WO2001033923A2

WO2001033923A2 - Soldering unit and use of a solder conveyor pump comprising a conveyor worm in a soldering unit

Info

Publication number: WO2001033923A2
Application number: PCT/EP2000/010944
Authority: WO
Inventors: Stefan Schubert; Siegfried Ott
Original assignee: Ltc Laserdienstleistungen Gmbh
Priority date: 1999-11-05
Filing date: 2000-11-06
Publication date: 2001-05-10
Also published as: WO2001033923A3; DE19953316A1; AU3003501A; DE10083462D2

Abstract

The invention relates to a soldering unit for soldering electrical components onto boards using a machine. The soldering unit comprises a solder storage container (4) for receiving liquid solder, a solder applicator device (20) wherewith the solder contained in said storage container (4) can be applied to the component to be soldered, in addition to comprising a controllable solder pump (3). The solder pump (3) comprises a motor-driven conveyor worm (10) wherewith the solder can be pumped in the required amount and within the desired time-frame from the storage container (4) and said solder can be fed to the solder applicator device (20).

Description

Soldering system and use of a solder feed pump with screw conveyor in a soldering system

Technical field

The present invention relates to a soldering system for mechanical soldering of electrical components on circuit boards. The invention further relates to the use of a special feed pump for conveying solder in a soldering system.

State of the art

In soldering systems, electrical components are mechanically attached to circuit boards by soldering. The electrical components can be soldered by immersing them in a solder bath or by applying solder using a so-called solder wave. With these two alternatives, all of the electrical components present on the circuit board are soldered in one soldering process. In contrast to this, however, soldering systems can also be used to solder individual electrical components, such as, for example, retrofitted connectors, onto a circuit board by using a soldering nozzle to selectively solder the respective electrical component

Component is soldered. All procedures have in common that solder is normally used as solder. For the present invention, the application of solder by means of a solder wave or solder nozzle is particularly relevant.

Vane pumps have hitherto been used to convey the solder from a storage container to the solder application means, here a soldering nozzle or a solder wave. This sometimes leads to problems with soldering systems. It is extremely difficult to achieve constant volume delivery of the solder. In addition, such pumps are relatively complex and expensive. Another problem with previous soldering systems is that the solder runs in the vertical line section to the solder wave or nozzle outside the liquid solder bath in the storage container, which can lead to blockages due to cooled solder in this line section. Furthermore, there is the risk that the solder has already changed to a doughy state when it emerges, which changes the soldering conditions considerably and, under certain circumstances, worsens the soldering result.

Presentation of the invention

The technical problem on which the invention is based is to achieve extremely constant solder conveyance in a soldering system and the technical effort required for this to be kept as low as possible.

This technical problem is solved by a soldering system with the characteristics of

Claim 1 as well as solved by the use according to claim 15. A soldering system according to the invention for the mechanical soldering of electrical components on printed circuit boards has a solder storage container for holding liquid solder. In addition, there is a solder application device with which the solder can be applied from the storage container to the component to be soldered.

With a controllable solder pump, the solder can be pumped out of the storage container in the desired quantity and time period and can be supplied to the solder application device in a precisely metered manner. The solder pump includes a motor driven screw conveyor to convey the solder. The use of a solder pump with a screw conveyor for conveying solder in a soldering system represents the core of the invention with respect to one aspect of the invention. A second aspect relates to the mounting of a workpiece table for holding and positioning at least one circuit board in a soldering system. The invention is therefore based on the idea of using a screw conveyor for conveying solder in a soldering system known per se for the first time. By using a screw conveyor, absolutely constant and therefore pulse-free volume delivery of the solder is achieved for the first time. Through the appropriate choice of the geometry of the screw conveyor (including, among other things, pitch, outside diameter, ratio of core diameter to outside diameter,

Ratio of tooth tip width to tooth root width etc.) and the speed of rotation, the delivery volume can be determined precisely in the simplest way. The screw conveyor is driven in a simple manner by a controllable motor. By using a screw conveyor, it is also possible for the first time to design the drive of the screw conveyor to be lower than previously with regard to the required output, since only the output is required to convey the solder volume actually required. A very simple and compact structure can thus be achieved. Finally, it should be emphasized that the screw conveyor ends immersed in the solder, so that according to the invention only clean solder is sucked in and conveyed, since scaled solder, such as solder, sand and similar particles, floats on top.

By appropriate selection of the material for a pump housing, the drive shaft and the screw conveyor, for example ceramic, it is also possible to master different expansions due to temperature.

At the same time, good thermal decoupling from the drive components is achieved.

