HK1237381A1 - Oxidation of copper in a copper etching solution by the use of oxygen and/or air as an oxidizing agent - Google Patents

Description

Oxidation of copper in copper etching solutions by using oxygen and/or air as oxidants

Field of the invention

The present invention relates to a process for oxidizing copper in a copper etching solution by using oxygen and/or air as an oxidizing agent, and an oxidized copper etching solution obtainable by the process. The invention also relates to a printed circuit board obtainable by etching using the oxidized copper etching solution, and to the use of the oxidized copper etching solution. The invention also relates to a system for a copper oxide etching solution.

Background

Etching is now a commonly used technique in the production of printed circuit boards. In the production of printed circuit boards, a substrate such as a plastic laminate is coated with a layer of an electrically conductive material such as copper. On top of the copper layer, a protective layer, for example an organic polymer, is provided photochemically to selectively cover certain parts of the copper layer. The coated substrate is etched in an etching machine where the coated substrate is exposed to a continuous flow of a copper etching solution to etch away at least a portion of the copper layer not covered by the protective layer leaving the protective portion of the copper layer unetched to produce a conductive layer of the printed circuit board.

In conventional etching processes, oxidizing agents, such as, for example, hydrogen peroxide, sodium chlorate, or gases including ozone or chlorine, are used to reoxidize the copper etching solution used in the etcher. However, such oxidizing agents are considered aggressive compounds that negatively affect the working environment and, in a broader sense, the environment.

EP 0048381B 1 teaches an alternative process for regenerating copper chloride hydrochloride etching solutions, wherein etching and regeneration are effected in separate apparatus between which the copper etching solution is circulated. The copper etching solution is pumped from the etcher and sprayed into a bell containing oxygen.

Despite the alternative processes in EP 0048381B 1, there remains a need in the art for an improved process for regenerating copper in a copper etching solution.

Summary of The Invention

It is an object of the present invention to provide an improved process for the regeneration of copper in a copper etching solution, such as an improved process for the oxidation of copper in a copper etching solution. Oxygen and/or air are desirable oxidants due to, for example, environmental aspects.

The present inventors have surprisingly found a more efficient process technique than the process taught in EP 0048381B 1. The invention is based on the following concept: the method includes the steps of generating bubbles of a gaseous oxidizing agent in a liquid copper etching solution, and mixing the solution, rather than spraying droplets of the liquid copper etching solution into the gaseous oxidizing agent as in the prior art. The process of the present invention improves in at least the rate of oxidation and the quality of the etch. This is due, at least in part, to the fact that the rate of mass transfer between two phases depends on the area of contact between the two phases and the respective densities of the two phases. The inventors have found that it is easier and more efficient to provide gaseous bubbles in a continuous liquid phase with a relatively high contact surface than in the opposite case. Furthermore, the density of gases is generally much lower than that of liquids.

After mixing, the process creatively provides a larger contact surface between the oxygen and/or air and the reduced copper etching solution by promoting mass transfer of oxygen from the oxygen and/or air into the liquid solution, thereby allowing oxidation reactions to occur.

According to a first aspect of the present invention, this and other objects are achieved by a process for oxidizing copper in a copper etching solution by using oxygen and/or air as an oxidizing agent, the process comprising the steps of:

a) introducing an oxidant comprising Cl^-And Cu⁺In an acidic reduced copper etching solution;

b) stirring the solution obtained in step a); and is

Thereby allowing reaction of 2Cu⁺+1/2O₂(aq)+2H⁺→2Cu²⁺+H₂O occurs to produce an oxidized copper etching solution containing less Cu than the reduced copper etching solution⁺。

In an example of the present invention, there is provided a process for oxidizing copper in a copper etching solution by using oxygen and/or air as an oxidizing agent, wherein the process comprises the steps of:

a) introducing an oxidant comprising Cl^-And Cu⁺By acidic reduction ofIn the copper etching solution of (1);

b) mixing the solution obtained in step a);

thereby allowing reaction of 2Cu⁺+1/2O₂(aq)+2H⁺→2Cu²⁺+H₂O occurs to produce an oxidized copper etching solution containing less Cu than the reduced copper etching solution⁺。

Oxidized copper etching solution containing Cu⁺In an amount less than the amount of Cu in the reduced copper etching solution⁺The amount of (c).

The pH of the reduced copper etching solution is below 7, allowing the consumption of free protons, H⁺Reaction 2Cu of (aq)⁺+1/2O₂(aq)+2H⁺→2Cu²⁺+H₂O occurs. The acidic pH is typically provided by HCl (aq).

The inventors have surprisingly found that oxygen and/or air can be used as oxidant in the process of the invention despite the fact that: both oxygen and air have substantially lower oxidizing power than conventional oxidizing agents such as hydrogen peroxide, sodium chlorate or gases including ozone or chlorine. However, it has been found that oxygen and/or air still meet the required level of oxidation capability of the inventive process, enable a desirable process etch rate and meet overall process conditions.

An advantage of replacing conventional oxidizing agents such as hydrogen peroxide and sodium chlorate is that the presence of harmful gases can be eliminated, thereby improving the working environment in which such agents are conventionally used. Therefore, the environment for maintenance work can be improved. A further advantage is the lower emissions of environmentally unfriendly compounds such as the conventional oxidizing agents themselves or any derivatives thereof or any by-products from their oxidation reactions.

The present inventors have also surprisingly found that the process of the present invention provides improved etching characteristics at the wing (flank) of the printed circuit board being etched. By using the process of the present invention, the wing results in a straighter vertical profile than can be obtained by conventional processes, indicating an improved etch factor. Thus, the conductive portions of the printed circuit board can be arranged closer to each other without jeopardizing the quality of the printed circuit board. Thus, the process of the present invention may allow for a more compact printed circuit board with acceptable quality. The improved etching may be due, at least in part, to improved oxidation of the copper facilitated by mixing.

