Method and equipment for testing a solder joint

Abstract

A method for inspecting a solder joint 2 is proposed, wherein a printed circuit board 3 and at least one surface-mountable component 5 are provided, the printed circuit board 3 having at least one soldering area 9 provided with solder paste 10; the component 5 being positioned on the solder paste 10 in the soldering area 9 during a placement process and being soldered to form a solder joint 2, such that the at least one component 5 and the printed circuit board 3 forming a common assembly 7; and at least one quality characteristic of the solder joint 2 being detected during an inspection process, wherein, according to the invention, at least one geometric parameter is detected during the placement process and at least one further geometric parameter is detected after the placement process, and a distance 100 between the printed circuit board 3 and the component 5 is determined as a quality characteristic based on the detected geometric parameters.

Description

[0001] The invention relates to a method for inspecting a solder joint. Furthermore, the invention relates to a computer program for carrying out the method, a machine-readable storage medium on which the computer program is stored, and a system for inspecting the solder joint. State of the art

[0002] Established solder joint inspection systems are used in SMT (Surface Mount Technology) manufacturing to check the quality of the solder joints. In SMT manufacturing, solder pads on printed circuit boards (PCBs) are printed with solder paste, and the amount of printed solder paste is checked by an automated solder paste inspection system in a process called SPI (Solder Paste Inspection). Subsequently, the components to be soldered are placed on the printed PCB, and the solder paste is melted in a soldering oven to create a solid bond between the components and the corresponding solder pads on the PCB. The quality of the resulting solder joints is then checked by an automated solder joint inspection system in a process called SJI (Solder Joint Inspection).

[0003] German patent application DE 10 2015 212 690 B3 discloses a system for solder joint inspection comprising a device for automatic solder paste testing, which determines the amount of solder paste applied to a soldering surface, and a device for automatic solder joint inspection, which detects at least one quality characteristic of a solder joint to be inspected within a predetermined inspection area of ​​the soldering surface and compares it with a predetermined threshold value. The device for automatic solder joint inspection evaluates the solder joint to be inspected as either a good or a poor solder joint depending on the comparison result. An evaluation and control unit determines the threshold value for the at least one quality characteristic based on the amount of solder paste applied to the solder joint to be inspected and specifies this threshold value to the device for automatic solder joint inspection to check the corresponding solder joint. Disclosure of the invention

[0004] The invention proposes a method, a computer program, a machine-readable storage medium, and a system with the features of the independent claims. Preferred or advantageous embodiments of the invention are described in the dependent claims, the following description, and the accompanying figures.

[0005] The invention relates to a method for checking a solder joint, wherein: - a printed circuit board (PCB) and at least one surface-mountable component (SMD) are provided, wherein the PCB has at least one soldering area covered with solder paste; - the component is positioned in the soldering area on the solder paste as part of an assembly process and is soldered to the circuit board via the solder paste as part of a soldering process, forming a solder joint, so that the at least one component and the circuit board form a common assembly; - at least one quality characteristic of the solder joint is recorded as part of an inspection process.

[0006] Depending on the recorded quality characteristic, it is possible, for example, to rate the solder joint as a good solder joint or as a bad solder joint.

[0007] In particular, the solder paste is printed onto the printed circuit board in a printing process prior to the assembly process, preferably using stencil printing, in which at least one soldering area is printed. The soldering area is understood here to be the area in which the component is to be soldered to the printed circuit board.

[0008] The component is then picked up during the assembly process, preferably using pick-and-place, and placed onto the solder paste in the soldering area. A defined force can be applied to place the component. For multiple soldering areas, this process is repeated for all components. Preferably, an SMD component is an electrical or electronic component that has no wire leads but is soldered directly onto the printed circuit board (PCB) via a solderable connection side. The component may have a contact pad or leads on this connection side. For example, the component can be a microprocessor, capacitor, integrated circuit, transistor, particularly a MOSFET package, etc.

