REFLOW CONDENSATION SOLDERING MACHINE

Abstract

Reflow condensation soldering machine comprising a circulation system for a heat transfer medium, the reflow condensation soldering machine comprising the circulation system, a centrifuge and a condensation device for the heat transfer medium.

Claims

1. Reflow condensation soldering machine comprising a circulation system for a heat transfer medium, wherein the circulation system comprises a centrifuge and a condensation device for the heat transfer medium.

2. Reflow condensation soldering machine according to claim 1, wherein the centrifuge is a disc separator.

3. Reflow condensation soldering machine according to claim 2, wherein the disc separator has a number of discs, and disc spacing and the speed of rotation of the disc separator is adapted to achieve a desired plant throughput, taking into account expected particle sizes of impurities of the heat transfer medium and viscosity of the contaminated heat transfer medium.

4. Reflow condensation soldering machine according to claim 3, wherein the disc separator comprises 4 to 250 discs.

5. Reflow condensation soldering machine according to claim 3, wherein the disc spacing between the discs is in the range of 0.2 mm-14 mm.

6. Reflow condensation soldering machine according to claim 5, wherein the discs are equally spaced.

7. Reflow condensation soldering machine according to claim 5, wherein the spacing between the discs in the inlet area is smaller or larger than at the end of a stack of the discs opposite the inlet area.

8. Reflow condensation soldering machine according to claim 1, wherein the centrifuge is adapted to perform 1-150,000 revolutions per minute, preferably 1,000 to 10,000 revolutions per minute.

9. Reflow condensation soldering machine according to claim 1, wherein the centrifuge is adapted to process 1-6 liters of condensed heat transfer medium.

10. Reflow condensation soldering machine according to claim 1, wherein the condensation device for the heat transfer medium is integrated in the centrifuge.

11. Reflow condensation soldering machine according to claim 10, wherein the condensation device for the heat transfer medium comprises temperature limiting means of one or more components of the centrifuge.

12. Reflow condensation soldering machine according to claim 11, wherein the temperature limiting means comprises active cooling of the one or more components of the centrifuge.

13. Reflow condensation soldering machine according to claim 11, wherein the temperature limiting means comprises passive cooling of the one or more components of the centrifuge.

14. Reflow condensation soldering machine according to claim 13, further comprising means for supplying purified PFPE during a cooling phase of passive cooling of the centrifuge.

15. Reflow condensation soldering machine according to claim 11, wherein the centrifuge is a disc separator and one or more components of the disc separator comprises at least one of the following: an inlet of the disc separator, a float of the disc separator, one or a plurality of separator discs, a separator drum.

16. Reflow condensation soldering machine according to claim 12, wherein a wall of said one or plurality of components has at least one cavity through which a cooling fluid can flow.

17. Reflow condensation soldering machine according to claim 12, wherein a heat pipe is integrated in a wall of the one or more components.

18. Reflow condensation soldering machine according to claim 13 wherein at least one component of said one or more components is configured such that a heat capacity of the at least one component is sufficient to absorb a quantity of heat of the vaporous heat transfer medium flowing past during a predetermined separation phase so that the heat transfer medium condenses.

19. Reflow condensation soldering machine according to claim 1, wherein the heat transfer medium has a boiling point of 260 C.

20. Reflow condensation soldering machine according to claim 1, wherein the heat transfer medium is Galden or PFPE.

21. Method of operating the reflow condensation soldering machine according to claim 1, comprising: injecting vaporous perfluoropolyethers into a hermetically sealed first process chamber containing an assembly to be soldered, heating the assembly by condensing the vaporous perfluoropolyether, suction of condensed and vaporous perfluoropolyethers including impurities, feeding the condensed and vaporous perfluoropolyethers including impurities to a separating condensate trap comprising a disc separator and condensing device for condensing the perfluoropolyether, condensing and separating the perfluoropolyether from the impurities with the separating condensate trap, and using a purified perfluoropolyether for a soldering process for a subsequent assembly.

22. Method according to claim 21, in which the disc separator is brought into a rest state during a soldering phase and in which the disc separator is prefilled with the purified or a fresh perfluoropolyether after the end of the rest phase, preferably with 0.5-3 liters of perfluoropolyether, and particularly preferably with 0.9-1.1 liters of perfluoropolyether.

23. Method according to claim 21, in which the disc separator is operated continuously, wherein the purified perfluoropolyether or vapor from a second process chamber, which operates with a time offset relative to the first process chamber, is fed to the disc separator during a soldering phase.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention is now described by means of the following Figures, in which

[0026] FIG. 1 shows a reflow condensation soldering machine with a circulation system of a heat transfer medium according to the state of the art,

[0027] FIG. 2 shows a reflow condensation soldering machine with a circulation system of a heat transfer medium according to an embodiment of the present invention, and

[0028] FIG. 3 schematically shows a disc separator with integrated condensation device according to an embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0029] FIG. 2 shows a reflow condensation soldering machine 200 with a circulation system 210 for a heat transfer medium according to an embodiment of the present invention. The circulation system comprises a reservoir 10, a first pump 20, a heater 30, a process chamber 40, a second pump 50 and a separating condensate trap 90.

