DE1521993C - Process for regenerating a chromic sulfuric acid solution for etching copper - Google Patents

Description

Recently, chromosulfuric acid solutions have been used gen often used in the manufacture of printed circuit boards. Printed circuits are well known Insulating panels with holes in the electrical wiring, into which the electrical components be inserted, the z. B. be electrically connected to the cables by dip soldering. the Manufacture of such printed circuits is carried out, for example, that of one with Metal, generally with copper, coated .Isolierstoffplatte assumed, the copper layer with an etch-resistant layer, which consists for example of photoresist, is covered in such a way that the pattern the desired cable runs is covered by the paint (positive process), and then die_ Platte in an etching bath, e.g. B. is immersed in a copper chloride etching solution. Another known practice that is particularly advantageous because it leads to reinforced cable runs, is, for example, that the covered with the copper layer insulating plate so with a cover layer, for. B. paint, is covered, that the areas are covered by the lacquer that are to be etched off (negative process). The places which correspond to the pattern of the desired cable runs are in this case from the cover layer free. These spots are galvanically reinforced by placing the entire plate in an electroplating bath is dived. For various reasons, tin in particular has become the galvanic amplifier very proven. Then the. Cover layer removed and 'the exposed areas of the The copper layer is etched off by simply dipping it in an etching solution. If the galvanic insists on the A metal layer made of a precious metal, ζ. B. made of gold, so can be etched of the undesired parts of the base metal layer, the known copper (II) chloride etching solution is used Find. But gold is very expensive. So one went over to the lines with others Metals, e.g. B. with tin to reinforce. In this case, however, the copper base layer can be etched off not the otherwise very advantageous copper chloride etching solution can be used because tin is attacked by the copper chloride and also by the well-known ferric chloride etching solution. For such Chromosulfuric acid etching solutions have proven to be particularly suitable. Against these etching solutions Not only do tin and of course gold show up, but a whole range of other than galvanic reinforcement of the lines of printed circuits suitable and im Relatively cheap metals in relation to gold, such as B. lead, silver and optionally nickel, chemically resistant. Likewise, rhodium is not attacked by chromosulfuric acid.

The large-scale use of chromosulfuric acid etching solutions has so far been several Difficulties. Chromosulfuric acid is very expensive, and no process has yet become known after used, copper-enriched chromosulfuric acid etching solutions are regenerated, d. H. could be made usable again. But it can also be the used ones Chromosulfuric acid etching solutions cannot simply be given into the sewer, because chromic acid is one of the most dangerous contaminants in wastewater. The chromium concentration must be the law that came into force on March 1, 1959, regulating the water balance below 1 mg per liter lie. Care must therefore be taken to ensure that the chromate ions still present are used up Chromosulfuric acid etching solutions by means of a reducing agent, e.g. B. sodium hydrogen sulfite, too Reduced trivalent chromium and this is precipitated as chromium hydroxide by neutralization. Therefor So a whole range of chemicals would have to be used. Through this kind of

ίο Preparation of the used chromosulfuric acid etching solutions However, not only would valuable chrome be lost, but also what has been etched off at the same time Copper, not to mention the additional costs involved in processing.

Although it is known to regenerate metal pickling in such a way that the dissolved metal salts through Concentrate, allow to crystallize to be removed. This alone is a regeneration of a chromium-sulfuric acid etching solution but not possible.

ao When etching copper with chromic acid solution the following reaction occurs mainly:

2H ₂ CrO ₄ + 3Cu ⁰ + 6H ₂ SO _4
a5 -> Cr ₂ (SO ₄ ) S + 3 CuSO ₄ + 8 H ₂ O

So hexavalent chromium is reduced to trivalent chromium. At the same time are hydrogen ions (Sulfuric acid) consumed.

The reaction can also be formulated as follows:

Cr ₂ O ₇ - + 14Ή + + 3Cu ⁰
- ^ 2Cr +++

3Cu +++ 7H ₂ O

During the etching of copper, the etching solution is depleted in etchable Cr ₂ O ₇ - or HCrO ₄ ^- ions and hydrogen ions. One consequence of this, of course, is the weakening of the caustic power of the solution. At the same time, the etching solution is enriched in Cu (IIHonen. Without regeneration of the etching solution carried out at the same time during the etching, ie

The regression of the etchable ions falls, hence the The etching speed of the solution continues until a point is finally reached at which the etching speed is reached becomes prohibitively long. At this point, however, the etchable ions are in the etching solution only about 30% consumed.

