Testing a unit comprising two components to be joined by resistance soldering for the presence of a solder element.

Abstract

Method for testing a unit (1) comprising at least two components (2) to be joined by resistance soldering, wherein the unit (1) is arranged at a solder joint (3) between a first electrode (6) and a second electrode (6) of a resistance soldering device (5) and an electrical test voltage is applied to the electrodes (6) to generate a current flow through the unit (1), wherein, by evaluating the contact resistance caused by the unit (1), it is determined whether the unit (1) comprises a solder element (4) at the solder joint (3), which is considered a positive result, or does not, which is considered a negative result, wherein - if the investigation is successful, an electrical soldering voltage is applied to the electrodes (6) in order to solder the at least two components (2) together and - if the investigation yields a negative result, the soldering voltage is not applied.

Description

[0001] The invention relates to a method for testing a unit comprising at least two components to be connected by resistance soldering.

[0002] When resistance soldering components, it may be necessary to use a solder element, i.e. an element made of a solder material that is different from the components and that is arranged between the components to be joined and that is melted during the soldering process, in order to ensure sufficient fatigue strength of the soldered joint to be formed.

[0003] For quality assurance of an automated soldering process, it may therefore be useful to check for the presence of such a solder element to ensure that the components to be joined do not have faulty or missing solder joints.

[0004] A camera-based check for the presence of a solder element is known in this regard, but this usually occurs before the unit with the components to be connected is positioned in a resistance soldering fixture. This carries the risk of the solder element being lost during transport of the unit from the camera-based inspection station to the resistance soldering fixture.

[0005] EP 3 825 445 B1 discloses a method for resistance soldering two components using a soldering element, wherein during the soldering process the electrical voltage applied to the welding point via two electrodes of a resistance soldering device is measured and based on this it is determined whether the soldering element is correctly positioned.

[0006] US 6 091 044 A describes a resistance soldering device with a contactless temperature sensor which determines the temperature of a solder element during a soldering process, whereby a current flow through electrodes of the resistance soldering device and through the solder element is terminated when a predefined temperature of the solder element is reached.

[0007] The invention is based on the object of providing an advantageous method for testing a unit with at least two components to be connected by resistance soldering with regard to the presence of a solder element at a soldering point.

[0008] This object is achieved by the method according to patent claim 1. A resistance soldering device suitable for the automated implementation of such a method is the subject of patent claim 8. A resistance soldering system with such a resistance soldering device is the subject of patent claim 9. Preferred embodiments of the method according to the invention as well as advantageous embodiments of the resistance soldering device according to the invention and the resistance soldering system according to the invention are the subject of the further patent claims and / or emerge from the following description of the invention.

[0009] A method for testing a unit having at least two components to be connected by resistance soldering comprises arranging the unit in the region of a solder joint, i.e. a section of the unit at which a solder connection is to be formed, between a first electrode and a second electrode of a resistance soldering device. An electrical test voltage is then applied to the electrodes to generate a current flow through the unit, wherein the contact resistance caused by the unit is evaluated to determine whether the unit comprises a solder element at the solder joint, which is interpreted as a positive determination result, or whether it does not comprise one, which is interpreted as a negative determination result. If the determination is positive, an electrical soldering voltage is applied to the electrodes to solder the at least two components.If the test result is negative, however, the soldering voltage is not applied, so that no attempt is made to create the intended solder connection, which would be faulty or missing due to the missing solder element.

[0010] If the test result is negative, the unit can therefore be assessed as unsuitable for soldering at the soldering point. As a consequence, the unit can be treated as scrap and no longer used. However, it is preferably provided that if the test result is negative, the unit is reworked and, for this purpose, provided with a solder element at the soldering point, which may also include correcting the positioning of the solder element at the soldering point. The reworked unit can then be used again. For such further use, the test method according to the invention can be repeated so that immediately before soldering, a new test can be carried out to determine whether the subsequently repositioned or corrected solder element is still present at the soldering point.

[0011] The method according to the invention has the advantage that loss or displacement of the solder element between the test and the actual soldering (in the case of a positive test result) can be essentially ruled out because no transport or other movement of the unit is required between these process steps. In addition, the positioning of the solder element between the components can be secured by pressure exerted by the electrodes on the unit at the soldering point. Accordingly, it can preferably be provided that the electrodes at the soldering point exert a pressure on the unit that corresponds to at least a defined minimum pressure as soon as the test voltage is applied. In the case of a positive test result, this pressure is maintained at at least the minimum pressure at least until the soldering voltage is applied, and preferably also during the application of the soldering voltage.Furthermore, the pressure on the unit can preferably be maintained for a defined period after the soldering voltage is applied, whereby the pressure may then also fall below the minimum pressure. The minimum pressure can be set such that slippage of the solder element is prevented with sufficient certainty.

