DISPENSING ASSEMBLY

Abstract: This invention relates to an assembly (5) for jetting droplets of a viscous medium. The assembly (5) is releasably mountable in a machine (1) using the assembly for providing a substrate (2) with deposits. The assembly comprises an assembly holder (24) having two holding means (35) mating with an assembly support (15) of a docking device (10) of the machine (1), a viscous medium container (23), a nozzle (25), an eject mechanism (55), and a signal interface means. The assembly is to be regarded as a separate, exchangeable unit. The invention also relates to the machine (1), to the docking device and to a method for exchanging the assembly (5).

Description: DISPENSING ASSEMBLY Technical field This invention relates to an assembly for jetting, also known as non-contact dispensing, which is separate from and provides for different requirements on the assembly than contact dispensing such as screening. Technical background A prior art jetting machine is disclosed in copend- ing patent application SE-9802079-5. Said patent application is focused on a certain part of the machine, which part is a new device for jetting droplets. The device comprises an eject chamber (37; 137) for containing a small volume of a viscous medium prior to the ejection thereof, an eject nozzle (36; 136) communicating with the eject chamber, eject means (22, 25; 122, 135) for rapidly ejecting said viscous medium from the eject chamber through said nozzle, and supply means for feeding said medium into the eject chamber. The supply means comprises a rotatably driven feed screw receiving the medium from a syringe containing the medium and forcing the medium towards the eject chamber. The medium contained within the syringe in turn is pressurised in order to force it out of the outlet of the syringe. This prior art device works well. However, there is a problem involved in exchanging syringes in the device, particularly when the new syringe contains a different type of medium than the one to be exchanged. In the last mentioned case the operator of the machine has to rinse the portions of the device containing the medium. These portions are, inter alia, the eject chamber, the eject nozzle, and the feed screw. In the case of a non-contact dispensing machine, the rinse of the nozzle and the associated ejection parts is particularly important in order to achieve a good operation. While the rinse operation is performed the machine is stopped. Another problem arising when exchanging syringes is that before resuming the production several dispensing operations must be performed, in order to refill the nozzle and the associated ejection parts with the new medium. Some extra ejections should be performed in order to guarantee that the medium is free from air bubbles. An attempt to reduce the exchange time is disclosed in JP- 10294557. The time reduction is obtained by arranging a separate syringe holder at the machine. At the holder, a syringe which later on is to be substituted for the one presently used, is pressurised in that an amount of the medium is dispensed into a container. Thereby it is secured that the medium at the outlet of the syringe is free from air bubbles. Consequently, when replacing the syringe presently at use with the new one the application of medium onto a circuit board can be resumed immediately. However, this prior art solution is only useful in machines using the syringe for direct dispensing, and does not improve a machine of the jetting type to the same extent. Since such a machine has a separate ejecting mechanism, which receives the medium from the syringe, this ejecting mechanism still has to be refilled with the new medium before the application operation is resumed. Consequently, the exchange of syringes causes an undesired fall in production. Additionally, the waste medium is generally environmentally hazardous and has to be carefully taken care of . Summary of the invention The object of this invention is to provide a solution to the above mentioned problems. The object is achieved by an assembly, a machine and a docking device as defined in the appended claims. The invention, in one aspect thereof, provides for an assembly for jetting droplets of a viscous medium, said assembly being releasably mountable in a machine using the assembly for providing a substrate with deposits, and comprising a nozzle, an eject mechanism connected with the nozzle, a viscous medium container con- nected with the eject mechanism, and signal interface means . By being releasably mountable the assembly is usable as a separate unit easily exchangeable and containing the medium. Consequently, the operator is relieved from the problem of handling the syringes and rinsing parts of the assembly. Additionally, the problem of handling the waste medium is eliminated. The