In-depth studies on which the invention is based have shown that the simple Reversal of the etching reaction in an electrolysis cell, so the reaction:

Cr ₂ (SOJ ₃ + 3CuSO ₄ + 8H ₂ O

2H ₂ CrO ₄ + 3Cu ⁰ + 6H ₂ SO ₄

or

2Cr ++++ 3Cu +++ 7H ₂ O

-> Cr ₂ O ₇ - "+ 14H ⁺ + 3Cu ⁰

with electrolytic deposition of copper on the cathode and oxidation of the chromium (III) ions at the anode of the electrolysis cell is not possible. As can be seen from the comparison of the normal potentials

3 4

of the redox systems E ₀ for the possible at the cathode The regeneration of the etching solution can in certain

Borrowed Responses: · Periodic intervals are made. Preference is given

however, they do so at the same time during the etching.

Cr ₂ O ₇ - "+ 14H ⁺ + Oe- ^ Cr ⁺ ++ + 7H ₁ O; is located in the cathode compartment during the

£ - ₀ = - 1360 mV j electrolysis the aqueous copper sulfate solution, from which Cu ++ - \ - 2e -> Cu °; E ₀ - 344mV the copper is deposited on the cathode, or

Sulfuric acid.

can be seen, the copper separation can only after the anode of the electrolysis cell is running the reduction of the reaction present in the etching solution:

Use δvalent chromium on the cathode. Even "·

practically exhausted, ie no longer etchable Cr ₁ (SO ₄ ) J + 8 H ₂ O

Chromosulfuric acid solutions, however, contain- -> 2H ₂ CrO ₁ + 3H ₂ SO ₄ + 6H ⁺ + 6e

understandably a certain amount of chromium (VI) - or

ions. In addition, at the anode of the elec-, _Γ , _Η , _{7μη Cr n} , _{14H +} '

Trolyzing cell chromium (VI) ions are continuously formed. »5 ^{2Cr + 7H} * °" * ^Cri ° ^{7 + 14H + 6 <?}

In the electrolytic treatment of an ", ...,",, ,,,, _n . .

Copper-enriched chromic acid etching solution, ^w ? ^h ™ ^{d the} reaction taking place at the cathode

z. B. with copper cathode and lead anode, can therefore be formulated as follows:

the trivalent chromium at the anode becomes hexavalent. 3CuSO + 6e -> 3 Cu ⁰ + 3SO

Chromium oxidizes, but at the cathode the ^ao * ■ ■ * ■

converted back to trivalent chromium again to trivalent "·, · ,," , ", ■

Chromium reduced so that in the end there is no change J? ^eT g ^bt ™ ^{h as} j ⁵ "™haben ⁵ ? ■ ^{Reactlons that is}

the bath composition occurs. Due to the ^volll S ^e reversal of the etching reaction:
Normal potentials is an electrolytic regeneration

ration of a used chromosulfuric acid etching »5 - ^> '- ^u: > ^IJ « + ^U A ^SU J »+ ^ÖH * ^U

solution with simultaneous deposition of the -> 2H ₂ CrO ₄ + 6H ₂ SO ₄ + 3Cu ⁰

etched copper on the cathode is therefore futile. or
Even if the cathodic current density is greatly increased

there is no copper deposition on the cathode 2Cr ⁺⁺⁺ + 3Cu ⁺ + 7H ₂ O

enables. Likewise leads between cathode 3 »-> Cr ₁ O ₇ - + 14H ⁺ + 3Cu ⁰

and anode compartment arranged diaphragm, which the ■

Deposition of the copper after the complete half of the sulfur reduction consumed in the etching The divalent chromium is converted back to trivalent acid at the anode. Chromium is supposed to make possible, not the goal. At the same time, hydrogen

At this point, the reference is also formed from 35 ions. These migrate through the diaphragm

"Galvanotechnik", 55, 1964, No. 1, pp. 42 to 44, on the cathode compartment and compensate for it there freely

"Recovery of metal from pickling," pointed out. sulphate ions. The one consumed in etching

The invention is therefore based on the object, sulfuric acid is half at the anode, for

a process for the regeneration of the chromium-sulfur- other half in the cathode compartment by the im

acid etching solutions, in which the free hydrogen ions and

Etching, the ions that have been used up in the cathode space are formed back by the copper deposition

will. The sulfate ions released by the insulating material should also be formed here.

Copper that has been etched away from the plates can be recovered. _ For example, 3 gram atoms of copper are used

This process should be economical and above that, etching dissolved in the chromosulfuric acid, then,

In addition, even on an industrial scale, 6 VaI hydrogen ions are easily found in the etching solution

be feasible. replaced by copper (II) ions, i.e. the etching solution

To solve this problem, a process is depleted by etching 3 gram atoms of copper

for the regeneration of a chromosulfuric acid etching 3 mol sulfuric acid. When regenerating, the

solution for the etching of copper specified, in the anode compartment 1.5 moles of sulfuric acid regressed,

According to the invention, one with a 5 »in the anode compartment. In addition, 3 VaI hydrogen ions are produced here.