For example, the following configurations are conceivable for the thermal decoupling of the pump and the drive unit. The pump housing is made entirely of ceramic. Alternatively, it is also possible to divide the pump housing and to manufacture the lower part, in which the screw conveyor is accommodated, from steel (for example VA steel) and the upper part, which receives the drive shaft, from ceramic. The screw conveyor itself can made of steel or ceramic or another suitable temperature-resistant

Material. A variant consists in attaching a metallic pump housing to a cover of the storage container. The metallic screw then runs in the metallic pump housing. Thermal decoupling is already achieved by using a ceramic drive shaft.

The screw conveyor can be driven in different ways. A simple and inexpensive solution is that the screw conveyor of the solder pump is driven directly or via a gear by an electric motor. In poor installation conditions or when e.g. If it is necessary to adjust the rotation and line of the motor to the pump, the interposition of a gearbox can be advantageous. This enables precise control of the screw conveyor and thus of the delivery volume by regulating the electric motor accordingly. In addition, adaptation to a wide variety of requirements is possible by simply replacing or adapting the gear.

As already mentioned at the beginning, the different lengths in the area of the solder bath can lead to different linear expansions. Since the pump housing surrounding the screw conveyor is made of ceramic, temperature-related expansion is largely excluded. In addition, a largely maintenance-free solder pump is created by the storage of the screw conveyor and the drive shaft in the ceramic pump housing, as a result of which the operating costs are reduced.

Since the drive shaft and / or the screw conveyor are also made of ceramic, thermal problems can be avoided to an even greater extent. Thermal insulation is also the simplest in this training

This is possible by accommodating the electric motor and the transmission in a housing which is insulated from the storage container by thermal insulators, such as ceramic components or temperature-resistant plastic parts. In the same way, the drive unit can also be mounted on the machine frame.

It was mentioned at the outset that a wide variety of solder application devices can be used in a soldering system according to the invention. In the event that selective soldering of components is desired, it is appropriate to design the solder application device as a solder application nozzle. It is advantageous if this is supplied with the solder via a heated riser, which in turn is connected to the pump.

A wider, area-wide soldering of components on circuit boards is possible by using a solder wave as the solder application device. By both

Alternatives for a solder application device, it is advantageous if the riser pipe running therein can be heated.

So far, among other things, a robot has been used to bring the components to be soldered onto the circuit board in the required manner to the solder application device. Corresponding soldering systems were extremely expensive and complex. In that for the first time a gimbal-mounted workpiece table, which can also be moved in the Z direction, is arranged above the solder application device, a component on a circuit board can also be easily, technically far less complex than before, extremely quickly and inexpensively Soldering can be introduced to the soldering device. A structure which has proven to be extremely expedient is an outer frame which can be pivoted about an axis, so that different inclinations of the frame can be set. There is an inner frame on this outer frame The frame is mounted in such a way that it can be pivoted about an axis that is offset by 90 °. On this inner frame, a support beam is in turn guided and driven in a longitudinally movable manner. This carrier, which can be moved along the inner frame, in turn has a holding arm attached to it, which can be moved along the carrier and on which the workpiece table for receiving the board to be soldered is arranged. This means that the inclination of the workpiece table can be adjusted and moved over the inner frame as well as the outer frame above the solder application device. The workpiece table can advantageously also be moved in the Z direction, ie perpendicular to the movable support beam. All traversing devices can be precisely positioned using stepper motors etc. or other suitable actuating devices such as linear motors. The

Pivoting of the frame is also very advantageously adjustable, for example, by means of pneumatic or hydraulic cylinders.

This ensures that the workpiece table in a Cartesian coordinate system is controlled and precisely displaceable in all three basic vector directions, so that extremely precise adjustment of a board to the solder application device is ensured. In particular, it is also possible to incline the component to be soldered at the required angle, for example between 0 ° and 12 °, with respect to the solder application device, as a result of which the best soldering results are achieved.

In an alternative embodiment of a cardanically suspended workpiece table, supporting beams are provided on two opposite side edges of a soldering system according to the invention, on which a transverse table supporting beam is movably mounted. In turn, a gimbal-suspended workpiece table is fastened to the table support beam so that it can move along the table support beam. Optionally, the workpiece table can also be moved vertically to the table support beam using an adjustment motor. In contrast to the previously explained embodiment, the workpiece table is here in its outer dimensions limited to a maximum size of a component to be clamped and accordingly the masses to be moved are smaller. Of course, due to the special suspension of the workpiece table, the component (circuit board) fastened therein can in turn be inclined in any desired angular position with respect to the soldering nozzle. This means that the component can be moved in relation to the soldering nozzle, on the one hand, in which the entire workpiece table with the component clamped in it is displaced in an X and / or Y direction (these directions are the support beam and table support beam direction), on the other hand the component can be rotated about two mutually perpendicular axes of rotation by the gimbal-suspended workpiece table, and can thus be positioned in any desired spatial position relative to the soldering nozzle.

