Method and device for printing substance on target surface of target

Abstract

A printing device (1) for printing a substance on a target surface (TS) of a target (T) is provided. The printing device comprises a carrier (2) having, on a first main side (21), a carrying surface (2s) for carrying a sample (SB1, SB2, SB3) of a substance to be printed. The printing apparatus further comprises: a heating device (23) for heating the bearing surface to evaporate a portion of the sample on the bearing surface side and generating a vapor pressure that transports a remaining portion of the sample toward a target surface; and a structured thermal buffer layer (25) that provides a position-dependent delay with which heat is transferred from the heating device to the bearing surface.

Description

Technical Field

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

[0002] The present application 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 of transferring a substance formed of an adhesive functional material onto a receiving substrate, wherein the deposited substance is subsequently cured or dried. The cured or dried substance transferred onto the target can be used as an electrical insulator, an electrical conductor, a thermal insulator, a thermal conductor, etc.

[0004] The known method includes heating the substance to evaporate an interfacial layer of a sample of the substance on the plate side so as to generate a vapor pressure between the substance and the plate. The vapor pressure exerts a force on the substance, and this force is used to discharge the remaining unevaporated portion of the substance away from the plate so that it is transferred from the plate to the target surface.

[0005] The inventors have found that the transfer of the heated substance is occasionally hindered if samples of different sizes have to be transferred. In Figures 1A to 1C , the inventors have identified various basic causes. Among them, Figure 1A shows an initial state in which samples SB1, SB2, SB3 of different sizes are arranged on the surface of a carrier 2 facing the target T. As Figure 1B shows, the inventors have noticed that due to local differences in the pressure generated between the carrier and the sample, the sample deforms and starts to vibrate (A, B) when the transfer is initiated. The amplitude and frequency of these vibrations depend on the material properties of the substance and also on the size of the substance. Therefore, as Figure 1B shows, even when transferring samples of the same substance, these vibrations will affect the transfer process in different ways. In this example, the smallest sample SB3 reaches the surface of the target T while it appears convex when observed from the target. Since the sample SB3 completely covers the target surface after the vibrations decay (see Figure 1C ), this is a better situation. However, the larger sample SB2 reaches the surface of the target T while it appears concave when observed from the target. In this case, the sample SB2 does not properly cover the substrate surface. As Figure 1C shows, after landing on its edge, the sample SB2 adheres to the target T and encloses a bubble C. For the largest sample SB1 in the sample, the vibrations cause a different phenomenon. In this example, the sample SB1 oscillates once and its center touches the heater B again while it cools down again (below the evaporation temperature). As Figure 1C shows, in this case the sample remains on the carrier 2 and is not transferred at all.

[0006] Figure 1D and Figure 1E and Figure 1F provide simulation results based on a 2D temperature vs. pressure model, showing the influence of various parameters on the printing process.

[0007] Figure 1D show the oscillations that occur in a sample of the material as it is transferred from the carrier 2 to the surface TS of the target. The oscillations depend on the size of the sample. The simulation was performed with the following parameters:

[0008] Heat flux 150 kW / cm2

[0009] The elastic modulus E of the material = 200 MPa

[0010] The viscosity η of the material = 10 Pa.s

[0011] In the order from left to right, Figure 1D the graphs in show simulations of samples with thicknesses of 5 μm, 10 μm, and 50 μm. In these graphs, the horizontal axis represents the distance y from the sample to the center of the printing plate. The vertical axis Δy represents the amount by which the distance y from the sample to the printing plate deviates at the edge of the sample due to the oscillations occurring in the sample. When the value of Δy is positive, the disk-shaped sample bends outward (relative to the plate), and when it is negative, it bends in the other direction. The relationship is shown for four values of the viscosity: 1 Pa.s, 10 Pa.s, 100 Pa.s, and 1000 Pa.s.

[0012] For example, when printing a 5-μm thick, 100-μm wide film (AR = 0.05), it will impact at a printing gap of approximately 150 μm and form a concave shape (-20 μm, see graph). This indicates that air will be trapped. The elastic modulus mainly affects the oscillation frequency, while the viscosity has a stronger influence on the amplitude.

[0013] Figure 1E show a second set of simulations. In the order from left to right, Figure 1E the graphs in show simulations of samples with widths of 50 μm, 100 μm, and 500 μm. Similarly in this case, the value chosen for the heat flux is 150 kW / cm2 and the viscosity η of the material = 10 Pa.s. The elastic modulus of the material varies in the range from 20 to 20000 MPa. The values are shown in MPa in the graph.

[0014] Figure 1F show another example, where the transfer of samples with a thickness of 5 μm and a diameter of 100 μm is simulated for various viscosity values. These viscosity values are expressed in Pa.s.

[0015] Assume that specimens of the same size and of the same sample are printed, and appropriate conveyance to the target T can be achieved by appropriately selecting the power supplied to the heat source for generating the conveyance.

[0016] However, in practice, it is necessary to appropriately convey specimens of different sizes and / or different components. Summary of the Invention

[0017] According to a first aspect of the present disclosure, in order to meet the above needs, a preferred apparatus for printing a substance on a target surface of a target is provided.

[0018] According to a second aspect of the present disclosure, in order to meet the above needs, a preferred method for printing a substance on a target surface of a target is provided.

[0019] An embodiment of the preferred printing apparatus includes: a carrier having a bearing surface on a first main side, the bearing surface for bearing a specimen of the substance to be printed; and a heating device for heating the bearing surface to evaporate a part of the specimen on the side of the bearing surface and generate a vapor pressure, the vapor pressure causing the remaining part of the specimen to be conveyed toward the target surface. The preferred printing apparatus further includes a structured thermal buffer layer that provides a position-dependent delay for heat to be transferred from the heating device to the bearing surface.

