DE1521745C - Process for the regeneration of ammonium persulfate solutions - Google Patents

Description

25th

The present invention relates to regeneration an ammonium persulfate solution used to etch copper.

Such solutions are usually used, for example in place of conventional machining Remove certain amounts of copper from the surfaces of fragile or specially shaped objects. A widespread application this process is the manufacture of printed electrical circuits. In this application a covering agent or a mask in the form of the desired circuit is applied to the surface a copper film laminated on a base, and the partially masked copper film becomes treated with the etchant. The copper surface not covered by the opaque material is peeled off, while the copper covered by the capping agent remains to form the desired circuit.

In such applications, ammonium persulfate solutions are desirable because they are not deleterious Generate vapors, are easy to work with and relatively non-corrosive to certain common construction materials such as stainless steels. When used, copper is used in the unmasked areas by the persulfate solution dissolved until the rate of dissolution is slow enough to be below technically acceptable Speeds drops. The resulting spent etchant is then used to remove the dissolved copper treated and eliminated. .

A serious problem with using this method is that substantial amounts of persulfate are contained in lost to the used etchant. It was not possible to do this on a commercial scale in the 6ö recovering or making use of the persulfate remaining from the etchant. the Simply adding fresh ammonium persulfate to a used etching solution to restore the original Restoring persulfate levels does not result in an acceptable caustic solution because such Solutions result in inferior and irregular etchings.

Another problem is that the treatment of spent persulfate solutions to remove Copper creates an additional process step that increases the cost of eliminating this Adds solution. Copper must be removed from the persulfate solutions because of the toxicity of the copper compounds be removed before discharging into the sewer system.

As a result, there is a need for a method of regenerating spent persulfate etch solutions insisted on a commercially acceptable basis to remove the remaining persulfate solution re-use and eliminate the cost of copper removal and solution destruction.

It has now been found that spent aqueous ammonium persulfate etching solutions which have been used to dissolve copper and which contain ammonium persulfate residues can be regenerated by cooling these solutions to a temperature (preferably about 0 ° C.) so that copper sulfate and ammonium sulfate are removed from the solution crystallize out without any significant amounts of ammonium persulfate crystallizing out. These crystallized solids are separated from the remaining solution, and the solution regenerated in this way is used again. Preferably, ^% ammonium persulfate is added to the etching solution before or after cooling in order to increase the ammonium persulfate content to 0.7 to 1.5 mol / l.

Surprisingly, the ammonium persulfate solutions regenerated in this way (with or without addition of fresh ammonium persulfate) can be used to make high quality etchings down to much lower ones To give persulfate residual concentrations as fresh, untreated ammonium persulfate solutions.

When the etching solution has reached a concentration of about 0.4 to 0.6 mol / l ammonium persulfate, it is able to continue etching, but the etching speed and etching quality decrease, and such solutions are usually discarded as "used" solutions.

According to the invention, such a "used up" solution is cooled to a temperature of 0 to 20 ° C., preferably 0 to 10 ° C., with copper sulfate and ammonium sulfate crystallizing out. The exact cooling temperature is not critical, but it is desirable that it is ^low% sufficient to crystallize to copper sulfate and ammonium sulfate without significant amounts of ammonium persulfate.

The resulting sulfate-containing precipitate is removed from the solution by filtration or centrifugation severed. During the separation, care must be taken to remove residual solution from the precipitate remove to prevent loss of ammonium persulphate. If necessary, the crystals can with Wash with water to remove any attached persulfate. The resulting regenerated Solution with a concentration of about 0.4 to 0.6 mol / l ammonium persulsate can be used without further Machining used to give a good copper etch until the persulfate concentration of the Solution reaches about 0.3 mol / l. After that, the quality of the etching decreases again.

