resistor, a large-area electrical connection and at the same time good mechanical support at the bottom of the switch are provided.

Further, because the bottom of the base is formed in an electrical contact surface to the first soldering surface and lying adjacent a thermal contact surface to the heating resistor, the surface of the bottom can almost completely for

the electrical and mechanical contact with the first soldering surface and the thermal contact with the heating resistor are utilized.

The problem underlying the invention is completely solved in this way.

The fixed mechanical connection by the surface soldering to the bottom of the base thus does not affect the switching behavior, for example, but provides compared with the prior art for a better thermal coupling both to the engine and to the heating resistor.

To solve the posing task, the inventor has not so from the DE 43 36 564 C2 known lateral solder joint improved by additional measures, but selected a different type of cohesive connection.

However, the inventor has not gone the way that offers itself at first glance, to connect the carrier plate in a force-fitting manner with the housing, as is known from the above-mentioned DE 41 42 716 A1 is known.

Rather, according to the invention, a large-area solder joint is produced between the bottom of the lower part and a soldering surface next to the heating resistor.

This planar connection can be produced, for example, by heating the carrier plate on a hotplate to liquefy tin tracts provided in addition to the heating resistor. Thereafter, the switch is pressed onto the carrier plates, so that the tin sheets make a large-area connection to the bottom of the switch.

This is taken care of for a firm grip of the support plate on the switch housing.

The new switch is now designed so that the heating resistor leads to a very rapid heating of the switch itself.

In general, it is preferred if solder pins are soldered to the second soldering surface and to the first external connection.

In fact, the inventor of the present application has recognized that the connection provided according to the invention is significantly stronger than in the case of lateral soldering according to the invention DE 43 36 564 C2 so that it can be dispensed with, the switch for mechanical stabilization even with a shrink cap to surround, which would hinder the heat input to the engine and thus the shutdown in overheated engine. Thus, the omission of an additional casing also allows other types of connection than laterally led away Pigtails, such as the use of pins. This type of connection is not possible with the known switches discussed in the introduction.

In general, it is preferred if the heating resistor is a thick-film resistor, wherein preferably a heating resistor is arranged between the heating resistor and a protective film.

Here it is advantageous that a planar heating resistor is used, so that the floor can be coupled over a large area. The protective foil prevents electrical short circuits.

In this case, it is preferred if the two contact surfaces cover at least 50%, preferably 80%, of the surface of the base, wherein preferably the contact surface to the heating resistor has a larger area than the contact surface to the first soldering surface, more preferably at least 30% greater.

The advantage here is that the ratio of the sizes of the contact surfaces to each other ensures both the required mechanical hold and the required thermal coupling.

Therefore, it is preferred if the derailleur comprises a bimetal snap-action disc which is mechanically connected to a movable contact part and presses this below its switching temperature against a stationary contact part and lifts above its switching temperature of this.

On the other hand, it is preferred if a spring snap-action disc, which biases the movable contact part in the sense of an abutment against the stationary contact part, and also a bimetal snap-action disc is provided, which lifts the movable contact part above its switching temperature of the stationary contact part, wherein further preferably the spring snap-action disc is arranged between stationary contact part and bimetal snap-action disc.

While it is quite sufficient, if only a bimetallic snap disk is provided which produces both the contact pressure and provides for the temperature-dependent opening, can by a spring-snap disk, which in addition to the bimetallic snap disk or alone causes the contact pressure, the bimetallic Snap disk are mechanically and electrically relieved in their low temperature position, which contributes to greater long-term stability of their switching behavior.

Alternatively, it is preferable if the derailleur has a current transmitting member which cooperates with two stationary contact parts, of which the first is connected to the first outer terminal and the second to the second outer terminal, preferably wherein the second contact part is electrically connected to the lower part on Preferably, the derailleur comprises a bimetallic snap disk, which is mechanically connected to the current transfer member and this below its switching temperature against the two stationary Contact parts pushes and lifts above their switching temperature of these, and further preferably the switching mechanism has a spring washer which biases the current transfer member in the sense of a plant against the stationary contact parts, the bimetallic snap-off the current transfer member above its switching temperature of the stationary contact parts.

