JPS61153285A - Conductive copper layer and its production - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a copper layer for conductor plates and electrical components having a coating and a method for producing the same.

Methods for producing conductive copper layers on conductor plates and components are known. That is, the conductive plate is manufactured by the additive method, semi-adjust method, and subtractive method. Conductive copper layers in high-grade conductor boards with through-contacts are mostly produced by the substractive method.

In this case, it is extremely important to use metal resist techniques, ie metals such as tin, lead or lead-tin alloys as a protection against etching. For reasons known to the expert, so-called copper tin is produced today in increasing quantities. An often preferred method of manufacturing copper strips is the so-called metal resist strip technique. The configuration of copper through-contacts and conductor images is
The same is true for metal resist technology. Copper surfaces that do not belong to the conductor image are coated with resist. The renst can be, for example, a photoresist or a layer produced by a screen printing method. metal resist
In the strip technique, in the first step, tin, lead or a lead-tin alloy is applied to the resist-free copper surface as an etch protection. In a second step, the resist is washed off, especially with alkaline water or a solvent. Next, copper
The areas that now have no resist are removed by etching. For this purpose, an ammoniacal solution of copper chloride is usually used. Sometimes iron chloride (FeC13) is still used. Similarly, sulfuric acid and peroxides are sometimes used.

Tin, lead or lead-tin alloy layers are stable both to copper chloride ammonia solutions and to sulfuric acid/peroxide treatments.

In the fourth step, the layer consisting of tin, lead or lead-tin alloy must be removed. For this purpose, for example, peroxide
and fluoride-containing solutions, or hydrochloric acid with other additives are used. Remaining metallic etch-resistant protective layers (metal resist technology) is undesirable. This is because solder-stop lacquer (solder-stop lacquer) is used in the soldering process.
This is because a so-called orange peel is formed under the ping varnisch layer due to heat load. This effect is due to the relatively low melting point of the metallic etch-resistant protective layer.

The essential drawbacks of this metal-resist strip technology are:
The point is that in an additional operating step the metal layer has to be removed again. This is undesirable for raw material economic and technical reasons as well as for reasons of cost. Moreover, the metal strip method
The problem is that copper is also partially violated. Also, difficulties arise in the process of applying the solder-lacquer because the protective metal layer is only incompletely removed. If residue remains in the bore, complete solder contact after that part is not ensured.

Soldering - To ensure better adhesion of the lacquer onto the copper tracks, the trunks are often oxidized and blackened (blackening oxidation) after removal of the metal protective layer. Originally, this blackening oxidation served to improve the adhesion between the resin layer and the copper sheet when pressing the copper film and base material.

Today, this blackening oxidation is also used because of the good optical properties of conductor plates.

The blackening oxidation process is carried out exclusively in alkaline media.

This treatment is carried out using a strongly alkaline chloride solution (NaOH+NaClO2) at a temperature of 50 DEG C. to 90 DEG C. The resulting layer is indeed temperature-stable and does not have the above-mentioned tendency to exhibit "orange peel". However, the mechanical stability and layer thickness of this layer are not large enough so that they cannot serve as etching protection layers. Since this oxidation is carried out at relatively high temperatures, adverse effects on the base material may occur.

Another disadvantage of the above method is that it has to be operated in an alkaline medium. As a result, this blackening oxidation can only be used when the alkali-soluble photoresist layer has served its purpose and has been washed away and the underlying copper etched away.

Following the blackening oxidation, the solder stop-lacquer (solder mask) is applied by printing. In the process, this solder area remains without a layer of lacquer.

More specifically, this is called "soldereye".
s) Applies to J and “solder holes”. In areas without lacquer, the black oxide layer must be removed again. This is done using dilute hydrochloric acid or aqueous peroxide solutions. This method is also problematic as incomplete removal of the oxide layer results in soldering defects.

In the subsequent step, sites without oxide are selectively tinned or tin-leadized. This operation helps improve solderability. Furthermore, this layer forms a corrosion protection on the steel.

Another possibility for the production of electrically conductive plates in state-of-the-art copper technology is to etch the copper layer not covered by the resist. The holes and conductor tracks that already have through contacts (vlas) are then coated with photoresist (
covered with a protective layer consisting of tenting). The disadvantage of this method is that it wastes a significant amount of copper and etchant. Moreover, very uniform copperization is necessary to achieve good results. Another possibility is the so-called differential enching technique in combination with semi-additive techniques. A disadvantage of this differential etching is the prerequisite of a completely uniform layer thickness distribution on the surface of the electroplated copper as well as in the holes.

In addition, German Published Application 29 30 88B discloses conductor plates with copper compounds which are stable to etching agents as anti-etching resists on electroplated steel during the construction of the conductor plates. Etching resists include copper oxide (n), which is produced by changes in the surface shape of electroplated steel.
layers are used. That is, the resist is manufactured by a chemical method. This conductor plate is then treated with an alkaline chloride solution as described in -L, and the copper layer is
゜5-5μ set has been changed to oxidized steel (II).

