US20070146442A1

US20070146442A1 - System, assembly and method for jetting viscous medium onto a substrate

Info

Publication number: US20070146442A1
Application number: US11/598,752
Authority: US
Inventors: William Holm; Hakan Sandell; Johan Kronstedt
Original assignee: MyData Automation AB
Current assignee: Mycronic Technologies AB
Priority date: 2005-11-14
Filing date: 2006-11-14
Publication date: 2007-06-28
Also published as: JP2009515677A; CN101356037A; CN101356425A; US20090278875A1; WO2007054372A1; US8453595B2; EP1963042A1; WO2007054371A1; JP2010509033A; EP1952099A1; US20090266906A1; JP5199107B2; CN101356425B

Abstract

System, jetting assembly and method for jetting viscous medium onto a substrate. The system comprises a plurality of ejector devices for jetting individual droplets of viscous medium onto the substrate, a plurality of viscous medium containers for holding and providing the viscous medium to be jetted, at least one holder for holding containers and ejector devices in a jetting machine, and a jetting machine.

Description

This application claims the benefit of U.S. Provisional Application No. 60/735/898, filed on 14 Nov. 2005, which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present application refers to systems for applying viscous mediums onto substrates using jet printing within the field of electronics production.

BACKGROUND

Systems, devices and methods for jetting droplets of viscous medium, e.g. solder paste or glue, onto a substrate, e.g. an electronic circuit board, are known in the art. See for instance International Patent Publications WO 99/64167, WO 00/61297, WO 00/62587, WO 02/05607, WO 02/05608, WO 02/32201, WO 02/89545, WO 03/04186, WO 03/51526, WO 2004/010753, and WO 2005/048678, which are incorporated herein by reference.
In the MY500 Jet Printer provided by Mydata automation AB, a system for jetting viscous medium comprises a jet printing machine, a solder paste tube for containing solder paste to be jetted, a residue receptacle for holding residue and surplus of solder paste resulting from the jetting process, an ejector element for performing the actual jetting of the solder paste, and a holder matable with the jet printing machine. The holder, jetting element, residue container, and solder paste tube are arranged to be assembled away from the jet printing machine, and to form an individual, aggregate unit which may be readily positioned in a matable holding elements provided in the jet printing machine. The ejector comprises a feeder in the form of a feed screw, which is powered by a stepper motor arranged in the holder matable via interface means of the stepper motor and the ejector.

