EP4049310A1

EP4049310A1 - Method for producing an smd solderable component, smd solderable component, electronics unit and field device

Info

Publication number: EP4049310A1
Application number: EP20800036.4A
Authority: EP
Inventors: Dietmar Birgel; Silke CZAJA
Original assignee: Endress and Hauser SE and Co KG
Current assignee: Endress and Hauser SE and Co KG
Priority date: 2019-10-25
Filing date: 2020-10-23
Publication date: 2022-08-31
Also published as: DE102019128900A1; WO2021078953A1

Abstract

The invention relates to a method for producing an SMD solderable component (5), said method comprising the following steps: A) providing a plurality of nanowires (ND) on the one first connection surface (3a) and on the one connection surface (3b), B) aligning the first connection surface (3a) and the second connection surface (3b) in such a way that the first connection surface (3a) and the second connection surface (3b) face one another, C) bringing the first connection surface (3a) and the second connection surface (3b) together, bringing the plurality of nanowires (ND) of the first connection surface (3a) into contact with the plurality of nanowires (ND) of the second connection surface (3b), and in which method, when said surfaces are brought together, a non-releasable 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 transition resistance between a first contact element (2a) and a second contact element (2b) is produced. The invention further relates to an SMD solderable component (5), an electronics unit and a field device based on automation technology with an SMD solderable component according to the invention.

Description

Method for producing an SMD-solderable component, SMD-solderable component,

Electronics unit and field device

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

In automation technology, especially in process automation technology, field devices are often used to determine and / or monitor process variables. In principle, all devices that are used close to the process and deliver or process process-relevant information are referred to as field devices. These are, for example, level measuring devices, flow measuring devices, pressure and temperature measuring devices, pH redox potential measuring devices, conductivity measuring devices, etc., which record the corresponding process variables level, flow, pressure, temperature, pH value and conductivity. Field devices often have a sensor unit, in particular at least temporarily and / or at least in sections, which is in contact with a process medium and which is used to generate a signal that is dependent on the process variable. Furthermore, these often have an electronic unit arranged in a housing, the electronic unit serving to process and / or forward signals generated by the sensor unit, in particular electrical and / or electronic signals. The electronics unit typically comprises at least one printed circuit board with components arranged thereon.

The electronics unit often has a large number of SMD components, which are provided with corresponding contact elements for soldering onto contact areas provided for this purpose on a surface of a printed circuit board. SMD-solderable components (short for 'Surface Mounted Devices', i.e. surface-mountable components) are soldered with their contact elements directly to the connections provided for them. For this purpose, the SMD components are automatically placed with automatic placement machines on the contact surfaces provided with solder paste on the circuit board and soldered together with a so-called reflow soldering process in a reflow soldering oven. This means that a large number of SMD-solderable components can be soldered onto the circuit board at the same time.

Such SMD components according to the prior art often themselves have a large number of solder connections, for example between the contact elements and / or between further components of the component. In the event that such a solder connection is present, it is often very demanding for manufacturing reasons to reliably set a predetermined contact resistance between the contact elements of the SMD-solderable component. The invention is therefore based on the object of specifying an SMD-solderable component which has a predetermined contact resistance between its contact elements with a sufficiently high level of reliability.

With regard to the method, the object is achieved by a method for producing an SMD solderable component, the SMD solderable component having:

-a first contact element and a second contact element, wherein the first contact element and the second contact element are provided for soldering onto contact areas provided for this purpose on a surface of a circuit board,

a first connection area and a second connection area, wherein the first connection area is formed by an end face of the first contact element, and wherein the method comprises the steps:

A) providing a plurality of nanowires on the first connection area and on the second connection area;

B) aligning the first connection area and the second connection area in such a way that the first connection area and the second connection area face one another;

C) Merging the first connection area and the second connection area, in which the plurality of nanowires of the first connection area is brought into contact with the plurality of nanowires of the second connection area, wherein during the merging a non-releasable electrically conductive first connection between the first connection area and the second connection surface is produced in such a way that there is a predeterminable contact resistance between the first contact element and the second contact element.

By using nanowires on the connection surfaces, an electrically highly conductive and mechanically stable form-fitting first connection can be created without the need for soldering. The SMD-solderable component is therefore preferably also free from solder connections. Due to the size of the nanowires, the surface area of the connection is increased.

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 area and the second connection area, a cross-sectional area of the nanowires and / or a length of the nanowires, and / or a selection of a material for the nanowires.

The nanowires preferably have a length in the range from 100 nm (nanometers) to 100 μm (micrometers). Furthermore, the nanowires preferably have a diameter in the range from 10 nm to 100 μm, in particular in the range from 30 nm to 2 μm. The The term “diameter” refers to a circular base area, with a comparable definition of a diameter being used for a base area that differs from this. It is particularly preferred that all nanowires used have the same length and the same diameter and the same material

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 trace etching method.

