RU2013467C1 - Method of processing waste copper-ammonium solution for etching copper - Google Patents

Abstract

FIELD: manufacturing microcircuit. SUBSTANCE: waste copperammonium solution is corrected with the help of ammonium chloride and ammonia. The process is carried out at stage having minimal etching rate, washing waters of stamped array additionally containing sodium chloride are used. Quantity of components are determined according to formulae given in specification. EFFECT: improves efficiency of the method. 2 dwg, 7 tbl

Description

 The invention relates to the field of chemical processing of copper and can be used in the process of manufacturing microcircuits at the enterprises of instrument-making and electronic industries using copper-ammonia solutions.

 The PCB manufacturing technology currently used at enterprises involves the one-time use of pickling solutions, which leads to large losses of etched copper, chemical consumption, and environmental pollution.

A known method of processing spent pickling solutions, based on the removal of part of the solution and replacing it with a fresh portion [1]. The disadvantage of this method is the complex composition of the solutions used for adjustment, the inability to maintain a constant concentration of one of the main components - chloride ions by introducing only NH ₄ Cl, since initially chloride ions were part of the two compounds CuCl ₂ and NH ₄ Cl - there is a gradual violation composition.

 There is a method of adjusting spent pickling solutions associated with the addition of solution components after saturating the pickling solution with copper (II) ions without taking part of the solution or removing the precipitate [2]. The disadvantage of this method is the gradual accumulation in the solution of concomitant ions that have an inhibitory effect on the etching rate of copper, the inability to maintain constant concentrations of all working components when using these correction solutions.

As a prototype of the selected method of processing spent copper-ammonia solutions for etching copper [3]. During the etching process, the optimal concentration of the components is maintained by adding a correction solution of the following composition: NH ₄ Cl 215-335 g / l; (NH ₄ ) ₂ CO ₃ 20-80 g / l; conc. NH ₄ OH 300-415 ml / l.

A significant disadvantage of this method is its criticality to changes in concentrations. A slight change in the concentration limits of components (for example, copper (II) ions, which can occur during etching, makes it impossible to adjust the solution by this method and its further use - the electrolyte life is shortened. In addition, the indicated concentration limits of the components are not optimal: point of view of maintaining a high etching rate; a high content of copper (II) ions affects a decrease in the etching rate and the etched copper capacitance; the presence of carbonate nova reduces the etching rate, causes a copious formation of sludge on the surface of copper in the form of its basic salts and malachite, the optimal proportion between Cu ²⁺ , NH ₃ and Cl ^{- is} violated, which is necessary for the formation of catalytically active particles in the solution that accelerate the etching process. After several adjustment cycles, the solution is gradually depleted of chloride ions, which is manifested in the deterioration of the etching quality, the appearance of sludge on the surface, a decrease in the etching rate, and a decrease in the solution stability.

 The disadvantages also include the lack of clear criteria for determining the moment of adjustment. The introduction of the correction solution too early - at the stage of increasing the etching rate - leads to a significant etching of the edges of the conductors, difficulty in controlling the quality of the products, artificially shortening the life of the etching solution in one cycle. The delay with adjustment occurs while maintaining the solution stability, however, while etching is carried out at a low speed, the quality of the products decreases due to contamination of the copper surface. Further introduction of a small amount of copper into the solution leads to an irreversible process of salting out the copper (II) compounds from the solution.

 Another disadvantage of this method is the short duration of the use of the etching solution. The solution used after the first adjustment cannot be corrected again, since due to the low content of chloride ions in the added solution, their concentration changes relative to the optimum, aggravated with each adjustment cycle. As a result, the etching rate and the solution capacity in copper decrease, the solution becomes unsuitable for further operation.

 The purpose of the invention is to increase environmental friendliness and cheaper process.