[0009] In particular, the component is soldered onto the printed circuit board (PCB) during the soldering process using soft soldering, preferably reflow soldering, also known as remelting. For this purpose, the PCB, which is populated with at least one component, can be heated, for example, in an oven, causing the solder paste to melt and the component to be soldered to the PCB. The resulting metallurgical bond between the PCB and the component is referred to as a solder joint in the application.

[0010] In particular, the quality of the resulting solder joints is examined and evaluated in the inspection process, also known as SJI (Solder Joint Inspection). This inspection process can be carried out before and / or after the soldering process and / or concurrently with the assembly and / or soldering process. In simplified terms, at least the recording of quality characteristics and / or the inspection process can be performed, at least temporarily, in parallel with the manufacturing process. Quality characteristics recorded during the inspection process can include, for example, the shape and / or surface finish of the solder joint, the position and orientation of the components, and / or short circuits and bridging. Based on at least one quality characteristic, the solder joint can then be classified according to an evaluation criterion, for example, as a "good solder joint" or a "poor solder joint."In the case of a "good solder joint," the assembly is released for a subsequent process, such as further processing in a production line. In the case of a "poor solder joint," the assembly is rejected and may require re-inspection and / or rework.

[0011] Within the scope of the invention, it is proposed that at least or exactly one geometric parameter is acquired during the assembly process and at least or exactly one further geometric parameter is acquired after the assembly process. Based on the acquired geometric parameters, a distance between the printed circuit board and the component, also referred to as stand-off, is determined as a quality characteristic. Preferably, the distance is defined between a surface of the printed circuit board on which the component is positioned and a terminal or underside of the component. The distance can be formed by the solder paste arranged in the soldering area and / or by a mechanical structure of the component, e.g., the leads. Preferably, a geometric parameter of the component and / or the printed circuit board and / or the solder joint is acquired to determine the distance. In particular, a threshold value for the distance can be defined or may already be defined.For example, the solder joint can be preferably evaluated as a "good solder joint" during the inspection process if the distance is equal to the specified threshold and / or within a tolerance range of the specified threshold, and evaluated as a "bad solder joint" if the distance deviates from the specified threshold and / or is outside the tolerance range of the specified threshold.

[0012] The invention is based on the understanding that, in addition to the load, the initial state of solder joints is also relevant for their reliability. Solder joint reliability depends on geometric parameters of the solder joint, which, however, are not captured during the assembly process of electronic components. Using optical inspection methods, the quality of the solder joint is inspected after the placement and soldering processes of electronic components, particularly SMD components, on printed circuit boards. Based on these inspections, the solder joints are evaluated according to defined criteria and standards. This process does not require precise measurement of specific geometric parameters of the component or the solder joints.

[0013] By measuring the distance between the component and the circuit board, a reliability-relevant and service life-determining parameter of the solder joint can be identified. For example, a distance that is too small can lead to insufficient wetting, as the solder has no room to spread evenly, thus impairing the mechanical strength of the solder joint. Conversely, a distance that is too large can result in a weak mechanical connection, as the component may not be soldered at all or only partially. Furthermore, an excessively large distance can cause the component's leads, such as its pins, to not make contact with the circuit board. Therefore, knowing the distance allows for an assessment of the solder joint quality. This means that knowing the distance is a reliability indicator for electronic assemblies.A method is therefore proposed which is characterized by an improved inspection process and a more reliable soldered joint.

[0014] In a more detailed implementation, the solder joint height within the soldering area is determined based on the distance between the component and the circuit board. Specifically, the geometric parameter before and after the soldering process can be recorded. This preferably allows verification of whether the solder joint height corresponds to the specified distance or has been altered, particularly reduced or increased, during the soldering process. This ensures that the solder joint is inspected after the soldering process, thus enabling a reliable evaluation of the solder joint.

