Method for continuous copper pickling using sodium chlorate

Abstract

Method for continuous copper pickling using sodium chlorate involves pickling copper with solution based on CuCl₂ , NaClO₃ , and HCl, followed by adjustment of the NaClO₃ and HCl concentrations using pH sensors. In pickling solution, there are narrow concentration ranges for the components, expressed in mol / L: CuCl₂ – 0.75-1.5, HCl – 0.6-0.8, NaClO₃ – 0.05-0.1, which ensure partial self-regeneration of CuCl₂ component; adjustment of solution after pickling begins with the removal of a volume ΔV, with purified water returned to solution being adjusted; ΔV is calculated using an equation based on the concentration of copper ions in initial solution C₀ and spent solution C₂ , and the volume of pickling bath V, namely: 202CV)CC(V , complete oxidation of Cu(I) and the establishment of the optimal concentration range 3NaClOC are achieved by introducing a quantity 3NaClOν into the volume of solution being adjusted, namely мольν 333NaClONaClONaClO ,C3)CCC(VCVC2020 .

Description

The utility model relates to dimensional chemical etching of copper and can be used in enterprises of the radio electronics and instrument-making industry, where etching solutions are used based on cuprum(II) chloride. A known method (EP 2 927 347 A1) consists in introducing an oxidant in the form of gaseous oxygen. (air) into spent acidic copper etching solution based on CuCl2 for oxidation of Cu(I) ions and regeneration of the etching solution. The advantages of this method are a large contact surface at creating oxidant bubbles, eliminating the presence of harmful gases. The disadvantages of the method are variation of oxygen mass transfer from the gaseous state to the liquid phase over a wide range size of oxygen bubbles, increased energy consumption to maintain a temperature of 50-55 °C, wide concentration range of solution components: CuCl2 - (80-260) g / l; HCl - (1-12) mol / l, introduction additives with various cations, which affects the copper etching process (NaCl, KCl, NH4Cl, MgCl2, CaCl2). A known method for regenerating spent copper etching solution based on CuCl2 (Adaikkalam P., Srinivasan GN, Venkateswaran KV (2002) The electrochemical recycling of printed-wiring-board etchant. JOM, Vol. 54), which consists in withdrawing a portion of the solution to maintain a constant concentration of Copper ions and sequential addition to the main volume of the etching solution oxidant in the form of NaClO3 to oxidize Cu(I) ions to Cu(II). The disadvantage of the method is the change in the composition of the etching solution during regeneration, namely the increase in pH as a result of the reaction reduction of chlorate ions ClO3- to chloride ions Cl-. The closest analogue is the etching system based on CuCl2 (JP2001348685A), in which The NaClO3 component is used to oxidize Cu(I) ions to Cu(II) while maintaining its concentration in the range of 0-1 mol / l and a constant pH value. The disadvantage of the closest analogue is too wide pH and NaClO3 concentration ranges, lack of justification for the upper limit value of C(NaClO3)=1.0, which is not related to the concentration of Cu+ ions; accumulation in the etching solution of reduction products of other proposed oxidants for Cu+ ions; loss of part of the Cuprous ions and the impossibility of the etching process at pH=3 as a result of the formation of Cu(OH)2; insufficient acidity of the etching solution (pH>0.5) with incorrect assertion about the formation of hazardous ClO2 and Cl2 at pH<0.5, which is impossible at a lower value of the redox potential of the reactions ΔЕ0 between ClO3- and Сl- ions (0.09 B) compared to ΔЕ0 during the interaction of ClO3- ions with free Cu+ ions (1.297 B), or in the form of CuCl (0.912 B): ClO3- + 6H+ + 6e → Cl- + 3H2O E0=1.45 B, (1) Cl2(g) + 2e → 2Cl- E0=1.36 B, (2) Cu2+ + e → Cu+ E0=0.153 B, (3) Cu2+ + Сl- + e → CuCl E0=0.538 B. (4) Also, the disadvantages of the closest analogue are the lack of data on the concentration of CuCl2, to which regenerate the etching solution, and the values ​​of copper etching indicators (etching rate, capacity solution by Copper ions, etching factor, possibility of sludge formation on the copper surface) after regeneration of the etching solution; ambiguity of the indicator by which decisions are made about regeneration of the solution, namely the redox potential of the system, which varies greatly with the presence in the solution of two oxidizing agents (ClO3- and Cu2+ ions) and two reducing agents (Cl- and Cu+ ions); the absence dumping part of the spent etching solution to maintain a constant volume of the etching solution without which either the volume of