ELECTRONIC DEVICE AND METHOD FOR DETECTING MECHANICAL OVERLOAD OF AN ELECTRONIC DEVICE

Description

[0001] The invention relates to an electronic device comprising a circuit arrangement. Furthermore, the invention relates to a method for detecting mechanical overload of an electronic device.

[0002] The electronic device in question is specifically a field device used in automation technology. Field devices in automation technology are used to determine and / or monitor process variables. In principle, the term "field device" refers to all devices that are used close to the process and provide or process process-relevant information. These include, for example, level gauges, flow meters, pressure and temperature gauges, pH / ORP meters, conductivity meters, etc., which measure the corresponding process variables such as level, flow rate, pressure, temperature, pH value, and / or conductivity. Field devices often have a sensor unit that is in contact with a process medium, at least temporarily and / or at least partially, and which serves to generate a signal dependent on the process variable.Furthermore, these often have at least one electronic unit arranged in a housing with a circuit arrangement, the electronic unit typically serving to process and / or forward signals generated by the sensor unit, in particular electrical and / or electronic signals.

[0003] Electronic devices used close to the process, such as the field devices mentioned above, are typically exposed to sometimes harsh operating conditions. These include, in particular, mechanical stresses, e.g., vibrations, impacts, and / or thermomechanical stresses caused by rapid temperature changes. The manufacturer of the electronic device therefore usually specifies, where possible, a maximum mechanical stress under which the reliable operation of the electronic device can be guaranteed or ensured during intended use. In the event of damage, proving that the electronic device was subjected to excessive mechanical stress, especially only temporarily, proves challenging, particularly retrospectively. A relevant prior art document for the invention is Huakang Li et al.: "Mechanism of Solder Joint Intermittent Faults and Its Detection", 2018 IEEE INTERNATIONAL SYMPOSIUM ON THE PHYSICAL AND FAILURE ANALYSIS OF INTEGRATED CIRCUITS (IPFA), IEEE, July 16, 2018, pages 1-5, DOI: 10.1109 / IPFA.2018.8452542.

[0004] The invention is therefore based on the objective of providing an electronic device whose temporary mechanical overload can be detected as easily as possible during a measurement operation.

[0005] The problem is solved by an electronic device according to claims 1-9 and a method for detecting mechanical overload of an electronic device according to claims 10-13.

[0006] With regard to the electronic device, the problem is solved by an electronic device comprising a circuit arrangement, wherein the circuit arrangement has a brittle-breaking solder joint in an electrically conductive path of the circuit arrangement, and wherein the circuit arrangement is designed to detect a maximum temporary voltage and / or current interruption in the path and to attribute a maximum partial brittle fracture of the brittle-breaking solder joint, which brittle fracture is caused by a maximum temporary mechanical overload of the electronic device, so that the maximum temporary mechanical overload of the electronic device can be detected on the basis of the circuit arrangement.

[0007] According to the invention, temporary mechanical overload of the electronic device can advantageously be detected solely based on the circuit arrangement of the electronic device itself, i.e., without the use of additional vibration and / or impact sensors. This is achieved by designing at least one solder connection of the circuit arrangement to be brittle-breaking.

[0008] In materials mechanics, materials are classified as brittle or ductile based on their fracture mechanics. Brittle materials are characterized under mechanical stress by a steep slope of Hooke's law in the stress-strain diagram, at the end of which fracture occurs without plastic deformation. In addition to this characteristic behavior, a brittle fracture is usually also recognizable as such afterward, for example, through appropriate materials mechanics analyses of the fracture surfaces.

[0009] Under temporary mechanical stress, the solder joint undergoes partial brittle fracture. This causes a temporary and noticeable increase in the contact resistance within the circuit arrangement, which is partly determined by the solder joint, to such an extent that a voltage and / or current interruption can be detected by the circuit arrangement itself.