[0015] In a further development, it is provided that the component height is recorded as a geometric parameter during the assembly process, and the total height of the component and the solder joint is recorded as a further geometric parameter after the assembly and / or soldering process, with the difference between the component height and the total height corresponding to the distance. Preferably, the component height is recorded after picking up and / or before positioning the component in the soldering area. Alternatively, the component height can also be recorded during positioning of the component in the soldering area. Preferably, the total height of the component and the solder joint is recorded after positioning and / or after soldering the component in the soldering area. Preferably, the component height is measured between the connection side or the underside of the component and a side opposite the connection side or a top side of the component.Preferably, the total height between the surface of the printed circuit board, preferably in the soldering area, and the top of the component is measured. In simplified terms, the total height is the sum of the component height and the distance or solder joint height. Subtracting the component height from the total height allows for easy determination of the distance or solder joint height.

[0016] In a more detailed specification, it is provided that the component height is determined by optical inspection of the component before positioning. Specifically, this optical inspection is performed during the assembly process to identify the component. This preferably verifies whether the correct component has been picked up and / or whether the component has been picked up correctly. Particularly preferably, the component is measured during the inspection. In addition to the component height, depending on the component's geometric design, other dimensions such as component length, component width, component diameter, or the like can be recorded. For example, a 2D or 3D measuring system can be used for this purpose. Alternatively or optionally, it is provided that the component height is determined during positioning based on a travel path.In particular, the component is positioned on the solder paste with a defined force, and the resulting travel distance can be used to determine the component height. For example, a reference position of the Z-axis or a zero point is located on the surface of the printed circuit board, especially in the soldering area. This reference position is used to determine the component height relative to the circuit board. Thus, a particularly simple method for determining the component height is proposed, which is carried out during the assembly process.

[0017] In a further specification, it is proposed that the overall height of the assembly be determined using automated optical inspection (AOI). In particular, automated optical inspection serves to ensure defect-free component placement and / or solder joints. Preferably, the automated optical inspection is performed after the component placement and / or soldering process. For example, the assembly, preferably at least the soldering area, can be optically scanned and analyzed using image processing. Specifically, the overall height of the component positioned on the solder paste or soldered on, i.e., the component height plus the spacing or solder joint height, can be determined. Thus, a particularly simple method for determining the overall height is proposed, which is performed during the inspection process.

[0018] In a further concrete implementation, it is envisaged that at least one additional quality characteristic of the solder joint is recorded before and / or after the assembly process and taken into account when evaluating the solder joint. In particular, the solder area, especially the solder paste, can be recorded as an additional quality characteristic after the printing process and / or before the assembly process. For example, a parameter of the solder paste, such as quantity, volume, surface area, or the like, can be recorded for this purpose. Alternatively or optionally, the solder joint can be recorded as an additional quality characteristic after the soldering process and / or as part of the inspection process. For example, a parameter of the solder joint, such as wetting quality, surface area, air inclusions, or the like, can be recorded for this purpose. Preferably, all quality characteristics can be correlated and / or weighted with each other within the inspection process.A method is therefore proposed which is characterized by a precise inspection of the solder joint or individual process steps.

[0019] In a specific implementation, it is planned that, as an additional quality criterion, a solder paste parameter will be recorded using solder paste inspection (SPI) before the assembly process. Specifically, solder paste inspection serves to check the solder paste applied to the printed circuit board before the components are placed and soldered. For example, solder paste parameters such as quantity, distribution, geometry, and impurities of the solder paste, particularly in the soldering area, can be optically detected. Alternatively or optionally, as a further quality criterion, a solder joint parameter will be recorded after the soldering process using automatic X-ray inspection (AXI). X-ray inspection is particularly useful for checking hidden or difficult-to-access solder joints that are difficult to detect using automated optical inspection (AOI).For example, solder joint parameters such as defects, wetting, short circuits, etc. of the solder joint, especially in the soldering area, can be detected using X-rays.

