DE102005023533A1 - Process for production of a screen printing pattern from a hardened pattern composition with application of a top layer space selectively by laser radiation - Google Patents

Abstract

Process for production of a screen printing pattern (1) in which a top layer (4) is applied space selectively to a printing cloth (3) from a hardened pattern composition (sic) (M) by means of laser radiation so that the printing cloth is exposed in the region of a predetermined pattern structure. The printing cloth can be a metal cloth or a metallized plastic cloth. Independent claims are included for: (1) a screen printing pattern; a device for preparation of the screen printing pattern including a CO2 laser source.

Description

The The invention relates to a method for producing a screen printing stencil. The invention further relates to a method according to this method screen printing stencil produced and to a device for carrying out the Process.

In a conventional method for producing a screen printing stencil, as for example from the DE 85 11 549 U1 as well as the DE 2 038 584 B is known, a cover layer of a stencil composition is applied to the screen fabric, which cures under the action of light. The stencil mass is exposed through a positive mask, which shadows the cover layer in the region of a predetermined template structure. In the areas of the cover layer located outside the template structure, the stencil mass becomes hard under the influence of the exposure. In contrast, in the areas shaded by the positive mask, the stencil mass remains soft. This uncured portion of the stencil mass is rinsed in a subsequent step by means of a suitable solvent to expose the mesh in the area of the stencil structure. The screen printing stencil finished in this way is ink-permeable in the region of the exposed screen fabric, and thus in the region of the stencil structure, while the screen printing stencil is impermeable to color outside the stencil structure by the hard cover layer remaining there. The screen printing stencil can now be used in a known manner for a graphic screen printing process by applying printing ink through the ink-permeable areas of the stencil to a substrate to be printed.

at modern variants of the process, the topcoat in the course of curing step using a screening method (or screening method) directly exposed in a location-selective manner.

As an alternative to the "direct" methods of stencil production described above, for example from US Pat EP 0 996 545 B1 (and the associated German translation DE 697 180 63 T2 ) - Alternative manufacturing methods are known in which the screen mesh and / or consisting of the stencil mass screen printing film are pretreated separately from each other site selective, so that adhering to the screen fabric next stencil structure on subsequent application of the screen printing film on the screen fabric only.

screen printing be - except for Production of graphic prints - before especially for the production of electrical circuits and printed conductors used. The substrate to be printed in this case by a circuit carrier, in particular a ceramic substrate or a circuit board blank, educated. Instead of printing ink are used here as a printing medium used conductive or insulating substances. In the course of circuit pressure become electrical and electronic components, such as tracks, resistors, Insulation layers, inductors, Glass covers, solder paste and conductive adhesive printed directly on the circuit board. Particularly Screen printing technique becomes common used for printing the contacts in solar technology. Especially in this application must extremely fine webs at the same time as possible greater Strength the printed conductors are printed.

The smallest conductor structures, using common commercial screen printing printable are typically on the order of magnitude today of 100μm. In the course of the ever-increasing miniaturization of electronic circuits There is an increasing demand for screen printing stencils that print even finer structures, especially on the order of magnitude of 10-50 μm, allow.

The Production of screen printing stencils with stencil structures in Sub-millimeter range is according to the conventional manufacturing process with associated with increasing miniaturization of the Template structures disproportionately grows. An important reason for the high production cost is that in the site-selective Exposure of such fine structures dust grains and other impurities in the air or on the surface the top layer of disruptive effects during the exposure process, which may increase the quality of the manufacturing template to the point of complete uselessness can. The production of screen printing stencils for the circuit printing takes place Therefore so far under clean room conditions of high quality. The exposure of the cover layer usually takes place under vacuum. The production of these environmental conditions is expensive and complicates the flow of operations in the production of a Screen printing stencil.

Furthermore, from the DE 297 08 329 U1 known to provide a screen printing stencil with openings in which both the cover layer and the screen fabric is removed. These breakthroughs are in this case produced by a mechanical punching method, laser cutting, water jet cutting, etching or a similar method.

Of the Invention is based on the object, in particular for circuit pressure particularly suitable screen printing stencil and a comparatively easy to perform Specify a method for producing such a screen printing stencil. The invention is further based on the object, a device indicate that to carry out such a method is particularly suitable.