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

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

In an alternative embodiment of the method according to the invention, an elongated resistance element is provided which has a first end section and a second end section essentially opposite the first end section in the longitudinal direction of the resistance element, the second connection surface being formed by an end face of the first end section.

In one embodiment of the method according to the invention, a third connection surface is formed by an end surface of the second contact element and a fourth connection surface is formed by an end surface of the second end section, and the method comprises the steps:

D) providing a multiplicity of nanowires on the third connection area and on the fourth connection area

E) aligning the third connection area and the fourth connection area in such a way that the third connection area and the fourth connection area face one another, F) Merging the third connection area and the fourth connection area, in which the plurality of nanowires of the third connection area is brought into contact with the plurality of nanowires of the fourth connection area, a non-releasable electrically conductive second connection being established between the third pad and the fourth pad.

The second connection is also form-fitting. All of the configurations mentioned so far and / or below that are / are mentioned in connection with the first connection area and the second connection area and the first connection present therebetween are mutatis mutandis also for the third connection area and the fourth connection area and ie present between them second connection includes.

In one embodiment of the method according to the invention, steps B) and C) are carried out following steps E) and F) or steps B) and C) are carried out essentially simultaneously with steps E) and F).

In one embodiment of the method according to the invention, after the establishment of the non-detachable first connection, the first connection is heated to a joining temperature and / or after the establishment of the non-detachable second connection, the second connection is heated to a joint temperature.

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

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.

In one embodiment of the method according to the invention, the joining temperature is achieved in that a voltage is applied between the first contact element and the second contact element, which voltage causes an electrical current to flow between the first contact element and the second contact element. The level of the electrical current is selected in such a way that the joining temperature of at least 150 ° C is reached.

One possibility is that an electrical power is introduced via a current flow between the two contact elements, via which the first or second connection to the Joining temperature heated. 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 configuration mentioned below), the heat can also be introduced inductively via the magnetic field induced by a current flow, similar to an inductive heating plate.

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

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

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 are a metal, in particular copper, gold, nickel, silver, Zinc, tin, indium and / or platinum.

To protect the environment and people, efforts are now being made to avoid the use of heavy metals such as lead or mercury. The RoHS directive (Restriction of Certain Hazardous Substances) of the European Union, which prohibits the use of certain hazardous substances, such as lead, in the electrical industry, also aims in this direction. It is therefore advantageous to specify an SMD-solderable component that is as lead-free as possible. Since the SMD-solderable component is free of solder connections, in particular no lead-containing solders are used.

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, the specified contact resistance being set in such a way that the tripping current of the overcurrent protection device is between 0.02 and 1 A is.

In one configuration 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 caused by heating to the joining temperature is present between the first contact element and the second contact element. In particular, the metals have different thermal expansion coefficients. By heating on the On the one hand, this improves the joining temperature of the first and / or second connection, on the other hand, the sensitivity of the overcurrent protection device is increased because, similar to a bimetal effect, a mechanical tension between them via the heating of the two interconnected contact elements is introduced. 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.

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.

In one embodiment of the SMD-solderable component, the resistance element is a wire wound in turns around an electrically insulating core, the wire in particular having a diameter of less than 50 μm (micrometers), and in particular the wire having a Tin-plating is coated, the melting temperature of which is greater than 225 ° C.

The joining temperature is therefore advantageously less than 225 ° C., so that there is no pre-aging of the resistor element when it is heated to the joining temperature.

The invention also relates to an electronics unit with a printed circuit board, the SMD solderable component according to the invention being soldered to contact areas provided for this purpose on the surface of the printed circuit board.

In one embodiment of the electronics unit, the electronics unit is designed for use in potentially explosive areas.

Such electronic units must meet very high safety requirements with regard to explosion protection. In the case of explosion protection, the main concern is to safely avoid the formation of sparks or at least to ensure that a spark that occurs in the event of a fault has no effect on the environment. For this purpose, a number of associated protection classes are defined in the relevant standards, in particular in the European standard IEC 600079-11 and / or EN60079-11

For example, in the protection class with the name "intrinsic safety" (Ex-i), explosion protection is achieved in that the values for an electrical variable (current, voltage, power) are always below a given limit value at all times Error case no Spark is generated. In the further protection class called "Increased Safety" (Ex-e), explosion protection is achieved by the spatial distances between two different electrical potentials being so large that sparks cannot occur due to the distance, even in the event of a fault. In the additional protection class called "Flameproof Enclosure" (Ex-d), electronic units designed according to this protection class must have sufficient mechanical strength or stability.