If the reconstituted ammonium persulfate solution is to be used for immersion etching, it is preferred to use the solution with added am-

3 4

monium persulfate up to a concentration of about · such is considered the standard, and that after -0.8 Reinforce mol / l ammonium persulfate. These subsequent immersion attempts can then be used for copper etching until the etching quality and etching speed are determined Persulfate concentration has fallen to 0.3 mol / l. compared. An etching speed of over For use in immersion etching, about 0.005 mm copper per minute is used for 5 than for the Best quality etch not recommended that would consider commercial use acceptable, reconstituted caustic with ammonium persulfate. The used solution from Experiment 1 is based on

is re-amplified above about 0.8 mol / l. Again- a temperature of about 2 to 3 ° C cooled, while intensified Solutions containing more than about 0.8 mol / l use copper sulphate and ammonium sulphate lower ammonium persulphate contained, result in no cancellation. These sulphate precipitates are High quality immersion etch run as removed from the mother liquor, and it will also be Solutions result in which no more than enough water is added to the mother liquor to remove the Contains 0.8 mol / l persulfate. In some cases the sulfate evaporated and used as water of hydration the restored etching solution. to replace the water removed with amine crystals. The ; monium persulphate to concentrations of 0.9 mol / l 15-giving solution is used as an etchant in experiment 2 verj be strengthened again, and another etch is applied without adding ammonium persulfate Get good quality by testing the application.

temperature is increased. However, in Experiment 2, the above solution is used for etching

Increase in temperature not desired, since it uses the additional test plates as in test I, and the stability of the ammonium persulphate in solution until the final etchant has an adverse effect of 0.35 mol / l. This limit contains ammonium monium persulphate. Thereafter, the etching solution K>, persulfate cooled in the restored, and there are copper sulfate and ammonium ■ '■■■' solutions to 0.8 mol / l need not separated sulphate in solutions as previously described. The resulting solution, used for spray etching, is mixed with water to make up for where reconstituted solutions with water loss by evaporation are made up, and ammonium persulfate concentrations of 1 mol / l - sufficient ammonium persulfate is added, give drawn results . a solution with a concentration of 0.82 mol / l

If preferred to get the used solution before ammonium persulfate. This restoring Cooling by adding ammonium persulfate solution is used as an etching agent in experiment 3 is re-strengthened, more copper turns 3 ° crystallizes.

sulfate and ammonium sulfate, as if the Ab- In Experiment 3 additional test plates are used

Cooling with spent solutions is carried out with the reconstituted solution by immersion. ■■ .. · - .. ■ etch at 38 to 39 ° C until the ammonium-According to a special embodiment of the pre-persulfate concentration falls to 0.39 mol / l. According to the invention, an ammonium persulphate can be used - the solution can be used for etching by cooling to 0 to 2 ° C. and unlimited, removal of the precipitated sulphates. The solution, if part of the etching solution is removed continuously, is cooled with additional ammonium persulphate, this part of the solution is cooled to precipitate the insoluble sulphates up to the total ammonium persulphate concentration, and the insoluble sulphates of 0.82 mol / l are restored. This solution is separated from the supernatant solution and the excess is used as an etchant in experiment 4. '. standing liquid containing persulfate to the main In experiment 4 the reconstituted solution is added amount of the etching solution again. Also used with 0.82 mol / l ammonium persulphate, at the same time ammonium persulphate is added to the etching solution continuously, further test plates are added by immersion etching at nuierlich ^{to etch the persulphate concentration at 38 to 39 0} C until the ammonium persulphate has the desired value, for example about 0, 8 to 45 concentration of the caustic 0.51 mol / l ammonium-1 mol / l, to be kept. 'reached persulfate. This etching solution is obtained by cooling. In general, the quality of the etching obtained at 0 to 2 ° C treated to precipitate ammonium and copper using reconstituted persulfate persulfates, the precipitated sulfate solutions is about the same as that obtained with are removed and sufficient ammonium persulfate solutions are obtained. 50 persulfate added to the remaining solution in order to The following examples are intended to further explain the present invention the ammonium persulfate concentration in the etching discovery: to increase the solution to 0.78 mol / l. This solution is at n 'el I. used when performing experiment 5. ■ .... P ■■ · .- In experiment 5, the above solution is used. A series of experiments is carried out, 55 µm further plates by immersion etching at 38 to µm photo-covered, one-sided with 28.35 g / 0.093 m ² 39 ° C until the ammonium persulphate copper-laminated test switchboards of the same size tration of the etching solution falls to 0.43 mol / l, the printed circuit board is etched. In experiment 1, the persulfate content of the etching solution both before and after 500 ml of a fresh aqueous etching solution with an also after etching and before and after the crystalline ammonium persulfate concentration of 1.11 mol / l and 60 sation step is shown in Table I. Table I shows 5 ppm HgCl _{2 used} as an activator to etch the shell- ^ additionally the amount of copper sulfate in the solutions fungsversuchsplatten, until the solution on '■■''before and after crystallization, the etching speed about 50% of the ammonium persulfate is exhausted. ;. ' _t ness that and '; Ä.tzqualitat, \; dte with the various The etching is performed by the Testplatteri' ■ '· solutions used * in the five tests are immersed Werin the air stirred etchant 65, .the, received. In all tests, which is kept at a temperature of 38 to 39 ° C contains: r · "· -Precipitation Copper sulphate and ammonium sulphate in etching speed and etching quality during a molar ratio of about 1: 1 This copper sulfate content of the solutions according to Table I.