SUMMARY OF INVENTIVE EMBODIMENTS

An object of the embodiments presented herein is to provide alternative or improved systems, assemblies and methods for jetting viscous medium onto substrates.
For the purposes of this application, it is to be noted that the term “viscous medium” should be interpreted as solder paste, flux, adhesive, conductive adhesive, or any other kind of medium used in connection with the mounting of components on a substrate, conductive ink, resistive paste, or the like; that the term “deposit” refers to a connected amount of viscous medium applied at a position on a substrate as a result of one or more jetted droplets; 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), wafers, flip-chips, or the like.
It is also to be noted that the term “jetting” should be interpreted as a non-contact dispensing process that utilizes a fluid jet to form and shoot individual droplets of a viscous medium from a jet nozzle onto a substrate, as compared to a contact dispensing process, such as “fluid wetting. Furthermore, it should be noted that the individual droplets can be jetted on at a time, i.e. with an individual trigger thereof. Thus, this is different to the provision of a continuous jet stream which is broken into as series of ensuing droplets.
In the following description, inventive embodiments of jetting systems and methods will be described which comprise a jetting machine, viscous medium ejectors, viscous medium containers, residue receptacles, and holders. The term “ejector” refers to the element for actuating the actual jetting of viscous medium droplets; “container” refers to the element in which viscous medium is stored in before and supplied from during jetting and is in fluid communication with the ejector; “receptacle” refers to a container for receiving and holding surplus or residue viscous medium, for instance surplus viscous medium transported from the outlet of the ejector by means of pressurized air; and “holder” refers to a holding frame having mechanical and electrical interface with the jetting machine and holds the ejector, container and receptacle, thus forming an aggregate unit or assembly in conjunction with the ejector, container and receptacle, which in the following description will sometimes be referred to as a “cassette”; and “jetting machine” refers to the framework into which the unit or assembly is mounted. The jetting machine comprises means for holding, positioning and providing trigger signals for the cassettes during the jetting operation, and also means for holding and transporting the substrates onto which viscous medium is to be applied. The jetting machine further comprises software and inspection means for controlling and monitoring the entire viscous medium application process.
The ejector comprises a jetting nozzle, from where droplets of viscous medium may be jetted, a feeder, for feeding viscous medium towards the jetting nozzle, and an impactor, i.e. an impacting element for impacting viscous medium fed by the feeder such that droplets of viscous medium is ejected through the nozzle. Following an impact on the viscous medium, the impactor is preferably immediately returned to a position ready for impact, so as to not interfere with the feeding of viscous medium for the droplet to be subsequently jetted.
The jetting nozzle, in turn, comprises a nozzle outlet through which the droplets are jetted towards the substrate, said nozzle outlet being located at one end of the nozzle. Furthermore, the nozzle has surrounding inner walls defining a nozzle space in open communication with the nozzle outlet. During jetting operation of the ejector, the nozzle space is filled with viscous medium to a varying degree prior to the jetting of individual droplets, the degree being adjusted in dependence on the volume of the droplet to be jetted.
A number of different means or devices for feeding viscous medium are conceivable within the scope of this application, such as pneumatic means, gear-driven pumps, piston pumps, etc. However, said feeder is in exemplifying embodiments provided in the form of a rotatable feed screw, for instance such as is disclosed in WO 99/64167.
In the MY500 Jet Printer referred to above, the stepper motor for powering the feeder of viscous medium within the ejector is provided in the holder unit. However, according to exemplifying embodiments of this application, a stepper motor, or the like, for powering a feeder may alternatively be provided in the ejector unit. Thereby, interface means between the holder and the ejector for interfacing the feeder and feeder driving means can be omitted.
According to embodiments of a method and system for jetting viscous medium, the jetting system comprises a number of differently configured ejectors for use in the same jet printing machine. According to exemplifying embodiments, the ejectors could be adapted to provide a specific range in terms of the size of jetted droplets, or to specific characteristics or properties of the viscous medium. For instance, in one embodiment, the jetting system can comprise a plurality of differently formed ejector types adapted for jetting extra-fine to fine sized droplets, fine to medium sized droplets, and medium to large sized droplets, respectively. Then, the dimensions of the feeder, impactor and nozzle may be adapted to a particular droplet size range.
In other embodiments, the jetting system can comprise a plurality of differently formed ejector types adapted for jetting, for instance, solder paste, conductive adhesive, glue, and resistive paste, respectively. Moreover, within each different type of medium, such as solder paste, the properties may differ such that different ejectors may be adapted to, for instance, particular types or ranges of solder pastes. Also, it may be desirable to separate ejectors used for the jetting of viscous medium containing lead from ejectors used for the jetting of lead-free medium.
Furthermore, in further embodiments, the system comprises ejector types adapted to different combinations of the above examples, i.e. relating to both different droplet sizes and different viscous medium characteristics.
According to embodiments in which the jetting system comprises a plurality of differently configured ejectors, the jetting machine is adaptable to the different configurations of the ejectors, when required. For instance, in a situation where it is determined that a particular sized droplet is to be jetted by the ejector, the control software of the jetting machine may adapt the control signals for controlling the feeding of viscous medium into the nozzle and possibly the impacting thereof by the impactor to the dimensions or characteristics of the ejector components. In other words, in an ejector dimensioned for fine to medium sized droplets, the nozzle may have to be fully filled with viscous medium before a medium sized droplet can be ejected, while in an ejector dimensioned for medium to large sized droplets, the nozzle may only have to be half-filled before a medium sized droplet can be ejected. Thus, the jetting machine, or the software thereof, may adapt the control of the jetting process in adaptation to the particular ejector provided. However, this requires that knowledge of ejector type and characteristics is provided to jetting process control circuitry.
Furthermore, in embodiments comprising ejectors having different characteristics, the ejectors comprise information elements for identifying the specific type of ejector. In one example, the information element merely provides an identification of the particular ejector specimen, i.e. a serial number or the like. However, this requires knowledge of the characteristics or ejector type for that particular specimen to be known by the control system. Alternatively, the ejectors can comprise information elements not only identifying the particular specimen, but also the ejector type or even the particular characteristics of that ejector type. Such information elements may be provided as machine readable information elements, preferably such that a jetting machine may more or less automatically read from, and possibly write to, the information elements when mounted in the jetting machine, or placed in a vicinity thereof. Furthermore, the information elements are suitably readable by other equipment used by a circuit board manufacturer, such as for registering shipment and arrival of new ejectors, for storage and inventory purposes, for preparing subsequent jetting processes and lining up job-queues, etc.
According to exemplifying embodiments, the information element is in the form of an electronic memory circuit provided on or in the ejector. Then, the ejector comprises an electronic interface for communicating with the jetting machine, either directly or via separate interfacing elements. For instance, electronic interfaces could be provided in the holder, as defined above, such that electronic connection between the jetting machine and the electronic circuit of the ejector is provided by mounting the ejector in the holder and the holder in the jetting machine.
Furthermore, embodiments are contemplated in which Radio Frequency Identification (RFID) is used for marking and identification of different ejectors and ejector types. RFID is an automatic identification method, relying on storing and remotely retrieving data using RFID tags or transponders. RFID tags contain antennas to enable them to receive and respond to radio-frequency queries from an RFID transceiver. In these embodiments, passive RFID tags are preferably used as said information elements, requiring no internal power source, which are provided on the surface of or in the ejector. Then, RFID transceivers for communicating with, i.e. reading, the RFID tags are provided in the jetting machines for identifying the ejectors and ejector types.
