Method and device for printing substance on target surface of target

Abstract

A printing apparatus (1) for printing a substance on a target surface (TS) of a target (T) is provided. The printing device comprises a carrier (2) having a hydrophobic coating (22) at a first main side (21) for carrying a sample (SB1, SB2, SB3) of the substance to be printed, said sample resting on the coating by means of a contact surface. The printing apparatus further comprises a heater arrangement (23) for locally heating the sample at the contact surface of the sample to vaporize a portion of the sample at one side of its contact surface and to generate a vapour pressure to transfer the remaining portion of the sample towards the target surface. Additionally, a printing method is provided.

Description

Technical Field

[0001] The present invention relates to a device for printing a substance on a target surface of a target.

[0002] The invention also relates to a method for printing a substance on a target surface of a target. Background Art

[0003] International patent application WO2021230746 discloses a method for transferring a substance formed of a sticky functional material to a receiving substrate, wherein the deposited substance is subsequently cured or dried. The cured or dried substance transferred to the target can be used as an electrical insulator, an electrical conductor, a thermal insulator, a thermal conductor, etc.

[0004] The known method provides a plate having a plurality of individually addressable resistive heater elements. In use, a substance is heated with the resistive heater elements to evaporate an interface layer of a sample of the substance at the plate side, thereby generating vapor pressure between the substance and the plate. The vapor pressure exerts a force on the substance, namely ejecting the remaining unvaporized portion of the substance from the plate to transfer it from the plate to a target surface.

[0005] The inventors have discovered that the transfer of heated material sometimes does not occur. Figures 1A to 1D In , the inventors identified various potential causes.

[0006] Figure 1A It is shown how a sample SBA, SBB of a substance SB is deposited on the first side 21 of the plate 2 using screen printing devices 41 , 42 .

[0007] Figure 1B and Figure 1C The plate 2 carrying the samples SBA, SBB, SBC is shown at two subsequent points in time after completion of the deposition process.

[0008] Figure 1D The steps in which the samples SBA, SBB, SBC on the plate are transferred to the target T are shown.

[0009] As Figure 1A As a result of the steps shown, the samples SBA, SBB, SBC are initially deposited on the plate 2 conforming to the openings in the screen 41 .

[0010] like Figure 1B As shown, due to capillary forces, the substances of samples SBA, SBB, and SBC tend to diffuse between the surface and the template or screen (a), resulting in underflow (b).

[0011] At a later point in time, Figure 1C As shown, material spread on the surface tends to dry (c).

[0012] As a result, Figure 1D In the operation shown, the following phenomena may occur. Due to evaporation in sample SBB, shear forces prevent (d) its transfer. Sample SBC is partially released from plate 2 but is retained at one side, so that the material therein is turned over (e) and retained at the plate. A dried residue (e) may also be retained at the plate.

[0013] Unless the plate is cleaned before further use, dried residues remaining on the plate can cause alignment problems and sometimes prevent transfer altogether. The second reason for non-transfer is primarily related to the material properties and geometry of the ink. If the viscosity, elastic modulus and aspect ratio are too low, then the ink may not transfer due to film oscillations.

[0014] As further background, reference is made to the following patent publications:

[0015] US2022 / 119659 discloses an indirect printing process in which the ink image is pre-treated (e.g., coated) with an aqueous formulation before being deposited onto the release surface of an intermediate transfer member (ITM). The ink image residue (e.g., together with a dried treatment film layer) is transferred to the printing substrate by pressure contact between the ITM and the printing substrate.

[0016] US2005 / 009327 discloses an apparatus and method for forming a wiring pattern on a substrate, an electronic device and a method for producing the same, wherein the viscosity of the wiring material when the material is supplied from the material supply to the transfer plate is different from the viscosity of the wiring material when the material is transferred from the transfer plate to the substrate by utilizing energy supplied from an energy supply.

[0017] US2014 / 199473 discloses a device for providing a patterned structure. The device may include one or more of a heat source, a photon radiation source, and a microwave source as a curing device for curing a conductive material precursor. Summary of the invention

[0018] It is a first object of the present disclosure to provide an improved apparatus for printing a substance on a target surface of a target which alleviates one or more of the above-mentioned disadvantages.