[0020] In a further development process, the distance between the printed circuit board and the component is taken into account when predicting the lifetime of the assembly and / or the solder joint. Specifically, based on this distance and optionally other quality characteristics, such as solder paste parameters and / or solder joint parameters, a predicted and / or average lifetime of the solder joint can be calculated. Preferably, the lifetime prediction can also provide an estimated number of operating cycles of the assembly and / or the solder joint before damage occurs. For example, the lifetime prediction can be generated during the inspection process and / or after evaluation of the solder joint. This allows for an efficient and precise assessment of the expected lifetime of the solder joint, taking the distance into account.

[0021] In a more detailed specification, it is envisaged that at least the distance used in lifetime prediction is combined with at least one load parameter and / or evaluated based on a lifetime model. In particular, a thermal and / or mechanical load, preferably a maximum load, of the assembly and / or the solder joint can be defined as a load parameter. For example, a temperature, particularly a maximum temperature, of the assembly and / or the solder joint in the soldering area can be defined as a thermal load. For example, a shear stress of the assembly and / or the solder joint in the soldering area can be defined as a mechanical load. The load parameters can be determined, for example, experimentally and / or empirically. In particular, an analytical lifetime model, such as the Coffin-Manson model, and / or a numerical lifetime model, such as [example missing in original text], can be defined as the lifetime model.Finite element method (FEM) is used. By taking into account the distance and the load on the solder joint, a more accurate lifetime prediction can be made for each individual solder joint.

[0022] A further aspect of the invention is a computer program. The computer program is stored and / or storable on a data carrier. The data carrier is preferably a hard drive, CD, DVD, or other mass storage device. The computer program is configured to perform the steps of the preceding method when executed on a computer, a computer, a control unit, or the like.

[0023] A further aspect of the invention is a machine-readable storage medium. The machine-readable storage medium is, in particular, the data carrier and specifically a hard drive, CD, USB flash drive, or SD card. The computer program is stored on the machine-readable storage medium as described above.

[0024] A further aspect of the invention relates to a system which is specifically designed and / or suitable for carrying out the method described above. The system can be designed as a production line or integrated into a production line.

[0025] The system includes a placement device designed and / or suitable for placing at least one surface-mount component onto the printed circuit board. In particular, the placement device is designed to carry out the placement process. Specifically, the placement device is designed as a pick-and-place system, preferably an automated placement machine.

[0026] The placement device has at least one or exactly one receiving device designed to hold the component and position it in the soldering area on the circuit board to form the assembly. In particular, the receiving device is designed as a placement head that is movable in three axes and can rotate about the Z-axis. The receiving device may include a suction nozzle or a gripper for receiving the component. Furthermore, the placement device may include a conveying device for supplying and transporting the circuit board.

[0027] The placement device also includes a component detection device designed to detect at least one geometric parameter of the component during the placement process. In particular, the component detection device is designed as a 2D or 3D measuring system, especially a camera, a scanner (e.g., a laser scanner), or the like. The component detection device can detect the component after it has been picked up by the receiving device to verify that the correct component has been picked up. Geometric dimensions, such as the component height, can also be detected by the component detection device.

[0028] The system includes an inspection device designed and / or suitable for inspecting the solder joint. In particular, the inspection device is designed to carry out the inspection process. Specifically, the inspection device is designed as an AOI system.

[0029] The inspection device includes at least one assembly detection device configured to capture the component's additional geometric parameters after the assembly process. In particular, the assembly detection device is configured as a 2D or 3D measuring system, especially a camera, a scanner (e.g., a laser scanner), or the like. The assembly detection device can capture the assembly after placement and / or after the component has been soldered in order to verify the solder joint quality. Geometric dimensions, such as the overall height, can also be captured by the assembly detection device.

[0030] Furthermore, the system can include a printing device for applying solder paste to the soldering areas and / or a soldering device for soldering components to the soldering areas. The printing device is designed to carry out the printing process, and the soldering device is designed to carry out the soldering process.