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

The SMD-solderable component, in particular the SMD-solderable overcurrent protection device, is therefore used in an electronic unit designed for use in potentially explosive areas. In particular, the electronics unit is therefore designed in accordance with a protection class of the aforementioned standards. The reliability of the overcurrent protection device according to the invention is particularly important here.

The invention also relates to a field device in automation technology with an electronic unit according to the invention.

In particular, the electronics unit is therefore an electronics unit of a field device in automation technology.

The invention is explained in more detail with reference to the following figures, which are not true to scale, with the same reference symbols denoting the same features. If it is necessary for clarity or if it appears to be useful in some other way, the reference symbols already mentioned are dispensed with in the following figures.

Show it:

1: A first embodiment of the SMD-solderable component according to the invention;

2: A second embodiment of the SMD-solderable component according to the invention;

3: A third embodiment of the SMD-solderable component according to the invention;

4: An embodiment of a field device in automation technology with an electronics unit which has an embodiment of the SMD-solderable component according to the invention. In Fig. 1, a first embodiment of the SMD-solderable component 5 according to the invention is shown. This is produced in that a first contact element 2a and a second contact element 2b are connected to one another, the end faces SF of which each form a first connection area 3a and a second connection area 3b.

For this purpose, in a first method step A, a plurality of nanowires ND are provided on each of the first connection surface 3a and the second connection surface 3b, for example by means of an ion trace etching method 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 as facing one another and brought together, as a result of which the nanowires ND applied to the respective connection surface 3a, 3b form a form-fitting connection. By means of the form-fitting connection between the nanowires ND, an electrically conductive first connection 4a is established between the first connection area 3a and the second connection area 3b.

In the context of the invention, the establishment of the first connection 4a advantageously results in a prescribable contact resistance between the first contact element 2a and the second contact element 2b. The specifiable contact resistance is set, for example, via the dimension of the first connection area 3a and the second connection area 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 competent person can carry out a corresponding series of tests. The specifiable 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 transition 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.

In an alternative embodiment to that shown in FIG. 1, an elongated resistance element 1 is additionally provided between the first contact element 2a and the second contact element 2b. As in FIG. 1, the first connection surface 3a is formed by an end surface SF of the first contact element 2a. The resistance element 1 now has a first end face SF on a first end section 1a, which forms the second connection face 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 is already positively connected to a fourth connection surface 3d by means of an electrically conductive second interlocking connection 4b between the second end section 1b and the second contact element 2b. Also the electrically conductive second Connection 4b is made using a plurality of nanowires ND. Only when the first electrically conductive connection 4a is established are the first contact element 2a and the second contact element 2b connected to one another in an electrically conductive manner with the predeterminable contact resistance.

When establishing the first connection 4a and / or the second connection 4b, the respective connection surfaces 3a, 3b; 3c, 3d are possibly pressed against one another by means of pressure with a contact force.

As an additional process step for establishing the first connection 4a or the first connection 4a and the second connection 4b, it can 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 picture. For heating purposes, electrical power can be introduced, for example, via the first and second contact elements 2a, 2b that are electrically connected to one another. Alternatively, the SMD-solderable component 5 can be heated in an oven.

In one embodiment, metals with a different coefficient of thermal expansion are used as materials for the first contact element 2a and the second contact element 2b. In this case, the heating to the joining temperature FT also advantageously creates a mechanical tension between the first contact element 2a and the second contact element 2b. caused (bi-meta II effect). An additional mechanical tension is advantageous, for example, if the SMD-solderable component 5 is designed as an overcurrent protection device, since its sensitivity and thus tripping reliability can be increased by means of an additional mechanical tension.

In a third embodiment shown in FIG. 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), with only the first in FIG End section 1a of the resistance element 1 and the first contact element 2a connected thereto are shown. The wire 8 is coated with a coating 6 designed as tinning.

The contact element 2a is a cup-shaped end cap with a, for example, rectangular or round bottom surface and an inner 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, the overcurrent protection devices being characterized on the basis of the contact resistance and the resulting tripping current between the contact elements 2a, 2b. In the case of a resistance element 1 with a wound wire 8, a current flow also always causes an induced magnetic field. As with an induction cooker, the heating to the joining temperature FT can also be generated here by means of a high-frequency alternating current circuit, which is applied to the electrically conductively connected contact elements 2a, 2b and which generates eddy currents that heat the SMD-solderable component 5.

However, the joining temperature FT is preferably lower than a melting temperature of the resistance element 1, in particular its coating 6; in the case of tin-plating, at least less than 230 ° C. Due to the joining temperature FT of less than 230 ° C. used during heating, pre-aging of the wire 8, in particular also a melting of a coating 6 of the wire 8 and the resulting formation of solder balls between, for example, adjacent turns, is effectively prevented.