The workpiece table itself comprises two mutually opposite support arms which are rigidly screwed to the table support beam. An outer swivel frame is fastened or rotatable about an axis to these support arms. An inner swing frame is in turn pivotably mounted in this outer swing frame. This pivot or rotation axis runs perpendicular to the previously explained axis. In the inner swivel frame there is a clamping device with which the component can be fastened in the inner frame.

Brief description of the drawings

In the following, an embodiment is described in more detail with reference to the accompanying drawings for further explanation and for a better understanding of the invention. It shows:

1 is a schematic perspective view of a soldering system according to the invention without a gimbaled workpiece table,

2 is a schematic perspective view of the main components of the soldering system of FIG. 1,

3 shows a schematic cross-sectional view through a solder application device,

4 shows a cross-sectional view of a feed pump with screw conveyor, as used in a soldering system according to the invention,

Fig. 5 is a very schematic representation of a gimbal for a workpiece table and

Fig. 6 is an overall perspective view of a soldering system according to the

Invention with a gimbal-mounted workpiece table.

As can be seen from FIG. 1, the soldering system according to the invention is installed in a machine frame 1, which is used to fasten a drive unit 2 and a soldering crucible 4. A feed pump 3, which is connected to the drive unit 2, is located in the soldering crucible. The feed pump 3 is in turn connected to a solder application device 20. Finally, one in FIG. Ending board 6 shown, which can be moved in any direction in an XYZ coordinate system, as will be explained later with reference to the other figures.

The more precise design of the drive unit and the elements such as the soldering pump and soldering device that are essential for the soldering system according to the invention can be seen more clearly from the perspective view according to FIG. 2. The drive unit 2 thus comprises an upper part 2a, in which a transmission is housed. The drive motor 13 is flanged to the side of this upper part 2a. The entire drive unit 2, consisting of the upper part 2a and the drive motor 13, is connected to a cover 7 of the soldering crucible 4 via thermal insulators 12.

The thermal insulators 12 are, for example, ceramic spacers, ceramic rods or temperature-resistant plastic parts.

The feed pump 3 with a screw conveyor 10 is located in the soldering crucible 4. The more precise structure of this feed pump can be seen in FIG. 4. The

Feed pump comprises a drive shaft 11 which is connected in a rotationally fixed manner to a pulley 25 via a shaft fastening 19. The toothed belt pulley 25 is coupled to the transmission (both elements are not shown) in the drive unit 2 via a toothed belt. The drive shaft 11 is mounted in a cylindrical pump housing 16 made of ceramic. At the lower end of the drive shaft 11, the screw conveyor 10 is mounted coaxially. The screw conveyor runs out in a pressure chamber 14 of the pump housing 16. The pressure chamber 14 is formed in that a taper is introduced into the screw conveyor 10. At the front of the pump housing 16, in the direction of the screw conveyor 10, there is an inlet flow 15 of solder. At the end of the screw 10 is the

Pressure chamber 14 is provided with an opening to which a riser 22 is connected. As can be seen from FIG. 4, the entire part of the pump housing 16 with the screw conveyor 10 is located below the solder surface 26. The entire solder crucible 4 is covered by the cover 7. As can be seen from FIG. 2, a nitrogen connection 30 opens into the cover 7, via which nitrogen can be introduced into the interior of the solder crucible 4. By adding nitrogen, a "covering" of the solder bath is ensured, whereby scaling of the soldering tin can be avoided in a simple manner. At the same time, nitrogen will also emerge from the solder application device, which achieves a better soldering result. From FIG. 2 it can be seen how the riser 22 leads into the solder application device and ends there in a soldering nozzle 20.

The exact structure of the solder application device (here soldering nozzle) can be seen from FIG. Thus, the riser 22 is surrounded by a heater 21 in a protective tube 23. The riser 22 ends above the protective tube 23 in the said nozzle 20. The riser is arranged coaxially in the protective tube 23. An annular space is created between the riser 22 and the protective tube 23, in which the solder that emerges and does not remain on the component can flow back into the solder pot. This intermediate space also offers the possibility of nitrogen 24 escaping around the nozzle 20, as a result of which a type of protective gas hood 5 is formed around the nozzle 20.

