CN110997981A

CN110997981A - Copper etching solution

Info

Publication number: CN110997981A
Application number: CN201880045782.7A
Authority: CN
Inventors: 希代诚; 渡口繁; 熊谷博之; 松原敏明; 中村惟之
Original assignee: Meltex Inc
Current assignee: Meltex Inc
Priority date: 2017-07-14
Filing date: 2018-07-09
Publication date: 2020-04-10
Also published as: JPWO2019013160A1; KR102472714B1; JP6949306B2; TWI745603B; KR20200029398A; WO2019013160A1; TW201908525A

Abstract

The invention provides a copper etching solution which can reliably inhibit electrochemical corrosion, is easy to manage a bath and has excellent etching speed. The copper etching solution is composed of an alkaline aqueous solution, and is characterized by containing 1-70 g/L of copper, 10-500 g/L of ammonia water when converted into 25% ammonia water, and 5-500 g/L of ammonium salt, wherein the ammonium salt is 1 or more than 2 ammonium salts selected from the group consisting of ammonium salts of inorganic acids, ammonium salts of sulfonic acids, ammonium salts of saturated fatty acids, ammonium salts of aromatic carboxylic acids, ammonium salts of hydroxy acids, and ammonium salts of dicarboxylic acids.

Description

Copper etching solution

Technical Field

The invention relates to a copper etching solution.

Background

Conventionally, as a method for forming a circuit pattern, a subtractive process has been known in which a resist is formed on a substrate having a copper foil of about 20 μm on the entire surface thereof, and then the exposed copper foil is removed by etching. As a method for forming a finer circuit pattern, a semi-additive Process (SAP) is known in which a seed layer is formed on the surface of a resin substrate by electroless copper plating, a plating resist is provided on the seed layer, a circuit is formed by electrolytic copper plating, and then the seed layer remaining on the substrate between the circuits is etched away.

In the semi-additive process, as a copper etching solution for etching and removing a seed layer, that is, electroless copper plating, for example, sulfuric acid/hydrogen peroxide (patent documents 1 to 3), hydrochloric acid/divalent copper (patent document 4), and hydrochloric acid/ferrous (patent document 5) copper etching solutions are known.

On the other hand, in order to reduce electrical contact resistance or improve solder wettability, there is known a technique of plating a surface of copper constituting a circuit with a metal more expensive than copper (a metal having a small ionization tendency), such as gold, silver, or palladium.

However, when copper that is conductive to a metal that is more expensive than copper is etched with the copper etching solution described in patent documents 1 to 5, the etching of copper that is conductive to a metal that is more expensive than copper is accelerated (electrochemical corrosion) compared to copper that is not conductive to the expensive metal. As a result, the resistance of the circuit increases, the circuit is broken, or the dissolution of the circuit is accelerated and the circuit is lost as the circuit is made finer, and the plating layer of the expensive metal provided on the surface of the circuit is peeled off (lost).

In order to solve the above problem, an etching solution containing hydrogen peroxide, an inorganic acid, chloride ions, and cyclohexylamine or piperidine is known as an etching solution for copper that conducts with a metal that is more expensive than copper (patent document 6). The copper etching solution preferably has a chloride ion concentration of 1 to 20ppm because the effect of suppressing electrochemical corrosion is reduced when the chloride ion concentration is 1ppm, and the etching rate is reduced when the chloride ion concentration exceeds 20 ppm. When copper in contact with gold and copper not in contact with gold (copper alone) are etched by the copper etching solution, the diameter of copper in contact with gold after etching exceeds 90% of the diameter of copper alone. Thus, the copper etching solution is considered to be excellent in the performance of suppressing electrochemical corrosion.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 4430990

Patent document 2: japanese patent No. 4434632

Patent document 3: japanese laid-open patent publication No. 2009-149971

Patent document 4: japanese laid-open patent publication No. 2006-111953

Patent document 5: japanese patent No. 3962239

Patent document 6: japanese patent laid-open publication No. 2013-245417

Disclosure of Invention

Problems to be solved by the invention

However, in the copper etching solution described in patent document 6, when the diameter of copper before etching is 0.45mm, the difference in diameter between copper electrically connected to gold and copper alone after etching is 0.045mm (45 μm) at most. Thus, the copper etching solution is required to further suppress electrochemical corrosion. Further, since the preferable range of the chlorine concentration of the copper etching solution is 1 to 20ppm, strict bath control is required, and bath control is difficult. Further, the etching rate of the copper etching solution is slow, and thus a higher etching rate is required.

The purpose of the present invention is to provide a copper etching solution which can reliably suppress electrochemical corrosion, is easy to manage, and has an excellent etching rate.

Means for solving the problems

The copper etching solution is an alkaline copper etching solution, and is characterized by containing 1-70 g/L of copper, 10-500 g/L of ammonia water when converted into 25% ammonia water, and 5-500 g/L of ammonium salt, wherein the ammonium salt is 1 or more than 2 ammonium salts selected from the group consisting of ammonium salts of inorganic acids, namely ammonium sulfate, ammonium bicarbonate, ammonium nitrate, ammonium salts of sulfonic acids, namely ammonium methanesulfonate, ammonium salts of saturated fatty acids, namely ammonium acetate, ammonium salts of aromatic carboxylic acids, namely ammonium benzoate, ammonium salts of hydroxy acids, namely ammonium lactate, and ammonium salts of dicarboxylic acids, namely ammonium oxalate.

