DK143830B - APPLICATION OF AN ALKALIC SOLUTION TO ESTABLISH COPPER CONDUCTORS IN THE PREPARATION OF PRINTED CIRCUITS - Google Patents

Description

in 143830

The present invention relates to the use of an alkaline solution for etching copper conductors in the production of printed circuits, which solution contains at least 1% by weight and is at most saturated with an ammonium peroxymono or disulfate 5 or a peroxymono or disulfate of a alkali or alkaline earth metal or an organic peroxoic acid or a salt thereof, further a metal ion complex such as ammonia or an ammonium derivative, and additionally at least 0.1% by weight of a stabilizer for the peroxo compound, which stabilizer may also be used. be complexing for metal ions, namely a mono- or polyamine, a carboxy-substituted mono- or polyamine, a mono- or polyoxyamine, a mono- or poly-amino ether, urea optionally mono- or dialkyl-substituted, or in the form of a of the following compounds: a C 2 -C 4 hydroxycarboxylic acid, especially glycolic acid, a C 1 -C 4 mono-alcohol, especially methanol, or a C 2 -C 4 -alcohol, especially 1,3-butanediol, a mono acylated dialcohol with up to a total of 6 C atoms, a ketal with up to 6 C atoms, an aliphatic ketone with 3-6 C atoms, an aliphatic ether with 2-6 C atoms, tri-sodium hydroxyethyl -ethylenediamine triacetate, Ν, Ν, Ν ', Ν'-tetra-kis- (2-hydroxypropyl) ethylenediamine or tetraethylene pentamine.

Many methods for selective dissolution or etching of copper are known in the manufacture of printed circuits or other products exhibiting a pattern of metallic copper.

For example, in the manufacture of printed circuits, one assumes a copper-laminated material and applies an etch-resistant reserve material on the copper surface to the formation of a pattern which, after etching the free copper surfaces, forms the desired pattern. Organic substances such as resins and wax, as well as suitable metals, e.g. tin-lead alloys or precious metals. Simply put, the requirement for the reservoir material is not to be attacked by the etching solution used to etch the copper.

35 So far, etch solutions which are universally applicable have not been known. For example, ferric chloride may be used with certain organic reservoir materials. However, ferric chloride attacks nickel and tin alloys, and the same goes for ferrous salt solutions, for example. Chromic acid attacks silver, while another commonly used etching agent ammonium peroxide disulfate in acidic solution attacks tin-lead alloys and, in addition, causes strong etching, ie. decomposition of the metal under the protective foil when silver or gold nickel is used as etching reservoir as these metals form a galvanic element with the copper in the etching solution.

From the specification of Austrian patent no.259.325, a method for removing copper-containing coatings from iron and steel surfaces is known, especially in boiler plants. In this process, one works in an aqueous-alkaline medium containing a complexing agent. As the oxidizing agent, halogen compounds are used alone or an oxidizing agent in addition to halogen compounds. For example, for the removal of copper-containing coatings from iron and steel surfaces, an aqueous solution containing up to 20% of at least one to 20 copper suitable / alkaline-effective complexes and 0.1-10% of a water-soluble bromine or iodine compound is used. . As the actual etching agent, according to the examples in the above-mentioned Austrian patent specification, potassium hypochlorite, sodium chlorate or soda solution saturated with chlorine is used. Furthermore, copper removal solutions containing both peroxo compounds and stabilizers for the peroxo compounds or complexing agents for metals are used.

From the specification of French Patent No. 1,468,759, a method for removing copper from iron surfaces is known, using an alkaline solution containing a complexing agent and an oxidizing agent. In this connection it should be noted that the solution contains a ferrous or ferric chelate of suitable salts of amino or polyamino-polyacetic acid and of ammonia or the like, and the process is carried out at a temperature at which the iron metal is practically Such a solution is not used, for certain saturations with the iron chelate, certain operating temperatures of 60 ° C or, for a saturation degree of approx. 91%, at 75 ° C.

The same solution must also serve to passivate 5 of ferrous surfaces.

From the specification of German Patent No. 1,289,720 a means for removing copper and cleaning metal surfaces is known.

This agent contains ammonia or an ammonia derivative and a peroxo compound, and is suitably used as a corrosive agent e.g. ammonium peroxide disulfate in an alkaline aqueous solution.

