DE1521993B1 - Process for regenerating a chromic acid solution for etching copper - Google Patents

Description

1 2

Recently, chromosulfuric acid solutions in the water balance have fallen below 1 mg per liter gen often lie in the manufacture of printed circuits. So it must be ensured that the used. As is well known, printed circuits are chromate ions that are still present in the used ones Insulating material- chromosulfuric acid etching solutions provided with electrical lines by means of a replay plate with holes in the electrical components 5 reducing means, z. B. sodium hydrogen sulfite, too be inserted, the z. B. reduced by dip soldering with trivalent chrome and this by Neuden Cable runs are electrically connected. The tralization as chromium hydroxide is precipitated. Here manufacture Such printed circuits would have to be used for a whole range of chemicals, for example carried out in such a way that one with kalien be expended. Through this kind of Metal, generally with copper, coated. Preparation of the used chromium-sulfuric acid insulating plate assumed that the copper layer with etching solutions would not only be valuable chrome an etch-resistant layer that was lost from photos, for example, but also the etched-off layer at the same time varnish is covered in such a way that the pattern is copper, not to mention the additional costs, the desired cable runs covered by the paint that result from the preparation, is (Positiwerfahren), and then die_ Platte in 15 It is known to pickling metals in this way an etching bath, e.g. B. in a copper chloride caustic solution, regenerate that the dissolved metal salts through is dived. Another known method, the concentration, allowing crystallization to be removed, It is particularly advantageous because it leads to increased lines leads, for example, is that sulfuric acid etching solution is not possible, the covered with the copper layer insulating plate 20 When etching copper with chromic acid so with a cover layer, e.g. B. varnish, is covered, solution mainly takes place the following reaction: that the places are covered by the paint that

should be etched away (negative experience). The digits ^ _n , ",.,"""

ten that correspond to the pattern of the desired cable runs ^ 2 ^ 4 + ^Jt - ^U + ÖM _a bU ₄ , are in this case of the cover 25 - »· Cr ₂ (SO ₄ ^ + 3CuSO ₄ + 8H ₂ O

shift free. These spots are galvanically reinforced by placing the entire plate in an electroplating bath

is dived. As a galvanic amplifier, it turns oval chromium into trivalent chromium

tin in particular is reduced for various reasons. At the same time are hydrogen ions very proven. The cover 30 (sulfuric acid) is then used up.

layer removed and the exposed areas of the one can follow the reaction

Formulate the copper layer by simply dipping it into a: etching solution. If the galvanic insists on the

A metal layer made of a Cr ₂ O ₇ - + 14H ⁺ + 3Cu ^{0 applied to the lines}

Precious metal, for example made of gold, can be used for etching 35 _{9Γ m,, r} ++ ι 7Ή0

of the unwanted parts of the base metal layer -> ^ r · + · j ^ u - + - / η ₂ υ

the well-known copper (II) chloride etching solution is used. But gold is very expensive. During the etching of copper, one has become impoverished, so the line runs with other etching solutions of etchable Cr ₂ O ₇ - or HCrO ₄ - metals, z. B. with tin to reinforce. In this 40 ions and hydrogen ions. One consequence of this is the case, but the etching of the copper base layer can of course weaken the etching power of the solution, not the otherwise very advantageous copper. Without being attacked at the same time during the etching of the copper chloride and also by the known regeneration of the etching solution, i.e. iron chloride etching solution proved particularly suitable. Against this etching a point is finally reached, at which the etching solutions show up not only tin and of course speed becomes intolerably long. At this also gold, but a whole series of point etchable ions of the etching solution, however, other than galvanic reinforcement of the management 50 only consumes about 30 ° / _0, trains of printed circuits appropriate and in-depth, underlying the invention Relatively cheap metals in relation to gold, such as B. Studies have shown that the simple lead, silver and optionally nickel, chemically reversing the etching reaction in an electrolyzer resistant. Likewise, rhodium is not attacked by chromium sulfur cells, ie the reaction: acid. 55
The large-scale use of chromium-Cr ₂ (SOi) ₃ + 3CuSO ₄ + 8H ₂ O

_Sulfuric acid etching solutions have so far been available several _ ^ 1t T n ~ n _ι_ τη ^ ο j_ <ti cn

", ..,.,. , - ,,,. , ... . - * ZiI ₂ V ^ rU ₄ + jcu + 0JtI ₂ OU ₄

Difficulties. Chromosulfuric acid is

very expensive, and no method is known or known up to now

become, after the consumed, with copper

enriched chromosulfuric acid etching solutions regene- 2Cr ⁺⁺⁺ + 3Cu ⁺⁺ + 7H ₂ O

red, ie made usable again -> Cr O + 14H ⁺ + 3Cu ⁰

could. However, the ^{2 7}

Chromosulfuric acid etching solutions are not readily available

be given into the sewer, because chromium-65 with electrolytic deposition of copper acid is one of the most dangerous impurities in the cathode and oxidation of chromium (III) ions the sewage. The chromium concentration does not have to be possible at the anode of the electrolysis cell the law that came into force on 3.1959. 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: intervals are made _; Preference is given

