DE1206976B - Process for producing printed circuits according to the build-up method - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. α .:

Number:
File number:
Registration date:
Display day:

HOIb

German class: 21c-2/34

S87402VIIId / 21c
September 19, 1963
December 16, 1965

The invention relates to a method for producing printed circuits according to the assembly method. It deals in particular with the problem of covering the conductor tracks during the Etching away the metal base layer.

The method of building is that on top of one with a metal base layer such as a copper layer a stencil is glued to the insulating material body, which covers the parts of the metal base layer, on which ducts are to be created, do not cover (negative stencil); Stencils in this one Senses are foils or plates that can only be used once or applied by screen printing or spraying Covers made from a material that is soluble in organic solvents. By galvanic Deposition of copper or other suitable metals on the stencil does not the ducts are created in the areas covered; after removing the stencil the undesired parts, namely the areas of the metal base layer that have not been galvanically reinforced etched away. λ

Such methods are known in the printed circuit board art. It is doing for example assumed insulation panels laminated with copper foils. The copper foil is through Binder anchored to the insulating carrier plate, in which case the laminated carrier plate is also often used exposed to high pressures to increase the adhesive strength of the copper foil on the insulating material will.

On the other hand, it is already known to use an insulating carrier plate instead of the copper-clad insulating carrier plate to use that by currentless, d. H. chemical processes or spray processes with a thin conductive base layer was provided. This thin conductive layer, like the copper foil, has the task of galvanizing all areas should be reinforced to connect electrically with each other. With the spraying process, you have silver or graphite is used as the conductive material, while the electroless chemical one Process the base layers are made from nickel-phosphorus alloys, but also from silver or copper Has.

A prior proposal gives a particularly advantageous method for producing printed Circuits according to the construction method. In this method, at least one adhesive layer is preferred two layers of adhesive applied to a roughened, non-laminated insulating material carrier; the Glue layer is then made with tin and palladium

Process for the production of printed circuits according to the build-up method

Applicant:

Siemens & Halske Aktiengesellschaft,

Berlin and Munich,

Munich 2, Wittelsbacherplatz 2

Named as inventor:
Dr. Joachim Kleffner,
Dr. Wilhelm Armbrüster, Munich

preactivated; by applying a maximum of 0.5 μΐη strong copper base layer by means of electroless chemical copper plating of the entire surface a metal layer is formed, with any holes in the carrier plate also being copper-plated will; The very thin copper base layer is then galvanically compacted and, if necessary, on 1 up to 2 μΐη galvanically reinforced; the one produced in this way Copper layer forms the metal base layer on which the negative stencil is applied, after which then the cable runs in the area of the uncovered parts are made by galvanic reinforcement and then further removed the negative stencil and the unwanted parts of the copper base layer be etched away. The etching away of the unwanted parts of the copper base layer can, for. B. can be produced in a simple manner by the difference method, after which, after removing the negative stencil the entire plate of an etching liquid, e.g. B. ferric chloride solution, is exposed, wherein both the conductor tracks, but especially the thin copper base layer, are etched in such a way that that the unwanted parts removed and the conductor tracks only slightly, just around the Thickness of the copper base layer, its thickness can be reduced. This method of difference-so method is only suitable for printed circuits in which the conductor tracks are very thick and where there are no high demands on accuracy

509 758/300

the resistance values of the conductor tracks will.

Are the conductor tracks following the procedure of the older proposal before removing the negative stencil covered with gold, the negative stencil can be easily removed, and also the unwanted parts of the copper base layer can easily be removed with iron (III) chloride solution be etched away. Now, however, means applying a gold plating to the conductor tracks on the one hand that a further electroplating is required, and on the other hand that in addition to this by the noble material increases the cost of manufacturing the printed circuit board. same for for rhodium supports.

In the silver or tin editions mentioned in the older proposal, there are also editions from tin-lead alloys are conceivable, another problem arises, which is that such pads cannot be exposed to ferric chloride etching fluid because the pad lose their solderability due to chlorine attack, which is why the removal of the undesired Parts of the copper base layer must be made in chromosulfuric acid.

If one of the difference method that is described above and the unsatisfactory results supplies, apart from, so must in each of the processes described above for the production of printed Circuits using the build-up method while etching away the unwanted parts of the metal base layer the conductor tracks are protected against attack by the etchant. You could do this remember to cover the conductor tracks with a positive stencil, e.g. after the negative stencil was removed. However, this handling causes difficulties insofar as it is for it it must be ensured that the positive template with very great precision actually all conductor tracks and only this covered. There is also the risk that the positive stencil of the etching process flaking off the conductor tracks.

