IL294060A - Recirculating paste dispensing head - Google Patents

Description

RECIRCULATING PASTE DISPENSING HEAD BACKGROUND OF THE INVENTION 1. TECHNICAL FIELD id="p-1" id="p-1" id="p-1" id="p-1" id="p-1" id="p-1" id="p-1" id="p-1" id="p-1"

[0001] The present invention relates to the field of dispensing paste, and more particularly, to dispensing conductive paste for applications in the field of electronics and solar cells. 2. DISCUSSION OF RELATED ART id="p-2" id="p-2" id="p-2" id="p-2" id="p-2" id="p-2" id="p-2" id="p-2" id="p-2"

[0002] U.S. Patent Application Publication No. 2010/0139509, which is incorporated herein by reference in its entirety, teaches a screen printing head which, in a printing operation, is displaceable in a first direction over a surface of a workpiece to print deposits of a print medium on the workpiece, the screen printing head comprising: a print head assembly comprising a print unit comprising a main body including a print medium, cavity, which in use contains print medium, and a delivery aperture, which is in fluid communication with the print medium cavity and through which print medium is in use delivered from the print medium cavity to the surface of the workpiece, and a rotatable unit which is disposed in the print medium cavity of the main body and rotatable to displace print medium as contained in the print medium cavity; and a drive unit for rotating the rotatable unit such as to displace print medium as contained in the print medium cavity, wherein the drive unit is operative to rotate the rotatable unit to apply a force to the print medium at the delivery aperture in the main body in a second direction which is opposite to the first direction of displacement of the screen printing head. id="p-3" id="p-3" id="p-3" id="p-3" id="p-3" id="p-3" id="p-3" id="p-3" id="p-3"

[0003] U.S. Patent No. 9,616,524, which is incorporated herein by reference in its entirety, teaches a method of depositing a material on a receiving substrate, the method comprising: providing a source substrate having a back surface and a front surface, the back surface carrying at least one piece of coating material; providing a receiving substrate positioned adjacent to the source substrate and facing the coating material; and radiating light towards the front surface of the source substrate, to remove at least one piece of the coating material from the source substrate and deposit said removed at least one piece onto the receiving substrate as a whole. 1 id="p-4" id="p-4" id="p-4" id="p-4" id="p-4" id="p-4" id="p-4" id="p-4" id="p-4"

[0004] U.S. Patent Application Publication No. 2017/013724, which is incorporated herein by reference in its entirety, teaches an apparatus for generating a transfer pattern to be used in a transfer printing process. The pattern is generated in a substrate that could be a web substrate and that bears one or more trenches. A filler to be transferred is made to fill the trenches within the web substrate. Upon completion of the trench by filler filling, the substrate, the scraper and the squeegee are translated from the working zone in a synchronized movement, such that in course of the translation movement at least the scraper remains in full contact with the substrate. id="p-5" id="p-5" id="p-5" id="p-5" id="p-5" id="p-5" id="p-5" id="p-5" id="p-5"

[0005] Lossen et al. (2015), Pattern Transfer Printing (PTP™) for c-Si solar cell th metallization, 5 Workshop on Metallization for Crystalline Silicon Solar Cells, Energy Procedia 67:156-162, which is incorporated herein by reference in its entirety, teaches pattern transfer printing (PTP™) as a non-contact printing technology for advanced front side metallization of c-Si PV solar cells, which is based on laser-induced deposition from a polymer substrate.

SUMMARY OF THE INVENTION id="p-6" id="p-6" id="p-6" id="p-6" id="p-6" id="p-6" id="p-6" id="p-6" id="p-6"

[0006] The following is a simplified summary providing an initial understanding of the invention. The summary does not necessarily identify key elements nor limit the scope of the invention, but merely serves as an introduction to the following description. id="p-7" id="p-7" id="p-7" id="p-7" id="p-7" id="p-7" id="p-7" id="p-7" id="p-7"

[0007] One aspect of the present invention provides a paste dispensing apparatus comprising: a printing head comprising at least two feeding openings, an internal cavity and at least one dispensing opening that are in fluid communication, and a pressurized paste supply unit configured to circulate paste through the printing head, wherein a pressure in the pressurized paste supply unit is adjusted to maintain continuous circulation of the paste through the feeding openings and the internal cavity and to control dispensing of the paste through the at least one dispensing opening. id="p-8" id="p-8" id="p-8" id="p-8" id="p-8" id="p-8" id="p-8" id="p-8" id="p-8"