In other embodiments, the information elements could be in the form of bar code labels, or the like, provided on an external surface of the ejector. Then, a bar code reader is preferably provided at or in the jetting machine.
Furthermore, the information elements referred to above could hold information of further properties of the ejectors, either via the identity of the particular specimen or as direct information held by the information elements. Examples of such further properties could include number of jetted droplets, manufacturing dates, time of latest ejected droplet, etc.
In further embodiments, a visual marking is provided on the ejector in order to provide an easily discernible indication of the ejector type for an operator. The visual marking could be in the form of a color marking, for instance provided as a label on a surface of the ejector, or as a coloring provided on all or a portion of the ejector surface. The visual marking could also, or alternatively, be in the form of a symbol, number or character indicating the ejector type, or provided as a pattern on a label on the ejector surface. Of course, the colors, symbols and patterns could be combined in order to further enhance the distinguishing effect, for instance to mitigate problems relating to operators suffering from color blindness or numeric dyslexia.
It should be noted that for embodiments having visual markings provided on the ejectors, the ejectors could also be provided with bar code labels, electronic memory circuits, or RFID tags, etc.
According to further embodiments, the jetting system could further comprise a number of viscous medium containers, i.e. for containing the viscous medium to be jetted in the jetting machine, holding different types of viscous mediums or similar type of viscous medium with different properties or characteristics. A further alternative could be to provide containers having different configurations, for instance in adaptation to the contained amount of viscous medium or other characteristics of the medium. Then, the containers could comprise information elements holding information related to characteristics of the container or of the contents thereof. For example, the information elements provided on or in the container can hold information of the tube specimen, type of container, type of viscous medium, the initial filling amount or degree, batch identity, best-before date, type of ejector (for which the container is intended to be used), etc.
There is a considerable advantage in providing these information elements in machine-readable form and not just as text on a label. An example of such an advantage is that a jetting machine can provide information about the containers to an operator, e.g. a warning that the best-before date has already passed for a particular containers. Also, the batch identity of the viscous medium can be stored together with other production data for future traceability. Furthermore, if each container is provided with a unique identity, then the machine can notice if the container has been replaced since the cassette was last used and take any appropriate action. One example of such an action could be to jet a sufficient amount of viscous medium in order to ensure that any air introduced when replacing the container is expelled from the cassette.
In the same manner as stated above in relation to the ejectors, the information elements of the containers could for instance be in the form of memory circuits, bar code markings, or RFID tags. Since the containers are intended for holding articles of consumption, use is preferably made of low-cost information elements, such as bar code labels and RFID tags. Thereby, the containers could be designed as disposable items while maintaining a reasonable manufacturing cost.
The RFID tags are further advantageous in that they are not sensitive to a particular orientation of the tag. On the contrary, an RFID tag could be read by a transceiver located in the vicinity of the RFID tag, regardless of the particular orientations of the tag. This is in contrast to the bar code label, which requires a certain proximity to a bar code reader, as well as an orientation which enables the reading of the bar code.
Furthermore, the containers could be provided with visual markings for providing an easily discernible indication of the type of container or container content for an operator. As stated above in relation to the embodiments of differently configured ejectors, the visual marking could be in the form of color markings, for instance provided as a label on a surface of the container, or as a coloring provided on all or a portion of the container surface. The visual marking could also, or alternatively, be in the form of a symbol, number or character indicating the type or content of the container, or provided as a pattern on a label on the container surface.
According to embodiments where differently configured ejectors are adapted for jetting of different media, there can be provided visual markings on the ejectors which correspond to visual markings provided on the containers. As an example, ejectors intended and adapted for jetting conductive glue of a certain type can be provided with a color marking of the same color as the color marking on a container holding conductive glue. Thereby, an operator can very easily select an ejector suitable for jetting medium from a particular container, i.e. with a particular type of medium.
Furthermore, the corresponding visual marking of the ejector and the container could be related to the mechanical interface between the interacting elements. Thus, in order to speed up the process for an operator in combining a container with an ejector having a matching mechanical interface, the container and ejector are for instance color coded to provide the indication of their association and enabled assembly.
Moreover, in further embodiments, the mechanical interface per se can be arranged for distinguishing between matching or associated containers and ejectors. In other words, differing mechanical interfaces can be used for preventing a container holding a particular viscous medium to be connected with an ejector not adapted to jetting that particular medium. As an example, ejectors to be used for jetting of lead-free solder pastes could be provided with a mechanical interface that is only connectable to containers holding lead-free solder paste and having a corresponding mechanical interface.
Preferably, the containers are generally in the form of syringe type tubes or cartridges. However, it should be noted that any other suitable shapes and forms of viscous medium containers and cartridges can be used without departing from the scope of this application.
As mentioned above, the system also comprises residue receptacles for receiving and holding surplus and residual viscous medium, such as viscous medium residue removed from the nozzle outlet in order to avoid such residue from interfering with the jetting process and negatively affecting jetting accuracy. Generally, the viscous medium residue is removed from the nozzle by providing an air flow passed the nozzle and into the receptacle. The receptacle comprises an inlet for receiving the viscous medium, the inlet suitably facing the area surrounding the nozzle outlet, a chamber for holding the viscous medium, and a filter allowing the flow of air to pass through the receptacle, while preventing viscous medium from escaping the receptacle with the flow. A more detailed description of such receptacles can be found in WO 02/89545, the contents of which is incorporated herein by reference. The receptacles can be provided as disposable items, i.e. to be used only once, but the scope of the present application also includes non-disposable receptacles, i.e. arranged as a multiple-use article.
According to exemplifying embodiments, the receptacle comprises coupling elements for mechanically interfacing the ejector, the viscous medium container, and/or the holder. Therefore, in embodiments in which the jetting system comprises differently configured ejectors and/or containers, the system can also comprise differently configured receptacles adapted to the configurations of the ejectors or containers. Furthermore, the size of the receptacles could be adapted to the size of the container, such that a smaller receptacle is adapted and intended for use with a smaller viscous medium container.
In a manner similar to that stated above in relation to containers and ejectors having differing configurations or properties and distinguishing therebetween, the receptacles may be provided with machine readable information elements, such as bar codes, RFID tags, and electronic memory circuits holding information on properties and characteristics of the receptacle. Furthermore, the receptacle can be provided with easily discernible visual markings of the type referred to above, such that an operator easily may combine a particular container and/or ejector with a suitable type of receptacle. The examples given above for identification, information and markings of ejectors and viscous medium containers, and the properties and contents thereof, are also conceivable for the embodiments of different types of receptacles.
As mentioned to some extent above, the holder is intended for constituting a mechanical interface between the jetting machine, on the one hand, and the ejector, container and receptacle, on the other hand. Thus, the jetting system according to embodiments thereof can comprise a number of differently configured holders adapted for interfacing and interacting with differently configured ejectors, viscous medium containers and residue receptacles. For instance, the holders can be adapted to the sizes of the containers in order to facilitate the provision of a steady and reliable mechanical coupling between the holder and the container, which in turn increases the accuracy of the jetting process.
