FI126365B - A method and system for providing conductive material to a substrate - Google Patents

Description

METHOD AND ARRANGEMENT FOR APPLYING A CONDUCTIVE MATERIAL ONTO A SUBSTRATE

TECHNICAL FIELD OF THE INVENTION

The invention relates generally to the technology of transferring electrically conductive material on a substrate to be printed.

BACKGROUND OF THE INVENTION

Recently it has become more and more attractive to produce electrically conductive patterns onto dielectric substrates such as paper, cardboard, fabric, or polymer films, by using printing processes. The technical field of printed electronics involves producing electrically conductive - and in some cases semiconductive - areas and tracks on the substrate, frequently augmented by attaching separate electronic components such as semiconductor chips to at least some of the conductive or semiconductive areas.

As such, printing on paper or the like has been known since the times of the Gutenberg press in the fifteenth century. However, simply replacing traditional, non-conductive printing inks or toners with electrically conductive ones is far from straightforward. Inherent characteristics of the prior art techniques may make it difficult or impossible to change to conductive inks or toners. Many planned applications of printed electronics involve disposable products such as packages for daily consumables, which sets considerable pressure on economical factors: the packaging or its printing should not cost very much. It is possible to take a conductive or semiconductive polymer in the form of a liquid solution and use it as an ink in a printing press or an inkjet printer, but most conductive polymers known at the time of writing this description are too expensive or difficult to handle for large-scale exploitation as inks and do not provide sufficient electrical properties, such as conductivity and (electron/ion) mobility. Many metallic compounds are relatively inexpensive as such and can be used in the form of small, solid granules to make a paste, but pulverizing them down to the particle size required to e.g. smoothly flow through inkjet nozzles or conveniently fit to gravure printing radically increases their price. A key question of producing printed electronics is how to ensure that conductive material is only distributed and attached to the desired portions of the substrate. A PCT application published with the publication number WO 2009/135985 contains a brief review of known methods, including electroplating, screen printing, flexo and rotogravure printing. Other known methods include inkjet printing and offset printing with conductive inks. Many of the known methods suffer from the drawback of requiring costly raw materials, like very fine-grained metal powder where the grain size is small enough not to clog spraying nozzles or the like.

Said PCT application discloses an improved method in which a substrate is first provided with patterns that attract conductive particles, by using either a spatially distributed electric charge or an adhesive or both. Conductive particles (which may in this case be much larger in size than in e.g. inkjet applications) are distributed onto the patterned substrate, so that they become attached only to the desired patterns. A sintering station with heated rolls is then used to sinter the particle-covered patterns into final conductive traces and areas that remain attached to the substrate. The PCT application published as WO 2009/135985 is incorporated herein by reference.

Although said improved method represents a clear advance compared to many previous methods, it leaves room for improvement in areas like peeling strength, continuity of conductivity, applicability of different conductive compounds and roll materials, as well as production speed and applying methods for applying conductive particles onto a substrate.

SUMMARY OF THE INVENTION

An object of the invention is to alleviate and eliminate the problems relating to the known prior art. Especially the object of the invention is to provide an arrangement for applying conductive particles onto a substrate fast, accurate and an economical way with a minimum volume of the conductive particles.

The object of the invention can be achieved by the features of independent claims.

The invention relates to a device for applying electrically conductive material onto an adhesion area of a substrate according to claim 1. In addition the invention relates to an arrangement according to claim 7, as well as to a method according to claim 9.

According to an embodiment of the invention electrically conductive material is applied onto a substrate by providing suspended substance comprising electrically conductive solid particles. The suspended substance means here especially the solid particles which are arranged and allowed to be in a free movement under gravity, and under no or only very minimal control (like suspended dust or dust particles, like fluidized particles). Examples of the substance are e.g. an insulating surface, paper, board, fibrous web, and plastics. Especially the aim of the invention is to apply the suspended substance onto an adhesion area of the substrate, where the adhesion area is provided onto the substrate before applying the suspended substance. Advantageously the adhesion area comprises a predetermined form so that after applying the suspended substance and suitable finishing treatment, like sintering, the substrate comprises electrically conductive patterns on it.