[0008] One aspect of the present invention provides a paste dispensing method comprising maintaining continuous paste circulation through an internal cavity of a printing head having at least one dispensing opening which is in fluid communication with the internal cavity. 2 id="p-9" id="p-9" id="p-9" id="p-9" id="p-9" id="p-9" id="p-9" id="p-9" id="p-9"

[0009] These, additional, and/or other aspects and/or advantages of the present invention are set forth in the detailed description which follows; possibly inferable from the detailed description; and/or learnable by practice of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS id="p-10" id="p-10" id="p-10" id="p-10" id="p-10" id="p-10" id="p-10" id="p-10" id="p-10"

[0010] For a better understanding of embodiments of the invention and to show how the same may be carried into effect, reference will now be made, purely by way of example, to the accompanying drawings in which like numerals designate corresponding elements or sections throughout. id="p-11" id="p-11" id="p-11" id="p-11" id="p-11" id="p-11" id="p-11" id="p-11" id="p-11"

[0011] In the accompanying drawings: id="p-12" id="p-12" id="p-12" id="p-12" id="p-12" id="p-12" id="p-12" id="p-12" id="p-12"

[0012] Figures 1A-1C, 2A-2C and 3 are high-level illustrations of paste dispensing apparatuses, according to various embodiments of the invention. id="p-13" id="p-13" id="p-13" id="p-13" id="p-13" id="p-13" id="p-13" id="p-13" id="p-13"

[0013] Figure 4 is a high-level flowchart illustrating paste dispensing methods, according to some embodiments of the invention. id="p-14" id="p-14" id="p-14" id="p-14" id="p-14" id="p-14" id="p-14" id="p-14" id="p-14"

[0014] It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.

DETAILED DESCRIPTION OF THE INVENTION id="p-15" id="p-15" id="p-15" id="p-15" id="p-15" id="p-15" id="p-15" id="p-15" id="p-15"

[0015] In the following description, various aspects of the present invention are described.

For purposes of explanation, specific configurations and details are set forth in order to provide a thorough understanding of the present invention. However, it will also be apparent to one skilled in the art that the present invention may be practiced without the specific details presented herein. Furthermore, well known features may have been omitted or simplified in order not to obscure the present invention. With specific reference to the drawings, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the 3 principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice. id="p-16" id="p-16" id="p-16" id="p-16" id="p-16" id="p-16" id="p-16" id="p-16" id="p-16"

[0016] Before at least one embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is applicable to other embodiments that may be practiced or carried out in various ways as well as to combinations of the disclosed embodiments.

Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. id="p-17" id="p-17" id="p-17" id="p-17" id="p-17" id="p-17" id="p-17" id="p-17" id="p-17"

[0017] Embodiments of the present invention provide efficient and economical methods and mechanisms for dispensing thick metallic paste and thereby provide improvements to the technological field of printing electronic circuits. Paste dispensing apparatuses and methods are provided, which maintain continuous paste circulation through feeding openings and the internal cavity of the printing head, while dispensing paste through one or more dispensing opening(s) which is in fluid communication with the internal cavity.

Pressurized paste supply unit(s) circulate the paste through the printing head, adjusting the pressure in the supply unit(s) to maintain the continuous circulation of the paste through the feeding openings and the internal cavity, and to control dispensing of the paste through the dispensing opening(s). For example, paste may be delivered via entry opening(s) in the printing head, and controllably-pressurized paste may be added to the paste that exits the printing head. id="p-18" id="p-18" id="p-18" id="p-18" id="p-18" id="p-18" id="p-18" id="p-18" id="p-18"

[0018] Disclosed paste dispensing may be used to print fine lines of thick metallic paste to produce electronic circuits, e.g., creating conductive lines or pads or other features on laminates for PCBs or other printed electronic boards. or on silicon wafers, e.g., for photovoltaic (PV) cells. Other applications may comprise creating conductive features in the manufacturing processes of mobile phones antennas, decorative and functional automotive glasses, semiconductor integrated circuits (IC), semiconductor IC packaging 4 connections, printed circuit boards (PCB), PCB components assembly, optical biological, chemical and environment sensors and detectors, radio frequency identification (RFID) antennas, organic light-emitting diode (OLED) displays (passive or active matrix), OLED illuminations sheets, printed batteries and other applications. id="p-19" id="p-19" id="p-19" id="p-19" id="p-19" id="p-19" id="p-19" id="p-19" id="p-19"