As understood by the skilled person, the holders can be provided with machine readable information elements, in a manner similar to the above description in connection with the distinguishing between differently configured containers, receptacles and ejectors, respectively. Thus, the alternatives of machine readable information elements, such as bar codes, RFID tags, and electronic memory circuits holding information on properties and characteristics of the carrier, also applies for the holders. Preferably, a readable and writable electronic memory circuit will be provided as said information element, since the holder comprises an electronic interface with the jetting machine. Furthermore, the holder will most likely not be manufactured as a disposable article.
Also, the holder can be provided with easily discernible visual markings of the type referred to above, such that an operator easily may combine a selected ejector and a selected container with a corresponding holder. The examples given above for identification, information and markings of ejectors and viscous medium containers, and the properties and contents thereof, are also conceivable for the embodiments of different types of holders.
Furthermore, according to exemplifying embodiments of this application, the holders in the jetting system can also be provided with information elements for providing a unique holder identity. Thereby, a jetting machine can identify holder-ejector combinations that has previously been inserted and calibrated in the machine. The term “calibrated” in this context refers to jetting a plurality of droplets from the ejector-holder combination, preferably onto a calibration surface, evaluating the results of said jetting, e.g. by measuring the position of the resulting deposits, and adjusting jetting parameters such as trigger timing and positioning on the basis of the evaluation. A more detailed description of a calibration procedure is disclosed in WO 02/32201, which is incorporated herein by reference. Thus, even though the holder may have been used with other ejectors, and possibly also in other jetting machines, the identity of the holder and the ejector can be determined by the jetting machine. Thereby, the results of a previous calibration process with that particular holder-ejector combination can be retrieved and, at least partly, re-used. If the ejector-holder assembly has not been separated since the latest use thereof, there is a high probability that the prior calibration results are still correct and can be fully re-used.
In the embodiments described above, the four elements of ejector, holder, container and receptacle are presented as being separate elements that are attachable for use in a jetting process, and separable when located away from the jetting machine. A major advantage of such a solution resides in the fact that if a malfunctioning should occur, e.g. due to wear, it will generally only be necessary to replace a single element. This would include the receptacle being prematurely filled with viscous medium residue, i.e. before the container runs out of viscous medium. However, as will be discussed in the embodiments disclosed below, these basic elements may be combined for use as integral units that are not intended to be separated.
Firstly, the ejector and the holder may be combined as a separate, integral unit. This would entail a number of advantages, in addition to the obvious advantage of enabling the number of information elements and visual markings to be reduced. For instance, a number of mechanical and electrical interface elements that are required for assembling the separate ejector and holder in the known jetting system may of course be omitted when providing the ejector and holder as an integral unit. For instance, if a feed screw is used as a feeder, the stepper motor can be arranged in the same unit as the feeder, which would reduce the number of interacting elements and, hence, manufacturing costs.
Furthermore, repeated assembling and disassembling of mating parts may provide a non-negligible strain and wear on interfacing elements. By omitting the requirement of assembling and disassembling the ejector to and from the holder, the wear on the ejector and holder may be reduced, thus enhancing the working life of the ejector-holder combination.
Secondly, the viscous medium container and the ejector may be provided as a separate, integral unit. Then, the number of required information elements and visual markings for identification and distinguishing between different types of ejectors and containers may of course be reduced. Also, the advantage of avoiding a number of interfacing elements also applies for this combination, even though there typically will not be an electrical interface between the ejector and the container. However, by providing the ejector and container as an integral unit, the problem of selecting a suitable ejector and container combination is completely eliminated. For instance, there is no longer any risk of an operator mistakenly selecting an ejector which previously has been used with one medium, which may have left residue in the ejector, for assembling and jetting of medium from a container holding a different medium.
Furthermore, by providing the ejector-container as one integral unit, a resulting integral viscous medium passageway from the container portion of the integral unit to the ejector portion thereof may be arranged. Thereby, there will be no risk of contamination of the viscous medium from foreign substances, which otherwise could be a problem if the assembly of separate ejector and container elements is not performed in a clean area environment. In other words, the risk of an operator bringing any of the respective interfaces of a separated viscous medium passageway into contact with foreign substances, which in turn could have a detrimental effect on the jetting operation, is completely eliminated by providing the ejector-container combination as an integral unit.
Moreover, in some embodiments, the ejector-container combination can be arranged as a disposable unit.
Thirdly, the container and the receptacle may be provided as an integral unit. This enables the omission of interfacing elements between these to elements, having the advantages of reducing manufacturing costs, etc. It also enables the design and dimensions of the receptacle to be adapted to the viscous medium type and volume since there is no doubt with which container the receptacle is to be used. Thereby, the receptacles can be made smaller when integrated with a smaller container, and the overall dimensions of the aggregate cassette may be reduced.
Furthermore, the container-receptacle combination can be manufactured as a disposable unit. Then, the receptacle is preferably made from a low-cost material, such as plastic.
Also, according to exemplifying embodiments, the ejector and the receptacle can be provided as an integral unit. Interfaces between the ejector and the receptacle can be omitted, and interfaces between the container and both the ejector and the receptacle can limited to one interface between the container and the integral ejector-receptacle unit. Thus, manufacturing and assembly of the different elements can be simplified, and the wear between otherwise required interface elements eliminated, which would enhance working life of the elements and reduce manufacturing costs.
As understood by the skilled person, the embodiments of having an integral receptacle-container combination could also be combined with the embodiments of having integral holder-ejector units and ejector-container units, respectively. Thus, embodiments are contemplated where the jetting system comprises two separate units for mounting and interacting in a jetting machine, an integral holder-ejector unit to be assembled with an integral container-receptacle unit, and a holder to be assembled with an integral container-receptacle-ejector unit.
According to further embodiments related to visual markings of ejectors, holders, containers, and/or receptacles, there may be provided a pallet of visually distinguishable labels, stickers or tag. Then, the operator can use similar labels for associating separate elements to be used together in the future. As an example, an operator may have a plurality of similar ejectors at his disposal, and a jetting process for jetting, for instance, solder paste and conductive glue. Then, the operator may allocate some ejectors for jetting solder paste and some for jetting glue, select suitable labels, and attach similar labels to the glue containers and glue ejectors, and other labels to the solder paste containers and solder paste ejectors, respectively. Thereby, an improved end-user flexibility is provided in associating separate elements, and visually indicating the different associations.
Even though the inventive embodiments has been described above using examples thereof, alterations, modifications, and combinations thereof, as understood by those skilled in the art, may be made without departing from the scope of this application. For instance, the above described embodiments and examples relating to the particular parts of the jetting system, i.e. to the ejector, holder, container, and receptacle, respectively, are contemplated to be combined in any conceivable manner. Even though each possible combination have not been explicitly stated herein, such conceivable combinations are intended to be comprised in the application. Furthermore, as readily understood by the skilled person, the parts of the jetting system as described above comprise further elements that have not been mentioned or described above. However, the omission of such elements must not be taken in a limiting sense.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES OF DRAWINGS