Diaphragm-equipped electrolysis cell _these 3 VaI hydrogen ions migrate through the

Etching chromium (III) ions in the etching solution diaphragm and form there with the corresponding

anodically oxidized in a known manner amount of sulfate ions, the remaining 1.5 moles of sulfur

and at the same time half of the acid consumed during etching.

When the etching process begins, the sulfuric acid becomes fresh Etching bivalent copper from the etching-etching solution, die_Chrom (VI) -oxid und Schwelösung contains in a known manner by concentration fusic acid. This etching solution is preferred and / or cooling the etching solution as copper sulfate in the circuit between the etching vessel and the anode space is removed as soon as the concentration of the copper electrolysis cell, optionally via a Vorfer (II) ions in the etching solution about 50 to 60 g / l 6 »advice vessel, led. In the cathode compartment of the same is that the crystallized copper sulfate in the electrolysis cell becomes an aqueous one. Copper sulfate water is dissolved, the solution is then poured into the cathodic solution. Besides this approach of solution; n In the case of the etching and regeneration cell according to the invention, the space for the electrics provided with the diaphragm are is supplied and that no chemicals are required from this process. in the Solution the copper in metallic form at the 65 anode compartment are constantly chromium (VI) ions after the cathode the electrolysis cell deposited and formed as well as half of that consumed during etching at the same time the second half of the sulfuric acid used during etching. The other part of the sulfuric acid required sulfuric acid is regressed. is formed in the cathode compartment. The etched

5 6

Copper is not lost either, but instead becomes fresher from the etching solution and formation after crystallization from the copper-rich etching-etching solution, line line was used. For the solution as copper sulphate in metallic form in the partial cycle of copper deposition recovered from the cathode. Sewage problems are crystallized copper sulfate is dash point point it is not, because the resulting rinse water can be used on the whole.

For example, the mother liquor of the copper sulfate crystals. In the etching machine 2, the chromium sulfurization is added or, in the case of the acid-etching solution of about 1.5 to 2.0 mol of chromium (VI) -crfollowing copper sulfate crystallization and 1.5 to 2.5 moles of sulfuric acid per liter of den. If the regeneration is introduced at the same time, carried out schematically by the arrow 19 dardcs etching, as it is made according to the invention, as well as the copper-coated insulating material in particular, the plates remain 1. For a better overview, this is on the etching speeds practically constant. Copper remaining under etching circuit boards with Cu _p , the downward speed is referred to here as the ratio of the copper to be etched with Cu _e . The etching solution decreases the weight of the etched body, e.g. B. is kept in circulation during the etching. You circuit board, understood about the etching duration. The etching times 15 are supplied via the line 20 to the anode compartment 54 of an electrolysis, which is provided with a diaphragm 53 for example when etching printed scarfs and which have a copper layer of about 35 μm cell 5, between its anode 51 and, are around 2 * / i minutes when the temperature cathode 52, an electrical DC voltage is held by the door of the etching solution between 50 ⁰ C 40And. is about 4 to 6 volts, and leaves the anode compartment

Appropriately, at the passage 54 you will be on line 21. You will then enter a chamber leadership of the etching and regeneration 73 according to the invention of a storage vessel 7 and reaches the Proceed in such a way that the etching and the given line 19 to the etching vessel 2. In this case, regeneration can be continued if copper is etched in the etching vessel, with the caustic solution of the chromium (VI) ions, which is strongly enriched in copper, is reduced to chromium (III) ions is thrown. Therefore, at the beginning of the equation: driving the proportion of the etching solution to be produced

expediently so choose that it is 3-fold 2HiCrO ₄ + 3Cu ⁰ + 6H ₂ SO ₄

The amount of _Γ / _ςη >,, / -., C _n , _{SH o} etching solution to be used in the etching vessel. Likewise, for the 30th

in the cathode chamber to be introduced copper sulfate l _m the anode chamber 54 are chromium (IlI) ions again

solution more appropriate * «. * choose the 3-fold approach. aufoxydiert _{to C} hrom (VI) ions and half of the

A third of the etching solution produced is back h "Erbei ^ _{n, etching spent} sulfuric acid

of the duty cycle in the first part for etching comparable _give a friend according to the equation: applies and for the simultaneous regeneration in 35

Circuit between the etching vessel and the anode space of the Cr, (SO ₄ ) _s + 8 HjO

Electrolysis cell provided with a diaphragm. "'

dated. In the cathode compartment there is also · - »■ -H _{1 CrU 4} -3H ₁ MJ ₄ ^ 6H ■ -r 6« · only a third of the copper sulfate solution produced.