[0031] The system also features an electronic control unit configured to determine the distance between the component and the circuit board as a quality characteristic based on the measured geometric parameters, and in particular to evaluate the solder joint based on this measured quality characteristic. One possible evaluation is the assessment of the solder joint as either good or poor. Specifically, the control unit is designed to perform one or more process steps of the previously described method, preferably determining the distance and evaluating the solder joint. In particular, the control unit is designed to control the printing device and / or the placement device and / or the soldering device and / or the inspection device.

[0032] In a specific implementation, the control unit is designed to include a calculation module and an evaluation module. For example, the calculation module and / or the evaluation module can be implemented as hardware or software modules. The calculation module is configured to calculate the distance from the two geometric parameters, in particular the component height and the overall height, and provide this information to the evaluation module. In the simplest case, the component height can be subtracted from the overall height to calculate the distance. The evaluation module is configured to evaluate the solder joint between the component and the circuit board based on this distance. In particular, the evaluation module can be provided with further quality characteristics relating to the solder joint, such as the solder paste and / or solder joint parameters, which are considered in addition to the distance when evaluating the solder joint.For example, an evaluation rule, in particular a threshold and / or a tolerance range, may be stored on the evaluation module, whereby the evaluation module is configured to evaluate the distance based on the evaluation rule or to compare it with the threshold and / or the tolerance range.

[0033] In a further specification, it is provided that the component detection device and / or the assembly detection device are designed to optically detect the component and provide it as image data, with the control unit having an image processing module designed to determine the geometric parameters based on the image data. In particular, the component detection device and / or the assembly detection device are designed as cameras that can capture one or more images of the soldering area as image data. The image processing module is designed to evaluate and / or analyze the image data. For example, the image processing module is designed to detect the edge profiles of the component or assembly. In particular, by using the placement device and the AOI overall height measurement of the component and solder joint, the distance or...The plumb gap can be determined, thus eliminating the need for the expensive oblique-view cameras, which are not available in all AOI systems.

[0034] Further features, advantages, and effects of the invention will become apparent from the following description of preferred embodiments of the invention and the accompanying figures. These show: Fig. 1 a schematic representation of a system for the production and testing of a solder joint as an embodiment of the invention; Fig. 2 a schematic representation of an assembly manufactured in the plant.

[0035] Fig. Figure 1 shows a schematic diagram of a system 1, which is designed for the production and testing of a solder joint 2 between a printed circuit board 3 and a component 5, also known as an SMD component, which can be mounted or is mounted on a surface 4 of the printed circuit board 3.

[0036] The system 1 includes a conveyor device 6, which can form an integral part of a production line. The conveyor device 6 serves to transport and provide the printed circuit board 3 or a finished assembly 7. For example, the conveyor device 6 can be designed as a conveyor belt that transports the printed circuit board 3 or the assembly 7 between several processing stations of the production line.

[0037] The system 1 includes a printing device 8, which is configured to print a solder paste 10 onto a soldering area 9 of the printed circuit board 3 as part of a printing process. For example, the solder paste 10 can be printed onto the surface 4 of the printed circuit board 3 in the soldering area 9 using a stencil printing process.

[0038] Furthermore, the system 1 includes a placement device 11, which is designed to place the component 5 onto the printed circuit board 3 during a placement process. For this purpose, the placement device 11 includes a receiving device 12, which is designed to receive the component 5, for example from a tape or roll, and to position it in the soldering area 9 printed with the solder paste 10 to form the assembly 7. The receiving device 12 is designed, for example, as a suction device, also referred to as a nozzle, which draws in the component 5 during placement.

[0039] The placement device 11 includes a component detection device 13, which is designed to detect the component 5 during the placement process in order to check whether the correct component 5 has been picked up or whether the component 5 has been picked up correctly. The component detection device 13 is, for example, designed as a camera that optically detects the component 5 and provides it as image data 14.

