METHOD AND DEVICE FOR CLEANING A PRINTED-CIRCUIT BOARD MASK OR A PRINTED-CIRCUIT BOARD

Abstract: A method and device are proposed for removing agents, in particular fluxes, adhesives or solder paste, which are adhering to a surface of a printed-circuit board mask or to a surface of a printed-circuit board in which the components may or may not have been inserted. The agents are removed by blasting at least one area of the surface of the printed-circuit board mask or of the printed-circuit board with at least one cleaning jet which contains carbon dioxide particles. The carbon dioxide particles are produced by shaving from a solid carbon dioxide body.

Description: Method and device for cleaning a printed-circuit board mask or a printed-circuit board The invention relates to a method for removing agents which are adhering to a surface of a printed- circuit board mask, to a method for removing agents which are adhering to a surface of a printed-circuit board, and to a device for removing agents which are adhering to a surface of a printed-circuit board mask or of a printed- circuit board. Electronic or electrical circuits have electrical or electronic components which are electrically connected to one another. These components are arranged on so- called printed-circuit boards. The printed-circuit boards have electrical connections which can be used to electrically connect the components to one another. The electrical connections are produced by printing the circuit board. The electrical connections are formed on one side of the printed-circuit board. The components are arranged on that side of the printed-circuit board which lies opposite to the printing, the terminal lugs of the components extending through holes which are formed in the printed-circuit board. The terminal lugs are soldered to the appropriate lines on the printed-circuit board. The components are soldered to the printed- circuit board essentially automatically. To do this, it is known for the soldering operation for all the terminal lugs of the components on a printed-circuit board to take place more or less simultaneously. Such a soldering operation is also known as "wave-soldering" . To carry out wave-soldering of the printed- circuit board into which the components have been inserted, all the components are inserted into the said printed-circuit board. Then, the underside, from which the terminal lugs of the components partially project, of the printed-circuit board with its components inserted is drawn over the surface of a liquid solder, so that the solder comes into contact with the terminal lugs and the appropriate connection points on the printed-circuit board. After the solder has solidified, the connection between the components and the electrical paths of the printed-circuit board are established. A prerequisite for carrying out this method is for the components to be arranged securely and reliably on the printed-circuit board, so that they do not leave their prescribed position when the printed-circuit board with its components inserted is being handled. This is achieved by adhesively bonding the components to the printed-circuit board. To this end, an adhesive is applied to the corresponding positions on the printed-circuit board. The adhesive is relatively quick- curing, in order to ensure that after appropriate components have been inserted into the printed-circuit board the said components do not move. Inserting the components into the printed-circuit board as such takes place automatically and at relatively high speed. As has already been explained, the adhesive is applied only at the appropriate positions on the printed- circuit board. The adhesive is applied to the printed- circuit board by means of a so-called printed-circuit board mask. The printed-circuit board mask has openings through which the adhesive can move onto or into the printed-circuit board. After the printed-circuit board has been provided with the adhesive, the components are inserted into the printed-circuit board. Owing to the fact that the adhesive is relatively quick-curing, there is the risk of residues of adhesive continuing to adhere to the walls of the openings in the printed-circuit board mask, with the result that correct application of the adhesive to the printed-circuit board can no longer be ensured. Furthermore, there is a risk of the adhesive being pulled off the printed-circuit board when the printed-circuit board mask is removed. It is therefore known to clean the printed- circuit board mask by means of hydrocarbon-containing solvents, in particular by means of alcohol. The cleaning operation has to take place in specially designed areas, since there is a risk of explosion when working with hydrocarbon-containing solvents. It is therefore impossible to integrate the cleaning operation into the production process of the circuits. Printed-circuit boards to which adhesive has been applied incorrectly are also cleaned and returned to the production operation of the circuits. Hitherto, the printed-circuit boards have also been cleaned by means of hydrocarbon-containing solvents. However, the use of hydrocarbon-containing cleaning agents is undesirable from the environmental pollution viewpoint. In addition to the wave-soldering method which has already been described