In the embodiment the adhesive area of the substrate is exposed to an interaction with the suspended substance, whereupon the electrically conductive solid particles of the suspended substance is allowed to attach into the adhesion area of the substrate via free collisions of the suspended substance particles with the area of the substrate.

The electrically conductive solid particles may comprise for example tin, bismuth, silver, copper, antimony, zinc, nickel, indium or combination of thereof. According to an example the size of particles of the suspended substance is in the range of 10 pm - 50 pm, advantageously about 25 pm (however it is to be noted that the particles and their sizes listed here are only examples and that the invention is not limited only to those).

According to an exemplary embodiment the substance comprising electrically conductive solid particles is fluidized into a form of the suspended substances, whereupon the substrate can be transferred over the fluidized substance in order to catch said electrically conductive solid particles from the suspended substance onto the area of the substrate. The substrate may be transferred in a planar way over the fluidized substance or bent towards it when transferred, for example.

The fluidization is advantageously implemented by providing a fluidized bed, where said electrically conductive solid particles are placed under appropriate conditions to cause the solid particles to behave as a fluid (and as is depicted in this document, as suspended substance). This is advantageously achieved by the introduction of pressurized gas flow, such as air via air conduits in the fluidized bed, through the medium comprising said electrically conductive solid particles, the medium then having many properties and characteristics of normal fluids; such as the ability to freeflow under gravity.

The fluidization of the electrically conductive solid particles offers clear advantages, namely the system and the process is very easy to maintain stable. In addition the fluidized, i.e. suspended substance allows very high and homogenous density of the electrically conductive solid particles thereby ensuring high quality of the electrically conductive patterns provided onto the surface of the substrate. Furthermore, the using of the fluidized bed like construction enables also a very long impact zone. In addition the fluidization does not induce any appreciable vibration, whereupon the working area can be kept comfortable, and additionally also the devices are not exposed to the vibration, which might cause malfunctions and mechanical breaking.

According to an exemplary embodiment the substance comprising electrically conductive solid particles is vibrated so intensively that a form of suspended substance is achieved. The vibration may be applied via a surface where said particles are provided. The surface is advantageously tilted towards the substrate so that when vibrating the substance is provided or drifted towards the substrate due to the tilting angle.

In addition, according to an exemplary embodiment the substance applying means is a vibrating or rotating belt, propeller or toothed wheel. The belt, propeller or wheel is arranged into a contact with a substance container so that under vibration or rotation the belt, propeller or wheel is configured to catch the substance from the substance container, and releasing it e.g. upwardly and thereby providing the suspended substance (allowing free movement of the substance). Advantageously the releasing angle is configured to be towards the substrate or an intermediate transferring means, which is arranged to transfer the substance into the area of said substrate.

Still according to an exemplary embodiment excess of the substance not consumed may be captured back to the substance container. This can be implemented via help of gravitational force, but also different kinds of capturing means can be applied, such as an air knife, or the like. The excess of the substance may be purified before reusing, such as for example dust from the substrate may be removed by using electrostatic methods.

The present invention offers clear advantages over the known prior art. Because of the suspended substance there is no need for any strict or accurate control of transferring the electrically conductive solid particles, as is the case with spraying methods for example, where the pressure and flow rate of the particles must be controlled very accurately. Thus the process controlling is quite simple and thereby also the suspended substance process as such is very cost effective.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

The exemplary embodiments of the invention presented in this patent application are not to be interpreted to pose limitations to the applicability of the appended claims. The verb "to comprise" is used in this patent application as an open limitation that does not exclude the existence of also unrecited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS

Next the invention will be described in greater detail with reference to exemplary embodiments in accordance with the accompanying drawings, in which:

Figure 1 illustrates a principle of an exemplary method and arrangement for applying electrically conductive material onto a substrate according to an advantageous embodiment of the invention, and

Figures 2-7 illustrate exemplary devices for applying electrically conductive material onto a substrate according to an advantageous embodiment of the invention.

