Selective soldering system for selective wave soldering of circuit boards comprising a clamping unit for replacing a solder nozzle

Abstract

A selective wave soldering system (10) for selective wave soldering of circuit boards includes a solder can (40) comprising a solder nozzle (22) detachably mounted on the solder can (40), wherein the solder nozzle (22) has a nozzle base and a nozzle neck (56), wherein a nozzle opening is provided at the free end of the nozzle neck (56), the solder can (40) is mounted on a moving unit (16) movable in the horizontal plane along the x and y axes and in the vertical direction along the z axis (44), and includes a control unit (32) for controlling the moving unit (16), characterized in that... The hopper (20) for receiving different solder nozzles (22) is arranged on the moving unit (16), characterized in that a clamping unit (34) is provided, the clamping unit (34) including clamping fingers (38) for clamping the solder nozzles (22), wherein the clamping unit (34) can be moved along the z-axis by a drive unit (36) controlled by a control unit (32), and wherein the control unit (32) is designed to control the moving unit (16), the drive unit (36) and the clamping unit (34) such that the solder nozzles (22) in the hopper (20) can be clamped, lifted and lowered in the solder can (40) by the clamping unit (34).

Description

Technical Field

[0001] This invention relates to a selective wave soldering system for selective wave soldering of circuit boards, comprising: a solder can including a solder nozzle detachably disposed on the solder can, the solder nozzle having a nozzle base and a nozzle neck, and a nozzle opening at the free end of the nozzle neck; the solder can being disposed on a moving unit movable in a horizontal plane along x-axis and y-axis and in a vertical direction along z-axis; and a control unit for controlling the movement of the moving unit along the x-axis, y-axis, and z-axis. The x-axis, y-axis, and z-axis are arranged orthogonally to each other. Background Technology

[0002] In the field of contacting electronic components, it is known to contact components from the underside of a circuit board, wherein the contacting electronic components are secured, for example, through holes in the circuit board from the top side via through-hole technology (THT). So-called selective wave soldering is well known to contact individual pins or pin rows by soldering, wherein the standing wave of the liquid solder is precisely positioned below the component or pin to be contacted. In so-called top fluxing, it is also known to first spray flux using a jet nozzle to improve the wetting of the solder on the pins / pin rows to be soldered, and then solder individual pins by spot soldering, or solder the pin row by moving a carrier from the first pin to the last pin.

[0003] It is also known that a positioning device is used to accurately position the circuit board above the standing wave of the solder can statically arranged in the soldering system, and then, for spot soldering, the soldering wave is lowered or raised until the standing wave of the solder contacts the pins. In this case, the entire circuit board is displaced relative to the standing wave generated in the solder can. However, this procedure has proven to be time-consuming.

[0004] Selective welding systems with features of the preamble to claim scheme 1 are known from DE 10 2004 063 488 A1 and WO 2014 / 086954 A1, in which a solder pot can be moved along the x, y, and z axes using a moving unit.

[0005] JPH05-208263Ahkl discloses an apparatus for immersing a printed circuit board in solder, JPH01-143763A discloses a spray soldering apparatus, and JP2000-228572 discloses terminal formation for a flexible circuit board.

[0006] Depending on the component to be soldered, solder nozzles with different nozzle openings may be required. The nozzle openings can have different diameters and / or different profiles. Furthermore, solder nozzles are prone to wear during operation, particularly due to the formation of an undesirable oxide layer on the nozzle surface, which leads to undesirable deformation of the solder wave.

[0007] According to existing technology, it is known to manually replace worn solder nozzles using appropriate tools. Due to the liquid solder in the solder can, this replacement requires special protective measures and is very time-consuming. It should also be considered that the solder nozzles should have a desired temperature when inserted to avoid undesirable hardening of the liquid solder when the nozzle is inserted into the solder can. To this end, it is known to hold the solder nozzle above the solder can for a few seconds before insertion, maintaining a close distance from the liquid solder, thereby heating the nozzle to be inserted, particularly with radiant heat from the solder can. Part of the solder nozzle can also be kept in the liquid solder, thus being washed and heated by the liquid solder. Once the solder nozzle has reached a certain preheated temperature, it is manually inserted into the solder can.

