Abstract
The invention relates to a method for applying an image of an electrically conductive material onto a recording medium. In the method, the recording medium is heated and the electrically conductive material is jetted onto the recording medium. The invention further relates to a device for ejecting droplets of an electrically conductive fluid onto a recording medium.
Claims
1. A method for applying an image of an electrically conductive material onto a recording medium, the method comprising the steps of: selecting an electrically conductive fluid and selecting a recording medium comprising a first material, wherein the electrically conductive fluid and the first material are capable of forming an eutectic alloy; heating at least a part of the recording medium; ejecting a droplet of the electrically conductive fluid onto the part of the recording medium, wherein the electrically conductive fluid is a molten metal or a molten semiconductor; and forming the eutectic alloy, wherein the at least a part of the recording medium is heated to a temperature above a melting point of the first material, and the recording medium is a silicon substrate.
2. The method according to claim 1, wherein in step b) the recording medium is heated using a laser.
3. The method according to claim 1, wherein electrically conductive fluid is selected from at least one of the group consisting of silver, gold, copper.
4. The method according to claim 1, wherein the electrically conductive fluid has a melting point of at least 300 C.
5. The method according to claim 2, wherein the electrically conductive fluid has a melting point of at least 300 C.
6. The method according to claim 3, wherein the electrically conductive fluid has a melting point of at least 300 C.
7. The method according to claim 1, wherein the at least a part of the recording medium is heated to the temperature above the melting point of the first material before ejecting the droplet of the electrically conductive fluid onto the part of the recording medium.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) These and further features and advantages of the present invention are explained hereinafter with reference to the accompanying drawings showing non-limiting embodiments and wherein:
(2) FIG. 1 shows a cross-sectional view of an embodiment of the device for ejecting droplets of an electrically conductive fluid.
(3) FIG. 2 shows a schematic representation of a two component phase-diagram.
(4) FIG. 3A-H show examples of the solidification of two different compositions according to the phase-diagram of FIG. 2.
(5) FIG. 4 shows a flow diagram of a method according to a first embodiment of the present invention.
(6) FIG. 5 shows a flow diagram of a method according to a second embodiment of the present invention.
DETAILED DESCRIPTION OF THE DRAWINGS
(7) In the drawings, same reference numerals refer to same elements.
(8) FIG. 1 shows a cross-sectional view of a part of a device 1 for ejecting droplets of an electrically conductive fluid, for example a molten metal or a molten semiconductor.
(9) The device for ejecting droplets 1 is provided with an orifice 4 through which a droplet of the fluid may be ejected. The orifice 4 is a through hole extending through a wall of a fluid chamber body 3. In the fluid chamber body 6 a fluid chamber is arranged. The fluid chamber 6 is configured to hold the electrically conductive fluid. In case the fluid to be ejected is a molten metal or a molten semiconductor, ejection of droplets of the fluid typically takes place at a high temperature. For example, the melting point of copper is 1085 C., the melting point of silver is 962 C. In that case, the fluid chamber body 6 needs to be heat resistant. Also, an inner wall of the through hole forming the orifice 4 needs to be wetting for the fluid in order to enable the fluid to flow through the orifice 4. If the surface of the fluid chamber body 6 is wetting with respect to the fluid, the fluid will not tend to form beads, but will easily spread and flow over the surface and is thus enabled to flow into and through the orifice 4.
