Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
2002-02-25
2004-10-19
Duda, Kathleen (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S311000, C430S329000
Reexamination Certificate
active
06806034
ABSTRACT:
DESCRIPTION
The invention relates to a method of forming a conductive pattern on dielectric substrates covered with a metal film, preferably a layer of copper.
Many different methods have been proposed in the past for producing conductive patterns on electric circuit carriers. In the panel plating method, first of all a copper layer enclosing the drilled printed circuit board material on all sides is produced in the thickness required for the conductor structures. Then the regions of the outer sides of the printed circuit boards, which correspond to the conductor structures to be produced, are covered by a resist layer, such that these layers are preserved during the subsequent etching process. In the pattern plating method, first of all just a thin copper layer is formed on the printed circuit board material. To this is then applied for example a photoresist layer and the copper layer is exposed again by photostructuring at those locations which correspond to the conductor structures to be formed. To the exposed copper regions is applied a metal film. Then the photoresist layer is removed and the exposed copper layer is etched away. If a metal resist method is used, a metal resist layer, for example a tin/lead layer is applied as the electroplating resist.
These methods have considerable disadvantages. In particular it is not possible to manufacture in a reproducible manner, under production conditions, conductor structures with structure widths of less than 100 &mgr;m. Admittedly there has been no lack of attempts to achieve this goal. Circuits of this kind have been successfully produced with some expensive methods and initial materials. However methods of this kind do not come into consideration for mass production, since they are too expensive and extravagant and/or require very expensive initial products. These methods are not suitable however for producing circuits with structure widths of the conductor tracks which are less than 50 &mgr;m.
As an alternative etching resist film, a layer formed from imidazole or benzimidazole derivatives has been proposed. For example, in EP 0 178 864 A2, has been described a method of producing a printed circuit board which is through-hole plated with copper, which method consists in first forming the desired circuit pattern on the copper coating with an alkali-soluble resist, then forming an etching resist film by bringing the board into contact with an aqueous solution of an alkylimidazole at the exposed locations, and by the board then being dried and the exposed copper subsequently being removed by etching with an alkaline etching solution.
In EP 0 364 132 A1 it is mentioned that solutions which are suitable for forming a protective layer to protect against tarnishing can also be used as etch resists. Solutions of this kind contain imidazole compounds with a C
5-21
-alkyl chain and in addition copper or zinc ions.
In EP 0 619 333 A2 are described methods of manufacturing conductor structures in which compounds containing nitrogen are used to form an etching resist film. As compounds containing nitrogen are used inter alia compounds, substituted with an alkyl chain with at least three carbon atoms, from the group imidazoles, benzimidazoles, triazoles pyrroles, pyrazoles, oxazoles, isoxazoles, thiazoles, benzothiazoles, indoles, adenine, purines, quinolines, pyrazines, quinazolines, guanine, xanthine, hypoxanthine, indazoles, creatinine, phenazines, and cupferron. To produce the conductor structures, first of all a negative image is formed with a standard resist which is removable in an alkaline solution, then the board is covered at the exposed regions with the etching resist film containing the nitrogen compounds, and thereafter the negative resist is removed again. Then the conductor structure can be formed by etching.
In DE 43 39 019 A1 is described a further method using a protective layer produced from imidazole and/or benzimidazole. In this case, the protective layer is formed exclusively on the perforation walls, after another layer has been formed on the outer sides of the printed circuit boards up to the edges of the perforations, which layer prevents the formation of the protective layer there. If a photosensitive lacquer is used for this other layer, the conductor structures can be produced by photostructuring.
In DE 37 32 249 A1 is quoted a method of manufacturing three-dimensional printed circuit boards in a subtractive/semi-additive technique with image transfer on an insulating substrate, in which the substrate covered with a copper layer is first coated on all sides with a tin-metal resist which can be deposited in an electroless manner and/or by electrodeposition, and the metal resist is then selectively irradiated with laser radiation but without any mask, such that the conductive pattern is produced as a negative. The exposed copper regions can then be removed by etching.
In DE 41 31 065 A1 is quoted a method of manufacturing printed circuit boards in which a metal layer and an etching resist film are applied in succession to an electrically insulating substrate, the etching resist film is removed by electromagnetic radiation in the regions directly adjoining the later conductor track pattern and the exposed regions of the metal layer are etched away down to the surface of the substrate in such a way that the conductor track patterns and island regions of the metal layer, electrically insulated therefrom by etching pits, remain on the substrate. Preferably the etching resist film is formed by electroless metal deposition. As an alternative to this, an organic material, for instance an electrodeposition paint can be used. To produce the electromagnetic radiation, a laser is preferably used, in particular an Nd-YAG laser. The etching pits are 150 &mgr;m wide. During the etching of the metal film, preferably a copper layer, under-etching of respectively 35 &mgr;m is detected at the edges of the etching pits.
In EP 0 757 885 B1 is disclosed a method of forming metallic conductive patterns with solderable and/or bondable connection regions on electrically insulating substrates, in which first of all a metallisation is applied to the substrate and then an organic, electroplating- and etch-resistant protective layer is deposited onto the metallisation in an electro-dipping bath; thereafter the protective layer is removed again in the later connection regions by means of laser irradiation, then an etch-resistant, solderable and/or bondable end surface is electrodeposited on the exposed regions of the metallisation, the protective layer is removed by means of laser irradiation at least in the regions directly adjoining the later conductive pattern, and finally the exposed regions of the metallisation are etched away again to the surface of the substrate. In this case too, an Nd-YAG laser is mentioned as the radiation source. The etching pits formed have a width of 150 &mgr;m.
The known methods are either extremely extravagant and therefore expensive, or it does not prove possible to manufacture in a reproducible manner very fine structures having a structure width of 50 &mgr;m and less, especially of at the most 20 &mgr;m. The only known possibility consists in proceeding from a material which has a copper layer which is at least 5 &mgr;m thick. However producing materials of this kind is extremely extravagant in terms of process technology and thus expensive. When standard materials having a thick copper layer are used it has emerged that the conductor structures generally do not have a rectangular cross-section on account of not inconsiderable under-etching, such that their bearing surface on the substrate is very small and thus the desired adhesive strength of the conductor tracks is not achieved.
Underlying the present invention, therefore, is the problem of avoiding the disadvantages of the known methods and in particular of finding a method by means of which simple structuring can be carried out even in mass production, which structuring makes it possible to manufacture in a reproducible manner extremely fine structu
Guggemos Michael
Kohnle Franz
Atotech Deutschland GmbH
Paul & Paul
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