Method for producing an SMD-solderable component, SMD-solderable component, electronic unit and field device

Abstract

Method for producing an SMD-solderable component (5), wherein the SMD-solderable component (5) comprises: -a first contact element (2a) and a second contact element (2b), wherein the first contact element (2a) and the second contact element (2b) are provided for soldering onto contact surfaces provided for this purpose on a surface of a printed circuit board (18), -a first connection surface (3a) and a second connection surface (3b), wherein the first connection surface (3a) is formed by an end face (SF) of the first contact element (2a), and wherein the method comprises the steps of: A) providing a plurality of nanowires (ND) on the first connection surface (3a) and on the second connection surface (3b); B) aligning the first connection surface (3a) and the second connection surface (3b) such that the first connection surface (3a) and the second connection surface (3b) face each other; C) merging the first connection surface (3a) and the second connection surface (3b), in which the plurality of nanowires (ND) of the first connection surface (3a) is brought into contact with the plurality of nanowires (ND) of the second connection surface (3b), wherein, during the joining, a non-detachable electrically conductive first connection (4a) is produced between the first connection surface (3a) and the second connection surface (3b) in such a way that a predeterminable contact resistance is present between the first contact element (2a) and the second contact element (2b).

Description

[0001] The invention relates to a method for producing an SMD-solderable component, an SMD-solderable component, an electronic unit and a field device in automation technology.

[0002] In automation technology, particularly in process automation technology, field devices are often used to determine and / or monitor process variables. Field devices essentially refer to all devices that are used close to the process and that provide or process-relevant information. These include, for example, level measuring devices, flow measuring devices, pressure and temperature measuring devices, pH-redox potential measuring devices, conductivity measuring devices, etc., which measure the corresponding process variables: level, flow, pressure, temperature, pH value or conductivity. Field devices often have a sensor unit that is in contact with a process medium, in particular at least temporarily and / or at least partially, and which serves to generate a signal dependent on the process variable.Furthermore, these often have an electronics unit arranged in a housing, wherein the electronics unit serves to process and / or transmit signals generated by the sensor unit, in particular electrical and / or electronic signals. Typically, the electronics unit comprises at least one printed circuit board with components arranged thereon.

[0003] The electronics unit often comprises a multitude of SMD components, each with its own contact elements for soldering onto designated contact pads on a circuit board surface. SMD solderable components (short for 'Surface Mounted Devices') are soldered directly onto designated terminals with their contact elements. For this purpose, the SMD components are mechanically placed onto the solder-pasted contact pads on the circuit board using automatic placement machines and then soldered together in a reflow soldering oven using a so-called reflow soldering process. This allows a multitude of SMD solderable components to be soldered onto the circuit board simultaneously.

[0004] Such state-of-the-art SMD components often feature numerous solder joints, for example, between the contact elements and / or between other components of the component. In the case of such a solder joint, it is often very challenging, due to manufacturing technology, to reliably adjust a specified contact resistance between the contact elements of the SMD-solderable component.

[0005] Possibilities for connecting components have become known from the published patent applications DE 10 2017 104 926 A1, US 6 297 063 B1, US 2005 / 0 224 975 A1, JP 2000- 114 434 A, AT 408 052 B, DE 10 2004 062 885 A1, DE 10 2006 031 322 A1, US 2017 / 0 162 536 A1 and DE 10 2018 106 959 A1.

[0006] The invention is therefore based on the object of providing an SMD-solderable component which has a predetermined contact resistance between its contact elements with a sufficiently high reliability.

[0007] With regard to the method, the object is achieved by a method for producing an SMD-solderable component, wherein the SMD-solderable component comprises: - a first contact element and a second contact element, wherein the first contact element and the second contact element are intended for soldering onto contact surfaces provided for this purpose on a surface of a printed circuit board, - a first connection surface and a second connection surface, wherein the first connection surface is formed by an end face of the first contact element, and wherein the method comprises the steps of: A) providing a plurality of nanowires on the first pad and on the second pad; B) aligning the first connection surface and the second connection surface such that the first connection surface and the second connection surface face each other; C) Bringing together the first connection surface and the second connection surface, in which the plurality of nanowires of the first connection surface are brought into contact with the plurality of nanowires of the second connection surface, wherein during the bringing together a non-detachable electrically conductive first connection is produced between the first connection surface and the second connection surface in such a way that a predeterminable contact resistance is present between the first contact element and the second contact element.