(10) Several techniques may be applied for actuating the electrically conductive fluid, such as piezoelectric actuation or thermal actuation. The device shown in FIG. 1, comprises actuating electrodes 12a, 12b and a magnet 8 as actuation means. The magnet 8 may be applied to provide a magnetic field. The actuating electrodes 12a, 12b may be applied to apply an electric current to the electrically conductive fluid. As explained above, providing a current through an electrically conductive fluid that is placed in a magnetic field, results in the generation of a Lorentz force in the fluid. Thus, in the device shown in FIG. 1, the electrically conductive fluid may be actuated by Lorentz actuation. For applying a Lorentz force in the conductive medium, the jetting device 1 is provided with permanent magnets 8. More than one magnet may be applied. Optionally, the magnet 8 may be arranged between magnetic field concentrating elements (not shown), for example magnetic field concentrating elements made of a magnetic field guiding material such as iron. The jetting device 1 is further provided with two actuating electrodes 12a, 12b (hereinafter also referred to as actuating electrodes 12) both extending into the fluid chamber body 6 through a suitable through hole such that at least a tip of each of the actuating electrodes 12 is in direct electrical contact with the conductive medium present in the fluid chamber 6. The actuating electrodes 12 are each operatively connected to a suitable electrical current generator (not shown) such that a suitable electrical current may be generated through the electrodes 12 and the electrically conductive fluid present between the tips of the electrodes 12. Optionally, the magnets 8 may be cooled by suitable cooling means.
(11) The electrodes 12 are made of a suitable material for carrying a relatively high current, and optionally, for being resistant against high temperatures. The electrodes 12 may be suitably made of tungsten (W), although other suitable materials are contemplated.
(12) A recording medium 10 is provided. By operation of the jetting device 1 described above the recording medium 10 may be provided with an image of the electrically conductive fluid comprised in the fluid chamber body 6. The recording medium 10 may be supported and positioned with respect to the jetting device 1 using suitable recording medium holding means (not shown). Optionally, the recording medium holding means may move the recording medium with respect to the jetting device 1, such that different parts of the recording medium 10 may be provided with the image of the electrically conductive medium. Alternatively, or additionally, the jetting device 1 may be provided with suitable moving means (not shown), such that the jetting device 1 may be moved with respect to the recording medium 10.
(13) The jetting device is further provided with heating means 13 for heating the recording medium 10. In the embodiment shown in FIG. 1, the heating means locally heats the recording medium 10 by locally applying radiation 13b to the recording medium. The heating means 13 may be e.g. a lamp or a laser. The radiation 13b may be e.g. visible light, infrared light or UV radiation. Alternatively, any suitable heating means may be applied. The heating means 13 may locally heat the recording medium 10 or may heat the whole recording medium 10 in one time. The heating means may heat the recording medium 10 using any suitable type of heat providing means, e.g. an electric current, a flame or radiation.
(14) In the embodiment shown in FIG. 1, the fluid chamber 6 is provided with a heating coil 24 for heating the material contained in the fluid chamber 23 and optionally also the fluid chamber body. By heating the fluid and keeping the fluid within a predetermined temperature range, the temperature op the recording medium 10 may be more easily controlled.
(15) The jetting device 1 as shown in FIG. 1 is further provided with a control unit 11. The control unit 11 is configured to control the heating of the substrate 11 by controlling the amount of energy provided to the recording medium 10 by the heating means 13. The control unit 11 is operatively connected to the heating means 13, for example via an electrical connection 14a. The amount of energy that is to be supplied to the recording medium 10 may depend e.g. on the type of substrate, temperature of environment, temperature and size of droplets of the electrically conductive fluid expelled through the nozzle 4, frequency of droplet ejection, etc. Based on any of these conditions, the control unit may suitable control the heating unit 13 to provide the desired amount of heat. As shown in FIG. 1, the control unit may also be operatively connected to the other parts of the jetting device, as is shown by connection 14b. For example, the control unit 11 may be connected to the heating coil 24 configured to heat the fluid in the fluid chamber 23.