Regarding the Manufacturing process, this object is achieved by The features of claim 1. Thereafter, in contrast to the a conventional one Process of preparation associated with the procedure provided Template mass first entire area cure and the applied as a cover layer on the mesh and cured stencil mass in the area of the proposed template structure subsequently site-selective this ablation process using Laser radiation is made. This laser ablation of the cover layer is done in such a way that after completion of the ablation process the Screen fabric is exposed in the region of the template structure.

core of the method is thus the laser-assisted and site-selective ablation the fully cured topcoat. For the previous application and curing of the top layer are in contrast several alternative method variants provided. Thereafter, the cover layer is optional in a still uncured Condition in the form of an emulsion or a film on the mesh applied and then hardened, or the stencil mass is in already cured state in the form of a Films applied to the mesh, in particular laminated or glued. Again, alternatively, is conceivable, already prefabricated Screen printing stencils with full surface applied and cured Cover layer as input product for the process, so that the application of the topcoat and the curing step Although a prerequisite, but not necessarily itself the method according to the invention are.

As a "cure" is generally one chemical or physical stabilization (e.g., in the form of a Polymerization, crystallization, amorphous solidification, etc.) of the Template mass referred, in the course of which the template mass a coherent one body forms, which are not dissolved by the intended pressure medium or is rinsed out. The "hardened" stencil mass can macroscopically still flexible, elastic and / or flexible stay.

Of the Use of laser ablation allows the realization of the finest stencil structures with a structure width of about 10-15 microns with very little at the same time Production expense. Likewise, by means of the method according to the invention Screen printing stencils with almost arbitrarily large layer thickness of the cover layer and excellent contour sharpness realizable. A particular advantage of the method is that it is opposite Contaminations of the surface layer surface and / or the ambient atmosphere during Manufacturing process has little or no sensitivity to interference. The requirements of the for Therefore, the cleanroom technology required for the manufacturing process can be significantly reduced and stencil structures with a minimal structure width over 120μm completely eliminated. Otherwise, the manufacturing process against the simplifies classical procedures, especially as the Production of a positive mask for the lighting process is just as unnecessary as a development or "stripping" process after done Exposure.

In an expedient embodiment of Invention is used as a template mass under the action of light (in particular UV light) hardening Material, in particular polymer material, used, as it also at conventional Manufacturing process applies. The curing step is in this embodiment of the Procedure by full-surface Exposure of the cover layer, in particular by UV light made.

Instead of a photosensitive material can in the course of the inventive method but alternatively also under temperature effect, chemical treatment or other ambient conditions hardening material used become. In particular, a template material is optionally used, that under mere change the ambient temperature or by evaporation of a solvent stiffens. In the former case, the stencil mass is melted applied to the mesh and cooled to cure. In the latter case takes place the curing the template mass by a mere drying process, the optionally can be accelerated by the action of temperature.

When Screen fabric is preferably in the context of the inventive method a metal mesh (in particular steel wire or stainless steel wire) or a metallized plastic fabric used.

Advantageously, the removal of the cured stencil mass takes place at least in the immediate vicinity of the screen fabric using laser radiation in the ultraviolet Spectral range. With such laser radiation, on the one hand, a particularly high spatial resolution can be achieved. On the other hand, a particularly high erosion selectivity is achieved when using UV laser radiation, in which the stencil mass is effectively removed, but the screen fabric is spared on the other hand. Suitable laser radiation in the UV spectral range is generated in particular by means of a frequency-tripled Nd laser, in particular Nd-YAG laser. In a particularly advantageous variant of this method, the UV laser radiation is used only for the removal of material in the vicinity of the screen fabric, while in an initial stage of material removal regions of the template mass, which are comparatively far away from the screen fabric, removed using infra-red laser radiation become. To generate the latter, in particular a CO ₂ laser is used. The two-stage ablation method using infra-red or ultra-violet laser radiation has the advantage in particular that the high ablation rate of an infra-red laser can be used for preliminary work and time is saved, while in the subsequent fine-work phase the advantages of the UV Lasers, namely the low beam thickness and the appropriate wavelength, especially come into play. Instead of a UV laser can also operate in the visible spectral range laser, z. B. a frequency doubled Nd-YAG laser can be used.

Especially for the said fine work is the intensity of the UV laser radiation such adjusted that the sieve fabric in the ablation of the surrounding cured Stencil mass not impaired, especially not damaged becomes. The one for this to set the laser intensity is determined by the type of screen mesh used and z. B. determine empirically.

