A method and apparatus for printing a substance onto a target surface of a target.

Abstract

A printing device (1) is provided for printing a substance onto a target surface (TS) of a target (T). The printing device comprises a carrier (2) having on a first major side (21) a hydrophobic coating (22) for carrying a specimen (SB1, SB2, SB3) of the substance to be printed. The specimen rests on the coating at a contact surface. The printing device further comprises a heater arrangement (23) for locally heating the specimen at the contact surface to evaporate a portion of the specimen on the side of the contact surface, thereby causing the remaining portion of the specimen to migrate towards the target surface. Additionally, a printing method is provided.

Description

[Technical Field]

[0001] The present application relates to an apparatus for printing a substance onto a target surface of a target.

[0002] The present application further relates to a method for printing a substance onto a target surface of a target. [Background technology]

[0003] International Patent Application No. WO2021230746 discloses a transfer method in which a substance formed by a viscous functional material is transferred onto a receiving substrate, and then the deposited substance is cured or dried. The cured or dried substance transferred to the target can function as an electrical insulator, an electrical conductor, a thermal insulator, a thermal conductor, etc.

[0004] A known method provides a plate with a plurality of individually addressable resistive heater elements. In use, the substance is heated by the resistive heater elements to induce vapor pressure between the substance and the plate, vaporizing an interfacial layer of the specimen of the substance at the side of the plate. The vapor pressure exerts a force on the substance, expelling the remaining unvaporized portion of the substance from the plate and causing transfer of the substance from the plate to the target surface.

[0005] The inventors have discovered that the transfer of heated material sometimes does not occur, and in Figures 1A-1D, the inventors have identified various underlying causes.

[0006] FIG. 1A shows how screen printing devices 41 , 42 are used to deposit specimens SBA and SBB of substance SB onto a first side 21 of a plate 2 .

[0007] 1B and 1C show the plate 2 carrying samples SBA, SBB and SBC at two points in time after the deposition process is completed.

[0008] FIG. 1D shows the process in which the specimens SBA, SBB, and SBC on the plate are transferred to the target T.

[0009] As a result of the process shown in FIG. 1A, specimens SBA, SBB, SBC are first deposited on the plate 2 along the openings in the screen 41 .

[0010] As shown in the situation in FIG. 1B, due to capillary forces, the material of specimens SBA, SBB, and SBC tends to spread between the surface and the stencil or screen (a), causing underflow (b).

[0011] At later times, the material spread on the surface tends to dry out, as shown in Figure 1C (c).

[0012] As a result, in the operation shown in Figure 1D, the following phenomena may occur: due to evaporation occurring in the specimen SBB, its migration is hindered by shear forces (d); the specimen SBC is partially released from the plate 2, but one side is retained, resulting in the material inside it turning over (e) and remaining on the plate; and a dried residue (e) may remain on the plate.

[0013] Unless the plate is washed before further use, the dried residue left on the plate will cause alignment problems and sometimes prevent transfer altogether. The second cause of non-transfer is mainly related to the material properties and morphology of the ink. If the viscosity, modulus and aspect ratio are too low, the ink is likely to not transfer due to film vibration.

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

[0015] U.S. Patent Application Publication No. US2022 / 119659 discloses an indirect printing process in which the release surface of an intermediate transfer member (ITM) is pretreated (e.g., coated) with an aqueous formulation prior to depositing an ink image thereon. Pressurized contact between the ITM and the printing substrate transfers the ink image residue (e.g., along with a dried treatment film layer) onto the printing substrate.

[0016] U.S. Patent Application Publication No. US2005 / 009327 discloses an apparatus and method for forming a wiring pattern on a substrate, and an electronic device and a method for manufacturing the same. By utilizing energy supplied from an energy supply device, the viscosity of the wiring material when the material is supplied from the material supply device to a transfer plate is made different from the viscosity of the wiring material when the material is transferred from the transfer plate to the substrate.

[0017] US Patent Application Publication No. US2014 / 199473 discloses an apparatus for providing a patterned structure, which may include one or more of a heat source, a photon radiation source, and a microwave source as a curing facility for curing a precursor of a conductive material. Summary of the Invention [Problem to be solved by the invention]

[0018] It is a primary object of the present disclosure to provide an improved apparatus for printing a substance onto a target surface of a target that alleviates one or more of the above-mentioned drawbacks.