[0008] It is also known from DE 10 2016 121 160 A1 that a disposal device is used to arrange and remove solder nozzles on a solder can. Summary of the Invention

[0009] The problem solved by the present invention is to provide a selective welding system that improves system efficiency while still ensuring functionally reliable operation.

[0010] This problem is solved by a selective welding system that has the features of claim protection scheme 1.

[0011] This selective welding system is characterized by a hopper for receiving different solder nozzles arranged on a moving unit. The hopper with the solder nozzles thus moves along with the moving unit. Because the hopper is arranged on the moving unit, no additional installation space is required for the stationary hopper. Furthermore, a clamping unit is provided, comprising clamping fingers for clamping the solder nozzles. This clamping unit can be controlled by a control unit, which can move the clamping unit at least along the z-axis using a drive unit, also controlled by the control unit. Therefore, when changing solder nozzles, the solder nozzles can be clamped by the clamping unit. The control unit is designed to control the moving unit, the drive unit, and the clamping unit so that the solder nozzles in the hopper can be clamped, lifted, and lowered into the solder canister. Before lowering, the solder nozzles can be briefly preheated on the welding wave. Advantageously, the control unit is also designed to allow the nozzles in the solder canister to be clamped and lifted by the clamping unit and discarded as worn parts or lowered into the hopper for reuse.

[0012] Therefore, according to the present invention, automatic replacement of the solder nozzle is possible. Because the hopper is arranged on the moving unit, no additional unit is needed to vertically position the hopper below the clamping unit along the x, y, and optionally z axes. Then, by moving the clamping unit, the solder nozzle can be clamped, raised, and lowered only along the z-axis.

[0013] It is advantageous if the clamping unit can only move along the z-axis and not along the x and y axes. This means that an xy-axis drive for the clamping unit is unnecessary; the clamping unit moves only in the vertical direction. The hopper can be moved horizontally by the moving unit, and preferably also vertically.

[0014] It is particularly advantageous if the control unit is designed so that the clamping unit and the moving unit move synchronously toward and / or away from each other along the z-axis. This allows for relatively short movement times and minimizes setup time for changing solder nozzles.

[0015] According to another advantageous embodiment of the invention, the finger heater is configured to heat the clamping fingers to a preheating temperature before and / or at least during the clamping process. As a result, the clamped solder nozzle can be heated by the clamping fingers, or maintained at a temperature that the nozzle may already be at during clamping. The preheating temperature is particularly between 100°C and 200°C, more particularly between 120°C and 180°C, and more preferably in the range of 160°C. Consequently, the solder nozzle start-up time, i.e., the time it takes for the solder nozzle to reach its operating temperature after insertion into the solder can, can be significantly reduced, or even eliminated.

[0016] Finger heaters can be designed as resistance heaters, arranged on or integrated into the gripping fingers. By appropriately energizing the resistance heater, the gripping fingers can be heated to the desired preheating temperature relatively quickly. Alternatively, other types of finger heaters, such as convection heaters or radiation heaters, are conceivable.

[0017] To achieve the desired preheating temperature, it is conceivable to place a temperature sensor on the clamping finger, which can be used to adjust the power supply to the clamping finger and the preheating temperature.

[0018] It is also advantageous to install a hopper heater to heat the hopper and / or the solder nozzles within it to a preheating temperature. With the hopper heater, the solder nozzles in the hopper can thus be heated to the desired preheating temperature before being clamped by the clamping unit. Especially when combined with finger heating, it ensures that the solder nozzles have the desired preheating temperature when inserted into the solder can, which is preferably within the subsequent operating temperature range. This means that preheating the solder nozzles above the can or solder wave is unnecessary. The start-up time of the solder nozzles in the solder can also be minimized or eliminated entirely. To achieve the desired preheating temperature here, it is also conceivable that a temperature sensor be installed on or inside the hopper, through which the heating of the hopper and the preheating temperature can be adjusted.