The pH of the copper etching solution of the present invention is preferably 7.8 to 11.

The copper etching solution of the present invention preferably contains ammonium sulfate as the ammonium salt, and the ammonium sulfate is contained in an amount of 5 to 300 g/L.

As the copper etching solution of the present invention, it is preferable that the ammonium salt contains ammonium sulfate and ammonium hydrogen carbonate, and the ammonium sulfate content is 5 to 80g/L and the ammonium hydrogen carbonate content is 0.5 to 200 g/L.

As the copper etching solution of the present invention, it is preferable that the ammonium salt contains ammonium sulfate and ammonium acetate, and the ammonium sulfate content is 5 to 80g/L and the ammonium acetate content is 5 to 100 g/L.

ADVANTAGEOUS EFFECTS OF INVENTION

The copper etching solution is alkaline copper etching solution containing 10-500 g/L of ammonium salt, and can inhibit electrochemical corrosion. Further, the copper etching solution contains copper, ammonia water and the ammonium salt, but the concentration of each component is not as low as ppm level and the concentration range is wide, so that bath management can be easily performed.

Drawings

FIG. 1 is a schematic sectional view showing the circuit shape before etching with the copper etching solution of the present embodiment.

FIG. 2 is a schematic sectional view showing a circuit shape after etching with a copper etching solution according to the prior art.

FIG. 3 is a schematic sectional view showing the shape of a circuit etched by the copper etching solution of the present embodiment.

Fig. 4 is an explanatory diagram illustrating an etching test method.

Description of the symbols

1 resin substrate, 2 seed crystal layers, 2a,2b seed crystal layer 2 portion to be removed by etching, 3a,3b circuit, 4 electrodes, 5 circuit gold film, 6 circuit nickel film, 7 electrode nickel film, 8 electrode gold film, 9 inner layer circuit, 11 copper etching liquid, 15 copper plate, 16 gold plate, L back-off amount, W circuit substrate

Detailed Description

Hereinafter, embodiments of the copper etching solution of the present invention will be described.

1. Copper etching solution

The copper etching solution of the present embodiment is based on an alkaline copper etching solution, and is characterized by containing 1 to 70g/L of copper, 10 to 500g/L of ammonia water in terms of 25% ammonia water, and 5 to 500g/L of an ammonium salt. The copper etching solution of the present embodiment is alkaline and can suppress electrochemical corrosion.

Copper: copper is a constituent copper ammonia complex ([ Cu ]^II(NH₃)₄]²⁺) The copper ammonia complex acts as an oxidizing agent for the copper etching solution. Examples of copper used in the copper etching solution include metallic copper, copper oxide, and copper salt. From the viewpoint of solubility in water, copper sulfate 5 hydrate (CuSO) is preferable₄·5H₂Copper sulfate 5 hydrate is particularly preferable from the viewpoint of ease of preparation, as a water-soluble copper salt such as O) and copper carbonate.

The content of copper in the copper etching solution is within the range of 1-70 g/L. When the copper content is within this range, a good etching rate can be ensured, and good bath stability can be obtained. When the copper content is less than 1g/L, the amount of copper is insufficient for ammonia, and the formed copper ammonia complex decreases, and the etching rate decreases, which is not preferable. When the etching rate is decreased, the productivity is decreased. On the other hand, if the copper content exceeds 70g/L, the copper is excessive in relation to ammonia, resulting in precipitation of copper (copper hydroxide), which is not preferable.

Ammonia water: ammonia water is a supply source of ammonia constituting the copper ammonia complex, and can also be used as a pH adjuster. The content of ammonia water in the copper etching solution is 10 to 500g/L in terms of 25% ammonia water. Within this range, the pH can be maintained within a range in which electrochemical corrosion can be suppressed while ensuring a good etching rate. When the content of the aqueous ammonia is less than 10g/L, the content of ammonia is not preferable because insufficient ammonia is contained in the aqueous ammonia, resulting in precipitation of copper. On the other hand, when the content of ammonia water exceeds 500g/L, the pH becomes too high, and it is difficult to maintain the pH within the range of 7.8 to 10 when the ammonia water is continuously used, which is not preferable.

Ammonium salt: the ammonium salt is a component that provides a counter ion of the copper ammonia complex, and has an effect of suppressing electrochemical corrosion. As the ammonium salt, 1 or 2 or more kinds of ammonium salts selected from the group consisting of ammonium salts of inorganic acids such as ammonium sulfate, ammonium bicarbonate and ammonium nitrate, ammonium salts of sulfonic acids such as ammonium methanesulfonate, ammonium salts of saturated fatty acids such as ammonium acetate, ammonium salts of aromatic carboxylic acids such as ammonium benzoate, ammonium salts of hydroxy acids such as ammonium lactate, and ammonium salts of dicarboxylic acids such as ammonium oxalate can be used.