[0019] Specifically, disclosed paste dispensing apparatuses and methods ensure stable and uniform dispensing of high viscosity paste during long time operation, by continuously recirculating the paste inside the dispensing head, e.g., preventing accumulation of paste material anywhere within the printing head or related components; and mixing the paste during circulation to ensure continuous conditioning of the paste composition, e.g., maintaining the components of paste well mixed and keeping volatile organic components uniformly within the paste – preventing drying and crumbling of the paste. id="p-20" id="p-20" id="p-20" id="p-20" id="p-20" id="p-20" id="p-20" id="p-20" id="p-20"

[0020] Advantageously, compared to prior art dispensing methods, evaporation of organic paste components (as in prior art doctor blade (ductor blade) type dispensing devices) and resulting deterioration of the thixotropic properties of the paste (paste rheology) are avoided; and compositional changes in the paste that result from excessive pressurization (as in prior art non-circulating devices), such as segregation among paste compounds, are prevented – yielding uniform paste composition and therefore stable printing quality. id="p-21" id="p-21" id="p-21" id="p-21" id="p-21" id="p-21" id="p-21" id="p-21" id="p-21"

[0021] For example, disclsoed paste dispensing apparatuses and methods may be used to generate transfer patterns to be used in transfer printing processes, e.g., by depositing the paste into trenches in substrate sheets, and using the transferred pattern, e.g., in a roll-to- roll manufacturing process (see, e.g., Lossen et al. 2015). id="p-22" id="p-22" id="p-22" id="p-22" id="p-22" id="p-22" id="p-22" id="p-22" id="p-22"

[0022] Figures 1A-1C, 2A-2C and 3 are high-level illustrations of paste dispensing apparatuses 100, according to various embodiments of the invention. Figures 1A, 1B and 1C are, respectively, a side view, a bottom perspective view and a side cross section view of some embodiments of paste dispensing apparatuses 100; Figures 2A, 2B and 2C are, respectively, a perspective view, a bottom perspective view and a perspective view with illustrated paste movements - of some embodiments of paste dispensing apparatuses 100; and Figure 3 is a cross sectional side view with illustrated paste movements - of some embodiments of paste dispensing apparatuses 100. Elements from 1A-1C, 2A-2C and 3 may be combined in any operable combination, and the illustration of certain elements in certain figures and not in others merely serves an explanatory purpose and is non-limiting. id="p-23" id="p-23" id="p-23" id="p-23" id="p-23" id="p-23" id="p-23" id="p-23" id="p-23"

[0023] Paste dispensing apparatus 100 comprises a printing head 150 comprising at least two feeding openings 161, 169, an internal cavity 165 and at least one dispensing opening 160 that are in fluid communication (see, e.g., Figures 1C, 2C and 3) and a pressurized paste supply unit 105 configured to circulate paste 90 through printing head 150. The pressure in the pressurized paste supply unit (see, e.g., Figures 1C, 2C and 3) is adjusted to maintain continuous circulation of the paste through feeding openings 161, 169 and internal cavity 165 and to control dispensing of the paste through dispensing opening(s) 160. For example, pressurized paste supply unit 105 may comprise a pressurized paste reservoir 120 and a paste pump 110 in fluid communication with internal cavity 165 of printing head 150, which are configurated to circulate the paste therethrough. In non- limiting examples, paste pump 110 may comprise rotating pressure-tight displacement systems with self-sealing, rotor/stator designs for dispensing precise volumes such as eco- PEN450™ from Dymax™. id="p-24" id="p-24" id="p-24" id="p-24" id="p-24" id="p-24" id="p-24" id="p-24" id="p-24"

[0024] In various embodiments, paste dispensing apparatus 100 comprises at least one pressure sensor 140 configured to measure the pressure of the circulating paste, e.g., pressure sensor 140 illustrated schematically in Figures 1A-1C and associated with a paste mixer 130 or pressure sensors 140A, 140B illustrated schematically in Figures 2A-2C and 3, at either ends of printing head 150, as non-limiting examples. Alternatively or complementarily, pressure measurement may be implemented within elements of pressurized paste supply unit 105, such as paste pump 110 and/or paste reservoir 120. Paste dispensing apparatus 100 may further comprise at least one controller 170 (shown schematically in Figures 1C and 2C), configured to adjust the pressure in pressurized paste supply unit 105 (or its components) with respect to the measured pressure of the circulating paste. Paste dispensing apparatus 100 may further comprise one or more paste mixer(s) 130 configured to mix the circulating paste. For example, paste mixer(s) 130 may be a static mixer, mixing the paste by utilizing its pressurization. In non-limiting examples, paste mixer(s) 130 may comprise plastic disposable static mixers such as GXF-10-2-ME™ 6 from Stamixco™ made of large diameter plastic housing that includes multiple mixing elements. id="p-25" id="p-25" id="p-25" id="p-25" id="p-25" id="p-25" id="p-25" id="p-25" id="p-25"