assembly provides for a recycling system where the whole assembly, when empty of medium, is sent back to the supplier who originally delivered it. For the purposes of this application, it is to be noted that the term "deposits" should be interpreted as single or groups of viscous medium dots deposited on the substrate; the term "viscous medium" should be inter- preted as solder paste, flux, adhesive, conductive adhesive or any other kind of medium used for fastening components on the substrate; and that the term "substrate" should be interpreted as a printed circuit board (PCB) , a substrate for ball grid arrays (BGA) , chip scale packages (CSP) , quad flat packages (QFP) , and flip-chips or the like. In another aspect thereof the invention provides for a machine for providing a substrate with deposits by jetting droplets of a viscous medium onto the sub- strate, comprising a docking device for receiving an assembly of the above described type, said docking device comprising an assembly support and complementary signal interface means . In a further aspect thereof the invention provides for a docking device for receiving an assembly of the above described type, said docking device comprising an assembly support and complementary signal interface means . The docking device facilitates the mounting/dismounting of the assembly at the machine by providing spe- cific means, such as the assembly support and the interface means, simplifying the docking of the assembly. The mounting/dismounting is further facilitated by the assembly support comprising pneumatically operable assembly locking means, enabling a fast mounting/dismounting. In accordance with another embodiment of the invention, there is provided an exchange assembly support for supporting at least one exchange assembly. By means of this support the invention is additionally improved by providing for an automatic exchange of assemblies at the docking device. Further, change over times are reduced due to the possibility of, while the machine is running, providing the exchange assembly support with new full assemblies, assemblies holding different types of paste, assemblies having different types of nozzles, etc., to be used later on by the machine. In yet another aspect thereof, the invention provides for a method of exchanging and calibrating an assembly for jetting droplets of a viscous medium, said assembly being releasably mounted in a machine using the assembly for providing a substrate with deposits, and comprising an assembly holder having first holding means mating with an assembly support of a docking device of the machine, comprising the steps of: - exchanging the assembly for an exchange assembly; - moving the assembly to a calibration surface ; - depositing a plurality of deposits on the calibration surface; - determining the position of said plurality of deposits by viewing it with a vision device comprised in the machine; and - determining an offset of the position from an expected position. This method, which is possible to perform by means of inventive constructions according to the invention, that is the separate jetting assembly releasably mount- able in a dispensing machine arranged for receiving such an assembly, is advantageous in that the operator of the machine does not have to deal with the assembly exchanges on-line. The steps of calibration assure that the new assembly is correctly mounted and that the accuracy of the dispensing process will be high. Further objects and advantages of the present invention will be discussed below by means of exemplary embodiments . Brief description of the drawings Exemplifying embodiments of the invention will be described below with reference to the accompanying draw- ings, in which: Fig. 1 is a schematic perspective view of an embodiment of the machine according to the present invention; Fig. 2 is a schematic perspective view from above of an embodiment of the docking device and assembly of the present invention; Fig. 3 is a schematic perspective view from below and from one side of the assembly shown in Fig. 2 ; Fig. 4 is a schematic perspective view from below and from another side of the assembly shown in Fig. 2; Fig. 5 is a perspective view from above of the assembly of Fig. 2 and of an embodiment of the exchange assembly support of the present invention; Fig. 6 is a schematic sectional view of the assembly shown in Fig . 