(16) FIG. 2 shows an example of a two component phase diagram of the two components M and S. A phase diagram is known in the art as a diagram used to show conditions at which thermodynamically distinct phases can occur at equilibrium. M represents the first component. For example, M may be a metal which is applied onto a recording medium. S represents the second component S. Component S may be a suitable material for the recording medium, such as Si or Ge. The two-phase diagram as depicted does not show any pressure dependencies. However, in practice, the dependency on pressure may be limited for solid and liquid systems. The vertical axis schematically shows the temperature. The horizontal axis represents the composition of the system. The leftmost part of the horizontal axis corresponds to a system consisting of component M. The rightmost part of the horizontal axis corresponds to a system consisting of component S. The phase-diagram as depicted in FIG. 2 shows a eutectic point. The eutectic point is located at the intersection of the eutectic temperature (T.sub.eut) and the eutectic composition (X.sub.eut). The eutectic composition X.sub.eut is a mixture of the components M and S and has a single chemical composition. For example, the phase-diagrams of SiAl and SiAg systems show a eutecticum. The eutectic composition solidifies at a temperature lower than any other composition made up of the same ingredients. 4 Different areas may be observed in the phase-diagram depicted in FIG. 2. The first area is delimited by the horizontal axis and T.sub.eut and is indicated as solid phase. In this first area, the material is solid for all possible compositions. In a second area, indicated as liquid phase, the material is fluid, irrespective of the composition. In a third area, indicated as Solid M+Liquid Phase, solid M and a liquid phase comprising both M and S may coexist. In a fourth area, indicated as Solid S+Liquid Phase, solid S and a liquid phase comprising both M and S may coexist.
(17) In FIG. 2, two compositions are indicated; X.sub.1 and X.sub.2. For each of these compositions, it will be explained below, with reference to FIG. 3A-H, what happens when a liquid having either of the compositions X.sub.1 or X.sub.2, cools down and solidifies. As mentioned above, the electrically conductive material may be jetted onto the recording medium. The droplet of electrically conductive material may preferably be fluid when it impacts on the recording medium. For elucidating the present invention, it is presumed that the electrically conductive material corresponds to component M and the material of the recording medium corresponds to component S. Further, it is presumed that at least an upper layer of the recording medium is locally in a molten state. If a droplet of the molten electrically material is jetted onto the partially molten recording medium, component M and component S may mix, e.g. because of the impact of the droplet. A mixed fluid may be formed, comprising both M and S. It is presumed that composition X.sub.1 (X.sub.1(L)) is formed when the droplet is applied onto the recording medium. This is depicted in FIG. 3A. Please note that in another embodiment, a different composition may be formed when a droplet is applied onto the recording medium.
(18) According to the phase-diagram, the fluid will cool down, without its composition being changed, until the line separating the area liquid phase from the area solid M+liquid phase is reached. Once this line is reached at T.sub.1, phase separation starts taking place. Pure M solidifies from the liquid phase, forming crystals of M 30, which is depicted in FIG. 3B. By crystallization of M, the liquid L becomes more rich in component S. The crystallization of M continues, upon further decrease in temperature. Therefore, more crystals of M 30 may be formed (see FIG. 3C) and the liquid L becomes even richer in S. Crystallization of M continues until the eutectic point is reached. When the eutectic point is reached, no more liquid L is present and the eutectic composition X.sub.eut solidifies, thereby forming X.sub.eut crystals 31. Thus, by cooling down a fluid having the composition X.sub.1, a solid may be formed, comprising crystals of M 30 and crystals of X.sub.eut 31, wherein the crystals of M 30 are surrounded by the X.sub.eut crystals 31, as is shown in FIG. 3D. In a second embodiment, composition X.sub.2 is formed when the droplet is applied onto the recording medium. According to the phase-diagram, the fluid (X.sub.2(L)) will cool down, without its composition being changed (FIG. 3E), until the line separating the area liquid phase from the area solid S+liquid phase is reached. Once this line is reached at T.sub.2, phase separation starts taking place. Pure S solidifies from the liquid phase, forming crystals of S 32 (FIG. 3F). By crystallization of S, the liquid L becomes more rich in component M. The crystallization of S continues, upon further decrease in temperature, thereby forming more crystals of component S 32 (FIG. 3G). Crystallization of S continues, the liquid phase L thereby becoming more rich in component M, until the eutectic point is reached. When the eutectic point is reached, no more liquid L is present and the eutectic composition X.sub.eut solidifies, thereby forming X.sub.eut crystals 31. Thus, by cooling down a fluid having the composition X.sub.2, a solid may be formed, comprising crystals of S 32 and crystals of X.sub.eut 31, wherein the crystals of S 32 are surrounded by the X.sub.eut crystals 31, as is shown in FIG. 3H.