the solution increases or the concentration of CuCl2 increases beginning of the cycle. The utility model is based on the task of creating a three-component copper etching solution based on CuCl2, NaClO3 and HCl with narrow concentration intervals justified by the flow certain redox reactions, and ensuring high rates of copper etching: rates process, capacity of the etching solution for copper ions, etching factor, absence sludge formation on the copper surface, when implementing continuity of copper etching due to selection part of the spent solution when giving a signal by pH sensors, adding NaClO3 components and HCl and complete regeneration of CuCl2. The problem is solved by the fact that the etching solution has narrow concentration intervals components are equal, mol / l: СuСl2 - 0.75-1.5, НСl - 0.6-0.8, NaСlО3 - 0.05-0.1, solution correction after etching, they begin by withdrawing part of the volume ΔV with the return of purified water to the solution volume, which is adjusted, and adding NaClO3 in an amount that ensures complete oxidation of Cu(I) and achieving initial optimal concentration of the component. The technical result achieved by using the utility model is to reduce material consumption at narrow concentration intervals of the etching solution components, high copper etching rate, etching solution capacity in terms of copper ions, etching factor, no sludge formation on the copper surface, continuity of the etching cycle during regeneration component CuCl2 both in the etching process and when adjusted with the NaClO3 component, rational water consumption, obtaining a by-product of copper(II) chloride oxide, which has fungicidal properties properties. The essence of the utility model is explained by the figures, which depict: Fig. 1 - dependence of the rate of copper etching in a solution based on CuCl2 and HCl with additives NaClO3; Fig. 2 - dependences of the copper etching rate: initial, mid-cycle, final and capacity solutions from the concentration of NaClO3 in a solution based on CuCl2 and HCl, which is not mixed; Fig. 3 - drawing showing the technological scheme of a continuous copper etching cycle when using sodium chlorate. Information confirming the possibility of implementing the utility model The method is implemented as follows (see drawing). From the etching bath (1) when a signal is given pH sensor (2) about exceeding the critical pH value of a part of the spent etching solution The solution is directed to the tank (5) for the precipitation of compounds using a dispenser (3) and a pump (4). Copper (mainly copper(II) chloride oxide), which is then disposed of. Part of the etching solution that remaining, from the pickling bath (1) using a pump (4) is directed to the tank (6) for the stage composition adjustment. Into the tank (6) with mixers (7) using a dispenser (8) from the container (9) is added sodium chlorate, then add water using a pump (10) from the tank (5) and adjust the volume solution to the volume of the pickling bath by adding clean water. After that, add to the tank (6) in the mixing mode, add concentrated hydrochloric acid using the pump (11) with tank (12) until the required pH value is reached, which is controlled by the pH sensor (13). Then The adjusted etching solution from the tank (6) is returned to the of the pickling bath (1) to the pickling stage. Justification of the method of continuous copper etching using sodium chlorate and the achievement of a technical result is confirmed by the determination of optimal concentration intervals of the etching solution components, by conducting special studies regarding the determination of the etching rate, the capacity of etching solutions by Cupric ions, the factor etching, as well as determining the acidity value of the solution to start adjusting the etching solution, the volume of spent etching solution taken at the beginning correction, the amount of NaClO3 added to the solution, and is illustrated by the following examples. Example 1. It concerns the justification of the possibility of certain redox reactions occurring, which is based on a comparison of the values ​​of their redox potentials ΔE0. Reactions occurring at Copper etching consists of oxidizing copper, most often to the Cu+ oxidation state, and successive oxidation of Cu+ ions to Cu2+, which contributes to increasing the stability of the etching solution, prolonging the etching process, increasing the capacity of the solution for Cu2+ ions and the absence of sludge formation on surface of copper boards due to poorly soluble Cu(I) compounds. In a solution of CuCl2 with additional component NaСlО3, in addition to the oxidant Cu2+, there is an even stronger oxidant СlО3-, as evidenced by higher value of E0 of electrode reaction (1), which is considered as the main one, compared to (3). СlО3-- ions can oxidize not only Cu+ by the reaction 6Cu+ + СlО3- + 6H+ → 6Cu2+ + Cl- + 3H2O ΔE0=1.297 B, (5) aluminum and metallic copper immediately to Cu2+ 3Cu + СlО3- + 6H+ → 3Cu2+ + Cl- + 3H2O ΔE0=1.113 B. (6) First of all, reaction (5) will occur with a larger value of ΔE0. That is, the component NaСlО3 provides self-regeneration of the etching solution. Electrode reduction reactions of ClO3- to ClO2 (E0=1.15 B) and to HClO2 (E0=1.21 B) are also possible, however, these compounds themselves are stronger oxidizers than ClO3- ClO2+4H+ + 5e → Cl- + 2H2O E0=1.50 B, (7) HClO2+3H+ + 4e → Cl- + 2H2O E0=1.56 B (8) and can oxidize both Cu+ and metallic copper, thereby promoting etching. The anionic composition of the etching solution does not change, since the product of reactions (5)-(8) is chloride ions. Reduction of ClO3- to chlorine by electrode reaction 2ClO3- + 12H+ + 10e → Cl2+6H2O E0=1.47 B (9) does not occur due to insufficient acidity of the solution. Example 2. It concerns the justification of optimal intervals of component concentrations according to series of experimental data on determining the etching rate and the content of copper ions in the solution when varying the concentrations of CuCl2, NaClO3 and HCl (Table 1). Table 1 Dependence of the initial copper etching rate and capacity etching solution by Copper ions from the ratio of solution components*) Etch component concentrations Output speed Etch capacity solution, mol / l copper etching ·10-4, kg / m2·s solution, mol / l СuСl2 НСl NaСlО3 0.75 0.80 0.10 11.0 1.16 1.50 - « - - « - 20.2 2.00 1.00 - « - - « - 14.5 1.36 0.50 - « - - « - 8.5 0.60 2.00 - « - - « - 21.9 2.32 0.75 0.60 0.10 10.8 1.12 - « - 0.80 - « - 11.0 1.16 - « - 0.70 - « - 10.8 1.14 - « - 0.50 - « - 10.0 0.88 « - 1.00 - « - 10.6 0.90 0.75 0.80 0 9.8 1.02 - « - - « - 0.05 10.2 1.19 - « - - « - 0.10 11.0 1.16 - « - - « - 0.075 10.7 1.17 - « - - « - 0.01 9.0 1.03 - « - - « - 0.20 12.0 1.10 *) For components with variable concentration, the results are given in the following order: for lower, upper limit, in the middle of the interval, outside the optimal interval less than and more. The concentration interval of CuCl2 0.75-1.5 mol / l ensures oxidation of metallic copper with high speed. At l / mol75.0C 2 CuCl < 0.75 mol / l, the digestion is slow, the capacity of the solutions for Cupric ions is low. Exceeding 2 CCuCl value of 1.5 mol / l leads to rapid achievement at etching the solubility limit of copper compounds. The concentration of HCl 0.6-0.8 mol / l provides the necessary acidity for the oxidation reaction to proceed. compounds Cu(I) with chlorate ions, achieving high capacity of the etching solution with Cupric ions at intensive etching. The initial introduction of HCl prevents the precipitation of Cu2(OH)3Cl. A concentration of HCl below 0.6 mol / l does not provide sufficient acidity of the etching solution for oxidation of Cu(I) by chlorate ions. At СНХЛ > 0.8 mol / L, the stability of the solution is disturbed, therefore its capacity decreases. In this case, during the process, the formation of ClO2 and Cl2 gases is possible. In addition This high acidity dissolves the photoresist of printed circuit boards and increases the viscosity etching solutions. The concentration range of NaСlО3 0.05-0.1 mol / l ensures the maintenance of a high rate etching of copper and the capacity of the solution by Cu2+ ions both due to the oxidation of Cu+ ions (reaction 5) and oxidation of metallic copper immediately to Cu2+ (6). When going beyond this range, the rate decreases process and capacity of the 3NaClO solution C <0.05 mol / l) or only the capacity of the 3NaClO solution C >0.10 mol / l). Example 3. Relates to additional justification of the optimal concentration interval component NaСlО3. Fig. 1 shows the dependences of the rate of copper etching in a solution that is not mixed, with a composition of 0.75 CuCl2+0.8 HCl mol / l with additives NaClO3, mol / l: 1-0; 2-0.05; 3-0.1; 4- 0.2; 5-0.4. The total concentration of copper ions in the solution corresponds to its capacity. With increasing NaСlО3 concentration increases the rate of digestion and the capacity of solutions, which is especially evident at the capacity in the middle of the cycle and at the end of the digestion (Fig. 1, curves 1-3). At 3NaClO C >0.2 mol / l rate practically does not change, and the capacity decreases (Fig. 1, curves 4, 5). Fig. 2 shows the dependence of the copper etching rate: 1 - initial; 2 - in the middle of the cycle; 3 - of the final and 4 - capacity of solutions from the concentration