2 ; and Fig. 7 is a flow chart of an exchange and calibration procedure of the present invention. Description of embodiments Fig. 1 illustrates a presently preferred embodiment of a machine 1 for providing a substrate 2 with deposits by jetting droplets of a viscous medium onto the sub- strate 2, in accordance with the present invention. Let us for simplicity assume that the viscous medium is solder paste, which is one alternative as defined above. In this embodiment the machine 1 is of a type comprising an X-beam 3 and an X-wagon 4 connected with the X-beam 3 via an X-rail 36 and reciprocatingly movable along the X-rail 36. The X-beam, in turn, is reciprocatingly movably connected with a Y-rail 37, thereby being movable perpendicularly to the X-rail 36. The Y-rail 37 is rigidly mounted in the machine 1. Generally, the movements are driven by linear motors (not shown) . Further, the machine 1 comprises a conveyor 38 for carrying the substrate 2 through the machine 1, and a fixing device 39 for fixing the substrate 2 when dispensing is to take place. Further, the machine 1 comprises a docking device 10 connected with the X-wagon 4 and an assembly 5 releasably mounted at the docking device 10. The assembly 5 is arranged for jetting droplets of solder paste, which impact and form deposits on the substrate 2. Further, the machine 1 comprises a calibration station 8, providing a calibration surface. The machine 1 also comprises an exchange assembly support 7, supporting further assemblies 9, which may be substituted for the assembly 5 currently carried by the docking device 10. Additionally, the machine 1 comprises a machine vision device 6, which in this embodiment is a camera. The camera 6 is used for determining the position and rotation of the substrate 2 and for checking the result of the dispensing process by viewing the deposits. As understood by those skilled in the art, the machine also comprises a control unit (not explicitly shown) executing software for running the machine. Briefly, the machine 1 works as follows. The sub- strate 2 is fed into the machine 1 by means of the conveyor 38, upon which the substrate 2 is put. When the substrate 2 is in proper position under the X-wagon 4 it is fixed with the aid of the fixing device 39. By means of the camera 6, fiducial markers prearranged on the sur- face of the substrate 2 are located. These markers determine the precise position of the substrate. Then, by moving the X-wagon 4 over the substrate 2 in a predetermined (preprogrammed) pattern and operating the assembly 5 at predetermined locations, solder paste is applied on the substrate 2 at the desired locations. Should the assembly 5 run out of solder paste or should a different medium be required at certain locations, etc., the machine 1 is programmed to automatically exchange the assembly 5 for one of the further assemblies, or exchange assemblies, 9 stored at the exchange assembly support 7, and the application process will continue. However, when acquiring a previously unknown assembly 9 from the exchange assembly support 7, the machine 1 will perform a calibration in order to ascertain that the dispensed droplets accurately will impact the substrate 2 at the predetermined locations. The calibration is preferred since the position of an eject nozzle 25 of the assembly 5, see Fig. 3, may differ slightly from one assembly to the other, and, since the alignment of the assembly 5 at the docking device 10 may differ slightly from one docking to the other. The exchange and calibration procedure will now be described in more detail with reference to the flow chart of Fig. 7. While dispensing, or jetting as will be explained below, in step 101 it is determined whether an assembly exchange is required. This is done by checking whether the assembly 5 runs out of solder paste, whether another type of nozzle is required, and whether another type of medium is required. If an assembly exchange is required, the procedure is continued in step 102 by performing an assembly exchange. This is done by moving the X-wagon to the exchange assembly support 7, releasing the assembly 5 from the docking device 10 and putting it at an available place of the exchange assembly support 7, and loading an exchange assembly 9, which may be a specific predetermined one, into the docking device 10. Then, in step 103, it is checked that the new assembly is properly docked at the docking device 10. If not an error signal is generated and the machine 1 is halted, otherwise the procedure is continued in step 104, where it is determined whether the new assembly 9 needs to be calibrated. If a calibra- tion is needed, the procedure is continued in step 105, otherwise it is finished and the dispensing is resumed. In step 105, the X-wagon 4 is moved to the calibration station 8. Then, in step 106, a plurality of deposits is generated on the calibration surface, which in this embodiment is a plate. It is preferred to generate a straight line of deposits, though any appropriate pattern is employable. Then, in step 107, the line of deposits is viewed by the camera 6. If not all deposits are found, in next step 108, an error signal is generated and the machine is halted. Otherwise, the procedure is continued in step 109, where the position