The cardanic suspension of a workpiece table 32 will now be explained with reference to FIGS. 5 and 6. The workpiece table 32 serves to receive a circuit board to be soldered with electrical components located thereon. Accordingly, it is provided with adjustment devices, so that any size of a circuit board is durable. The workpiece table 32 itself is mounted on a support beam 45 via a holding arm 47 which can be moved in the Z direction. The holding arm 47 is on the

Support beam 45 is longitudinally displaceable, and can be moved very precisely, for example, by means of a stepper motor. The support beam 45 in turn is precisely adjustable on an inner frame 41 via a motor drive 48 along the frame and perpendicular to the displaceability of the holding arm 47. So that's one Any 3-dimensional positioning of the workpiece table can be achieved. The inner frame 41 is in turn rotatably mounted in an outer frame 40 via joints 43. The outer frame 40 can in turn be pivoted perpendicularly to the mounting of the inner frame 41 by means of rotary bearings, specifically via pneumatic cylinders 42. The entire frame structure is attached to the machine frame 1. The outer frame is thus pivoted relative to the machine frame 1 via the pneumatic adjustment 42, the inner frame 41 can be pivoted by 0 ° to 20 ° to this by means of a pneumatic cylinder 49. The motor 48 for adjusting the XY coordinate system on the inner frame, ie the workpiece table, can be supplied with the necessary supply units (electrics, etc.) by lines 46.

The operation of the soldering system according to the invention will now be described. A circuit board to be soldered with the electrical components located thereon is fastened on the workpiece table 32. Via the adjustment motors for the XYZ coordinate system on the inner frame and by pivoting the inner as well as the outer frame 41, 42, the position of the circuit board to be soldered can be placed above the soldering nozzle 20, and also at the required angle , Then the feed pump 3 is put into operation, so that solder is sucked out of the soldering crucible 4 by means of the screw conveyor 10 and conducted to the nozzle 20 via the riser 22. To freeze or a

To prevent solidification of the solder when rising to the solder nozzle 20 in the riser 22, the riser 22 is heated to the required temperature by a heating device 21 or kept at this temperature. By continuously introducing nitrogen via the connection 30 and nitrogen escaping through the intermediate space around the riser 22 and the protective tube 23, the soldering point on the nozzle 20 is “covered” at the same time, and thus the soldering result is improved. Returning solder passes back into the solder pot 4 via this space. Via a control device, not shown, the screw conveyor 10 can be operated in the most precise manner over the required period of time, so that a precisely determined volume of solder is supplied to the solder application device. By rotating the screw conveyor in the opposite direction, the entire riser 22 can be emptied. This is particularly useful for cleaning purposes.

Claims

claims

1. Soldering machine for the mechanical soldering of electrical components on circuit boards with a solder storage container (4) for receiving liquid solder, - a solder application device (20) with which the solder from the

Storage container (4) can be applied to the component to be soldered, and a controllable solder pump (3), which has a motor-driven screw conveyor (10) with which the solder can be pumped out of the storage container (4) in the desired amount and for a period of time and the solder Application device (20) can be fed.

2. Soldering system according to claim 1, characterized in that the screw conveyor (10) of the solder pump is driven directly or via a gear by an electric motor (13).

3. Soldering system according to claim 1 or 2, characterized in that the screw conveyor (10) is mounted in a pump housing (16) made of ceramic.

4. Soldering system according to claim 1, 2 or 3, characterized in that the drive shaft (11) and / or the screw conveyor (10) consist of ceramic.

5. Soldering system according to claim 2, characterized in that the electric motor (13) and the gearbox are housed in a housing (17) which is insulated from the storage container (8) by thermal insulators (12).

6. Soldering system according to claim 1, characterized in that the solder application device comprises one or more solder nozzles (20).

7. Soldering system according to claim 1, characterized in that the solder application device comprises a solder wave.

8. Soldering system according to claim 1, characterized in that a gimbal-mounted workpiece table (32) is arranged above the solder application device (20).

9. Soldering system according to claim 8, characterized in that the workpiece table (32) can be displaced in a Cartesian coordinate system in a controlled manner in all three basic vector directions.

10. Soldering system according to claim 8, characterized in that the workpiece table (32) about its suspensions (42, 43, 44) can be rotated in a controlled manner.

11. Soldering system according to one of claims 8-10, characterized in that - the cardanic workpiece table on a movable in one plane

Support beam is attached, - the gimbal workpiece table along the movable support beam and can be moved vertically relative to this and the gimbal tool table has essentially the dimensions of a largest component to be clamped.

12. Soldering system according to claim 1, characterized in that a feed line (22) connecting the feed pump (3) with the solder application device (20) in at least one outside of the liquid solder in Storage container (4) lying riser section can be heated by a heating device (21).

13. A soldering system according to claim 1, characterized in that the solder storage container (4) is closed and nitrogen can be introduced between the surface of the solder located therein and the storage container cover (7) via a connection (30).

14. Soldering system according to claim 13, characterized in that the nitrogen can advance to the solder application device (20), at which it emerges with the solder.

15. Use of a solder pump with screw conveyor (10) for conveying solder in a soldering system.