[0019] A second object of the present disclosure is to provide an improved method for printing a substance onto a target surface of a target that alleviates one or more of the above-mentioned drawbacks. [Means for solving the problem]

[0020] According to a first object, an improved printing device for printing a substance onto a target surface of a target is defined as follows: The improved printing device comprises a carrier having on a first major side a hydrophobic coating for carrying a sample of the substance to be printed, whereby the sample rests on the hydrophobic coating at a contact surface. The hydrophobic coating has a relatively low surface energy, for example 50 mJ / m 2 In the following example, 30 mJ / m 2 This causes the specimen of material to be deposited to exhibit a relatively high contact angle on the hydrophobic surface. A contact angle of about 90° is often desirable, since the specimen of material tends to maintain its shape on the hydrophobic surface onto which it was deposited in the preparation process. However, a high contact angle may be desirable if the specimen is intended to be printed as a droplet on the target surface.

[0021] The printing device also includes a heater arrangement for locally heating the specimen at the contact surface to vaporize a portion of the specimen on the side of the contact surface, thereby inducing a vapor pressure that migrates the remaining portion of the specimen toward the target surface.

[0022] Due to the hydrophobic nature of the coating on the first major side of the support, the specimen of material does not tend to flow off but instead exhibits a relatively high contact angle with the support surface, thereby mitigating shear forces due to evaporation of liquid components within the specimen during the time interval between deposition on the support and transfer to the target.

[0023] Additionally, as a result of the large contact angle, the specimen has a high aspect ratio (thickness divided by diameter), which reduces the amplitude of the oscillating film (higher stiffness) during transfer, thereby reducing the risk of the ink re-contacting the heater plate and increasing the likelihood of the ink being deposited in a convex shape.

[0024] Smaller features can be printed due to the limited spreading behavior on the hydrophobic coating.

[0025] Another advantage is that the temperature gradient (and the resulting viscosity gradient) across the thickness of the film makes ink ejection from the stencil onto the non-sticky hydrophobic coating more efficient. The shear forces between the ink and the stencil are low due to the low viscosity, while adhesion to the cool hydrophobic coating is increased due to the high viscosity. Particularly for high aspect ratio openings in the stencil, the relatively high contact area with the stencil facilitates complete ink ejection onto the heater plate.

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

[0027] During operation, the heater fixture rapidly heats the material on the side facing the hydrophobic surface, vaporizing the interfacial layer of the material on the side of the plate. The vapor induces 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 disposed between the carrier and the hydrophobic coating. This embodiment is advantageous in that the heater arrangement requires minimal space and can be easily controlled.

[0029] In another embodiment, the heater arrangement is provided on the second main side of the carrier opposite the first main side as a pulsed photon radiation source, such as a laser or flash lamp. During operation, the pulsed photon radiation source generates a pulsed light beam that should be transmitted through the carrier and the hydrophobic coating and absorbed at the contact surface of the sample of material to be printed. Alternatively, a light absorbing layer is provided between the transparent carrier and the hydrophobic coating. This alternative is similar to the embodiment with a resistive heater layer, in that the material is indirectly heated by heat conduction through the hydrophobic coating.

[0030] In some embodiments, the printing device further includes a cooling facility for forcibly cooling the carrier when the material transfer operation is not being performed. In one embodiment, the support unit includes a plurality of support elements supporting the carrier on the second major side and defining cooling channels for conducting a cooling liquid, such as water. This allows the carrier to be rapidly cooled or maintained at a low temperature. It may be preferable to maintain the carrier at a low temperature until the material is transferred to maintain a high viscosity. In some instances of the latter embodiment, the support elements further define an evacuation groove facing the second major side of the carrier. The evacuation channel is surrounded by the walls of the evacuation groove and the surface of the carrier supported by the support unit. When the evacuation channel is evacuated with a vacuum pump, excellent thermal contact between the support elements and the carrier is achieved. Such a temperature-controlled vacuum chuck for the carrier optimizes control over print quality and reproducibility. For example, when an ink layer with an initial temperature of approximately 20°C is printed onto a cooled carrier with a much lower temperature, the viscosity increases significantly. Simulations and experiments have shown that high viscosity reduces the amplitude of the material's vibration film during transfer, reducing the likelihood that the material will re-contact the carrier after its ejection from the carrier surface. Because the film thickness is typically on the order of 100 microns or less, the material quickly reaches the relatively low temperature of the carrier (less than 1 second). This means that temperature control is only required via the support unit and the carrier supported by it, rather than the entire system. Therefore, deposition of material onto the carrier by stencil / screen printing can be performed at room temperature, for example, thereby reducing the cost and complexity of the printer system. Metal stencils have relatively high thermal conductivity, but when using a printing gap, the total contact time between the warm stencil and the cold plate is short. Therefore, the amount of heat transferred from the stencil to the carrier is limited.When printing specimens with high aspect ratios, it is particularly advantageous if the temperature of the stencil or mask is higher than that of the carrier. On the one hand, due to the relatively high temperature of the mask, the substance specimen can be released therefrom with relatively low shear force due to the relatively low viscosity of its interface with the mask. On the other hand, the viscosity of the interface of the substance specimen in contact with the cold surface of the hydrophobic coating increases, resulting in increased adhesion of the specimen to the hydrophobic surface. The higher the ratio of the area of ​​the interface with the mask to the area of ​​the interface with the hydrophobic coating, the more advantageous this effect becomes.