above, a so-called reflow soldering method can also be used to connect the components to the printed-circuit board. For this purpose, a solder paste is applied at the connection points between the components and the printed-circuit board. Then, the printed-circuit board, together with the components and the solder paste, is subjected to a heat treatment in which the solder paste is liquefied. The solder paste is also applied by means of printed-circuit board masks. These printed-circuit board masks also have to be cleaned. This also applies to printed-circuit boards in which the solder paste has been applied incorrectly to the printed-circuit board. The printed-circuit board masks which are used for the application of a solder paste have to date also been cleaned by means of hydrocarbon-containing solvents. The solder paste also contains fluxes. In the case of aggressive fluxes, it is necessary to clean the finished printed-circuit board, since otherwise there is a risk of corrosion. On the basis of the above, the object underlying the present invention is to provide a method for removing agents, in particular adhesives, solder paste, which are adhering to a surface of a printed-circuit board mask or of a printed-circuit board, in which it is intended to dispense with the use of hydrocarbon-containing solvents. A further aim of the method is to design it in such a way that it can be integrated in a production process for circuits. A further object of the invention is to provide a device for removing agents which are adhering to a surface of a printed-circuit board mask or of a printed- circuit board, which device allows the agents to be removed safely and reliably. It is also intended for such a device to be able to be integrated in a production line for circuits. This object is achieved by means of a method or a device having the features of Claim 1, Claim 2 and Claim 18. Advantageous configurations and refinements form the subject-matter of the respectively dependent claims. In order to remove agents, in particular adhesives, solder paste or the like, which are adhering to a surface of a printed-circuit board mask, a method is proposed in which at least one area of the surface is blasted with at least one cleaning jet. The cleaning jet contains carbon dioxide particles. Surprisingly, it has been found that it is possible to remove the adhering agents from the surface of the printed-circuit board mask by means of carbon dioxide particles which have been produced by shaving from a solid carbon dioxide body without the printed-circuit board mask or a printed- circuit board being damaged. A solid carbon dioxide body is a relatively large body which consists of solid carbon dioxide, so-called dry ice. As a result of being shaved off the body, the carbon dioxide particles are given properties which allow gentle cleaning of the printed- circuit boards. The carbon dioxide particles have a greater mass than carbon dioxide snow, so that they strike the surface of the printed-circuit board with a higher kinetic energy. However, the shaved carbon dioxide particles are not as hard as carbon pellets produced individually. The production of carbon dioxide particles by shaving from a solid carbon dioxide body is known, for example, from US-A-5, 520, 572. As a result of being struck by the solid carbon dioxide, the adhering agents are removed without the surface of the printed-circuit board mask being abraded. When the carbon dioxide particles strike the surface of the printed-circuit board mask, the carbon dioxide also sublimes, with the result that the agents which are adhering to the surface of the printed-circuit board mask become brittle owing to a reduction in temperature, thus improving the cleaning action of the cleaning jet. This configuration of the method according to the invention makes it possible to dispense with hydrocarbon-containing solvents. It is no longer necessary to clean the printed- circuit board masks in a specially secured room. The procedure for removing agents which are adhering to a surface of a printed-circuit board mask also provides the possibility of integrating this method in a production line as well. The method according to the invention also makes it possible to reduce the number of printed-circuit board masks which need to be provided, since the cleaning operation as such takes place relatively quickly. According to a further inventive idea, a method for removing agents, in particular fluxes, adhesives, solder paste, which are adhering to a surface of a printed-circuit board into which the components may or may not have been inserted is proposed, in which method at least one area of the surface of the printed-circuit board is blasted with a cleaning jet. The cleaning jet contains carbon dioxide particles. The cleaning jet makes it possible to remove the agents which are adhering to the surface of a printed-circuit board without the printed-circuit board itself or the electrical or electronic components which have already been arranged on the printed-circuit board being damaged. The use of carbon dioxide in this method is particularly environmentally compatible, since carbon dioxide is a constituent of the atmosphere. The carbon dioxide particles preferably have an average diameter of at most approx. 