[0020] The structured thermal buffer layer controls the heat flux and thus releases time. The structured thermal buffer layer may be a continuous layer having a thickness variation, but may also be locally absent, i.e., having a thickness of 0.

[0021] It has been found that a relatively thin thermal insulation layer (such as a ceramic material layer such as SiO2), the heat flux, and thus the release time can be controlled so as to appropriately convey specimens of different sizes and / or different components.

[0022] In some embodiments, the heating device is an electric heating layer for resistively heating the bearing surface. This is advantageous because an electric heating layer can be accommodated in the carrier and thus requires a minimum amount of space. Alternatively, if there are no space restrictions, the heating device may be provided as a photon radiation source. In the latter case, the carrier may have a photon radiation absorption layer, wherein the structured thermal buffer layer provides a position-dependent delay for heat generated by absorbing radiation from the photon radiation source to be transferred to the specimen.

[0023] In some embodiments, the carrier surface includes at least a first specimen carrier region and a second specimen carrier region for separately carrying a first specimen and a second specimen of the substance to be printed, wherein the thickness of the thermal buffer layer within the one having the largest dimension among the at least a first specimen carrier region and a second specimen carrier region is greater than the thickness of the thermal buffer layer within the one having the smallest dimension among the at least a first specimen carrier region and a second specimen carrier region. The structured thermal buffer layer locally reduces the heat flux and controls the vibration frequency of each specimen. By making all frequencies closer to each other and controlling the printing gap, the working range can be increased and various droplet sizes can be landed without air entrapment.

[0024] Changing the heat flux at the substrate surface only requires a thin layer of silica (or any other low CTE material with low thermal conductivity). For SiO2, when using a heat flux on the order of 50 to 250 kW / cm2, the effective layer thickness is in the range of 10 to 1000 nm. The heat flux also changes the transfer speed of the ink film, which directly affects the landing shape at a given printing gap. Empirically, larger specimens require a locally larger thickness of the structured thermal buffer layer.

[0025] In some embodiments, the device has a specimen carrier region configured to carry a specimen of the substance to be transferred to a target, and the structured thermal buffer layer has a thickness distribution within the specimen carrier region to control the dynamic behavior of the remaining portion of the specimen when it is transferred to the target surface.

[0026] Due to the thickness distribution of the thermal buffer layer within the specimen carrier region, the thermal buffer layer creates a position-dependent delay in transferring heat from the heating device to the surface within the specimen carrier region. It should be noted that the structured thermal buffer layer with a varying thickness includes the special case where regions of the structured thermal buffer layer have a thickness of 0 and other regions have a predetermined thickness. In this special case, compared to the regions of the structured thermal buffer layer with a thickness of zero, the regions of the structured thermal buffer layer with a non-zero thickness, such as a predetermined thickness value, provide a delay in heat transfer from the heating device to the specimen. Therefore, the pressure distribution that changes over time due to the evaporating specimen can be controlled. At the locations where the thermal buffer layer is thicker, compared to the locations where the thermal buffer layer is thinner or where there is no thermal buffer layer, the heat flux delay is longer and the intensity is reduced more. Therefore, the delay and speed of the transfer of the remaining portion of the specimen in its different sections can be controlled. This also determines the dynamic behavior of the remaining portion of the specimen being transferred.

[0027] In one application, the thickness distribution of a thermal buffer layer within a specimen carrier region is used to control the dynamic behavior of the remaining portion of a specimen being transferred to optimize its coverage on a non-planar surface of a target. For example, in the case of a linear specimen, a portion within a region of the structured thermal buffer layer having a small or zero thickness is transferred earlier and with less or no delay compared to a portion within a region of the structured thermal buffer layer having a higher thickness value.

[0028] In another application, the thickness distribution of a thermal buffer layer within a specimen carrier region is used to control the dynamic behavior of the remaining portion of a specimen being transferred in order to control its oscillation during transfer. In one example, the thermal buffer layer has a thickness that decreases in a radially outward direction from a central position of the specimen carrier region. As a result, oscillation can be suppressed. Thus, the printing gap can be selected from a wide range while avoiding the risk of generating bubbles. Alternatively, the thickness distribution of the thermal buffer layer can be used to generate a special oscillation, for example, in order to achieve deposition of the remaining portion of the specimen in a predetermined pattern.

[0029] In one example of this application, the specimen carrier region has: a first portion that will be positioned opposite a surface portion of the target that is relatively closer to the carrier; a second portion that will be positioned opposite a surface portion of the target that is relatively farther from the carrier and laterally closer to the surface portion of the target; and a third portion that will be positioned opposite a surface portion of the target that is relatively farther from the carrier and laterally farther from the surface portion of the target, and wherein the thickness of the structured thermal buffer layer in the second portion is less than or zero compared to the thickness of the structured thermal buffer layer in the first and third portions. As a result, it can be achieved that the specimen is transferred along its length with a velocity distribution such that it is deposited in a manner consistent with the target surface.

[0030] It should be noted that the thermal buffer layer can have a superposition of a first structure and a second structure, the first structure for locally controlling a vibration frequency, and the second structure for locally controlling the transfer velocity of the specimen.