[0012] According to a preferred embodiment of a method according to the invention, it can be provided that values ​​or value ranges provided for the test voltage on the one hand and for the soldering voltage on the other hand are selected differently. In this case, it can be particularly preferably provided that the value or value range for the test voltage is selected to be smaller than the value or value range for the soldering voltage. The value or value range for the test voltage can in particular be selected to be so low that, although the intended determination can be carried out, the components to be connected are not damaged in the event that no solder element is present at the soldering point. The value or value range for the soldering voltage, on the other hand, can be selected to be significantly higher in order to ensure that the material of the solder element melts.This could result in damage to the components if no solder element is present at the soldering point. A relatively low value or range of values ​​for the test voltage can therefore ensure the preferred reworking of the unit with the goal of further use by subsequent soldering.

[0013] According to a preferred embodiment of a method according to the invention, the solder element may comprise or consist of a material having a liquidus temperature of at least 450°C. This allows a relatively high strength of the solder joint to be formed to be achieved.

[0014] A resistance soldering device according to the invention comprises at least a first electrode, a second electrode, an electrical voltage source for applying an electrical (soldering and testing) voltage to the electrodes, and a control device for controlling the voltage source. The control device is configured to automatically carry out a method according to the invention. For this purpose, the control device comprises at least one memory on which a computer program is stored, the execution of which by a processor of the control device performs a method according to the invention.

[0015] A resistance soldering device according to the invention may also preferably comprise a pressing device to actively press at least one of the electrodes against the unit so that the preferably provided minimum pressure at the soldering point can be realized.

[0016] A resistance soldering system according to the invention, which can advantageously be used within the framework of an automated manufacturing process for an assembly comprising the unit, comprises at least one resistance soldering device according to the invention, a first handling device for feeding the unit to the resistance soldering device, and a second handling device for removing the unit from the resistance soldering device. It can be provided that the unit is removed by means of the second handling device only in the soldered state, while a third handling device is used to remove the unit in the unsoldered state. As a result, the unit can advantageously be removed from the automated manufacturing process in the unsoldered state for post-processing.

[0017] The invention is explained in more detail below with reference to an exemplary embodiment illustrated in the drawings. The drawings show, partly in simplified form: Fig. 1: a resistance soldering device according to the invention and a unit arranged therein with two components to be connected by resistance soldering and a soldering element.

[0018] The Fig. The unit 1 shown in Figure 1 comprises two components 2, each of which may, for example, be a sheet metal component made of copper. A solder element 4 is arranged between the components 2 at a soldering point 3. The solder element 4 consists, for example, of silver (e.g., 15% by mass), phosphorus (e.g., 5% by mass), and copper (the remainder).

[0019] The unit 1 is arranged within a resistance soldering device 5 such that the soldering point 3 is positioned between two oppositely arranged electrodes 6.

[0020] In addition to the electrodes 6, the resistance soldering device 5 comprises an electrical voltage source 7 which is electrically connected to the electrodes 6, as well as a control device 8 by means of which the voltage source 7 can be controlled in order to generate at least one defined test voltage and a defined soldering voltage at the electrodes 6.

[0021] The resistance soldering device 5 further comprises a pressing device 9, which is configured to press at least one of the electrodes 6 against the unit 1, with the unit 1 then being supported on the other of the electrodes 6. This is intended to generate a defined pressure on the unit 1 in the area of ​​the soldering point 3, as needed. For pressing the at least one electrode 6, the pressing device 9 can comprise a linear drive of any design (not shown) for moving this at least one electrode 6. The pressing device 9 can also be controlled by means of the control device 8.

[0022] To solder the unit 1, it is transported to the resistance soldering device 5, including the solder element 4 previously positioned between the components 2 at the soldering point 3, and positioned therein. At least one of the electrodes 6 is then pressed against the unit 1 by means of the pressing device 9, which is supported by the other electrode 6. In doing so, the electrodes 6 exert a pressure on the unit 1 at the soldering point 3 that corresponds to at least a defined minimum pressure. An electrical test voltage is then applied to the electrodes 6 by the electrical voltage source 7 in order to generate a current flow through the unit 1. This current flow and / or a drop in the electrical voltage can be evaluated by the control device 8, and the total electrical resistance can be determined therefrom.This total resistance is composed of the material resistances of components 2 and, if present, of the solder element 4, of several contact resistances of elements in contact with one another, and of the system resistance of the control device 8 acting as a measuring device between its taps (excluding unit 1). The several contact resistances each comprise a contact resistance between the electrodes 6 and the associated component 2 contacting the respective electrode 6. Furthermore, a contact resistance results between the components 2 and the solder element 4, if present. If the solder element 4 is not present, however, only an additional contact resistance exists between the directly contacting components 2.