[0025] Pressurized paste supply unit 105 may be further configured to introduce the paste into internal cavity 165 via at least one entry opening 161 of the at least two feeding openings and to receive the circulated paste via at least one exit opening 169 of the feeding openings in printing head 150. Typically, entry opening(s) 161 and exit opening(s) 169 are at the top of printing head 150, opposite to dispensing opening(s) 160 which faces the substrate onto which the paste is deposited. Alternatively or complementarily, entry opening(s) 161 and/or exit opening(s) 169 may be positioned on sides and/or extension(s) of printing head 150. id="p-26" id="p-26" id="p-26" id="p-26" id="p-26" id="p-26" id="p-26" id="p-26" id="p-26"

[0026] Pressurized paste supply unit 105 may comprise pressure-controlled paste reservoir 120, paste pump 110 and mixer 130 that are in fluid communication. Pressure-controlled paste reservoir 120 may be configured to deliver paste to paste pump 110, which may be configured to deliver the paste through mixer 130 to entry opening(s) 161. Pressurized paste supply unit 105 may be further configured to mix paste from exit opening(s) 169 with the paste delivered from pressure-controlled paste reservoir 120 to paste pump 110. The exit of the pressure-controlled paste reservoir 120 is in fluid communication with the entry of the paste pump 110. For example, as illustrated schematically in Figures 2C and 3, paste 90 in paste reservoir 120 may be delivered (91) to paste pump 110, mixing (92) with paste 97 exiting from exit opening(s) 169 of printing head 150, to be pumped by paste pump 110 into mixer 130. Paste 93 from mixer 130 may be delivered (94) to entry opening(s) 161 of printing head 150, wherein paste 96 moves along internal cavity 165 and some paste 95 may be dispensed through dispensing opening(s) 160 to form patterns such as lines on the substrate (e.g., silver lines of about 20µm width on silicon wafers for PV cells, see, for non-limiting examples, Lossen et al. 2015). Remaining paste 97 is then mixed with paste 91 from paste reservoir 120 (e.g., delivered through nozzle 122 at junction 112) to compensate for the dispensed amount, and the paste is circulated through paste dispensing apparatus 100 to maintain its mechanical characteristics and support continued mixing of the paste to maintain its chemical composition. In certain embodiments, paste dispensing apparatus 100 may be further configured to modify paste composition, e.g., by adding 7 additives such as solvents to keep the paste homogenized, possibly in relation to the monitored pressures throughout paste dispensing apparatus 100. For example, additives such as solvents may be added to the paste entering mixer 130 if needed. id="p-27" id="p-27" id="p-27" id="p-27" id="p-27" id="p-27" id="p-27" id="p-27" id="p-27"

[0027] In various embodiments, printing head 150, internal cavity 165 and dispensing slit as opening 160 limited by slit edges 162 (e.g., metallic slit lips 162) may be elongated (see, e.g., Figures 1B and 2B) and configured with respect to paste properties (e.g., viscosity values), specified throughput and specified features (e.g., length, width and optionally cross section) of the lines or other elements that are to be dispensed by printing head 150.

In certain embodiments, dispensing opening 160 may comprise one or more slits, one or more opening, a plurality of linearly-arranged openings, e.g., one or more lines of circular or elliptical openings, and so forth. id="p-28" id="p-28" id="p-28" id="p-28" id="p-28" id="p-28" id="p-28" id="p-28" id="p-28"

[0028] In various embodiments, paste material may comprise conductive silver based metallic paste, and may typically be of high viscosity (e.g., in the range of several tens to several hundreds of Pa·s). For example, in non-limiting solar applications, the metallic paste may comprise metal powder(s), optional glass frits and modifier(s), volatile solvent(s) and non-volatile polymer(s) and/or or resin(s). A non-limiting example for the paste includes SOL9651B™ from Heraeus™. id="p-29" id="p-29" id="p-29" id="p-29" id="p-29" id="p-29" id="p-29" id="p-29" id="p-29"

