COMPONENT THAT CAN BE SOLDERED IN SMD TECHNOLOGY AND METHOD FOR PRODUCING A COMPONENT THAT CAN BE SOLDERED IN SMD TECHNOLOGY

Abstract

An SMD-solderable component comprises a resistance element, a first contact element, and a second contact element, wherein the first contact element is connected with a first end section of the resistance element by means of a first soldered connection and the second contact element is connected with a second end section of the resistance element by means of a second soldered connection. At least one of the first soldered connection and the second soldered connection is a lead-free soldered connection that is made with a lead-free solder preform. Further disclosed is a method for producing an SMD-solderable component.

Claims

1-16. (canceled)

17. A surface-mounted device (SMD)-solderable component for soldering to a circuit board of an electronics unit, comprising: a resistance element; a first contact element; and a second contact element, wherein the first contact element and the second contact element are provided for soldering to contact areas provided on the circuit board, wherein the first contact element is connected with a first end section of the resistance element via a first soldered connection and the second contact element is connected with a second end section of the resistance element via a second soldered connection, wherein at least one of the first soldered connection and the second soldered connection is a lead-free soldered connection that is made with a lead-free solder preform.

18. The SMD-solderable component as claimed in claim 17, wherein the SMD-solderable component is an overcurrent protection device having a tripping current, and wherein the tripping current of the overcurrent protection device lies between 0.02 and 1 A.

19. The SMD-solderable component as claimed in claim 17, wherein the SMD-solderable component has a dimension of maximum 20 mm, and wherein a separation between the first contact element and the second contact element is less than 15 mm.

20. A method for producing an SMD-solderable component having a resistance element. a first contact element, and a second contact element, the method comprising: producing a first soldered connection via which a first end section of the resistance element is connected with the first contact element; and producing a second soldered connection via which a second end section of the resistance element is connected with the second contact element; wherein for producing at least one of the first soldered connection and the second soldered connection a lead-free solder preform is used, which is arranged between the first end section and the first contact element or the second end section and the second contact element.

21. The method as claimed in claim 20, wherein the solder preform is coated with a flux.

22. The method as claimed in claim 20, wherein the lead-free solder preform has melting temperature less than a melting temperature of a coating of the resistance element.

23. The method as claimed in claim 21, wherein the lead-free solder preform has melting temperature less than 230° C.

24. The method as claimed in claim 23, wherein the lead-free solder preforms are used which have, facing the first end section or the second end section end surface, a face in which a guide is present extending into the solder preform with a specified depth and serving for receiving the first end section or the second end section, and the method further comprising: introducing the first end section and the second end section, respectively, each into a guide of an associated solder preform before producing the first soldered connection and the second soldered connection.

25. The method as claimed in claim 24, wherein the guide is conically tapered.

26. The method as claimed in claim 24, wherein the lead-free solder preform is embodied in a form of a complete torus, wherein the interior of the complete torus forms the guide.

27. The method as claimed in claim 24, wherein the resistance element is a wire wound around an electrically insulating core, and wherein upon introduction of the first end section or second end section, in each case, a predetermined minimum number of turns of the wire is located in the guide of a solder preform.

28. The method as claimed in claim 27, wherein a diameter of the guide amounts to 1.1 times a diameter of the insulating core.

29. The method as claimed in claim 24, wherein the first contact element and/or the second contact element are/is pot shaped, wherein the lead-free solder preform is placed in a contact element before a soldered connection is made and then an end section of the resistance element is introduced into the guide, and wherein the lead-free solder preform is fitted to the contour of the interior of a pot shaped contact element.

30. An electronics unit, comprising: a circuit board, the circuit board including an SMD-solderable component, including: a resistance element; a first contact element; and a second contact element, wherein the first contact element and the second contact element are provided for soldering to contact areas provided on the circuit board, wherein the first contact element is connected with a first end section of the resistance element via a first soldered connection and the second contact element is connected with a second end section of the resistance element via a second soldered connection, wherein at least one of the first soldered connection and the second soldered connection is a lead-free soldered connection that is made with a lead-free solder preform, and wherein the SMD-solderable component is soldered onto contact areas provided on the surface of the circuit board.