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

Cr ₂ O ₇ - + 14H ⁺ + 6e -> ■ 2Cr +++ + 7H ₂ O; In the cathode compartment is during the

£ _o = -i36o mV 5 electrolysis the aqueous copper sulfate solution from which Cu ⁺ + + 2e - »Cu ⁰ ; _{£ o =} - 344mν the copper is deposited on the cathode, or

Sulfuric acid.

can be seen, the copper deposition can only run after the anode of the electrolysis cell

the reduction of the reaction present in the etching solution:
Use δvalent chromium on the cathode. Even ¹⁰
practically exhausted, ie no longer etchable Cr ₂ (SO ₄ ) ₃ + 8H ₂ O

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

understandably a certain amount of chromium (VI) - _oc i _er

ions. In addition, at the anode of the elec-. , _ürt _ _,.

Trolyzing cell chromium (VI) ions are continuously formed. »5 ^ Cr ++++ / H ₂ O -> Cr ₂ O ₇ + 14H + be

In the electrolytic treatment of an an ... ..., _T , ',, ,,,, ",.

Copper-enriched chromic acid etching solution, ^w ? ^h f ^nd _f ^{the a} ?. ^the K & ihods running reaction z. B. with copper cathode and anode lead, is therefore ^{such as M} & ^formuher t ^expectant can en:

the trivalent chromium at the anode becomes ovalent _1AlCr . , «- _l5r " ₀ , _lcr >

Chromium oxidizes, but at the cathode the 20 *

6-valent chromium that has been formed back to 3-valent ".,." ,,.,, ^ t- 1

Chrome reduced so that in the end no change "gs ^he £ ^{lbt, s! ch} as the sum of the reactions, i.e. that of the bath composition, occurs. Due to the complete reversal of the etching reaction:
Normal potential is an electrolytic regeneration, _Ρι , ς _Π , _Γ * «ιη \ α. sw n
ration of a used chromosulfuric acid etch- »5 ^ ¹ - ¹¹ ^ -r ^ r ₂ (SU ₄ J ₃ - + · 8W ₂ 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 30 - ^ Cr ₂ O ₇ - + 14H ⁺ + 3Cu ⁰

and anode compartment arranged diaphragm that the

Deposition of the copper after the complete half of the sulfur consumed during the etching

Reduction of the 6-valent chromium to 3-valent acid is formed 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, to the cathode compartment and compensate for the free »recovery of metal from pickling«, pointed out there. sulphate ions. The invention is therefore based on the object of providing half of the sulfuric acid at the anode and the other half of the chromium-sulfur in the cathode compartment by means of the acid-etching solutions in which the free hydrogen ions formed in the anode compartment are used and etching, used ions are formed back in the cathode space by the copper deposition. 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 made through

This process is said to be economical and, above it, to dissolve in the chromosulfuric acid, then etching 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, d. 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 it rains, 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 water stdffions are produced here. Electrolysis cell equipped with a diaphragm, the 3 VaI hydrogen ions migrate through the Etching chromium (III) ions in the etching solution diaphragm and form there with the corresponding the amount of sulfate ions is anodically oxidized in a manner known per se, 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 and etching solution, the chromium (VI) oxide and carbonization solution 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, possibly also via a Vorfer (II) ions in the etching solution about 50 to 60 g / l 60 advice vessel out. In the cathode compartment of the same is that the crystallized copper sulfate in the electrolyzer becomes one wäßrigi copper sulfate-water is dissolved, the solution is then poured into the cathodic solution. Besides this approach of solutions The space of the electrodes provided with the diaphragm are in the etching and regeneration cell according to the invention 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) -ion2n 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. That seared

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 sulfate in metallic form in the partial cycle of copper deposition from the cathode recovered. 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 crystal In the etching machine 2, the chromium sulfur