[0010] Since the solder joint is only partially brittle (i.e., only partially, and therefore not completely, permeated by a crack), the typically smooth fracture surfaces of the partial brittle fracture are once again in close mechanical contact with each other after the at most temporary mechanical overload. This may lead to a re-joining of the fracture surfaces of the brittle fractured area of ​​the solder joint, similar to cold welding.

[0011] In this case, the contact resistance, which is partly determined by the solder joint, returns to a normal value (i.e., a value for the contact resistance before the occurrence of the overstress) after the temporary overload. In this sense, the partial brittle fracture can therefore also be described as reversible. In the case of such a reversible brittle fracture event in the solder joint, not only a single instance of mechanical overload, but also repeated occurrences, can be observed.

[0012] In one embodiment of the invention, the brittle-breaking solder joint is produced by means of a soldering process comprising the following steps: Providing solder containing bismuth with a proportion of at least 50% by weight; melting the solder, whereby the solder is brought to a maximum temperature; subsequently cooling the solder, whereby the solder solidifies so that the solder joint is formed, wherein the cooling is carried out at a cooling rate greater than 6°C / s.

[0013] Investigations by the applicant have shown that a solder compound produced in this way surprisingly exhibits brittle-breaking properties. This is primarily due to the high bismuth content, combined with rapid cooling rates greater than 6°C / s.

[0014] The solder is provided in particular by means of a solder paste.

[0015] In one embodiment of the invention, the provided solder contains tin with a proportion of at least 40 percent by weight and / or silver with a proportion of at most 2 percent by weight.

[0016] In one embodiment of the invention, the cooling rate is greater than 10°C / s and in particular less than 50°C / s.

[0017] In connection with the manufacturing process for producing the brittle-breaking solder compound, reference is made to the patent application with application number 102020105180.8, which was still unpublished at the time of filing this application, and to whose disclosure content for the production of the brittle-breaking solder compound reference is made here.

[0018] In one embodiment of the invention, the circuit arrangement for detecting the at most temporary voltage and / or current interruption comprises at least one comparator element.

[0019] In one embodiment of the invention, the circuit arrangement includes a microcontroller which is connected to the comparator element(s) in such a way that the comparator element(s) transmits a detected, at most temporary, voltage and / or current interruption to the microcontroller.

[0020] The microcontroller can thus detect and, if necessary, store the number of at most temporary voltage and / or current interruptions that can be attributed to mechanical overload, e.g. in a memory module of the microcontroller and / or in a storage unit connected to the microcontroller via a communication link.

[0021] In one embodiment of the invention, the circuit arrangement includes a capacitor which, in the event of a temporary voltage and / or current interruption, provides a voltage stored in the capacitor as an operating voltage for the electronic device for the duration of the interruption in order to bridge the interruption.

[0022] The capacitor thus acts as an energy storage device, compensating for any temporary voltage and / or current interruption. The capacitor is charged, for example, during normal operation of the electronic device, i.e., before and after the voltage and / or current interruption. The circuit design can therefore detect the overload without limiting the availability of the electronic device for the duration of the interruption.

[0023] In one embodiment of the invention, the voltage and / or current interruption is at most temporary and lasts for a duration of at least 3.5 ns (nanoseconds). Modern circuit arrangements are capable of detecting interruptions of at least 3.5 ns.

[0024] In one embodiment of the invention, the voltage and / or current interruption is at most temporary and lasts for a maximum of 20 ms (milliseconds).

[0025] In one embodiment of the invention, the electronic device is a field device of automation technology with at least one electronic unit, wherein the electronic unit comprises the circuit arrangement.

[0026] With regard to the method, the problem is solved by a method for detecting mechanical overload of an electronic device according to the invention, comprising the step of: Determining a maximum temporary mechanical overload of the electronic device, in the event that a maximum temporary voltage and / or current interruption is detected in a path of the circuit arrangement, which can be attributed to a maximum partial brittle fracture of the brittle-breaking solder joint.