Here it is advantageous that the switch can lead significantly higher currents than the above-mentioned switch, in which the current is passed through the bimetallic snap-action disc or through the spring snap-action disc. This is particularly advantageous when the switch is used to power powerful electric motors that require high operating currents.

Temperature-dependent switch with a current transmitting member, which cooperates with two stationary contact parts are, for example, from DE 26 44 411 A1 known. In these switches, the two stationary contact parts, which are arranged in the upper part, are connected in series with the supply current of the device to be protected, so that the current flows through the current transmission element, when the switch is at a temperature below the switching temperature.

The power transmission member may be a separate contact plate, but it is also possible in individual cases, to use the bimetallic snap disk or a spring snap-action as a power transmission member.

In order to be able to use the carrier plate already described above with the two soldering surfaces and the associated advantages, according to the invention the second stationary contact part is electrically connected to the electrically conductive lower part, which in turn is connected to the first soldering surface, which via the heating resistor with the second Soldering surface is connected. As a result, the current flows from the second external terminal through the heating resistor in the lower part and from there to the second stationary contact part, from there through the current transmitting member and then via the first contact part to the first outer terminal.

Due to the unusual at first glance interconnection of the second contact part with the lower part, it is possible to use the advantages of the support plate for switches with a power transmission element.

Further advantages will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

Fig. 1

einen schematischen, nicht maßstabsgetreuen Längsschnitt durch einen bekannten temperaturabhängigen Schalter, bei dem ein bewegliches Kontaktteil mit einem stationären Kontaktteil zusammenwirkt;

Fig. 2

in einer schematischen Seitenansicht die Anordnung des Schalters aus Fig. 1 auf einer Trägerplatte, auf der ein Heizwiderstand und ein Lötanschluss vorgesehen sind;

Fig. 3

eine Draufsicht auf die Anordnung aus Fig. 2, jedoch ohne Anschlussstifte;

Fig. 4

eine Draufsicht auf die Trägerplatte aus Fig. 2 und 3;

Fig. 5

eine perspektivische Ansicht der Trägerplatte aus Fig. 4.;

Fig. 6

eine Unteransicht des Schalters aus Fig. 1, wobei auf dem Boden Kontaktflächen angedeutet sind;

Fig. 7

in einer Darstellung wie in Fig. 1 einen weiteren temperaturabhängigen Schalter, bei dem zwei stationäre Kontaktteile mit einem Stromübertragungsglied zusammenwirken;

Fig. 8

in perspektivischer Ansicht von schräg oben den auf die Trägerplatte aus Fig. 5 aufgelöteten Schalter aus Fig. 7, an dem außen zwei mit den stationären Kontakten verbundene Anschlussstücke zu sehen sind; und

Fig. 9

den mit Anschlusslitzen versehenen Schalter aus Fig. 8 in Seitenansicht und Draufsicht.

Embodiments of the invention are illustrated in the accompanying drawings and are explained in more detail in the following description. Show it:

Fig. 1

a schematic, not to scale longitudinal section through a known temperature-dependent switch, wherein a movable contact part cooperates with a stationary contact part;

Fig. 2

in a schematic side view of the arrangement of the switch Fig. 1 on a support plate on which a heating resistor and a solder terminal are provided;

Fig. 3

a plan view of the arrangement Fig. 2 but without pins;

Fig. 4

a plan view of the carrier plate FIGS. 2 and 3 ;

Fig. 5

a perspective view of the carrier plate Fig. 4 .

Fig. 6

a bottom view of the switch Fig. 1 , wherein contact surfaces are indicated on the ground;

Fig. 7

in a representation like in Fig. 1 another temperature-dependent switch in which two stationary contact parts cooperate with a current transmitting member;

Fig. 8

in a perspective view obliquely from above the on the support plate Fig. 5 soldered switch off Fig. 7 on the outside of which two connecting pieces connected to the stationary contacts can be seen; and

Fig. 9

the provided with pigtails switch off Fig. 8 in side view and top view.