1 mm. Particularly good cleaning results on the printed-circuit board mask and the printed-circuit board are achieved in particular if the cleaning jet is at a pressure of at least 1 bar. Higher pressures are possible, but the cleaning result is not necessarily improved by increasing the pressure. The pressure of the cleaning jet is preferably set at 4 bar. According to a further advantageous idea, it is proposed for the method for removing agents which are adhering to a surface to be carried out over a period of at least 10 seconds, preferably 15 seconds. Good cleaning results are achieved within this period in which a cleaning jet is blasted onto at least one area of the surface. Blasting the surface for longer periods does not necessarily lead to an improvement in the cleaning result. However, it does lead to an increased consumption of carbon dioxide, which is uneconomic. Preferably, the cleaning jet is directed towards the surface of the printed-circuit board mask at an angle, in particular at an angle of approx. 45°. The cleaning jet is moved in such a manner that it gradually covers the printed-circuit board mask in a longitudinal direction and then covers the surface of - the printed- circuit ■ board mask at an angle of approx. 90° to the original direction of movement. As a result, even the peripheral surfaces of holes which are formed in the printed-circuit board mask are cleaned. According to a further advantageous idea, it is proposed for the cleaning jet to contain a carrier gas. The carrier gas is preferably inert. This contributes to the safety of the method. Also, no reactions take place between the agents which are adhering to the surfaces of the printed-circuit board mask or of the printed-circuit board. According to a further advantageous configuration of the method, it is proposed for the printed-circuit board mask or the printed-circuit board to be subjected to a drying operation after it has been blasted with the cleaning jet. This has the advantage that there is no condensed water from the ambient atmosphere on the surface of the printed-circuit board mask or the printed- circuit board. Preferably, a gas stream, in particular a stream of hot air, is used to dry a printed-circuit board mask or a printed-circuit board. The temperature of the gas stream or of the air stream is adapted to the demands placed on the drying operation. The use of a gas stream also has the advantage that the printed-circuit board mask or the printed-circuit board is dried relatively uniformly. According to a further advantageous configuration of the method, it is proposed for at least that area of the printed-circuit board mask or of the printed-circuit board which is to be blasted to be earthed during a blasting operation. This measure ensures that the printed-circuit board mask and the printed-circuit board do not become electrostatically charged during the cleaning operation, which is important in particular if it is intended to clean a printed-circuit board into which electrical or electronic components have been inserted. The problem of the printed-circuit board mask or a printed-circuit board becoming electrostatically charged can also be solved by connecting at least that area of the printed-circuit board mask or of the printed- circuit board which is to be blasted to at least one electrostatically chargeable element during the blasting operation, which element brings about a discharge which in particular does not take place in the region of the electronic components on " the printed-circuit board, so that these electronic components are not damaged by the discharge. In particular, lamettas may be connected to various areas on the printed-circuit board. As an alternative, or in addition, it is proposed for the printed-circuit board mask or the printed-circuit board to be blasted in an inert atmosphere. Particularly advantageous in this case is a nitrogen/argon atmosphere. According to a further advantageous idea, it is proposed for the blasting operation to take place in a deionized chamber, with the result that electrostatic charging of the printed-circuit board mask or of the printed-circuit board is also avoided. According to yet another advantageous idea, it is proposed for at least one electrically conductive component to be arranged in the area of the path of the cleaning jet. Preferably, this is a soft metal brush which is arranged in particular in the vicinity of the outlet opening for the cleaning jet. This also avoids electrostatic charging of the printed-circuit board mask or of the printed-circuit board. According to a further advantageous configuration of the method, it is proposed for a printed-circuit board mask or a printed-circuit board to be blasted in a closed chamber in which the printed-circuit board mask or the printed-circuit board is arranged. The advantage of this procedure is that if the chamber is of gas-tight design the surrounding atmosphere is not affected by the cleaning. Preferably, the printed-circuit board mask or the printed-circuit board is cleaned in a sound-insulated chamber, with the result that emission of noise during the cleaning operation is avoided or reduced. As a result of this measure, the method is particularly suitable for integration in an existing production line. According to a further