of the line of deposits is determined and compared to an expected position. The deviation, if any, is defined as a nozzle offset. As mentioned above, the nozzle 25 may not be positioned exactly at the same position as the nozzle 25 of the previously docked assembly 5. In order to ascertain a high accuracy of the point of impact of the droplets on the substrate a trigger window for the machine 1 is adjusted by means of the offset . Trigger window is understood by those skilled in the art as a time window within which a droplet has to be jetted, while moving the X-wagon 4 over the substrate 2, in order to impact the substrate 2 at the desired location. In Fig. 2 preferred embodiments of the docking device 10 and the assembly 5 are illustrated in greater detail. The assembly 5 is further illustrated in Fig. 3- 6. The docking device 10 comprises an assembly support 15 and a stand 11. The assembly support 15 is arranged at the stand 11 and is reciprocatingly movable along the length of the stand 11. Consequently, the direction of movement is in a Z-direction substantially perpendicular to the substrate 2. This motion is realised with the aid of a Z-motor 14 and a ball screw 12, appropriately interconnected. The motion along the stand 11 is used for docking the assembly 5 and for adjusting the height over the PCB when dispensing. The assembly 5 comprises an assembly holder 24 having first holding means, in the form of two opposite L- shaped legs 35 and a wall 36 connecting them, wherein the legs 35 and wall 36 together defines a first slot. The first slot mates to the assembly support 15 of the docking device 10. When docked, the assembly 5 is accurately positioned and retained by means of an assembly alignment means, constituted by a spring 16, exerting a force on one of the legs 35, and a pneumatically operable assembly locking means, here constituted by a locking piston 17 exerting a force on the wall 36. Further, the assembly 5 comprises a viscous medium container, or solder paste container, 23, a nozzle 25, and an eject mechanism 55, see Fig. 6, connected to the container 23 and the nozzle 25. The eject mechanism 55 is arranged for feeding solder paste from the container 23 out through the nozzle 25 in a way which is defined as jetting or non-contact dispensing. The eject mechanism 55 will now be further described. It is similar to the one disclosed in the above-mentioned Swedish patent application 9802079-5. The eject mechanism 55 from the outside is hidden by assembly holder 24 and by a cooling flange 30. In the cross sectional view in Fig. 6 a proposed outline of the eject mechanism 55 is shown. The solder paste is forced by means of pressurised air out of a hole 51 in the bottom of the solder paste container 23. The pressurised air is supplied through a nipple 52, a hose and suitable connection means (not shown) in the container 23. Preferably, the solder paste is held in a solder paste bag (not explicitly shown) placed in the container 23. An outlet of the bag is connected to the feed hole 51. The pressurised air squeezes the bag. Further, the solder paste is forced through a hole in a motor support 50 and in a motor axis 42 of a stepper motor 41. A feed screw 44 is mounted on the motor axis 42. The feed screw 44 has an axial bore 53 through which the solder paste flows. The solder paste is further transported by the feed screw 44 rotated by the motor 41. The feed screw 44 rotates in a stack of o-rings 45. These o-rings 45 prohibit undesired smearing of the solder balls in the paste. The feed screw 44 transports the paste into an active chamber formed by the end of the feed screw 44, the nozzle 25 and a bushing 54. To eject droplets an actuator 31 is rapidly discharged thus moving the nozzle 25 towards the feed screw 44 and diminishing the volume of said active chamber. The actuator 31 is pre-loaded with a cup spring 48 and an actuator support 49. To have stable temperature during dispensing a thermometer 46 and a heater 47 are provided. The assembly 5 uses pressurised air for several tasks, e.g. providing a slight overpressure for forcing the solder paste into the eject mechanism 55, cooling of the actuator 31, and cooling of the stepper motor 41. Pressurised air is supplied via pneumatic interface means comprising inlets 26, positioned to interface with complementary pneumatic interface means comprising nipples 20, of the docking device 10. Cooling of the actuator 31 is realised with the aid of the cooling flange 30 provid- ing a slit between its walls and the actuator 31 where cooling air can flow freely. Signal connections are provided as interface means at the assembly 5 and connectable to complementary signal interface means of the docking device 10. These connections of the assembly 5, inter alia, are for supplying the stepper motor 41, the actuator 31 