DE102007043396A1 - Method for manufacturing electrical conducting structures, involves producing channels on surface of substrate by mechanical and additionally thermal effects and ink is applied on channels - Google Patents

Abstract

The method involves producing channels on the surface of the substrate by mechanical and additionally thermal effects. An ink is applied on the channels, with which electrical conducting structures are produced. The channels are filled with ink by capillary force. The ink is changed into conducting structure by insertion of energy. The electrically conductive material or precursor connection for an electrically conducting material of the ink has carbon nanotubes, electrically conducting polymer or metal nano-particles, particularly silver nano-particle or metal oxide nano-particles. Independent claims are also included for the following: (1) a substrate with electrically conducting structures (2) an application of ink is produced with the conducting structures.

Description

The The present invention describes a process which comprises the preparation small and smallest conductive structures on surfaces allows. Small and smallest structures are in this Context regarded as structures governed by the human Eye generally only with the help of optical aids are perceptible. This is achieved through the production of microchannels by (hot) embossing and / or imprinting nanoscale Wells, the subsequent, targeted introduction of conductive Material in the wells produced with the aid of the physical effect of the capillary force, and finally by a suitable after-treatment of the conductive material.

It there is a need surfaces in particular of electrical not or poorly conductive transparent objects with electric to equip conductive structures without their optical or to impair mechanical or physical properties. Furthermore, there is a need for the surfaces with such Equip structures that are imperceptible to the human eye, where z. B. transparency, translucence and gloss of the surface not possible to negatively influence. Generally is here recognized as having the structure for this purpose characteristic dimension must be less than 25 microns. For example So a line of any length but with a maximum width and depth of 25 μm.

One way to apply small structures to substrates is through various printing techniques. One of these printing techniques is the so-called ink-jet technique, which is present in various embodiments. By means of a positionable nozzle while drops or jets of liquid are applied to a substrate. The main influence on the width of a line generated by an inkjet in this case has the diameter of the nozzle used. Furthermore, there is a rule not yet refuted, according to which the line width is at least as large or mostly larger than the diameter of the nozzle used. This results in a line width ≥ 60 μm, for example, when using a nozzle with an outlet opening of 60 μm [ J. Mater. Sci. 2006, 41, 4153 ; Adv. Mater. 2006, 18, 2101 ]. An example of a carbon nanotube-based ink as a conductive substrate for printing conductive lines is shown in FIG US 2006/124028 A1 disclosed.

It So it is obvious, this opening simply on a size from about 15-20 μm to the desired one Line width of ≤ 25 microns to get. This solution is not feasible in practice, as with the reduction the diameter used rheological restrictions Printing substances (inks, inks, conductor pastes etc.) in influence win. In many cases, the printing substances for the purpose unusable. Possible here are in particular Complications due to blocking of the nozzle, as the pressure substance contains dispersed particles. Furthermore you can the rheological requirements (specific viscosity and surface tension, as well as contact angle and wetting of the substrate) are not independent be adjusted by each other, so that one with such Nozzle still printable ink not the desired Properties in the printed image on the substrate shows.

Alternative, commercial printing technologies, such as offset or screen printing generally not capable of such fine structures on a surface bring to.

Another approach to producing small and minute structures is to treat the substrate by suitable methods (eg, plasma method) such that regions of different wettability are formed, for example, using masks containing a negative of the structure to be generated. This results, for example, in line widths of 5 μm using aqueous polymers [ Science 2000, 290, 2123 ]. Using a similar approach, structures with widths smaller than 5 μm could already be produced. However, complicated lithography steps are necessary for these processes. [ Nature Mater. 2004, 3, 171 ].

In US 2006/188823 A1 discloses a method in which an additional photoactive coating is applied to the substrate. This is then physically provided by impressing with a structure. The resulting structure is then cured by means of UV light. Furthermore, subsequent etching and hardening steps are provided. However, the exact nature of the conductive materials used in the resulting structures is not disclosed. This method is relatively cumbersome and expensive due to the many processing steps.

A simple, mechanical process for producing small structures without producing a conductive structure, in particular on polymers, makes use of (hot) embossing or nanoscale impressions. In essence, here stamps are pressed with pressure on the substrate and thus an impression of the negative of the structure of the stamp is achieved on the surface. In particular, the hot embossing of polymeric substrates with punches above the glass transition temperature of the polymer has already been used herein to produce structures with a diameter of 25 nm. in the Contrary to the lithography methods mentioned above, the stencil used (also called master) can always be reused in embossing processes. [ Appl. Phys. Lett. 1995, 67, 3114 ; Adv. Mater. 2000, 12, 189 ; Appl. Phys. Lett. 2002, 81, 1955 ].