inventive idea, a device is proposed for removing agents, in particular adhesives, solder paste, fluxes, which are adhering to a surface of a printed-circuit board mask or a printed-circuit board. The device has a chamber. A holding device for holding at least one printed-circuit board mask or at least one printed-circuit board is arranged inside the chamber. A moveable blasting device is also arranged inside the chamber, which device has at least one blasting nozzle through which a cleaning jet, which is directed towards at least one area of the surface, can emerge. Outside the chamber, the device has a supply unit which is connected to the blasting device via at least one supply line. The chamber is preferably delimited by a housing which is of sound-insulating design. According to a further advantageous idea, it is proposed for the housing to be at least partially gas- permeable. The cleaning jet contains carbon dioxide particles and a carrier gas. The carrier gas is preferably compressed air. If the housing were designed to be essentially airtight, the pressure inside the chamber would build up. Therefore, in order to avoid this, it is proposed for the housing to be at least partially gas-permeable. Preferably, the housing is designed in such a way that it is impermeable to dirt particles. This prevents particles which come free during a cleaning operation from passing into the environment, which is important in particular if the device is disposed in an environment under clean room conditions. Preferably, the housing has at least one particle filter which is exchangeable. The particle filter retains the particles which come free during the cleaning in the filter, thus avoiding pollution of the surrounding atmosphere as a result of the cleaning operation. The exchangeability of the particle filter also increases the readiness for use of the device. According to a further advantageous configuration of the device, it is proposed for the handling device to have a central processing unit and at least one arm which is connected to the central processing unit and on which the blasting unit is arranged, it being possible to arrange the central processing unit outside the housing and the arm extending through a wall of the housing. Printed-circuit board masks and printed-circuit boards may be of various shapes and designs. In particular, printed-circuit board masks may have a different number and different distribution of through- openings. The cleaning jet is therefore to be directed towards the surface of the printed-circuit board or of the printed-circuit board mask in such a way that it preferably cleans the entire surface gradually. In order to achieve this, the device has a handling device on which the blasting device, in particular the cleaning nozzle or nozzles, is arranged. The handling device makes it possible to change the location of a cleaning jet emerging from a cleaning nozzle, so that the surface of a printed-circuit board or of a printed-circuit board mask is completely cleaned by the cleaning jet which contains carbon dioxide particles. If the structure and geometry of the printed-circuit board or of the printed-circuit board mask is known, the movement sequence of the cleaning nozzle can be controlled by means of a corresponding control unit, the control unit making it possible for the cleaning nozzle to continuously or sequentially sweep individual areas of the surface with the cleaning jet. It is also possible to guide the cleaning jet manually. However, automatic cleaning of the printed-circuit board mask or of the printed-circuit boards is preferred, since the controlled movement sequence makes it possible to optimize the cleaning times and the cleaning action as well as the consumption of carbon dioxide particles. Further details and advantages of the methods and of the device are explained with reference to the exemplary embodiments illustrated in the drawing, in which: Fig. 1 diagrammatically and partially in section shows a first exemplary embodiment of a device according to the invention, and Fig. 2 diagrammatically shows a second exemplary embodiment of a device according to the invention. Fig. 1 diagrammatically shows a first exemplary embodiment of a device for removing agents, in particular adhesives, solder paste, fluxes, which are adhering to a surface of a printed-circuit board mask or of a printed- circuit board. Where a printed-circuit board mask is referred to below, the same correspondingly applies to a printed-circuit board in which electrical and/or electronic components have been inserted. The device has a housing 6 which delimits a chamber 5. A blasting device 8 is arranged inside the chamber 5. The blasting device 8 has at least one blasting nozzle 18. A cleaning jet 4 emerges through the blasting nozzle 18. The cleaning jet 4 contains solid carbon dioxide particles and a carrier gas. The blasting device 8 is connected to a supply unit 12 via supply lines (not shown) " . The supply unit 12 preferably comprises a device for generating carbon dioxide particles and a carrier-gas source, which may, for example, be a gas cylinder. The carrier gas is pressurized. The device for generating carbon dioxide particles may, for example, be a device such as that which is described in US-A-5, 520, 572. The