[0027] In one version of the procedure, this includes the following step: Recording a point in time at which the overstressing is detected; saving a detected overstressing along with a timestamp that marks the recorded point in time of the overstressing.

[0028] The detection of overstress is stored, for example, in the aforementioned memory module of the microcontroller or storage unit. By reading the stored timestamp, the time of the mechanical overstress can advantageously be determined, even retrospectively, for example, when processing returns of the electronic device.

[0029] In one embodiment of the method, the mechanical overload is repeatedly detected and stored.

[0030] In one embodiment of the procedure, this includes the step of creating and / or adapting a lifetime prediction for the electronic device, based on the identified mechanical overload(s).

[0031] In one embodiment of the method, at least one of the following is taken into account when predicting lifetime: a number of identified mechanical overloads; the time(s) of the identified mechanical overload(s).

[0032] The invention and further advantageous embodiments are explained in more detail below with reference to exemplary embodiments. Identical parts are provided with the same reference numerals in all figures; where clarity requires it or it otherwise appears appropriate, previously mentioned reference numerals are omitted in subsequent figures.

[0033] They show: Fig. 1 a, b : Detailed view of an embodiment of an electronic unit of an electronic device according to the invention with an at least partially brittle solder joint; Fig. 2 : Cooling rate during the production of the at least partially brittle solder joint; Fig. 3: Detailed view of an embodiment of an electronic unit of an electronic device according to the invention with an at least partially brittle solder joint under temporary mechanical overload; Fig. 4 : A circuit diagram in one embodiment of the invention; Fig. 5 : A flowchart for an embodiment of the process according to the invention; Fig. 6 : An embodiment of an electronic device according to the invention as a field device for automation technology.

[0034] In Fig 1a,1b The steps of the manufacturing process for producing a brittle solder joint 3 between a contact surface 9 of a printed circuit board of an electronic unit 10 and a component 8 arranged on the contact surface 9 are shown, with the printed circuit board being shown in a sectional view. The electronic unit 10 is part of an electronic device 11 and has a circuit arrangement 1 (see figure). Fig. 6The component 8 is placed onto the contact surface 9. Subsequently (or – depending on the soldering method – before placing the component 8), a solder 5 is provided. According to the invention, this is a high-bismuth solder 5 dh with a bismuth content of at least 50% by weight. The component 8 is then soldered in a mass or selective soldering process to create the brittle-breaking solder joint 3, e.g., by means of a wave or reflow soldering process.

[0035] All common soldering processes have in common that, during the soldering process, a process control is implemented that... Fig. 2The temperature profile shown in more detail is controlled and followed. This is a temperature-time function that describes at which point during soldering the component (e.g., the component 8) and / or the solder 5 reach which temperature. For example, preheating typically occurs in the first part of the temperature profile, followed by heating to a maximum temperature Tmax. This is typically above the liquidus temperature LQ of the solder 5. Subsequently, controlled cooling dh takes place with a defined, set cooling rate dT / dt. In a soldering process, the cooling rate dT / dt is defined as the maximum rate of temperature change during cooling, immediately after the point at which the liquidus temperature LQ of the solder 5 is reached.

[0036] According to the invention, the high-bismuth solder 5 is combined with a cooling rate dT / dt greater than 6°C / s. This is higher than the cooling rates typically used in the prior art. Surprisingly, investigations by the applicant have shown that this results in the formation of a brittle-breaking solder compound 6.

[0037] This is in Fig. 3 This is described in more detail below. If a mechanical overload of the electronic device 11 occurs (e.g., due to impacts, vibrations, or thermomechanical twisting caused by temperature gradients, etc.), an excessive force F acts on the solder joint 3. This leads to a partial brittle fracture SB in the solder joint 3. This partial brittle fracture SB is interrupted by a voltage and / or current interruption, especially a brief one, in a safety circuit (see circuit diagram in [reference]). Fig. 4) detected by the circuit arrangement 1 itself. The circuit arrangement 1 therefore serves as a warning system indicating that the device has been subjected to mechanical overload.