If c'i: sc etching solution to crystallize out the 40 die that was created at the same time in the anode space 54 Copper sulphate is concentrated (second part of the working hydrogen migrates through the diaphragm 53

cycle), with the second third of the produced cathode 52.

Etching solution etched. In the third part of the working cycle, the reaction takes place in the cathode compartment 55:

(Purification of the copper sulphate and production of the -

Copper sulfate solution) then the third third of the 45 3CuSO ₄ - ~ 6e -v3Cu ° - 3SO, - prepared etching solution is used to etch the copper. Out

the first third has meanwhile the copper from the sulfate ions released and the through

sulfate settled. This becomes, for example, in the third the diaphragm 53 migrated hydrogen

Part of the working cycle is freed from the mother liquor, the other half is that used in etching

washed, dissolved in water and can be formed as copper 50 sulfuric acid.

sulfate solution at the beginning of the next working cycle When the first working day is over and the copper

the cathode compartment of the electrolysis cell to reduce the concentration in the etching solution to about 50 to 60 g / l

separation of copper. From which has risen. this etching solution is over the line

Mother liquor of the copper sulfate crystallization and the 25 fed to the evaporator vessel 8. In this

cathode space fluid depleted of copper becomes 55 Vessel 8 on the second day the solution is exemplified

jewcils. if necessary with addition or removal, adjusted to a quarter of the initial volume.

of water, fresh caustic solution is prepared. steamed and left to stand overnight. During the

To further explain the invention, a second day is etched with the etching solution from the Kambcvorzugtcs exemplary embodiment on the basis of the figure 72 of the storage vessel 7 (which describes at the same time that for factory operation the 60 regenerated during the etching in the anode compartment 54, the preferred method of the side by side expiring). On the third day. on the one with the etching solution from etching. Regenerating und Kupferabscheidcns represents the chamber 71 is etched, the crystallized represents, using the example of the etching of printed copper sulfate CuSO ₄ · 5 HO schematically with 10 lines. The individual circuits are denoted by, they are purified by recrystallization (different schematic line hatching in Fig. 11) and the purified copper sulfate is placed in water. The etching vessel-anode chamber cycle is released (chamber 12). This solution is given to the cathode, schematically indicated by a dashed line, dashed line, through the line 34. For the circuit for enrichment of the space 55 of the electric booster cell 5 is supplied. Here will

from this solution on the fourth day the copper is deposited on the cathode 52, which is obtained as Cu _e 6 on the cathode 52. After the copper has been deposited, the cathode space liquid, which is optionally diluted with water or concentrated by evaporation, is returned to the chamber 73 of the storage vessel 7 via the line 26, together with the mother liquor from the copper sulfate crystallization.

The printed circuits are rinsed after leaving the etching vessel 2. As Cu _p 4 they leave the working group. The rinsing water from the chamber 3 is optionally fed via the line 37 to the copper-depleted cathode space fluid 13 (and thus to the new etching solution to be prepared). If necessary, however, this liquid 13 can be concentrated. The water evaporating in the process is collected in a container 9 (indicated by the arrow 38). Likewise, in this container 9, the water escaping from the copper-enriched etching solution when it is concentrated in the crystallizer 8 is taken up (arrow 27). It is then available, for example, for rinsing the etched plates, indicated schematically by the arrow 36, or for producing the copper sulphate solution 12, indicated schematically by the arrow 33, and for cleaning the crystallized copper sulphate 11, shown schematically by the arrow 30.

Claims (3)

Patent claims: 1. Process for regenerating a chromic acid etching solution for etching copper, characterized in that im The anode compartment of an electrolysis cell provided with a diaphragm is the result of etching Chromium (III) ions are anodically oxidized in the etching solution in a manner known per se and at the same time half of the sulfuric acid consumed during etching is regenerated, the bivalent copper obtained during etching from the etching solution in a known manner Concentrating and / or cooling the etching solution as copper sulfate is removed as soon as the concentration is increased the copper (II) ions in the etching solution is about 50 to 60 g / l that the crystallized Copper sulfate is dissolved in water, the solution then the cathode compartment of the with. the diaphragm provided electrolysis cell is supplied and that from this solution the copper in metallic form deposited on the cathode of the electrolysis cell and at the same time the second Half of the sulfuric acid consumed in the etching process is regenerated. 2. The method according to claim 1, characterized in that that from the mother liquor of the copper sulfate crystallization and that after the deposition of the remaining cathode space liquid, optionally with the addition of or Removal of water, etching solution is formed again. 3. The method according to claim 1 or 2, characterized in that etching and regeneration - as well as the copper deposition carried out at the same time will. 1 sheet of drawings 009 640/222