[0031] Importantly, during operation, the material to be transferred is heated to hundreds of degrees at the interface with the hydrophobic surface in microseconds. This causes the remainder of the material to be expelled by vapor pressure before it can be heated. For materials with low thermal conductivity (<1 W / mK), the thermal penetration depth is typically less than 2 μm. This means that the majority of the film thickness remains cool and therefore, on average, highly viscous and harder. This improves the printability of low-viscosity fluids (<10 Pa*s at 20°C) and expands the aspect ratios and film widths that can be printed.

[0032] It is preferable to take measures to prevent condensation when cooling the heater plate. In the event of condensation, the entire surface of the carrier will be covered with small water droplets. If rapidly heated, all of these water droplets will be transferred along with the ink film. Therefore, it is important to maintain the carrier above the dew point when cooling. This can be easily achieved by blowing dry air or nitrogen onto the surface. For example, if the relative humidity is 25% and the air temperature is 20°C, the carrier can be cooled to 0°C without any condensation. Therefore, low humidity increases the drying rate and the likelihood of dry edges. However, a low carrier temperature offsets this effect. In one embodiment, the printing device is equipped with a controller for controlling environmental conditions, such as temperature and ambient gas composition. This ensures that the environmental conditions are sufficient to avoid condensation while minimizing evaporation of the material before transfer to the target.

[0033] In some embodiments, one or more of the support elements is fitted with a thermal sensor, allowing the temperature of the support to be accurately determined, especially when good thermal contact is achieved by evacuating the exhaust channel.

[0034] In an example embodiment in which the heater arrangement comprises a resistive heater layer, the carrier comprises, on its second major side (opposite the first major side), a plurality of electric contact elements of the resistive heater layer. The printing device may further comprise a support unit for supporting the carrier comprising spring-loaded electrical contact pins. When the support unit supports the carrier on the second major side, the plurality of spring-loaded electrical contact pins cooperate with individual electrical contact elements of the plurality of electrical contact elements. When the support unit comprises the above-mentioned support elements, these support elements can be arranged between the plurality of spring-loaded electrical contact pins. In one such example, the tips of the plurality of spring-loaded electrical contact pins are movable at least in the range from a level defined by a support surface of the support element to above the support surface.

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

[0036] In one embodiment, the printing device further comprises a screen or stencil printing unit for depositing the substance onto the hydrophobic coating. It is advantageous, especially for high aspect ratio structures, if the 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] In accordance with the second object, an improved method for printing a substance onto a target surface of a target is provided.

[0038] According to the improved method, a support is provided on a first major side having a hydrophobic coating.

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

[0040] The specimen is then heated at the contact surface, vaporizing a portion of the specimen on the side of the contact surface, which induces vapor pressure and migrates the remaining portion of the specimen toward the target surface.

[0041] Heating is rapid, so that only the interface layer of the material is evaporated, and the rest is transported by vapor pressure. For example, once the material has cooled completely, it can reach a temperature of 50-250 kW / cm. 2 and a heat flux of approximately 0.2 to 2 J / cm 2 A fluence of 1000 keV is used to evaporate a thin layer, say a few microns of liquid at the interface, which builds up pressure and transfers the remainder of the material, say a film of material that is tens of microns thick or more.