device for generating carbon dioxide particles comprises a shaving device, by means of which carbon dioxide particles are shaved off a solid carbon dioxide body. These carbon dioxide particles are then fed to the blasting device via the supply line. The blasting device 8 is arranged on a handling device 9. The handling device 9 may, for example, be a multi-axis robot. The handling device 9 has an arm 10 which is connected to a central processing unit 11. The central processing unit 11 is arranged outside the chamber 5. The arm 10 extends into the chamber 5. As can be seen from Fig. 1, a connecting plate 15, which is connected to a flexible wall 16 of the housing 6, is connected to the arm 10. The flexible wall 16 has the advantage that it allows the arm 10 to move. The supply unit 12 and the central processing unit 11 are arranged on a frame 13. The frame 13 has a protective housing 14, inside which the central processing unit 11 and the supply unit 12 are arranged. The housing 6 and the protective housing 14 are designed in such a way that they are sound-insulating. Preferably, the flexible wall 16 is at least partially gas-permeable. It may also have a particle filter. A suction opening inside the chamber 5, by means of which the atmosphere can be sucked out of the chamber 5, is not shown. The suction preferably takes place with the interposition of sound absorbers, so that no noise, or only very little noise, is emitted. A holding device 17 is arranged inside the chamber 5. The holding device is used to hold at least one printed-circuit board mask 1. In the exemplary embodiment illustrated, the printed-circuit board mask is positioned vertically in the chamber 5. Other positions are also possible. The holding device is preferably designed in such a way that it can be adapted to different sizes of a printed-circuit board mask 1. The printed-circuit board mask 1 has agents 2 which are adhering to its surface 3 and are to be removed by a cleaning jet 4. The agents 2 which are adhering to the surface 3 may also be present in openings 7 in the printed-circuit board mask " 1. By suitably programming the handling device, the cleaning jet 4 is directed towards the surface 3 of the printed-circuit board mask, preferably at an angle of approx. 45°. The carbon dioxide particles strike the surface 3 and the agents 2, with the result that the agents 2 are removed from the surface 3 and out of the openings 7. In a corresponding manner, it is also possible to clean printed-circuit boards (not shown) by means of the device illustrated in Fig. 1. Fig. 2 shows a second exemplary embodiment of a device for removing agents, in particular adhesives, solder paste, fluxes, which are adhering to a surface of a printed-circuit board mask or of at least one printed- circuit board. The device has a housing 6. The housing 6 is preferably of sound-insulating design, with the result that little or no noise is emitted into the environment during an operation of cleaning a printed-circuit board mask. The housing 6 delimits a chamber 5. A blasting device 8 is arranged inside the chamber 5. The blasting device 8 has at least one blasting nozzle 18. The blasting device 18 is connected to a supply unit 12 and a central processing unit 17 via supply lines 19. The supply unit 12 preferably comprises a device for generating carbon dioxide particles and a compressed-gas source . The blasting device 8 is arranged on a handling device 9. The handling device 9 is preferably a multi- axis robot. The handling device 9 is designed in such a way that a cleaning jet 4 can clean the entire surface 3 of a printed-circuit board mask 1. The handling device 9 is connected to the central processing unit 11 via supply lines 19. The central processing unit 11 forms a control unit for the handling device 9. The handling device 9 is arranged on a wall 20 of the housing 6. A holding device " 17, which is used to hold a printed-circuit board mask 1, is provided inside the chamber 5. In order to remove agents 2 which are adhering to the surface 3 of the printed-circuit board mask 1, at least one cleaning jet 4 is directed towards the surface 3. The agents 2 which are adhering to the surface 3 are removed by the carbon dioxide particles in the cleaning jet 4. Preferably, the holding device 17 is designed in such a way that the printed-circuit board mask 1 is earthed during the cleaning operation. As a result, the printed-circuit board mask 1 is prevented from becoming electrostatically charged as a result of the cleaning operation. Such an earthing or avoidance of an electrostatic charging is important in particular if, instead of printed-circuit board masks, printed-circuit boards into which electrical and/or electronic components have already been inserted are being cleaned. The cleaning jet is preferably directed towards the surface 3 at a pressure of at least 1 bar. The duration of action of the jet on an area to be cleaned is preferably 15 seconds. In order to avoid damage to the surface of the printed-circuit board mask or of a printed-circuit board, the solid carbon dioxide is in particle form, in which case the mass of the carbon dioxide particles should be relatively low. Preferably, the cleaning jet contains carbon dioxide particles with an average diameter of at most approx. 1 mm.