31. The electronics unit as claimed in claim 30, wherein the electronics unit is embodied for use in explosion endangered areas.

32. A field device of automation technology, comprising: an electronics unit, including: a circuit board, the circuit board including an SMD-solderable component, including: a resistance element; a first contact element; and a second contact element, wherein the first contact element and the second contact element are provided for soldering to contact areas provided on the circuit board, wherein the first contact element is connected with a first end section of the resistance element via a first soldered connection and the second contact element is connected with a second end section of the resistance element via a second soldered connection, wherein at least one of the first soldered connection and the second soldered connection is a lead-free soldered connection that is made with a lead-free solder preform, and wherein the SMD-solderable component is soldered onto contact areas provided on the surface of the circuit board.

Description

[0052] The figures of the drawing show as follows:

[0053] FIG. 1 an SMD-solderable component according to the state of the art,

[0054] FIG. 2 an embodiment of the SMD-solderable component of the invention;

[0055] FIG. 3a a perspective view of an embodiment of the solder preform, which is used in the production of the SMD-solderable component of the invention;

[0056] FIGS. 3b,c sectional views of details in the production of the first soldered connection in an embodiment of the invention.

[0057] FIG. 4 an embodiment of an automation field device having an electronics unit, which has an embodiment of the SMD-solderable component of the invention.

[0058] FIG. 1 shows an SMD-solderable component according to the state of the art. The SMD-solderable component includes two contact elements 12a,12b, which are provided for soldering to contact areas provided on a circuit board of an electronics unit. Arranged between the contact elements 12a,12b is a resistance element 14, which is connected at its end sections with the contact elements 12a,12b by material bonding, thus, in each case, by means of a lead-containing, soldered connection 13a,13b. In the case of the SMD-solderable component according to the state of the art, the soldered connections 13a,13b are produced by means of a lead-containing solder wire. Because of the demanding handling of the solder wire, an optimum orientation of the resistance element 14 relative to the contact elements is not always obtained in the production of the soldered connection. This is true especially for the case, in which the SMD-solderable component is especially small, i.e. having a maximum dimension of 1 cm or less.

[0059] Investigations of the applicant on a series of SMD-solderable components produced in equal manner according to the state of the art show that in the case of some of the SMD-solderable components the soldered connection 13b is only present at the edge of the contact element 12b, such as shown in FIG. 1, and, furthermore, the resistance element 14 extends slightly inclined between the two contact elements 12a,12b.

[0060] The resistance element 14 is a wire 15 wound around an insulating core. The investigations of the applicant show further that in some cases an undesired forming of solder beads 16 (also solder bridges) between neighboring turns of the wound wire 15 can occur. Such is shown, by way of example, in the detail of the dashed circle. The solder beads 16 arise from an at least partial melting the wire 15 caused by a high soldering temperature in the production of the soldered connections 13a,13b. The solder beads 16 short circuit mutually adjoining turns of the wire 15, such that the effective length and therewith the resistance of the resistance element 14 is influenced.

[0061] The combination of the undesired properties (inclination of the resistance element 1; soldered connection 13b on the edge of the contact element 12b; forming of the solder beads 16) shown in FIG. 1 and caused in the production of the SMD-solderable component during production of the soldered connections 13a,13b, can in the most unadvantageous case lead to the SMD-solderable component no longer satisfying the relevant specifications. For example, a predetermined resistance between the contact elements 12a,12b and/or a predetermined tripping current of an SMD-solderable component formed as an overcurrent protection means cannot be achieved.

[0062] Another great disadvantage is that the investigated soldered connections 13a;13b are lead-containing soldered connections 13a;13b.