[0030] The first pump 20 pumps liquid heat transfer medium in the form of perfluoropolyether (PFPE) from the reservoir 10 to the heating means 30. In the heating means 30 the PFPE is vaporized and then fed to the process chamber 40. The medium (vaporous PFPE) then condenses on the printed circuit board 45 to be soldered and thus heats the components to be soldered on the printed circuit board 45 in the process chamber 40 and the soldering paste. The PFPE is adapted so that the boiling point of the PFPE is slightly higher than the melting point of the solder. This ensures that the soldering temperature is reached at the same time and that the components do not overheat during soldering, as the boiling temperature of the PFPE is also the maximum temperature. After this soldering phase, in a first phase of a regeneration phase or separation phase, both the components of the heat transfer medium in the vaporous and liquid aggregate state are sucked out of chamber 40 with a second pump 50. After the suction, condensation of the vaporous part of the heat transfer medium takes place in the separating condensate trap 90 and the heat transfer medium is separated from the residuals (impurities). Accordingly, the separating condensate trap 90 comprises a condensation device 90A and a separator 90B. During this regeneration phase the printed circuit board 45 is also freed from the PFPE coating, removed from the process chamber 40 and is available as product 45b. A new printed circuit board 45a is then placed in the process chamber 40 and a new soldering phase with recycled (remanufactured) PFPE can begin.

[0031] After condensation in the condensation device 90A, a mixture (emulsion) of liquid components (PFPE, flux, soldering paste, etc.) which are not soluble in each other is obtained. It is possible that even small amounts of solids of all impurity particles (for example tin particles) are contained. In the present invention a disc separator 90B is used to separate the liquid and solid components from the PFPE. A disc separator is a special type of centrifuge. The underlying idea of a centrifuge is based on the processes in a settling tank. There, particles, sediments and solids sink slowly to the bottom following the force of gravity, and liquids of different densities separate under the influence of gravity. However, this separation process is very slow. A separator is a sedimentation tank that rotates around an axis. When the entire unit rotates quickly, gravity is replaced by a controllable centrifugal force. By inserting special discs, the surface on which the different phases can settle is increased, which accelerates the separation process. Disc separators are known, for example, in the dairy industry to separate the cream from the milk.

[0032] Optionally (drawn in dashed line), the circulation system of the reflow condensation soldering machine can have a means 91, 91A, with which purified and liquid PFPE is returned to the separating condensate trap 90 during the soldering phase, so that the cooling process of the separating condensate trap 90 is accelerated and the PFPE is better purified. It must be noted that the soldering phase is also the cooling phase of the separating condensate trap 90. Furthermore, this means can be used in intermittent operation as well as in continuous operation. In continuous operation, this device is used for cooling and maintaining optimum separating conditions. In intermittent operation, i.e. when the separator is temporarily at rest, for example during a soldering phase, the device can be used to prefill the separator in order to create more reproducible separating conditions.

[0033] FIG. 3 exemplarily and schematically shows a cross-section of a disc separator as used in the present invention. FIG. 3 shows a disc separator 300 with a drum 310, an inlet 320, a first outlet 330, a second outlet 340 and a set of stacked discs 370. Separation in a disc separator occurs due to differences in density, which means that in the first outlet 330 the liquid with the relatively lower density can be discharged and in the second outlet 340 the liquid with the relatively higher density can be discharged. With the current applications and materials used, the PFPE has a higher density than the impurities, so in the illustration in FIG. 3, the first outlet 330 is for the impurities 335 and the second outlet 340 is for the purified PFPE 345. However, the present invention is not limited to this example. For example, in other applications materials may be used where the PFPE has a lower density than the impurities. In this case, the first outlet 330 would be for the purified PFPE and the second outlet 340 would be for the impurities. It is also possible that some of the impurities have a lower density than the PFPE and some have a higher density than the PFPE and/or additional solids. With appropriately designed disc separators, the fractions of the liquid phases can be separated. For example, the disc separator may have a sludge chamber in which the solids collect. To separate more than two liquid phases, for example, a plurality of separators can be connected in series. For example, if the condensed, unpurified heat transfer medium consists of a low density phase with impurities, a medium density PFPE phase and a high density phase with impurities, the purified PFPE can be extracted with two separators connected in series.

[0034] In the embodiment shown in FIG. 3, the inlet 320 is provided with a cavity through which a cooling liquid 325 can flow in the case of a design with active cooling. Alternatively, the inlet 320 can be in contact with a device that can dissipate heat in any suitable way, for example a heat pipe or fluid-cooled heat sink. However, FIG. 3 shall not be understood to mean that the present invention is limited to active cooling. As will be described in more detail below, instead of the cavity for the coolant or cooling liquid 325 shown in FIG. 3, in alternative designs the inlet can be solid, so that it has a correspondingly high heat capacity to absorb sufficient heat and provide passive cooling.