[0029] Paste dispensing apparatus 100 may comprise one or more pressure sensor (s) 140, 140A, 140B configured to measure the pressure of the circulating paste at one or more respective locations along the paste circulation path. For example, pressure sensor(s) 140, 140A, 140B may be set adjacent to entry opening(s) 161, exit opening(s) 169, in fluid communication with internal cavity 165 of printing head 150 and/or in association with any of mixer 130, paste reservoir 120 and/or paste pump 110. Pressure-related indications from pressurized paste reservoir 120 and/or paste pump 110 may also be used to monitor paste circulation through paste dispensing apparatus 100 and/or to monitor and possibly modify the paste properties such as its viscosity, e.g., by adding solvent. Paste dispensing apparatus 100 may further comprise at least one controller 170 (e.g., in communication with any of the components of paste dispensing apparatus 100, e.g., via communication link(s)) configured to adjust the pressure in pressure-controlled paste reservoir 120 and/or paste pump 110 with respect to the measured pressure of the circulating paste, e.g., as 8 received from one or more pressure sensor (s) 140, 140A, 140B. In non-limiting examples, any of pressure sensor(s) 140 may comprise, e.g., small profile, media compatible, piezoresistive silicon pressure sensors packaged in a stainless-steel housing (e.g., MEAS 86A™ from T.E. connectivity™ or equivalent sensors). id="p-30" id="p-30" id="p-30" id="p-30" id="p-30" id="p-30" id="p-30" id="p-30" id="p-30"

[0030] In various embodiments, pressure-controlled paste reservoir 120 and paste pump 110 may open adjacently to exit opening(s) 169 of printing head 150 and paste dispensing apparatus 100 may comprise a conduit 135 connecting the exit of mixer 130 to entry opening(s) 161 of printing head 150 (see, e.g., Figures 2A-2C and 3). In some embodiments, pressure-controlled paste reservoir 120 and paste pump 110 may open adjacently to exit opening(s) 169 of printing head 150, mixer 130 may be adjacent to entry opening(s) 161 of printing head 150, and conduit 135 may connect paste pump 110 to mixer 130. Pressure sensor 140 may be associated with mixer 130 (see, e.g., Figures 1A-1C).

The dimensions and orientations of paste reservoir 120 and paste pump 110 may vary, e.g., both paste reservoir 120 and paste pump 110 may be set perpendicularly to printing head 150 (see, e.g., Figures 2A-2C and 3), or one or both of paste reservoir 120 and paste pump 110 may be set at an angle to printing head 150. For example, paste pump 110 may be set obliquely to spread its weight more evenly over printing head 150, as illustrated schematically in Figures 1A-1C. id="p-31" id="p-31" id="p-31" id="p-31" id="p-31" id="p-31" id="p-31" id="p-31" id="p-31"

[0031] In various embodiments, conduit 135 may be adjusted to conform to any arrangement of paste reservoir 120, paste pump 110 and mixer 130, so as to make paste dispensing apparatus 100 more compact or adjust it to a given space and weight distribution requirements within the printing machine. Holder 145 (see, e.g., Figures 2A-2C) is illustrated schematically as an attachment element for attaching paste dispensing apparatus 100 to the printing machine (see, e.g., U.S. Patent No. 9,616,524 for a non-limiting example). In non-limiting examples, conduit 135 may be connected between an opening (e.g., an exit) 131 in mixer 130 and an opening 138 of connector 137 at entry opening 161 in printing head 150 (see, e.g., Figure 2A), or conduit 135 may be connected between opening 131 in paste pump 110 and opening (e.g., an entry) 138 in mixer 130 (see, e.g., Figure 1A paste pump, with mixer attached to connector 137 at entry opening 161 in printing head 150). 9 id="p-32" id="p-32" id="p-32" id="p-32" id="p-32" id="p-32" id="p-32" id="p-32" id="p-32"

[0032] Figure 4 is a high-level flowchart illustrating a paste dispensing method 200, according to some embodiments of the invention. The method stages may be carried out with respect to paste dispensing apparatus 100 described above, which may optionally be configured to implement method 200. Method 200 may comprise the following stages, irrespective of their order. id="p-33" id="p-33" id="p-33" id="p-33" id="p-33" id="p-33" id="p-33" id="p-33" id="p-33"