[0019] The silo is advantageously provided with a silo base, and the silo heater is disposed in or on the silo base. The silo heater is particularly likely to be a resistance heater, preferably in the form of a surface or annular heating element. Depending on the geometry of the silo, other types of heaters, such as convection heaters or radiation heaters, may also be provided.

[0020] It is also conceivable that the hopper has a covering element, and that the hopper heater is disposed in or on the covering element. The advantage of the covering element is that it protects the nozzles in the hopper from contamination. The hopper heater in or on the covering element is preferably a resistance heater, especially in the form of a surface or annular heating element.

[0021] According to another advantageous embodiment, a contact material is provided between the hopper heater and the solder nozzle for contacting the solder nozzle. Preferably, the contact material is in physical contact with both the hopper heater and the solder nozzle, which provides advantageous heat transfer.

[0022] It is advantageous if the material is in contact with at least the nozzle neck of the nozzle in the hopper.

[0023] The contact material can be formed of, for example, metal wool, which can be arranged on the inside of the cover element. Accordingly, the metal wool can be designed to be elastic and flexible, so that when the cover element is placed on, the metal wool is elastically compressed due to contact with the nozzles in the hopper. This allows for advantageous heat transfer.

[0024] The contact material can also be formed of metal elements mounted so that they can be moved parallel to each other, with their free ends acting on the solder nozzles in the hopper. The metal elements are preferably arranged vertically on the cover element so that their weight acts on the solder nozzles. This also ensures good heat transfer between the hopper heater and the solder nozzles.

[0025] According to another advantageous embodiment, a cleaning unit is provided for cleaning at least the nozzle base of the solder nozzle removed from the solder can. The cleaning unit is preferably arranged on the moving unit and can be controlled by a control unit, which is designed such that the nozzle, held and lifted from the solder can by the clamping unit, is moved into the cleaning unit, cleaned there, and then lowered into the hopper. The advantage of this is that the solder nozzle removed from the solder can does not need to be separated but can be reused. The clamping unit then holds the solder nozzle in the solder can. Due to the control of the moving unit and the drive unit, the clamped solder nozzle can be moved into the cleaning unit. If the clamping unit includes heated clamping fingers, it is possible to ensure that the solder nozzle does not cool down too much when it is moved from the solder can to the cleaning unit, making cleaning by the cleaning unit impossible or very difficult. Of course, it is particularly advantageous if the clamping fingers are heated to ensure that the solder adhering to the solder nozzle does not harden. The solder nozzle cleaned in the cleaning unit can be lowered into the hopper after cleaning.

[0026] It is conceivable that monitoring cameras will track the cleaning process and results. Only when it is ensured that the solder nozzle has been properly cleaned will the relevant solder nozzle be moved to the hopper and placed there.

[0027] The cleaning unit itself may include a rotating metal brush for cleaning the nozzle base.

[0028] The control unit is also designed so that a solder pump, located in or on the solder can for pumping liquid solder, can also be controlled using the control unit. Control can be performed such that, shortly before reaching the lowering position, liquid solder is pumped through or into the nozzle holder, and the solder nozzle is held directly above the holder for preheating until the solder nozzle is at least substantially and uniformly preheated. The solder pump can then be turned off, and the solder nozzle is lowered onto the solder can's holder.

[0029] The problem mentioned at the beginning is also solved by a method for replacing the solder nozzle, particularly the selective welding system according to the present invention, which includes the following steps:

[0030] a. Move the moving unit along the x, y, and / or z axes to the replacement position. In the replacement position, the solder nozzle to be clamped is vertically below the clamping unit along the z-axis.

[0031] b. Move the clamping unit vertically downward along the z-axis to the clamping position, and clamp the solder nozzle in the hopper using the clamping unit. While the clamping unit moves vertically downward along the z-axis, the moving unit can simultaneously move vertically upward.

[0032] c. Move the clamping unit and solder nozzle vertically upward along the z-axis to the raised position. Simultaneously, the moving unit can move vertically downward along the z-axis.