[0040] The system 1 includes a soldering device 15, which is designed to solder the component 5 to the printed circuit board 3 in a soldering process, forming the solder joint 2. For this purpose, the soldering device 15 is designed, for example, as a heat source that heats the printed circuit board 3, which is populated with the component 5, so that the solder contained in the solder paste 10 melts.

[0041] Furthermore, the system 1 includes an inspection device 16, which is designed to inspect the soldering area 9 before and after the assembly process in order to evaluate the quality of the solder joint 2. For this purpose, the inspection device 16 has several detection devices 17, 18, 19, which detect the soldering area 9 during the printing process, the assembly process, and the soldering process.

[0042] The inspection device 16 includes a solder paste detection device 17, which is configured to optically detect the soldering area 9 during the printing process after the application of the solder paste 10 and to provide it as further image data 20, a process also known as SPI (solder paste inspection). The inspection device 16 includes an assembly detection device 18, which is configured to optically detect the soldering area 9 of the assembly 7 during the soldering process and to provide it as further image data 21, a process also known as AOI (automated optical inspection). The inspection device 16 also includes a solder joint detection device 19, which is configured to detect the solder joint 2 during the soldering process using X-rays and to provide it as further image data 22, a process also known as AXI (automated X-ray inspection).

[0043] The system 1 includes a control unit 23, which is configured to control the system, in particular the transport device 6, the printing device 8, the assembly device 11, and the soldering device 15. The control unit 23 includes an image processing module 24, which is configured to determine geometric parameters of the component 5 and the assembly 7 based on the image data 14, 21.

[0044] Fig. Figure 2 shows assembly 7 in a schematic representation. For the reliability of solder joints 2, their initial state is relevant in addition to the load. Solder joint reliability depends on the geometric parameters of solder joint 2. An important geometric parameter is a distance of 100 mm, also referred to as stand-off, between component 5 and the printed circuit board 3. To measure this distance of 100 mm, and thus the height of solder joint 2 below component 5, component detection device 13 and assembly detection device 18 are used during the placement and soldering process.

[0045] The image processing module 24 is configured to determine the component height 101 of component 5 as a geometric parameter based on the image data 14 from the component detection device 13, and to determine the overall height 102 of the assembly 7 as a further geometric parameter based on the additional image data 21 from the assembly detection device 18. The component height 101 is measured between a connection side 27 and a top surface 28 of component 5. The connection side 27 is understood to be the side of component 5 on which it is soldered or electrically contacted. In this embodiment, the overall height 102 is measured between the top surface 28 of component 5 and the surface 4 of the printed circuit board 3 after the soldering process.

[0046] As in Fig.As shown in Figure 1, the control unit 23 has a calculation module 25, which is configured to determine the distance 100 based on the component height 101 and the overall height 102. For this purpose, the component height 101 is subtracted from the overall height 102. The control unit 23 also has an evaluation module 26, which is configured to evaluate the solder joint 2 based on one or more quality characteristics, where at least one quality characteristic is defined by the distance 100. The evaluation of the solder joint is based on defined quality characteristics, which are recorded by the detection devices 17, 18, and 19 during the printing, assembly, and soldering processes.

[0047] The output of evaluation module 26 can, for example, be the classification of solder joint 2 as "good solder joint" or "bad solder joint" taking into account the distance of 100. Furthermore, evaluation module 26 is designed to generate a lifetime prediction for solder joint 2, also taking into account the distance of 100.