[0008] By using nanowires on the connection pads, a positive-locking, electrically conductive and mechanically stable first connection can be created without the need for soldering. Therefore, the SMD-solderable component is preferably also free of solder joints. Due to the size of the nanowires, the surface area of ​​the connection is increased.

[0009] In one embodiment of the method according to the invention, the predeterminable contact resistance is set by means of the dimension of the first connection surface and the second connection surface, a cross-sectional area of ​​the nanowires and / or a length of the nanowires, and / or a selection of a material for the nanowires.

[0010] The nanowires preferably have a length in the range of 100 nm (nanometers) to 100 µm (micrometers). Furthermore, the nanowires preferably have a diameter in the range of 10 nm to 100 µm, in particular in the range of 30 nm to 2 µm. The term "diameter" refers to a circular base area; if the base area differs from this, a comparable definition of a diameter is to be used. It is particularly preferred that all nanowires used have the same length and diameter and are made of the same material.

[0011] In one embodiment of the method according to the invention, the nanowires are provided on the first connection surface and the second connection surface by means of an ion track etching process.

[0012] In one embodiment of the method according to the invention, the nanowires are applied to the first connection surface and the second connection surface in such a way that - the nanowires are attached to one side of the respective first connection surface or second connection surface and extend in a direction substantially perpendicular to the respective first connection surface or second connection surface, and - the nanowires essentially cover the respective first connection surface or second connection surface.

[0013] In one embodiment of the method according to the invention, the second connection surface is formed by an end face of the second contact element.

[0014] In an alternative embodiment of the method according to the invention, an elongate resistance element is provided which has a first end section and a second end section substantially opposite the first end section in the longitudinal direction of the resistance element, wherein - the second connection surface is formed by an end face of the first end section.

[0015] In one embodiment of the method according to the invention, a third connection surface is formed by an end face of the second contact element and - a fourth connection surface is formed by an end face of the second end section, and wherein the method comprises the additional steps of: D) Providing a plurality of nanowires on the third connection surface and on the fourth connection surface E) aligning the third connection surface and the fourth connection surface such that the third connection surface and the fourth connection surface face each other, F) Bringing together the third connection surface and the fourth connection surface, in which the plurality of nanowires of the third connection surface are brought into contact with the plurality of nanowires of the fourth connection surface, wherein during the bringing together a non-detachable electrically conductive second connection is established between the third connection surface and the fourth connection surface.

[0016] The second connection is also form-fitting. All previously and / or subsequently mentioned configurations in connection with the first connection surface and the second connection surface and the first connection present therebetween are encompassed by the invention, mutatis mutandis, also for the third connection surface and the fourth connection surface and the second connection present therebetween.

[0017] In one embodiment of the method according to the invention, steps B) and C) are carried out subsequently to steps E) and F) or steps B) and C) are carried out substantially simultaneously to steps E) and F).

[0018] In one embodiment of the method according to the invention, after the non-detachable first connection has been produced, the first connection is heated to a joining temperature and / or after the non-detachable second connection has been produced, the second connection is heated to a joining temperature.

[0019] The additional heating to the joining temperature results in an improved first / second connection.

[0020] In one embodiment of the method according to the invention, the joining temperature is more than 150°C and / or less than a melting temperature of the resistance element, in particular a coating of the resistance element.

[0021] In one embodiment of the method according to the invention, the joining temperature is achieved by applying a voltage between the first contact element and the second contact element, causing an electric current to flow between the first contact element and the second contact element. The magnitude of the electric current is selected such that the joining temperature of at least 150 °C is reached.

[0022] One possibility is to introduce electrical power via a current flow between the two contact elements, which heats the first or second connection to the joining temperature. In particular, the power can be introduced via a current flow through the resistance element. In the case of a resistance element with a wire wound in turns around an electrically insulating core (see the design mentioned below), the heat can also be introduced inductively via the magnetic field induced by a current flow, similar to an inductive heating plate.

[0023] Another possibility is, for example, to heat the SMD solderable component in an oven.

[0024] In one embodiment of the method according to the invention, the contact resistance is measured after the first connection surface and the second connection surface have been brought together in step C).

[0025] With regard to the SMD-solderable component, the object is achieved by an SMD-solderable component which is produced according to the method according to the invention, wherein the SMD-solderable component is lead-free and wherein the nanowires comprise a metal, in particular copper, gold, nickel, silver, zinc, tin, indium and / or platinum.