In Fig. 1 is denoted by a temperature-dependent switch 10, which includes a cup-shaped lower part 11 which is closed by an upper part 12 which is held with the interposition of an insulating film 13 by a flanged edge 14 on the lower part 11.

In the housing formed by the lower part 11 and upper part 12 of the switch 10, a temperature-dependent switching mechanism 15 is arranged, which comprises a Federschnappscheibe 16, which carries a movable contact member 17 centrally on which a freely inserted bimetallic disc 18 is seated.

The Federschnappscheibe 16 is supported on a bottom 19 inside of the lower part 11, which is made of electrically conductive material.

The movable contact part 17 is in contact with a stationary contact part 20, which is provided on an inner side 21 of the upper part 12, which is also made of metal in this embodiment.

In this way, the temperature-dependent switching mechanism 15 in the in Fig. 1 shown low-temperature position an electrically conductive connection between the upper part 12 and the lower part 11 forth, the operating current via the stationary contact part 20, the movable contact part 17 and the spring snap disk 16 flows.

Alternatively, it is also possible, instead of the spring snap disk 18, to use directly a bimetallic part which carries the movable contact part 17 and thus conducts the operating current when the switch 10 is closed.

Increases in the switch 10 off Fig. 1 the temperature of the bimetallic disc 18 beyond its response temperature, so it snaps from the in Fig. 1 shown convex position in its concave position in which it lifts the movable contact member 17 against the force of the spring washer 16 of the stationary contact member 20 and thus opens the circuit.

Such a temperature-dependent switch 10 is for example from the DE 196 23 570 A1 The contents of which are hereby incorporated by reference.

A first pad 22 is off at the switch Fig. 1 arranged in a central region of the upper part 12. A second connection surface 23 may be provided on the edge 14.

At these pads 22, 23 can be soldered in a known manner depending on a terminal lug with its respective inner end.

So that the switch 10 can be thermally coupled to an electrical device to be protected, it has a flat, outer bottom 24, which is designed as a heat transfer surface and comes into contact with the electrical device to be protected.

To now provide the switch with a heating resistor, it is soldered to a thin carrier plate 25, as in Fig. 2 in a schematic side view and in Fig. 3 is shown in plan view.

The carrier plate 25 is formed as a ceramic substrate, on the upper side 26 in Fig. 2 from right to left side by side, a first soldering surface 27, a heating resistor 28 in the form of a thick-film resistor and a second soldering surface 29 are arranged.

To the soldering surface 29 and the pad 22 are soldered pins 31, 32, which serve the external connection. These pins are in Fig. 3 Not shown.

The 4 and 5 show the support plate 25 without soldered switch 10th

The heating resistor 28 is formed as a thick-film resistor, which at its in Fig. 4 right side with the soldering surface 29 is connected directly via a conductive layer 31.

In Fig. 4 to the left of the heating resistor, the soldering surface 27 is arranged, which has in the non-soldered state, three tin tracks 33, 34, 35 which are parallel to each other. At least one of the tin traces 33, 34, 35 is connected to the heating resistor 28 via a conductive layer 32 over which they project upwardly.

If the switch 10 is to be mounted on the support plate 25, this is heated to the extent that the tin traces 33, 34, 35 liquefy. Thereafter, the switch 10 is pressed with the bottom 24 on the top 26 of the support plate 25, so that the tin sheets 33, 34, 35 connect to the soldering surface 27 and provide a full-surface cohesive connection to the bottom 24.

At the same time, the floor passes into fixed mechanical contact with the heating resistor 28, which may be covered by a thin protective film 36, which electrically insulates the thick-film resistor from the floor 24.

Between bottom 24 and soldering surface 27 and heating resistor 28 form two contact surfaces 37, 38, which in Fig. 6 are indicated, in which the switch 10 off Fig. 1 from below, so that its bottom 24 can be seen.