of NaСlО3 in an immiscible solution with the composition 0.75 СuСl2+0.8НСl mol / l. The initial rate of copper etching practically does not change with increasing 3NaClO C (Fig. 2, curve 1). Cu etching rates in the middle and at the end of the cycle increase, reaching a certain value (Fig. 2, curves 2, 3). The capacity of solutions for copper ions is extremely dependent on 3NaClO C , the highest values ​​are observed for 3NaClO C =0.05-0.2 mol / l, which are considered optimal for a given ratio of components (Fig. 2, curve 4). In the general case the optimal interval is narrower than 3NaClO C =0.05-0.1 mol / l. In this case, СlО3- ions provide partial self-regeneration of the solution, but their quantity does not ensure the course of undesirable reactions with the formation of ClO2 and chlorine even at high acidity of the solution. Example 4. Relates to the assessment of etching accuracy using the etching factor K. Cross-sections etched areas in most cases have the shape of a trapezoid, so K is calculated as the ratio of the depth of the etched area x to the deviation y of the lateral etching in the upper part section from its base in x K  , (10) where y = y2-y1, that is, the difference between the width of the base of the trapezoid y2 and its upper part y1. The smaller the width of the upper part of the trapezoid differs from the width of the lower part of the cross section, the more accurate is considered an etching process. The maximum etching accuracy corresponds to K→∞ at y→0. The etching factor was determined using test boards with a copper layer 60 μm thick, applied to chrome-plated (0.1 μm) bases made of optical borosilicate glass grade K-8, with using protective negative photoresist FN-11. Etching was measured under a microscope in the cross-section of the board perpendicular to the line of the drawing at a distance of 10 mm from the edge. Results The experimental results are given in Table 2. Table 2 Results for calculating the etching factor when performing the copper etching process in solutions with variable concentrations of CuCl2 and NaClO3 components and a HCl concentration of 0.8 mol / l; copper layer thickness 60 microns Concentrations of etching components solution, mol / l y2, μm y1, μm y, μm K СuСl2 НСl NaСlО3 0.75 0.8 0.10 295.0 274.9 20.1 2.99 1.50 - « - - « - 294.8 273.1 21.7 2.77 2.00 - « - - « - 276.7 238.2 38.5 1.56 0.50 - « - - « - 281.4 249.7 31.7 1.89 0.75 - « - 0.05 287.8 267.9 19.9 3.02 - « - - « - 0.20 277.7 241.6 36.1 1.66 - « - - « - 0.01 289.9 255.0 34.9 1.72 Thus, in etching solutions with an optimal interval of the CuCl2 component (0.75-1.5 mol / l) in a solution of 0.8M HCl + 0.1M NaClO3 mol / l K has a value of 2.77-2.99. When varying the concentration of the component NaСlО3 (0.05-0.1 mol / l) in a solution of 0.75 M СuСl2+0.8M HCl mol / l K is 2.99-3.02. Going beyond the optimal concentrations of components reduces the value digestion factor to a level of less than 2. Example 5. This concerns the justification of the effectiveness of using NaClO3, based on experimental data in Table 1. The capacity of the etching solution consists of the total amount Copper ions (Cu+ and Cu2+) present in the solution. In the absence of NaСlО3, the capacity of the etching solution of the composition (СuСl2+НСl) С1 can be expressed as follows С1 = С0+а, (11) where С0 is the initial concentration of CuCl2 in the etching solution, mol / l; a - the amount of copper, mol / l, dissolved due to the reaction Cu+Cu2+→2Cu+ ΔE0=0.184 B. (12) In the presence of the component NaСlО3, the capacity of the C2 etching solution is equal to С2 = С0+b, (13) where b is the amount of copper, mol / l, dissolved due to reactions (6) and (12) or b = a+d, (14) where d is the amount of copper, mol / l, that passed into the solution during its oxidation by chlorate ions (reaction (6)). d can also be found by the difference in the capacities of the etching solutions d = C2-C1. (15) The difference in the capacities of the solutions (mol / l) 0.75CuCl2+0.8HCl+0.1NaClO3 and 0.75CuCl2+0.8HCl (table 1) is d=1.16 - 1.02=0.14 mol / l. The value of b is 1.16 - 0.75=0.41 mol / l. Then the efficiency dissolution of copper due to oxidation by chlorate ions is %.34 41.0 %10014.0 %100 b d    According to reaction (6), the consumption of ClO3- ions is three times less than the dissolved copper. The fraction of the consumed NaClO3 is equal to 47.0 1.03 14.0 C3 d 3     NaClO or 47%. The remaining NaClO3 was previously used for reaction (5), which provides partial oxidation Cu+ ions and self-regeneration of the solution. Example 6. Refers to the complete oxidation of Cu+ ions by chlorate ions. When introduced into spent etching solution based