In one in particular for the realization of particularly fine template structures advantageous variant of the method is after curing of the Template mass first a metal coating applied to the surface of the cover layer. This metal coating has in particular a thickness of about 1-3 microns and consists for example, copper, chromium or nickel. The metal coating acts as a shadow mask for the material removal by infra-red laser radiation and is so far interrupted in the area of the given template structure. The Effect of the metal coating is that they are the underlying Mask mass shields against the infra-red laser radiation, causing an IR laser can also be used to engrave filigree stencil structures, for their realization of the IR laser due to the comparatively bad spatial resolution could not be used or only with high inaccuracy.

The provided in the area of the template structure breakthroughs of Metal coating can already during remain exposed to the application of the metal coating, e.g. by making this area the deck area while the coating in turn covered by a suitable positive mask becomes. In terms of process rationalization is preferred the metal coating initially on the entire surface applied to the topcoat and then in the area provided Template structure by means of ultra-violet laser radiation site-selective ablated.

Regarding the Screen printing template, the object is achieved by the features of claim 12. Thereafter, the screen printing stencil comprises a screen fabric on which a cover layer of a cured stencil mass applied is, wherein the cover layer in the region of a given on the layer surface Template structure by site-selective removal of the hardened template mass is scoured by laser radiation such that the mesh in this area is exposed.

With regard to the apparatus provided for carrying out the above-described method, the object is achieved according to the invention by the features of claim 15. Thereafter, the apparatus comprises a laser ablation unit for the location-selective removal of the hardened stencil mass. This laser ablation unit comprises, in an expedient embodiment, a first laser source for generating infra-red laser radiation and a second laser source for generating ultra-violet laser radiation, which are selectively controllable. The laser ablation unit may comprise two independent laser sources with separate beam guidance. In particular, however, a so-called duo-laser system or hybrid laser system is used as the laser ablation unit. The laser ablation unit comprises in a preferred embodiment a CO ₂ laser as the first laser source and a frequency-tripled Nd laser, in particular Nd-YAG laser as a second laser source.

following Be exemplary embodiments of Invention explained in more detail with reference to a drawing. Show:

1 in plan view a schematically simplified raw form of a screen printing stencil with a screen fabric frame spanned in a stencil frame,

2 in illustration according to 1 the finished screen printing stencil with a deck excavated in the area of a template structure layer,

3 in perspective view a greatly enlarged section of a realistic screen printing stencil according to 2 .

4 - 9 a method for producing a screen printing stencil according to 2 by means of six schematic, sectional sectional views through the screen printing stencil in successive stages of the process, and

10 - 14 in illustration according to 4 - 9 an alternative embodiment of the method.

each other corresponding parts and sizes are in all figures with the same reference numerals.

1 shows a screen printing stencil 1 (hereafter short stencil 1 ) in a raw state present at the beginning of the process described below. In this state, the template includes 1 a template frame 2 (or screen frame), in which a screen mesh 3 is stretched.

The template frame 2 is preferably formed from a steel, stainless steel or aluminum tube profile with a square, rectangular or trapezoidal cross-section. In the example shown, four sections of the pipe section are welded at the corners to form a rectangular, closed frame, wherein in particular a good flatness of the template frame 2 respected.

The mesh 3 is made of steel or stainless steel wire or metallized plastic braid, in particular polyester thread formed. The mesh 3 is with homogeneous tension on the template frame 2 applied and is freed in the run-up to the process of impurities, dust and grease residues.

In the course of the procedure is applied to the mesh 3 a cover layer 4 ( 2 ) are applied such that the from the template frame 2 framed inner surface 5 at least one surface area to be used for the printing through the cover layer 4 covered and thus sealed against printing ink or other printing media. Only in the area of one within the inner surface 5 predetermined template structure 6 is the topcoat 4 in the 2 shown finished state of the template 1 recessed or excavated, so that in this area the mesh 3 to both plan pages of the template 1 exposed. The template 1 is thus in the finished state in the area of the template structure 6 permeable to printing inks or other print media.

The template structure 6 can be any, the intended application adapted form within the inner surface 5 take, in particular filigree branched or circular closed be formed or consist of several separate surfaces.