via leads 28, for measuring temperature via leads 29 and the thermometer 46, which constitutes a Pt-100 sensor or the like, etc. Said signal interface means is implemented as a male contact 27 and interfaces the corresponding signal interface means implemented as a female contact 19 at the docking device 10. The male contact 27 is in this embodiment a reinforced part of a flexible circuit board. Not previ- ously mentioned signals, which can be provided via this interface are heater current, assembly identity information, and driving signals for the stepper motor 41. Extensions of this list are obvious for those skilled in the art. In excess to the above mentioned female contact 19, signal connections at the docking device 10 comprise a flexible circuit board 18, connected to control electronics (not shown) located on the X-wagon 4. The nipples 20 of the complementary pneumatic interface means of the docking device 10 are connected, via internal channels of the docking device 10, to a set of valves 13 and to input nipples 22. The airflow is controlled by said set of valves 13 arranged at the upper end of the docking device 10. In a conventional fashion, external hoses (not shown) are connected to the input nipples 22. The above-described piston 17 is pneumatically actuated with pressurised air supplied through a nipple 21 and one of the valves 13. As shown in Fig. 5, the above mentioned exchange assembly support 7 has an exchange wheel 40 comprising at least two, and in this embodiment three, assembly seats. Each seat is defined by a suction cup 32 to hold the assembly 9 firmly and a slotted jaw 33 which mates with cuts 34 in the assembly. The exchange wheel 40 is rotatable . Above preferred embodiments of the machine, assembly and docking device according to the present invention have been described. These should be seen as merely non- limiting examples. Many modified embodiments will be possible within the scope of the invention as defined by the claims. Below a few examples of such modifications will be given. There are many alternative structures of the signal interface means. In alternative embodiments, at least parts of said means are implemented with optical fibres or microwave guides . There are many possible embodiments of the assembly holder of the assembly and the corresponding assembly support of the docking device. For example, the slot can be formed at the docking device and a mating guide at the assembly. Or, mating pins and holes can be formed, etc. The solder paste container 23 may hold the paste in different ways. An alternative to the bag described above is to directly fill the container with the paste and pressurise the top surface thereof. In addition, the paste could be covered by a guided transversely movable plate, wherein the pressurised air is let in above the plate. At the calibration station the calibration surface in an alternative embodiment is constructed as a tape cassette. Thereby, there is no need for cleaning the surface after each calibration. Instead, the tape is simply driven forward for a short moment. In the method, the step of determining if calibration is required may be deleted, so that the calibration is always done. Alternatively, the calibration is never done, this approach, however, resulting in a decreased accuracy.

Claims: CLAIMS 1. An assembly for jetting droplets of a viscous medium, said assembly being releasably mountable in a machine using the assembly for providing a substrate with deposits, and comprising an assembly holder having first holding means mating with an assembly support of a docking device of the machine, a nozzle, an eject mechanism connected to the nozzle, a viscous medium container con- nected to the eject mechanism, and signal interface means . 2. An assembly according to claim 1, further comprising pneumatic interface means. 3. An assembly according to claim 2, said pneumatic interface means comprising a plurality of inlets. 4. An assembly according to claim 1, 2 or 3, wherein the assembly holder comprises second holding means for mating an exchange assembly support of the machine. 5. An assembly according to any one of the preceding claims, wherein the container is pressurisable . 6. An assembly according to any one of the preceding claims, wherein the container is adapted for receiving a bag holding the medium. 7. An assembly according to any one of claims 1-5, wherein the container comprises a syringe. 8. An assembly according to any one of the preceding claims, said signal interface means comprising terminals for power supply of elements for operation and control and terminals for transmitting measurement signals. 