Another advantage is that the oxygen and/or air oxidant provides a more economical alternative than conventional oxidants. The cost savings may be at least 80%, such as at least 90%, relative to using an oxidizing agent as a raw material.

Another advantage is that if the concentration of the free acid of hydrochloric acid is kept low compared to that in conventional etching solutions, there is a possibility of an integrated process removing the excess copper accumulated in the system. This technique is also described in WO 2009/008801. By the term "copper etching solution" is meant herein an etching solution comprising copper. Copper is dissolved in the etching solution and is in the form of Cu⁺And/or Cu²⁺In the form of (1). The copper etching solution is an aqueous solution.

By the term "oxidant" is meant herein a compound, such as oxygen and/or air, which is capable of accepting an electron from another atom, ion or molecule. In the process of the present invention, oxygen and/or air is used in the oxidation reaction (ii): 2Cu⁺+1/2O₂(aq)+2H⁺→2Cu²⁺+H₂O acts as an oxidant and accepts oxygen from Cu⁺Thereby Cu⁺Is oxidized into Cu²⁺。

By the term "reduced copper etching solution" is meant herein an aqueous copper etching solution in which an amount of divalent copper ions (Cu)²⁺) Has been reduced to monovalent copper ions (Cu) in the etching reaction (i)⁺). The reduced copper etching solution is the copper etching solution that exits the etcher upstream of the oxidation reactor.

By the term "oxidized copper etching solution" is meant herein aqueous copper etchingEtching solution containing a certain amount of monovalent copper ions (Cu)⁺) Has been oxidized to divalent copper ions (Cu) via oxidation reaction (ii)⁺). The oxidized copper etching solution contains lower Cu than the reduced copper etching solution⁺The content of (a). The oxidized copper etching solution is the copper etching solution exiting the oxidation reactor.

By the term "mixed solution" is meant herein an intermediate copper etching solution mixed with an oxidizing agent. In the mixed solution, the oxidizing agent is at least partially dissolved in the liquid phase. The mixed solutions are mixed by, for example, an impeller and/or a static mixer or any other mixing device known in the industry. The mixed solution may be present in an oxidation reactor. The mixed solution may also be present in the feed conduit downstream of the inlet of the feed conduit for the oxidant. The intermediate copper etching solution may comprise a mixture of an oxidized copper etching solution and a reduced copper etching solution. Cu contained in intermediate copper etching solution⁺In the reduced copper etching solution⁺Content of (D) and Cu of oxidized copper solution⁺In the middle of the content of (A).

By the term "oxidation reactor" is meant herein a continuous reactor, a tubular reactor, or a pipeline or batch reactor.

By the term "stirring", it is meant herein a specific type of mixing, i.e. active mixing by means of a stirrer. This agitation can improve the mass transfer rate between the gas and liquid phases by, for example, further reducing the size of the oxidant bubbles in the oxidation reactor. The stirrer can increase reaction 2Cu⁺+1/2O₂(aq)+2H⁺→2Cu²⁺+H₂The oxidation rate of O. The agitator may be embodied with a movable part such as a baffle which mechanically reduces the size of the bubbles of the oxidizing agent. The inventors have noted that by increasing the velocity of the baffle, a higher yield of the introduced oxidant can be obtained. The inventors believe that the agitation in step b) may be a key factor in the success of the process for oxidizing copper in a copper etching solution in providing a satisfactory and industrially applicable oxidation rate of the oxidizing agentAnd (4) element. The agitator may be any agitator known in the industry that can reduce the size of bubbles of the oxidant during operation. In certain examples, the diameter of the oxygen bubbles formed in the liquid phase of the etching solution during mixing may be up to 5mm, such as in the range from 0.001mm to 5mm, or such as in the range from 0.01mm to 1 mm. The oxygen bubbles preferably provide a large contact surface between the two phases (gas and liquid). Preferably, the gas bubbles are present in the bulk of the liquid, not at the surface of the liquid inside the oxygen reactor.

In certain embodiments, the process of oxidizing copper in a copper etching solution is in a system comprising an etcher and an oxidation reactor fluidly connected by a feed conduit.

In certain embodiments, the oxidant is introduced in a feed line comprising Cl^-And Cu⁺In an acidic reduced copper etching solution.

In certain embodiments, the solution obtained in step a) is stirred in the oxidation reactor.

In certain embodiments, the resulting oxidized copper etching solution exiting the oxidation reactor contains less Cu than the reduced copper etching solution exiting the etcher⁺。

In certain embodiments, the reduced copper etching solution comprises Cl at a concentration of at least 2.5mol/L^-. In other embodiments, the reduced copper etching solution comprises Cl at a concentration of at least 3mol/L, such as at least 3.5mol/L, or such as at least 4mol/L^-. The advantage of having the lowest chloride ion concentration is to ensure that the reaction rate is maintained at a high level.

In certain embodiments, Cl^-Chloride salts derived from copper, ammonium, alkali and alkaline earth metals, and hydrochloric acid. In certain embodiments, Cl is included^-The compound(s) is selected from the group consisting of HCl, NaCl, KCl, MgCl₂、CaCl₂、NH₄Cl.

In certain embodiments, step b) is performed by at least one agitator, such as an impeller.

In certain embodiments, the process further comprises the step of mixing an oxidizing agent with the acidic reduced copper etching solution in the feed line.

In certain embodiments, the mixing is performed by at least one static mixer.

In certain embodiments, the pressure in the oxidation reactor is lower than the pressure in the feed conduit.