Depending on the embodiment penetrates the cover layer 4 the mesh 3 more or less strong, is thus either essentially one-sided on the mesh 3 on or embeds the latter completely and on both sides.

3 shows a greatly enlarged section through a template 1 , as it can be produced by the method described in more detail below. In the illustrated embodiment, the template structure is 6 formed by a number of mutually parallel strips, each by web-like strips of the cover layer 4 are separated. To recognize is off 3 especially in the area of the template structure 6 exposed mesh 3 ,

At the beginning of the process is on the in the template frame 2 clamped, cleaned screen mesh 3 ( 4 ) the initially soft, in particular viscous template mass M is applied ( 5 ) and optionally mechanically smoothed. As the stencil material M, it is preferable to use a photosensitive polymeric emulsion or a photosensitive film which chemically cures under the action of light.

After the areal application of the template mass M, the surface becomes 7 the topcoat 4 by means of a UV light source 8th irradiated to the stencil mass 4 cure. It should be noted here that, in contrast to conventional methods, the template 1 irradiated over the entire surface, whereby the template mass M within the entire top surface 4 becomes fixed ( 6 ).

After curing of the template mass M, the cover layer 4 now selectively removed using laser ablation to the mesh 3 in the area of the intended template structure 6 to expose again.

The material removal takes place by means of a laser ablation unit 9 , In the laser ablation unit 9 is a duo-laser system that generates a laser beam L1 in the infra-red spectral range, a CO ₂ laser as the first laser source, and to generate laser radiation L2 in the ultra-violet spectral range of a frequency-tripled Nd-YAG laser 11 as a second laser source. The laser ablation unit 9 further comprises an actuator 12 that is the way of one XY-writer for two-dimensional displacement of the laser ablation unit 9 generated laser beam 13 concerning the surface 7 the topcoat 4 is trained. The displacement of the laser beam 13 opposite the template 1 This is done optionally by the laser ablation unit 9 or parts of it relative to the stationary template 1 be adjusted and / or by shifting the template 1 opposite the stationary laser beam 13 ,

The removal of the template mass M takes place according to 7 in a first ablation step using the infra-red laser radiation L1. This is the comparatively high ablation rate of the CO ₂ laser 10 exploited to areas of the template mass M, that of the screen mesh 3 are relatively widely spaced, quickly ablate. The first ablation step will be at sufficient approximation to the mesh 3 stopped so as not to expose the latter to the comparatively high heat development in the IR ablation. The the sieve fabric 3 immediately surrounding region of the template mass M is in a second removal step according to 8th removed using the ultra-violet laser radiation L2, which is particularly suitable for this purpose due to the relatively small wavelength and the relatively small beam width.

Deviating from this, we engrave rough template structures 6 to save time also only IR laser radiation L1, for engraving very fine stencil structures 6 also used exclusively UV laser radiation L2.

The material removal is terminated when the cured stencil mass M in the region of the template structure 6 is completely removed, leaving the screen mesh 3 in this area both to the surface 7 as well as to the opposite side ( 9 ).

In the 10 to 14 On the other hand, a modified variant of the method is shown which, in particular, is used to realize particularly filigree template structures 6 is particularly suitable.

In the course of this process variant is first analogous to the 4 to 6 the template mass M on the mesh 3 applied and cured. On the surface 7 the cured topcoat 4 becomes now (by steaming, sputtering, etc.) a metal coating 14 made of copper, chromium or nickel with a thickness of about 1-3 microns applied, which serves as a shadow mask for the subsequent removal process.

The metal coating 14 this is first according to 10 all over the entire inner surface 5 on the topcoat 4 applied. In a subsequent step according to 11 becomes the metal coating 14 in the area of the intended template structure 6 removed by laser ablation using the ultra-violet laser radiation L2.

The metal coating 14 shields the outside of the template structure during the first ablation step 6 lying areas of the cover layer 4 against the infra-red laser radiation L1 and thus prevents particularly filigree areas of the template structure 6 be injured by the in terms of their spatial resolution comparatively imprecise infra-red laser radiation L1 ( 12 ).

In the vicinity of the mesh 3 lying areas of the template mass M are again removed in the second removal step using ultraviolet laser radiation L2 ( 13 ), so that after completion of the process, the mesh in the area of the template structure 6 is again exposed ( 14 ).

