CH681758A5 - Plastics foil micro-sieve - Google Patents

Abstract

A novel microsieve (S1,S2) has a specific arrangement of recesses (4) and passages (5), the passages being formed as etched openings in a foil (1) having an etch resistant patterned coating (2,2') on one or both sides. The etch resistant material (2,2') forms a system of conduits (S,K) by means of which microsieves (S1,S2) can be connected together. Also claimed are (a) a composite body, produced from the microsieves and (b) prodn. of the microsieve or the composite body. The conduits may be tubular to form channels (I) or may be solid to form conductors. Etching is pref. carried out by an anisotropic plasma etching process. The etch resistant layer may be a metal layer or a photoresist layer.

Description

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CH 681 758 A5

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The invention relates to a method for producing holes in a plastic film coated on both sides and to a plastic film with holes produced by the method.

In many applications in technology, it is necessary to make small holes in film-shaped plastic sheets. Such holes can be created by fine punching or by mechanical drilling. In some cases, punching with fine needles is sufficient.

For the production of printed circuit boards from flexible foils made of various plastics, which is increasingly common in electronics, it is also necessary to make holes as small as possible at precisely specified locations. These holes can then be used to electrically connect two conductive metal layers to one another.

Mechanical punching as well as mechanical drilling of holes in foils is technically very complex. On the one hand, the minimum diameter of the holes that can be achieved is limited to a few tenths of a millimeter, on the other hand, during punching and mechanical drilling, there are always burrs that can disrupt further processing. In addition, the cost of a stamping tool with the required accuracy is very high. With mechanical drilling, on the other hand, the process itself is very slow, even if several foils can be drilled together, since mostly hole by hole has to be drilled one after the other and also very expensive if many holes have to be made.

A large number of methods, mostly photochemical, are known from the electronics industry, by means of which structured metal surfaces or conductor tracks can be applied to plastic circuit boards or plastic films on one or both sides. Various tools and methods are known from practice with which the holes for plated-through holes can be made at the required points with the desired accuracy in a mechanical manner by drilling, punching or piercing. The main disadvantage here is that the holes cannot be made arbitrarily small when drilling and punching.

The invention, as characterized in claim 1, solves the problem of producing a plastic film coated on both sides with holes in a simple and quick manner.

For the perforation of plastic films, which must be provided with a metal layer on both sides for functional reasons - such as in the printed circuit board technology of the electronics industry, a method of chemical hole production can be used. The metal layers applied to the plastic film on both sides are used as the etching resist. An etching resist is a substance that is resistant to the etching medium or at least significantly more resistant than the material to be etched.

If an etching process is used, this can be a wet chemical process in which the

Etching medium is in liquid form. In another etching process, the etching medium can also be gaseous, which e.g. is the case with plasma etching. Combinations of the methods mentioned are also possible. With all etching methods, however, it is generally necessary to ensure that those parts which are not to be etched away are protected by an etching resist layer. The advantage of etching processes is that a large number of holes can be etched out at the same time.

The accuracy of this method is determined by the accuracy of the structuring of the etching resist layer and the thickness of the plastic film to be etched. If, for example, as is known in the electronics industry, a photochemical structuring and a photoresist are used as etching resist for the window openings in the metal layer, through holes with diameters of 10-100 μm can be easily produced. Etching processes also have the advantage that the holes can be much smaller than can be produced by mechanical means. Of course, it is also possible to obtain through holes with larger diameters or any contours. For large holes, not all of the material needs to be etched out; in such cases, it is sufficient to cut through the edges of the holes and the loose parts will fall out.

Plasma etching can be used on foil materials that resist wet chemical attack. This method has the advantage that anisotropic, i.e. can be directionally etched, thereby largely avoiding undercutting. An undercut is usually an undesirable etch under the etch resist, i.e. in the case of holes in a lateral direction with respect to the hole axis. Plasma etching systems can be designed so that the plastic film is processed from roll to roll in a continuous process.

If holes in a plastic film without a metal layer are required, the plastic film can be temporarily metallized by evaporating a metal layer and the metal layer can be etched away after the plastic film has been perforated.

Another process variant provides that, with a suitable combination of film material and photoresist for the structuring, the photoresist itself is used as an etching resist for producing the holes, as a result of which a process step can be saved. If the photoresist is also attacked by the etching medium, the removal from the photoresist must take place more slowly than the removal of the film material, so that after the perforation has taken place, a remainder of the photoresist or etching resist remains on the surface. If necessary, the remaining part of the photoresist can also be stripped here, that is, removed using suitable, known methods.