In certain embodiments, step a) occurs upstream of the oxidation reactor.

In certain embodiments, step b) occurs in a feed conduit disposed upstream of and inside the oxidation reactor.

In certain embodiments, step b) occurring upstream of the oxidation reactor is carried out by at least one static mixer for obtaining turbulent flow, and wherein step b) occurring inside the oxidation reactor is carried out by at least one impeller for obtaining agitation.

In certain embodiments, an overpressure is present in the feed conduit, and wherein the overpressure is preferably in the range of from 0.01 bar to 15 bar.

The pressure in the feed line must exceed the pressure exerted on the inlet of the oxidation reactor by the liquid in the oxidation reactor. The pressure applied depends on the height and density of the liquid present in the oxidation reactor. Thus, the pressure inside the oxidation reactor is typically lower than the pressure inside the feed conduit. An advantage of increasing the pressure in the feed conduit is that the solubility of oxygen in the liquid increases, thereby promoting the oxidation reaction. It is advantageous from a mass transfer point of view that small gas bubbles are generated from the supersaturated liquid throughout the liquid volume of the reactor after a pressure drop in the oxidation reactor.

In certain embodiments, the oxidation reactor is a continuous reactor, the size being selected to ensure optimal process conditions that allow sufficient mixing to create turbulence throughout the volume of the reactor.

In certain embodiments, a plurality of oxidation reactors are coupled in parallel. In certain embodiments, a plurality of oxidation reactors are coupled in series.

In certain embodiments, the reduced copper etching solution and the oxidized copper etching solution have a temperature in the range of from 20 ℃ to 60 ℃, such as 45 ℃ to 55 ℃, or such as about 50 ℃. The temperature of the mixed solution, reduced copper etching solution and oxidized copper etching solution is preferably in the range from 45 ℃ to 55 ℃, and more preferably in the range from 50 ℃ to 55 ℃. On the one hand, the etching reaction becomes undesirably slow below 45 ℃. On the other hand, etchers are sensitive to temperatures above 55 ℃. However, the oxidation reaction is promoted by the relatively high temperature. Preferably, the temperature of the solution is maintained at a substantially constant value in the system. For example, the oxidation reactors and/or piping of the system may be separate.

In certain embodiments, the oxidized copper etching solution comprises copper at a total concentration in a range from 80g/L to 260g/L, Cu at a concentration in a range from 0g/L to 19.5g/L⁺HCl (aq) at a concentration in the range from 1 to 4mol/L and Cl at a total concentration in the range from 2.5 to 12mol/L^-。

In certain examples, the reduced copper etching solution comprises a total concentration of copper in a range from 81g/L to 260g/L, a concentration of Cu in a range from 0.5g/L to 20g/L⁺HCl (aq) at a concentration in the range from 1 to 4mol/L and Cl at a total concentration in the range from 2.5 to 12mol/L^-。

In certain embodiments, the reduced copper etching solution comprises copper at a total concentration in the range of from 81 to 260g/L, Cu at a concentration in the range of from 0.01 to 20g/L⁺HCl (aq) at a concentration in the range from 1 to 4mol/L and a total in the range from 2.5 to 12mol/LCl of concentration^-。

In certain embodiments, the oxidized copper etching solution comprises copper at a total concentration in a range from 80g/L to 260g/L, Cu at a concentration in a range from 0g/L to 19.5g/L⁺HCl (aq) at a concentration in the range from 0.01 to 1mol/L and Cl at a total concentration in the range from 2.5 to 12mol/L, such as in the range from 3.5 to 12mol/L^-。

In certain examples, the reduced copper etching solution comprises a total concentration of copper in a range from 81g/L to 260g/L, a concentration of Cu in a range from 0.5g/L to 20g/L⁺HCl (aq) at a concentration in the range from 0.01 to 1mol/L and Cl at a total concentration in the range from 2.5 to 12mol/L^-。

In certain embodiments, the reduced copper etching solution comprises copper at a total concentration in the range of from 81 to 260g/L, Cu at a concentration in the range of from 0.01 to 20g/L⁺HCl (aq) at a concentration in the range from 0.01 to 1mol/L and Cl at a total concentration in the range from 2.5 to 12mol/L^-。

In certain embodiments, the oxidized copper etching solution comprises a total concentration of copper in a range from 104g/L to 239g/L, a concentration of Cu in a range from 3g/L to 6g/L⁺HCl (aq) at a concentration in the range from 0.01 to 0.5mol/L and Cl at a total concentration in the range from 3.4 to 7.7mol/L^-。

In certain embodiments, the reduced copper etching solution comprises a total concentration of copper in a range from 105g/L to 240g/L, a concentration of Cu in a range from 5g/L to 8g/L⁺HCl (aq) at a concentration in the range from 0.01 to 0.1mol/L and Cl at a total concentration in the range from 3.4 to 7.7mol/L^-。

In certain embodiments, step b) occurs inside a feed conduit disposed upstream of and/or inside the oxidation reactor.

In a further aspect, the present invention provides an oxidised copper etching solution obtainable by a process according to the present invention.

In another aspect, the invention provides a printed circuit board obtainable by etching using an oxidized copper etching solution according to the invention.

In another aspect, there is provided the use of an oxidized copper etching solution according to the invention for etching printed circuit boards.

In another aspect, a method is provided for allowing reaction of 2Cu⁺+1/2O₂(aq)+2H⁺→2Cu²⁺+H₂A system for copper oxide etching solution wherein O occurs, wherein the system comprises:

an etching machine having an outlet for reduced copper etching solution;

an oxidation reactor having an inlet for the mixed copper etching solution of the oxidation reactor and an outlet for the oxidized copper etching solution of the oxidation reactor, the oxidation reactor further comprising at least one agitator; and

a feed conduit connected between the outlet of the etcher and the inlet of the oxidation reactor, the feed conduit comprising an inlet for an oxidant which is oxygen and/or air.

The effects and features of this aspect of the invention are similar to those described above in relation to the previous aspect of the invention.

The system may be adapted to allow reaction of 2Cu⁺+1/2O2(aq)+2H⁺→2Cu²⁺+H₂O occurs in at least the oxidation reactor, thereby producing an oxidized copper etching solution exiting the oxidation reactor that contains less Cu than the reduced copper etching solution exiting the etcher⁺。

The oxidant may be adapted to be introduced in the feed conduit to contain Cl^-And Cu⁺By acidic reduction ofIn the copper etching solution of (1).

In certain embodiments, the inlet for the reduced copper etching solution is disposed in the bottom of the oxidation reactor and the outlet for the oxidized copper etching solution is disposed at the top of the oxidation reactor.

In certain embodiments, the pressure in the oxidation reactor is lower than the pressure in the feed conduit.

In certain embodiments, at least one agitator is positioned proximate to the inlet of the oxidation reactor.

In certain embodiments, at least one agitator is an impeller.

In certain embodiments, the oxidation reactor comprises at least two agitators.

In certain embodiments, the feed conduit further comprises at least one static mixer disposed downstream of the inlet for the oxidant.

In certain embodiments, the oxidation reactor further comprises an internal circulation system comprising at least one pump and at least one venturi injector (venturi injector).

In certain embodiments, the impeller comprises a baffle.

Brief Description of Drawings

Referring now to the drawings, which are exemplary embodiments, wherein:

fig. 1 is a flow chart depicting one example of a process for oxidizing copper in a copper etching solution by using oxygen and/or air as an oxidizing agent in accordance with the present invention.

Fig. 2 is a schematic illustration depicting one example of direct introduction of oxygen and/or air into an oxidation reactor.

FIG. 3 is a schematic illustration depicting one example of introducing oxygen and/or air into a feed conduit that directs a reduced copper etching solution upstream of an oxidation reactor.

Figure 4 is a schematic illustration depicting one example of the inventive process.

FIG. 5 is a schematic illustration depicting a full scale example (full scale example) of the process of the present invention.

Fig. 6 is a cross-section of a copper conductor of a printed circuit board that has been produced in a conventional etching process using a conventional copper etching solution containing a large amount of acid.

Fig. 7 is a cross-section of a copper conductor of a printed circuit board that has been produced in the process of the present invention using a conventional copper etching solution containing a large amount of acid. Fig. 8 is a portion of a printed circuit board prepared from a cross-section of a copper conductor of the printed circuit board that has been produced in the process of the present invention using a modified copper etching solution containing a small amount of acid.

Detailed Description

Examples of processes according to two embodiments of the present invention will now be described in more detail with reference to the schematic illustrations in figures 3-4 and 5, respectively. However, the general concept of the process will first be described with reference to the flow diagram in fig. 1 and the simple embodiment shown in fig. 2. Referring to fig. 6-8, the results of the experiment will be described in more detail.

Fig. 1 shows a flow diagram of a process 100 for oxidizing copper in a copper etching solution by using oxygen and/or air as an oxidant in accordance with the present invention. In a first step 101, an oxidizing agent is introduced into a reduced copper etching solution, the reduced copper etching solution including Cl^-And Cu⁺. In a second step 102, the solutions obtained in step 101 are mixed to form a mixed solution. The mixing step may be performed, for example, by a static mixer in the feed line and/or by an impeller in the oxidation reactor. Usually, the mixing is carried out by means of at least one impeller, so-called stirring.

The process of the present invention generally occurs in a system for producing etched printed circuit boards. Two main components of such a system are the etcher and the oxidation reactor, which are fluidly connected directly to each other, e.g. by a feed conduit, forming a closed loop. In fig. 2, the oxidation reactor 22 is schematically shown.

In an etching machine, a printed circuit board and a substrate including Cu²⁺So as to allow the etching reaction (i) to take place.

Cu⁰+Cu²⁺→2Cu⁺(i)

Will contain Cu²⁺Is introduced into an etcher and subsequently subjected to an etching reaction (i) to obtain a copper-containing etching solution containing less Cu than the oxidized copper etching solution²⁺The reduced copper etching solution of (1). Subsequently, the reduced copper etching solution 20 is removed from the etcher and supplied to the oxidation reactor via a feed line.

In the oxidation reactor 22, the reduced copper etching solution 20 is oxidized by an oxidizing agent 21, i.e. oxygen and/or air, according to the oxidation reaction (ii), thereby producing an oxidized copper etching solution 23 leaving the oxidation reactor, and which can be reused in the etcher.

2Cu⁺+1/2O₂(aq)+2H⁺→2Cu²⁺+H₂O(ii)

In FIG. 2, the schematically illustrated continuous oxidation reactor may have a 0.5m³The reactor volume of (a). There may be more than one continuous oxidation reactor, typically in parallel as shown in fig. 5. The steady state flow of liquid may be selected to provide a retention time of the liquid in each successive oxidation reactor to ensure that the Cu is present⁺And (4) fully reducing. This is known to be done by the skilled person by varying the reactor volume or volumes and the liquid flow through the reactor or reactors.

An oxidant, i.e., pure oxygen and/or air, may be introduced into the reduced copper etching solution upstream of the oxidation reactor, such as in the feed line (as shown, for example, in fig. 3-4) or inside the oxidation reactor (as shown, for example, in fig. 2). The oxidant may be introduced both in the feed line and in the oxidation reactor (embodiments not shown).

In fig. 3-4, oxygen and/or air 31,41 is introduced into a feed line that directs the reduced copper etching solution 30,40 upstream of the oxidation reactor 32,42, thereby forming a solution 34, 44. The feed lines fluidly connect the etcher 45 (shown in fig. 4) and the oxidation reactors 32, 42. The solution 34,44 is introduced into the oxidation reactor 32,42 via the bottom of the oxidation reactor 32, 42. The oxidation reactor herein comprises two impellers for obtaining agitation in the oxidation reactor. One of the impellers is positioned proximate and above the inlet of the oxidation reactor 32,42, and the oxidation reactor 32,42 may draw the incoming solution and spray it toward the periphery of the oxidation reactor 32,42, wherein the baffle of the impeller is promoting agitation of the oxygen in the solution. The size of the oxygen bubbles is further reduced so as to increase the total contact surface between the gas and liquid phases to promote mass transfer of oxygen into the liquid solution. The dissolved oxygen is then available for contact with the Cu in the solution⁺And H⁺React to convert Cu⁺Oxidation to Cu²⁺. Less Cu is contained than in the reduced copper etching solutions 30,40⁺An amount of oxidized copper etching solution 33,43 exits the oxidation reactor 32,42 from the top of the oxidation reactor 32, 42.

In the oxidation reactors 22,32,42,52, the pressure can be reduced compared to the pressure in the feed line that conducts the reduced copper etching solution 20,30,40,50 and optionally the oxidant 31,41, 51. Typically, the pressure in the oxidation reactor is in the range of from 0 bar to 0.1 bar overpressure. Due to the pressure difference, a portion of the previously dissolved oxygen forms small bubbles after entering the oxidation reactor.

The reduced copper etching solution and the oxidizing agent, either in a combined stream (shown, for example, in fig. 3-5) or in separate streams (shown, for example, in fig. 2), are typically introduced into the oxidation reactor via the bottom of the oxidation reactor. The oxidized copper etching solution is typically removed from the top of the oxidation reactor. Thus, the inlet of the oxidation reactor is typically arranged in the bottom of the oxidation reactor and the outlet of the oxidation reactor is typically arranged at the top of the oxidation reactor.

The reduced copper etching solution and the oxidized etching solution may include a relatively high or relatively low content of HCl (aq) (see table 1). At relatively low levels of HCl (aq), additional chloride salt is added to ensure Cl^-In the range of from 2.5mol/L to 12mol/L in both solutions, i.e. in an oxidized copper etching solution containing a small amount of acid and in a reduced copper etching solution containing a small amount of acid. Table 1 shows different concentration intervals of different compounds contained in the reduced copper etching solution (including a low concentration of acid and a high concentration of acid, respectively) and the oxidized copper etching solution (including a low concentration of acid and a high concentration of acid, respectively).

The relatively high content of HCl (aq) has the advantage of promoting the oxidation reaction.

The relatively low content of HCl (aq) has the advantage of improved etching results and improved working environment. At low HCl (aq) content, Cl is added^-Salts such as NaCl may be necessary in order to react with Cu⁺The ions complex and combine so that these ions will not negatively affect the etch rate.

Thus, Cl^-Can be at very similar levels in two copper etching solutions that include low and high amounts of acid, respectively.

Table 1. concentration intervals for different compounds contained in an oxidized copper etching solution (including low amounts of acid and high amounts of acid, respectively) and a reduced copper etching solution (including low amounts of acid and high amounts of acid, respectively).

The concentration of HCl (aq) in the oxidized copper etching solution is higher than 0.01 mol/L. By keeping the concentration of HCl (aq) above 0.01mol/L, precipitation of copper hydroxide and negative effects on the rate of oxidation reaction (ii), respectively, can be avoided. Cu in the range from 0.01 to 20g/l has also been used in solutions containing low amounts of acid and solutions containing high amounts of acid, respectively⁺Was tested.

More specific concentration ranges for the chemical composition of the reduced copper etching solution with low amounts of acid obtained subsequent to reaction (i) are shown in table 2.

TABLE 2 composition of reduced copper etching solution with low amount of acid obtained following reaction (i)

Total concentration of copper [ g/l]	105-240g/L
		Cu+	5-8g/L
Total Cl-	3.4-7.7mol/L
		HCl(aq)	0.05mol/L

More specific concentration ranges for the chemical composition of the oxidized copper etching solution with low amounts of acid obtained subsequent to reaction (ii) are shown in table 3.

TABLE 3 composition of oxidized copper etching solution with low amount of acid obtained following reaction (ii)

Monovalent copper ion Cu⁺Concentration and divalent copper ion Cu²⁺The ratio of the concentrations of (a) to (b) is generally kept substantially constant in the etcher.

Copper (Cu) in the system⁺And Cu²⁺Combined) generally remains substantially constant. The total copper content may range from 80g/L to 260 g/L.

Importantly, the reduced copper ion Cu⁺Is kept low in the oxidized copper etching solution. By adding high amounts of chloride salts to the copper etching solution, chloride ions can combine these copper ions to form the complex CuCl₂ ^-Which forms a complex according to reaction (iii) during the etching process. Examples of suitable chloride salts are NaCl, KCl, MgCl₂、CaCl₂And/or NH₄Cl。

Cu⁺+2Cl^-→CuCl₂ ^-(iii)

The supply of the oxidant into the reduced copper etching solution may occur through a valve controlled by a sensor that measures the Oxidation Reduction Potential (ORP) in the copper etching solution present in the etcher. The sensor may have two critical extremes with respect to redox potential, wherein a first extreme indicates a demand for additional supply of oxidant and a second extreme indicates a demand for a maximum supply of oxidant required. When using a sensor based on a Pt electrode, with an Ag/AgCl electrode as reference, a divalent copper ion concentration of about 180g/L, a monovalent copper ion concentration of about 8g/L, a sodium chloride concentration of about 3.5mol/L corresponding to 9.4mol/L of total chlorine, two critical extremes have been measured as +510mV and +505mV, respectively.

Process control system as described in the preceding paragraphThe system can sense Cu in the etching machine by measuring oxidation-reduction potential⁺The level of (c). Reduced Cu in Cu etching solution⁺The increased level of (b) causes a drop in the potential, eventually to a value below the critical extremum. At the critical extrema, a given oxidant stream may be supplied to the oxidation system. If the potential continues to drop, the flow of oxidant can be set to successively higher levels. Finally, at the second critical extreme of the lowest redox potential, the level of maximum gas flow is supplied, allowing the potential to increase and oxidize, and a steady state condition of equilibrium can be reached in the oxidation reactor.

Thus, a steady state flow condition can be achieved by means of a process control system, with a relatively low content of Cu⁺The oxidized copper etching solution of (a) equilibrates Cu by etching reaction⁺Such that the concentration of monovalent copper ions is maintained at a substantially constant level as seen in the etcher.

The feed conduit typically comprises at least one static mixer, preferably a plurality of static mixers, such that turbulence and overpressure can be achieved inside the feed conduit. Typically, the oxidant is introduced into the feed conduit upstream of the static mixer. The turbulent conditions will ensure that the dissolved oxygen is evenly distributed in the liquid phase. The feed conduit may further comprise a valve adapted to further regulate the pressure inside the feed conduit and maintain turbulence. In this context, the feed conduit has an overpressure of 1 bar. Referring to Henry's Law, overpressure increases the solubility of the oxidizing agent, here pure oxygen, in the copper etching solution.

Example 1: full scale testing including the process

Full scale testing was conducted in a system comprising two oxidation reactors arranged in parallel, schematically illustrated in fig. 5. The volume of each oxidation reactor was 0.5m³. The system also includes an etcher 55 comprised of three modules. The etching module has a total of 1.2m³Copper etching solutionThe operating capacity of (c). Thus, the system has a total of 2.2m³Total working capacity of copper etching solution.

The reduced copper etching solution 50 is supplied to the pump from the bottom of the etcher via a feed line. A common feed line directs the reduced copper etching solution to the pump and from the pump to the oxidation reactors 52a-b, with the reduced copper etching solution being directed in two parallel feed lines, one to each oxidation reactor.

Downstream of the pump, each of the two feed pipes is provided with an inlet for the oxidant comprising a valve. The valve is controlled by a sensor.

Downstream of the inlet for the oxidizing agent 51a-b, each of the two feed pipes is provided with a static mixer 56a-b, providing overpressure and turbulence.

In between the static mixer and the oxidation reactors, a pressure gauge and further valves may be provided to regulate the flow and overpressure of the fluids before entering each oxidation reactor. This example was carried out at an overpressure of 0.8 bar, which 0.8 bar overpressure increased the solubility of the oxidizing agent, here pure oxygen, in the copper etching solution, with reference to henschel's law.

The feed pipe is arranged such that it forms an inlet for the mixed copper etching solution 54a-b in the bottom of the oxidation reactor. A first impeller is disposed above the inlet to agitate the mixed copper etching solution 54a-b within the oxidation reactor. The impeller creates turbulent agitation, promoting mass transfer of oxygen between the gas and liquid phases and further distribution throughout the liquid volume. A second impeller is disposed above the first impeller to provide further agitation.

The oxidation reactor comprises an agitator, in this case an impeller, having a speed of 294rpm, in order to also create agitation and turbulence inside the oxidation reactor. Preferably, the stirrer is chosen so as to allow agitation throughout substantially the entire reactor volume. The agitation disperses the oxygen gas bubbles in the liquid phase of the copper etching solution, creating a large contact surface between the liquid phase of the copper etching solution and the gas phase of the bubbles, thereby accelerating the oxidation reaction (ii) by promoting mass transfer of oxygen across the contact surface between the gas phase and the liquid phase. Due to the turbulent state in the liquid phase, the oxygen that has passed the phase boundary will be evenly distributed in the liquid phase where it is consumed according to the above reaction (ii).

The oxidation reactor also includes an internal circulation system that includes a pump and a venturi injector. The internal circulation system helps to create small bubbles within the liquid phase, which increases the efficiency of the oxidant used in the system.

At the top of each oxidation reactor 52a-b, an outlet, here an overflow, for oxidized copper etching solution 53a-b is arranged. The outlet streams from each of the two oxidation reactors may be combined 53 and connected to a return conduit (return pipe) that is fluidly connected to an etcher 55.

In full scale testing, a copper etching solution having a relatively low content of HCl (aq), a divalent copper ion concentration of about 180g/L, a monovalent copper ion concentration of about 8g/L, a sodium chloride concentration of about 3.5mol/L corresponding to 9.4mol/L of total chlorine, and at 28Nm³Pure oxygen flow per hour, the system manages an etching load of 45kg copper per hour without dropping below the oxidation-reduction potential (ORP) of +505 mV.

In full scale testing, a conventional pH electrode was used to control the dose of concentrated hydrochloric acid in the copper etching solution fed into the etcher in order to keep the concentration of HCl (aq) constant and low, here at 0.05 mol/L. Furthermore, a conventional density sensor was used to control the dosage of water in the copper etching solution fed into the etcher in order to keep the total concentration of copper constant, here at 190 g/L. The target value of the density was 1.42g/cm³。

TABLE 4 parameters in the specific examples

The venting device of the oxidation reactor is connected to the etcher, whereby excess oxidizing agent can be removed by process venting (process venting) of the etching line. The exiting oxidant may be recycled to the oxidation reactor.

Example 2: etched wing of copper conductor

As described above, the conductor of the printed circuit board preferably has a wing with a vertical cross-section. The process of the invention produces a wing with a straighter vertical profile than that obtained in conventional processes. In this way, the conductors of the printed circuit board can be produced closer to each other without jeopardizing the quality of the printed circuit board.

Fig. 6 shows a cross-section of a portion of a printed circuit board, and more specifically a copper conductor 60 of a printed circuit board, that has been produced by a conventional combined etching and oxidation process using a conventional copper etching solution containing a high amount of acid.

In conventional etching and oxidation processes, the oxidizing agent is hydrogen peroxide. Hydrogen peroxide is added to the etcher via a venturi. Thus, oxidation of copper occurs in the etcher. No additional mixing is performed unless mixing naturally occurs in the venturi and the internal circulation between the three etching modules performed by the circulation pump.

Conventional copper etching solutions used in conventional etching and oxidation processes, containing high amounts of acid as measured in the etcher, have a composition comprising:

total copper: 115 g/L;

Cu⁺：2g/L；

HCl(aq)：3.5mol/L；

NaCl：0mol/L；

total Cl^-：7.1mol/L。

The copper conductor is photographed in a microscope, allowing the dimensions of the copper conductor to be measured. The copper conductor 60 has an upper width x₂Lower width x₁A first wing width x₃And a second wing width x₄. Upper width x₂Has been measured as 230.9 μm, lower width x₁Has been measured as 289 μm, the first wing width has been measured as 29.1 μm and the second wing width x₄Has been measured as 28 μm. The height y of the copper conductor 60 is 84 μm.

Fig. 7 shows a cross-section of a portion of a printed circuit board, and more particularly a copper conductor 70 of a printed circuit board, that has been produced by a conventional etching process combined with the inventive oxidation process using a conventional copper etching solution.

In the oxidation process of the invention, the oxidant is oxygen. Oxygen is added to the feed line downstream of the etcher and upstream of the oxidation reactor. Thus, the oxidation of copper takes place in the feed conduit and/or the oxidation reactor. The mixing is carried out using one static mixer in the feed line and/or using two impellers in the oxidation reactor.

Conventional copper etching solutions used in the inventive oxidation process, containing high amounts of acid as measured in the etcher, have a composition comprising:

total copper: 115 g/L;

Cu⁺：2g/L；

HCl(aq)：3.5mol/L；

NaCl：0mol/L；

total Cl^-：7.1mol/L。

Copper conductor inPhotographed in a microscope, allowing the dimensions of the copper conductor to be measured. The copper conductor 70 has an upper width x₂Lower width x₁A first wing width x₃And a second wing width x₄. Upper width x₂Has been measured to be 257.3 μm, lower width x₁Has been measured as 293.3 μm, a first wing width has been measured as 19.4 μm and a second wing width x₄Has been measured to be 17.2 μm. The height y of the copper conductor 70 is 82.3 μm.

Thus, copper conductor 70 shows a smaller wing width than copper conductor 60 of fig. 6. Thus, the inventive oxidation process using a conventional copper etching solution is resulting in an improved printed circuit board compared to when a conventional combined etching and oxidation process using a conventional copper etching solution is used.

Fig. 8 shows a cross-section of a portion of a printed circuit board, and more specifically a copper conductor 80 of a printed circuit board, that has been produced by a conventional etching process combined with the inventive oxidation process using a copper etching solution containing a low amount of acid.

In the oxidation process of the invention, the oxidant is oxygen. Oxygen is added to the feed line downstream of the etcher and upstream of the oxidation reactor. Thus, the oxidation of copper takes place in the feed conduit and/or the oxidation reactor. The mixing is carried out using one static mixer in the feed line and/or using two impellers in the oxidation reactor.

The copper etching solution used in the inventive oxidation process, containing a high amount of acid as measured in the etcher, has a composition comprising:

total copper: 190 g/L;

Cu⁺：8g/L；

HCl(aq)：0.05mol/L；

NaCl：3.5mol/L；

total Cl^-：9.4mol/L。

Copper etching solutions containing low amounts of acid have significantly lower concentrations of HCl (aq) than conventional copper etching solutions. Instead, the chloride ions of the copper etching solution containing a low amount of acid are provided by adding a chloride salt, i.e., NaCl.

The copper conductor is photographed in a microscope, allowing the dimensions of the copper conductor to be measured. The copper conductor 80 has an upper width x₂Lower width x₁A first wing width x₃And a second wing width x₄. Upper width x₂Has been measured to be 264.8 μm, lower width x₁Has been measured to be 294.9 μm, the first wing width has been measured to be 14.5 μm and the second wing width x₄Has been measured to be 12.9 μm. The height y of the copper conductor 80 is 85 μm.

Thus, copper conductor 80 shows a smaller fin width than both copper conductor 60 of fig. 6 and copper conductor 70 of fig. 7. Thus, the inventive oxidation process using a copper etching solution containing a low amount of acid is leading to an improved printed circuit board compared to when a conventional combined etching and oxidation process using a conventional copper etching solution, and when an inventive oxidation process using a conventional copper etching solution, respectively, are used.

Claims (30)

1. A process for oxidizing copper in a copper etching solution by using oxygen and/or air as an oxidizing agent (21,31,41,51a,51b), the process comprising the steps of:

a) introducing the oxidant to contain Cl^-And Cu⁺In an acidic reduced copper etching solution;

b) stirring the solution obtained in step a); and is

Thereby allowing reaction of 2Cu⁺+1/2O₂(aq)+2H⁺→2Cu²⁺+H₂O occurs to thereby generate oxidationThe oxidized copper etching solution (23,33,43,53a,53b) comprises less Cu than the reduced copper etching solution (20,30,40,50), the oxidized copper etching solution (23,33,43,53a,53b) comprising⁺。

2. The process of claim 1, wherein the process of oxidizing copper in a copper etching solution is in a system comprising an etcher (45,55) and an oxidation reactor (22,32,42,52a,52b) fluidly connected by a feed conduit.

3. The process of claim 2, wherein the oxidant is introduced in the feed conduit comprising Cl^-And Cu⁺In the acidic reduced copper etching solution of (a).

4. The process according to claim 2 or 3, wherein the solution obtained in step a) is stirred in the oxidation reactor.

5. The process of any one of claims 2 to 4, wherein the resulting oxidized copper etching solution exiting from the oxidation reactor contains less Cu than the reduced copper etching solution exiting from the etcher⁺。

6. The process of any one of the preceding claims, wherein the reduced copper etching solution comprises a total concentration of Cl of at least 2.5mol/L^-。

7. The process of any one of the preceding claims, wherein Cl^-At least one compound derived from a group selected from: chloride salts of copper, ammonium, alkali and alkaline earth metals and hydrochloric acid.

8. Process according to any of the preceding claims, wherein step b) is carried out by at least one stirrer, such as an impeller.

9. The process of any one of claims 2 to 8, wherein the process further comprises the step of mixing the oxidizing agent with the acidic reduced copper etching solution in the feed conduit.

10. The process of claim 9, wherein the mixing is performed by at least one static mixer.

11. The process of any one of claims 2 to 10, wherein the pressure in the oxidation reactor is lower than the pressure in the feed conduit.

12. Process according to any one of claims 2 to 11, wherein the feed conduit has an overpressure, preferably in the range of from 0.01 to 15 bar.

13. The process of any one of the preceding claims, wherein a plurality of oxidation reactors are coupled in parallel.

14. A process according to any one of the preceding claims, wherein the reduced copper etching solution and the oxidized copper etching solution have a temperature in the range from 20 ℃ to 60 ℃, such as 45 ℃ to 55 ℃ or such as about 50 ℃, respectively.

15. The process of any one of the preceding claims, wherein the oxidized copper etching solution comprises copper at a total concentration in the range from 80 to 260g/L, Cu at a concentration in the range from 0 to 19.5g/L⁺HCl (aq) at a concentration in the range from 1 to 4mol/L and Cl at a total concentration in the range from 2.5 to 12mol/L^-。

16. The process of any one of the preceding claims, wherein the reduced copper etching solution comprises copper at a total concentration in the range from 81 to 260g/L, Cu at a concentration in the range from 0.01 to 20g/L⁺HCl (aq) at a concentration in the range from 1 to 4mol/L and Cl at a total concentration in the range from 2.5 to 12mol/L^-。

17. The process of any one of claims 1 to 14, wherein the oxidized copper etching solution comprises copper at a total concentration in the range from 80 to 260g/L, Cu at a concentration in the range from 0 to 19.5g/L⁺HCl (aq) at a concentration in the range from 0.01 to 1mol/L and Cl at a total concentration in the range from 2.5 to 12mol/L^-。

18. The process of any one of claims 1 to 14, wherein the reduced copper etching solution comprises copper at a total concentration in the range from 81 to 260g/L, Cu at a concentration in the range from 0.01 to 20g/L⁺HCl (aq) at a concentration in the range from 0.01 to 1mol/L and Cl at a total concentration in the range from 2.5 to 12mol/L^-。

19. An oxidized copper etching solution obtainable by the process according to any one of claims 1 to 18.

20. A printed circuit board obtainable by etching using the oxidized copper etching solution of claim 19.

21. Use of the oxidized copper etching solution of claim 19 for etching printed circuit boards.

22. A system for copper oxide etching solution allowing reaction

2Cu⁺+1/2O₂(aq)+2H⁺→2Cu²⁺+H₂O, the system comprises:

-an etching machine (45,55) having an outlet for reduced copper etching solution (20,30,40, 50);

an oxidation reactor (22,32,42,52a,52b) having an inlet for a mixed copper etching solution (34,44,54a,54b) of the oxidation reactor and an outlet for an oxidized copper etching solution (23,33,43,53a,53b) of the oxidation reactor, the oxidation reactor further comprising at least one agitator; and

-a feed conduit connected between the outlet of the etcher and the inlet of the oxidation reactor, the feed conduit comprising an inlet for an oxidant (31,41,51a,51b) being oxygen and/or air.

23. The system of claim 22, wherein the inlet for reduced copper etching solution is disposed in a bottom of the oxidation reactor and the outlet for the oxidized copper etching solution is disposed at a top of the oxidation reactor.

24. The system of claim 22 or 23, wherein the pressure in the oxidation reactor is lower than the pressure in the feed conduit.

25. The system of any one of claims 22 to 24, wherein the at least one agitator is positioned proximate to the inlet of the oxidation reactor.

26. The system of any one of claims 22 to 25, wherein the at least one agitator is an impeller.

27. The system of any one of claims 22 to 26, wherein the oxidation reactor comprises at least two agitators.

28. The system of any one of claims 22 to 27, wherein the feed conduit further comprises at least one static mixer disposed downstream of the inlet for the oxidant.

29. The system of any one of claims 22 to 28, wherein the oxidation reactor further comprises an internal circulation system comprising at least one pump and at least one venturi injector.

30. The system of any one of claims 22 to 29, wherein the impeller comprises a baffle.