lization is added or, in the case of the acid-etching solution from about 1.5 to 2.0 mol of chromium (VI) -sulting copper sulfate crystallization by cooling, concentrated oxide and 1.5 to 2.5 mol of sulfuric acid per liter. If the regeneration is introduced at the same time, carried out schematically by the arrow 19 dardes etching, as it is set according to the invention, and the copper-coated insulating material is carried out in particular, the plates 1 remain. For a better overview, this is on the Etching speeds practically constant. Copper remaining under etching circuit _{boards with Cw 2} ,, 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 transmitted via the line 20 to the anode compartment 54 of an electrolyzation, which is provided with a diaphragm 53 for example when etching printed circuit boards and which have a copper layer of about 35 μπα cell 5, between its anode 51 and, are around 2 ¹ J ₂ Minutes when the temperature cathode 52 receives an electrical direct voltage from the etching solution between 40 and 50 ° C. is about 4 to 6 volts, and leaves the anode compartment. Expediently, at the passage 54 via the line 21. It then enters a chamber guide of the etching and regeneration 73 of a storage vessel 7 according to the invention and arrives in this way via the method proceed that the etching and given line 19 back to the etching vessel 2. In this case, regeneration can be continued when copper is etched in the etching vessel, whereby the highly enriched copper etching solution of the chromium (VI) ions to chromium (III ) ions are reduced by treatment for copper sulphate crystallization and sulfuric acid is consumed after throwing. Therefore, at the beginning of the equation: drive the proportion of the etching solution to be produced

expediently choose so that it is 3 times the 2H ₂ CrO ₄ + 3Cu ⁰ + 6H ₂ SO ₄

Amount of each to be used in the etching vessel. _n " / cn \ 1 1 η ,, υη _i_ 0 τι r»

Etching solution corresponds. Likewise, for the 30th

Copper sulfate ions to be introduced into the cathode space _{In the anode space 54,} chromium (III) ions are restored

solution expediently choose the 3-fold approach. _is oxidized to chromium (VI) ions and half of the one third of _{the etching} solution produced is formed back in the first part of the etching work _cycle according to the equation: turn and for simultaneous regeneration in the 35th

Circuit between the etching vessel and the anode compartment of the Cr ₂ (SO ₄ ) ₃ + 8 H ₂ O

Electrolysis cell provided with a diaphragm. In the cathode compartment there is also - ^ 2H ₂ CrO ₄ + 3H _{2 JsO 4} + 6Jd + 6e

only a third of the copper sulfate solution produced.

If this etching solution is used to crystallize out the 40 die that has arisen at the same time in the anode space 54 Copper sulfate is concentrated (second part of the working hydrogen ions migrate 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 manufacture of the

Copper sulfate solution) then serves the third third of the 45 3CuSO ₄ + 6e -> 3Cu ⁰ + 3SO ₄

prepared etching solution for etching the copper. the end

the first third has meanwhile the copper from the sulfate ions released and the through sulfate settled. This is, for example, in the third the diaphragm 53 migrated hydrogen ions Part of the working cycle is freed from the mother liquor, the other half is that used in the 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

be fed to the cathode compartment of the electrolysis cell to reduce the concentration in the etching solution to about 50 to 60 g / l separation of the copper. From which has risen, this etching solution is fed via the mother liquor line to the copper sulfate crystallization and the 25 to the evaporator vessel 8. In this copper-depleted cathode space liquid, the solution is prepared on the second day, for example , fresh etching solution, optionally with additions or removal, to a quarter of the initial volume with water. steamed and left to stand overnight. During the

To further explain the invention, a second day is etched with the etching solution from the chamber preferred embodiment using the figure 72 of the storage vessel 7 (which is described at the same time, the 60 during the etching in the anode compartment 54 is regenerated schematically for factory operation preferred method of the side by side will). On the third day, on which the chamber 71 is etched with the etching solution from etching, regeneration and copper deposition, the crystallized image is, using the example of the etching of printed copper sulfate CuSO ₄ -5H ₂ O, schematically with 10 lines. Here, the individual circuits are denoted by, 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, a dashed line, a regeneration system. For the circuit for the depletion of the space 55 of the electrolysis 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 liquid 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, the water which escapes when the copper-enriched etching solution is concentrated in the crystallizer 8 is taken up in this container 9 (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 one provided with a diaphragm in the anode compartment Electrolysis cell the chromium (III) ions in the etching solution that occur during etching are known to be anodically oxidized and at the same time half of that consumed during etching Sulfuric acid is re-formed, the divalent copper that is obtained during etching is removed the etching solution in a manner known per se by concentrating and / or cooling the etching solution as Copper sulfate is removed as soon as the concentration of copper (II) ions in the etching solution about 50 to 60 g / l is that the crystallized copper sulfate is dissolved in water, the solution then fed to the cathode compartment of the electrolysis cell provided with the diaphragm and that from this solution the copper in metallic form at the cathode of the electrolysis cell deposited and at the same time the second half of the sulfuric acid consumed during the etching is regressed. 2. The method according to claim 1, characterized in that the copper sulfate crystallization from the mother liquor and the cathode space liquid remaining after the copper has been deposited, optionally with the addition or removal of water, etching solution is formed again. 3. The method according to claim 1 or 2, characterized in that etching and regeneration and the copper deposition can be carried out at the same time. 1 sheet of COPY drawings 009508/174