In order to obtain conductive structures from the structures obtained, they must be filled with suitable material. For this approach doctoring and wiping processes are in principle suitable. Such a method is for example from the WO 1999 45375 A1 known. Here, an excess of the material with which the structures are to be filled is applied to the substrate and distributed in the structures in which the material is to remain, while the remaining substrate is largely cleaned with the wiping technique used by the material. A disadvantage of this procedure is that in addition to the possibly high losses of filling material and a complete freedom of the substrate from residues of the filling material can not be ensured at places not filled to be difficult. In US 6911385 B1 discloses a method using a continuous and discontinuous embossing process. In both cases, a conductive ink is applied as a homogeneous film on a surface and subsequently removed by embossing at those locations material where the surface should not be conductive. Alternatively, a method is disclosed in which a conductive ink is applied through the openings while leaving a porous embossed pattern (stamp) on the substrate. Therefore, at the points where the stamp is in direct contact with the substrate at the time of applying the ink, no ink is applied and thus the desired patterning is achieved.

A filling of fine structures can basically be brought about by using the capillary force, but their sensible use presupposes a targeted introduction of the filling material into the structure produced, in order to avoid material waste. The filling of small structures (or tubes, see J. Colloid Interface Sci. 1995, 172, 278 ) by means of capillary action has already been described, in particular with liquid prepolymers (for example polymethyl acrylate; J. Phys. Chem. B 1997, 101, 855 ), or aqueous solutions of biomolecules such as DNA in microfluidic components ( ChemPhysChem 2003, 4, 1291 ). However, filling such structures with material that is later rendered conductive has not yet been disclosed.

It So task was the present invention, on surfaces create conductive structures that are below the threshold of perception of the human naked eye (i.e., less than 25 μm) and do not affect the properties of the component in any other way. The other disadvantages of the known methods described above should be avoided.

It has been found that a combination of the embossing of a depression into the substrate surface and the use of conductive nanoparticles containing ink formulations with subsequent sintering of the nanoparticles can be used to continuously conductive webs. A brief illustration of the processes there 1 ,

object The invention is a process for producing electrically conductive Structures that in two dimensions have a dimension of not more than 25 μm, on a substrate with a moldable surface, in which on the surface of the substrate by mechanical and optionally in addition thermal action channels which are preferably dimensioned in one dimension not more than 25 microns (for example, a width at the base of the channels of less than 25 μm), on the channels an ink, preferably a suspension conductive Particles being applied with the conductive structures can be generated, the channels by capillary force be filled with the ink, and the ink by introducing of energy, in particular by thermal treatment, in conductive Structures is transformed.

object the invention are also according to the above new method available substrates having structures that are known in two dimensions a dimension of not more than 25 microns to have.

Preferably, first a press die or a press roll, each provided with a raised microstructure (positive), is pressed onto the substrate, which is preferably a polymer substrate in order to emboss a negative of the structure of the punch into the surface of the substrate. If a polymer substrate is used, the stamp or the press roll preferably has at least the temperature of the glass transition point of the polymer substrate used. More preferably, the punch or press roll temperature is at least 20 ° C above the glass transition temperature. Further preferably, the stamp or the pressure roller has small structures on its surface, which have in one dimension a dimension of not more than 25 microns, preferably from 25 .mu.m to 100 nm, more preferably from 10 .mu.m to 100 nm, most preferably from 1 μm to 100 nm. The period of time of pressing the stamp into the substrate should be in particular 1 to 60 minutes, preferably 2 to 5 minutes, more preferably it is pressed in for 3 to 4 minutes. In contrast, the use of a press roller requires shorter press times, since a higher press pressure is used in this case. The produce In this case, embossing structures are carried out continuously.

The relative speed from substrate to roll is at this Process at 10 to 0.00001 m / s, preferably 1 to 0.0001 m / s, especially preferably 0.1 to 0.0001 m / s.

The Parameters contact pressure, temperature and duration of pressing in However, they correlate in the way that with higher temperature or higher pressure the Einpresszeit can be reduced. This means correspondingly lower times and thus higher Component throughputs conceivable with methods presented here. Also conceivable are methods that are applied high contact pressures for a short period of time even when appropriate low temperature of the stamp or rolls the desired result demonstrate.