[0019] It is a second object of the present disclosure to provide an improved method for printing a substance on a target surface of a target which alleviates one or more of the above-mentioned disadvantages.

[0020] According to a first object, there is provided an improved printing device for printing a substance on a target surface of a target, as defined below. The improved printing device comprises a carrier having a hydrophobic coating at a first main side for carrying a sample of the substance to be printed. Thus, the sample rests on the hydrophobic coating via a contact surface. The hydrophobic coating has a relatively low surface energy, for example at most 50 mJ / m 2 , or in some examples up to 30 mJ / cm 2 . Therefore, the sample of the substance to be deposited has a relatively high contact angle on the hydrophobic surface. In many cases, a contact angle of about 90° is advantageous, because in this case the sample of the substance tends to maintain the shape on the hydrophobic surface by which it was deposited during the preparation step. However, if the sample is intended to be printed as a droplet on the target surface, a larger contact angle may be advantageous.

[0021] The printing apparatus further comprises a heater arrangement for locally heating the sample at a contact surface of the sample to evaporate a portion of the sample at one side of the contact surface thereof and to generate vapor pressure to transfer the remaining portion of the sample towards the target surface.

[0022] Due to the hydrophobicity of the coating on the first main side of the carrier, the sample of the substance does not tend to flow out, but rather presents a relatively large contact angle with the carrier surface. As a result, in the time interval between the deposition on the carrier and the transfer to the target, the shear forces generated by the evaporation of the liquid components of the sample are relieved.

[0023] Furthermore, due to the large contact angle, the specimen has a high aspect ratio (thickness divided by diameter). This reduces the amplitude of the oscillating membrane during transfer (higher stiffness), which reduces the risk of the ink hitting the heater plate again. This also increases the chances of the ink falling in a convex shape.

[0024] Due to the limited spreading behavior on the hydrophobic coating, smaller features can be printed.

[0025] Another advantage is that the release of the ink from the stencil onto the non-stick hydrophobic coating will be better because the temperature gradient (and therefore, the viscosity gradient) is quite large over the film thickness. The shear forces between the ink and the stencil will be lower due to the lower viscosity, while the adhesion to the cold hydrophobic coating will increase due to the higher viscosity. Especially for high aspect ratio openings in the stencil, where the contact area with the die handle is relatively large, it is easier to completely release the ink onto the heater plate.

[0026] The hydrophobic coating is preferably relatively thin so that its thermal resistance is low, for example in the range of about 0.001 microns to about 10 microns. Suitable materials for the hydrophobic coating are ceramic materials such as Si3N4 or Al2O3.

[0027] In operation, the heater facility rapidly heats the material at the side facing the hydrophobic surface. As a result, the interface layer of the material at the plate side is evaporated. The vapor creates vapor pressure between the material and the plate. The vapor pressure exerts a force on the remaining material, causing it to transfer from the plate to the target surface.

[0028] In one embodiment, the heater arrangement comprises a resistive heater layer arranged between the carrier and the hydrophobic coating. An advantage of this embodiment is that the heater arrangement requires only minimal space and can be easily controlled.

[0029] In another embodiment, the heater means is provided as a pulsed photon radiation source, such as a laser or a flash lamp, at a second main side of the carrier opposite to the first main side. In operation, the pulsed photon radiation source generates a pulsed light beam which is transported through the carrier and the hydrophobic coating and is absorbed at the contact surface of the sample of the substance to be printed. As an alternative, a light absorbing layer is provided between the transparent carrier and the hydrophobic coating. This alternative is more similar to the embodiment comprising a resistive heater layer, the substance being heated indirectly by conduction via the hydrophobic coating.