FIG. 1 is a perspective view showing the general outline of a apparatus for application of solder paste according to exemplifying embodiments;
FIGS. 2 a and 2 b are perspective views of an embodiment of a jetting assembly shown in both separated and assembled state;
FIG. 3 is a perspective view of an aggregated viscous medium container and viscous medium receptacle;
FIG. 4 is a sectional view of an embodiment of a jetting assembly showing a portion of an ejector and a receptacle according to exemplifying embodiments;
FIG. 5 is an alternative sectional view of the embodiment shown in FIG. 4;
FIG. 6 is an enlarged sectional view of the embodiment of FIG. 4 showing a portion thereof in greater detail; and
FIG. 7 is an enlarged sectional view illustrating the flow path at the jetting outlet of the embodiment shown in FIG. 4.

DESCRIPTION OF EXEMPLARY EMBODIMENT

FIG. 1 illustrates the general outline of a preferred embodiment of an apparatus 1 for providing a substrate (not shown) with deposits by dispensing droplets of a viscous medium onto the substrate, i.e. jetting, in accordance with the embodiments disclosed in the present application. For ease of description, the viscous medium will hereinafter be referred to as solder paste, which is one of the alternatives defined above. For the same reason, the substrate will be referred to as an electric circuit board and the gas will be referred to as air. In the following, a jetting assembly will be depicted as an assembly of separate elements including a holder, an ejector, a receptacle and a container. However, as described above, the separate elements can be combined in several combinations to form an integral unit, respectively, making up part of the assembly. Thus, the ejector and the holder may be combined as a separate, integral unit; the viscous medium container and the ejector may be provided as a separate, integral unit; the container and the receptacle may be provided as an integral unit, the ejector and the receptacle can be provided as an integral unit; and the container, the receptacle, and the ejector can be provided as a separate, integral unit. All these stated combinations are contemplated for the purposes of this application, although not all are explicitly shown in the figures or described in detail below.
In the described embodiments, the jetting apparatus or machine 1 is of a type comprising an X-beam 3 and an X-wagon 4, which is connected to the X-beam 3 via an X-rail 10 and is movable in a reciprocating way along the X-rail 10. The X-beam 3, in turn, is movably connected to a Y-rail 2, the X-beam 3 thereby being movable to the X-rail 10. The Y-rail 2 is rigidly mounted in the jetting apparatus 1. Generally, the movements are provided by linear motors (not shown).
Furthermore, the jetting apparatus 1 comprises an internal conveyor 7 for carrying the board through the jetting apparatus 1, and a locking device for locking the board when jetting is to take place.
A docking device is attached to the X-wagon 4 for enabling releasable mounting of an assembly 5 at the docking device. The assembly 5 is arranged for dispensing droplets of solder paste, i.e. jetting, which impact and form deposits on the board. The jetting apparatus 1 also comprises at least one vision device, e.g. a camera. The camera is used for determining the position and rotation of the substrate or board and for checking the result of the dispensing process by viewing the deposits on the board. Furthermore, a cassette calibration unit 9 and a camera calibration unit 8 are provided for calibration of the jetting apparatus.
Additionally, the jetting apparatus 1 comprises a vacuum ejector 6 (schematically shown in FIG. 5) arranged on the X-wagon 4, and a source of compressed air (not shown). The vacuum ejector, as well as the source of compressed air, is in communication with the docking device via air conduit interface means which are connectable to complementary air conduit interface means, of the docking device.
As readily understood by those skilled in the art, the jetting apparatus also comprises a processor or control unit 80 (schematically shown in FIG. 5) for executing software running the apparatus.
Briefly, the jetting apparatus works as follows. The board is fed into the jetting apparatus 1 by means of the conveyor 7, upon which the board is placed. When the board is in the correct position under the X-wagon 4, the board is fixed with the aid of the locking device. By means of the camera, fiducial markers are located, which markers are prearranged on the surface of the board and used to determine the precise position thereof. Then, by moving the X-wagon over the board in a predetermined (pre-programmed) pattern and operating the jetting assembly 5 at predefined locations, solder paste is applied on the board at the desired locations.
With reference to FIGS. 2 a, 2 b and 3, an exemplifying embodiment of a jetting assembly 5 will now be described in more detail. In FIG. 2, the assembly 5 is illustrated in an exploded view showing its separate elements, as well as when assembled in the form of an aggregate unit. The jetting assembly 5 comprises an assembly holder 11 having holding means 12 for connecting the jetting assembly 5 to an assembly support of the docking device, as well as a holding element 13 for securing the assembly of the aggregate unit 5. Furthermore, in this embodiment the jetting assembly 5 comprises a viscous medium container 14 providing a supply of solder paste, and a viscous medium receptacle 15 for receiving viscous medium residue produced during the jetting operation. The jetting assembly 5 is connected to the vacuum ejector 6 and the source of pressurised air via a pneumatic interface 50, which will be further illustrated below. Furthermore, the assembly 5 comprises a jetting device or ejector 16, as well as a motor unit 17 provided for driving the feeding, i.e. a rotatable feed screw 32, of viscous medium into an eject chamber 28 of the jetting device 16. In this embodiment, the motor unit 17 is pivotally mounted to the holder 11, such that the motor unit may be folded away for providing easy assembly of the assembly element, which is illustrated in the exploded view of FIG. 2.
Also, in FIG. 3, the container 14 and the receptacle 15 are shown as an aggregate unit separate from the ejector 16, the motor unit 17 and the holder 11. In this embodiment, the container 14 and receptacle 15 are assembled prior to mounting them into the holder 11 for forming the assembly 5. Preferably, the receptacle 15 and the container 14 are delivered to the manufacturing site as an already assembled unit, to be mounted with the holder 11, ejector 16 and motor unit 17 to form the assembly 5 for performing the jetting operation.