Prefers so the roll is pressed onto the substrate while the substrate is dragged under this roll and the roll becomes it rotates, or the roller is driven and thus the substrate promoted under impressions of the channels in the substrate.

In the resulting channels are then filled with an ink, with the conductive structures can be generated. In the simplest case, the ink consists of a solvent or a suspension liquid and an electric one conductive material or a precursor compound for an electrically conductive material.

The For example, ink can be electrically conductive polymers, Contain metals or metal oxides, carbon particles or semiconductors. Preferred is an ink, the nanoparticles of a conductive Materials, in particular carbon nanotubes (carbon nanotubes) and / or metal particles dispersed in a solvent, For example, water that contains by sintering too lead a continuously conductive structure. Especially Preferably, the ink contains silver nanoparticles Water, which by sintering the silver particles to a continuously conductive Lead structure. Suitable metal oxides are, for. Indium tin oxide, Fluorine-tin-oxide, antimony-tin-oxide, zinc-aluminum-oxide. semiconductor include, for example, zinc selenite, zinc tellurite, zinc sulfide, cadmium selenite, Cadmium tellurite, cadmium sulfide, lead selenite, lead sulfide, lead tellurite and indium arsenite. Furthermore, for better utilization of the Capillary forces preferred in the new method used Ink wet the substrate as well as possible, d. H. one lowest possible contact angle on the substrate of not more than 60 °, preferably not more than 30 ° and the highest possible surface tension of more than 20 N / m, preferably more than 40 N / m, more preferably more than 50 N / m. Should the ink contain nanoparticles as described above, in particular, they should be smaller than 1 μm, preferably less than 100 nm. Particularly preferably, the nanoparticles are smaller than 80 nm, especially smaller than 60 nm and have a bimodal Particle size distribution on.

These Ink is then transferred to the channels as described above dosed. Preference is given to individual drops in the channels dosed. It is particularly preferable to use an ink jet for dosing Printer with a printhead whose print nozzles are exactly above the channels are arranged and individual drops in the Dosed channels.

Around as far as possible with the new method in a preferred variant long stretches of the channels on the substrate with the ink It may be necessary to fill several times in one Channel be dosed. Therefore, the ink is preferably in regular Intermittent dosing along the channels. Alternatively, the ink may be from the preferred ink jet printer continuously on the substrate passing under the print head be dosed. This is preferably done at suitable intervals, which depend on the type and shape of the channels on the substrate. For example, along along the direction of passage of the substrate oriented, continuous lines abandoned a continuous ink jet become. For example, with broken lines adjusted for the duration of the interruption, the dosage. In this case, the term broken line can also be used as a not parallel to the direction of passage of the substrate running Be understood line, z. B. at right angles to the direction of passage running lines. Here then can be in regular Interspaced pressure nozzles be provided to the entire channel structure during to fill a single passage.

In In a preferred variant, movable printheads are provided, during the relative movement of the substrate under them follow the impressed channel structure. This is for example the Case when curved along the orientation of the substrate, preferred corrugated channels were imprinted. When the printheads perpendicular to the direction of passage of the substrate are movable leads an oscillation of the printheads in the direction perpendicular to Substrate relative to this to a wave motion. Thus, a Wavy structure continuously filled with ink become. This is especially true for interrupted structures as well expandable to mounting versions in which the Print heads follow the passage direction of the substrate. That is, an apparatus of the printheads is provided which allows movement in two dimensions.

The Substrates applicable in the process according to the invention are substrates with moldable surfaces, eg. Glass, ceramics or polymers, in particular transparent polymers. These substrates are electrical insulators. However, it is desirable that resulting from the substrate components at least at certain Provide points with conductive properties.

Polymer Materials often have special properties that they have in many applications to make preferred materials. This includes, for example, theirs comparatively high flexibility, many times in comparison to inorganic materials lower density for the same or similar mechanical resilience, as well as the great design Freedom through the easier moldability of these materials. simultaneously show some materials (eg polycarbonate, polypropylene, polymethylmethacrylate (PMMA) and some types of PVC) in addition to special properties such as optical transparency. Preferably in the new process polymers to be used are transparent and / or they have one high glass transition temperature. Called polymers with high glass transition temperature Polymers with a glass transition temperature above 100 ° C. Particularly preferred to use in the new process a polymer from the series: polycarbonate, polyurethane, polystyrene, polymethyl (meth) acrylate or polyethylene terephthalate.

To The steps described above are located in the generated Channels an ink, from which by appropriate aftertreatment the structures with the desired conductivity be generated.