DETAILED DESCRIPTION

Fig. 1 is a principle-level schematic illustration of both a method and an apparatus according to an embodiment of the invention. A substrate handler mechanism comprises a substrate feeder 101, which can be for example an unwinding station where a fibrous web is unwound from a roll, or a stack handler where sheets or corresponding planar substrate pieces are taken from a stack. The substrate is generally designated with the reference designator 102, and it can be of any of a wide variety of materials, shapes and thicknesses. Paper, board and polymer films (plastics) have been considered good substrates, but other similar especially non-conductive surfaces may be also used.

The reason for the non-conductivity assumption is the fact that making patterns that are specifically conductive, especially for the purposes of printed electronics, has little importance if the substrate is also conductive so that it would short circuit the patterns to each other. As such, paper or board can be coated, uncoated, wood-free or wood-containing. Multilayered substrates are also usable, in which case the substrate does not need to be thoroughly non-conductive; it is sufficient if the surface onto which the conductive patterns will be printed is non-conductive. Other possible substrates include for example textiles, non-woven materials, circuit boards of electronics industry, moulded articles, and glass. Further possibilities involve construction materials, such as wallpapers and floor coatings, unfired and fired ceramics, (bio)polymer bases and composites. Each one of the listed substrates has its own application areas and advantages.

In the example of fig. 1 we assume that the substrate feeder 101 comprises also means for creating an adhesion area 103 on the surface of the substrate 102. An adhesion area is characterised in that adhesion of electrically conductive solid particles (which will be transferred onto the surface of the substrate in the next step) to the substrate is stronger within the adhesion area than outside it. For the purposes of the present invention it is not important, what is the actual mechanism of increasing adhesion; it may be for example dispersive adhesion (i.e. glueing) or electrostatic adhesion. As an example of the former, the substrate feeder 101 may comprise an adhesive printing, lacquering, or starching section or the like (not separately shown) that is configured to spread an adhesive, lacquer, starch or other fluid-phase materials onto the substrate and thereby to provide the necessary adhesion area of predetermined form for conducive particles. If electrostatic adhesion is relied upon, the substrate feeder 101 may comprise an electric charger section that is configured to create a spatial distribution of static electric charge in the substrate (or on the substrate surface) to create an adhesion area of predetermined form.

The predetermined form is according to an embodiment a pattern provided on the substrate to where and only where the electrically conductive particles of the suspended substance are to be attached when they are released by the suspended substance applying means. Thus the predetermined pattern should be provided onto the surface of the substrate before exposing the surface to the free moving particles.

The process step that is illustrated as taking place in section 104 in fig. 1 involves providing suspended substances of electrically conductive solid particles and allowing them to collide with an area of predetermined form on the surface of the substrate 102. Consequently the part of the apparatus responsive for the operation in section 104 may be called a particle handler, and it is configured to implement said transfer of electrically conductive solid particles onto said area of predetermined form on the surface of the substrate 102. Possible exemplary implementations of the particle handler will be described in detail later in connection with figs 2-7.

The method step and apparatus section schematically illustrated as 105 comprises heating the electrically conductive solid particles to a temperature that is higher than a characteristic melting point of the electrically conductive solid particles. Using a heater configured to apply a non-contacting heating method involves the advantageous characteristic that the heating will not easily cause smearing or unwanted macroscopic changes in the spatial distribution of conductive material on the surface of the substrate. In other words, the electrically conductive matter stays in place where it was meant to be. However, the invention does not specifically exclude heating methods that are contacting. Especially if a contacting heating method involves the use of a very low contact pressure, it may well have the same advantageous non-smearing characteristics. As a result of the heating, a melt is created.

The method step and apparatus section schematically illustrated as 106 is a cooling element cooling the melt temperature below the characteristic melting point that was discussed above. The cooling element may be implemented by various ways, such as by the so-called cold nip, where the designator “cold” must be understood to mean “relatively cold” compared to the heating section that precedes it. In the cold nip, the melt that was created by heating in section 105 is pressed against the substrate 102. Because the invention allows (but does not require) using an adhesive agent on the surface of the substrate to create the adhesion area 103, pressing the melt against the substrate conceptually covers both pressing a melt directly against a substrate and pressing a melt against an adhesive layer that is located on the surface of the substrate between the melt and the substrate. A surface temperature of a portion of the cold nip that comes against the melt is lower than the characteristic melting point that was discussed above. Thus the cold nip will cause the previously molten material of the originally solid electrically conductive particles to solidify again, but this time not in the form of separate particles but in the form of an essentially continuous, electrically conductive layer that covers that area on the surface of the substrate onto which the electrically conductive solid particles were transferred in the particle handler 104.

It is to be noted that the invention is not limited to the cold nip but also other suitable cooling means may be used. In addition, saying that the produced conductive patterns are essentially continuous means that they need to be continuous only to the extent that throughout each pattern they offer the desired cross section of conductive substance, so that electric resistance does not becomes prohibitively high. Another factor that defines the required continuity (and accuracy in location) is the size of contact pads in components that will be attached to the printed conductive patterns, as well as the accuracy at which such attaching will be performed. It is easy to understand that if the typical size of contact pads is in the order of magnitude of a square millimetre, individual pores in the corresponding printed conductive pattern may be quite acceptable if they are smaller than that, for example in the order of a few hundred micrometres or smaller.

The substrate handler mechanism that is schematically illustrated in Fig. 1 comprises a substrate collector 107, in which the substrate with the completed conductive patterns on its surface is collected. The substrate collector 107 may comprise for example a winder station or a stacker, in which a continuous-web like substrate is wound into a roll or the pieces of a sheet-like substrate are stacked respectively. The substrate collector 107 may comprise also post processing means that are configured to post process the substrate after forming the conductive patterns, for example by cooling, removing static electric charge, coating, evaporation of volatile components of substances present within or on the substrate, or the like.

Figures 2-7 illustrate exemplary methods, devices and arrangements 200 for applying electrically conductive material onto a substrate according to an advantageous embodiment of the invention, which are responsive for the operation in section 104 in fig 1 (they may be called the particle handlers also).

Figures 2 and 3 illustrate an idea of a fluidized bed 201 over which the substrate 102 is transferred in the direction of the arrow. The bottom area of the fluidized bed 201 is provided advantageously with conduits 202 in order to introduce pressurized gas flow into the vessel holding the electrically conductive solid particles 204. The pressurized gas flow may be e.g. pressurized air or the like suitable for providing the functionality of said fluidized bed and form suspended substances 203 from the electrically conductive solid particles 204.

The substrate 102 and especially its adhesion area 103 is transferred and let to have contact with said suspended substances 204, thereby allowing the electrically conductive solid particles 203 of the substance 204 being attached into the substrate 102 and especially with the adhesion areas 103 via free collisions of the substance particles with the substrate. After interacting (collisions) with the adhesion area 103 the electrically conductive solid particles 203 are advantageously attached into the predetermined pattern of the adhesion area 103 on the surface of the substrate 102 thereby forming a predetermined pattern of conductive solid particles 205 (as controlled by the predetermined pattern of the adhesion area provided e.g. by the substrate feeder 101, which advantageously comprises also means for creating the adhesion area 103 on the surface of the substrate 102).

Figure 2 illustrate a mechanism 206 for bending the substrate towards the fluidized bed 201 and suspended substrates 203 thereby possibly increasing the collision density with the particles. However, it has also been noticed with the test of the invention that the arrangement illustrated in figure 3 works very well, where the substrate is transferred in planar way over the bed (e.g. if the substrate is of the material which is not allowed to bend).

Figure 4 illustrates an arrangement 200 where the means for applying suspended substance 203 from the electrically conductive solid particles 204 contained in the vessel is implemented by a rotating means 207, such as by a toothed wheel or propeller or the like. There the toothed wheel or propeller catches electrically conductive solid particles 204 from the container, throws them e.g. upwardly and rejects them into a free movement advantageously towards the substrate.