With further reference to FIGS. 4-7, the contents and function of the device enclosed in the jetting assembly 5 will be explained in greater detail. As can be seen in these sectional views, the jetting assembly 5 includes a ejector or jetting device 16 comprising an actuator locking screw 20 for supporting an actuator, and a piezoelectric actuator 21 formed by a number of thin, piezoelectric elements stacked together to form the actuator 21, which is rigidly connected to the locking screw 20. The jetting device 16 further comprises a bushing 25 rigidly connected to a housing 19, and a plunger 23 rigidly connected to the end of the piezoelectric actuator 21, opposite the position of the locking screw 20. The plunger 23 is axially movable while slidably extending through a bore in the bushing 25. Cup springs 24 are provided to resiliently balance the plunger 23 against the housing 19, and for providing a preload for the actuator 21. An eject control unit (not shown) applies a drive voltage intermittently to the piezoelectric actuator 21, thereby causing an intermittent extension thereof and hence a reciprocating movement of the plunger with respect to the housing 19, in accordance with solder pattern printing data.
Further, the jetting device comprises an eject nozzle 26 operatively directed against the board 2, onto which small droplets of solder paste are to be jetted. In the nozzle 26, there is comprised a jetting orifice 27 through which the droplets are jetted. The surfaces of the nozzle 26 surrounding the jetting orifice 27 and facing the substrate 2 will be referred to as a jetting outlet. The plunger 23 comprises a piston portion which is slidably and axially movably extending through a piston bore 35, an end surface of said piston portion of the plunger 23 being arranged close to said nozzle 26. An eject chamber 28 is defined by the shape of the end surface of said plunger 23, the inner diameter of the bushing 25 and the nozzle orifice 27. Axial movement of the plunger 23 towards the nozzle 26, said movement being caused by the intermittent extension of the piezoelectric actuator 21, will cause a rapid decrease in the volume of the eject chamber 28 and thus a rapid pressurisation and jetting through the nozzle orifice 27, of any solder paste contained in the eject chamber 28.
Solder paste is supplied to the chamber from the supply container 14, see FIG. 2, via a feeding device. The feeding device comprises an electric motor, arranged in the motor unit 17, having a motor shaft 29 partly provided in a tubular bore 30, which extends through the housing 19 to an outlet 36 communicating via a tubular bore 31 with said piston bore 35. An end portion of the motor shaft 29 forms a rotatable feed screw 32 which is provided in, and coaxial with, the tubular bore 30. An essential portion of the rotatable feed screw 32 is surrounded by an array of resilient, elastomeric o-rings 33 arranged coaxially therewith in the tubular bore 30, the threads of the rotatable feed screw 32 making sliding contact with the innermost surface of the o-rings 33.
The pressurised air obtained from the above-mentioned source of pressurised air (not shown) is arranged to apply a pressure on the solder paste contained in the supply container 12, thereby feeding said solder paste to an inlet port 34 communicating with the tubular bore 30. An electronic control signal provided by a supply control unit (not shown) to the motor causes the motor shaft 29, and thus the rotatable feed screw 32, to rotate a desired angle, or at a desired rotational speed. Solder paste captured between the threads of the rotatable feed screw 32 and the inner surface of the o-rings 33 are then made to travel from the inlet port 34 to the piston bore 35 via the outlet port 36 and the tubular bore 31, in accordance with the rotational movement of the motor shaft 29. A sealing o-ring 22 is provided at the top of the piston bore 35 and the bushing 25, such that any solder paste fed towards the piston bore 35 is prevented from escaping from the piston bore 35 and possibly disturbing the action of the plunger 23.
The solder paste is then fed into the eject chamber 28 from an outlet port 36 of the tubular bore 30 via the conduit 31 and a channel 37. The channel 37 is provided in the piston portion of the plunger 23, wherein said channel 37 has a first portion extending axially into said plunger and communicating with the conduit 31, and a second portion extending coaxially with and within said plunger 23 from said first portion to the end surface of the plunger facing the eject chamber 28.
As can most clearly be seen in FIG. 6, the jetting device 15 of the jetting assembly 5 comprises a support plate 40 located below or downstream of the nozzle orifice 27, as seen in the jetting direction. The support plate 40 is provided with a through hole 41, through which the jetted droplets may pass without being hindered or negatively affected by the support plate 40. Consequently, the hole 41 is concentric with the nozzle orifice 27.
According to this embodiment, the ejector 16 comprises an air flow passage 38 consisting of a first portion defined by the nozzle orifice 27, the nozzle 26 and the support plate 40, said first portion defining a disc shaped space concentric with the piston bore 35; a second portion defined by the nozzle 26 and the support plate 40, connected to said first portion and extending coaxially about the nozzle 26; and a third portion defined by the housing 19 and the bushing 25, connected to the second portion, parallel with the piston bore 35 and extending coaxially around the part of the bushing 25 facing said third portion. The air flow passage 38 is further in communication with an air flow conduit 39 located on the side of the piston bore 35 opposite that of the tubular bore 31. The air flow conduit 39 extends from the third portion of the air flow passage 38 and the viscous medium waste container or receptacle 15.
Thus, when the assembly 5 is assembled, the receptacle 15 for collecting fragments of residue solder paste will be connected to the ejector 16. The receptacle 15 can be best seen in FIG. 5, where it is schematically shown in its entirety. The receptacle 15 is connected to the ejector 16 at an interface provided on the ejector 16, via a corresponding interface 50 arranged on the receptacle 15. The receptacle 15, which will be described in more detail below, also provides an interface 51 and communication between the jetting assembly 5 and the vacuum ejector 6. Thereby, the negative pressure or vacuum produced by the vacuum ejector is conveyed to the ejector 5, and to the communicating air flow conduit 39 and airflow passage 38.