[0033] d. Move the moving unit along the x, y and / or z axes to the receiving position, where the solder can into which the solder nozzle is to be inserted is positioned below the clamped solder nozzle along the z axis;

[0034] e. Move the clamped solder nozzle vertically downward along the z-axis to the lower position. In the lower position, the solder nozzle is located in the solder container and is released by the clamping unit. As the solder nozzle moves vertically downward along the z-axis, it is conceivable that the moving unit moves vertically upward along the z-axis.

[0035] f. Move the clamping unit vertically upward along the z-axis to the stationary position. While moving the clamping unit vertically upward along the z-axis, the moving unit can move vertically downward.

[0036] g. Liquid solder is pumped through a solder nozzle.

[0037] It is conceivable that during steps a to e, liquid solder is pumped into the solder can, either through or into the nozzle holder of the solder can. In step e, the solder nozzle is briefly held directly above the solder can to preheat the solder can before reaching the lowering position, such that the solder nozzle is heated from below by the liquid solder and optionally washed by the liquid solder until the solder nozzle is at least substantially uniformly preheated. The solder pump can then be turned off, and the solder nozzle is lowered into the solder can or nozzle holder. According to step g, the liquid solder is then pumped through the solder nozzle; steps f and g can also occur simultaneously.

[0038] Then, it's conceivable to perform solder wave height testing to ensure the solder nozzle has the appropriate wave height. It's also conceivable to use a camera to monitor the solder nozzle or the liquid solder flowing from it.

[0039] It is particularly advantageous if the described method is performed such that the clamping fingers are heated to a preheating temperature before clamping the solder nozzle, and / or if the solder nozzle in the hopper is heated to a preheating temperature before being clamped. As a result, preheating is not required, and in particular, the start-up time of the solder nozzle after insertion into the solder can be reduced or even eliminated.

[0040] Further details and advantageous embodiments of the invention can be found in the following description, on which one embodiment of the invention will be described and explained in more detail. Attached Figure Description

[0041] In the attached diagram:

[0042] Figure 1 This is a front view of the selective welding system according to the present invention;

[0043] Figure 2 It is based on Figure 1 Side view of a selective welding system;

[0044] Figure 3 It is based on Figure 1 and 2 A schematic diagram of the moving unit and clamping unit of the selective welding system;

[0045] Figure 4 It is based on Figure 3 A side view of the moving unit and clamping unit in their changing positions;

[0046] Figure 5 It is based on Figure 4 A view of the device in the clamping position;

[0047] Figure 6 It is based on Figure 5 The view in the elevated position;

[0048] Figure 7 It is based on Figure 6 The view at the receiving position;

[0049] Figure 8 It is based on Figure 7 A view of the solder can in its lowered position;

[0050] Figure 9 It is based on Figure 8 A view of the cleaned position;

[0051] Figure 10 It is based on Figure 9 A view of the material in its lowered position within the hopper;

[0052] Figure 11 This is the first embodiment of the silo;

[0053] Figure 12 This is the second embodiment of the silo; and

[0054] Figure 13 This is the third embodiment of the silo. Detailed Implementation

[0055] Figure 1 and 2A selective soldering system 10 for wave soldering of circuit boards is shown. The system includes a housing 12 with a cover 14 that can close the housing 12, and the cover 14 is closed when the selective soldering system 10 is in operation. A moving unit 16 is disposed within the housing 12, which is movable in the horizontal plane along the x-axis and y-axis, and is movable in the vertical direction along the z-axis.

[0056] The moving unit 16 in Figure 3 The diagram is schematically shown. A solder can 40 for receiving liquid solder and a hopper 20 for receiving a total of ten solder nozzles 22 are disposed on a moving unit 16, with a total of five solder nozzles 22 inserted into the hopper. One of the solder nozzles 22 can be inserted into the solder can 40. The solder can 40 has a holder 42 for receiving the solder nozzles 22.