Peroxo compounds, especially ammonium persulphate, would be ideal etching agents. However, these compounds have the disadvantage that they are not resistant to alkaline solutions. There have, for the time being, been used exclusively for e.g. ammonium persulfate in acidic solutions.

However, the use of such acidic solutions causes significant disadvantages, especially in such circuit boards, where the base material's copper foil layer is initially coated with other metals, e.g.

20 galvanically, whereupon the copper foil, which does not correspond to the circuit pattern, is etched away using the applied metal as a reservoir material. In these cases, during the etching process in acidic medium due to the formation of a galvanic element, a very annoying "sub-etching" occurs, ie.

25, a considerable degree of degradation of the copper foil under the galvanically applied metal layer.

Therefore, it has been attempted to use alkaline solutions in place of the usual acidic solutions containing peroxo compounds to avoid the said undesirable formation of galvanic element and the associated etching. However, the usual alkaline solutions of the corresponding peroxo compounds are unstable and decompose rapidly during the etching process during disruptive heat generation.

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Although acidic ammonium persulfate solutions produce very good results in the production of conventional circuit boards / to date, unsuccessful preparation of alkaline antnonium persulfate solutions for the microcircuit technique has resulted in severe undercuts caused by the formation of galvanic elements / cannot be tolerated, since conductor wires cannot be tolerated. plates are very narrow, which is why the avoidance of undercuts is particularly important.

In view of this, it is therefore very surprising that using the above-defined alkaline solution for etching copper conductors in the production of printed circuits, it is possible to avoid all the disadvantages mentioned above.

In the application of the invention of the described solution, neither the organic layers nor the metal layers are attacked. This means that all conventional backup materials can be used without disadvantage.

In particular, in conjunction with the use of the inventive etching solutions of the invention, plastic reservoir materials which have found increasing use may also be used, which is surprising as it is expected that plastics reservoir materials would be attacked and damaged by peroxo compounds. .

Furthermore, there is no danger of spontaneous decomposition of the etching solution during uncontrollable heat generation.

The stabilized alkaline solutions used according to the invention also have the advantage of having a relatively high etching rate which remains constant throughout the life of the bath.

In particular, it is also surprising that in the present application of the described alkaline solutions when etching copper foil coated with other metal as a reservoir material, formation of galvanic elements does not occur, which is why the hitherto very inconvenient undercuts are largely avoided. as a result of electro erosion. This effect of the invention is particularly valuable when using etching reservoirs of e.g. nickel-gold or tin-lead.

The effect described above is further illustrated in the experiments below.

Particularly favorable results are obtained in experiments with nickel gold, solder and shiny tin.

The "etching factor" for various etching solutions is determined experimentally and expressed numerically by the ratio of the thickness of the copper layer (V) to the maximum distance from the copper layer present after the etching to the edge of the reservoir (X):

Etching factor = V / X

The following table lists average values for etching factors obtained with different etching solutions:

Table

Solder Shiny tin Gold-nickel

Acidic ammonium persulfate 1.9 1.5 0.9

Chromic sulfuric acid 2.0 1.1 0.7 20 Iron (III) chloride NV NV 0.9

Copper (II) chloride NV NV 0.7

Alkali Chlorite 1.6 2.0 1.5

Alkali piperoxide disulfate 2.1 2.3 2.0 NV = not compatible 25 A high average etching factor means a relatively low etching of the copper layer.

It is clear from the table that the use of alkali-peroxydisulfate-etching solutions results in a substantial reduction in the copper etching of the copper layer. This is particularly important in the manufacture of very narrow conductor circuit patterns, as such narrow conductor wires are particularly disturbing when there is an under-etching of the copper layer.

An embodiment of the invention consists in the use of an alkaline solution for etching copper conductors in the production of printed circuits, which solution as peroxide disulfate, for example, contains ammonium peroxide disulfate which complexes ammonium hydroxide and as a stabilizer e.g. tetra-sodium ethylenediaminetetraacetic acid, tetraethylene pentamine, glycolic acid, 1,3-butanediol, methanol, 1-butanol, isopropanol, diacetone alcohol or glycol monoacetate.

The complexing agent can also serve as a stabilizer. A typical example of such a complexing agent is ethylenediamine.