[0030] In some embodiments, the printing device also provides cooling facilities for forced cooling of the carrier when the carrier is not operable to transfer the substance. In one embodiment, the support unit includes a plurality of support elements that support the carrier at the second main side and define a cooling channel for conducting a cooling liquid, such as water. Therefore, the carrier can be quickly cooled or maintained at a low temperature. It may be advantageous to maintain the carrier at a low temperature until the point in time when the substance is transferred so as to keep the viscosity of the substance at a high value. In some examples of the latter embodiment, the support element also defines an emptying groove facing the second main side of the carrier. The emptying channel is surrounded by the wall of the emptying groove and the surface of the carrier supported by the support unit. When the emptying channel is evacuated with a vacuum pump, good thermal contact between the support element and the carrier is achieved. This temperature-controlled vacuum chuck for the carrier optimizes the control of printing quality and repeatability. For example, when an ink layer with an initial temperature of about 20°C is printed on a cooled carrier with a much lower temperature, the viscosity increases significantly. Simulations and experiments show that higher viscosity helps to reduce the amplitude of the oscillating film of the substance when it is transferred, thereby reducing the chance of the substance touching the carrier again after being ejected from the carrier surface. Since the film thickness is usually in the order of 100 microns or less, the substance quickly (<1 second) reaches a relatively low carrier temperature. This means that only the support unit and the carrier supported by it need to be temperature controlled, rather than the entire system. Therefore, the deposition of the substance on the carrier, for example by template / screen printing, can be done at room temperature, which makes the printer system cheaper and simpler. Although the metal template has a relatively high thermal conductivity, the total contact time between the hot template and the cold plate is very short when a printing gap is used. Therefore, the heat transfer from the template to the carrier is limited. When printing samples with a high aspect ratio, this is even particularly advantageous when the temperature of the template or mask is higher than the temperature of the carrier. On the one hand, due to the relatively high temperature of the mask, the sample of the substance can be released from the mask with relatively low shear forces, because its interface with the mask has a relatively low viscosity. On the other hand, the viscosity of the interface of the sample of the substance in contact with the cold surface of the hydrophobic coating increases, so the adhesion of the sample on the hydrophobic surface increases. The higher the ratio of the interface area with the mask to the interface area of ​​the hydrophobic coating surface, the more favorable this effect is.

[0031] Importantly, in operation, the material to be transferred is heated to hundreds of degrees Celsius in microseconds at its interface with the hydrophobic surface. Therefore, before it can be heated, the remaining material has been ejected by vapor pressure. For low thermal conductivity materials (<1W / mK), the heat penetration depth is typically less than 2μm. This means that most of the film thickness remains low temperature, so the viscosity will remain high, and the average hardness is higher. This improves the printability of low viscosity fluids (<10Pa*s at 20℃) and expands the printable aspect ratio and film width.

[0032] When cooling the heater plate, it is best to take measures to prevent condensation. If condensation occurs, the entire surface of the carrier will be covered with small water droplets. When heated quickly, all these droplets will be transferred along with the ink film. Therefore, it is important to keep the carrier above the dew point when it is cooled. This can be easily achieved by blowing dry air or nitrogen over the surface. If the relative humidity is, for example, 25% and the air temperature is 20°C, the carrier can be cooled to 0°C without any condensation occurring. Therefore, lower humidity increases the drying speed and increases the chance of edge drying. However, the lower temperature of the carrier offsets this effect. In one embodiment, the printing device includes a controller for controlling environmental conditions, such as temperature and ambient gas composition. Therefore, the environmental conditions should be sufficient to avoid condensation while minimizing evaporation of the substance before it is transferred to the target.

[0033] In some embodiments, a thermal sensor is mounted in one or more of the support elements. Thus, the temperature of the carrier can be accurately determined, in particular if good thermal contact is achieved by draining the drain channel.

[0034] In an example of an embodiment in which the heater facility includes a resistive heater layer, the carrier includes a plurality of electrical contact elements of the resistive heater layer at its second main side opposite to the first main side. The printing device may also include a support unit for supporting the carrier, the carrier being provided with spring-loaded electrical contact pins. When the support unit supports the carrier at the second main side, the spring-loaded electrical contact pins cooperate with the corresponding electrical contact elements. In the case where the support unit includes support elements as described above, these support elements can be arranged between the spring-loaded electrical contact pins. In an example thereof, the ends of the spring-loaded electrical contact pins can move at least in a range from a level defined by a support surface of the support element to above the support surface.

[0035] In some embodiments, the printing apparatus is configured to maintain the carrier at a predetermined temperature prior to the step of causing the transfer by a combination of cooling with the support unit and selective heating with the resistive heater layer. By selectively heating the carrier with the resistive heater layer, spatial distribution variations of temperature (if any) can be quickly minimized. In another embodiment, a separate temperature control layer (e.g., on a PCB) with a resistive heater is used to equalize the temperature across the printed board. For example, the separate temperature control layer is controlled by an appropriate temperature control system that provides a uniform temperature based on input from temperature sensors distributed on the separate temperature control layer.

[0036] In one embodiment, the printing device further comprises a screen printing unit or a stencil printing unit for depositing the substance on the hydrophobic coating. In particular for high aspect ratio structures, it is advantageous when components of the printing unit are also provided with a hydrophobic coating, so that the substance to be printed is easily transferred from the stencil or screen to the surface of the hydrophobic coating.

[0037] According to a second object, an improved method for printing a substance on a target surface of a target is provided.

[0038] According to an improved method, the carrier is provided with a hydrophobic coating at the first main side.

[0039] A sample of the substance to be printed is deposited on the hydrophobic coating so that the sample is in contact with the contact surface on the hydrophobic coating.

[0040] The sample is then heated at its contact surface to evaporate a portion of the sample at one side of the contact surface, thereby generating vapor pressure that causes the remainder of the sample to transfer to the target surface.

[0041] Heating is performed at such a high rate that only the interface layer of the material evaporates, while the rest is transferred by vapor pressure. For example, once the material is completely cooled, use 50-250kW / cm 2 The heat flux is about 0.2-2 J / cm 2 The flux is used to evaporate a thin layer, such as a few microns of liquid at the interface. This causes pressure to build up and causes the remaining part, such as a material film with a thickness of tens of microns or more, to be transferred.

[0042] In an embodiment according to the improved method, the step of providing the carrier with a hydrophobic layer is preceded by the step of providing a resistive heater layer at the first main side of the carrier and performing local heating by means of the resistive heater layer arranged between the carrier and the hydrophobic coating.

[0043] Various options are available for providing a support with a hydrophobic or oleophobic coating. For example, atomic layer deposition, sputtering, chemical vapor deposition, evaporation. The hydrophobic coating achieves high thermal conductivity when it is relatively thin, for example less than a few micrometers. The small value of the thickness of the hydrophobic coating also contributes to its stability under the rapid temperature changes that occur during use. Atomic layer deposition is particularly suitable for obtaining extremely thin coatings. For example, an Al2O3 coating can be applied by this process.

[0044] In an embodiment of the improved method, the substance to be printed is deposited on the hydrophobic coating by stencil printing or screen printing.

[0045] In an embodiment of the improved method, the carrier with the hydrophobic coating is at least partially kept at a temperature below ambient temperature, at least from the moment the substance is deposited thereon until the substance is transferred. This minimizes evaporation and increases the viscosity of the substance. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] These and other aspects are described in more detail with reference to the accompanying drawings, in which:

[0047] Figures 1A to 1DVarious phenomena that may hinder the process of thermally induced transfer of matter to a target surface are shown;

[0048] Figure 2 schematically illustrates an embodiment of an improved printing apparatus as disclosed herein;

[0049] Figure 3 A further embodiment of the improved printing apparatus is shown in more detail;

[0050] FIG. 4A to FIG. 4D The steps of an embodiment of an improved printing method as disclosed herein are shown;

[0051] Figure 5 The simulation results of the improved printing device are shown;

[0052] Fig. 6A shows the relationship between temperature and viscosity of a typical substance to be transferred by an embodiment of the improved printing apparatus or the improved printing method;

[0053] Figure 6B The estimated oscillation amplitudes of the samples of the substances during transfer are shown, which depend on their viscosity. DETAILED DESCRIPTION

[0054] In the drawings, like reference numerals refer to like elements unless otherwise specified.