[0026] To protect the environment and people, efforts are now being made to avoid the use of heavy metals such as lead or mercury. The European Union's RoHS (Restriction of Certain Hazardous Substances) directive, which prohibits the use of certain hazardous substances such as lead in the electrical industry, also aims in this direction. Therefore, it is advantageous to specify a lead-free SMD solderable component, if possible. Since the SMD solderable component is free of solder joints, no lead-containing solders are used.

[0027] In one embodiment of the SMD-solderable component, the SMD-solderable component is an overcurrent protection device, in particular a fuse, with a tripping current, wherein the predetermined contact resistance is set in particular such that the tripping current of the overcurrent protection device is between 0.02 and 1 A.

[0028] In one embodiment of the SMD-solderable component, the first contact element has a first metal and the second contact element has a second metal, so that a mechanical stress is present between the first contact element and the second contact element caused by heating to the joining temperature. In particular, the metals have different thermal expansion coefficients. By heating to the joining temperature, the above-mentioned first and / or second connection is improved, and the sensitivity of the overcurrent protection device is increased because, similar to a bi-metal effect, a mechanical stress is introduced between the two connected contact elements when they are heated. This increases the sensitivity of the overcurrent protection device and thus, for example,causes faster tripping compared to an overcurrent protection device without mechanical tension between the first contact element and the second contact element.

[0029] In one embodiment of the SMD-solderable component, the SMD-solderable component has a maximum dimension of 20 mm, and in particular a distance between the first contact element and the second contact element is less than 15 mm.

[0030] In one embodiment of the SMD-solderable component, the resistance element is a wire wound in turns around an electrically insulating core, wherein in particular the wire has a diameter of less than 50 µm (micrometers), and wherein in particular the wire is coated with a tin plating whose melting temperature is greater than 225°C.

[0031] It is therefore advantageous if the joining temperature is lower than 225°C, so that when heated to the joining temperature, there is no pre-aging of the resistance element.

[0032] The invention further relates to an electronic unit with a printed circuit board, wherein the SMD-solderable component according to the invention is soldered onto contact surfaces provided for this purpose on the surface of the printed circuit board.

[0033] In one embodiment of the electronic unit, the electronic unit is designed for use in potentially explosive atmospheres.

[0034] Such electronic units must meet very high safety requirements regarding explosion protection. Explosion protection is primarily concerned with reliably preventing the formation of sparks or at least ensuring that a spark generated in the event of a fault has no impact on the surrounding environment. For this purpose, a number of corresponding protection classes are defined in relevant standards, particularly in the European standard IEC 600079-11 and / or EN 60079-11.

[0035] For example, in the protection class called "Intrinsic Safety" (Ex-i), explosion protection is achieved by ensuring that the values ​​for an electrical quantity (current, voltage, power) remain below a specified limit at all times, so that no ignition spark is generated even in the event of a fault. In the further protection class called "Increased Safety" (Ex-e), explosion protection is achieved by ensuring that the spatial distances between two different electrical potentials are so large that sparking cannot occur even in the event of a fault due to the distance. In the further protection class called "Flameproof Enclosure" (Ex-d), electronic units designed according to this protection class must have sufficient mechanical strength and stability.

[0036] Comparable protection classes are defined in the American standard FM3610 and / or ANSI / UL60079-11 and / or the Canadian standard CAN / CAS C22.2 No. 60079-11.

[0037] The SMD-solderable component, in particular the SMD-solderable overcurrent protection device, is used in an electronic unit designed for use in potentially explosive atmospheres. In particular, the electronic unit is designed according to a protection class of the aforementioned standards. The reliability of the overcurrent protection device according to the invention is of particular importance here.

[0038] The invention further relates to a field device in automation technology with an electronic unit according to the invention.

[0039] In particular, the electronic unit is an electronic unit of a field device in automation technology.

[0040] The invention is explained in more detail with reference to the following figures, which are not to scale. Like reference numerals denote like features. For reasons of clarity or where otherwise appropriate, previously mentioned reference numerals have been omitted in the following figures.

[0041] They show: Fig. 1: A first embodiment of the SMD-solderable component according to the invention; Fig. 2: A second embodiment of the SMD-solderable component according to the invention; Fig. 3: A third embodiment of the SMD-solderable component according to the invention; Fig. 4: An embodiment of a field device of automation technology with an electronic unit which has an embodiment of the SMD-solderable component according to the invention.