[0057] Furthermore, a cleaning unit 24 for cleaning the solder nozzle 22 is provided on the moving unit 16. Figure 3 It can also be clearly seen that a driver 26 is provided along the x-axis and a driver 28 is provided along the y-axis for moving the moving unit 16. A z-axis driver 30 is provided for moving the moving unit 16 along the z-axis. The three drivers 26, 28, and 30 are controlled by a control unit 32.

[0058] A clamping unit 34 is provided vertically above the plane where the moving unit 16 is located. The clamping unit 34 can move vertically along the z-axis via the drive unit 36. The clamping unit 34 has two clamping fingers 38, which can move closer to and further away from each other. The movement of the clamping fingers 38 of the drive unit 36 ​​and the clamping unit 34 can be controlled by the control unit 32. The cleaning unit 24 is also actuated by the control unit 32.

[0059] The control unit 32 is designed to use the drive unit 36 ​​to control the moving unit 16 and the clamping unit 34, so that the solder nozzle 22 in the hopper 20 can be clamped, lifted and lowered into the solder can 40 by the clamping unit 34.

[0060] This arrangement is preferably such that the clamping unit 34 can only move along the z-axis, and not along the x-axis and y-axis.

[0061] In order to replace solder nozzle 22, Figure 4 In the first step shown, the moving unit 16 can move along the x, y and z axes to a change position, in which the solder nozzle 22 to be clamped in the hopper is located below the clamping unit 34 along the z axis 44.

[0062] In the next step, the clamping unit 34 then moves vertically downwards along the z-axis 44 as shown in the image. Figure 5 The clamping position is shown. Upon reaching or after reaching the clamping position, the clamping fingers 38 move toward each other, and the solder nozzle 22 is clamped.

[0063] Then, as Figure 6 As shown, by moving the clamping unit 34 vertically upward along the z-axis 44, the clamped solder nozzle is moved to the lifting position.

[0064] In the next step, such as Figure 7 As shown, the moving unit 16 is horizontally moved along the x, y and z axes such that, in the receiving position, the solder can 40 or the holder 42 of the solder can 40 is located below the clamped solder nozzle 22 along the z axis 44.

[0065] Then, as Figure 8 As shown, the clamping unit 24 moves vertically downward along the z-axis to the lowering position, the clamping unit 34 is then released, and in the next step, the clamping unit 24 can be moved vertically upward to the resting position.

[0066] To shorten the described nozzle changing process, it is conceivable that as the clamping device moves along the x-axis 44, the moving unit 16 simultaneously moves along the z-axis in the opposite direction to the clamping unit 34, which could result in a shorter overall cycle time.

[0067] It is conceivable that during the movement of the moving unit 16, liquid solder is pumped into or through the holder 42. Shortly before reaching the lowering position, the solder nozzle 22 may be held directly above the solder wave flowing into or out of the holder 42, such that the solder nozzle 22 is heated from below by the solder wave and optionally washed until the nozzle 22 is at least substantially preheated uniformly. The solder pump can then be turned off, and the solder nozzle 22 can be lowered into the solder tank 40.

[0068] The control unit 32 can also be designed so that the nozzle 22 in the solder can 40 is clamped and lifted by the clamping unit 34, and discarded if the nozzle 22 is no longer needed. If the nozzle 22 is needed again, it can be cleaned and then placed in the hopper 20.

[0069] Cleaning of nozzle 22 Figure 9 As shown, the nozzle 22, removed from the solder can 40, is moved to the cleaning unit 24 and cleaned there before being placed in the hopper 20. For this purpose, the cleaning unit 24 includes a rotating metal brush 46, such as... Figure 9 As shown, the nozzle base of the relevant nozzle 22 can be placed on the metal brush. This allows at least the metal base to be cleaned. After cleaning the metal base, the nozzle 22 can be placed on the hopper 20 at its designated position.

[0070] To maintain or increase the temperature of the solder nozzle 22 during clamping, a finger heater 48 is provided on or within the clamping finger 38, such as... Figure 3 As shown. The finger heater 48 is, in particular, a resistance heater, which preheats the gripper fingers by applying a corresponding current. The finger heater 48 can be located, in particular, in the cavity holding the fingers 38, for example, in a hole provided for this purpose. This design preferably allows the gripper fingers 48 to be heated to a preheating temperature of approximately 160°C.