[0055] In the following detailed description, many specific details are set forth to provide a thorough understanding of the present invention. However, it will be appreciated by those skilled in the art that the present invention can be implemented without these specific details. In other cases, well-known methods, procedures, and components are not described in detail in order not to obscure aspects of the present invention.

[0056] Figure 2 A printing device 1 for printing a substance on a target surface TS of a target T is schematically shown. For example, the target T is a component to be manufactured, and the substance can have predetermined physical characteristics, such as a specific electrical conductivity and a specific thermal conductivity. For example, the substance can be an electrically insulating and thermally insulating material, an electrically insulating and thermally conductive material, an electrically conductive and thermally insulating material, and an electrically conductive and thermally conductive material. These substances are also commonly referred to as inks or pastes, for example, including nanoparticles or microparticles or mixtures thereof suspended in a (high boiling point) solvent. Epoxy materials, such as adhesives or conductive adhesives with silver microparticles, are also used. Alternatively or additionally, the substance can include one or more of a positive or negative photoresist, a polymer solution, a molten polymer, a monomer or a silicon-based material. For the purpose of the present invention, it is sufficient for the substance to contain a component that can evaporate at a relatively moderate temperature, i.e., not higher than several hundred degrees Celsius.

[0057] like Figure 2 As shown, the printing device 1 comprises a carrier 2 , for example a silicon wafer, which is configured at a first main side 21 to carry a sample SB1 , SB2 , SB3 of a substance to be printed.

[0058] like Figure 2 As further shown, the printing device 1 also comprises a heater device 23. In operation, the heater device 23 rapidly heats the sample at its contact surface at the first main side 21 of the carrier 2. As a result, a portion of the sample at one side of the contact surface evaporates and thereby generates vapor pressure, causing the remaining portion of the sample to be transferred towards the target surface. Figure 2 In the example shown, the heater means 23 is a resistive heater layer, for example formed from molybdenum or tungsten.

[0059] like Figure 2 As shown, the carrier 2 is provided with a hydrophobic coating 22 at the first main side 21 for carrying the samples SB1, SB2, SB3 of the substance to be printed. As a result of the hydrophobic coating 22, the samples SB1, SB2, SB3 carried by the carrier 2 have a larger contact angle than without the hydrophobic coating 22. Therefore, the hydrophobic coating 22 reduces the outflow of the substance and thus also reduces the drying of the sample at its periphery. As an example, the hydrophobic coating has a maximum of 50 mJ / m 2 More preferably, the hydrophobic coating has a surface energy of at most 30 mJ / m 2 surface energy.

[0060] In some cases, superhydrophobic or superoleophobic coatings may also be used. This may occur, for example, if it is desired to print a sample of the substance as droplets. In the case of highly viscous substances, the formation of droplets may be avoided if the sample of the substance SB1, SB2, SB3 is quickly transferred to the target T after being deposited on the coating 22, for example by a stencil / screen printing process.

[0061] Figure 3 An embodiment of the improved printing device 1 is shown in more detail. Figure 2 Corresponding parts have the same reference numerals.

[0062] exist Figure 3 In the embodiment shown, the support unit 3 comprises a plurality of support elements 32 for supporting the carrier 2 at the second main side 25. The support elements 32 define cooling channels 33 for conducting a cooling liquid. In operation, a cooling liquid, for example water at a temperature slightly above 0°C, is pumped through the cooling channels 33.

[0063] Figure 3 It is also shown that in this improved embodiment of the printing device, the support element 32 also defines an emptying groove 34 facing the second main side 25 of the carrier 2. Figure 3As shown, the evacuation channel is surrounded by the walls of the evacuation groove 34 and the carrier when the support unit 3 supports the carrier 2. In order to improve the thermal contact between the cooled support element 32 and the carrier 2, the evacuation channel thus formed is evacuated by a vacuum pump (not shown).

[0064] Figure 3 A temperature sensor 35 is installed in one or more supporting elements 32 of the printing device.