(C

-С

)˙(V_кон-V_нач); (1)
аммиак - М

(C

-С

)˙(V_кон-V_нач); (2)
хлористый натрий - 2M_NaCl(C

-C

)˙(V_кон-V_нач) (3)
вода - остальное, где С_нач, С_{пром.вод.} - начальная концентрация указанного компонента в травильном растворе и его концентрация в промывных водах, моль/л;
С_отр. - концентрация Cu (II) в отработанном травильном растворе моль/л;
М - молекулярная масса указанного компонента, г;
V_нач, V_кон - объем отработанного и откорректированного травильных растворов, л,
и при соотношении V_кон./V_нач. = 1,2-1,5.The goal is achieved in that the adjustment is carried out at the stage of the minimum etching rate while slowing down the increase in the total concentration of copper in the solution. Solutions for adjustment are washing water for the production of printed circuit boards based on ammonia and ammonium chloride, additionally containing sodium chloride, with amounts of components (g) that provide a return to the initial concentrations and determined by the formulas:
ammonium chloride - M

(C

-WITH

) ˙ (V _con -V _beg ); (1)
ammonia - M

(C

-WITH

) ˙ (V _con -V _beg ); (2)
sodium chloride - 2M _NaCl (C

-C

) ˙ (V _con -V _beg ) (3)
water - the rest, where C _beg , C _{prom. water.} - the initial concentration of the specified component in the etching solution and its concentration in the wash water, mol / l;
From _neg. - the concentration of Cu (II) in the spent etching solution mol / l;
M is the molecular weight of the specified component, g;
V _beg , V _con - the volume of spent and adjusted etching solutions, l,
and with a ratio of V _con. / V _beg. = 1.2-1.5.

The combination of the claimed features allows the processing of the etching solution with any initial ratio of components: CuCl ₂ , NH ₄ Cl, NH ₃ and H ₂ O, ensures that the concentrations of the components NH ₄ ⁺ , NH ₃ , Cl ^are maintained at a constant level, which creates conditions for high etching rates and solution capacities. The content of Cu ²⁺ ions varies within the limits that are optimal for copper etching.

 The correction solution is prepared on the basis of ammonia wash water used in the manufacture of printed circuit boards at the washing stage after etching. Flushing is carried out twice. The concentrations of ammonia and copper (II) in the initial and final ammonia washings are shown below before (initial) and after (spent) washing (Table 1).

 The concentration of ammonia, thus, depending on the degree of production of wash water, can take values in the range (g / l) 82-21.

 The concentration of copper (II) in the initial ammonia leaching can reach 10-15 g / l.

_{+ пром.вод}. , предусматривающая наличие в промывных водах NH₄Cl. Техническими процессами производства печатных плат допускается использование аммиачных промывных вод как с NH₄Cl, так и без него. Если техпроцессом предусмотрено применение NH₄Cl то в формулу (1) появляется концентрация NH₄Cl в промывных водах. Данное значение С

_{+ пром.вод} не изменяется, так как NH₄ ⁺- ионы, в отличие от аммиака практически не расходуются на образование комплексов с ионами меди (II).The formulas for calculating the quantities of components of the correction solution indicate the concentration C

_{+ industrial water} providing for the presence in the wash water NH ₄ Cl. The technical processes for the production of printed circuit boards allow the use of ammonia wash water with and without NH ₄ Cl. If the process involves the use of NH ₄ Cl, then the concentration of NH ₄ Cl in the wash water appears in formula (1). Given value C

_{+ industrial water} does not change, since NH ₄ ⁺ ions, in contrast to ammonia, are practically not spent on the formation of complexes with copper (II) ions.

 Improving the environmental friendliness of the method of processing the solution is achieved due to the fact that the solution is to be prepared only in the initial stage, then it is repeatedly adjusted by the claimed method without losing its characteristics, which significantly increases the service life of the electrolyte without volley discharges.

 In addition, the method allows to significantly reduce the volume of discharged solutions through the use of spent washing ammonia water.

The process is cheaper due to the use of waste washing water based on NH ₃ and NH ₄ Cl, which significantly reduces the consumption of chemicals.

 An additional introduction of chloride ions in the form of NaCl leads to stabilization of the solution, impossibility of precipitation of excess pickled copper. In addition, chloride ions are part of mixed copper-ammonia-chloride complexes that have a catalytic effect on copper etching, which helps to maintain the etching rate and solution capacity at a high level.