[0035] The material 390 (liquid and vaporous PFPE and impurities) pumped out of the process chamber by a pump reaches the inlet 320 of the disc separator 300. The vaporous PFPE condenses on the walls of the cooled inlet 320 and then enters the interior of the disc separator together with the liquid PFPE and the impurities. The components separate due to the centrifugal forces caused by the rotation of the separator (interrupted circular arrow 315), so that the heavy PFPE is forced outwards (arrows 345) and the lighter impurities are forced inwards (arrows 335). Separate outlets 330 and 340 then separate the purified PFPE and the impurities.

[0036] FIG. 3 shows a particularly advantageous embodiment of a separating condensate trap for a reflow condensation soldering machine. By integrating a separating condensate trap into the circuit of the heat transfer medium, the separation of PFPE and impurities is accelerated. The disc separator used in this process fulfills a double function: gaseous heat transfer medium condenses and impurities contained in the condensate are separated. The condensation of the heat transfer medium is achieved by limiting the maximum temperature of the separator components (e.g. inlet, float, disc, drum). The limitation of the temperature can be achieved by active cooling and/or by a high mass of the discs, drum, inlet and/or other components in relation to the flow rate. The separation of impurities is achieved by two main mechanisms. Firstly, the condensation temperature of the PFPE is higher than that of the impurities, so that the PFPE condenses first and the pure PFPE flows out through the separator. Secondly, the difference in density between the PFPE and the impurities is exploited, so that separation of the two condensates for temperatures below the condensation temperature of the impurities takes place via the centrifugal forces. By means of this separating condensate trap the separation of the PFPE and the impurities can be accelerated. Thus, the heat transfer medium bound in the machine can be made available to the process again more quickly and an increase in the plant throughput is made possible.

[0037] It should be noted that the integration of the condensation into the disc separator is particularly advantageous, since the condensation already causes a pre-separation, which is then further refined by the disc centrifuge/disc separator. This makes the separation process more efficient, i.e. more accurate. However, it is also possible to separate condensation in a special condensation device from separation in a disc separator.

[0038] Passive cooling can take advantage of the fact that separation in a reflow condensation soldering machine is not continuous, but is suspended during the soldering process times and can cool down during this time. If the components of the disc separator are equipped with a sufficiently large thermal mass, corresponding to the expected flow rates and flow times, to absorb the thermal energy during condensation during a regeneration phase, and if the components of the disc separator are still designed in such a way that they can release the previously absorbed heat quantity to the environment during the soldering phase, neither an upstream condensation device nor an internal active cooling system is necessary.

[0039] The cooling process can be supported, for example, by introducing condensed and purified PFPE into the disc separator during the soldering phase, i.e. the phase during which no vapor is introduced into the separator. For example, the condensate purified during the separation phase can be collected in the means marked with the reference numeral 91 in FIG. 2 and returned to the disc separator 300 shown in FIG. 3 via a return 91 A (only shown in FIG. 2) during the soldering phase. On the one hand, this ensures that the hydrodynamic separation conditions always remain the same, as the disc separator does not run empty. Furthermore, by feeding in the condensed and purified PFPE, the heat stored in the condensation device is removed more quickly. Finally, the condensed and purified PFPE is subjected to a new separation so that maintenance cycles can be increased. This support of the cooling process is possible for both passive and active cooling.

[0040] Another way to maintain continuous operation of the disc separator would be to continuously feed vapor into the disc separator, for example from two or more separate process chambers which, offset from each other, carry out the soldering process and the regeneration process. To ensure heat dissipation in this case of a continuously operated disc separator with integrated condensation device, the thermal conductivity of the heat dissipating components must be sufficiently high.

[0041] When designing the disc separator, the number, shape, structure and arrangement of the discs, the volume of the separator, the geometry of the inlet and the speed of rotation can be designed in such a way that a specific plant throughput can be achieved with a specific purification performance, taking into account the properties of the contaminated heat transfer medium. For example, depending on particle sizes and the density of the particles, an optimum disc spacing can be selected which is in the range of 0.2 mm to 14 mm. The number of discs, the speed of rotation and the volume of the disc separator determine the separation efficiency, i.e. how much heat transfer medium is purified to a certain degree in a certain time unit. Typical reflow condensation soldering machines with a circulation system for the heat transfer medium contain 20-40 liters of heat transfer medium, of which 1-6 liters are consumed in one soldering process run, which must then be purified after the soldering process. Usually 4-250 discs are used, which rotate at up to 30,000 revolutions per minute. For use in reflow condensation soldering machines with a circulation system for the heat transfer medium, at least 50 discs rotating at least 10,000 rpm are preferred. The inlet is advantageously designed in such a way that condensation takes place in the inlet and an associated pre-separation takes place.