[0065] Figure 3 It is also shown that the carrier 2 comprises a plurality of electrical contact elements 24, ..., 24b, ... of the resistive heater layer 23 at its second main side 25. The support unit 3 is provided with spring-loaded electrical contact pins 31, 31a, 31b, ... to cooperate with the electrical contact elements 24, ..., 24b, .... Thus, the heating of the surface formed by the hydrophobic coating 22 can be controlled by area or by pixel for selectively transferring samples SB1, SB2 of a substance on the surface. A thermal and electrical insulation layer 26 is provided between the carrier 2 and the resistive heater layer 23. For example, in the case where the carrier is a silicon wafer, the thermal and electrical insulation layer 26 can be provided by oxidizing the surface of the wafer. In other examples, there is no thermal and electrical insulation layer.

[0066] exist Figure 3 In the embodiment shown, the spring-loaded electrical contact pins 31, 31a, 31b are arranged transversely between the support elements 32. The ends 311 of the spring-loaded electrical contact pins 31, 31a, 31b are movable at least in a range between the level defined by the support surface of the support element and above the support surface.

[0067] Figure 3 The printing device 1 comprises means (not shown) for generating a drying air flow F in order to avoid condensation of moisture on the hydrophobic coating 22 or on substances present thereon.

[0068] The printing device 1 has a controller 5, which is configured to control, for example FIG. 4A to FIG. 4D For the sake of clarity, the supporting unit ( Figure 3 3). For clarity, the contact elements of the resistive heater layer 23 ( Figure 3 24, ..., 24b, ...) in are also not shown.

[0069] like Figure 4A As shown, in step S1 , a carrier 2 provided with a hydrophobic coating 22 on a first main side 21 is provided.

[0070] Figure 4AIt is also shown that the samples SB1, SB2, SB3 of the substance to be printed are deposited on the hydrophobic coating 22. Therefore, the samples rest on the coating by contacting the surface. The controller 5 controls the screen printing devices 41, 42 to perform this step S2. Optionally, the controller 5 can control the device (not shown) to generate a dry air flow F, and / or control the device to provide a cooling liquid to circulate through the cooling channel ( Figure 3 33), and / or a control device to empty the gas formed in the emptying groove ( Figure 3 In addition, the controller may receive information from one or more temperature sensors ( Figure 3 35). Based on the input from the temperature sensor, the controller is configured to maintain the carrier 2 at a predetermined temperature before the step of causing the substance transfer. In one example, the controller is configured to maintain the low temperature of the carrier by adjusting the flow rate of the cooling liquid. In some examples, the controller selectively heats the carrier 2 through the resistive heater layer 23. In this case, the controller can achieve that the temperature of the carrier 2 does not exceed a predetermined reference temperature through the cooling liquid, and further control the heater layer 23 to locally heat a location that would otherwise be substantially below the reference temperature.

[0071] like Figure 4B , Figure 4C As shown, at a subsequent point in time after the removal of the printing screen 41, the samples SB1, SB2, SB3 of the substance remain in their corresponding deposition areas. Due to the large contact angle formed with the surface by the hydrophobic coating, the evaporation effect at its edges is mitigated. Evaporation is further mitigated in these examples, where the carrier 2 is cooled during this stage. Cooling also leads to an increase in the viscosity of the substance, which reduces any tendency of the substance to flow, thereby limiting the shape changes of the deposited samples SB1, SB2, SB3.

[0072] exist Figure 4D In the subsequent step S3 shown, the controller ( Figure 3 5) in which a heater means, such as a resistive heater layer 23 or a pulsed photon radiation source, locally heats the samples SB1, SB2, SB3 at their contact surfaces to evaporate a portion of the samples at the side of their contact surfaces with the hydrophobic layer 22. This generates vapor pressure, which causes the remaining portion of the sample to be transferred toward the target surface TS of the target T. Figure 4D As shown, Figure 1DCompared with the situation shown in FIG. 2 , the transfer process occurring in step S3 is improved. This improvement is achieved by the hydrophobic coating 22 in the following manner. First, the liquid substance is more difficult to dry on the edge, which can prevent any undesirable shear force. And secondly, due to the relatively large contact angle between the sample and the hydrophobic coating surface, the aspect ratio (thickness / lateral dimension) of the sample increases, which reduces the oscillation amplitude of the sample during transfer. This reduces the risk of the substance touching the carrier again. It also increases the chance of the ink falling in a convex shape, which helps the sample to be properly covered on the target surface TS. The reduction in oscillation amplitude is due to the fact that the high aspect ratio of the sample causes an increase in rigidity. In this embodiment, a further increase in rigidity is achieved, which helps to reduce the oscillation amplitude, wherein the carrier 2 is cooled until the time point of performing the transfer step S3. Due to the fact that the sample is quickly heated in step S3, most of the material of the sample is ejected from the hydrophobic surface 22 before it can be heated, so that the low temperature obtained when contacting the hydrophobic coating surface of the cooled carrier 2 is basically maintained.