[0031] In some embodiments, the carrier has at least one recess on the first main side for accommodating a sample of the material to be printed and the thickness of the structured thermal buffer layer near the boundary of the recess is smaller than the thickness of the structured thermal buffer layer in the central part of the recess. In these embodiments, the preferred printing device is particularly suitable for controlling the transfer of high-viscosity materials from the recess. For high-viscosity material inks, it is important to avoid shearing. Therefore, there should be no difference or limited difference in the delay of heating the material in the recess. This delay time is preferably less than 1 microsecond, otherwise the material will be subjected to significant shear forces and produce severe deformation and even cause the material to break and splash or prevent the material from being transferred toward the receptor substrate. The structured thermal buffer layer present in the bottom of the recess locally reduces the heat flux and thus delays the release. By adjusting the thickness of the thermal buffer layer, the material can be released (nearly) simultaneously, which significantly improves the printing quality and can even print smaller microstructures. Although the material can be released from the side walls first, it is preferred to release these sides with a slight delay (0.1 to 0.5μs). This deforms the substance into a convex shape, thereby helping to prevent the generation of bubbles when impacting the receptor substrate.

[0032] In another embodiment, the structured thermal buffer layer of the preferred printing device has a plurality of microwells in at least one sample-carrying area, wherein the sample of the material to be printed is distributed on these microwells. Unlike the (near) shear-free printing of high-viscosity fluids, low-viscosity materials can actually benefit from shear forces to form microjets. In order to generate microjets, microwells (<50 μm) are etched in the thermal buffer layer (SiO2) and no heat dissipation structure is added in these wells. When a heat pulse is applied, vapor bubbles are formed only in the bottom of the microwell. Because the material has a low viscosity (<1 Pa*s), there is enough pressure to deform the liquid into a jet. When impacting the receptor substrate, the material can be dispersed and flow together to form a uniform coating. These microwells can have different depths or can have the same depth. The time and volume of ink released can be controlled by the depth of these microwells.

[0033] In some embodiments of the preferred printing device, the structured thermal buffer layer has a plurality of micro-pillars in at least one sample-carrying area. These embodiments of the preferred printing device are particularly suitable for printing relatively large metal particles having a relatively high thermal conductivity compared to the medium in which they are embedded. If the metal particle is in close proximity to the heater (<2 μm), it can act as a strong heat sink. This causes the temperature to rise more slowly near the metal particles, thus producing a delayed release. If the heat dissipation is asymmetric, the ink / paste is not transported perpendicular to the heating plate and lands in the wrong position on the receptor substrate. In these embodiments of the preferred printing device, the presence of these micro-pillars prevents the micro-particles from contacting the heated surface, thus avoiding the heat dissipation from occurring.

[0034] Examples of preferred methods for printing a substance on a target surface of a target include:

[0035] Providing a carrier having a bearing surface on a first major side for bearing a sample of the substance to be printed;

[0036] Providing a heating device for heating the bearing surface;

[0037] Providing a structured thermal buffer layer between the resistive heating layer and the bearing surface;

[0038] Actuating the heating device;

[0039] Transferring heat from the heating device to the bearing surface with a position-dependent delay through the structured thermal buffer layer;

[0040] Wherein the heat transferred to the bearing surface causes a portion of the sample in contact with the bearing surface to evaporate and thus generate a vapor pressure that conveys the remaining portion of the sample towards the target surface, and the evaporation has a position-dependent delay determined by the structured thermal buffer layer.

[0041] A first exemplary embodiment includes: providing the bearing surface having at least a first sample bearing area and a second sample bearing area for respectively bearing first and second samples of the substance to be printed; and providing the thermal buffer layer having a thickness greater in one of the at least a first sample bearing area and a second sample bearing area having the largest dimension than in one of the at least a first sample bearing area and a second sample bearing area having the smallest dimension.

[0042] A second exemplary embodiment includes: providing the structured thermal buffer layer having a variable thickness to provide a position-dependent delay for the sample in being transferred to the target to optimize the coverage of the deposited sample of the substance on a non-planar surface of the target.

[0043] A third exemplary embodiment includes: providing the carrier having at least one recess on the first major side for receiving a sample of the substance to be printed; and providing the structured thermal buffer layer having a thickness less at a boundary adjacent to the recess than in a central portion of the recess.

[0044] A fourth exemplary embodiment includes: providing the structured thermal buffer layer having a plurality of micro-wells in at least one sample bearing area, wherein the sample of the substance to be printed is distributed on these micro-wells.

[0045] A fifth exemplary embodiment includes: providing the structured thermal buffer layer having a plurality of micro-columns in at least one sample bearing area. Description of the Drawings

[0046] These and other aspects will now be described in more detail with reference to the drawings. In the drawings:

[0047] Figures 1A to 1C shows the phenomena occurring during the operation of a known printing device used in a first application;

[0048] Figures 1D to 1F shows the simulation results representing the dynamic behavior of a viscous substance related to this application;

[0049] Figures 2A to 2C shows the operating phases of an embodiment of the preferred printing device in the first application;

[0050] Figures 3A to 3C shows the phenomena occurring during the operation of a known printing device used in a second application;

[0051] Figures 4A to 4C shows the operation of an embodiment of the preferred printing device in this second application;

[0052] Figures 5A to 5C shows the phenomena occurring during the operation of a known printing device used in a third application;

[0053] Figures 6A to 6C shows the operation of an embodiment of the preferred printing device in this third application;

[0054] Figure 6D and Figure 6E shows the simulation results related to this third application;

[0055] Figure 7 shows the phenomena occurring during the operation of a known printing device used in a fourth application;

[0056] Figure 8 shows the operation of an embodiment of the preferred printing device in this fourth application;

[0057] Figure 9A and Figure 9B shows aspects of another embodiment of the preferred printing device. Wherein Figure 9A shows the first main side of the lateral part of the carrier 2, and Figure 9B shows according to Figure 9A a cross-sectional view of IXB - IXB in;

[0058] Figures 10A to 10C shows the operation of another embodiment of the preferred printing device;

[0059] Figures 11A to 11C shows the simulation results. DETAILED DESCRIPTION

[0060] Unless otherwise indicated, like reference symbols in different drawings represent like components.