[0033] Paste dispensing method 200 may comprise maintaining continuous paste circulation through an internal cavity of a printing head having at least one dispensing opening which is in fluid communication with the internal cavity (stage 210). Paste dispensing method 200 may further comprise mixing the paste during the continuous paste circulation (stage 220). id="p-34" id="p-34" id="p-34" id="p-34" id="p-34" id="p-34" id="p-34" id="p-34" id="p-34"

[0034] In certain embodiments, paste dispensing method 200 may comprise adjustably pressurizing the paste to maintain the paste circulation and control the dispensing of the paste through the dispensing opening(s) (stage 230), possibly by measuring paste pressure and adjusting the pressure respectively (stage 232). id="p-35" id="p-35" id="p-35" id="p-35" id="p-35" id="p-35" id="p-35" id="p-35" id="p-35"

[0035] In certain embodiments, paste dispensing method 200 may comprise mixing paste exiting the internal cavity of the printing head with pressurized paste to compensate for paste dispensed through the dispensing opening(s) (stage 240). id="p-36" id="p-36" id="p-36" id="p-36" id="p-36" id="p-36" id="p-36" id="p-36" id="p-36"

[0036] Advantageously, paste dispensing apparatus 100 and methods 200 maintain continuous paste circulation through the printing head assures continuous and efficient mixing of the metal paste – and thereby assure the paste retains its specified mechanical and composition characteristics, and also thereby prevent accumulation of paste residues within the printing head – overcoming the challenge of maintaining long term effective deposition of the metal paste filler, while retaining specified mechanical and composition characteristics of the metal paste.. id="p-37" id="p-37" id="p-37" id="p-37" id="p-37" id="p-37" id="p-37" id="p-37" id="p-37"

[0037] In the above description, an embodiment is an example or implementation of the invention. The various appearances of "one embodiment", "an embodiment", "certain embodiments" or "some embodiments" do not necessarily all refer to the same embodiments. Although various features of the invention may be described in the context of a single embodiment, the features may also be provided separately or in any suitable combination. Conversely, although the invention may be described herein in the context of separate embodiments for clarity, the invention may also be implemented in a single embodiment. Certain embodiments of the invention may include features from different embodiments disclosed above, and certain embodiments may incorporate elements from other embodiments disclosed above. The disclosure of elements of the invention in the context of a specific embodiment is not to be taken as limiting their use in the specific embodiment alone. Furthermore, it is to be understood that the invention can be carried out or practiced in various ways and that the invention can be implemented in certain embodiments other than the ones outlined in the description above. id="p-38" id="p-38" id="p-38" id="p-38" id="p-38" id="p-38" id="p-38" id="p-38" id="p-38"

[0038] The invention is not limited to those diagrams or to the corresponding descriptions.

For example, flow need not move through each illustrated box or state, or in exactly the same order as illustrated and described. Meanings of technical and scientific terms used herein are to be commonly understood as by one of ordinary skill in the art to which the invention belongs, unless otherwise defined. While the invention has been described with respect to a limited number of embodiments, these should not be construed as limitations on the scope of the invention, but rather as exemplifications of some of the preferred embodiments. Other possible variations, modifications, and applications are also within the scope of the invention. Accordingly, the scope of the invention should not be limited by what has thus far been described, but by the appended claims and their legal equivalents. 11

Claims (20)

CLAIMS CLAIMED IS:

1. A paste dispensing apparatus comprising: a printing head comprising, in fluid communication, at least two feeding openings, an internal cavity and at least one dispensing opening, wherein paste in the internal cavity is dispensed through the at least one dispensing opening on a workpiece, and a pressurized paste supply unit configured to circulate paste through the printing head, wherein a pressure in the pressurized paste supply unit is adjusted to maintain continuous circulation of the paste through the feeding openings and the internal cavity and to control dispensing of the paste through the at least one dispensing opening.

2. The paste dispensing apparatus of claim 1, wherein the pressurized paste supply unit is further configured to adjust a pressure of the paste in the internal cavity.

3. The paste dispensing apparatus of claim 2, further comprising at least one pressure sensor configured to provide a signal indicative of the pressure of the paste in the internal cavity.

4. The paste dispensing apparatus of claim 3, wherein the at least one pressure sensor is configured to be adjacent to the entry opening and/or the exit opening.