also the approximate molar concentration of ammonium sulfate in the etchant.

Example 2 Experiment A

A used aqueous persulfate etching solution with a concentration of 0.48 mol / l ammonium persulfate and 0.50 mol / l CuSO ₄ is treated by cooling the solution to about 2 ° C., during which copper sulfate and ammonium sulfate crystallize out, and the remaining solution is filtered off will. This solution is then reconstituted by adding more ammonium persulfate to a concentration of 0.82 mol / l ammonium persulfate. The percentages of copper sulfate and ammonium sulfate that are removed from the solution in the precipitate are determined.

Attempt B

A spent aqueous solution of ammonium persulfate etchant at a concentration of 0.48 mol / l ammonium persulphate and 0.50 mol / l copper sulphate only become sufficient after adding Ammonium persulfate fortified to bring the persulfate concentration to 0.82 mol / l. This Solution is then cooled to about 2 ° C, while copper sulfate and ammonium sulfate are removed will. The percentages of copper sulfate and ammonium persulfate removed are as in Experiment A definitely.

The content of ammonium persulfate and copper sulfate, in the used etching solutions and the Amount of copper sulfate obtained during the cooling and crystallization step in experiments A and B are shown in Table II.

As can be seen from table II, are in experiment A by pre-cooling the solution, and later adding ammonium persulfate only 51.4 ⁰ Zo of copper sulfate in the solution-entfernt. In contrast, in Experiment B, wherein the ammonium persulfate before Cooling and crystallization is added, 63.5% of the copper sulfate in the solution is removed. This illustrates that the procedure of Run B, in which ammonium persulfate is added to the solution prior to cooling and removal of the sulfates, is preferred as more sulfate and copper can be removed in this way. .

Example 3 '.

Three tests are carried out in which photo-covered, one-sided copper-laminated test pieces

■ 5 control panels of the same size printed circuits be spray etched. In experiment 1, 15.1 1 become one 1.11 molar ammonium persulfate solution brought to 41 to 46 ° C and from a nozzle onto the test plates sprayed. The test plates are with the

ίο solution etched until it has an ammonium persulfate concentration of 0.50 mol / l. Etch speeds and etch quality are determined during the experiment determined periodically.