[0042] In one embodiment of the improved method according to the step of providing a hydrophobic layer on the carrier, a step of providing a resistive heater layer on the first major side of the carrier is performed, and localized heating is provided by the resistive heater layer disposed between the carrier and the hydrophobic coating.

[0043] Various methods are available for applying a hydrophobic or oleophobic coating to the support. Examples include atomic layer deposition, sputtering, chemical vapor deposition, and evaporation. High thermal conductivity of the hydrophobic coating is achieved when the latter is relatively thin, for example, less than a few microns. The small thickness of the hydrophobic coating also contributes to its stability against sudden temperature changes that occur during use. Atomic layer deposition is particularly suitable for obtaining ultra-thin coatings. For example, an Al2O3 coating can be applied using this process.

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

[0045] In an embodiment of the improved method, the support having the hydrophobic coating is maintained at least locally at a temperature below ambient temperature from the time of depositing the substance thereon until the substance is transferred, thereby minimizing evaporation and increasing the viscosity of the substance.

[0046] These and other aspects are described in more detail with reference to the drawings. [Brief explanation of the drawings]

[0047] [Figure 1A] FIG. 1A illustrates various phenomena that can interfere with the process of thermally induced transfer of material to a target surface. [Figure 1B] FIG. 1B illustrates various phenomena that can interfere with the process of thermally induced transfer of material to the target surface. [Figure 1C] FIG. 1C illustrates various phenomena that can interfere with the process of thermally induced transfer of material to the target surface. [Figure 1D] FIG. 1D illustrates various phenomena that can interfere with the process of thermally induced transfer of material to the target surface. [Figure 2]FIG. 2 shows a schematic representation of an embodiment of the improved printing device disclosed herein. [Figure 3] FIG. 3 shows a further embodiment of the improved printing device in more detail. [Figure 4A] FIG. 4A illustrates the steps of an embodiment of the improved printing method disclosed herein. [Figure 4B] FIG. 4B illustrates the steps of an embodiment of the improved printing method disclosed herein. [Figure 4C] FIG. 4C illustrates the steps of an embodiment of the improved printing method disclosed herein. [Figure 4D] FIG. 4D illustrates steps of an embodiment of the improved printing method disclosed herein. [Figure 5] Figure 5 shows the results of a simulation of the improved printing device. [Figure 6A] FIG. 6A shows the relationship between temperature and viscosity of a typical substance to be transferred in an embodiment of the improved printing device or improved printing method. [Figure 6B] FIG. 6B shows the estimated oscillation amplitudes of a sample of materials during the transition as a function of their viscosity. DETAILED DESCRIPTION OF THE INVENTION

[0048] In the drawings, like reference symbols refer to like elements unless otherwise noted.

[0049] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure aspects of the present invention.

[0050] FIG. 2 schematically illustrates a printing device 1 for printing a substance onto a target surface TS of a target T. The target T may be, for example, a component to be manufactured. The substance may have predetermined physical characteristics, such as a specific electrical conductivity and a specific thermal conductivity. For example, the substance may be an electrically and thermally insulating substance, an electrically and thermally insulating substance, an electrically and thermally insulating substance, or an electrically and thermally conductive substance. The substance, commonly referred to as an ink or paste, may contain, for example, nanoparticles or microparticles suspended in a (high-boiling) solvent, or a combination thereof. Also used are epoxy-based substances, such as adhesives or conductive adhesives, containing silver microparticles. Alternatively or additionally, the substance may include one or more of a positive or negative photoresist, a polymer solution, a molten polymer, a monomer, or a silicone-based substance. For purposes of the present invention, it is sufficient that the substance contains components that can be evaporated at relatively low temperatures, i.e., below a few hundred degrees Celsius.

[0051] As shown in FIG. 2, the printing device 1 comprises, on a first main side 21, a carrier 2, for example a silicon wafer, configured to carry specimens SB1, SB2, SB3 of a substance to be printed.

[0052] As further shown in Figure 2, the printing device 1 further comprises a heater arrangement 23. During operation, the heater arrangement 23 rapidly heats the specimen at a contact surface in contact with the first main side 21 of the carrier 2. As a result, part of the specimen evaporates on the side of the contact surface, thereby inducing a vapor pressure that migrates the remaining part of the specimen towards the target surface. In the example shown in Figure 2, the heater arrangement 23 is a resistive heater layer, for example formed by molybdenum or tungsten.

[0053] As further shown in Figure 2, the carrier 2 is provided on a first major side 21 with a hydrophobic coating 22 for carrying specimens SB1, SB2, SB3 of the material to be printed. As a result of the hydrophobic coating 22, specimens SB1, SB2, SB3 carried by the carrier 2 have a higher contact angle than they would have in the absence of the hydrophobic coating 22. The hydrophobic coating 22 thereby reduces the bleeding of the material and thereby also reduces drying of the specimens around their periphery. By way of example, the hydrophobic coating has a hydrophobicity of 50 mJ / m 2 More preferably, the hydrophobic coating has a surface energy of 30 mJ / m 2 It has the following surface energy:

[0054] In some cases, it is also possible to use a superhydrophobic or superoleophobic coating. This is the case, for example, when it is desirable to print the specimens of the substance as droplets. In the case of highly viscous substances, the formation of droplets can be avoided if specimens SB1, SB2, SB3 of the substance are deposited on the coating 22, for example, using a stencil / screen printing process, and then quickly transferred to the target T.

[0055] Figure 3 shows in more detail an embodiment of the improved printing device 1. Parts corresponding to those in Figure 2 have the same reference numbers.

[0056] 3, the support unit 3 comprises a plurality of support elements 32 for supporting the carrier 2 on the second main side 25. The support elements 32 define cooling channels 33 for conducting a cooling liquid. During operation, the cooling liquid, for example water having a temperature slightly above 0° C., is pumped through the cooling channels 33.

[0057] Figure 3 further shows that in this embodiment of the improved printing device, the support element 32 further defines an exhaust groove 34 facing the second main side 25 of the carrier 2. As can be seen in Figure 3, when the support unit 3 supports the carrier 2, an exhaust channel is surrounded by the walls of the exhaust groove 34 and the walls of the carrier. In order to improve the thermal contact between the cooled support element 32 and the carrier 2, the exhaust channel so formed is evacuated by a vacuum pump (not shown).

[0058] One or more of the support elements 32 of the printing device of Figure 3 has a temperature sensor 35 mounted therein.

[0059] 3 further shows that the carrier 2 is provided on its second main side 25 with a plurality of electrical contact elements 24, 24b, 24c of the resistive heater layer. The support unit 3 is provided with a plurality of spring-loaded electrical contact pins 31, 31a, 31b, 31d, 31e, 31f ...

[0060] 3, the plurality of spring-loaded electrical contact pins 31, 31 a, 31 b,... are arranged laterally between a plurality of support elements 32. Tips 311 of the plurality of spring-loaded electrical contact pins 31, 31 a, 31 b,... are movable at least in the range from a level defined by the support surface of the support element to above the support surface.

[0061] The printing device 1 of FIG. 3 is provided with means (not shown) for inducing a dry air flow F to avoid condensation of moisture on the hydrophobic coating 22 or on any material present thereon.

[0062] The printing device 1 has a controller 5 configured to control the operation steps of the printing device, as shown in Figures 4A to 4D. For clarity of the figures, the support unit (3 in Figure 3) for supporting the carrier 2 is not shown therein. Also, the contact elements (24,..., 24b,... in Figure 3) of the resistive heater layer 23 are not shown for clarity.

[0063] As shown in step S1 of FIG. 4A, on a first major side 21 of the support 2, a hydrophobic coating 22 is applied.

[0064] FIG. 4A further shows that specimens SB1, SB2, and SB3 of the material to be printed are deposited on the hydrophobic coating 22. As a result, the specimens rest on the coating at their contact surfaces. A controller 5 controls the screen printing devices 41 and 42 to perform this step S2. Optionally, the controller 5 may control a device (not shown) for inducing a dry air flow F and / or a device for providing a cooling liquid circulating through the cooling channel (33 in FIG. 3 ) and / or a device for venting the exhaust channel formed in the exhaust groove (34 in FIG. 3 ). Additionally, the controller may receive input from one or more temperature sensors (35 in FIG. 3 ). Based on the input from the temperature sensors, the controller is configured to maintain the carrier 2 at a predetermined temperature prior to the step of inducing material transfer. In one example, the controller is configured to maintain the low temperature of the carrier by adjusting the flow of the cooling liquid. In some examples, the controller selectively heats the carrier 2 with the resistive heater layer 23. In that case, the controller may use a cooling liquid to prevent the temperature of the support 2 from exceeding a predetermined reference temperature, and may further control the heater layer 23 to locally heat areas that are significantly lower than the reference temperature.