[0038] Within the scope of the invention, there are no restrictions on the path in which the brittle-breaking solder joint 3 is arranged within the circuit arrangement 1. For example, the component 8 is designed as a fuse with a contact resistance of < 1 ohm. Similar to in Fig. 1 a, b The solder joints used to attach the fuse to the circuit board are shown as the brittle-breaking solder joint 3. However, solder joints within the fuse itself can also be designed as the brittle-breaking solder joint 3. Furthermore, the brittle-breaking solder joint 3 can be located in a path of the circuit arrangement 1 that is not associated with a specific component 8, but, for example, only with a conductor track, etc.

[0039] Due to the partial brittle fracture SB, the fracture surfaces of the brittle fractured area of ​​the solder joint 3 are subsequently in close contact with each other again, leading to the voltage and / or current interruption SU. If cold welding of the fracture surfaces occurs, a contact resistance determined by the solder joint 3 normalizes to a normal value after the temporary overload, so that a voltage and / or current interruption SU associated with a mechanical overload can be observed several times.

[0040] In Fig. 4A circuit diagram is shown for an embodiment of a circuit arrangement 1, by means of which a voltage and / or current interruption SU in the path 2 with the brittle-breaking solder connection 3 (here: the component 8, which is designed as a resistive element, e.g., a fuse) can be detected. Preferably, the voltage and / or current interruption SU can be detected in at least two essentially independent, different ways (here: three).

[0041] First route:A brief voltage increase across component 8, caused by a temporary voltage interruption SU, is detected, for example, by a first comparator element 4, which provides a comparator voltage. When the first comparator element 4 detects the voltage and / or current interruption SU, it switches a first flip-flop 9. The first flip-flop 9 signals its switching to a connected microcontroller 6, which then detects and records the voltage interruption SU in path 2, either in its own memory chip or in a memory unit 16 connected to the electronic unit 10. After the microcontroller 6 detects the voltage and / or current interruption SU, it resets the first flip-flop 9 to its initial state, so that a future voltage and / or current interruption SU in path 2 can be detected again.

[0042] Second way: A current sink 15 and a second comparator element 41 are used to detect the voltage and / or current interruption SU, with the second comparator element 41 providing a comparator voltage. Similar to the first method, a second flip-flop 91 is also used in the second method, by means of which the voltage and / or current interruption SU is detected by the microcontroller 6.

[0043] Third way: The case of a temporary current interruption is detected by means of a comparator current from a third comparator element 42 and an associated measuring resistor 14. In this case, a third flip-flop 92 is set to transmit the voltage and / or current interruption SU to the microcontroller 6.

[0044] At the beginning of the circuit diagram, directly following a power supply 24, there is also a measuring diode 23, which serves for reverse polarity protection.

[0045] Regardless of the aforementioned methods, in the event of a voltage and / or current interruption SU, an operating voltage is provided for the electronic device 11 for the duration of the interruption. This is achieved by a capacitor 7, which is connected to a voltage regulator 13 in the circuit arrangement 1. This allows the microcontroller 6 to reliably detect mechanical overload, i.e., without interrupting the operation of the electronic device 11 for the duration of the voltage and / or current interruption SU.

[0046] A voltage and / or current interruption SU with a duration of at least 3.5 nsec can be readily detected using modern comparator elements 4,41,42, e.g. with a comparator of type NCP22.

[0047] Fig. 5Figure 1 shows steps of the inventive method for detecting a maximum temporary mechanical overload of the electronic device 11. In a first step A), the occurrence of a mechanical overload is detected as described above by means of the voltage and / or current interruption SU.

[0048] Preferably, the occurrence of the mechanical overload is stored in a storage unit 16, together with a timestamp 12 that uniquely marks the time of occurrence. As mentioned above, the storage unit can be part of the electronic unit 10 and thus of the electronic device 11 itself.