The receptacle 15 comprises an air conduit 53, forming an air flow path or channel within the receptacle 15. The air conduit 53 has a first portion communicating with said connecting interface 50 and is aligned with the air flow conduit 39 of the jetting assembly, and a second portion extending perpendicularly from said first portion. At the end thereof, the air conduit 53 takes the form of a guiding tubing which is in communication with a collection chamber 55, arranged for collection of solder paste residue removed from the jetting outlet. Preferably, the conduit 53 has an outlet 54 that is directed downwards, thus guiding the carried solder paste towards the bottom of the chamber. At the top of the collection chamber 55, a narrow air conduit 52 leads the air flow out of the collection chamber 55. Thereby, the air will flow from the outlet 54 of the conduit 53 and deflect into the air conduit 52 at the top of the collection chamber, while the main portion of the solder paste residue will be released, due to the momentum thereof and gravity, from the air stream and fall into the collection chamber.
Even if the majority of collected solder paste residue carried by the air flow is released and collected in the collection chamber, a small portion thereof may still be carried onwards by the air flow. Therefore, the receptacle further comprises a filter 57, into which said narrow air conduit guides the flow of air. The filter 57 is of conventional type and provided for preventing any fragments of solder paste not collected in the collection chamber 55 from reaching the vacuum ejector. The filter is arranged in a longitudinal bore 56 and is in communication with an outlet conduit 58, in communication with the outlet interface 51 provided for interface with the vacuum ejector 6.
The receptacle 15 is releasably connected to the vacuum ejector 6, of conventional type, which is arranged for evacuating the receptacle 15. The vacuum ejector 6 is connected to the receptacle 15 via the air outlet 58, a connector 60 and an air tube 61. Even though the vacuum ejector is illustrated as being separate from the solder paste ejector 16 and/or the receptacle 15, a number of other placements or combinations of the vacuum ejector 6, the ejector 16, and the receptacle 15 are of course conceivable within the scope of the embodiments presented in the present application. However, the vacuum ejector 6, the connector 61 and the air tube 61 are preferably arranged in the jetting machine 1, i.e. separate from the elements making up the jetting assembly 5.
Furthermore, a flow sensor 70 is arranged and positioned in the air tube 61. The flow sensor is arranged for measuring the air flow in the air flow path of the jetting apparatus, i.e. including the air flow conduit 39 and air flow passage 38 of the ejector; the conduit 53, the collection space 55, the narrow air conduit 52, the filter 57, and the outlet conduit 58 of the receptacle 15; as well as the connector 60 and the air tube 61. Use can be made of any available flow meter suitable for the particular flow range and having a suitable size for positioning and measuring in the flow path of the air tube 61, for instance the MEMS Mass Flow Sensor provided by Omron Electronic Components Europe B.V.
The flow sensor 70 is electronically connected to he control unit 80, which is also arranged for receiving and evaluating the measurement signal 71 output by the flow sensor.
In operation, the vacuum ejector 6 evacuates the waste container 15, including evacuation of the air conduit 53, the collection space 55, the narrow air conduit 52, the filter 57, the outlet conduit 58, the connector 60 and the air tube 61. This evacuation produces an air flow through the waste container as indicated by the arrows in FIG. 5. As a consequence, air flow conduit 39 and air flow passage 38 of the ejector 16 are also evacuated via their interface. Thus, air is sucked in through the outlet hole 41, which gives rise to a strong air flow in a direction reverse to that of the jetted droplets. This air flow will pass the jetting outlet and remove any undesired residue of solder paste that may have become adhered to the jetting outlet, for reasons described above.
According to the preferred embodiments, the air flow is continuously provided before, during and after the jetting of each droplet. Also, the air flow could be provided intermittently, following a predetermined time period of jetting, or following a predetermined number of jetted droplets. It is also contemplated that the accumulation or build-up of solder paste residue at the jetting outlet is monitored, and that the flow of air is provided when the accumulation reaches a certain level. However, it is preferred that the air flow is constantly provided during the jetting process.
Thus, the air will flow through the air flow passage 38 and continue into the receptacle 15 via the air flow conduit 39. Due to the force of the air flow, solder paste fragments removed from the vicinity of the jetting outlet will be transported or carried through the air flow passage 38, the air flow conduit 39 and into the receptacle 15. Inside the receptacle 15, the air will flow through the air conduit 53 and into the collection chamber 55. Due to the force of gravity, the majority of the solder paste residue transported by the air flow will fall into the collection chamber 55, while the air flow will continue into the narrow conduit 52. Any residue of solder paste that may continue along with the air flow into the narrow conduit 52, will be collected by the filter 57, thus preventing fragments of solder paste from reaching the outlet conduit 58.
Furthermore, as the jetted droplets face a strong head wind immediately following the jetting thereof, any droplets having a jetting trajectory with an angular deviation from that intended, will encounter a slight side wind. The effect of the side wind on a jetted droplet will be dependent of the magnitude of angular deviation. As a consequence, the angular deviation can be enhanced to such an extent that the jetted droplet will “miss” the hole 41 and instead be collected by the support plate 40. The above may also be the case for any satellites, described above, which due to their angular deviation will encounter a side wind and be collected by the support plate 40. Then, the air flow present or later produced in the air flow passage will transport away any solder paste collected by the support plate 40. Due to the lower velocity and significantly smaller volume of the satellites, as compared to the solder paste droplets, the satellites will be much more prone to be affected by the side wind.
The preceding specific examples are illustrative of the embodiments of the present application. It is to be understood, therefore, that other expedients known to those of skill in the art or disclosed herein may be employed without departing from the invention as defined by the appended claims. It is therefore understood that the embodiments may be practiced otherwise than what is specifically described herein without departing from the scope of the present application.