The invention is explained in more detail below with the aid of two possible embodiments with drawings. Show it

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1 and 2 a method for perforating a plastic film provided on both sides with metal layers,

3 shows a method for perforating an uncoated plastic film using photoresist,

Fig. 4 shows a method for producing holes in plastic films on conveyor systems.

FIGS. 1a to 1f and FIGS. 2a to 2f show the different stages of a method for perforating a plastic film provided on both sides with metal layers. Since the perforation is carried out using the same method steps, the individual steps are essentially only explained with reference to FIGS. 1a to 1f.

FIG. 1 a shows a coated plastic film 1, for example made of polyimide with a thickness of 25 μm, not to scale. The plastic film 1 is covered on both sides with a layer 2, 2 'of metal, for example copper of 12 (in thickness). Such layers of metal can be applied by a known electrolytic process, by lamination or by a sputtering technique.

1b shows the plastic film 1 after the application of one layer 3, 3 'of photoresist or photoresist on the metal layer 2, 2'. The application of this layer 3, 3 'can be carried out in a manner known per se e.g. with a roller coater and a continuous furnace.

1c shows the plastic film 1 after exposure and development of the layers 3, 3 'made of photoresist with the desired hole pattern. In such a process, the hole pattern is exposed on both sides of the plastic film 1, not shown, photo templates in the form of films or etched metal masks on the layers 3, 3 'of photoresist and then developed. The latter then have recesses 4, 4 'at those locations where holes are to be created. In a frequent application, the plastic film 1 is to be provided with through holes 5. For this purpose, as shown, recesses 4 ′ of the same shape are made in the layer 3 ′ in relation to the recesses 4 in the layer 3 of photoresist at opposite points of the double-sided coating of the plastic film 1. The openings 4 'can be opened simultaneously with the openings 4.

Other applications include holes 6 in the plastic film, i.e. the holes 6 to be produced in a later process step should only extend to the opposite layer 2 'made of metal. In these cases, no recess 4 'is made at the relevant point in layer 3', as can be seen from FIG. 2c.

1d shows the plastic film 1 after metal etching has taken place. In such a process, the layer 2, 2 'of metal on the plastic film 1 is etched using conventional metal etching agents, such as are used in printed circuit board technology. Thereafter, the layers 2, 2 'of metal also have recesses 4, 4' at those points at which through holes 5 or holes 6 are to be created. The purpose of the procedural steps acc. 1 a to 1 d and according to FIGS. 2a to 2d, it is therefore to expose the plastic film 1 coated on both sides at precisely the locations of the layer 2, 2 ', 3, 3' at which through holes 5 or holes 6 are to be formed . Basically, the etching of the through holes 5 or the holes 6 can begin after this step.

1 e shows the plastic film 1 after the removal of the layers 3, 3 'of photoresist or photoresist that are no longer required. This process can also be carried out in a manner known per se, e.g. with a photoresist stripper common in the electronics industry. The plastic film 1 now has a structured metal layer on both sides which corresponds to the hole pattern and which serves as an etching resist for the subsequent hole etching process.

1f shows the plastic film 1 after the through holes 5 have been etched with a wet chemical or with a plasma etching method. In this way, burr-free through holes 5 or, as shown in FIG. 2f, burr-free holes 6 are formed. If an anisotropic, i.e. a directional, plasma etching method is used, the etching takes place practically without any undercutting, i.e. there is no undesired lateral removal of the plastic film below the etching resist. In addition, it is also possible to precede the plasma etching process for the production of the through holes 5 or the holes 6 with a treatment (not shown) in a solution, which then reduces the etching time in the plasma etching process.

From the sequence described, it is of course also apparent that through holes 5 and holes 6 - the latter being able to be introduced from one side as well as from the other side - can easily be produced in the same operation and on the same metal-coated plastic film.

A copper-coated plastic film 1, for example made of polyimide, can be copper-plated after the perforation has been carried out in a strip electroplating process using the known methods of printed circuit board technology, and this means that the metal layers are contacted through at the same time.

3a to 3d show the different stages of a method for perforating a plastic film provided on both sides with photoresist. 3a shows a plastic film 1, for example made of polyimide, in a representation that is not to scale.

3b shows the plastic film 1 after it has been covered on both sides with a layer 3, 3 'of photoresist or photoresist. Such coatings made of photoresist can be applied using one of the techniques known in printed circuit board manufacture.

