Patent Application
20070215376
The invention concerns a method for printing electrical and/or electronic structures, in particular electrical conductors and/or electronic circuits.
There are various well-known methods for transferring electrical and/or electronic circuit components or the entire circuit to a carrier substrate and/or a material to be printed by printing methods such as offset printing. Because very small elements can be represented in offset printing, offset printing is generally preferred for manufacturing components or a complete electronic circuit. This is widely known from lithographic methods for circuit production.
In relation to other printing methods, such as ink jet printing, offset printing also has the fundamental advantage that a comparatively high productivity can be achieved with the permanent printing plate of offset printing, and very high degrees of structural fineness can be achieved by optimizing the imaging process. The essential advantage of offset printing, however, is that the package of an electronic component, such as an RFID-label, can be manufactured in one work step. The components of an RFID label can be printed directly on the package in the first printing units of an offset printing machine, and the remainder of the package can be finished in the remaining printing units.
In principle, offset printing can utilize three different application methods: wet offset printing, waterless offset printing, also referred to as the Toray method, and dry offset printing, also referred to as the letterset method. In strict terms, the letterset method is a relief printing method, since a letterpress plate is clamped instead of a lithographic printing plate. All methods share the characteristic that the printed image is transferred from the printing plate (photolithography plate) to the printing material via a rubber blanket as an intermediate member.
Unlike with classic printed materials, the critical point when electronic circuits are printed is not a good visual rendition, but rather the satisfaction of electrical and physical requirements. Thus, for instance, the resistance of a conductor depends not only on the material properties of the conductive material that has been applied, but also on the geometry of the cross section of a line. The thinnest point of the conductor defines the effective electrical resistance. A reproducible, defined electrical function thus demands an optimally even, homogeneous application of the conductive printing ink.
If one considers the different methods of offset printing, they all have weaknesses, either in the attainable resolution or in the insufficient homogeneity of the application of conductive ink. In wet offset printing, a problem is that part of the moistening agent is emulsified into the offset ink and is present to a certain extent as free surface water. If this printing ink/moistening agent emulsion is transferred to the material to be printed, an inhomogeneous distribution of the moistening agent results which can lead to ink transfer irregularities. This can lead to defects in the conductors, and in conjunction therewith, changes of the electric/physical properties.
In comparison to wet offset printing, the waterless offset printing method (Toray method) offers a more cohesive print surface, and therefore can be better suited to the application of electrical conductors. A disadvantage with this method, however, is that the ink must contain a certain amount of silicone oil for the separation between image and non-image sections. This silicone oil is a very good insulator, and therefore can impair the conductivity of the conductors in an unpredictable manner.
The dry offset method with letterset plates has the advantage that higher layer thicknesses can be transferred than in wet offset printing, but the relatively low resolution of the image elements with letterset plates is a disadvantage. Nevertheless, indirect printing with dry offset printing plates is a suitable method, at least with simple circuit designs, for transferring conductive structures indirectly, via the intermediate rubber blanket, to a material to be printed.
Another disadvantage of the offset printing method for the application of conductors is that the relatively thin layers that can be applied with offset printing (maximum of 3 μm) are often only marginally acceptable for layers of the required type. This produces a relatively high volume resistance. In addition, the quality of the layers is highly susceptible to technical defects in printing. The absorption of the printing ink into the printing material can also lead to changes in the electrical/physical characteristics.
While the printing of conductive structures with appropriately modified sheet-fed offset inks having conductive components is possible, the conductivity is hampered by the fact that pigments or conductive structures are bound in a vehicle. In the production of sheet-fed offset inks, the pigments and the vehicle are ground until the individual pigments are wetted as optimally as possible with the vehicle. The pigments and vehicle have no or hardly any direct contact with one another. As a result, metallic pigments that are ground up in an unmodified vehicle do not necessarily produce a properly conductive structure.
In view of the foregoing, an object of the present invention is to create a new method for printing electrical and/or electronic structures, in particular electrical conductors and/or electronic circuits.
According to the invention, in one or more first printing units, a design of the electrical and/or electronic structure to be printed is applied with an adhesive onto a printing material. The printing material partially printed with the adhesive, is then fed to one or more second printing units, in which an electrically conductive material is applied to the areas of the material to be printed that are imprinted with the adhesive.
The present invention also provides a film for use in a method for printing electrical and/or electronic structures, in particular electrical conductors and/or electronic circuits.
Embodiments of the invention, without it being limited thereto, will be described in greater detail below on the basis of the drawings.