Figures 5-7 illustrates an arrangement 200 where the means for applying suspended substance 203 from the electrically conductive solid particles 204 contained in the vessel is implemented by a rotating and/or vibrating means, such as a (conveyor) belt 208. In figures 5-6 the belt catches electrically conductive solid particles 204 from the container throwing and rejecting them into a free movement advantageously towards the substrate. The surface of the rotating and/or vibrating means 208 may be in a horizontal plane or tilted in an angle.

Figure 7 illustrates still another example of a surface of the rotating and/or vibrating means 208 (such as a conveyor belt), where the electrically conductive solid particles 204 are provided onto the surface of the means 208 for example from the container. The means 208 is then rotated and/or vibrated in order to provide the suspended substance 203 and apply it towards the substrate 102 due to the downward tilting angle.

In addition the arrangements 200 in figures 2-7 may also comprise means 209 for capturing excess of the substance not consumed back to the substance container 210, such as is illustrated in figure 7. The capturing means 209 may be implemented e.g. by an air knife or the like, or even by the help of gravitational force.

Figures 2-7 do not illustrate any feeding, heating or cooling elements. Few examples of them are however depicted in more details in connection with fig. 1. It is to be noted that the present invention is however not limited to those described in fig. 1, but numbers of different pre- and after managing elements may be used with the devices illustrated in figures 2-7.

The invention has been explained above with reference to the aforementioned embodiments, and several advantages of the invention have been demonstrated. It is clear that the invention is not only restricted to these embodiments, but comprises all possible embodiments within the spirit and scope of the inventive thought and the following patent claims.

Claims (6)

An apparatus for providing an electrically conductive material within the adhesive region (103) of a substrate (102), comprising: - means for applying a suspended material (203) comprising electrically conductive solid particles (204), and - means (101, 102, 107). for contacting said substrate (102) with said substance and allowing said electrically conductive solid particles of the substance thereby to become attached to the substrate (102) adhesion region (103) by free collisions of said substance with said substrate adhesive region, characterized in that: 208) comprising at least one surface inclined at an angle downwardly to said substrate (102), wherein the surface further remains inclined with respect to a substantially vertical direction of gravity, and wherein said solid particles The lit (204) is disposed on a surface extending toward said substrate (102) of said conveyor belt (208) such that, as the conveyor belt rotates, the suspended material (203) is applied to said substrate (102) due to its inclination angle. The device of claim 1, wherein said device comprises means for retrieving unused excess material back into the material container. A system for providing an electrically conductive material to a substrate adhesive region, comprising: - means for forming said adhesive region on the surface of said substrate, - a device for applying a suspended material according to any one of claims 1-2, comprising electrically conductive solid particles, and for transferring the substrate and configured to provide said adhesive region of the substrate with contact with said agent and thereby allow said suspended conductive solid particles to become attached to said adhesive region of the substrate by free collisions of said material with said region of the substrate. The system of claim 3, wherein said system also comprises: a heating element for heating the electrically conductive solid particles to a temperature higher than the characteristic melting point of the electrically conductive solid particles, thereby forming a melt, and a cooling element for cooling the melt of electrically conductive solid particles to a temperature than said characteristic melting point. A method for providing an electrically conductive material to a substrate adhesive region, the method comprising: - applying a suspended substance (104, 105, 106) comprising electrically conductive solid particles, - arranging (101, 107) an adhesive region of said substrate thereby allowing attachment of said electrically conductive solid particles of the suspended material to said substrate adhesion region by free collisions of said suspended matter particles with said region of the substrate, characterized in that - said suspended material is applied on a conveyor belt (208) comprising at least the surface additionally remaining inclined with respect to the substantially vertical direction of gravity and wherein said solid particles are arranged in said on said surface of the conveyor belt such that suspended material is applied to said substrate due to the inclination angle as the conveyor belt rotates. The apparatus or system or method of any one of claims 1-5, wherein the electrically conductive solid particles comprise tin, bismuth, silver, copper, antimony, zinc, nickel, indium, or a combination thereof.