Claims

1. A system for jetting viscous medium onto a substrate, comprising:

a plurality of ejector devices for jetting individual droplets of viscous medium onto the substrate,

a plurality of viscous medium containers for holding and providing the viscous medium to be jetted,

a receptacle for receiving and collecting viscous medium residue produced during said jetting of individual droplets,

at least one holder for holding containers and ejector devices in a jetting machine, and

a jetting machine.

2. An assembly for jetting viscous medium onto a substrate, comprising:

an ejector device for jetting individual droplets of viscous medium onto the substrate,

a viscous medium container for holding and providing the viscous medium to be jetted,

a receptacle for receiving and collecting viscous medium residue produced during said jetting of individual droplets, and

a holder for holding said ejector device, viscous medium container and receptacle as one aggregate unit.

3. A method of jetting viscous medium onto a substrate, comprising the steps of:

providing an ejector device for jetting individual droplets of viscous medium onto the substrate,

providing a viscous medium container for holding and providing the viscous medium to be jetted,

providing a receptacle for receiving and collecting viscous medium residue produced during said jetting of individual droplets,

providing a holder for holding said ejector device, viscous medium container and receptacle as one aggregate unit,

assembling said aggregate unit,

mounting said unit in a jetting machine, and

jetting droplets of viscous medium onto a substrate.