 The proposed method of processing the solution allows you to make adjustments at a strictly defined point in time before the start of the deposition of excess pickled copper in the form of a precipitate, which ensures an increase in the performance of the etching process by achieving a sufficiently high speed throughout the entire etching process and the copper capacity, helps to stabilize the solution, and causes a high etching quality: absence of sludge and etching of the edges of copper conductors under the photoresist layer.

 The advantages of the proposed technical solution compared with the prototype are given in table. 2.

Examples illustrating an etching solution processing method are shown in FIG. 1 and 2, and in table. 3 and 4. Sequential adjustments are shown with alternating strong (1: 1.5) and insignificant (1: 1.2) dilutions for etching solutions with initial copper (II) concentrations of 1.0 and 1.28 mol / L. The etching rate was determined gravimetrically at ²⁵ ° C on a rotating disk electrode made of copper grade M-99. Intensive (73 r / s) electrode rotation simulates the hydrodynamic regime of copper jet etching. The *) marks the optimal conditions for processing the etching solution. As can be seen from FIG. 1, 2, the optimal adjustment leads to the production of a new solution with a high etching rate and an extreme dependence of the rate on the amount of etched copper: as copper accumulates in the solution, the etching rate increases and then decreases. Correction anticipates the precipitation in the solution, namely: it is carried out after a period of speed reduction, at the moment of its slight increase, after which the solution loses stability - excess etched copper precipitates in the form of compounds of variable composition. This corresponds to the last point of the graphical dependencies seen in FIG. 1 (solutions 1 and 5) and in FIG. 2 (solutions 2, 5, 6, 7).

 Solutions for which the etching rate is low, and the dependence of the etching rate on the amount of etched copper has a dropping character, were considered unsuitable for use in the conditions of their preparation by adjusting the previous etching solution that went beyond the optimal range.

 Optimum dilution of pickling solutions in the range of 1.2-1.5. The alternation of a slight dilution of 1: 1.2 and a strong 1: 1.5 is recommended. When diluted 1: 1.1, the solution loses stability. It is inappropriate to dilute 1: 1.6, since, despite the increase in the capacity of the solutions, the etching rate is low and decreases in time (Fig. 1, solutions 6, 8, 9, 10).

PRI me R 1. Etching of copper is carried out in 1 l of a solution of the composition, mol / l: Cu ²⁺ - 1,04; NH ₄ + - 1.48; NH ₃ - 6.04; Cl ^- - 2.97; Na ⁺ - 0.10. The etching rate at the beginning was 2.18 ˙ 10 ^-4 kg / m ² ˙ s (Fig. 1, curve 2), gradually increasing, it reached a maximum value of 23.9 ˙ 10 ^-4 kg / m ² ˙ s. Subsequently, the speed decreases to 11.4 ˙ 10 ^-4 kg / m ² ˙ s. Not leading to the precipitation of copper compounds at a total copper concentration of 1.51 mol / L while maintaining a constant minimum velocity value, an adjustment is carried out at a dilution of 1: 1.35. The correction solution is prepared on the basis of ammonia wash water, which is not discharged, but is used to process the solution. The amounts of added components are calculated according to formulas 1-4 and provide a return to the original concentrations. Wash water was used with component concentrations (mol / L): NH ₃ - 4.0; NH ₄ + - 0.6. Added components, g:
NH ₄ Cl - 53.45 ˙ (1.48-0.6) ˙ (1.35-1.0) = = 16.46
NH ₃ - 17.0 ˙ (6.04-4.0) ˙ (1.35-1.0) = = 12.14
NaCl - 2 ˙ 58.44 ˙ (1.51-1.04) ˙ (1.35-1.0) = 19.23
H ₂ O - the rest to a volume of 1350 ml.

 The result is a solution with high etching characteristics: copper capacity and copper speed and copper etching rate (Fig. 1, cr. 3).

PRI me R 2. Obtained in example No. 1 after adjustment, a solution of the composition, mol / l: Cu ²⁺ - 1.05; NH ₄ ⁺ - 1.48; NH ₃ - 6.96; Cl ^{- -} 3,48; Na ⁺ - 0.89 correct after etching with a dilution of 1: 1.35. All components are introduced in an amount of 50% in relation to the set according to formulas 1-4. The resulting solution has a broken composition, mol / L: Cu ²⁺ - 1.17; NH ₄ ⁺ - 1.29; NH ₃ - 5.99; Cl ^- - 3.04; Na ⁺ - 0.92, namely, a reduced content of the components NH ₃ , NH ₄ ⁺ and Cl ^- and, as a result, low etching characteristics (Fig. 1, curve 4).