The used solution from Experiment 1 is cooled to a temperature of 0 to 2 ° C during this time Crystallize copper sulfate and ammonium sulfate in a molar ratio of about 1: 1. This Sulphate precipitates are removed from the mother liquor and there is sufficient ammonium persulphate and water was added to make an ammonium persulfate concentration of 1.0 mol / l in the solution create. This solution is used as the etchant in Experiment 2. . ·

In experiment 2, the reconstituted 1.0 molar ammonium persulphate solution is used to prepare further test plates under the same conditions and temperatures as in experiment 1 to etch until the etchant reaches a concentration of 0.52 mol / l ammonium persulfate. It is then treated by putting it on 0 to 2 ° C is cooled to precipitate copper sulfate and ammonium sulfate. The precipitation is from the remaining mother liquor is separated off, and there is sufficient ammonium persulfate for the remaining solution added to obtain an ammonium persulfate concentration of 0.9 mol / l. This solution will be used when performing experiment 3 used. . ·

In Experiment 3, the above solution is used to prepare additional experimental panels in the same way as in experiment 1 to etch until the ammonium persulfate concentration of the etching solution to 0.42 mol / l falls.

The persulfate content of the etching solution both before and after the etching and before and after the crystallization step is shown in Table III. Table III also shows the amount of copper sulfate in solutions before and after crystallization and the etching rate and etching quality obtained in the three experiments. · '. ■ '

Table I.

Ver Initial etching solution CuSO ₁ =) Final etching solution CuSO ₁ Etching properties
speed quality Tem crystallization step 7o) search (NH ₄ ) AO ₈ (NH ₁ ) AO ₈ mm ¹ ) Well temperature removed ( CuSO ₁ (Minor) (Minor) 0.46 Cu./Min. Well ( ⁰ C) (NHO ₂ S ₈ O ₈ 56.6 1 1.11 .0.17 0.64 0.39 0.0076 Well 2 to 3 .2.9 50.0 .2 ») 0.57 0.17 0.35 0.59 0.0061 Well 2 to 3 2.4 58.0 .3 0.82 0.23 0.39 0.51 0.0066 Well 0 to 2 5.7 58.7 4th 0.82 0.18 0.55 0.43 0.00635 0 to 2 6.7 ■ - 5. 0.78 0.52 0.00635 - -

^a ) Average etching speeds for the entire etching period.

^b ) The etching solution from experiment 2 is not strengthened again with added ammonium sulfate.

^c ) The CuSCV concentration that remains for the analysis after the removal of the crystallized sulfates and the etchant samples.

Table II

Temperature ( ⁰ C)

Crystallization step

removed (%) * (NH ₄ ) JS ₁₁ O ₈ I CuSO ₄

2
2

2.6

51.4 63.5

Table III

attempt

Initial etching solution

(NH ₄ ) AO ₈ I CuSO ₄ »)
(Minor)

Final etching solution

₈ I SuCO ₄ (mol / l)

Etching properties speed

mm ")

Cu / min.

quality

Crystallization step temperature

(NH ₄ ) AO ₈

removed (%)

CuSO ₄

1.11
1.0 "
0.9

0.25
0.29

0.50
0.52
0.42

0.019 0.014 0.015

Well
Well
Well

0 to 2 0 to 2

2.5 2.6

58.0 59.0

^a ) Average etching speed for the entire etching period.

^b ) The concentration of CuSOd that remains for analysis after removal of the crystallized sulfates and the caustic samples.

Claims (2)

Patent claims: 1. A method of regenerating an ammonium persulfate solution used to etch copper with a residual ammonium persulfate concentration of at least 0.4 mol / l, thereby characterized in that the copper sulfate crystallized out by cooling the solution and ammonium sulfate is separated and the solution regenerated in this way is used again. 2. The method according to claim 1, characterized in that the etching solution before or after cooling ammonium persulfate is added to increase the ammonium persulfate content to 0.7 to 1 mol / l and the etching solution to 0 to 20 ° C, preferably 0 to 10 ° C, is cooled . ■ ■: