DD159932A1 - ADDITIVE PROCESS FOR THE PRODUCTION OF PCB - Google Patents

Abstract

The invention relates to a method for the chemically additively structured deposition of conductor tracks on temperature-resistant plastics and can be used for the production of printed circuit boards, especially micro printed circuit boards, for the manufacture of components and the decorative design of plastic surfaces. According to the invention, the germs applied to the pretreated plastic surface in an emulsifier are produced with light, adhesively fixed by a temperature treatment, deactivated in a solution and the carrier substance destroyed. The seed structures are used to deposit metal layers from chemical baths. Depending on the desired layer thickness, the microstructures have accuracies of (formula).

Description

Title of the invention

Additive-Verfahren.für the production of printed circuit boards

Field of application of the invention '''

The method allows chemically additively structured conductor tracks to be deposited firmly on temperature-resistant polymers.

Characteristic of the known technical solutions

The currently most common methods for the additive manufacture of printed circuit boards are the following:

PD method PDR method Photocircuit method

Addigathe method ·

CC 4 - Method Laser sensitization Photolithography Print

This o.g. Procedures work essentially according to the following three principles:.

1 · Use of a Photosensitive Substrate 2 Selective activation of the substrate surface

3. Apply a photosensitive layer to the substrate

Using a photosensitive substrate, e.g. the FDR method,

Already at. the preparation of catalytically active substances incorporated into the substrate, which • are released either by irradiation or _o by selective etching of the substrate surface. One disadvantage of this is the fact that the selection of the basic materials in question is severely restricted and requires special elaborate production methods.

Selective activation also includes conventional layer deposition techniques such as printing, evaporation and sputtering, which require high material usage and equipment. On the other hand, activated surface areas can be formed by the action of a laser beam, but also by the action of corona discharges.

In the case of laser activation or "corona discharge (DOS 2300 48.1, or DOS 2815 696.) takes place in the photosensitive layer by the action of radiation of a certain wavelength either the conversion of photosensitive substances to catalytically active nuclei or as a result of the development of the elimination of for the. Structure not, needed germs.

In both cases, the organic carrier remains on the substrate surface in which the germs are incorporated. This results in a lower adhesive strength compared with the method according to the invention and reduced thermal resistance, e.g. when soldering. To operate on this principle, the method also includes the application of a photosensitive layer

, aqueous solution. The metal salts used adhere to the substrate surface without effect of an organic T-carrier. To generate the catalytically effective for the subsequent metal deposition nuclei is a high power of the radiation source with a

  Emission maximum required according to the activation energy of the metal salt. The achievable adhesive strengths are "low.

It is an object of the invention to provide an improved process which does not have the essential disadvantages of the processes described above.

Object of the invention

The invention has the object to provide a rational material-saving method of chemical solutions for the structured metallization of temperature-demanding high polymer printed circuit board materials, which avoids the disadvantages of said methods and allows high geometric accuracy adherent ^ etallschichten different composition applied, which are good solderable and bondable ' ,

Explanation of the essence of the invention

The present invention allows chemically additively structured metal layers to be deposited on temperature-stable plastic materials,

The deficiency set out in the prior art can only be avoided if

- The conductor lines structured .additiv with high geometric accuracy, can be applied,

Residues of the applied emulsion can be removed by a heat treatment,

the method allows the deposition of layer sequences in a continuous process,

- the applied conductor tracks remain solderable without additional protection,

- Internal metallizations of contact points in multi-level orders with the same layer thickness are possible.

According to the invention, this is achieved in that metal nuclei are applied to a specifically etched polymerized surface by a toto process, fixed by an annealing process and subsequently used for the deposition of the conductor layer sequences catalytically for the reduction of metal ions from chemical baths. First, the surface must be pickled specifically according to the polymer to be coated. Suitable for this purpose are flux-chromic acid mixtures, mixtures of chromic and sulfuric acid, NaOH and KOH solutions.