3c shows the plastic film 1 after exposure and development of the layers 3, 3 'with the desired hole pattern. The layers 3, 3 'now have recesses 4, 4' at those locations where holes are to be created. For the production of through holes 5, recesses 4, 4 'of the same shape are created in the layer 3, 3' at opposite locations of the coating on both sides of the plastic film 1. Also the-

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This process takes place in a manner known per se, e.g. through UV exposure and subsequent development. The plastic film 1 now has a structured photoresist layer on both sides, which corresponds to the hole pattern and which serves as an etching resist for the subsequent hole etching process.

FIG. 3d shows the plastic film 1 after the through holes 5 have been etched using a wet chemical or a plasma etching method. In this way, burr-free through holes 5 are formed. If an anisotropic, i.e. a directional, plasma etching method is used, the etching also takes place without under-etching, i.e. there is no undesired lateral spreading of the etching. Since in this example the etch resist consists of a material that is only more etch-resistant than the plastic film 1, material is also removed from the etch resist. The remaining layer of etch resist after the through holes 5 have been produced is thus thinner than at the beginning. If the layer thickness of the plastic film 1 is not to be attacked or reduced, the layer thickness and etch resistance of the etch resist must be selected accordingly. If the remaining etching resist interferes with the further use of the perforated film, it is stripped in a further process step using conventional techniques, i.e. away. It is even possible for the through holes 5 to be etched and the photoresist or the etching resist to be finally removed in a single operation.

4 finally shows a method for producing holes in plastic films on conveyor systems. The advantage of continuous processes is that films can be processed from roll to roll. The etching of holes in plastic films coated on both sides, e.g. 1a-1f and 2a-2f is shown and described, can be done with a belt system of this type.

From a supply roll 10, the plastic film 1, which is provided on both sides with a layer 2, 2 'made of metal, is finally fed via various process steps and transport rolls 11 to a take-up roll 12 which picks up the finished product, namely the perforated film. In a first process step, the plastic film 1 is provided on both sides with a layer 3, 3 'of photoresist in a roller coater 13. The layer 3, 3 'is then dried in a continuous oven 14. Then the necessary structuring of the hole pattern takes place by exposure in a UV exposure unit 15 with subsequent development in a development system 16. Then, in a metal etching and photoresist stripper 17, first the layer 2, 2 'of metal at the recesses 4, 4' where the Through holes 5 or holes 6 are to be formed, etched away and then the remaining photoresist is removed. Finally, the through holes 5 and / or the holes 6 are etched out in a plasma reactor 18.

If a belt system of the type shown in FIG. 4 is used, it is also possible for the two-sided coating of the plastic film 1 with layers 2, 2 'of metal to also take place with the addition of further process steps (not shown) in the continuous process . This can be done with a known technique such as e.g. Lamination or sputtering take place.

The invention as it was described with reference to FIGS. 1-3 is not only suitable for the production of through holes. It is also possible that the plastic film coated on both sides is only on one side by means of a known, e.g. structure of the photochemical process and that the etching only starts on this one side. In this way it is also possible to create holes 6 or other depressions.

Claims (7)

Claims 1. A method for producing holes in a plastic film (1) coated on both sides, the coating having at least one thin layer (2, 2 ', 3, 3') made of a different material than the plastic film (1), characterized in that the at least one thin layer (2, 2 ', 3, 3') consists of an etch-resistant material or of a material that is more etch-resistant than the plastic film (1) that at least one thin layer (2, 2 ', 3, 3 ') in a separate process step, recesses (4, 4') are etched at locations where holes are to be made and that the holes are produced in a further process step using an etching process. 2. The method according to claim 1, characterized in that the at least one thin layer (2, 2 ', 3, 3') at opposite points of the coating on both sides has substantially uniformly shaped recesses (4, 4 '), so that by the etching Through holes (5) arise. 3. The method according to claim 1 or 2, characterized in that the etching process is a plasma etching process. 4. The method according to claim 3, characterized in that the etching process is an anisotropic plasma etching process. 5. The method according to any one of claims 1 to 4, characterized in that the at least one thin layer (2,2 ') is made of metal. 6. The method according to any one of claims 1 to 4, characterized in that the at least one thin layer (3,3 ') is made of photoresist. 7. Perforated plastic film, produced by the method according to one of claims 1 to 6. 5 10th 15 20th 25th 30th 35 40 45 50 55 60 65