[0063] The invention provides an improved SMD-solderable component 5, and an improved method for producing an SMD-solderable component 5, for overcoming the disadvantages observed in the state of the art. FIG. 2 provides more detail.

[0064] Used for producing first and second soldered connections 3a,3b are PFDS400® lead-free solder preforms 4a,4b. The solder preforms 4a;4b are arranged between respective first and second end sections 1a,1b of a resistance element 1 and respective contact elements 2a,2b. The solder preforms 4a,4b are composed of a composite material, in the case of which an Sn or In-containing solder alloy is embedded as a first composite component CK1 (here shown as dotted areas) essentially layer shaped in a copper- or silver matrix forming the second composite component CK2 (here shown as white areas). The solder preforms 4a,4b are, in such case, placed on the solderable surface of their contact elements 2a,2b in such a manner that the layers, or plies, of the first composite component CK1, i.e. the solder alloy, are arranged essentially in parallel with the solderable surfaces of the contact elements 2a,2b.

[0065] A significant advantage of the solder preforms 4a,4b are their comparatively low soldering temperature, namely they have a melting temperature Tsolder (also soldering temperature) of under 230° C. In this way, a deterioration of the resistance element 1 in the production of the soldered connections 3a,3b caused by a high soldering temperature can be avoided.

[0066] The melting temperature Tsolder of the solder preform 4a,4b in the production of the soldered connections 3a,3b is reached, for example, by a reflow process using a vapor phase heat transfer medium, or by a selective soldering method. Selective soldering methods include soldering with a soldering iron or gun, light soldering methods, for instance, with a laser or infrared radiation, induction soldering or soldering by means of microwaves, as well as the hot bar selective soldering method, in the case of which a bar is pressed against the solder joint and the soldering temperature is obtained by means of an electrical current flowing through the bar.

[0067] Since a lead-free solder preform 4a,4b is involved, the soldered connections 3a,3b produced therewith and, thus, also the SMD-solderable component 5 are advantageously lead-free. The use of the lead-free solder preform 4a,4b in the production of the soldered connections 3a,3b is, additionally, recognizable in the case of the SMD-solderable component 5 in that intermetallic phases formed in the soldering are distributed essentially uniformly over the entire thickness of the soldered connection 3a,3b. In the case of a lead-containing soldered connection 13a;13b produced in a soft soldering, the intermetallic phases are, in contrast, essentially limited to a first boundary layer between the soldered connection 13a;13b and the contact element 12a;12b and a second boundary layer between the soldered connection 13a;13b and the first end section 1a, second end section 1b.

[0068] The solder preform 4a,4b is advantageously fitted to the contact elements 2a,2b and the resistance element 1. This is shown in greater detail in FIGS. 3a-3c for the first soldered connection 3a and a solder preform 4a used for its production. Naturally, all examples of embodiments and explanations shown in connection with FIGS. 3a-3c hold equally also for the second soldered connection 3b and for a solder preform 4b used for its production.

[0069] The solder preform 4a is advantageously very easily completely coatable, i.e. on all its surfaces, with a flux, for example, in the context of a drum coating.

[0070] FIG. 3a shows a perspective view of a solder preform 4a, which is used in the production of the soldered connection 3a between an elongated, especially essentially completely cylinder shaped, resistance element 1 and a contact element 2a. The solder preform 4a is fitted in its shape to the resistance element 1 and to the contact element 3a.

[0071] This is shown in greater detail in FIG. 3b, which shows a sectional view of a detail of the components 2a,1a to be connected in the production of the soldered connection 3a.

[0072] Thus, the contact element 2a is in such case a pot shaped end cap having a rectangular floor, in which the solder preform 4a is placed before the production of the soldered connection 3a. For this, the solder preform 4a is embodied essentially prismatically. The shape of the solder preform 4a, especially its outer contour, is, thus, fitted to the inner contour of the contact element 2a in the form of a pot shaped end cap.