However, it is impossible to form a uniform layer with such a copper(II) oxide layer. In particular, when the layer thickness is increased, the structure becomes increasingly irregular. Besides, this 2e ao e
The method of No. ee, moreover, proved to be practically impracticable.

The object of the invention is to provide an improved coating for electrically conductive copper layers of conductor plates and components. A further object of the invention is to develop a new and improved method for producing electrically conductive copper layers with coatings on electrically conductive plates.

This problem is solved according to the invention in that the coating is an acid-soluble black metal coating that can be coated in acidic media. One good method of its manufacture is to a) electrically apply a black metal coating in an acidic medium to a conductor plate with a resist, exposed copper surface, and optionally through contacts, and b) to remove the resist. , then etching away the exposed copper surfaces, C) applying an adhesive solder mask to the conductor plate, d) removing the black metal coating in areas not covered by the solder mask, and optionally: The feature is that a metal layer that can be easily soldered is applied to the exposed copper surface.

The method of the invention starts from a finished conductor plate which is coated with copper and optionally has through-contacted holes. This copper layer can be electroplated, for example. The pond and part of the copper surface are still covered with resist. In this case, it can also be a photoresist layer or a resist layer produced by a screen method.

Surprisingly, it has been found in accordance with the present invention that the black metal coating can also be used as an etch resist for conductive copper layers and as an adhesion improving coating layer. This layer is mechanically and thermally stable. Regarding this point, R. Bulger (DE
- Book Publishing ``Electrician Sokel Plating'' Onnogen G, Leutze Verlag, Saulgau 1967) teaches quite the opposite. That is, according to it, the black two Sokel layers are:
Extremely fragile. Furthermore, its corrosion stability is extremely limited, and it is said that it can withstand only a small amount of external force. Therefore, those layers are lacquered or petroleum jelly,
Had to rub in oil or fat. Moreover, the wear resistance of black nickel precipitates is extremely low;
The precipitate is said to decompose at 180°C. However, according to the present invention, the opposite fact was observed. Although it is for a short time, the black chrome layer of the present invention is heated to 300℃1
And beyond that, they remain perfectly adequate for equipment and soldering purposes.

71 According to an advantageous variant of the invention, the black metal coating is applied electrically in an acidic medium onto the copper surface from which the resist has been removed. Preferred black metal coatings are black chrome and black nickel coatings.

Additionally, other electrically depositable black metals can be used, such as chrome, silver, or alloys of these metals. Similarly, trivalent or hexavalent chromium compounds can also be used to precipitate chromium.

In principle, it can be applied chemically or electrically in an acidic medium, forming a coating that has good adhesion, is stable to alkaline etching, can be completely removed again in an acidic medium, and is well recognized optically. All black metal coatings can be used.

In this case, the color can vary from black to gray or brown, provided that sufficient optical contrast to the substrate occurs. This black metal coating has hitherto been used for decorative purposes, especially as a black chrome or black nickel coating. It was known from Galvano, Technical Handbook, Volume 2, Karl Hanser Publishing, Munich 1966 that black chrome coatings can be deposited with good adhesion strength and optical black body properties. However, according to the description, such black chrome coatings are not very stable mechanically and easily become shiny when subjected to frictional loads, which then makes them unusable for the above purpose. Furthermore, Robert Vienna, “Chrome Radio”, Eugen G. Leutze Publishing, Saulgau 1974.
) describes the production of a chromium coating with a black, dull color and very good radiometric properties. Such coatings are used in optical and thermal equipment and in x-ray equipment. However, these coatings were not of great importance. This is because the extremely dull coating quickly becomes shiny and loses its desired effectiveness when subjected to mechanical loads and external frictional forces.

In addition to the above-mentioned convenience, black chrome plating has other industrial applications, such as measuring equipment and control equipment, electrical engineering industry.

Surprisingly, according to the invention, black Chrome and black nickel coatings are also highly suitable for use as etch resist and adhesion improving coating layers for electrically conductive copper layers.These layers are mechanically and thermally stable up to at least 300°C; Provides excellent adhesion resistance to the solder mask remaining on the conductor plate.2.3
In this case, the quality of the black metal coating is modified by applying it not directly on the copper, but on a thin layer of bright metal with a thickness of 0.5-3 μm. Since these bright metal layers are thin, they can be removed equally well and completely.

The thickness of the black chrome layer is usually from 0.1 to 10 μm, in particular from 0.5 to 4 μm. For nickel, the layer thickness is between 0.1 and 2 μm, preferably between 0.5 and 2 μm. A particularly good range is from 0.5 to 1.5 μι.

Surprisingly, this black chrome layer is about 3 to IOA
/d-2 current density. The state of the art, on the contrary, teaches the use of current densities of 2 OA/dm2 and above.

A particular advantage of the black metal layer used according to the invention is its better mechanical and chemical stability compared to known black oxide layers.

A similar good stability is also achieved in some individual cases with a thick nickel layer, which is used according to the state of the art. The disadvantage of these layers is that if their removal is necessary,
This means that it can only be removed very incompletely or is extremely difficult to remove.

In the next step, the photoresist layer is conventionally removed using an aqueous alkaline agent or an organic solvent. Next, copper etching is performed on the copper surface from which the resist has been removed. For this purpose, alkaline chemicals,
For example, ammonia-alkaline copper chloride solution (CuC1
2) is used. An anti-etch lacquer is then applied as a solder mask. The lacquer adheres particularly well to the black metal layer according to the invention.

In a further step, the black metal layer is removed again in the areas not covered by the solder lacquer (solder mask). This selective etching process
In particular, the holes and etched eyes are freed from the coating and evacuated again. This etching is carried out in an acidic medium using mineral acids or acidic peroxide solutions. Optionally, in a final step, the areas of the copper from which the copper black metal has been removed are tinned or otherwise provided with a good solderable metal layer. There is no problem with this tinization. This is because the etching protection made of black metal can be easily and completely removed. Furthermore, the black metal layer according to the invention comprises:
Very good, moreover, since the copper tracks mostly remain under the solder mask, which adheres well.

The mechanical strength and adhesion properties are better than those of previously known copper oxide layer solder masks. That is, the adhesion of the solder mask is not satisfactory, especially if the copper oxide layer is too thick.

Further research into the method of manufacturing the conductive layer revealed that the black metal coating electrically applied in an acidic medium is susceptible to artifacts in areas not covered by the solder mask due to the action of prolonged heat. It has been found that when not aged, it is always completely removed in acidic media. However, the temperature of the soldering mask is about 100~150℃.
Additional changes occur in the black metal layer when it is fully cured at a temperature of . The change, especially in the case of black chrome, results in leaving a residue after etching in hydrochloric acid, which leads to defective conductor plates in the case of subsequent selective hot air tinning. vinegar. Residues produced by aging are extremely difficult to remove. Various acid-based solutions with various additives have not given any satisfactory results.

It has now been found that aged black metal layers may also be removed without leaving any residue by an alkaline hexacyanoferrate (DI) solution containing a wetting agent. This solution must contain at least 0.2 mol/1 potassium hexaneanoferrate (DI).

However, it may also be saturated. The content of caustic potash must be low (both 0.1 mol/l and 5 mol/l).
may be increased to The content of the wetting agent is 0.001 to 1
Must be g/l. As wetting agents it is possible in principle to use all alkalis and all agents which are not sensitive to oxidizing agents.

How to remove aged or non-aged black metal coatings:
It can be carried out at temperatures between room temperature and 70°C. Under this condition, no damaging corrosion of the solder mask or other parts of the conductor occurs. The evaporated copper surface will not be corroded by the solution. The solder spots opened according to the invention can then be completely tinned or lead-tined, respectively, selectively.

The following examples illustrate the invention in more detail.

- The walls of the conductor tracks and bore holes of the resist-printed conductor plate are coated with a 25 μm layer in a commercially available copper electrolyte, namely Cobrostar LPI (a product of Blasberg Surface Technology Gbn). Copper was applied to the thickness. After cleaning this conductive plate, a gray-black layer containing nickel oxide and having a thickness of about 1 μm was applied to it. The deposition was carried out using a commercially available black nickel electrolyte, namely Black Pearl J (a product of OMI). The deposition parameters were as follows.

pH value: 5.8 Temperature 2 30~32℃ Current density: 0.8-IA/dw+2 Deposition time: Approximately 5 minutes After washing and drying the resist, remove it under alkaline water conditions and remove the exposed copper surface. Removed in an ammonia solution of copper chloride. The black nickel layer served as sufficient protection against etching.

Even better results were obtained when a thin bright nickel layer of about 3 μm was applied between the copper layer and the black nickel layer.

Example-2 A copper-plated conductor plate was cleaned as described in Example 1 and washed with a commercially available black chrome bath, namely Nerostar CR (
(a product of Blasberg Surface Technology GmbH).

At a current density of about 15A/dm2, about 4μ within about 15 minutes
A black chrome layer with a thickness of m was deposited. The operating temperature was approximately 20°C to 25°C, and the pH was strongly acidic (approximately 1).

This black chrome layer was completely protected against etching when etched in an ammoniacal solution of copper chloride.

The printed circuit boards treated in Examples 1-2 were then each coated with a solder resist (solder mask) without coating the printons, solder eyes and bores. The etching protection layer was then selectively removed at those locations. Finally, tin plating was performed using hot air. The plates treated according to the invention passed these last steps without any disadvantages. Thus, the solder mask showed excellent adhesion and the underlying copper layer was pale black and optically contrasted well with the substrate.

The copper surface, without the black metal etch protection layer, accepted the tin well and gave a stable and perfect solder bond.

Example-1 Through-hole contact
tact) and a conductor plate with resist print,
Commercially available copper electrolyte (i.e. Kotsurostar LP1)
Copper plated to a thickness of 25μm, and then plated to a thickness of about 2~3μm.
coated with a black chrome layer of m (operating conditions were 5A/d@
current density of 2, deposition time of 20 minutes).

After stripping the resist and removing (etching) the excess copper, the board was covered with a solder mask, leaving the solder eyes and bores uncovered. Curing of the solder mask is between 100° C and 150° C depending on its type.
It was carried out at a temperature of The black chrome layer was then coated with 260 g/l of hexacyanoferrate (■) and 35 g/l of potassium hydroxide.
l and 0.035 g of wetting agent (Triton BGlo)/
The solder was selectively removed from the eyes and bores using a solution of 1 ml of solder. The operating temperature was 40° C. and the precipitation time was 2 minutes. In contrast to the removal of the correspondingly aged black chrome layer in acidic conditions, this black layer was removed without leaving any residue.

It was then possible to selectively plate the locations with tin or lead-tin.

Potassium salt of hexacyanoferrate(III) acid, caustic potash,
And when changing the concentration of the wetting agent and, if necessary, the operating temperature and precipitation time, good conditions were reliably obtained in each case.

Example-1 Adhesion strength of black nickel after tempering.

The preparation of the black nickel plate was carried out at 3.5V for 6 minutes.

This was followed by tempering at 180'C for 8 minutes. No change was observed in the black nickel. Furthermore, there was no deviation from basic materials. Subsequent tempering tests were conducted at 130'C for 30 minutes and at 130'C for 12 minutes.
It lasted 0 minutes. Again, no changes or withdrawals were observed.

These tests reveal that black nickel can be used for the purposes of the present invention. No physical changes occurred during tempering.

The structure of a typical conductor plate consisting of a conductive copper layer and a black metal coating used in accordance with the invention is further illustrated by the accompanying drawings.

In the figure, 1) shows the substrate, 2) shows the conductor steel layer of the conductor tracks, 3) shows the black metal coating, and 4) shows the copper layer of the through contact hole. Solder mask not shown. More particularly, the mask still leaves the points to be soldered uncovered and, if desired, the conductor tracks, if present, and the solder points on the back side of the conductor plate. It is.

The black metal layer according to the invention is made of prepreg (prepreg).
) and the copper sheet can be advantageously used to laminate multiple layers to create improved adhesion between the copper sheet and the copper sheet.

[Brief explanation of drawings]

The accompanying drawings are cross-sectional views of the conductor plate of the present invention. 1. Substrate 2. Copper layer 3, black metal coating 40 through contact hole copper layer agent Patent attorney (8334) Sunagawa Gobe Telephone (402
)8088

Claims (1)

[Scope of Claims] 1) Conductive copper layers in conductor plates and electrical components having a coating characterized in that the coating is a black metal that is acid-soluble and can be applied in an acidic medium; Copper layer 3) according to claim 1, characterized in that it is a black chrome layer with a thickness of 0.1 μm.
4) Copper layer according to claim 2, characterized in that its thickness is 0.5-4 μm; 4) Claim characterized in that the coating is a black nickel layer with a thickness of at least 0.1 μm. 1 copper layer 5)
6) A conductor with an exposed copper surface, with through-contacts, and optionally with a resist. The board is a) electrically coated with a black metal coating in an acidic medium, b) the resist is removed and the exposed copper layer is then etched away, c) the conductor board is provided with an adhesive solder mask, and d ) A coated conductor plate, characterized in that the black metal coating is removed in the areas not covered by the solder mask and, if desired, the exposed copper surface is coated with a metal layer that is easily solderable. 7) Process according to claim 6, characterized in that a black chrome coating or a black nickel coating is used as the black metal coating 8) Removal of the black metal coating in an acidic medium In the method 9) step d) of claim 6 or 7, the black metal coating is applied with an alkaline potassium hexacyanoferrate (III) solution containing a wetting agent in the areas not covered by the solder mask. 10) The method according to claim 9, characterized in that the removal is carried out at a temperature from room temperature to 70° C. 11) Alkaline containing wetting agent Potassium hexacyanoferrate (III) solution is 0.2Mol/l of potassium hexacyanoferrate (III), 0.1 to 5Mo
l/) of caustic potassium and 0.001 to 1 g/l
12) Use of a black metal coating that can be applied in an acidic medium as an etch resist and adhesion improving coating layer of a conductive copper layer.