(19) Thus, by suitably controlling the temperature of the recording medium, the composition of the recording medium provided with the image may be suitably controlled. Please note that the heating means 13 configured to heat the recording medium 10 may not only be used to heat the recording medium 10 before application of a droplet, it may also be applied to let the recording medium 10 provided with the image of the electrically conductive material cool down in a controlled manner, by suitably applying heat to the recording medium 10 provided with the image after the electrically conductive material has been provided to said medium 10. By controlled cooling of the system, the system may solidify in a controlled way, thereby allowing the desired solids to be formed.
(20) Depending on the conditions of the jetting process, e.g. the amount of material of the recording medium that is molten, the volume of a droplet applied on said medium and the extent of mixing between the electrically conductive medium and the material of the recording medium, different solid compositions may be formed upon cooling of the system. Moreover, the solid compositions formed during solidification of the mixed fluids may be present in addition to crystals of the electrically conductive material. For example, solid electrically conductive material may be present, due to limited mixing with molten material of the recording medium. The presence of crystals, comprising a component comprising both M and S may provide the printed medium with improved properties, such as improved electrical conductivity. The mixed crystals may be randomly distributed throughout the image provided on the recording medium. Alternatively, the mixed crystals may only be present at an interface layer between recording medium and electrically conductive material.
(21) FIG. 4 shows a flow diagram of a method according to a first embodiment of the present invention for applying an image of an electrically conductive material onto a recording medium. In step 40, the print job is started. The device 1 for jetting droplets of the electrically conductive fluid is then in an operative state and may be jetting, thereby expelling droplets of the electrically conductive fluid. The control unit 11 may control expelling of droplets by the inkjet device 1. In a second step 41, the recording medium is heated. Heating of the recording medium may be done using suitable heating means. In addition to heating the recording medium, the fluid chamber body comprising the electrically conductive material may optionally be heated as well. In a third step 42, the temperature of the recording medium T.sub.rec. med. may be measured. The temperature of the recording medium may be measured using suitable temperature measuring means, such as, but not limited to a thermocouple or a pyrometer. Furthermore, in the third step 42, T.sub.rec. med. may be compared to predetermined temperatures T.sub.min and T.sub.max. In case the temperature of the recording medium is in the predefined temperature range between T.sub.min and T.sub.max, the print job may be continued in the fourth step 43. When the print job is continued, the second step may be repeated and the recording medium may be heated again. After heating of the recording medium, its temperature may be measured, etc. In case the temperature of the recording medium exceeds T.sub.max, and thus is higher than the predefined temperature range, the heating of the recording medium is paused in the fifth step 44. By pausing the heating, the recording medium may cool down and its temperature may drop. After pausing the heating, the temperature may be measured again and it may again be compared to predetermined values. As long as the temperature of the recording medium exceeds the predefined limit T.sub.max, the cycle defined by the third step 42 and the fifth step 44 may be repeated. When the temperature is again within the predefined temperature range, the print job may be continued in the fourth step 43.
(22) In case the temperature of the recording medium is lower than T.sub.min, the second step 41 is repeated and the recording medium is heated. After repeating the second step, the temperature of the recording medium may be measured again in the third step 42. The cycle defined by the second step 41 and the third step 42 may be repeated as long as the temperature of the receiving medium is lower than T.sub.min, thereby bringing the temperature within the predefined temperature range.