The use according to the invention of the alkaline solution for etching has the following advantages: a) High etching rate.

b) The copper is etched without other metals being attacked.

C) The etching reservoir remains undamaged by the released reaction products.

d) Undercutting is largely prevented or reduced.

e) The etching rate remains constant throughout the etching solution life.

25 f) The solutions used are extremely cheap.

Advantageously, the etching can be carried out in a spray etching apparatus which causes uniform distribution of the etching solution.

The pH value of the etching solutions used according to the invention is usually greater than 7, e.g. between 8 and 13, preferably from 9-10. It has been found that maintaining this pH range prevents etching of metal reservoirs. At the same time, the formation of a galvanic element or sub-etching is prevented. In some cases, for example, using ammonium hydroxide as a complexing agent, it has been found advantageous to add a buffer to the etching solution to keep the pH at the desired value. It has been found that the addition of a buffer often results in a greater etching rate and an improved etching capacity. Such buffers are, for example, ammonium hydrogen carbonate, ammonium acetate, ammonium chloride, ammonium bromide, ammonium phosphate, sodium bicarbonate, potassium acetate, sodium carbonate and urea.

As complexing agents, all substances capable of forming copper complexes or chelates may be used in the pH range in which the solution is used. A preferred complexing agent is ammonium hydroxide because of its low cost.

Other suitable complexing agents are, for example, primary, secondary and tertiary amines, primary, secondary and tertiary oxyamines, ethylenediaminetetraacetic acid and salts thereof.

Examples of peroxo compounds include ammonium peroxydisulfate, disodium peroxymonosulfate, peroxoacetic acid and peroxobenzoic acid. It is believed that the stabilizer in the solution prevents the hydrolysis of the peroxo compound to an unstable peroxide.

Despite the significant importance of the stabilizer to the function of the solutions of peroxo compounds used, it has surprisingly been found that as small amounts as 0.1 wt% 25 are sufficient. Since it does not entail the disadvantages of using the stabilizers in larger concentrations, larger concentrations are preferred, especially since it has been found that the stabilizers usually also promote the etching process.

Examples of stabilizers include n-butylamine, ethylene diamine, diethylenetriamine and tetraethylenepentamine, ethylenediaminetetraacetic acid and the tetrasodium salt thereof, ethanolamine, triethhanolamine, trisodium hydroxyethylethylenediaminetetraacetic acid and tetracis acid (2-hydroxyethyl) bis (aminoethyl ether) tetraacetic acid, urea, N-methylurea, N-diethylurea, N, Ν'-methylurea and N, N'-dibutylurea, glycolic acid, lactic acid and tartaric acid, methanol, ethanol, isopropanol and 5 1-butanol, ethylene glycol, propyl glycol and 1,3-butanediol, ethylene glycol monoacetate, ethylene glycol monobutylate and propylene glycol monopropionate, diacetone alcohol, acetone, butanone-2, diethyl ether and dibutyl ether.

The use of the alkaline solutions for etching copper conductors in the preparation of printed circuits can be carried out at temperatures between 0 and 100 ° C, preferably between 25 and 50 ° C. Water is the preferred solvent, but in some cases non-aqueous solvents may be needed.

When an alcohol or an ether is used as a stabilizer, it can also be used as a solvent.

The invention is further illustrated by the following examples.

Example 1.

20 liters of aqueous solution containing the following ingredients are prepared: (a) Ammonium peroxide disulfate 240.0 g (b) Ammonium hydroxide (29% NH 2) 350 ml (c) Ammonium chloride (buffering agent) 30.0 g (d) Methanol 5 ml

Additional ammonium hydroxide solution is then added to maintain a pH of about 9.75.

Example 2.

The procedure of Example 1 is repeated as the amount of 30 ammonium hydroxide added is sufficient to prepare solutions having the following pH level: pH 7.0 4 pH 8.0 pH 10.0 pH 13.0.

Example 3.

The procedure of Example 1 is repeated, using the following buffering agents instead of ammonium chloride with comparable results: ammonium bicarbonate, ammonium acetate, ammonium bromide, ammonium iodide, ammonium phosphate, sodium hydrogen carbonate, potassium acetate, sodium carbonate and potassium carbonate.