[0065] As shown in Figures 4B and 4C, at a subsequent time after removing the printing screen 41, the material specimens SB1, SB2, and SB3 remain within their corresponding deposition areas. The high contact angle with the surface formed by the hydrophobic coating reduces the effects of evaporation at their edges. In instances where the support 2 is cooled at this stage, evaporation is further reduced. Cooling also increases the viscosity of the material, reducing its fluidity and thereby limiting shape changes of the deposited specimens SB1, SB2, and SB3.

[0066] In the next step S3 shown in FIG. 4D, the controller (5 in FIG. 3) controls the heater equipment, such as the resistive heater layer 23 or a pulsed photon radiation source, to locally heat the specimens SB1, SB2, and SB3 at their contact surfaces, causing a portion of the specimen to evaporate on the side of the contact surface with the hydrophobic layer 22. This vapor pressure then drives the remaining specimens to migrate toward the target surface TS of the target T. As shown in FIG. 4D, the migration process performed in this step S3 is improved compared to the situation shown in FIG. 1D. This improvement is achieved by the hydrophobic coating 22 in the following ways: First, the liquid substance is less likely to dry at the edges, thereby preventing unnecessary shear forces. Second, the relatively high contact angle between the specimen and the surface of the hydrophobic coating increases the specimen's aspect ratio (thickness / lateral size), thereby reducing the amplitude of the specimen's vibration during migration. This reduces the risk of the substance re-contacting the carrier. It also increases the likelihood of ink deposition in a convex shape, which contributes to proper coverage of the specimen on the target surface TS. The reduction in vibration amplitude is due to the fact that the stiffness increases with increasing aspect ratio of the specimen. A further increase in stiffness, which contributes to a reduction in vibration amplitude, is achieved in embodiments in which the carrier 2 is cooled until the transition step S3 is performed. Due to the fact that heating the specimen in step S3 is performed rapidly, most of the specimen's material is expelled from the hydrophobic surface 22 before it can be heated, and therefore it substantially maintains the low temperature it obtained when it contacted the surface of the hydrophobic coating of the cooled carrier 2.

[0067] Figure 5 illustrates the results of the simulation. The top part of Figure 5 shows the sample SB of material on the surface of the hydrophobic coating 22 of the support 2 just before being transferred to the target. Here, the simulated heat flux to be generated by the heater fixture is 150 kW / cm. 2This simulation reveals that evaporation of less than a 2 μm interfacial layer of a material with low thermal conductivity (0.4 W / mK) is sufficient to transfer the material from the surface of the hydrophobic layer 22 to the target. Thus, for a 25-micron thick film of material SB, it remains largely highly viscous during transfer. Transfer speeds are typically on the order of 5-30 m / s, which means that the material is transferred only in less than 200 μs (print gaps of 1-6 mm). Over this short time interval, the temperature, and therefore the viscosity, of the material changes very little.

[0068] The lower part of Figure 5 shows the temperature profile of material SB3 3 microseconds after the onset of the heat flux. The temperature profile confirms that the interface layer of material SB3 is heated to a temperature of about 300°C, at which point evaporation of the material occurs and the vapor pressure rises. If the support 2 is pre-cooled, most of the thickness, up to a depth of 2 microns or more, remains at the original temperature, e.g., room temperature (about 20°C) or lower.

[0069] FIG. 6A illustrates that there is a significant dependency between viscosity and temperature for a typical material.

[0070] FIG. 6B shows the vibrations induced in a specimen of material during its transfer from the carrier 2 to the target surface TS, depending on the viscosity of the material. The horizontal axis indicates the center distance y from the specimen to the printing plate and the lateral position y along the specimen. The vertical axis Δy indicates how much the distance y from the specimen to the printing plate shifts due to vibrations at the specimen edge, resulting in vibrations at the specimen edge. A positive Δy value indicates that the pancake-shaped specimen bends outward (relative to the plate), and a negative value indicates that it bends in the opposite direction. Relationships are shown for four values ​​of viscosity: 1 Pa.s, 10 Pa.s, 100 Pa.s, and 1000 Pa.s. As is clear from FIG. 6B, increasing viscosity has the effect of reducing vibration amplitude. This is achieved by cooling the carrier 2 until the point of transfer. As mentioned above, the hydrophobic coating 22 results in structures with higher aspect ratios, which makes the film of material stiffer and more flexible. Additionally, the viscosity of the material can be increased by cooling the support. The higher the curvature, aspect ratio, and viscosity, the more likely the film will assume a convex shape and prevent trapped air bubbles.