[0048] By measuring the distance 100 mm between component 5 and circuit board 3, a reliability-relevant and service life-determining parameter can be determined. Knowing this distance 100 mm allows for an assessment of the solder joint quality. This means that knowing the distance 100 mm is a reliability indicator for electronic assemblies 7. In combination with knowledge of the load and existing service life models, this also offers the advantage of a more accurate service life prediction for each individual solder joint 2. This is particularly important for reducing scrap in electronic assembly manufacturing and for sustainable electronics that can potentially be reused or repurposed. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2015 212 690 B3

[0003]

Claims

[1] Method for checking a solder joint (2) wherein: - a printed circuit board (3) and at least one surface mountable component (5) are provided, wherein the printed circuit board (3) has at least one soldering area (9) provided with solder paste (10); - the component (5) is positioned on the solder paste (10) in the soldering area (9) as part of a placement process and is soldered in a soldering process to form a solder joint (2), so that the at least one component (5) and the printed circuit board (3) form a common assembly (7); characterized by , that at least one geometric parameter is recorded during the assembly process and at least one further geometric parameter is recorded after the assembly process, whereby a distance (100) between the printed circuit board (3) and the component (5) is determined as a quality characteristic based on the recorded geometric parameters. [2] Method according to claim 1, characterized by, that on the basis of the distance (100) a solder joint height of the solder joint (2) within the soldering area (9) is determined. [3] Method according to claim 1 or 2, characterized by , that a component height (101) of the component (5) is recorded as the geometric parameter during the assembly process and a total height (102) of the component (5) and the solder joint (2) is recorded as the further geometric parameter after the assembly process and / or after the soldering process. [4] Method according to claim 3, characterized by , that the component height (101) is determined before positioning the component (5) by means of an optical inspection of the component (5) and / or during positioning of the component (5) on the basis of a travel path. [5] Method according to claim 3 or 4, characterized by , that the overall height (102) is recorded as part of an automatic optical inspection of the assembly (7). [6] Method according to any one of the preceding claims, characterized by, that at least one further quality characteristic of the solder joint (2) is recorded before the assembly process and / or after the soldering process and is taken into account when evaluating the solder joint (2). [7] Method according to claim 6, characterized by , that as a further quality feature, a solder paste parameter is recorded before the assembly process by means of a solder paste inspection (SPI) and / or a solder joint parameter is recorded after the soldering process by means of an automatic X-ray inspection (AXI). [8] Method according to any one of the preceding claims, characterized by , that the distance (100) is taken into account in a lifetime prediction for the assembly (5) and / or the solder joint. [9] Method according to claim 8, characterized by , that at least the distance (100) is combined with at least one load parameter in the lifetime prediction and / or is evaluated on the basis of a lifetime model. [10] Computer program, in particular on a data carrier, for carrying out the method according to any of the preceding claims. [11] Machine-readable storage medium on which the computer program according to claim 10 is stored. [12] Annex (1), in particular for carrying out the method according to any one of claims 1 to 9, - with a placement device (11) for placing at least one surface-mountable component (5) on a printed circuit board (3), wherein the placement device (11) has at least one receiving device (12) and a component detection device (13), wherein the receiving device (12) is configured to receive the component (5) and to position it in a soldering area (9) on the printed circuit board (3) to form an assembly (7), and wherein the component detection device (13) is configured to detect at least one geometric parameter of the component (5) during a placement process, - with an inspection device (16) for inspecting the soldering area (9), wherein the inspection device (16) has an assembly detection device (18) which is configured to detect at least one geometric parameter of the assembly (5) after the assembly process, - with an electronic control unit (23) which is designed to determine a distance (100) between the circuit board (3) and the component (5) as a quality characteristic based on the recorded geometric parameters and in particular to evaluate the solder joint (2). [13] Plant (1) according to claim 12, characterized by, that the control unit (23) has a calculation module (25) and an evaluation module (26), wherein the calculation module (25) is configured to calculate the distance (100) from the two geometric parameters, in particular a component height (101) and a total height (102), and to provide it to the evaluation module (26), wherein the evaluation module (26) is configured to evaluate the solder joint (2) between the component (5) and the printed circuit board (3) on the basis of the distance (100). [14] Annex (1) according to claim 12 or 13, characterized by , that the component detection device (13) and / or the assembly detection device (18) are configured to optically detect the component and provide it as image data (14, 21), wherein the control unit (23) has an image processing module (24) which is configured to determine the geometric parameters on the basis of the image data (14, 21).

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