Claims: CLAIMS 1. Method for removing agents (2), in particular adhesives, solder paste or fluxes, which are adhering to a surface (3) of a printed-circuit board mask (1), in which method at least one area of the surface (3) is blasted with at least one cleaning jet (4) which contains carbon dioxide particles, the carbon dioxide particles being produced by shaving from a solid carbon dioxide body. 2. Method for removing agents (2), in particular fluxes, adhesives, solder paste, which are adhering to a surface (3) of a printed-circuit board which may or may not have its components inserted, in which method at least one area of the surface (3) is blasted with at least one cleaning jet (4) which contains carbon dioxide particles, the carbon dioxide particles being produced by shaving from a solid carbon dioxide body. 3. Method according to Claim 1 or 2, in which the carbon dioxide particles have an average diameter of at most approx. 1 mm. 4. Method according to Claim 1, 2 or 3, in which the cleaning jet (4) is at a pressure of at least 1 bar. 5. Method according to one of Claims 1 to 4, in which at least one area of the surface (3) is blasted by the cleaning jet (4) for a period of at least 10 s, preferably 15 s. 6. Method according to one of Claims 1 to 5, in which the cleaning jet (4) contains a carrier gas. 7. Method according to Claim 6, in which the carrier gas is inert. 8. Method according to one of Claims 1 to 7, in which the printed-circuit board mask (1) or the printed- circuit board is subjected to a drying operation after it has been blasted with the cleaning jet (4) . 9. Method according to Claim 8, in which the printed-circuit board mask (1) or the printed-circuit board is dried by means of a gas stream. 10. Method according to one of Claims 1 to 9, in which at least that region of the printed-circuit board mask (1) or of the printed-circuit board which is to be blasted is earthed during a blasting operation. 11. Method according to one of Claims 1 to 10, in which at least that area of the printed-circuit board mask (1) or of the printed-circuit board which is to be blasted is connected to at least one electrostatically chargeable element during " a blasting operation. 12. Method according to one of Claims 1 to 11, in which the blasting takes place in an inert atmosphere. 13. Method according to Claim 12, in which the blasting takes place in a nitrogen/argon atmosphere. 14. Method according to one of Claims 1 to 11, in which the blasting takes place in a deionized chamber (5) . 15. Method according to one of Claims 1 to 14, in which at least one electrically conductive component is arranged in the area of a path of the cleaning jet (4) . 16. Method according to one of Claims 1 to 15, in which the printed-circuit board mask (1) or the printed-circuit board is arranged in a chamber (5) prior to a blasting operation. 17. Method according to Claim 16, in which the printed-circuit board mask (1) or the printed-circuit board is arranged in a sound-insulated chamber (5) . 18. Device for removing agents (2), in particular adhesives, solder paste or fluxes, which are adhering to a surface (3) of a printed-circuit board mask (1) or a printed-circuit board, in particular according to one of Claims 1 to 17, characterized 2 by a chamber (5) , a holding device (17) for holding at least one printed- circuit board mask (1) or at least one printed-circuit board in the chamber (5) , a movable blasting device (8) which is arranged inside the chamber (5) and has at least one blasting nozzle (18) through which a cleaning jet (4), which is directed towards at least one area of the surface (3) , preferably at an angle of approx. 45°, emerges, and a supply unit (12) which is connected to the blasting device (8) via at least one supply line (19) . 19. Device according to Claim 18, characterized in that a housing (6), which is of sound- insulating design, at least partially delimits the chamber (5) . 20. Method according to Claim 19, characterized in that the housing (6) is at least partially gas-permeable. 21. Device according to Claim 20, characterized in that the housing (6) has at least one particle filter. 22. Device according to one of Claims 18 to 21, characterized in that the blasting device (8) is arranged on a handling device (9), in particular a robot. 23. Device according to Claim 22, characterized in that the handling device (9) has a central processing unit (11) and at least one arm (10) which is connected to the central processing unit (11) and on which the blasting unit (8) is arranged, the central processing unit (11) being arranged outside the housing (6) and the arm (10) extending through a wall (16) of the housing (6).

Inventors: KIECKER HANS-ERDREICH, TRAMPUSCH BERTHOLD, KIECKER, HANS-ERDREICH, TRAMPUSCH, BERTHOLD
Applicants: AIR LIQUIDE, KIECKER HANS ERDREICH, TRAMPUSCH BERTHOLD, KIECKER, HANS-ERDREICH, L'AIR LIQUIDE, SOCIETE ANONYME POUR L'ETUDE ET L'EXPLOITATION DES PROCEDES GEORGES CLAUDE, TRAMPUSCH, BERTHOLD
Application year: 1999
Main classification: B24C1
IPC codes: B24C1, B24C3, H05K3