[0049] Alternatively, the storage unit 16 can also be assigned to a higher-level unit to which the electronic device 11 is connected via a communication link. The higher-level unit could be, for example, a higher-level control unit, such as a process control system with a computer, or a programmable logic controller (PLC).

[0050] The communication link is, for example, a wired communication link, such as an analog measurement transmission link, especially according to the 4-20mA standard, or a wired fieldbus used in automation technology, such as Foundation Fieldbus, Profibus PA, Profibus DP, HART, or CANbus. It can also be a communication link of a modern industrial communication network, such as an "Industrial Ethernet" fieldbus, especially Profinet, HART-IP, or Ethernet / IP, or a communication network known from the communications sector, such as Ethernet using the TCP / IP protocol.

[0051] In the event that the communication link is wireless, it could be, for example, a Bluetooth, ZigBee, WLAN, GSM, LTE, UMTS communication network or a wireless version of a fieldbus, especially 802.15.4 based standards such as WirelessHART.

[0052] In a second step B), a lifetime prediction LDV for the electronic device 11 is created and / or adjusted based on the stored voltage and / or current interruptions SU and, if applicable, the timestamp 12. The number of voltage and / or current interruptions SU, as well as their timing, are taken into account.

[0053] By means of the stored voltage and / or current interruptions SU and / or the adapted lifetime prediction LDV, in the event of a permanent failure of the electronic device 11, this failure can potentially be attributed to the mechanical overload experienced by the electronic device 11. The failure is not caused by the partial brittle fracture SB of the solder joint 3, but by further damage to the electronic device 11, which, however, can also be attributed to the mechanical overload that caused the brittle fracture. Within the scope of the invention, the brittle fracture SB associated with the voltage and / or current interruption SU thus serves only to reliably detect the occurrence of the mechanical overload.

[0054] The method according to the invention therefore facilitates the settlement of claims between the manufacturer and a user of the electronic device 11 who has mechanically overloaded it.

[0055] The steps of the procedure are carried out by the electronic device 11 itself, or in combination with the aforementioned superior unit.

[0056] Preferably, the electronic device 11 is designed as a field device for automation technology. Such an electronic device 11 is in Fig. 6 A more detailed explanation.

[0057] The field device 11 has a sensor unit 17 which is in contact with a process medium, at least temporarily and / or at least sectionally, and which serves to generate a measurement signal representing the process quantity, e.g. electrical and / or electronic.

[0058] The electronic unit 10, arranged in a transmitter housing 21 of the field device 11, serves to process and / or forward the measurement signals generated by the sensor unit 17. The electronic unit 10 comprises a printed circuit board 22 with the circuit arrangement 1, which has a brittle-breaking solder connection 3 in one path, by means of which the mechanical overload of the field device, e.g. during measurement operation, can be detected.

[0059] An advantage for the field device is that its mechanical overload can also be detected retrospectively by reading out the recorded events of voltage and / or current interruptions SU stored in the storage unit 16.

[0060] In the Fig. 6In the embodiment shown, the field device 11 has a further electronic unit 10a, serving as a display / input unit 20, with a (touch) display mounted on it. If the field device 11 has several electronic units 10, 10a, ..., it is of course possible that the brittle-breaking solder joint 3, by means of which mechanical overload can be detected, is used in one or both of the electronic units 10, 10a. Reference signs and symbols

[0061] 1 Circuit arrangement 2 Path 3 Solder connection 4, 4, 1, 42 Comparator element 5 Solder 6 Microcontroller 7 Capacitor 8 Component 9, 9, 1, 92 Flip-flop 10, 10a Electronic unit 11 Electronic device 12 Timestamp 13 Voltage regulator 14 Measuring resistor 15 Current sink 16 Storage unit 17 Sensor unit 20 Display / input unit 21 Transmitter housing 22 Circuit board 23 Measuring diode SUS Voltage and / or current interruption SBS Brittle fracture dT / dt Cooling rate LQ Liquid temperature Tmax Maximum temperature F Force