[0073] Figure 5 The results of the simulation are shown. Figure 5 The upper part of FIG. 1 shows a sample SB of a substance on the surface of the hydrophobic coating 22 of the carrier 2 immediately before being transferred to the target. The simulated heat flux to be generated by the heater facility is 150 kW / cm 2 . It is clear from this simulation that evaporating an interfacial layer of a low thermal conductivity material (0.4 W / mK) of less than 2 μm is sufficient to transfer it from the surface of the hydrophobic layer 22 to the target. Therefore, for a 25 μm thick film of SB material, most of it remains highly viscous during the transfer. The transfer speed is typically in the order of 5-30 m / s, which means that the material is only transported for less than 200 μs (1 mm-6 mm printing gap). During this short time interval, the temperature of the material and its viscosity remain almost unchanged.

[0074] Figure 5 The lower part of FIG. 1 shows the temperature curve of the substance SB 3 microseconds after the heat flux starts to be generated. The temperature curve confirms that the interface layer of the substance SB is heated to a temperature of about 300° C., at which temperature the substance evaporates to build up vapor pressure. When the carrier 2 is pre-cooled, most of the thickness with a depth of 2 micrometers or more remains at the original temperature, such as room temperature (about 20° C.) or lower.

[0075] Fig. 6A The significant correlation between the viscosity of typical substances and temperature is shown.

[0076] Figure 6BThe oscillations of a sample of a substance during its transfer from a carrier 2 to a surface TS of a target are shown as a function of the viscosity of the substance. The horizontal axis represents the distance y from the center of the sample to the printing plate, i.e. the lateral position y along the sample. The vertical axis Δy represents the amount of deviation of the distance y from the sample to the printing plate at the edge of the sample due to the oscillations occurring at the edge of the sample. When the value of Δy is positive, the pancake-shaped sample (relative to the plate) bends outwards, and when it is negative, it bends in the other direction. The relationship shows four values ​​of viscosity: 1 Pa.s, 10 Pa.s, 100 Pa.s and 1000 Pa.s. From Figure 6B As can be clearly seen in Figure 2, increasing viscosity has the effect of reducing the amplitude of oscillation. This can be achieved by cooling the carrier 2 until the transfer time point. As mentioned above, the hydrophobic coating 22 leads to a higher aspect ratio structure, which makes the material film harder and more curved. In addition, the viscosity of the material can be increased by cooling the carrier. The higher the curvature, aspect ratio and viscosity, the greater the possibility that the film falls in a convex shape and prevents bubble retention.

[0077] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single component or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain means are recited in mutually different claims does not indicate that a combination of these means cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A printing device (1) for printing a substance on a target surface (TS) of a target (T), the printing device comprising a carrier (2) having a hydrophobic coating (22) at a first main side (21) for carrying a sample (SB1, SB2, SB3) of the substance to be printed, the sample resting on the coating via a contact surface, The printing apparatus further comprises a heater arrangement for locally heating the sample at its contact surface to evaporate a portion of the sample at one side of its contact surface, thereby generating vapor pressure to transfer the remaining portion of the sample towards the target surface.

2. The printing device (1) according to claim 1, characterized in that The hydrophobic coating has a thickness in a range of about 0.001 microns to about 10 microns.