With the present invention, a design of the electrical and/or electronic structure to be printed can be applied with an adhesive to the printing material in one or more first printing units, represented by printing unit 11 in the embodiment of
In a particularly preferred embodiment of the present invention, the printing material that has been partially imprinted with adhesive is applied to a film 15 in the second printing unit 12, as shown in
The second printing unit 12 has at least one impression cylinder 1 and a press roller 2. The press roller 2 preferably corresponds to the blanket cylinder of an offset printing unit or the form cylinder of a varnishing module. The film 15 is led around the press roller 2 either in the manner shown in
After transfer of the conductive material to the areas of the printing material that are imprinted with adhesive, the film 15 is wound up on a drum and/or a winding reel 18. Thus, a film completely or fully covered with conductive material is present on the supply reel 16, while parts of the conductive material on the winding reel 18 have been transferred from the film 15 to the printing material. The film wound on the winding reel 18 is therefore a used film with an incomplete layer of conductive and/or semiconductive material. If the film 15 is coated, for example, with an aluminum layer or some other type of conductive material layer, parts of this layer have been removed by transfer in the transfer gap 3 to the printing material. The rest of the coating remains on the film 15.
The present invention also encompasses recoating the used film 15 with conductive material following transfer of the conductive material to the areas of the printing material that are imprinted with adhesive. This can be done, for example, via electrostatic coating, sputtering, powder-coating or spraying. A circulating endless film that is coated repeatedly with conductive substance by, for instance, a doctor blade system or by electrostatic coating is another conceivable way to perform the coating. This could be done, for instance, by sprinkling an electrically charged film over and over again with oppositely-charged conductive carbon blacks and removing excess material by vibration, with a doctor blade, a brush, or some other type of device.
It is also possible to apply the conductive substance in liquid form for renewing the coating of the consumed film. In such a case, the application can be performed by an ink chamber blade system, a spraying device or a roll mill. Surplus coating is removed after coating by a doctor blade system, an air knife or a roller system. Once a homogeneous film of the coating is present on the belt or the cylinder, the coating is dried by a drying unit with the goal of obtaining as solvent-free a coating as possible which is not contaminated by nonconductive substances. It is also possible to produce a defined layer thickness of a conductive substance on a film without a subsequent drying process by transferring the conductive substance to the printing material by laser pulses.
Following application of the conductive material to the areas of the printing material that are imprinted with adhesive, the printing material can be fed to a third printing unit 13. The third printing unit 13 can execute further processing such that the layer thickness of the transferred conductive material is adjusted to a defined dimension. This can be done, for example, with a doctor blade mechanism having a positive or negative blade position, a calendering unit or an air knife. The printing material that is coated with electrically conductive material can also be subjected to a pressing or smoothing operation in the third printing unit 13. The layer thickness of the conductive material can be adjusted to a defined dimension using such operations as well.
In contrast to the embodiment of
In connection with the embodiment of the invention shown in
The carrier film and/or the separation layer is formed as a low-energy film or layer with a surface energy of preferably less than 35 mNm, so that a low adhesion is imparted to the electrically conductive functional layer. The electrically conductive functional layer thus easily detaches from the carrier film and/or the separation layer and consequently can be transferred with relatively little power or pressure to the areas of the printing material that are coated with adhesive.
The electrically conductive functional layer can be connected to the carrier film preferably by lamination via the intermediate separation layer. Alternatively, it is possible for the electrically conductive functional layer to be directly connected to the carrier film by adhesion or by electrical charge forces or electrostatic adhesion.
The electrically conductive functional layer is preferably formed as a predominantly metallic layer. It can be formed, for example, of highly conductive carbon blacks. Alternatively, the electrically conductive functional layer can be formed as a coating of intrinsic functional polymers. Typical functional polymers can be polythiophenes, polypyrroles, polyanilines, or polyethylene dioxythiophenes, among others.
The present invention provides a method for printing electrical and/or electronic structures which uses the advantages of the very high resolution of offset printing and at the same time transfers layers of very high and homogeneous thickness to the printing material. This is achieved by applying the structure of the electrical component to the printing material in one or more first printing units 11 by means of an adhesive. In a subsequent step, the printing material that has been imprinted with a design corresponding to the electrical structure is preferably brought into contact in one or more second printing units 12 with a transfer film (film 15) with a conductive coating. The conductive coating is transferred from the film 15 to the areas of the printing material that are imprinted with adhesive. The conductive coating can be, for instance, of a metallic type, or can consist of conductive carbon blacks or functional polymers. The coating process can be performed inline in printing units of an offset printing machine or in operating units, such as varnish modules, integrated into the offset printing machine.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2004 019 412.2 | Apr 2004 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP05/04061 | 4/16/2005 | WO | 1/3/2007 |