[0071] The hopper heater 52 is also installed in the hopper 20, especially in the hopper base 50, such as Figures 11 to 13 As shown. The silo heater can also be designed as a resistance heater and can be used as, for example, a surface or annular heating element.

[0072] In order to receive the solder nozzle 22 at a precise position, a receiving element 62 in the form of a base can be provided on the upper side of the bottom 50 of the hopper.

[0073] exist Figures 11 to 13 In the case of the provided hopper 20, the hopper bottom 50 is covered by a cover element 54, which can be designed as a lid element, for example. A side wall 55 is disposed between the associated hopper bottom 50 and the cover element 54. The side wall 55 can preferably be arranged on the hopper bottom 50. In particular, the cover element 54 can be arranged to be movable, allowing it to be accessible to the solder nozzle 22 in the open position.

[0074] This cover element 54 can protect the solder nozzles 22 in the hopper 20 and also help ensure that these nozzles are set at a substantially constant preheating temperature.

[0075] exist Figure 11 In the illustrated embodiment, the hopper heater 52 is disposed in the hopper base 50, which is designed as a resistance heater and extends more or less over the entire bottom 50 as a surface heating element. The hopper heater 52 may also be disposed in the cover element 54, so that the solder nozzle 22 is also preheated from above.

[0076] According to Figure 12In this embodiment, a contact material in the form of metal pins 58 is provided between the nozzle neck 56 of the nozzle 22 and the cover element 54, the metal pins 58 being mounted so as to be displaceable parallel to each other. Due to the weight of the individual metal pins displaceable within the cover element 54, they act vertically downwards on the nozzle neck 56. Because of the hopper heater 52 disposed within the cover element 54, which can here be designed as a ring-shaped element around its circumference, the metal pins 58 are preheated, thereby conducting heat to the nozzle neck 56. The metal pins 58 preferably have the same length, such that with the free ends of the metal pins 58 resting on the upper side of the nozzle neck 56, the metal pins 58 protrude vertically beyond the cover element 54. Overall, this results in favorable heat transfer from the hopper heater 52 located in or on the cover element 54 to the solder nozzle 22.

[0077] According to Figure 13 In this embodiment, a hopper heater 52 is also disposed in the cover element 54. Furthermore, a contact material in the form of metal wool 60 is disposed on the inner side of the cover element 54 facing the solder nozzle 22. The metal wool 60 is elastically deformable, so that when the cover element 54 is in place, the metal wool 60 rests on the nozzle neck 56. In this embodiment, appropriate heat transfer from the hopper heater 52 disposed in the cover element 54 to the nozzle neck 56 can also be implemented.

[0078] When the cover element 54 is provided, the design preferably allows the cover element 54 to be automatically lifted or pivoted to one side before the solder nozzle 22 is clamped, so that the clamping unit 34 can clamp the nozzle neck of the solder nozzle, which is then freely accessible.

Claims

1. A selective soldering system (10) for selective wave soldering of circuit boards, the selective soldering system (10) comprising a solder can (40), the solder can (40) comprising solder nozzles (22), the solder nozzles (22) being detachably disposed on the solder can (40), wherein, The solder nozzle (22) has a nozzle base and a nozzle neck (56), wherein a nozzle opening is provided at the free end of the nozzle neck (56), the solder can (40) is arranged on a moving unit (16), the moving unit (16) is movable in the horizontal plane along the x and y axes, and in the vertical direction along the z axis (44), and the selective soldering system (10) includes a control unit (32) for controlling the moving unit (16). The selective welding system is characterized in that... A hopper (20) for receiving different solder nozzles (22) is arranged on the moving unit (16). A clamping unit (34) is provided, the clamping unit (34) including clamping fingers (38) for clamping the solder nozzle (22), the clamping unit (34) being controllable by the control unit (32), wherein the clamping unit (34) is movable along the z-axis using a drive unit (36) controlled by the control unit (32), and wherein the control unit (32) is designed to control the moving unit (16), the drive unit (36) and the clamping unit (34) so ​​that the solder nozzle (22) in the hopper (20) can be clamped, lifted and lowered into the solder can (40) by the clamping unit (34), and A hopper heater is provided for heating the hopper (20) and / or the solder nozzle (22) in the hopper (20) to a preheating temperature.