[0042] In Fig. 1 shows a first embodiment of the SMD-solderable component 5 according to the invention. This is produced by connecting a first contact element 2a and a second contact element 2b to one another, the end faces SF of which each form a first connection surface 3a and a second connection surface 3b. For this purpose, in a first method step A, a plurality of nanowires ND are provided on the first connection surface 3a and the second connection surface 3b, for example by means of an ion track etching process or another method known from the prior art for providing nanowires ND. Subsequently, in steps B and C, the two connection surfaces 3b are aligned facing one another and brought together, whereby the nanowires ND applied to the respective connection surface 3a, 3b form a positive connection.By means of the positive connection between the nanowires ND, an electrically conductive first connection 4a is established between the first connection surface 3a and the second connection surface 3b.

[0043] Within the scope of the invention, by establishing the first connection 4a, a predeterminable contact resistance is advantageously present between the first contact element 2a and the second contact element 2b. The predeterminable contact resistance is set, for example, via the dimensions of the first connection surface 3a and the second connection surface 3b, a cross-sectional area of ​​the nanowires ND and / or a length of the nanowires ND and / or a selection of a material for the nanowires ND. For this purpose, the expert can carry out appropriate series of tests. The predeterminable contact resistance is preferably set via the cross-sectional area of ​​the nanowires ND and the material for the nanowires ND. The presence of the predeterminable contact resistance between the first contact element 2a and the second contact element 2b can then be checked, for example.by applying a constant voltage and measuring the current flowing between the first contact element 2a and the second contact element 2b, see . Fig. 1, last picture.

[0044] In one to the in Fig. 1, an elongated resistance element 1 is additionally provided between the first contact element 2a and the second contact element 2b. As already shown in Fig. 1, the first connection surface 3a is formed by an end face SF of the first contact element 2a. The resistance element 1 now has a first end face SF at a first end section 1a, which forms the second connection surface 3b. At a second end section 1b opposite the first end section 1a in the longitudinal direction of the elongated resistance element 1, a third connection surface 3c is formed by an end face SF. This third connection surface 3c is already positively connected to a fourth connection surface 3d by means of an electrically conductive second positive connection 4b between the second end section 1b and the second contact element 2b. The electrically conductive second connection 4b is also produced by means of a plurality of nanowires ND.Only by establishing the first electrically conductive connection 4a are the first contact element 2a and the second contact element 2b electrically conductively connected to one another with the predeterminable contact resistance.

[0045] When establishing the first connection 4a and / or the second connection 4b, the respective connection surfaces 3a, 3b; 3c, 3d are pressed against each other by means of pressure with a contact force.

[0046] As an additional method step for producing the first connection 4a or the first connection 4a and the second connection 4b, it may also be advantageous to finally heat the SMD-solderable component 5 to a joining temperature FT, preferably a joining temperature FT of at least 150°C, see again Fig. 1, last image. For heating, electrical power can be applied, for example, via the electrically connected first and second contact elements 2a, 2b. Alternatively, the SMD-solderable component 5 can be heated in an oven.

[0047] In one embodiment, metals with different thermal expansion coefficients are used as materials for the first contact element 2a and the second contact element 2b. In this case, heating to the joining temperature FT advantageously causes additional mechanical stress between the first contact element 2a and the second contact element 2b (bi-metal effect). An additional mechanical stress is advantageous, for example, if the SMD-solderable component 5 is designed as an overcurrent protection device, since its sensitivity and thus triggering reliability can be increased by means of additional mechanical stress. In one embodiment, Fig. In the third embodiment shown in Figure 3, the resistance element 1 is an electrically conductive wire 8 wound in turns around an insulating core 9 with a diameter of less than 50 µm (micrometers), wherein in Fig. 3 Here, only the first end section 1a of the resistance element 1 and the connected first contact element 2a are shown. The wire 8 is coated with a coating 6 in the form of tin plating.

[0048] The contact element 2a is a cup-shaped end cap with, for example, a rectangular or round base surface and an inner end face SF as the first connection surface 3a. Such cup-shaped contact elements 2a, 2b are used, for example, in the manufacture of SMD-solderable overcurrent protection devices, wherein the overcurrent protection devices are characterized by the contact resistance and the resulting tripping current between the contact elements 2a, 2b.