3. The printing device (1) according to claim 1 or 2, characterized in that: The heater arrangement comprises a resistive heater layer (23) arranged between the carrier (2) and the hydrophobic coating (22).

4. A printing device (1) according to any one of the preceding claims, characterized in that Also included is a support unit (3) having a plurality of support elements (32) for supporting the carrier (2) at a second main side opposite to the first main side, the support elements defining cooling channels (33) for conducting a cooling liquid.

5. The printing device (1) according to claim 4, characterized in that The support element (32) further defines an exhaust groove (34) facing the second main side of the carrier, the exhaust groove (34) forming an exhaust channel when the carrier is supported, the exhaust channel being configured to be exhausted by a vacuum pump.

6. The printing device (1) according to claim 4 or 5, characterized in that: One or more of the support elements (32) has a temperature sensor (35) mounted therein.

7. The printing device (1) according to claim 3, characterized in that The carrier (2) includes a plurality of electrical contact elements (24, ..., 24b, ...) of the resistive heater layer (23) at its second main side opposite to the first main side, and wherein the printing device also includes a supporting unit (3), which is used to support the carrier (2) at the second main side, and the supporting unit (3) is provided with spring-loaded electrical contact pins (31, 31a, 31b, ...) to cooperate with corresponding electrical contact elements of the electrical contact elements (24, ..., 24b, ...).

8. The printing device (1) according to claim 7 in combination with any one of claims 4, 5 and 6, characterized in that The support element (32) is arranged between the electrical contact pins (31, 31a, 31b) of each of the spring-loaded electrical contact pins (31, 31a, 31b), and wherein the tips (311) of the electrical contact pins (31, 31a, 31b) of the spring-loaded electrical contact pins (31, 31a, 31b) can move at least in a range from the level defined by the support surface of the support element to above the support surface.

9. The printing device according to claim 4, 5, 6 or 8, characterized in that The printing device is configured to maintain the carrier (2) at a predetermined temperature prior to the step of causing the transfer by a combination of cooling by means of the support unit (3) and selective heating by means of a resistive heater layer (23) or by means of a separate temperature control layer having a resistive heater, so as to equalize the temperature over the entire printing plate controlled by an appropriate temperature control system.

10. The printing device (1) according to claim 1 or 2, characterized in that: The heater facility comprises a pulsed light source, which is arranged at a second main side of the carrier (2) opposite to the first main side and is configured to generate a pulsed light beam, which is transported through the carrier (2) and the hydrophobic coating (22) and absorbed in a contact surface of a sample of the substance to be printed or in a radiation absorbing layer at the first main side of the carrier, the radiation absorbing layer optionally being a hydrophobic coating.

11. Printing device (1) according to one or more of the preceding claims, characterized in that Also included is a controller (5) for controlling environmental conditions, such as temperature and ambient gas composition.

12. Printing device (1) according to one or more of the preceding claims, characterized in that A screen printing unit (41, 42) or a template printing unit is also included to deposit the substance on the hydrophobic coating.

13. The printing device (1) according to claim 12, characterized in that The components (41, 42) of the printing unit are also provided with a hydrophobic coating.

14. A method for printing a substance on a target surface (TS) of a target (T), the method comprising: Providing (S1) a carrier (2) having a hydrophobic coating (22) at a first main side (21); depositing (S2) a sample (SB1, SB2, SB3) of the substance to be printed on the hydrophobic coating, the sample resting on the coating via a contact surface; The sample is locally heated at its contact surface to evaporate a portion of the sample at one side of the contact surface, thereby generating vapor pressure to transfer the remaining portion of the sample toward the target surface (S3).

15. The method according to claim 14, characterized in that The step of providing a carrier (2) is preceded by the step of providing a resistive heater layer at a first main side (21) of the carrier (2), and wherein local heating is performed by means of the resistive heater layer (23) arranged between the carrier (2) and the hydrophobic coating (22).

16. The method according to claim 14 or 15, characterized in that The carrier (2) having the hydrophobic coating (22) is maintained at least locally at a temperature below ambient temperature, at least from the moment the substance is deposited thereon until the substance is transferred.

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