The invention was based on the object of creating a substantial simplification by adding a Method is specified that allows the masking difficulties to be resolved effortlessly.

In the process of manufacturing printed circuits using the build-up method, an insulating material carrier is used first with a metal base layer and then with a negative stencil made in organic Solvent-soluble material provided at the points of the conductor tracks to be built up the metal base layer leaves free, whereupon these free areas for generating the conductor tracks with Metal are reinforced, then the template from the metal base layer and then the superfluous Metal base layer parts are removed. According to the invention, this method is for solving the problems Task characterized in that after the production of the conductor tracks both these and the Negative stencil can be covered with a protective layer made of a material that is against the negative stencil dissolving solvent is resistant and adheres to the conductor tracks, and that afterwards the negative stencil is dissolved away, the protective layer on the stencil areas being infiltrated and is thus lifted off while it remains on the conductor tracks and then the superfluous metal base layer is removed by methods known per se. For the negative stencil is preferably a screen printable material, such as. B. Printing varnishes based on with Colophony-modified stand oil (a drying oil that has been thickened exclusively by the application of heat Oil, such as linseed oil level oil) is used, which is in trichlorethylene and / or in white spirit, gasoline or aliphatic hydrocarbons is soluble, while for the protective layer material, such as. B. Shellac, is used that is resistant to these solvents, but possibly even in other solvents, such as B. in ethanol, is soluble and sprayed, printed or painted on.

The use of the method according to the invention in the method of the older one is particularly advantageous Proposal. Here, the negative stencil is in a thickness of 5 to 30 μΐη to about 0.5 to 2 μΐη strong, through electroless copper plating and galvanic Compression produced on the insulating support body provided with at least one adhesive Applied copper base layer, and the conductor tracks generated up to a thickness of about 30 μΐη and the negative stencil are with a 5 to 15 μm thick protective layer, e.g. B. made of shellac, covered, with parts of the stencil to initiate the dissolution and to infiltrate the protective layer be left free or the protective layer in these places opened before dissolving the stencil will.

Since the protective layer remains on the conductor tracks after the negative stencil has been removed, you can these can also be covered with silver or tin-lead alloy, with the etching away of the undesirable Parts of the metal base layer, preferably the copper base layer, nevertheless in the very simple one Etching agent »iron (III) chloride solution« can be carried out.

This is a major advantage of the process according to the invention, because the etching in the can only be handled with great care Chromosulfuric acid is not required.

Another important advantage occurs when bare, i.e. H. without any finishing or covering present copper layers are provided with the protective layer according to the invention; in this case This is because the copper remains solderable because it does not come into contact with an oxide skin which would impair the solderability covers.

Another advantage is given by the elimination of gold plating, i. H. that caustic and expensive Noble electroplating can be dispensed with, whereby the quality of the conductor tracks is not impaired. In addition, one is no longer dependent on the manufacture of very cheap printed circuits Method of differential etching, which in any case is not very specific and reliable because it does not provides a bare surface and cracks can arise in the ducts.

Last but not least, it should be pointed out that the method according to the invention is particularly easy to carry out is. This can be seen from the description of the figures which now follows, which are only given as examples are to be understood.

F i g. 1 shows a section from a circuit board with printed conductor tracks;

F i g. 2 to 7 show the individual steps involved in carrying out the method according to the invention are necessary;

F i g. 8 shows a section from a circuit board for a measuring device, and

F i g. 9 shows a section along the line IX-IX in FIG. 8.

In Fig. 1, 1 is the insulating material plate, for example made of hard fiber material, and 2 is used to denote conductor paths that are located on the insulating material plate 1 and are firmly attached to it. FIGS. 2 to 7 represent the manufacturing process of the printed circuit according to FIG. 1 in section I-I. For this purpose, FIG. 2 that an adhesive layer 3 is first applied to an insulating carrier plate 1 is. The metal base layer 4 is applied to this adhesive layer 3 and with the negative stencil parts 5 covered. The conductor track 2 was created by reinforcing the metal base layer 4.

According to FIG. 3 is the arrangement according to FIG. 2 provided with the protective layer 6, which both the negative stencil parts 5 as well as the conductor track 2 covered.

In Fig. 4 is the insulating plate 1 with the adhesive layer 3 and the metal base layer 4 as well as the Conductor track 2 and the protective layer 6 shown, namely after the removal of the negative stencil parts and the protective layer parts above it. At this point it should be said that it is surprising that the protective layer 6 is not also lifted off the conductor track 2 when the negative stencil 5 is dissolved will. This is probably not the case because the negative stencil swells when it is dissolved and in the process the protective layer 6 becomes cracked and, as it were, washed away upon further dissolution will. However, since the protective layer adheres to the conductor tracks, it is not stressed there in the way that as in the areas above the negative stencil. The protective layer therefore tears, as with all Test pieces was found, always with precise edges on the conductor tracks, as shown in FIG. 4 is shown.

F i g. 5 shows the circuit board after the metal base layer 4 has been etched away on the conductor tracks free areas, so that only the adhesive layer 3 is exposed at these points. In Fig. 6 are also removed the superfluous adhesive layer parts. In this form the printed circuit board is in the Usually usable. If shellac is used as a protective layer material, this has the advantage that the conductor tracks, e.g. made of copper, remain solderable (no oxide skin formation), the shellac layer is only destroyed during soldering and then only exposes the soldering area. The remaining conductor track surfaces remain covered with the protective layer 6 as before. But it is also possible to use the protective layer, z. B. to remove shellac, which is soluble in ethanol, as shown in FIG. 7 is shown.

F i g. 8 shows an insulating plate 7 with the conductor tracks 8, 9, 10, 11, 12 and 13, which are in dome-shaped Pass over circular segments which are arranged around a metallic center circle 14. Such Arrangements of the printed circuits are, for. B. common with measuring devices, the metal ring 14, which was also made by the methods of the printed circuit, as a sanding base for a switching element applies.

In Fig. 9 is a section along line IX-IX of FIG. 8 shown. Here is the insulating plate 7 also provided with an adhesive layer 15 and a metal base layer 16. The negative stencil parts 17 are located both between the conductor tracks and between the outer conductor tracks and the edge. In the middle part 18 of the metal ring 14, the solvent would be used to detach the negative stencil parts find no access. For this purpose is over the middle part in the protective layer an opening 20 is left free so that the solvent can pass through there. Even in the peripheral areas 21 and 22, the protective layer is not applied, so that the dissolution of the Negative stencil can begin. But it is also possible to apply the protective layer to these areas 20, 21, 22 and, if necessary, at other points only before the stencil is dismantled with a scratching tool only to open. In any case, the plate according to FIG. 9 is described as in FIGS. 2-7 treated.

Claims (4)

Patent claims: 1. Process for the production of printed circuits according to the construction method in which a Insulating material first with a metal base layer and then this with a negative stencil made of material soluble in organic solvents, which forms the metal base layer at the points of the conductor tracks to be built up leaves free, whereupon these vacancies to generate the conductor tracks with metal are reinforced, then the template from the metal base layer and then the superfluous Metal base layer parts are removed, characterized in that after Create the conductor tracks, both these and the negative stencil with a protective layer a material that adheres to the conductor tracks and against which the negative stencil is covered dissolving solvent is resistant, and that then the negative stencil dissolved away is, whereby the protective layer located on the stencil areas is infiltrated and thus is lifted off while it remains on the conductor tracks, after which the superfluous Metal base layer is removed by methods known per se. 2. The method according to claim 1, characterized in that one for the negative stencil screen-printable material, such as printing varnishes based on modified with rosin Stand oil, which is used in trichlorethylene and / or gasoline or aliphatic hydrocarbons is soluble and for the protective layer material, such as. B. shellac is used, which is resistant to these solvents and is sprayed on, printed on or painted on. 3. The method according to claim 1 or 2, characterized in that the negative stencil in a thickness of 5 to 30 μm to an approximately 0.5 to 2 μm thick, by electroless copper plating and galvanic compression on the insulating material carrier body provided with at least one adhesive produced copper base layer is applied and that the up to a thickness of about 30 μΐη generated conductor tracks and the negative stencil with a 5 to 15 μπα strong Protective layer are covered, whereby to initiate the dissolution of the stencil and to infiltration the protective layer parts of the stencil are left free or the protective layer is opened at these points before dissolving the stencil. 4. The method according to one or more of claims 1 to 3, characterized in that the protective layer is only applied after £ the conductor tracks were covered with silver or tin-lead alloys. References considered: U.S. Patent No. 2,728,693. 1 sheet of drawings 509 758/300 12.65 © Bundesdruckerei Berlin