From the Fig. 6 It can be seen that both the heating resistor 28 via the serving as a heat transfer surface contact surface 38 and the soldering surface 27 via the electrical connection and the mechanical stop serving contact surface 37 over a large area and side by side with the bottom 24 in conjunction. In this way, more than 80% of the area of the bottom 24 is covered by the two contact surfaces 37, 38. The contact surface 38 to the heating resistor 28 is greater than about 30% greater than the contact surface 37 to the soldering surface 27th

In Fig. 7 is denoted by 40 another temperature-dependent switch, which together with the support plate 25 from Fig. 4 can be used as the switch 10 off Fig. 1 ,

The switch 40 includes a temperature-dependent switching mechanism 41 which is housed in a housing 42. The housing 42 has an upper part 43 made of insulating material, which closes an electrically conductive lower part 44 whose edge 45 defines the upper part 43 on the lower part 44.

The switching mechanism 41 comprises a spring snap-action disc 46 and a bimetal snap-action disc 47, which, together with the spring snap-action disc 46, is centrally penetrated by a pin-like rivet 48, by which these are mechanically connected to a current transfer member 49 in the form of a contact plate.

The spring snap-action disc 46 is clamped with its edge 51 between a circumferential shoulder 52 inside in the lower part 44 and a spacer ring 53, on which the upper part 43 rests with its inner side 54

The bimetallic snap disk 47 is supported with its edge 55 inside on the bottom 56 of the lower part 44.

The round, in the present case circular current transfer member 49 has in the direction of the upper part 43 in the circumferential direction, an electrically conductive contact surface 57 which cooperates with two stationary contact parts 58, 59, which are arranged on the inner side 54 of the upper part 43.

The stationary contact parts 58, 59 are formed as inner heads of contact rivets 61, 62, which pass through the upper part 43 and with their outer portions 63, 64 serve the external connection. Between the sections 63, 64 an insulating web 65 is provided. Remote from the web 65, a bottom 66 of the lower part 44 is formed as a thermal contact surface.

At the outer portions 63, 64 each have a connector 67 and 68 attached, which serves the external connection.

In Fig. 8 the switch 40 is off Fig. 7 shown on the support plate 25, in connection with the 4 and 5 has been described. The lower part 44 was with the in Fig. 8 soldered to unrecognizable first soldering surface 27 and lies with its bottom 66 with the interposition of the protective film 36 on the heating resistor 28.

Between the bottom 66 and the first soldering surface 27 and the heating resistor 28, the two contact surfaces are formed again, which in Fig. 6 for the switch 10 off Fig. 1 are indicated.

In Fig. 8 are also the attached to the two outer portions 63, 64 of the contact rivets 61, 62 connecting piece 67 and 68 can be seen, each having an upper, U-shaped tab 69 and 71, respectively. To contact the switch 40, the upper, U-shaped tabs 69, 71 folded down on the sections 63 and 64 and inserted into the form of "tunnel" usually stripped ends of connecting strands and soldered.

In Fig. 9 In this way, it is shown that the tab 69 associated with the first stationary contact part 58 has been connected to a first pigtail 72 which forms the first external connection of the switch 40.

The tab 71 associated with the second stationary contact part 59 is electrically connected in a comparable manner to a connecting part 73 which is connected to the conductive lower part 44 via its edge 45. In the simplest case, the connecting part 73 is solder which electrically and mechanically connects the edge 45 to the connecting piece 68.

To the second. Soldering surface 29 is soldered to a second pigtail 74, which forms the second outer terminal.

Since the power transmission member 49 in Fig. 7 is in contact with the two stationary contact parts 58, 59, there is a continuous electrically conductive connection from the first pigtail 72 via the connector 67 to the first stationary contact part 58, from there via the current transfer member 49, the second stationary contact part 59, the second connector 68 and the connecting part 73 to the edge 45 and from there to the lower part 44th

The lower part 44 is connected to its bottom 66 via the first soldering surface 27 with the heating resistor 28 which is connected at its other end to the second soldering surface 29, to which the second pigtail 74 is soldered.