According to the invention this post-treatment the entry of energy into the generated, with Ink filled channels. In the case of the preferred use of inks with conductive polymers in solvent suspensions are present in suspension in the solvent Polymer particles z. B. by heating the suspension the substrate fused together while the solvent evaporated. The post-treatment step is preferred at the melting temperature of the conductive polymer, especially preferably above its melting temperature. This creates consistent Interconnects.

in the Case of alternative preferred use of carbon nanotubes containing inks is through the thermal aftertreatment of Substrate surface, the solvent between the dispersed present carbon particles evaporated to continuous, Percolatable sheets of conductive carbon to obtain. The treatment step is in the range of the evaporation temperature of the solvent contained in the ink, preferably above the evaporation temperature of the solvent. Once the percolation limit has been reached, the inventive compositions are formed Interconnects.

used one in another preferred variant of the method the above described suspensions of metal nanoparticles in solvents, Thus, the aftertreatment takes place by the entire component or deliberately heats the tracks to a temperature at which sinter the metal particles together and the solvent at least partially evaporated. Here are metal particles with as possible Small particle diameter advantageous because of nanoscale particles the sintering temperature proportional to the particle size is, so that with smaller particles a lower sintering temperature than is required for larger ones. This is the boiling point of the solvent as close as possible at the sintering temperature of the particles and is possible low to thermally protect the substrate. Preferably used as the solvent of the ink one with a boiling temperature of <250 ° C, particularly preferably a temperature <200 ° C, in particular one Temperature ≤ 100 ° C. All temperatures given here refer to boiling temperatures at a pressure of 1013 hPa. Particularly preferred solvents are n-alkanes with bis to 12 carbon atoms, alcohols having up to four carbon atoms, such as As methanol, ethanol, propanol and butanol, ketones and aldehydes with up to five carbon atoms, such as. Acetone and Propanal, water, and acetonitrile, dimethyl ether, dimethylacetamide, Dimethylformamide N-Methyl-pyrrolidone (NMP) and tetrahydrofuran Der Sintering step is carried out at the specified temperature until a continuous track has been created. Prefers is a period of one minute to sinter 24 hours, more preferably from five minutes to 8 Hours, more preferably from two to eight hours.

object The invention also relates to the use of an ink with which conductive Structures can be produced for the production of substrates, the conductive structures on their surface having in one dimension a dimension of not more than 25 μm, preferably from 20 μm to 100 nm, particularly preferably from 10 μm to 100 nm, very particularly preferably from 1 μm to 100 nm, the ink being preferred A suspension of conductive particles is as they are above and the substrate is preferably transparent, for example glass, transparent ceramic or a transparent polymer as described above.

The Invention will be exemplified below using the figures explained in more detail. Showing:

1 A scheme of carrying out the method according to the invention by means of a press die with A) pressing the press punch at the top into the substrate, B) lifting the press ram, C) applying the ink to the formed channel of the substrate, and D) sintering the ink material in the channel

2 : A photomicrograph of a cross-section through a polystyrene plate with embossed channels

3 : An enlarged view of the cross section through a polystyrene plate with sintered silver conductor

Examples

example 1

A grid of channels on a polymer substrate was prepared by pressing a grating structure (MASTER) in a polystyrene substrate having a glass transition temperature T _g of 100 ° C (N5000, Shell AG). For this purpose, the MASTER was heated to 180 ° C and by means of a small press (Tribotrak, DACH Instruments, Santa Barbara, CA, USA) 3 min. long with a load of 3 kg pressed onto the substrate. The MASTER had a spacing of the lines of 42 microns, seen in cross-section, the wells in the MASTER appear as truncated triangles that are upside down ( 2 ). The elevations in the MASTER have a height of 20 microns and are also seen in cross-section truncated triangles. The base width of the elevations in the MASTER was 32 μm and the width of the peak of the elevations was about 4.5 μm.

A single drop of silver ink (Nanopaste ^™ , Harima Chemicals, Japan) was placed on one of the lines prepared as described above. The ink consists of a dispersion of silver nanoparticles with a mean diameter of about 5 nm in tetradecane. The capillary force immediately formed a line of ink in the channels. It could be obtained about 4 mm long uniform line. The precise positioning of the ink drop was achieved by means of an ink-jet system (Autodrop ^™ system, Microdrop Technologies, Norderstedt, Germany.) The system was equipped with a 68 μm die head. The maximum width of the resulting silver line was about 6.3 μm at fill level, as in 3 can be seen. At its thinnest point, the width was about 3.7 μm (see 3 Base). Finally, the substrate was annealed at 200 ° C for 1.5 hours, whereby the ink was transferred to a continuous line made of sintered silver. The deviation between the width of the wells at their bottom (3.7 μm) and the corresponding width of the top edges of the MASTER profile (4.5 μm) is consistent with the swelling of the substrate under the action of the ink solvent and the heating of the substrate during embossing to explain. At a distance of 6 mm, a resistance of 2.5 Ω was measured on 4 parallel lines.