9. A docking device mountable in a machine for providing a substrate with deposits by jetting droplets of a viscous medium onto the substrate, said docking device comprising an assembly support for receiving an assembly to be used in the machine for said jetting, said assembly comprising an assembly holder having first holding means mating with the assembly support, a nozzle, an eject mechanism connected to the nozzle, a viscous medium con- tainer connected to the eject mechanism, and signal interface means, said docking device having complementary signal interface means. 10. A docking device according to claim 9, further comprising complementary pneumatic interface means. 11. A docking device according to claim 9 or 10, said assembly support comprising pneumatically operable assembly locking means . 12. A docking device according to claim 9, 10 or 11, wherein said docking device comprises a stand, the assembly support being arranged at the stand and being reciprocatingly movable along the length of the stand. 13. A docking device according to any one of claims 9-12, the assembly support comprising alignment means. 14. A machine for providing a substrate with deposits by jetting droplets of a viscous medium onto the substrate, comprising a docking device, said docking device comprising an assembly support for receiving an assembly to be used in the machine for said jetting, said assembly comprising an assembly holder having first holding means mating with the assembly support, a nozzle, an eject mechanism connected to the nozzle, a viscous medium container connected to the eject mechanism, and signal interface means, said docking device having complementary signal interface means. 15. A machine according to claim 14, comprising an exchange assembly support for supporting at least one exchange assembly. 16. A machine according to claim 15, further com- prising means for automatic exchange of an assembly at the docking device for an exchange assembly at the exchange assembly support . 17. A machine according to claim 15 or 16, said exchange assembly support comprising pneumatically controllable means for retaining said at least one exchange assembly. 18. A machine according to any one of claims 14-17, further comprising a calibration surface. 19. A machine according to any one of claims 14-18, said docking device further comprising complementary pneumatic interface means. 20. A machine according to any one of claims 14-19, wherein the assembly support of the docking device comprises pneumatically operable assembly locking means. 21. A machine according to any one of claims 14-20, wherein said docking device comprises a stand, the assembly support being arranged at the stand and being reciprocatingly movable along the length of the stand for moving the assembly support towards or away from the surface of the substrate. 22. A machine according to any one of claims 14-21, said assembly support of the docking device comprising alignment means. 23. A machine according to any one of claims 14-22, further comprising machine vision means. 24. A method of exchanging and calibrating an assembly for jetting droplets of a viscous medium, said assembly being releasably mounted in a machine using the assembly for providing a substrate with deposits, and comprising an assembly holder having first holding means mating with an assembly support of a docking device of the machine, comprising the steps of: - exchanging the assembly for an exchange assembly; - moving the exchange assembly to a calibration surface; - depositing a plurality of deposits on the calibration surface; - determining the position of said plurality of deposits by viewing it with a vision device comprised in the machine; and - determining an offset of the position from an expected position. 25. A method according to claim 24, further comprising the step of using the offset to adjust a trigger window for the machine . 26. A method according to claim 24 or 25, wherein the step of exchanging is performed automatically and comprises the steps of: - moving a docking device supporting the assembly to an exchange assembly support; - releasing the assembly from the docking device and receiving it at the exchange assembly support; and - receiving an exchange assembly at the docking device from the exchange assembly support. 27. A method according to claim 26, wherein the step of receiving comprises the steps of aligning the exchange assembly and locking the exchange assembly. 28. A method according to any one of claims 24-27, further comprising the step of exchanging, while jetting, at least one of the exchange assemblies of the exchange assembly support for a new one.

Inventors: HOLM WILLIAM, KRONSTEDT JOHAN, SANDELL HAAKAN, HOLM, WILLIAM, KRONSTEDT, JOHAN, SANDELL, HAAKAN
Applicants: HOLM WILLIAM, KRONSTEDT JOHAN, MYDATA AUTOMATION AB, SANDELL HAAKAN, HOLM, WILLIAM, KRONSTEDT, JOHAN, SANDELL, HAAKAN
Application year: 2000
Main classification: H05K3
IPC codes: B05B1, B05B12, B05C5, B05C11, B23K3, H05K3