The content of ammonium salt in the copper etching solution is 5-500 g/L, which is the total amount of all ammonium salts. When the content of the ammonium salt is within this range, electrochemical corrosion can be suppressed. When the content of the ammonium salt is less than 5g/L, the electrochemical corrosion cannot be suppressed, which is not preferable. On the other hand, when the content of the ammonium salt exceeds 500g/L, the etching rate becomes too high, which is not preferable. If the etching rate is too high, the etching time becomes short and it becomes difficult to control the etching time. Further, it is not preferable because it is not possible to suppress electrochemical corrosion or cause an increase in cost. The content of the ammonium salt is preferably 20 to 300g/L, and more preferably 50 to 200 g/L.

In the case of a copper etching solution containing ammonium sulfate as an ammonium salt, the content of ammonium sulfate is preferably 5 to 300 g/L. When the content of ammonium sulfate is less than 5g/L, the etching rate is lowered, which is not preferable. On the other hand, when the content of ammonium sulfate exceeds 300g/L, the etching rate becomes too high, and precipitation is liable to occur after the bath stability is lowered, which is not preferable.

In the case of a copper etching solution containing ammonium sulfate and ammonium bicarbonate as ammonium salts, the content of ammonium sulfate is preferably 5 to 80g/L, and the content of ammonium bicarbonate is preferably 0.5 to 200 g/L. Ammonium bicarbonate can also be used as a pH buffer. When the content of ammonium sulfate is less than 5g/L, the etching rate is lowered, which is not preferable. On the other hand, when the content of ammonium sulfate exceeds 80g/L, the etching rate becomes too high, and precipitation is liable to occur after the bath stability is lowered, which is not preferable. Further, when the content of ammonium hydrogencarbonate is less than 0.5g/L, the etching rate is lowered, which is not preferable. On the other hand, when the content of ammonium hydrogencarbonate exceeds 200g/L, the etching rate becomes too high, and precipitation is liable to occur after the bath stability is lowered, which is not preferable.

In the case of a copper etching solution containing ammonium sulfate and ammonium acetate as ammonium salts, the ammonium sulfate content is preferably 5 to 80g/L, and the ammonium acetate content is preferably 5 to 100 g/L. Ammonium acetate may also be used as a pH buffer. When the content of ammonium sulfate is less than 5g/L, the etching rate is lowered, which is not preferable. On the other hand, when the content of ammonium sulfate exceeds 80g/L, the etching rate becomes too high, and electrochemical corrosion cannot be suppressed, which is not preferable. Further, when the content of ammonium acetate is less than 5g/L, the etching rate is lowered, which is not preferable. On the other hand, when the content of ammonium acetate exceeds 100g/L, the etching rate becomes too high or electrochemical corrosion cannot be suppressed, which is not preferable.

In addition to the above components, the copper etching solution of the present embodiment may contain an inhibitor for inhibiting copper etching, a surfactant for reducing surface tension, and the like.

The copper etching solution of the present embodiment contains copper, ammonia water, and the ammonium salt, but the concentration is not as low as ppm level and the concentration range is wide, so that bath management can be easily performed.

pH: the pH value of the copper etching solution is preferably 7.8-11. The pH of the copper etching solution can be adjusted by, for example, the amount of ammonia added. When the pH of the copper etching solution is within this range, electrochemical corrosion can be reliably suppressed, and excellent bath stability can be obtained. When the pH is less than 7.8, precipitation of copper is formed, which is not preferable. On the other hand, it is difficult to make the pH more than 11 by adding only ammonia water. When the pH exceeds 10, it is difficult to maintain the pH within a predetermined range, which is not preferable.

Bath temperature: the bath temperature of the copper etching solution is preferably adjusted to 10-60 ℃. When the bath temperature is less than 10 ℃, the etching rate becomes slow, which is not preferable. On the other hand, when the bath temperature exceeds 60 ℃, the etching rate becomes too high and the bath stability is lowered, which is not preferable.

Etching speed: the copper etching solution contains 1-70 g/L of copper, 10-500 g/L of ammonia water in terms of 25% ammonia water, and 5-500 g/L of the ammonium salt, and can etch copper (chemical copper plating) at a rate of 0.2-40 μm/min at a pH of 7.8-11 and a bath temperature of 10-60 ℃.

Therefore, according to the copper etching solution of the present embodiment, a higher etching rate can be obtained than in the copper etching solution composed of an acidic aqueous solution. The etching rate can be easily controlled by adjusting the concentration of the components of the copper etching solution.

2. Etching method using copper etching solution

Next, an etching method using the copper etching solution of the present embodiment will be described. The copper etching solution of the present embodiment is suitable for use in, for example, etching and removing a seed layer remaining on a substrate between circuits after manufacturing a printed wiring board by a semi-additive method.

The etching reaction of copper by the copper etching solution is represented by the following formula (1). The formula (1) represents a reaction in which a copper ammine complex (valence: 2) contained in a copper etching solution acts as an oxidizing agent to dissolve metallic copper, i.e., a seed layer, thereby generating a copper ammine complex (valence: 1).