2. The selective welding system (10) according to claim 1, characterized in that, The drive unit (36) is designed such that the clamping unit (34) can only move along the z-axis (44), and the moving unit (16) moves the solder can (40) along the x, y and z axes when the solder nozzle (22) is clamped and lifted.

3. The selective welding system (10) according to claim 1 or 2, characterized in that, The control unit (32) is designed to control the moving unit (16) and the driving unit (36) such that the hopper (20) and the clamping unit (34) move toward and / or away from each other along the z-axis (44).

4. The selective welding system (10) according to claim 1, characterized in that, A finger heater (48) is provided for heating the clamping fingers (38) to a preheating temperature before and / or during the clamping process.

5. The selective welding system (10) according to claim 4, characterized in that, The finger heater (48) is designed as a resistance heater, which is arranged on or integrated into the clamping finger (38).

6. The selective welding system (10) according to claim 1, characterized in that, The hopper (20) has a hopper bottom, and the hopper heater is disposed in or on the hopper base.

7. The selective welding system (10) according to claim 6, characterized in that, The hopper (20) has a covering element, and the hopper heater is disposed in or on the covering element.

8. The selective welding system (10) according to claim 6 or 7, characterized in that, The contact material is disposed between the hopper heater and the solder nozzle (22) for contacting the solder nozzle (22).

9. The selective welding system (10) according to claim 8, characterized in that, The contact material is formed from metal wool.

10. The selective welding system (10) according to claim 8, characterized in that, The contact material is formed of metal elements that are mounted to be able to move parallel to each other, and the free ends of the metal elements act on the solder nozzles (22) in the hopper (20).

11. The selective welding system (10) according to claim 1, characterized in that, A cleaning unit (24) is arranged to clean the nozzle base of the solder nozzle (22) removed from the solder can (40). The cleaning unit (24) is controllable by the control unit (32), and the control unit (32) is configured such that the solder nozzle (22) held and lifted from the solder can (40) by the clamping unit (34) is moved into the cleaning unit (24) and cleaned at the cleaning unit before being placed in the hopper (20).

12. The selective welding system (10) according to claim 11, characterized in that, The cleaning unit (24) is disposed on the moving unit (16).

13. The selective welding system (10) according to claim 11 or 12, characterized in that, The cleaning unit (24) includes a rotating metal brush (46) for cleaning at least the nozzle base.

14. A method for replacing the solder nozzle (22) of a selective welding system (10) according to any one of the preceding claims, the method comprising the steps of: a. Move the moving unit (16) along the x, y and / or z axes to a replacement position, where the solder nozzle (22) to be clamped in the hopper (20) is located vertically below the clamping unit (34) along the z axis (44). b. Move the clamping unit (34) vertically downward along the z-axis (44) to the clamping position, and clamp the solder nozzle (22) in the hopper (20) through the clamping unit (34). c. Move the clamping unit (34) and the solder nozzle (22) together vertically upward along the z-axis (44) to the lifting position. d. Move the moving unit (16) along the x, y, and / or z axes to a receiving position, in which the solder nozzle (22) is positioned vertically below the held solder nozzle (22) along the z axis (44) with the solder can (40) to be inserted therein. e. Move the clamped solder nozzle (22) vertically downward along the z-axis (44) to the lower position, in which the solder nozzle (22) is located in the solder can (40), and release the solder nozzle (22) through the clamping unit (34). f. Move the clamping unit (34) vertically upward along the z-axis (44) to the rest position.

15. The method according to claim 14, characterized in that, The clamping finger (38) is heated to a preheating temperature before clamping the solder nozzle (22), and / or the solder nozzle (22) in the hopper (20) is heated to a preheating temperature before being clamped.

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