Claims

1. An electronic device having a circuit configuration (1), wherein the circuit configuration (1) has a brittle solder connection (3) in an electrically conductive path (2) of the circuit configuration, and wherein the circuit configuration (1) is configured to detect an at most temporary voltage and / or power outage (SU) in the path (2) and to attribute it to an at most partial brittle failure (SB) of the brittle solder connection (3), said brittle failure (SB) being caused by an at most temporary mechanical overload of the electronic device so that the at most temporary mechanical overload of the electronic device can be detected using the circuit configuration (1), wherein the brittle solder connection is established by means of a soldering process comprising the following steps: - Supplying solder (5), said solder containing at least 50 percent by weight of bismuth (Bi); - Melting the solder (5), during which melting process the solder (5) is brought to a maximum temperature (Tmax); - Subsequently cooling the solder (5), during which cooling process the solder (5) sets to form the solder connection (3), wherein cooling takes place at a cooling rate (dT / dt), said cooling rate (dT / dt) being faster than 10 °C / s.

2. The electronic device as claimed in claim 1, wherein the solder (5) supplied contains at least 40 percent by weight of tin (Sn) and / or a maximum of 2 percent by weight of silver (Ag).

3. The electronic device as claimed in claim 2 or 3, wherein the cooling rate (dT / dt) is slower than 50 °C / s.

4. The electronic device as claimed in at least one of the preceding claims, wherein the circuit configuration for detecting the at most temporary voltage and / or power outage (SU) has at least one comparator element (4).

5. The electronic device as claimed in at least one of the preceding claims, wherein the circuit configuration has a microcontroller (6), said microcontroller (6) being connected to the comparator element(s) (4) in such a way that the comparator element(s) (4) transmits / transmit a detected, at most temporary voltage and / or power outage (SU) to the microcontroller (6).

6. The electronic device as claimed in at least one of the preceding claims, wherein the circuit configuration has capacitor (7), which provides a voltage stored in the capacitor (7) as operating voltage for the electronic device for the duration of the outage (SU) to bridge the outage (SU) in the event of an at most temporary voltage and / or power outage (SU).

7. The electronic device as claimed in at least one of the preceding claims, wherein the at most temporary voltage and / or power outage (SU) occurs for a duration of at least 3.5 ns (nanoseconds).

8. The electronic device as claimed in at least one of the preceding claims, wherein the at most temporary voltage and / or power outage (SU) occurs for a duration of at most 20 ms (milliseconds).

9. The electronic device (11) as claimed in at least one of the preceding claims, wherein the electronic device (11) is an automation technology field device with at least one electronic unit (10), and wherein the electronic unit (10) has the circuit configuration (1).

10. A method for detecting a mechanical overload of an electronic device (11) as claimed in at least one of claims 1 to 9, comprising the step: - Detecting an at most temporary mechanical overload of the electronic device (11) for the event that an at most temporary voltage and / or power outage (SU) is detected in a path (2) of the circuit configuration (1), which can be attributed to an at most partial brittle failure (SB) of the brittle solder connection (3).

11. The method as claimed in claim 10, comprising the step: - Recording a time point at which the overload is detected; - Saving a detected overload together with a timestamp (12), said timestamp (12) representing the recorded time point of the overload.

12. The method as claimed in claim 10 or 11, wherein the mechanical overload is detected and saved on a recurring basis.

13. The method as claimed in at least one of claims 10 to 12, comprising the step: Creating and / or adapting a service life prediction (LDV) for the electronic device (11), based on the detected mechanical overload(s), wherein the service life prediction (LDV) considers at least one of the following: - A number of detected mechanical overloads; - The time point(s) of the detected mechanical overload(s).