The thus pretreated surface is covered without delay with an emulsion containing compounds which upon exposure to e.g. generate metal nuclei or electrons with UV light to reduce Me.talliohen. When the exposure takes place through a photo stencil, an image corresponding to the desired structure is formed, the image elements of which are nuclei for the subsequent chemical metallization. At the uncoated

22 8 5

At the surface, the compounds must be deactivated by ί chemical reactions to preclude reduction to metal nuclei in the subsequent baths. insoluble stable metal sulfides or chlorides for deactivation.

By baking at temperatures between 473 K and 633 K or dissolving in a suitable solvent, the excipients used for the preparation of the emulsion, e.g. Gelatin, removed. The temperature treatment also serves to improve the adhesion of the germs. As metal germs are various precious metals, ZoB. Pd and Ag used. In the following chemical nickel, copper, gold or Sn, (PbSn) baths, the nuclei serve for the catalytic reduction of the corresponding metal ion complexes up to the surface coverage of the metal layer.

The deposition rate is low to avoid internal stress and is between 0.05 and 0.5 μm per minute.

Typical layer thicknesses of the conductor tracks are 2-5 uiii. If very thick layers are required for special applications, subsequent galvanic reinforcement in conventional baths is possible.

embodiment

The invention will be explained below with reference to an embodiment. A film of low roughness polytetrafluoroethylene is pretreated as follows:

1 ", degreasing in 3 % G _r Amulgol solution at 60 ° G

2 β rinse

3. Pickling in 20 % NaOH solution at 80 ° C

- β-

4 «Neutralize in a mixture of 1 part 4-0 / hydrazoric acid and 3 parts of 36% hydrochloric acid

5. ' do the washing up

The substrate thus pretreated is coated after Y / arm air drying with photosensitive silver-containing emulsion (ORWO-Mikratemulsion) Conveniently this is done to achieve a uniform layer thickness by spin coating at a speed of about _β 1500 U min ». The emulsion is kept at a temperature of 35 ° C. for application to the substrate. After the gelatin has been dried (20 minutes at 25.degree. C. in a stream of air), the image is exposed to light with the desired conductor structure. _genommen. The light source is a quartz lamp with a power consumption of 400 W. The exposure time is 5 s. After exposure, ORWO A 71 is developed for 2 min at 20 ° C. in hard-working developer. The unreacted silver halide is removed by fixation in ORWO fixer A 300 according to the working instructions of OEWO, followed by thorough watering (1.5 min, 15 ° C). The sample is now dried at 25 ° C in a stream of air. To remove the gelatin, a heat treatment is carried out in the oven at 230 ° C for 45 min.

The treatment steps "application of the emulsion" to "fixation" are to be carried out in the darkroom with red light (OKtfO filter 107 red) «; The silver nuclei present on the substrate surface are converted by immersion in an O, 5 $ PdCIp solution in for the subsequent metallization catalytically active / germs. Rinsing in deionized HpO completes the process of germination,

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The prepared sample is placed in a chemically-reductive metallization bath , -Z..B. a Mckelbad introduced and treated to the layer thickness of 5 microns. The layers thus produced are characterized by good adhesion, sharp contours, no migration under stress, good solderability and bondability and corrosion resistance.

Claims (2)

- 8 - O ft invention claim Additive process for the production of printed circuit board ^ characterized in that the necessary for the catalytic reduction of metal ions from chemical baths germs by a ϊό.οϊό process en structured on the polymeric surface and adherent fixed by a temperature treatment on the surface. 2. The method according to item 1, characterized in that are used for the structured production of the "germs" on the surface of emulsions containing compounds that generate light with a certain wavelength metal nuclei or electrons that are suitable for the reduction of metal ions. .... 3β method according to item 1, characterized in that for the germ attachment, the polymeric surfaces preferably temperature-resistant plastics and Plastverbündwerkstoffe preferably pickled with a series of lye or an acid mixture v / earth. , ,