[0071] In the claims, the word "comprises" 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 measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be interpreted as limiting the scope.

Claims

1. A printing device (1) for printing a substance onto a target surface (TS) of a target (T), said printing device comprising a carrier (2) having on a first major side (21) a hydrophobic coating (22) for carrying a specimen (SB1, SB2, SB3) of said substance to be printed, said specimen resting on said coating at a contact surface; the printing device further comprises a heater arrangement for locally heating the specimen at the contact surface to vaporize a portion of the specimen at the contact surface side, thereby inducing a vapor pressure that migrates a remaining portion of the specimen towards the target surface; The printing device (1).

2. The printing device (1) of claim 1, wherein the hydrophobic coating has a thickness ranging from about 0.001 microns to about 10 microns.

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

4. 4. The printing device (1) according to claim 1, further comprising a support unit (3) comprising a plurality of support elements (32) for supporting the carrier (2) on a second main side opposite the first main side, the plurality of support elements defining cooling channels (33) for conducting a cooling liquid.

5. 5. The printing device of claim 4, wherein the support element further defines an exhaust groove facing the second major side of the carrier, the exhaust groove forming an exhaust channel configured to be evacuated by a vacuum pump when supporting the carrier.

6. 6. A printing device (1) according to claim 4 or 5, wherein one or more of the plurality of support elements (32) has a temperature sensor (35) mounted therein.

7. 4. The printing device (1) according to claim 3, wherein the carrier (2) comprises, on a second main side thereof opposite the first main side, a plurality of electrical contact elements (24, ..., 24b, ...) of the resistive heater layer (23), and wherein the printing device further comprises a support unit (3) for supporting the carrier (2) on the second main side, the support unit (3) being provided with a plurality of spring-loaded electrical contact pins (31, 31a, 31b, ...) cooperating with individual electrical contact elements of the plurality of electrical contact elements (24, ..., 24b, ...).

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

9. 9. A printing device (1) according to claim 4, 5, 6 or 8, configured to maintain the carrier (2) at a predetermined temperature prior to the transfer step by a combination of cooling by the support unit (3) and selective heating by the resistive heater layer (23) or by a separate temperature control layer comprising a resistive heater, to achieve a uniform temperature across the printing plate controlled by a suitable temperature control system.

10. 3. The printing device (1) according to claim 1 or 2, wherein the heater arrangement comprises a pulsed light source arranged on a second main side of the carrier (2), opposite the first main side, and configured to generate a pulsed light beam that should be transmitted through the carrier (2) and the hydrophobic coating (22) and absorbed at the contact surface of the specimen of the substance to be printed or in a radiation absorbing layer on the first main side of the carrier, optionally the radiation absorbing layer being the hydrophobic coating.

11. A printing device (1) according to any one or more of the preceding claims, further comprising a controller (5) for controlling environmental conditions, such as temperature and ambient gas composition.

12. 12. The printing device (1) according to any one or more of the preceding claims, further comprising a screen printing unit (41, 42) or a stencil printing unit for depositing said substance onto said hydrophobic coating.

13. 13. A printing device (1) according to claim 12, wherein the components of the printing units (41, 42) are also provided with a hydrophobic coating.

14. A method for printing a substance onto a target surface (TS) of a target (T), comprising: Providing (S1) a support (2) on a first major side (21) having a hydrophobic coating (22); depositing (S2) a sample (SB1, SB2, SB3) of the substance to be printed on the hydrophobic coating, wherein the sample rests on the coating with a contact surface; (S3) locally heating the specimen at the contact surface to vaporize a portion of the specimen on the side of the contact surface, thereby inducing a vapor pressure that causes migration of the remaining portion of the specimen toward the target surface; The method comprising:

15. 15. The method of claim 14, wherein the step of providing a carrier (2) is preceded by a step of providing a resistive heater layer on the first main side (21) of the carrier (2), wherein localized heating is performed by the resistive heater layer (23) disposed between the carrier (2) and the hydrophobic coating (22).

16. 16. The method according to claim 14 or 15, wherein the support (2) having the hydrophobic coating (22) is maintained at least locally at a temperature lower than the ambient temperature at least from the time of depositing the substance thereon until the substance is transferred.

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