[0049] In the case of a resistance element 1 with a wound wire 8, a current flow always causes an induced magnetic field. As with an induction cooker, heating to the joining temperature FT can also be achieved using a high-frequency alternating current circuit applied to the electrically conductively connected contact elements 2a, 2b, generating eddy currents that heat the SMD-solderable component 5.

[0050] Preferably, however, the joining temperature FT is lower than a melting temperature of the resistance element 1, in particular its coating 6; in the case of tinning, therefore, at least lower than 230°C. Due to the joining temperature FT used during heating of less than 230°C, pre-aging of the wire 8, in particular melting of a coating 6 of the wire 8 and the resulting formation of solder beads between, for example, adjacent turns, is effectively prevented.

[0051] The SMD-solderable component 5 with the predeterminable contact resistance between its contact elements 2a, 2b can then be soldered with the contact elements 2a, 2b onto designated contact surfaces of a printed circuit board 18 of an electronics unit 10 using an SMD mass soldering process (e.g., reflow soldering). The SMD-solderable component 5 is preferably used in an electronics unit 10 of a field device 11 of automation technology. Such a field device 11 of automation technology is Fig. 4. The field device 11 has a sensor unit 17, which is in contact with a process medium, in particular at least temporarily and / or at least in sections, and which serves to generate a measurement signal, e.g., an electrical and / or electronic signal, representing the process variable.

[0052] The electronics unit 10, located in a transmitter housing 19 of the field device 11, serves to process and / or transmit the measurement signals generated by the sensor unit 17. Typically, the electronics unit 10 comprises at least one printed circuit board 18 with components arranged thereon. The SMD-solderable component 5 according to the invention is soldered onto the printed circuit board 18.

[0053] In the Fig. In the embodiment shown in Figure 4, the field device 11 has a further electronics unit 20 configured as a display / input unit, with a (touch) display mounted thereon. The SMD-solderable component 5 according to the invention can, of course, also be soldered onto a circuit board of the electronics unit 20 configured as a display / input unit.

[0054] In one embodiment, the SMD-solderable component 5 is the above-mentioned overcurrent protection device (i.e. with the above-mentioned dimensions or the above-mentioned tripping current), which is used in a field device 11 that is designed for use in potentially explosive atmospheres. Reference signs and symbols 1 resistance element 1a,1b first, second end section 2a,2b first, second contact element 3a,3b,3c,3d first-fourth connection surface 4a,4b first, second connection 5 SMD solderable component 6 Coating 8 wire 9 insulating core 10 Electronic unit 11 Field device 17 Sensor unit 18 circuit board 19 Transmitter housing 20 Display / input unit FT joining temperature SF frontal area ND nanowires