[0061] Figures 2A to 2C Schematically shown are the operating stages of an embodiment of an improved printing device 1 for printing a substance on a target surface TS of a target T. The target is, for example, a rigid substrate made of, such as glass, or a flexible substrate made of, such as a polymer. As Figure 2A shown, the printing device 1 includes a carrier 2 having a bearing surface on a first major side 21 for bearing a specimen of the substance to be printed. The substance may have predetermined physical characteristics, such as specific conductivity and specific heat conductivity. For example, the substance may be an electrically insulating and thermally insulating material, an electrically insulating and thermally conductive material, a conductive and thermally insulating material, and a conductive and thermally conductive material. Substances commonly referred to as, for example, inks or slurries include nano-particles or micro-particles or mixtures thereof suspended in a (high-boiling point) solvent. Epoxy-based materials such as adhesives or conductive adhesives having silver micro-particles may also be used. Alternatively or additionally, the substance may include one or more of the following: positive photoresist or negative photoresist, polymer solution, molten polymer, monomer, or polysiloxane-based material. For the purposes of the present invention, it is sufficient as long as the substance includes components that can evaporate at a relatively moderate temperature (i.e., not greater than several hundred degrees C).

[0062] In this case, three specimens SB1, SB2, SB3 of the substance having different sizes are present on the bearing surface.

[0063] The preferred printing device includes a heating device. By actuating the heating device, the bearing surface is heated so as to evaporate a part of the specimen on the bearing surface side and generate a vapor pressure that conveys the remaining part of the specimen toward the target surface. In the example shown, the heating device is an electric heating layer 23 for resistively heating the bearing surface.

[0064] In the figure shown here, a thermal insulation layer 22 is disposed between the carrier 2 and the resistive heating layer 23. The thermal insulation layer 22 is optional and reduces heat loss in a direction away from the bearing surface, and thus contributes to more efficient operation. The thermal insulation layer 22 is made of, for example, a ceramic material and has a thickness, for example, in the range of several hundred nm to several microns. The thermal insulation layer thus also serves as an electrical insulation layer. In an efficient processing manner, the thermal insulation layer is obtained by oxidizing the material of the carrier 2. For example, in the case where the carrier is provided with a silicon (1-0-0) wafer, a thermal insulation layer 22 of SiO 2 can be obtained by oxidizing the carrier.

[0065] In one embodiment, the figures also show an electrically insulating layer 24 disposed between the resistive heating layer 23 and the structured thermal buffer layer 25. In this case, a ceramic material layer having a thickness in the range of several hundred nanometers (nm) to several micrometers is also suitable. In one example, the material used for this layer is Si 3 Ni 4 . In the case where the printing device is only used for depositing an electrically insulating substance, the electrically insulating layer 24 can be omitted. In the case where the structured thermal buffer layer 25 has a non-zero thickness in the region for carrying the substance to be printed, the electrically insulating layer 24 can also be omitted.

[0066] As Figure 2A further shown, the preferred printing device further includes a structured thermal buffer layer 25, which provides a position-dependent delay for heat to be transferred from the resistive heating layer 23 to the position of the carrying surface.

[0067] In Figure 2A the shown embodiment, the carrying surface includes at least a first specimen-carrying area 261 and a second specimen-carrying area 262 for carrying a first specimen SB1 and a second specimen SB2 of the substance to be printed, respectively. The structured thermal buffer layer 25 has the maximum thickness in the first specimen-carrying area 261 for carrying the largest specimen SB1. Compared with the thickness in the first specimen-carrying area 261, the structured thermal buffer layer 25 has a smaller thickness in the second specimen-carrying area 262 for carrying a specimen SB2 other than the largest specimen. In the third specimen-carrying area 263 for carrying the smallest specimen SB3, the thickness of the structured thermal buffer layer 25 is zero.

[0068] Figure 2B shows an operation stage, in which the resistive heating layer 23 has heated the carrying surface to evaporate a part of the specimen on the side of the carrying surface and thus generate a vapor pressure to transfer the remaining part of the specimen towards the target surface. What is achieved by the structured thermal buffer layer 25 is that heat from the resistive heating layer 23 is transferred to the carrying surface with a position-dependent delay according to the size of the specimen to be printed. For a larger specimen, the delay is longer. Thus, it is achieved that all specimens have a convex shape when reaching the target surface TS. As Figure 2C shown, thus each specimen SB1, SB2, SB3 appropriately covers the target surface and avoids entrapping air bubbles. In addition, what is also avoided is that the specimen contacts the heater again due to the oscillation after starting to be transferred towards the target. Although the same effect can be achieved by a heating device that supplies heat flux controlled according to the size of the specimen, this involves a rather high cost.

[0069] For example, in the obtained experimental results, the substance to be printed is SunChemical silver flake ink with a template thickness of 100 μm on the carrier surface. For printing, heat has a fixed flux of 0.5 J / cm 2 and the maximum printable droplet diameter Dmax (μm) is determined according to this heat flux (kW / cm 2 ), as shown in the following table.

[0070] <![CDATA[Heat flux (kW / cm 2 )]]> Dmax (μm) 100 1000 125 750 150 350

[0071] Therefore, as long as the structured thermal buffer layer 25 has a non-zero thickness at the positions of larger specimens with sizes of 750 μm and 1000 μm to moderate the local heat flux to 125 kW / cm 2 and 100 kW / cm 2 respectively, specimens with diameters of 350 μm, 750 μm and 1000 μm, for example, can be printed by the same heating device with a fixed heating pulse flux of 0.5 J / cm 2 and a heat flux of 150 kW / cm 2 . The structured thermal buffer layer 25 can have a zero thickness at the position of the smallest specimen.

[0072] Figures 11A to 11C The simulation results shown further confirm that when the structured thermal buffer layer has a thickness decreasing from the central position of the specimen to be transferred towards the radially outward direction, the oscillation of the transferred specimen can be substantially reduced.

[0073] Figure 3A 、 Figure 3B 、 Figure 3C shows another application performed with a known printing device. The application shown here is related to printing a strip of substance SB on a target T, and the target has a height distribution in the direction of the strip to be printed. In the example shown, the strip to be printed SB is composed of a conductive material that can be connected by docking points C1, C2. Here, the height distribution is defined by a first target surface portion TS1 that configures the contact point C1 and has a relatively large distance from the carrier 2 and a second target surface portion TS2 that configures the contact point C2.

[0074] Figure 3B shows an operating stage in which the resistive heating layer 23 has heated the carrier surface to evaporate a small specimen SB layer on the carrier surface side and thus generate a vapor pressure that conveys the remaining portion of the specimen towards the target surface. As Figure 3BAs shown, the strip SB moves substantially forward along its length at a substantially constant speed towards the target T. Since the vapor pressure distribution is mainly determined by the distance to the side of the strip SB (which is substantially constant in the direction x), and if the width of the strip is substantially smaller than its length, the speed is only slightly less at its ends SBL, SBR than at its central part SBC.

[0075] Accordingly, as Figure 3C shown, the side SBL reaches the target first at the second target surface portion TS2 which is elevated relative to the first target surface portion TS1. At this point in time, the speed of the central part SBC of the strip decreases, and accordingly the side SBR of the strip SB contacts the first target surface portion TS1. Due to the cohesion of the material of the specimen, the central part SBC does not cover the first target surface portion TS1 but leaves a space E. This results in a fragile connection.

[0076] Figure 4A , Figure 4B , Figure 4C shows the same application as that Figure 3A , Figure 3B and Figure 3C described, this time being carried out with an embodiment of the preferred printing device.

[0077] Figure 4A The embodiment of the preferred printing device shown in Figure 4A has a specimen carrier zone 264 configured to carry a specimen SB of the material, the specimen SB being to be transferred to a target T having a non-planar surface TS1, TS2. That is, the structured thermal buffer layer 25 has a varying thickness within the specimen carrier zone 264. Since the thickness of the structured thermal buffer layer 25 changes according to position, heat is also transferred from the resistive heating layer 23 to the material SB with a position-dependent delay. Accordingly, the transfer of the material SB to the non-planar surface TS1, TS2 is also carried out with a position-dependent delay. Thus, the coverage of the deposited specimen SB of the material on the non-planar surface can be optimized as exemplified below. In the Figure 4A , Figure 4B , Figure 4CIn an exemplary application of a preferred printing device, the specimen carrier region 264 has a first part 2641 that will be positioned opposite a surface part TS2 of the target T that is relatively close to the carrier 2. It has a second part 2642 that will be positioned opposite a surface part TS1 of the target T that is relatively far from the carrier 2 and laterally close to the surface part TS2. A third part 2643 of the specimen carrier region will be positioned opposite a surface part TS1 of the target T that is relatively far from the carrier 2 and laterally further from the surface part TS2 of the target T. In this example, the thickness of the structured thermal buffer layer 25 in the second part 2642 is less than or zero compared to the thickness of the structured thermal buffer layer 25 in the first part 2641 and the third part 2643.

[0078] The function of the thermal buffer layer 25 configured in this way is shown in Figure 4B and Figure 4C . As Figure 4B shows, what is achieved by the relatively small thickness of the second part 2642 of the structured thermal buffer layer 25 is that the central part SBC of the strip SB is transmitted with a delay that is shorter than those of the end parts SBL, SBR. Thus, it can reach the first target surface part TS1 before it is decelerated by the end part TS2. Thus, the coverage rate of the deposited specimen strip SB of the substance on the non-planar surface can be achieved, as Figure 4C shows.

[0079] Figure 5A , Figure 5B , Figure 5C shows another application performed with a known printing device. In this example, the carrier 2 has at least one recess 211 at the first main side 21 for accommodating specimens SB1, SB2, SB3 of the substance to be printed. These recesses 211 are provided in a low thermal conductivity coating 27 on the carrier 2. Figure 5A shows the operating state in which these recesses 211 are filled with the substance. In Figure 5A , the symbol 28 represents a heat dissipation layer.

[0080] Figure 5B shows an operating stage in which the resistive heating layer 23 has heated the carrier surface to evaporate a small specimen layer on the carrier surface side in order to generate a vapor pressure that conveys the remaining part of the specimen towards the target surface.

[0081] Although the heat dissipation layer 28 is used to provide a heat flow towards the side walls of these recesses 211, this involves a delay. Therefore, the specimen starts to be conveyed while its periphery is still adhered to the side walls of the recess that houses it. As can be seen in the figure, the following phenomena occur. In this example, the relatively large specimen SB1 breaks at the central part towards the target conveyance, breaks at two intermediate parts also towards the target but in a deviated direction, and breaks at the peripheral part remaining on the side walls of the recess. Since it is adhered to these side walls, the specimen SB2 remains integrally within its recess. Finally, the central part of the specimen SB3 is conveyed to the target, but its central part remains around the side walls of the recess 211 and the surrounding surface of the low thermal conductivity coating 27.

[0082] Therefore, as Figure 5C shown, a part of the specimen to be printed is not conveyed at all, or is only partially conveyed or not conveyed properly.

[0083] Figure 6A , Figure 6B , Figure 6C shows the same applications as those Figure 5A , Figure 5B , Figure 5C described, this time implemented with an embodiment of the preferred printing device.

[0084] As Figure 6A , Figure 6B , Figure 6C shown, the preferred printing device includes a structured thermal buffer layer 25 that has a thickness less at the boundary near the recess 211 than at the central part of the recess 211. More specifically, the structured thermal buffer layer 25 has a non-zero thickness at the bottom of the central part of the recess, but has a zero thickness at the side walls near the boundary of the recess.

[0085] Figure 6A shows the operating states of the specimens SB1, SB2, SB3 in which these recesses 211 are filled with the substance.

[0086] Figure 6B shows an operating stage in which the resistive heating layer 23 has heated the bearing surface to evaporate a small layer of the specimen on the side of the bearing surface in order to generate a vapor pressure that conveys a remaining part of the specimen towards the target surface. In this operating stage of the preferred device, the structured thermal buffer layer 25 delays the heat flux from the resistive heating layer 23 in the bottom of the recess such that the delay is comparable to the delay of the heat flux towards these side walls. Therefore, the specimens SB1, SB2, SB3 are heated substantially uniformly at the interface in contact with the carrier within the recess 211. Therefore, it prevents the substance of the specimens SB1, SB2, SB3 from remaining adhered to the side walls of the recess 211.

[0087] As Figure 6C shown, the specimens SB1, SB2, and SB3 are thus printed on the surface of the target in a manner consistent with the shape defined by the recess 211 of the carrier.

[0088] There is no need to fully compensate for the delay in heat transfer to the sidewalls of the recess. It is more advantageous to release the substance with a slight delay (0.1 to 0.5 μs). As Figure 6B the example of

[0089] Figure 6D and Figure 6E shows the simulation results.

[0090] wherein Figure 6D shows the temperature change over time at three positions in the recess, which are Figure 6E the top center TC, the top edge TE, and the bottom B shown in Figure 6E shows the simulated temperature distribution that occurs 3 μs after the start of the heating pulse.

[0091] In this simulation, a 1-μm-thick heat dissipation layer 28 with a thermal conductivity of 60 W / mK is preset. For the recess 211 with a width of 10 microns (w10) and for the recess 211 with a width of 20 microns (w20), various thicknesses d25 of the structured thermal buffer layer 25 (preset here as SiO 2 ) show the microsecond delay td relative to its center when the heating pulse reaches the sidewalls of the recess 211. These results are shown in the following table.

[0092] d25 (μm) Td (μs) for w10 Td (μs) for w20 0 2.4 3.0 0.5 1.2 1.8 1 0.8 1.0 2 -4 -5

[0093] The cross-sectional view shows the temperature distribution at a time point 3 microseconds after the heating pulse generated in the resistive heating layer 23.

[0094] As can be seen from this example, by only using the silica in the bottom of the 1-μm recess, the relative delay td can be reduced to equal to or less than 1 microsecond.

[0095] Figure 7 shows another application performed with a known printing device.

[0096] In this application, the material SB to be printed comprises particles SBp in a suspending agent SBs. One example is a solder paste comprising relatively large metal particles having a high thermal conductivity, these larger metal particles being suspended in a suspending agent which generally has a relatively low thermal conductivity. The thermal penetration depth dt in the suspending agent is thus typically only on the order of a few micrometers. However, when the particle SBp approaches the bearing surface (<2 μm), it can act as a strong heat sink. This is shown in the figure above the carrier 2. Due to this heat dissipation effect, the temperature rises more slowly near the metal particle compared to a part of the material SB where no heat dissipation occurs. Thus, the release of the material SB is delayed near these particles. Generally, this heat dissipation is asymmetric, and thus the material is not conveyed vertically away from the carrier and lands at the wrong position on the target.

[0097] Figure 8 Shows the same application as Figure 7 executed with an embodiment of the preferred printing device. As shown here, the structured thermal buffer layer 25 has a plurality of micro-columns 252 in at least one specimen bearing area (264). These micro-columns have a height of the same order of magnitude as or slightly higher than the thermal penetration depth of the suspending agent, and are separated from each other by a distance small enough to prevent the particles SBp from directly contacting the surface below the structured thermal buffer layer 25. Thus, uniform heating of the material SB on the surface where it contacts the structured thermal buffer layer 25 is achieved, and at the same time, as shown in the figure above the carrier 2, a uniform distribution of its release time is also achieved.

[0098] Figure 9A and Figure 9B Shows aspects of another embodiment of the preferred printing device. Where Figure 9A shows the first main side of the lateral part of the carrier 2, and Figure 9B shows a cross-sectional view according to Figure 9A IXB - IXB in. As Figure 9A and Figure 9B shown, the structured thermal buffer layer 25 has a plurality of micro-wells 253 in at least one specimen bearing area 264, where specimens SB1a,..., SB1n of the material to be printed are distributed on these micro-wells. The micro-wells 253 in the specimen bearing area 264 have a diameter of less than about 50 micrometers and a center-to-center distance between 1 times and 2 times that diameter.

[0099] As Figures 10A to 10C shown, this other embodiment is particularly suitable for printing low-viscosity materials, i.e., materials having a viscosity of less than 1 Pa*s.

[0100] Figure 10AShows an operating state in which these micro-wells 253 are filled with a low-viscosity material. In this example, the isolated micro-wells 253 on the left are filled with a specimen SB2 of a low-viscosity material and the micro-wells 253 within the at least one specimen carrier region 264 are filled with respective specimens SB1a, …, SB1n of another low-viscosity material. In the example shown, the micro-wells 253 are substantially hemispherical, where the micro-wells 253 abut against the electrical insulation layer 24. In an alternative embodiment that is only used for printing electrical insulation material, there is no electrical insulation layer 24 and the micro-wells 253 directly abut against the resistive heating layer 23. In another example, there is no electrical insulation layer 24 and the structured thermal buffer layer 25 is formed of an electrical insulation material and has a non-zero thickness at the bottom of the micro-wells 253. It should be further noted that the micro-wells can have a shape other than hemispherical.

[0101] Figure 10B Shows an operating stage in which the resistive heating layer 23 has heated the carrier surface. As shown herein, a portion of the low-viscosity material near the bottom of the micro-well 253 is first heated and evaporated, while the low-viscosity material near the sidewall of the micro-well 253 remains fluid in the absence of a heat dissipation layer and will remain within the micro-well due to the adhesion force between the material and the structured thermal buffer layer 25. Thus, a shear force Fs is generated in the specimen of the low-viscosity material in the micro-well, and this shear force conveys the specimen as a micro-jet towards the target T. For example, the specimen SB2 is conveyed as a micro-jet J2 and the specimens SB1a, …, SB1n are conveyed as micro-jets J1a, …, J1n.

[0102] As Figure 10C shown, when hitting the target surface Ts, the specimens SB1a, …, SB1n of the low-viscosity material from the specimen carrier region 264 and conveyed through the micro-jets J1a, …, J1n can disperse and flow together to form a uniform coating SB2.

[0103] Although in the illustrated embodiment, all of the micro-wells 253 abut against the electrical insulation layer 24, the micro-wells can have different depths. For example, in some micro-wells, the structured thermal buffer layer 25 can have a non-zero thickness at its bottom to provide a delay in the conveyance of the material therein relative to the conveyance from other micro-wells.

[0104] Figure 11A 、 Figure 11B 、 Figure 11C Shows other simulations of the deformation of the specimen when investigating its conveyance.

[0105] The simulation is performed under the following conditions:

[0106] Heat flux generated by the electrical heating layer: 150 kW / cm 2 .

[0107] The substances specified in this simulation have the following properties:

[0108] Density: 2650 kg / m 3 .

[0109] Thermal conductivity: 0.4 W / mK.

[0110] Modulus of elasticity: 2 MPa

[0111] Viscosity: 1 Pa·s.

[0112] It is assumed that the substance is conveyed as a rotationally symmetric specimen with a diameter of 1.2 mm and a maximum height of 100 μm.

[0113] Figure 11A , Figure 11B and Figure 11C The top of each of the figures shows the relative delay (if any) in μs generated by the thermal buffer layer (if any) according to the change in the radial part r in μs. The bottom of these figures shows the simulated shapes of the specimens conveyed at subsequent time points t1 to t7. The specimen is shown as a cross-section through its center.

[0114] In Figure 11A the case shown, the heat pulse reaches the entire surface below the specimen at the same time point. Row 0 represents the cross-section of the specimen when the specimen is still on the donor plate surface. It can be seen that at time points t1 to t3, the specimen has become concave. This implies that in this case, if the printing gap between the donor plate surface and the target surface is in the range of approximately 250 μm to approximately 750 μm, the specimen will generate bubbles.

[0115] In Figure 11B the case shown, the heat pulse reaches the donor plate surface with a delay increasing radially from 0 μs at the center of the specimen to 5 μs at the edge of the specimen. As shown in the lower part of Figure 11B , this affects the way the shape of the specimen changes during conveyance of the specimen. Figure 11B shows that there is still a risk of the specimen generating bubbles if the specimen reaches the target at time points t1, t3 or t6.

[0116] In Figure 11C the case shown, the heat pulse reaches the donor plate surface with a delay decreasing radially from 5 μs at the center of the specimen to 0 μs at the edge of the specimen. As shown in the lower part of Figure 11C , through this delay pattern, the oscillation of the specimen can be substantially suppressed. Therefore, the printing gap can be selected from a large range while avoiding the risk of generating bubbles.

[0117] In other embodiments, what can be achieved through the thickness distribution of the thermal buffer layer is to generate a desired oscillation to achieve a specific desired deposition pattern for the remaining specimens.

[0118] In the claims, the term "comprising" does not exclude other elements or steps, and the indefinite article "a" does not exclude a plurality. A single element or other unit may fulfill the functions of several items recited in the claims. The fact that certain methods are recited in mutually different claims does not indicate that these methods cannot be used in combination 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 on a first main side (21) a bearing surface (2s) for bearing specimens (SB1, SB2, SB3) of the substance to be printed; and a heating device (23) for heating the bearing surface to evaporate a part of the specimen on the side of the bearing surface and generate a vapor pressure, the vapor pressure causing the remaining part of the specimen to be conveyed towards the target surface; and a structured thermal buffer layer (25) providing a position - dependent delay for heat transfer from the heating device to the bearing surface.

2. The printing device (1) according to claim 1, wherein the heating device (23) is an electrically - heated layer (23) for resistively heating the bearing surface.

3. The printing device (1) according to claim 1, wherein the heating device (23) is a photon radiation source.

4. The printing device according to any one of the preceding claims, wherein the bearing surface comprises at least a first specimen - bearing zone (261) and a second specimen - bearing zone (262) for bearing respectively a first and a second specimen (SB1, SB2) of the substance to be printed, wherein the thickness of the thermal buffer layer in the zone having the largest dimension among the at least one first specimen - bearing zone (261) and the second specimen - bearing zone (262) is greater than the thickness of the thermal buffer layer in the zone having the smallest dimension among the at least one first specimen - bearing zone (261) and the second specimen - bearing zone (262).

5. The printing device according to claim 1, 2 or 3, the printing device having a specimen - bearing zone (264) configured to bear a specimen (SB) of the substance to be conveyed to the target (T), and wherein the structured thermal buffer layer (25) has a thickness distribution within the specimen - bearing zone (264) to control the dynamic behavior of the remaining part of the specimen when being conveyed to the target surface.

6. The printing device according to claim 5, wherein the specimen - bearing zone (264) is configured to bear a specimen (SB) of the substance to be conveyed to a target (T) having a non - planar surface (TS1, TS2), and wherein the structured thermal buffer layer (25) has a variable thickness within the specimen - bearing zone (264) to provide a position - dependent delay for the specimen when being conveyed to the non - planar surface (TS1, TS2) to optimize the coverage rate of the deposited specimen (SB) of the substance on the non - planar surface (TS1, TS2).

7. The printing device according to claim 6, wherein The specimen bearing area (264) has: a first part (2641) that will be positioned opposite a surface part (TS2) of the target (T), the surface part (TS2) being relatively close to the carrier (2); a second part (2642) that will be positioned opposite a surface part (TS1) of the target (T), the surface part (TS1) being relatively far from the carrier (2), and the second part being laterally close to the surface part (TS2) of the target (T); and a third part (2643) that will be positioned opposite the surface part (TS1) of the target (T) that is relatively far from the carrier (2), and the third part being laterally further from the surface part (TS2) of the target (T), and wherein the thickness of the structured thermal buffer layer (25) in the second part (2642) is less than or zero compared to the thickness of the structured thermal buffer layer (25) in the first part (2641) and the third part (2643).

8. The printing device according to claim 5, wherein, the thermal buffer layer has a thickness that decreases in a radially outward direction from the central position of the specimen bearing area.

9. The printing device according to claim 1, 2 or 3, wherein, the carrier (2) has at least one recess (211) on the first main side (21) for accommodating a specimen (SB1) of the substance to be printed, and wherein the thickness of the structured thermal buffer layer (25) at the boundary close to the recess is less than the thickness of the structured thermal buffer layer (25) in the central part of the recess.

10. The printing device according to claim 1, 2 or 3, wherein, the structured thermal buffer layer (25) has a plurality of micro-wells within at least one specimen bearing area (264), and wherein specimens of the substance to be printed are distributed on the micro-wells.

11. The printing device according to claim 10, wherein, the micro-wells provided in the structured thermal buffer layer (25) have different depths.

12. The printing device according to claim 1, 2 or 3, wherein, the structured thermal buffer layer (25) has a plurality of micro-columns within at least one specimen bearing area (264).

13. A method for printing a substance on a target surface (TS) of a target (T), the method comprises: providing a carrier (2) having a bearing surface (2s) on a first main side (21), the bearing surface for bearing specimens (SB1, SB2, SB3) of the substance to be printed; providing a heating device (23) for heating the bearing surface; providing a structured thermal buffer layer (25) between the resistive heating layer (23) and the bearing surface (2s); actuating the heating device; transferring heat from the heating device to the bearing surface through the structured thermal buffer layer (25) with a position-dependent delay; Wherein, the heat transferred to the bearing surface causes a part of the specimen in contact with the bearing surface to evaporate with a position-dependent delay determined by the structured thermal buffer layer (25), and thus generates a vapor pressure that conveys the remaining part of the specimen towards the target surface.

14. The method according to claim 13, the method comprises: providing the bearing surface having at least a first specimen bearing area (261) and a second specimen bearing area (262) for respectively bearing first and second specimens (SB1, SB2) of the substance to be printed; and providing the thermal buffer layer having a thickness greater in the one with the maximum dimension within at least the first specimen bearing area (261) and the second specimen bearing area (262) than in the one with the minimum dimension within at least the first specimen bearing area (261) and the second specimen bearing area (262).

15. The method according to claim 13, the method comprises: providing the structured thermal buffer layer (25) having a variable thickness to provide a position-dependent delay for the specimen when being conveyed to the target (T), so as to optimize the coverage rate of the deposited specimen (SB) of the substance on the non-planar surface (TS1, TS2) of the target.

16. The method according to claim 13, the method comprises: providing the carrier (2) having at least one recess (211) on the first main side (21) for accommodating a specimen (SB1) of the substance to be printed; and providing the structured thermal buffer layer (25) having a thickness less at the boundary near the recess than in the central part of the recess of the structured thermal buffer layer (25).

17. The method according to claim 13, the method comprises: providing the structured thermal buffer layer (25) having a plurality of micro-wells within at least one specimen bearing area (264), wherein specimens of the substance to be printed are distributed on the micro-wells.

18. The method according to claim 13, the method comprises: providing the structured thermal buffer layer (25) having a plurality of micro-columns within at least one specimen bearing area (264).

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