Cu^o+[Cu^II(NH₃)₄]²⁺→2[Cu^I(NH₃)₂]⁺...(1)

The copper ammonia complex (valence 1) is regenerated into a copper ammonia complex (valence 2) by ammonia and dissolved oxygen in the copper etching solution. The regeneration reaction is represented by the following formula (2). The regenerated copper ammonia complex (valence 2) is used again in the etching reaction of formula (1).

2[Cu^I(NH₃)₂]⁺+4NH₄ ⁺+1/2O₂+2OH^-→2[Cu^II(NH₃)₄]²⁺+3H₂O...(2)

Fig. 1 shows the seed layer removed by the copper etching liquid of the present embodiment. A seed layer 2 is formed on the surface of a resin substrate 1 by electroless copper plating, and

circuits

3a,3b and electrodes 4 are formed on the seed layer 2 by electrolytic copper plating. Subsequently, the copper etching solution of the present embodiment is used to remove the portion 2a between the

circuits

3a,3b of the seed layer 2 and the portion 2b between the circuit 3a and the electrode 4. Hereinafter, the portions 2a and 2b are referred to as portions of the seed layer 2 to be removed by etching.

In order to reduce electrical contact resistance or to improve solder wettability, a gold coating 5 is provided on the surfaces of the

circuits

3a,3b by electroplating or electroless plating. Further, in order to prevent copper from diffusing from the

circuits

3a,3b to the gold film 5, a nickel film 6 is provided between the

circuits

3a,3b and the gold film 5 by electroplating or electroless plating. That is, a nickel coating 6 is provided on the surface of the

circuits

3a,3b, and a gold coating 5 is provided thereon.

Similarly to the

circuits

3a and 3b, a nickel coating 7 and a gold coating 8 are formed on the surface of the electrode 4 by electroplating or electroless plating.

The circuit 3a is electrically connected to a gold film 5 provided on the surface thereof, and is electrically connected to a gold film provided on the surface of an object other than the circuit itself. In the present embodiment, the circuit 3a is electrically connected to the gold film 8 provided on the surface of the electrode 4 via the inner layer circuit 9 embedded in the resin substrate 1. The inner layer circuit 9 is made of a metal having excellent conductivity, and in the present embodiment, is made of copper. Hereinafter, the circuit 3a is referred to as a "circuit that conducts electricity to a metal that is more expensive than copper". The expensive metal referred to herein is referred to as "gold".

On the other hand, the circuit 3b is electrically connected only to the gold film 5 provided on the surface thereof, and is not electrically connected to the

gold films

5 and 8 provided on the surfaces of other objects than the circuit itself. In the state before etching shown in fig. 1, the circuit 3b is electrically connected to the gold film 5 provided on the surface of the circuit 3a via the seed layer 2, but is not electrically connected to the circuit 3a after the seed layer 2 is removed by etching. Therefore, it is considered that the circuit 3b is not electrically connected to the

gold film

5,8 other than the gold film 5 provided on the surface of the circuit 3b itself. Hereinafter, the circuit 3b is referred to as a "circuit which is not electrically connected to a metal which is more expensive than copper".

When the resin substrate 1 shown in fig. 1 is immersed in a copper etching solution, it is desirable to etch only the portions 2a,2b of the seed layer 2 to be removed by etching. In practice, however, not only the portions 2a and 2b but also the portions directly under the

circuits

3a and 3b and the electrodes 4 of the seed layer 2 and the side surfaces of the

circuits

3a and 3b and the electrodes 4 themselves are dissolved (undercut). Hereinafter, the amount of undercut removal of the

circuits

3a,3b is referred to as "receding amount L". It is preferable that the etching be terminated at a point in time when the portions 2a and 2b of the seed layer 2 to be removed by etching disappear and the surface of the underlying resin substrate 1 is exposed. Hereinafter, the time point at which the surface of the underlying resin substrate 1 is exposed after etching is referred to as "proper etching". Further, the thickness of the seed layer 2 is not completely uniform over the entire surface. Therefore, in order to completely and reliably remove the portions 2a and 2b of the seed layer 2 to be removed by etching, it is necessary to perform etching more than a proper amount.

The retreat amount L can be obtained by, for example, the following equation (3).

The amount of retreat L ═ diameter [ (diameter of

circuit

3a,3b before etching) - (diameter of

circuit

3a,3b after etching) ]/2 … (3)

Alternatively, the nickel coating 6 and the gold coating 5 on the upper surfaces of the

circuits

3a and 3b are not etched by the copper etching solution of the present embodiment, and therefore the distance from the end surface of the nickel coating 6 or the gold coating 5 to the side surface of the

circuits

3a and 3b may be set to the receding amount L.

The resin substrate 1 shown in fig. 1 is provided with a circuit 3a that is electrically connected to a metal more expensive than copper and a circuit 3b that is not electrically connected to a metal more expensive than copper. When etching the portions 2a,2b of the seed layer 2 to be removed by etching with the conventional copper etching solution described in patent documents 1 to 5, as shown in fig. 2, the amount of retreat L of the circuit 3a becomes significantly larger than that of the circuit 3 b. At this time, the thinning (undercut) of the circuit 3a progresses, which causes an increase in resistance or disconnection, and further, the nickel film 6 and the gold film 5 on the surface of the circuit 3a are peeled off (disappear) as the circuit 3a disappears.