The templates made with the method described above 1 in particular, have a template structure 6 on, which has at its narrowest points a (minimum) structure width up to 10μm. In this case, in particular the distance which is formed between opposing shaft walls in the region of the template structure is formed as the structure width D 6 excavated cover layer 4 is formed (see 14 ).

1

(Screen printing) Template

2

stencil frame

3

mesh

4

topcoat

5

palm

6

template structure

7

surface

8th

UV-light source

9

Laserablationseinheit

10

CO ₂ laser

11

Nd-YAG laser

12

actuator

13

laser beam

14

metal coating

M

template mass

L1

laser radiation

L2

laser radiation

D

structure width

Claims (16)

Method for producing a screen printing stencil ( 1 ), in which one on a mesh ( 3 ) applied cover layer ( 4 ) out of a hardened stencil mass (M) by means of laser radiation (L1, L2) is selectively removed, so that the screen mesh ( 3 ) in the area of a predefined template structure ( 6 ) is exposed. A method according to claim 1, characterized in that for applying the cover layer ( 4 ) the template mass (M) in an uncured state on the mesh ( 3 ) is applied and cured over the entire surface. A method according to claim 1, characterized in that for applying the cover layer ( 4 ) the template mass (M) in an already cured state in the form of a film on the screen fabric ( 3 ) is applied. Method according to one of claims 1 or 2, characterized in that as stencil mass (M) a light-curing, in particular polymeric material is used, and that the curing step by full-surface exposure of the cover layer ( 4 ) is made. Method according to one of claims 1 to 4, characterized in that as Siebgewebe ( 3 ) a metal mesh or a metallized plastic fabric is used. Method according to one of claims 1 to 5, characterized in that at least for the removal of a sieve fabric ( 3 ) surrounding part of the cured stencil mass (M) ultra-violet laser radiation (L2) is used. A method according to claim 6, characterized in that for applying the ultra-violet laser radiation (L2) a frequency-tripled Nd laser, in particular Nd-YAG laser ( 11 ) is used. A method according to claim 6 or 7, characterized in that the intensity of the ultraviolet laser radiation (L2) is adjusted such that the screen mesh ( 3 ) is not affected in the removal of the surrounding cured stencil mass (M). Method according to one of claims 6 to 8, characterized in that in the course of material removal in a first removal step, one of the screen fabric ( 3 ) spaced first part of the ablated cured stencil mass (M) using infra-red laser radiation (L1) is removed, and that in a second removal step a the Siebgewebe ( 3 ) surrounding portion of the cured stencil mass (M) is removed using ultra-violet laser radiation (L2). A method according to claim 9, characterized in that before the removal of the stencil material (M) on the stencil structure ( 6 ) surrounding area of the surface ( 7 ) of the cured stencil mass (M) a metal coating ( 14 ), in particular of Cu, Cr or Ni, as a mask for the material removal by infrared laser radiation (L1) is applied. Method according to claim 10, characterized in that the metal coating ( 14 ) in a first step applied over the entire surface, and in a second step site-selective in the area of the template structure ( 6 ) is removed by means of ultraviolet laser radiation (L2). Screen printing stencil ( 1 ) with a mesh ( 3 ) as well as with a cover layer applied thereto ( 4 ) from a cured stencil mass (M), wherein the top layer ( 4 ) in the region of a given template structure ( 6 ), so that the mesh ( 3 ) is exposed, characterized in that the cover layer ( 4 ) is excavated by location-selective removal of the cured stencil mass (M) by means of laser radiation (L1, L2). Screen printing stencil ( 1 ) according to claim 12, characterized in that the screen cloth ( 3 ) is a metal mesh or a metallized plastic fabric. Screen printing stencil ( 1 ) according to claim 12 or 13, characterized in that the template structure ( 6 ) has a minimum feature width (D) of the order of 10 μm. Device for producing a screen-printing stencil ( 1 ) using the method according to one of claims 1 to 11, with a laser ablation unit ( 9 ) for the location-selective removal of the hardened template mass (M). Device according to claim 15, characterized in that the laser ablation unit ( 9 ) selectively controllable a first laser source ( 10 ), in particular a CO ₂ laser ( 10 ), for generating infra-red laser radiation (L1), and a second laser source ( 11 ), in particular a frequency-tripled Nd laser, in particular Nd-YAG laser ( 11 ) for generating ultra-violet laser radiation (L2).