 Losses of the etching solution during jet etching partially compensate for the increase in the volume of the electrolyte when it is diluted, which is typical for all methods of correcting etching solutions. In fact, for example, with a dilution of 1: 1.5, the increase in volume is much less than one and a half.

 A significant increase in the volume of pickling solution from cycle to cycle can be avoided by using the excess part of the solution after adjustment for the production of copper-ammonia fiber. It is recommended to add sodium hydroxide to the etching solution before dissolving the cellulose.

 Slight fluctuations in the concentration of copper (II) ions after adjustments do not have a significant effect on the etching process, provided that a constant concentration of other components is maintained. So, from FIG. 1 shows that it is possible to change the concentration of copper (II) in the range of 0.89-1.05 mol / l, while the etching solutions retain their qualities. However, with a strong dilution of 1: 1.6 (solutions 6 and 8, Fig. 1), the concentration of copper (II) decreases, the etching rate is low. In this case, the solutions are unsuitable for use, despite their relatively large copper capacity and the extreme temporal dependence of the etching rate. Subsequent adjustment with a dilution of only 1: 1.2 and 1: 1.3 does not give the corresponding result. So, the treatment carried out in this way violates the adjustment cycle, makes the solutions unsuitable for use, despite the use of strong dilutions in the future.

 In FIG. 1 and 2 it is seen that the addition of correction components at a concentration lower than the initial leads to a decrease in the etching rate, the capacity of the solutions, and shortening the life of the electrolyte. The exception is solution 2 (Fig. 1). The use of such a half adjustment for ammonia gives a positive result only at the first stage of processing, its further use is impractical.

 The appearance of concomitant sodium ions in the solution does not adversely affect etching, since sodium ions do not belong to particles inhibiting this process.

 In the table. 3 and 4, the main characteristics of the etching process are presented. The first three indicators: the initial, maximum, and final rates of copper etching show the nature of the dependence of the etching rate on the amount of copper in the solution: a curve with a maximum or a drop-down curve. This determines the degree of stability of the solution, its service life.

 The percentage of the maximum speed during correction shows the etching uniformity over time. The higher this indicator, the less speed fluctuations during etching, the more uniformly and efficiently processed surface of the products.

 Using the above experimental data, we can conclude by comparing the comparative characteristics of the solutions formed by various methods of processing spent pickling solutions, summarized in table. 5-7.

 Thus, the advantages of the invention compared with the prototype are to increase environmental friendliness by reducing the number of volley discharges of toxic copper-containing solutions, increasing the life of the electrolyte and its stability, in reducing the cost of the process by reducing the consumption of chemicals, in maintaining high characteristics of the etching solutions: high speeds etching and etched copper tanks, ensuring high quality surface treatment of copper.

Claims (1)

METHOD FOR TREATING A WASTE COPPER-AMMONIA SOLUTION FOR COPPER ETCHING, including adjusting the solution with ammonium chloride and ammonia, characterized in that, in order to improve the environmental friendliness, cheapening the process, the adjustment is carried out at the stage of the minimum etching rate with ammonium washing water containing printed circuit boards produced in addition to sodium chloride , with the quantities of components providing a return to the initial concentrations and determined by the formulas
Ammonium chloride
M

(C

+ _start -C

+ _ex.water ) ×
× (V _con -V _beg );
Ammonia
M

(C

-C

) ×
× (V _con -V _beg );
Sodium chloride
2M _NaCl ˙ (C

-C

) ×
× (V _con -V _beg );
Water Else
where C _beg , C _{prom. water.} - the initial concentration of the specified component in the etching solution and its concentration in the wash water, mol / l;
C _neg - concentration of Cu (II) in the spent etching solution, mol / l;
V _beg , V _con - the volume of spent and adjusted etching solutions, l;
M is the molecular weight of the specified component, g,
and with respect
V _con / V _beg = 1.2 - 1.5.

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