Example 4

The procedure of Example 1 is repeated, using the following peroxy compounds in stoichiometric equivalent amounts in place of ammonium peroxide disulfate, with comparable results: sodium peroxydisulfate, lithium peroxydisulfate, barium peroxydisulfate peroxydisodate sulfate, potassium peroxydisulfate, potassium peroxydisulfate, potassium peroxydisulfate, potassium peroxydisulfate

Example 5.

The procedure of Example 1 is repeated, using the following complexing agents in stoichiometric equivalent amounts in place of ammonium hydroxide with comparable results: n-butylamine, di-butylamine, tert-butylamine, ethanolamine, diethanolamine, triethanolamine, ethylenediaminetetraacetic acid and tetrasodium acid.

Example 6

The procedure of Example 1 is repeated, using a stoichiometric equivalent amount of tetraethylene pentamine instead of methanol with comparable results.

Example 7

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The procedure of Example 1 is repeated using a stoichiometric equivalent amount of ethylene diamine tetraacetic acid instead of methanol with comparable results.

Example 8.

The procedure of Example 1 is repeated, using a stoichiometric equivalent amount of Ν, Ν, Ν ', N'-tetrakis- (2-hydroxypropyl) -ethylenediamine instead of methanol with comparable results.

Example 9.

The procedure of Example 1 is repeated using a stoichiometric equivalent amount of trisodium hydroxyethyl-ethylenediamine triacetate instead of methanol with comparable results.

Example 10.

The procedure of Example 1 is repeated using a stoichiometric equivalent amount of ethylenediamine instead of methanol with comparable results.

Example 11.

The procedure of Example 1 is repeated, using a stoichiometric equivalent amount of glycolic acid instead of methanol with comparable results.

Example 12.

The procedure of Example 1 is repeated, using a stoichiometric equivalent amount of 1,3-butanediol instead of methanol with comparable results.

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Example 13

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The procedure of Example 1 is repeated, using a stoichiometric equivalent amount of diacetone alcohol instead of methanol with comparable results.

Example 14.

The procedure of Example 1 is repeated using stoichiometric equivalent amounts of the following stabilizers instead of methanol with comparable results: triethanolamine, tartaric acid, lactic acid, urea, ethanol, isopropanol, n-butanol, acetone, butanone-2, diethyl ether, dibutyl ether, ethylene glycol monoacetate, ethylene glycol monobutyrate and propylene glycol propionate.

Example 15

The procedure of Example 1 is repeated, using the same ingredients (a), (b) and (c) in the following amounts: (a) Ammonium peroxide disulfate 25 g (b) Ammonium hydroxide (29% NH 2) 100 ml (c) Ammonium chloride (buffering agent) 10 g (d) Methanol 5 ml 20 Equivalent results are obtained.

Example 16.

1 liter of aqueous solution is prepared containing the following ingredients: (a) Ammonium peroxide disulfate 170.0 g (b) Ethylenediamine 100 ml

Then, enough ammonium hydrogen carbonate (120 g) is added to obtain a pH of 9.45 for the resulting etching solution.

Example 17

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The procedure of Example 1 is repeated, using the following substances both as a stabilizer and as a solvent instead of water: methanol, ethanol and diethyl ether.

Example 18.

The etching solutions described above are tested in a syringe etching apparatus, measuring the time required to etch a copper strip of 0.036 mm thickness at different temperatures. Plates with circular patterns coated with nickel, gold and solder are tested with the syringe solutions under the same conditions to determine the effect of the current etching solutions on them. The following results are obtained: 15 Etching Solution Time for Etching Temperature

___cobber___ C

Example 1 1.5-3 minutes 30

Example 6 5 minutes 40

Example 7 1.7 minutes 40

Example 8 3 minutes 40 20 Example 9 2 minutes 40

Example 10 1.7 minutes 40

Example 11 1.75 minutes 40

Example 12 2 minutes 40

Example 13 2.5 minutes 40 25 Example 16 5 minutes 40

Control (Example 1 without stabilizer) 7-10 minutes 40 In all cases, the circuit patterns coated with nickel, gold or solder were not attacked. There was no evidence of galvanic etching or undermining of the circuit patterns.

30 The unstabilized control solution spontaneously decomposed shortly after manufacture and used almost all etching ability.