[0073] In another embodiment, the solder preform 4a has essentially the form of a complete torus. Such is advantageous, for example, for an as uniform as possible distribution of the melted solder upon melting of the solder preform 4a and/or in the case of a hollow cylinder shaped contact element 2a, i.e. a pot shaped end cap having a round floor.

[0074] The solder preform 4a includes a guide 7, embodied e.g. as a blind hole, although it can also pass all the way through. Guide 7 starts, in such case, from that face F of the solder preform 4a, which during soldering faces the first end section 1a of the elongated, resistive element 1. Guide 7 serves for introducing the first end section 1a into the solder preform 4a. It enables an especially easy orientating of the resistance element 1 relative to the solder preform 4a and the contact element 2a before the soldering of the contact element 2a with the first end section 1a. The guide 7 assures that the first end section 1a extends at least to a specified depth h in the solder preform 4a. Preferably, such as shown in FIG. 3b, guide 7 tapers conically.

[0075] As shown in FIG. 3b, the elongated resistance element 1 is a conducting wire 8, which is wound around an insulating core 9. The specified depth h assures that a minimum number of turns of the wire 8 required for a sufficiently well conducting contact between resistance element 1 and contact element 2a is located in the solder preform 4a.

[0076] The guide 7 and/or the fitted shape of the solder preform 4a simplify the production of the SMD-solderable component 5. Thus, an SMD-solderable component 5 is produced with a soldered connection 3a of a reliably high quality. Such is shown in FIG. 3c.

[0077] Furthermore, due to the temperatures of under 230° C. used in the production of the soldered connection 3a, a premature aging of the wire 8, especially also a melting of a coating 6 of the wire 8 and an accompanying forming of solder beads between, for example neighboring, turns, are effectively prevented.

[0078] The risk of forming of solder beads is especially large, when the SMD-solderable component 5 is especially small, or when a separation of neighboring turns of the wound wire 8 is especially small. Such is e.g. the case for overcurrent protection devices, which have a tripping current between 0.02 to 1 A and a dimension of less than 2 cm. The invention is thus especially suited for such SMD-solderable components.

[0079] The SMD-solderable component 5 is applied in an electronics unit 10 of a field device 11 of automation technology. FIG. 4 shows such a field device 11 of automation technology in greater detail. Field device 11 includes, especially standing, at least at times and/or at least sectionally, in contact with a process medium, a sensor unit 17, which serves for producing a, for example, electrical and/or electronic, measurement signal representing the process variable.

[0080] The electronics unit 10 arranged in a transmitter housing 19 of the field device 11 serves for processing and/or forwarding of the measurement signals produced by the sensor unit 17. Typically, the electronics unit 10 includes at least one circuit board 18 with components arranged thereon. One of these components soldered on the circuit board 18 is the SMD-solderable component 5 of the invention.

[0081] In the embodiment shown in FIG. 4, the field device 11 includes another electronics unit 20, embodied as a display/input unit and having a (touch-)display. The SMD-solderable component 5 of the invention can, of course, also be soldered onto a circuit board of the electronics unit 20 embodied as the display/input unit.

[0082] In an embodiment, the SMD-solderable component 5 is the above mentioned overcurrent protection device (i.e. with above mentioned dimension, and the above mentioned tripping current) applied in the case of a field device 11 embodied for use in explosion endangered areas.

REFERENCE CHARACTERS AND SYMBOLS

[0083]

TABLE-US-00001 Reference Characters and Symbols 1 resistance element 1a, 1b first, second end section 2a, 2b first, second contact element 3a, 3b first, second soldered connection 4a, 4b solder preform 5 SMD-solderable component 6 coating 7 guide 8 wire 9 insulating core 10 electronics unit 11 field device 12a, 12b contact element 13a, 13b soldered connection 14 resistance element 15 wire 16 solder bead 17 sensor unit 18 circuit board 19 transmitter housing 20 display/input unit T.sub.solder melting temperature CK1 first composite component CK2 second composite component F face h depth