on CuCl2 and HCl with a concentration of Cu+ ions of 2.9.10-3 mol / l amounts of NaClO3, providing a concentration interval of 3.10-4-2,4.10-3 mol / l, Cu+ ions are practically are completely oxidized (Table 3). During further digestion, their concentration increases insignificantly, reaching at the end of digestion a value of ~10-3 mol / l. Thus, at the level of low concentrations at this ratio Cu C :  3 C ClO undergoes almost complete self-regeneration etching solution. Therefore, the total concentration of Copper after etching can be equated to concentration of Cu2+ ions. Table 3 Change in the concentration of Cu+ ions during copper etching in NaСlО3 regenerated with additives in spent etching solutions with the initial composition, mol / l: Сu2+ - 2.1; Сu+ - 2.9·10-3; НСl - 0.8 СNaСlО 3 ·10-4, mol / l CCu+·10-4, mol / l in the middle of the digestion cycle at the end of digestion 3.0 5.3 11.8 7.2 7.8 19.4 14.4 6.2 28.0 24.0 3.1 22.0 Example 7. This concerns the determination of the acidity of etching solutions based on CuCl2 and NaClO3 for beginning of the etching solution adjustment. The hydrolysis process is ensured by an acidic environment solutions of CuCl2, mol / l: 0.75 CuCl2 - pH=3.48; 1.5CuCl2 - pH=3.32. However, this acidity is insufficient for reactions (5) and (6) to occur in the presence of ClO3- ions. Suggested HCl concentrations are 0.6-0.8 mol / l provide a pH range of 0.1-0.22. During digestion, H+ ions are completely consumed by HCl, therefore, pH control is necessary. The critical value of pH ≥ 3 determined using pH sensors indicates about the need to stop digestion and adjust acidity by adding concentrated HCl until the initial concentration interval СHCl=0.6-0.8 mol / l or pH = 0.1-0.22. Example 8. Relates to the adjustment of the composition of the etching solution. The first stage The adjustment is the removal of a portion of the spent etching solution, which is necessary for the reason concentration of the solution by Copper ions. The portion of the solution volume that is taken, ΔV, is 2 02 C V)CC( V   , (16) where V is the volume of the pickling bath, l. Then, the NaСlО3 component is added to the etching solution in the form of a solid salt in an amount that is necessary for the complete oxidation of Cu(I) according to reaction (5) and ensuring the optimal concentration interval of this component. Calculation of the concentration of Cu(I) remaining in the spent in the etching solution, is carried out according to the equation d2C6a2C  3NaClOCu(I), mol / l, (17) where 3NaClO WITH - NaClO3 concentration, which corresponds to the optimal interval of 0.05-0.1 mol / l. To oxidize Cu(I) in solution, it is necessary to create a concentration of ClO3- ions that is 6 times less than 3 C3CC 3 dC3a Cx 33 3 NaClO02NaClO NaClO     , mol / L. (18) Taking into account the volume of solution remaining for adjustment, the amount of added component NaClO3 is equal to 2 020 C3 )C3CC(VC 3 3 NaClO NaClO ν  x , mol. (19) The amount of NaClO3 required for complete oxidation of Cu(I) in solution and ensuring the optimal concentration interval of this component is ., C3 )CCC(VC VC 2 020 moln 3 33 NaClO NaClONaClO   (20) To bring the volume of the solution being corrected to the volume of the etching bath V, first of all add water formed during the precipitation of copper compounds from the previously selected volume of etching solution solution. Then add additional clean water. In the last stage, the etching solution is adjusted for acidity by adding concentrated HCl acid until the optimal pH value is reached = 0.1-0.22.

Claims

Method for continuous copper etching using sodium chlorate, comprising a process copper etching with a solution based on CuCl2, NaClO3 and HCl with subsequent adjustment concentrations of NaClO3 and HCl using pH sensors, which differs in that in The etching solution has narrow concentration intervals of components, equal to, mol / l: CuCl2 - 0.75-1.5, HCl - 0.6-0.8, NaClO3 - 0.05-0.1, provide partial self-regeneration component СuСl2, the adjustment of the solution after etching begins with the selection of a part volume ΔV with the return of purified water to the volume of the solution being corrected, and ΔV calculated according to the equation of dependence on the concentration of copper ions in the initial С0 and spent solution C2 and the volume of the etching bath V, namely: 2 02 C V)CC( V   , complete oxidation of Cu(I) and creation of an optimal concentration interval 3NaClO C are reached when the amount of the correcting solution is introduced into the volume 3NaClO ν , namely moln 3 33 NaClO NaClONaClO , C3 )CCC(VC VC 2 020   .

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