Example 2

A grid of channels was determined by pressing a grid in a polycarbonate film having a glass transition temperature T _g of 205 ° C (Bayfol ^®, Bayer MaterialScience AG), which was heated to 270 ° C, is generated. All other parameters of the embossing corresponded to Example 1. Likewise, in the same manner as in Example 1, a conductive line was generated. The obtained line width and lengths of the electrically conductive silver conductors were the same as those produced in Example 1.

Example 3:

It was carried out as in Example 1, but instead of the embossing process used a press roll with a press die.

continuous Structures on a 10 mm thick polycarbonate substrate (Makrolon, Bayer, Germany, glass transition temperature 148 ° C) were by means of a a small press (Tribotrak, DACH instruments, Santa Barbara, CA, USA). The purpose-built role, which had been mounted on the small press had sublime ones Line structures with a width of 10 microns and a distance of 3 mm. At this time, the surface of the substrate was raised Heated to 60 ° C, while the role of a temperature of 155 ° C. The pressure of the press was determined by means of a Weight of 10 kg set on the above device. For the set temperatures and the used Contact pressure became a relative propulsion speed of roll to the substrate of 0.25 mm / s chosen here was the substrate pulled by a carriage under the roll along the To achieve the above relative speed. The contact pressure was enough to turn the roll on the substrate into a rotary motion to move.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• US 2006/124028 A1 [0003]
• US 2006/188823 A1 [0007]
• - WO 199945375 A1 [0009]
• - US 6911385 B1 [0009]

Cited non-patent literature

• - J. Mater. Sci. 2006, 41, 4153 [0003]
• - Adv. Mater. 2006, 18, 2101 [0003]
• Science 2000, 290, 2123 [0006]
• - Nature Mater. 2004, 3, 171 [0006]
• - Appl. Phys. Lett. 1995, 67, 3114 [0008]
• - Adv. Mater. 2000, 12, 189 [0008]
• - Appl. Phys. Lett. 2002, 81, 1955 [0008]
• - J. Colloid Interface Sci. 1995, 172, 278 [0010]
• - J. Phys. Chem. B 1997, 101, 855 [0010]
• ChemPhysChem 2003, 4, 1291 [0010]

Claims (11)

Method for producing electrically conductive structures, which in two dimensions a dimension of not more than 25 microns have, on a particular optically transparent substrate with moldable surface, in which ii) on the surface of the substrate by mechanical and optionally in addition thermal impact channels are generated iii) on the channels an ink is applied, with the conductive Structures can be created iv) the channels be filled with the ink by capillary action, v) the ink by introducing energy into conductive structures is converted. A method according to claim 1, wherein the ink is a suspension of particles of an electrically conductive Material or a precursor compound for a electrically conductive material in a solvent is. Method according to one of the claims 1 or 2, characterized in that as electrically conductive Material or precursor compound for an electrical conductive material of the ink at least one means the series: carbon nanotubes, electrically conductive Polymer or metal nanoparticles, in particular silver nanoparticles is used. A method according to claim 2 or 3, characterized in that the conductive particles have a diameter of less than 1 micron. Method according to one of the claims 1 to 4, characterized in that the channels at the base have a width of not more than 25 μm. Method according to one of the claims 1 to 5, characterized in that the channels by means of a Press stamp or a press roll in the surface of the Substrate to be embossed, wherein the press die or the press roll are heated if necessary. Method according to one of the claims 1 to 6, characterized in that the substrate is a transparent Polymer is and the press die or the press roll in particular have a temperature above, preferably at least 20 ° C above the glass transition temperature of the polymer is. Method according to one of the claims 1 to 7, characterized in that the ink by means of the ink jet printing method is introduced on the channels. Substrate with electrically conductive structures, the in two dimensions a dimension of not more than 25 microns available according to a method according to one of claims 1 to 8. Using an ink, with the conductive structures can be produced for the production of particular transparent substrates that are conductive on their surface Having structures in two dimensions, a dimension of not more than 25 μm. Use according to claim 10, in which the ink is a suspension of conductive particles is.