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 the contact surfaces provided for this purpose on a printed circuit board 18 of an electronics unit 10 in 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 in automation technology. Such a field device 11 of automation technology is shown in more detail in 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, which serves to generate a measurement signal, for example electrical and / or electronic, which represents the process variable.

The electronics unit 10 arranged in a transmitter housing 19 of the field device 11 is used to process and / or forward the measurement signals generated by the sensor unit 17. The electronics unit 10 typically 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.

In the embodiment shown in FIG. 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 printed circuit board of the electronics unit 20 configured as a display / input unit.

In one embodiment, the SMD-solderable component 5 is the aforementioned overcurrent protection device (ie with the aforementioned dimension or the tripping current mentioned above), which is used in a field device 11 which is designed for use in potentially explosive areas.

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 plating 8 wire

9 insulating core

10 electronics unit 11 field device 17 sensor unit 18 printed circuit board

19 T ransmitter housing

20 Display / input unit

FT joining temperature SF end face ND nanowires

Claims

1. A method for producing an SMD-solderable component (5), wherein the SMD-solderable component (5) has:

-a first contact element (2a) and a second contact element (2b), the first contact element (2a) and the second contact element (2b) being provided for soldering onto contact areas provided for this purpose on a surface of a 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:

A) providing a multiplicity 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) in such a way that the first connection surface (3a) and the second connection surface (3b) face one another;

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) , during the merging a non-releasable electrically conductive first connection (4a) between the first connection surface (3a) and the second connection surface (3b) is established in such a way that a predeterminable contact resistance between the first contact element (2a) and the second contact element ( 2b) is available.

2. The method according to claim 1, wherein the predeterminable contact resistance 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 Selecting a material for the nanowires (ND) is set.

3. The 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. The 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) on one side of the respective first connection surface (3a) or second connection surface (3b) are attached and are in a substantially perpendicular direction to the respective first connection area (3a) or second connection area (3b), and the nanowires (ND) cover the respective first connection area (3a) or second connection area (3b) essentially flat.

5. The 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. The method according to at least one of the preceding claims 1 to 4, wherein an elongated resistance element (1) is provided which has a first end section (1a) and a second end section substantially opposite the first end section (1a) in the longitudinal direction of the resistance element (1) (1b), wherein the second connection surface (3b) through an end surface (SF) of the first end section

(la) is formed.

7. The method according to claim 6, wherein a third connection surface (3c) through an end face (SF) of the second contact element (2b) and a fourth connection surface (3d) through an end face (SF) of the second end section

(lb), and wherein the method comprises the steps of:

D) providing a multiplicity 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) in such a way that the third connection surface (3c) and the fourth connection surface (3d) face one another;

F) bringing together the third connection surface (3c) and the fourth connection surface (3d), in which the plurality of nanowires (ND) of the third connection surface (3c) is brought into contact with the plurality of nanowires (ND) of the fourth connection surface (3d) , a non-releasable electrically conductive second connection (4b) being produced between the third connection surface (3c) and the fourth connection surface (3d) during the merging.

8. The method according to claim 7, wherein steps B) and C) are carried out subsequent to steps E) and F) or wherein steps B) and C) are carried out essentially simultaneously with steps E) and F).

9. The method according to at least one of the preceding claims, wherein after the production of the non-releasable first connection (4a) the first connection (4a) is heated to a joining temperature (FT), and / or wherein after the production of the non-releasable second Connection (4b) the second connection (4b) is heated to a joining temperature (FT).

10. The 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 in that a voltage is applied between the first contact element (2a) and the second contact element (2b) which is one between the first contact element (2a) and the second contact element (2b) causing electric current to flow.

12. The 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) which is produced according to at least one of claims 1 to 12, wherein the SMD-solderable component (5) is lead-free and wherein the nanowires (ND) are a metal, especially 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 set in such a way, in particular, 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 the 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 claim 13 to 15, wherein the SMD-solderable component (5) has a dimension of a maximum of 20 mm, and wherein in particular a distance between the first contact element (2a) and the second contact element ( 2b) is smaller than 15 mm.

17. SMD-solderable component (5) according to claim 13 to 16 wherein it is the

Resistance element (1) is a wire (8) wound in turns around an electrically insulating core (9), and in particular the wire (8) has a diameter of less than 50 μm (micrometers), and 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. Electronics unit (10) with a printed circuit board (18), the SMD-solderable component (5) according to at least one of claims 13 to 17 being soldered to the respective contact areas provided on the surface of the printed circuit board (18).

19. Electronics unit (10) according to claim 18, wherein the electronics unit (10) is designed for use in potentially explosive areas.

20. Field device (11) of automation technology with an electronics unit (10) according to at least one of the preceding claims 18 to 19.