5. The paste dispensing apparatus of claim 3, further comprising at least one controller, configured to control the pressurized paste supply unit based on the signal from the at least one pressure sensor to adjust the pressure of the paste in the internal cavity.

6. The paste dispensing apparatus of any one of claims 1-5, wherein the pressurized paste supply unit is further configured to introduce the paste into the internal cavity via at least one entry opening of the at least two feeding openings and to receive the circulated paste via at least one exit opening of the at least two feeding openings.

7. The paste dispensing apparatus of claim 6, wherein the pressurized paste supply unit comprises a pressure-controlled paste reservoir, a paste pump and a mixer that are in fluid communication, wherein the pressure-controlled paste reservoir is configured to deliver paste to the paste pump, which is configured to deliver the paste through the mixer to the at least one entry opening, and wherein the pressurized paste supply unit 12 P-604380-IL is further configured to mix paste from the at least one exit opening with the paste delivered from the pressure-controlled paste reservoir to the paste pump.

8. The paste dispensing apparatus of claim 7, further comprising at least one pressure sensor configured to measure a pressure of the circulating paste and at least one controller, configured to adjust a pressure in the pressure-controlled paste reservoir and/or the paste pump with respect to the measured pressure of the circulating paste.

9. The paste dispensing apparatus of claim 8, wherein the pressure-controlled paste reservoir and the paste pump open adjacently to the at least one exit opening and a conduit connects an exit of the mixer to the at least one entry opening.

10. The paste dispensing apparatus of claim 8, wherein the pressure-controlled paste reservoir and the paste pump open adjacently to the at least one exit opening, the mixer is adjacent to the at least one entry opening, and a conduit connects the paste pump to the mixer.

11. The paste dispensing apparatus of any one of claims 1-10, wherein the pressurized paste supply unit comprises a pressure-controlled paste reservoir and a paste pump, and wherein the paste pump has an entry fluidly communicating with an exit opening of the pressure-controlled paste reservoir so as to pump paste from the pressure-controlled paste reservoir into the internal cavity of the printing head.

12. The paste dispensing apparatus of claim 11, wherein the pressurized paste supply unit further comprises at least one paste mixer fluidly communicating an exit of the paste pump to an entry opening of the printing head and configured to mix the circulating paste.

13. The paste dispensing apparatus of claim 12, wherein the entry of the paste pump is in fluid communication with the exit opening thereof.

14. The paste dispensing apparatus of claim 12 or 13, wherein the at least one paste mixer is a static mixer that mixes the paste under pressure.

15. The paste dispensing apparatus of any one of claims 12-14, further comprising a first conduit connecting an exit of the at least one mixer to the entry opening.

16. The paste dispensing apparatus of any one of claims 12-15, further comprising a second conduit connecting the paste pump to the at least one paste mixer. 13 P-604380-IL

17. The paste dispensing apparatus of any one of claims 12-15, further comprising a pressure sensor associated with the at least one paste mixer.

18. A paste dispensing method comprising maintaining continuous paste circulation through an internal cavity of a printing head having at least one dispensing opening which is in fluid communication with the internal cavity.

19. The paste dispensing method of claim 18, further comprising at least one of: mixing the paste during the continuous paste circulation, adjustably pressurizing the paste to maintain the paste circulation and control the dispensing of the paste through the at least one dispensing opening, measuring paste pressure and adjusting the pressure respectively, or mixing paste exiting the internal cavity of the printing head with pressurized paste to compensate for paste dispensed through the at least one dispensing opening.

20. A paste dispensing method for a paste dispensing apparatus, wherein the paste dispensing apparatus comprises a printing head and a pressurized paste supply unit, and wherein the printing head comprises an entry opening, an exit opening, an internal cavity communicating with the entry and exit openings, and at least one dispensing opening, the paste dispensing method comprising: circulating paste successively through the entry opening, the internal cavity and the exit opening of the printing head, dispensing the paste in the internal cavity via the at least one dispensing opening on a workpiece and at least one of: adjusting a pressure of the paste in the internal cavity by the pressurized paste supply unit, providing a signal indicative of the pressure of the paste in the internal cavity by at least one pressure sensor, wherein the pressurized paste supply unit is controlled based on the signal from the at least one pressure sensor to adjust the pressure of the paste in the internal cavity, or mixing paste exiting the internal cavity of the printing head with the paste supplied by the pressurized paste supply unit to compensate for paste dispensed through the at least one dispensing opening. 14