The switch 40 is like the switch 10 thermally coupled very well to the heating resistor 28, while at the same time electrically isolated from this. At the same time, the switch 40 is mechanically fixedly connected to the carrier plate 25 via the bottom 66 of the lower part 44 and the first soldering surface 27.

Claims (14)

1. Temperature-dependent switch (10, 40) having a temperature-dependent switching mechanism (15, 41), a housing receiving said switching mechanism (15, 41), said housing comprising an upper part (12, 43) having a first external connection (22, 63) and an electrically conductive lower part (11, 44) having an external base (24, 66), with a carrier plate (25) having arranged on its upper side (26) a heating resistor (26) and two solder pads (27, 29) connected to said heating resistor (28), wherein the base (24, 66) of the lower part (11, 44) is supported on said heating resistor (28) and the lower part (11, 44) is soldered to the first solder pad (27) and the second solder pad (29) serves as second external connection,
   characterized in that at said base (24, 66) and lying side-by-side an electrical contact pad (37) to said first solder pad (27) and a thermal contact pad (38) to said heating resistor (28) are embodied, said base (24, 66) is soldered flat onto said first solder pad (27), and said first solder pad (27) is embodied by at least two tin conductors tracks (33, 34, 25) arranged beside the heating resistor (28).
2. Switch according to claim 1, characterized in that said heating resistor (28) is a thick-film resistor.
3. Switch according to claim 1 or 2, characterized in that connector pins (32, 31) are soldered to said second solder pad (29) and to said first external connection (22).
4. Switch according to anyone of claims 1 to 3, characterized in that a protective film (36) is arranged between heating resistor (28) and base (24, 66).
5. Switch according to anyone of claims 1 to 4, characterized in that said two contact pads (37, 38) cover at least 50% of the surface of the base (24, 66).
6. Switch according to claim 5, characterized in that said two contact pads (37, 38) cover at least 80% of the surface of the base (24, 66).
7. Switch according to anyone of claims 1 to 6, characterized in that the contact pad (38) to the heating resistor (28) covers a surface greater than the contact pad (37) to the first solder pad (27).
8. Switch according to claim 7, characterized in that the contact pad (38) to the heating resistor (28) is by at lest 30% greater than the contact pad (37) to the first solder pad (27).
9. Switch according to anyone of claims 1 to 8, characterized in that the switching mechanism (15) comprises a bimetal snap-action disc (18) that is mechanically connected to a movable contact part (17) and presses the latter against a stationary contact part (20), when being below its switching temperature, and lifts the latter off from the stationary contact part, when being above its switching temperature.
10. Switch according to claim 9, characterized in that a spring disk (16) is provided that presses the movable contact part (17) in the sense of contact with the stationary contact part (20), whereby the bimetal snap-action disc (18) lifts the movable contact part (17) off from the stationary contact part (20), when being above its switching temperature.
11. Switch according to anyone of claims 1 to 8, characterized in that the switching mechanism (41) comprises a current transfer element (49) cooperating with two stationary contact parts (58, 59), of which the first (58) is connected to the first external connection (72) and the second (59) is connected to the second external connection (73).
12. Switch according to claim 10, characterized in that the second contact part (59) is electrically connected to the lower part (44).
13. Switch according to claim 11 or 12, characterized in that the switching mechanism (44) comprises a bimetal snap-action disc (47) that is mechanically connected to said current transfer element (49) and presses the latter against said two stationary contact parts (58, 59), when being below its switching temperature, and lifts the latter off from said two stationary contact parts, when being above its switching temperature.
14. Switch according to claim 13, characterized in that the switching mechanism (41) comprises a spring disk (46) that presses the current transfer element (49) in the sense of contact with said two stationary contact parts (58, 59), whereby the bimetal snap-action disc (47) lifts the current transfer element (49) off from said stationary contact parts (58, 59), when being above its switching temperature.

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