Claims

[1] Method for producing an SMD-solderable component (5), wherein the SMD-solderable component (5) comprises: -a first contact element (2a) and a second contact element (2b), wherein the first contact element (2a) and the second contact element (2b) are provided for soldering onto contact surfaces provided for this purpose on a surface of a printed circuit board (18), -a first connection surface (3a) and a second connection surface (3b), wherein the first connection surface (3a) is formed by an end face (SF) of the first contact element (2a), and wherein the method comprises the steps of: A) providing a plurality of nanowires (ND) on the first connection surface (3a) and on the second connection surface (3b); B) aligning the first connection surface (3a) and the second connection surface (3b) such that the first connection surface (3a) and the second connection surface (3b) face each other; C) merging the first connection surface (3a) and the second connection surface (3b), in which the plurality of nanowires (ND) of the first connection surface (3a) is brought into contact with the plurality of nanowires (ND) of the second connection surface (3b), wherein, during the joining, a non-detachable electrically conductive first connection (4a) is produced between the first connection surface (3a) and the second connection surface (3b) in such a way that a predeterminable contact resistance is present between the first contact element (2a) and the second contact element (2b). [2] Method according to claim 1, wherein the predeterminable contact resistance is adjusted by means of the dimension of the first connection surface (3a) and the second connection surface (3b), a cross-sectional area of ​​the nanowires (ND) and / or a length of the nanowires (ND), and / or a selection of a material for the nanowires (ND). [3] Method according to at least one of the preceding claims, wherein the nanowires (ND) are provided on the first connection surface (3a) and the second connection surface (3b) by means of an ion track etching process. [4] Method according to at least one of the preceding claims, wherein the nanowires (ND) are applied to the first connection surface (3a) and the second connection surface (3b) in such a way that - the nanowires (ND) are attached on one side to the respective first connection surface (3a) or second connection surface (3b) and extend in a direction substantially perpendicular to the respective first connection surface (3a) or second connection surface (3b), and - the nanowires (ND) cover the respective first connection surface (3a) or second connection surface (3b) substantially flatly. [5] Method according to at least one of the preceding claims 1 to 4, wherein the second connection surface (3b) is formed by an end face (SF) of the second contact element (2b). [6] Method according to at least one of the preceding claims 1 to 4, wherein an elongate resistance element (1) is provided which has a first end portion (1a) and a second end portion (1b) substantially opposite the first end portion (1a) in the longitudinal direction of the resistance element (1), wherein - the second connection surface (3b) is formed by an end face (SF) of the first end section (1a). [7] Method according to claim 6, wherein - a third connection surface (3c) by an end face (SF) of the second contact element (2b) and - a fourth connection surface (3d) is formed by an end face (SF) of the second end section (1b), and wherein the method comprises the additional steps of: D) providing a plurality of nanowires (ND) on the third connection surface (3c) and on the fourth connection surface (3d); E) aligning the third connection surface (3c) and the fourth connection surface (3d) such that the third connection surface (3c) and the fourth connection surface (3d) face each other; F) merging the third connection surface (3c) and the fourth connection surface (3d), in which the plurality of nanowires (ND) of the third connection surface (3c) are brought into contact with the plurality of nanowires (ND) of the fourth connection surface (3d), wherein, during the joining, a non-detachable electrically conductive second connection (4b) is produced between the third connection surface (3c) and the fourth connection surface (3d). [8] Method according to claim 7, wherein steps B) and C) are carried out subsequently to steps E) and F) or wherein steps B) and C) are carried out substantially simultaneously with steps E) and F). [9] Method according to at least one of claims 7-8, wherein after the non-detachable first connection (4a) has been produced, the first connection (4a) is heated to a joining temperature (FT), and / or wherein after the non-detachable second connection (4b) has been produced, the second connection (4b) is heated to a joining temperature (FT). [10] Method according to claim 9, wherein the joining temperature (FT) is more than 150°C and / or less than a melting temperature of the resistance element (1), in particular a coating (6) of the resistance element (1). [11] Method according to claim 9 or 10, wherein the joining temperature (FT) is achieved by applying a voltage between the first contact element (2a) and the second contact element (2b) which causes an electric current to flow between the first contact element (2a) and the second contact element (2b). [12] Method according to at least one of the preceding claims, wherein the contact resistance is measured after the first connection surface (3a) and the second connection surface (3b) have been brought together in step C). [13] SMD-solderable component (5) manufactured according to at least one of claims 1 to 12, wherein the SMD-solderable component (5) is lead-free and wherein the nanowires (ND) comprise a metal, in particular copper, gold, nickel, silver, zinc, tin, indium and / or platinum. [14] SMD-solderable component (5) according to claim 13, wherein the SMD-solderable component (5) is an overcurrent protection device, in particular a fuse, with a tripping current, and wherein the predeterminable contact resistance is in particular set such that the tripping current of the overcurrent protection device is between 0.02 and 1 A. [15] SMD-solderable component (5) according to claim 14, wherein the first contact element (2a) comprises a first metal and the second contact element (2b) comprises a second metal, so that a mechanical stress caused by heating to the joining temperature (FT) is present between the first contact element (2a) and the second contact element (2b). [16] SMD-solderable component (5) according to claims 13 to 15, wherein the SMD-solderable component (5) has a dimension of at most 20 mm, and wherein in particular a distance between the first contact element (2a) and the second contact element (2b) is less than 15 mm. [17] SMD-solderable component (5) according to claims 13 to 16, wherein the resistance element (1) is a wire (8) wound in turns around an electrically insulating core (9), and wherein in particular the wire (8) has a diameter of less than 50 µm (micrometers), and wherein in particular the wire (8) is coated with a coating (6) designed as tinning, the melting temperature of which is greater than 225°C. [18] Electronic unit (10) with a printed circuit board (18), wherein the SMD solderable component (5) according to at least one of claims 13 to 17 is soldered onto contact surfaces provided for this purpose on the surface of the printed circuit board (18). [19] Electronic unit (10) according to claim 18, wherein the electronic unit (10) is designed for use in potentially explosive atmospheres. [20] Field device (11) of automation technology with an electronic unit (10) according to at least one of the preceding claims 18 to 19.

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