[0023] Due to the design of the electrodes 6 and the components 2 made of highly electrically conductive metals, the material resistances of these elements are relatively small compared to the contact resistances. The contact resistances therefore already account for a significant portion of the total resistance and thus also of the transition resistance caused by the unit 1 (total resistance minus system resistance), so that a lack of contact resistance in the absence of the solder element 4 can be determined by evaluating the current flow and / or the voltage drop. Added to this is the missing material resistance of the solder element 4, which is usually relatively high, especially compared to the material resistances of the electrodes 6 and the components 2.For evaluation, a simple comparison can be made between the measured current flow / voltage drop and an expected current flow / voltage drop, and the actual contact resistance can be derived based on this. The expected current flow / voltage drop can be determined in advance through testing. For this purpose, a corresponding unit 1 with an existing solder element 4 can be subjected to the test voltage, and the current flow / voltage drop can be determined as reference value(s).

[0024] If the evaluation shows that the solder element 4 is arranged at the soldering point 3, which is considered a positive determination result, an electrical soldering voltage, which can be higher than the electrical test voltage, is applied to the electrodes 6 by means of the control device 8 in order to solder the components 2. In this case, the material (solder) of the solder element 4 is melted in a known manner by a current flow through the unit 1 generated by the soldering voltage generating sufficient thermal energy at the soldering point 3 due to the electrical resistance. A relatively high material resistance of the solder can ensure that the thermal energy is generated primarily in the solder element 4 itself and that its material is consequently melted in a targeted manner.

[0025] If, however, the evaluation reveals that the solder element 4 is missing at the soldering point 3, which is considered a negative result, the soldering voltage is not applied (initially). Instead, the unit 1 is removed from a manufacturing process for which the soldering of the unit 1 is one of several process steps. This reprocessing involves placing the previously missing solder element 4 at the soldering point 3 between the components 2 and feeding the reworked unit 1 back to the resistance soldering device 5. The reworked unit 1 is then tested again and, if the result is positive, soldered.

[0026] The method according to the invention can additionally comprise a test of the connection quality of the soldered unit 1. For this purpose, it can be provided that the height of the unit 1 between the electrodes 6 is measured, on the one hand, before and, on the other hand, after soldering, and these measured values ​​are compared with one another. This makes it possible to test whether the material of the solder element 4 was essentially completely melted during soldering and has thus been distributed in the thinnest, most even layer possible between the components 2. This can be determined by a relatively low height of the unit 1 after soldering, compared to insufficient melting of the solder. The measurement before soldering can be carried out either before or after the at least one electrode 6 is pressed against the unit 1. The measurement after soldering can be carried out before or after the pressure exerted on the unit 1 by the electrodes 6 is released. List of reference symbols 1 unit 2 components 3 solder joint 4 plumb element 5 resistance soldering device 6 Electrode 7 electrical voltage source 8 Control device 9 Pressing device

Claims

[1] Method for testing a unit (1) comprising at least two components (2) to be connected by resistance soldering, wherein the unit (1) is arranged at a soldering point (3) between a first electrode (6) and a second electrode (6) of a resistance soldering device (5) and an electrical test voltage is applied to the electrodes (6) in order to generate a current flow through the unit (1), wherein by evaluating the contact resistance caused by the unit (1) it is determined whether the unit (1) comprises a solder element (4) at the soldering point (3), which is considered a positive determination result, or does not comprise it, which is considered a negative determination result, wherein - if the result of the investigation is positive, an electrical soldering voltage is applied to the electrodes (6) in order to solder the at least two components (2) and - if the test result is negative, the soldering voltage is not applied. [2] Method according to claim 1, characterized by that in the event of a negative test result, the unit (1) is provided with a solder element (4) at the soldering point (3) and is used further. [3] Method according to claim 2, characterized by that for further use the process according to claim 1 is repeated. [4] Method according to one of the preceding claims, characterized by that a pressure corresponding to at least a defined minimum pressure is exerted on the unit (1) by the electrodes (6) at the soldering point (3) as soon as the test voltage is applied, said pressure being maintained at at least the minimum pressure in the case of a positive determination result at least until the soldering voltage is applied. [5] Method according to one of the preceding claims, characterized by that different values ​​or value ranges are chosen for the test voltage on the one hand and for the soldering voltage on the other. [6] Method according to claim 5, characterized by that the value or value range for the test voltage is selected to be smaller than the value or value range for the soldering voltage. [7] Method according to one of the preceding claims, characterized by that the solder element (4) comprises or consists of a material which has a liquidus temperature of at least 450°C. [8] Resistance soldering device (5) with a first electrode (6), a second electrode (6), an electrical voltage source (7) for applying an electrical voltage to the electrodes (6) and a control device (8) for controlling the voltage source (7), wherein the control device (8) is designed to carry out a method according to one of the preceding claims in an automated manner. [9] Resistance soldering device (5) according to claim 8, characterized bya pressing device (9) adapted to press at least one of the electrodes (6) against the unit (1). [10] Resistance soldering system with a resistance soldering device (5) according to claim 8 or 9, a first handling device for feeding the unit to the resistance soldering device, a second handling device for removing the unit in the soldered state from the resistance soldering device and a third handling device for removing the unit in the unsoldered state from the resistance soldering device

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