In contrast, when the seed layer 2 is etched by the copper etching liquid of the present embodiment, as shown in fig. 3, the amount of retreat L of the circuit 3a can be controlled to the same extent as that of the circuit 3 b. Further, even when the etching is performed more than a proper amount, the difference in the receding amount L between the circuit 3a and the circuit 3b can be suppressed from increasing.

Therefore, according to the copper etching solution of the present embodiment, the electrochemical corrosion can be suppressed, and the etching amounts of copper (circuit 3a) that is electrically connected to a metal more expensive than copper and copper (circuit 3b) that is not electrically connected to the expensive metal can be made equal. This prevents the problem of resistance increase and disconnection due to excessive etching of copper that conducts to a metal more expensive than copper that does not conduct to the expensive metal. Further, by preventing the copper (circuit 3a) electrically connected to a metal more expensive than copper from disappearing, the problem of the nickel coating 6 and the gold coating 5 provided on the surface of the copper from peeling off can be prevented.

In the present embodiment, the case where gold is used as the expensive metal as the circuit 3a that is copper electrically connected to a metal that is more expensive than copper has been described, but silver, palladium, iridium, platinum, or an alloy of these metals may be used as the metal that is more expensive than copper, in addition to gold.

In the present embodiment, an example is given in which a gold film 5 is provided on the surface of the circuit 3b itself via a nickel film 6 as the circuit 3b that is copper that is not electrically connected to a metal that is more expensive than copper, but a circuit (copper that is not in contact with a metal that is more expensive than copper and is not electrically connected) may be given in which no film is provided and no film is also electrically connected to a gold film provided on the surface of an object other than itself, as the surface (upper surface) of the circuit is exposed. In the copper etching solution of the present embodiment, the amount of draw-back L of the circuit and the amount of draw-back L of the circuit 3a that is electrically connected to the metal more expensive than copper may be controlled to the same level as each other. In addition, in the case where no film is provided on the upper surface or no circuit with an exposed surface is provided, since both the circuit side surface and the circuit upper surface are etched, the amount of retreat L of such a circuit is preferably determined by the above equation (3).

The present invention will be specifically described below based on examples and the like.

Examples

1. Etching test Using Circuit substrate

1-1 preparation of copper etching solution

Here, an etching test was performed using the circuit substrate. First, copper etching solutions of examples 1 to 3 shown in Table 1 were prepared. In table 1, "-" indicates that the component was not added. In table 1, the values shown in the column () of copper sulfate 5 hydrate are values converted into copper. In comparative example 1, a commercially available copper etching solution (sulfuric acid-hydrogen peroxide, pH1 or less) was used. In comparative example 2, a commercially available copper etching solution (chlorine-containing acidic bath, pH1 or less) was used. In comparative example 3, an acidic copper etching solution (pH1 or less) containing iron sulfate was prepared, and the bath temperature was set to 35 ℃.

TABLE 1

	Example 1	Example 2	Example 3
				Ammonium sulfate (g/L)	31.2	31.2	31.2
Copper sulfate 5 hydrate (g/L)	80(20)	12(3)	80(20)
				25% ammonia water (g/L)	47.1	14.6	93
Ammonium bicarbonate (g/L)	50	-	-
				Ammonium acetate (g/L)	-	-	18.3
pH	8.5	8.5	8.5
				Bath temperature (. degree. C.)	25	35	35

1-2, etching test

Next, an etching test was performed on the circuit board as described below. As the test piece, a circuit board in which a circuit that is electrically connected to a metal more expensive than copper and a circuit that is not electrically connected to a metal more expensive than copper are provided on a resin substrate is used. As shown in fig. 1, the test piece is a circuit board W in which a seed layer 2 is formed on the surface of a resin substrate 1 by electroless copper plating, and

circuits

3a and 3b and electrodes 4 are formed on the seed layer 2 by electrolytic copper plating. The

circuits

3a,3b each have a diameter of 40 μm, and a nickel coating 6 and a gold coating 5 are provided on the surfaces thereof. The electrode 4 has a diameter of l00 μm and a diameter larger than the

circuits

3a,3b, and has a nickel coating 7 and a gold coating 8 formed on the surface thereof. The circuit 3a is electrically connected to the gold film 8 of the electrode 4 via an inner layer circuit 9 embedded in the resin substrate 1. On the other hand, the circuit 3b is electrically connected to the gold film 5 provided on the surface of the circuit 3b itself, but is not electrically connected to the

gold films

5 and 8 other than the circuit itself. In this test piece, 10 circuits 3a, 50 circuits 3b, and 10 electrodes 4 are provided on a resin substrate 1 in a mixed manner, and 1 circuit 3a is connected to 1 electrode 4.

The test piece was immersed in the copper etching solution of this example. Removing the seed layer 2 by etchingThe time point when the etching of the portions 2a and 2b disappears and the surface of the resin substrate 1 therebelow is exposed is defined as a proper etching, and the time from the start of immersion to the proper etching is defined as "T_JE". Immersing the test piece in a copper etching solution until T is reached_JE3 times time (T)_JEX 3). In addition, the time T from the beginning of immersion to the appropriate amount of etching_JEThe copper etching solution varies depending on its composition, pH, bath temperature, and the like.

Then, after T_JE、T_JE×2、T_JEAt the time point of the immersion time × 3, the test piece was taken out from the copper etching solution, and the test piece was cut in parallel to the thickness direction thereof. Subsequently, the receding amounts L of the 5

circuits

3a,3b were measured on the cut surface of the test piece by a digital microscope, and the average value thereof was obtained. The results are shown in Table 2.

In table 2, each symbol in the column "etching rate" means the following.

○, the etching rate is 1 μm/min to 3 μm/min.

△, the etching rate is more than 3 μm/min and 7 μm/min or less.

X: the etching rate is 0 μm/min to 1 μm/min, or more than 7 μm/min.

In table 2, each symbol in the column "back-off amount" indicates the following meaning. Here, Δ L is an absolute value of a difference between the amount of retreat of the circuit 3a and the amount of retreat of the circuit 3 b. When Δ L is large, it is considered that electrochemical corrosion occurs at least in the circuit 3 a.

○, Δ L is 0 μm to 0.3 μm.

△, the DeltaL is more than 0.3 μm and not more than 1 μm.

X: Δ L exceeds 1 μm, or at least one of the

circuits

3a,3b disappears, and the nickel film 6 and the gold film 5 on the surface thereof are peeled off.

TABLE 2

In addition, the method is as follows: the circuit 3a disappears, but the circuit 3b does not.

In addition, 2: both

circuits

3a,3b disappear.

Evaluation of

As shown in Table 2, the copper etching solutions of examples 1 to 3 had a time T until an appropriate amount of etching had elapsed_JE3 times time (T)_JEX 3) was also evaluated as "○", it was found that the copper etching solutions of examples 1 to 3 had a time T until the appropriate amount of etching had elapsed_JE3 times time (T)_JEX 3) is not electrochemically etched in the circuit 3 a.

Further, the copper etching solutions of examples 1 to 3 were evaluated as "○" or "△" in terms of etching rate, and it was found that the copper etching solutions of examples 1 to 3 were excellent in etching rate.

On the other hand, the copper etching solutions of comparative examples 1 to 3 were inferior to those of examples 1 to 3 in both the receding amount and the etching rate. Even in the copper etching solution of comparative example 2 in which the evaluation of the amount of recession was the highest among comparative examples 1 to 3, the time T until the proper amount of etching elapsed_JE3 times time (T)_JEX 3) was also evaluated as "△" only in the amount of receding, and it was found that the copper etching liquid of comparative example 2 had a time T until the appropriate amount of etching had elapsed_JE3 times time (T)_JEX 3) the electrochemical corrosion of the circuit 3a occurred.

Evaluation of the amount of recession in comparative examples 1 to 3 the copper etching solution of comparative example 1, which was the second highest in evaluation of the amount of recession, was etched for a proper amount of time T _JE2 times time (T)_JEX 2), the amount of retreat was evaluated as "× (" 1 in color "). From this, it is understood that the copper etching solution of comparative example 1 has a time T until an appropriate amount of etching has elapsed_JE2 times time (T)_JEX 2) the electrochemical corrosion of the circuit 3a occurred.

In addition, in the comparative example 1 ~ 3 evaluation of the lowest amount of recession of the copper etchant, in comparison with example 3, after the right amount of etching time T_JEAt the time point of (a), the amount of retreat was evaluated as "× (" in 2) ". Thus, it can be seen that the copper etching in comparative example 3The time T until the etching is properly performed_JEAt the time point (3 a), electrochemical corrosion occurs in the circuit (3 a). Further, it was found that electrochemical corrosion occurred in both the

circuits

3a and 3b, and that the nickel coating 6 and the gold coating 5 on the surfaces of the

circuits

3a and 3b peeled off after the

circuits

3a and 3b disappeared.

From these results, it is understood that the copper etching solutions of examples 1 to 3 are superior in the effect of suppressing electrochemical corrosion to the copper etching solutions of comparative examples 1 to 3.

Further, the copper etching solutions of comparative examples 1 to 3 were evaluated for etching rate as "x". As a result, the etching rates of the copper etching solutions of comparative examples 1 to 3 were low.

The copper etching solutions of examples 1 to 3 are discussed in detail with reference to Table 1. Since the copper etching solution of example 2 had a low content of copper sulfate 5 hydrate, which was about 1/6 in example 1, the content of aqueous ammonia had to be controlled to about 1/3 in example 1 so as not to cause excessive ammonia. Thus, it is considered that the copper etching solution of example 2 has a lower etching rate than that of example 1 because the amount of the copper ammonia complex produced is less than that of example 1, and the etching rate is 1 μm/min to 3 μm/min.

The copper etching solution of example 3 had the same copper sulfate 5 hydrate content as in example 1, and the amount of ammonia water was about 2 times that of example 1, and it is considered that the amount of copper ammonia complex produced was larger than that of example 1. The total amount of ammonium sulfate and ammonium bicarbonate was 81.2g/L in example 1, and the total amount of ammonium sulfate and ammonium acetate was 49.5g/L in example 3, and the amount of ammonium sulfate was the same as in example 1, but ammonium acetate was about 1/2.7 of ammonium bicarbonate. Thus, it is considered that in example 3, the etching rate was suppressed as compared with example 1 by using ammonium acetate, and the etching rate was 1 μm/min to 3 μm/min.

2. Etching test Using Metal plate

2-1 preparation of copper etching solution

Here, an etching test was performed using a metal plate. First, copper etching solutions of examples 4 to 25 and comparative examples 4 to 9 shown in tables 3 to 7 were prepared. As shown in Table 3, in the copper etching solutions of examples 4 to 8 and comparative example 4, the amount of ammonium sulfate added was fixed at 50g/L, the amount of copper sulfate 5 hydrate added was varied within a range of 0.4 to 200g/L (a range of 0.1 to 50g/L in terms of copper), and the amount of 25% aqueous ammonia was varied within a range of 6 to 500 g/L. In the copper etching solutions of example 9 and comparative example 5, the amount of ammonium sulfate added was fixed at 250g/L, the amount of 25% aqueous ammonia added was fixed at 500g/L, and the amount of copper sulfate 5 hydrate added was varied within a range of 250 to 300g/L (62.5 to 75g/L in terms of copper). As shown in Table 4, in the copper etching solutions of examples 6 and 10 to 15 and comparative examples 6 to 7, the amount of copper sulfate 5 hydrate added was fixed at 120g/L (30 g/L in terms of copper), the amount of 25% aqueous ammonia was fixed at 150g/L, and the amount of ammonium sulfate added was varied within a range of 2.5 to 400 g/L. As shown in Table 5, ammonium hydrogencarbonate was added to the copper etching solutions of examples 16 to 17 and comparative example 8 in a range of 0.5 to 250g/L, based on the composition of the copper etching solution of example 6. As shown in Table 6, ammonium acetate was added to the copper etching solutions of examples 18 to 20 and comparative example 9 in a range of 5 to 120g/L based on the composition of the copper etching solution of example 6. As shown in Table 7, the copper etching solutions of examples 21 to 25 were prepared by adding 20g/L of different kinds of ammonium salts to the copper etching solution of example 6.

2-2, etching test

Next, an etching test was performed using a metal plate as described below. As shown in FIG. 4, first, the copper etching solutions (copper etching solutions of examples 4 to 25 and comparative examples 4 to 9) 11 were placed in a beaker 12, heated in a constant-temperature water tank 13, and stirred by a stirrer 14. Subsequently, the copper plate 15 and the gold plate 16 as test pieces were immersed in the copper etching solution 11 for 3 minutes. As the copper plate 15, an electrolytic copper foil having a thickness of 18 μm was used. As the gold plate 16, a metal plate, not shown, in which a gold coating film having a thickness of 1 μm was formed on a copper plate by plating was used, and the surface area thereof was about 15 times that of the copper plate 15. The copper plate 15 and the gold plate 16 are immersed in a state where the copper plate 15 and the gold plate 16 are not electrically connected to each other and in a state where they are electrically connected to each other through the lead 17. In both cases where the copper plate 15 and the gold plate 16 were not electrically connected, the etching rate of the copper plate 15 was calculated based on the weight difference before and after the immersion. The results are shown in tables 3 to 7. In tables 3 to 7, the symbols in the column "bath stability" have the following meanings. In tables 3 to 7, "-" indicates that the components were not added or that the pH and etching rate were not measured after the bath could not be constructed.

○ self-decomposition of the bath did not occur and the bath was stable.

X: the bath itself decomposed and the bath could not be constructed.

As shown in fig. 4, in a state where the copper plate 15 and the gold plate 16 are electrically connected, electrochemical corrosion occurs. On the other hand, in a state where the copper plate 15 and the gold plate 16 are not electrically connected, electrochemical corrosion does not occur. As can be seen, in the etching test, the state in which the copper plate 15 and the gold plate 16 are electrically connected corresponds to the circuit 3a which is electrically connected to the metal more expensive than copper in the etching test using the circuit board W, and the state in which the copper plate 15 and the gold plate 16 are not electrically connected corresponds to the circuit 3b which is electrically connected to the metal more expensive than copper in the etching test using the circuit board W. Therefore, the present etching test can be regarded as a simplified version of the etching test using the circuit substrate W. The determination of whether the etching rate is good or not varies depending on how the metal to be etched is produced, whether or not the film is formed, and the etching amount to which the metal needs to be etched. Therefore, in this etching test, the numerical value of the etching rate itself was not evaluated.

TABLE 3

TABLE 4

TABLE 5

TABLE 6

TABLE 7

Evaluation of

As shown in Table 3, the copper etching solutions of examples 4 to 9 showed almost no difference in etching rate between the case where the copper plate 15 and the gold plate 16 were not electrically connected and the case where they were electrically connected. From this, it is understood that the copper etching solutions of examples 4 to 9 are excellent in the effect of suppressing electrochemical corrosion. On the other hand, it is understood that the copper etching solution of comparative example 4 has an etching rate 3 times faster in the on state than in the off state, and thus has electrochemical corrosion. Further, the copper etching solution of comparative example 5 had low bath stability, and the etching test could not be performed. As is clear from the above, a copper etching solution having a copper content of 1 to 62.5g/L and a 25% ammonia content of 10 to 500g/L is excellent in the effect of suppressing electrochemical corrosion.