(23) FIG. 5 shows a flow diagram of a method according to a second embodiment of the present invention for applying an image of an electrically conductive material onto a recording medium. In step 50, the print job is started. The device 1 for jetting droplets of the electrically conductive fluid is then in an operative state and may be jetting, thereby expelling droplets of the electrically conductive fluid. The control unit 11 may control expelling of droplets by the inkjet device 1. In a second step 51, the control unit may read the job settings of a print job. The job settings may be stored on a memory means. The job settings may comprise e.g. the type of electrically conductive fluid contained in the fluid chamber body 6, the frequency of droplet ejection and the image to be applied on the recording medium. These job settings may influence the temperature of the recording medium. For example, if the fluid has a high temperature (e.g. is a molten metal), providing the droplet onto the recording medium may provide the recording medium with heat. The amount of heat applied to the recording medium may therefore be influenced by the number and size of droplets applied to the recording medium; the more electrically conductive material is applied to the recording medium, the more heat may be supplied to the recording medium. In a third step 52, the temperature of the fluid is measured. The temperature of the fluid may be at least the melting point of the fluid. The fluid may be measured directly, or may be measured indirectly, e.g. by measuring the temperature of the fluid chamber body 6. In a fourth step 53, the temperature of the recording medium is measured. This may be done by using suitable means, as described with regard to FIG. 4. Please note that in an alternative embodiment, the respective order of the second step 52, the third step 52 and the fourth step 53 may be interchanged. However, when the second to fourth step 51-53 are carried out, sufficient data may be available to determine a future temperature of the recording medium T.sub.rec. med. fut.
(24) In a fifth step 54, the future temperature of the recording medium T.sub.rec. med. fut, is determined by the control unit. The future temperature of the recording medium T.sub.rec. med. fut may be determined based on the data acquired in the second to fourth step 51-53. In addition, to determine the future temperature T.sub.rec. med. fut data stored on a memory means may be used. For example, the future temperature T.sub.rec. med. fut may be calculated based on the data acquired in the second to fourth step 51-53, using an algorithm. Alternatively, the future temperature T.sub.rec. med. fut may be calculated based on the data acquired in the second to fourth step 51-53 using a look up table. A look up table may comprise data based on previously carried out measurements.
(25) Additionally, in the fifth step 54, the future temperature of the recording medium T.sub.rec. med. fut, is compared to predetermined temperatures T.sub.min and T.sub.max. In case the future temperature of the recording medium is in the predefined temperature range between T.sub.min and T.sub.max, the print job may be continued in the sixth step 55. When the print job is continued, the second step 51 may be repeated.
(26) In case the future temperature of the recording medium exceeds T.sub.max, no heating of the medium may take place. Moreover, the print job may not be continued, thereby being paused. When the temperature exceeds T.sub.max, the third to fifth step 52-54 may be repeated. If the future temperature of the recording material then still exceeds T.sub.max, then the third to fifth step 52-54 may be repeated again. However, if the future temperature of the recording medium T.sub.rec. med. fut, is then within the predetermined range between T.sub.min and T.sub.max, the print job may be continued in the sixth step 55.
(27) In case the future temperature of the recording medium is lower than T.sub.min, the recording medium may be heated in the seventh step 56. Then, the fourth step 53, wherein the temperature of the recording medium is measured, may be repeated and based thereon, the future temperature of the recording medium T.sub.rec. med. fut may be determined again. The cycle of the fourth, fifth and seventh step 53, 54, 56, may be repeated until the future temperature of the recording medium T.sub.rec. med. fut is within the predetermined temperature range. When the future temperature of the recording medium T.sub.rec. med. fut is within the predetermined temperature range, the print job may be continued in the sixth step 55.
(28) Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. In particular, features presented and described in separate dependent claims may be applied in combination and any advantageous combination of such claims are herewith disclosed.
(29) Further, the terms and phrases used herein are not intended to be limiting; but rather, to provide an understandable description of the invention. The terms a or an, as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms including and/or having, as used herein, are defined as comprising (i.e., open language).
(30) The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