As shown in Table 4, the copper etching solutions of examples 6,10 and 15 showed almost no difference in etching rate between the case where the copper plate 15 and the gold plate 16 were not electrically connected and the case where they were electrically connected. From this fact, it is understood that the copper etching solutions of examples 6,10 to 15 are excellent in the effect of suppressing electrochemical corrosion. On the other hand, the copper etching solutions of comparative examples 6 to 7 were found to have electrochemical corrosion at an etching rate 1.12 to 2.1 times faster at the time of conduction than at the time of non-conduction. As is apparent from the above, the copper etching solution containing 5 to 300g/L of ammonium sulfate is excellent in the effect of suppressing electrochemical corrosion.

As shown in Table 5, the copper etching solutions of examples 16 to 17 showed almost no difference in etching rate between the case where the copper plate 15 and the gold plate 16 were not electrically connected and the case where they were electrically connected. From this, it is clear that the copper etching solutions of examples 16 to 17 are excellent in the effect of suppressing electrochemical corrosion. On the other hand, the copper etching solution of comparative example 8 had low bath stability, and the etching test could not be performed. As is clear from the above, a copper etching solution containing ammonium sulfate and ammonium hydrogencarbonate as ammonium salts and having an ammonium hydrogencarbonate content of 0.5 to 200g/L is excellent in the effect of suppressing electrochemical corrosion.

As shown in Table 6, the copper etching solutions of examples 18 to 20 showed almost no difference in etching rate between the case where the copper plate 15 and the gold plate 16 were not electrically connected and the case where they were electrically connected. From this, it is understood that the copper etching solutions of examples 18 to 20 are excellent in the effect of suppressing electrochemical corrosion. On the other hand, the copper etching solution of comparative example 9 was found to have electrochemical corrosion at an etching rate 23.5 times higher in the case of conduction than in the case of no conduction. As is apparent from the above, a copper etching solution containing ammonium sulfate and ammonium acetate as ammonium salts and having an ammonium acetate content of 5 to 100g/L is excellent in the effect of suppressing electrochemical corrosion.

As shown in Table 7, the copper etching solutions of examples 21 to 25 showed almost no difference in etching rate between the case where the copper plate 15 and the gold plate 16 were not electrically connected and the case where they were electrically connected. From this, it is clear that the copper etching solutions of examples 21 to 25 are excellent in the effect of suppressing electrochemical corrosion. As described above, it was found that when ammonium sulfate is combined with 1 ammonium salt selected from the group consisting of ammonium nitrate, ammonium methanesulfonate, ammonium benzoate, ammonium lactate, and ammonium oxalate, an etching solution having an excellent effect of suppressing electrochemical corrosion can be obtained.

From the above results, it is understood that the same results as those obtained in the case of the copper etching solutions of examples 1 to 3 can be obtained when the copper etching solutions of examples 4 to 25 are used in the etching test of the circuit board W shown in FIG. 1.

Industrial applicability

The copper etching solution can inhibit electrochemical corrosion and obtain high etching speed. The copper etching solution of the present invention can suppress electrochemical corrosion, and is therefore suitable for etching a plating object in which copper is present in contact with a metal more expensive than copper and copper is not present in contact with the metal more expensive than copper. The copper etchant of the present invention can be applied to various fields of electronic circuit boards, semiconductors, and the like.

Claims

1. A copper etching solution is an alkaline copper etching solution and is characterized in that,

contains 1 to 70g/L of copper, 10 to 500g/L of ammonia water in terms of 25% ammonia water, and 5 to 500g/L of ammonium salt,

the ammonium salt is 1 or more than 2 kinds of ammonium salts selected from the group consisting of ammonium salts of inorganic acids, i.e., ammonium sulfate, ammonium bicarbonate, ammonium nitrate, ammonium salts of sulfonic acids, i.e., ammonium methanesulfonate, ammonium salts of saturated fatty acids, i.e., ammonium benzoate, ammonium salts of aromatic carboxylic acids, i.e., ammonium lactate, and ammonium salts of dicarboxylic acids, i.e., ammonium oxalate.

2. The copper etching solution according to claim 1, wherein the pH of the copper etching solution is 7.8 to 11.

3. The copper etching solution according to claim 1 or 2, wherein the ammonium salt is ammonium sulfate, and the ammonium sulfate is contained in an amount of 5 to 300 g/L.

4. The copper etching solution according to claim 1 or 2, wherein the copper etching solution contains ammonium sulfate and ammonium bicarbonate as the ammonium salt, the ammonium sulfate is contained in an amount of 5 to 80g/L, and the ammonium bicarbonate is contained in an amount of 0.5 to 200 g/L.

5. The copper etching solution according to claim 1 or 2, wherein the copper etching solution contains ammonium sulfate and ammonium acetate as the ammonium salt, the ammonium sulfate is contained in an amount of 5 to 80g/L, and the ammonium acetate is contained in an amount of 5 to 100 g/L.