JPH0811835B2 - Etching method - Google Patents

Description

The present invention relates to a method for continuously etching a metal such as copper with a ferric chloride solution.

[Conventional Technology / Problems] In the etching of copper with a ferric chloride solution, the concentration of copper ions and ferrous ions in the etching solution increases due to the reaction of the following equation as the etching progresses, and the etching rate increases accordingly. descend.

Fe ⁺⁺⁺ ＋ Cu ⁰ → Fe ⁺⁺ ＋ Cu ⁺ Fe ⁺⁺⁺ ＋ Cu ⁺ → Fe ⁺⁺ ＋ Cu ^{++ In} order to solve this problem, in the conventional continuous etching method of copper with a ferric chloride solution, etching is performed. By increasing the effective distance (or using multiple tanks), the ferric chloride solution or this and hydrochloric acid are continuously supplied in large amounts to relatively lower the concentrations of dissolved copper and ferrous ions. In this way, a method of ensuring a practical line speed of the object to be etched has been adopted. However, this method has drawbacks in that the etching tank must be long (or multiple tanks), the equipment cost is high, and the chemical solution is consumed in large amounts, resulting in cost increase.

Further, U.S. Pat.No. 3,951,711 is provided with a specific gravity detector and a redox potential detector, and water, ferric chloride, and copper in a ferric chloride solution for supplying an oxidizing agent are supplied according to the outputs of these detectors. A continuous etching method is described. In this method, in order to suppress the ferrous ions generated by etching to a low level, as an etching chemical, water, an oxidizing agent for oxidizing ferrous ions to ferric ions is added to ferric chloride, and etching is performed. The present invention proposes to oxidize ferrous ions generated with the progress to ferric ions as much as possible and perform etching while maintaining a high concentration of ferric ions. However, the oxidizing agent used in this method is chlorine gas or a combination of hydrochloric acid and ammonium chlorate. Chlorine gas is not only dangerous in handling high-pressure gas, but also has a pH of 1 or less. Since chlorine gas has a low solubility in the highly acidic etching solution of, most of it dissipates as chlorine gas,
The effect as an oxidizing agent is small, and on the etching tank,
Alternatively, there is a problem in practical use that there is a problem such as damage to equipment and buildings, damage to the environment, and the like due to scattering around. In addition, ammonium chlorate is a very unstable compound, and is a substance that easily explodes at room temperature [published by Maruzen Co., Ltd., Revised 3rd Edition, Basic Edition I, I-156, Compound 22]
In addition to the difficulty in handling, the effect as an oxidant is also small.

In fact, the ratio of ferrous ion / ferric ion in the etching solution in this method is almost 1, and the etching rate is slow.

[Means for Solving the Problems] The object of the present invention is to provide copper, iron, nickel, chromium, brass, stainless steel, 4,2-alloy, and other iron by ferric chloride solution without the above-mentioned drawbacks. Another object of the present invention is to provide a continuous etching method for metals such as copper, alloys of nickel and the like.

The method for continuously etching copper and other metals with the ferric chloride solution of the present invention is 6-9 mols of hydrogen chloride based on 1 equivalent of a chlorate selected from sodium chlorate, potassium chlorate and calcium chlorate. An aqueous solution containing ferric chloride in an amount of 2.5 to 15 mol is supplied as a drug.

The chlorate used in the present invention is preferably used in the form of an aqueous solution, for example, in the case of sodium chlorate, it is preferable to use an aqueous solution of 35 to 40% by weight.

Hydrogen chloride is also preferably supplied as an aqueous solution of hydrochloric acid, for example, 30 to 35% by weight hydrochloric acid is preferably used.

Further, ferric chloride is also preferably supplied as an aqueous solution, for example, it is preferable to use a 40 to 45 ° Be 'solution.

The above concentration is not particularly limited, but it is preferable to maintain the concentration of ferric chloride in the etching solution at 40 g / or more in order to maintain the etching rate.

The mixing ratio of chlorate / hydrogen chloride / ferric chloride is 1 equivalent / 6 to 9 mol / 2.5 to 15 mol, but the preferable range is as follows depending on the metal.

For copper, brass or other copper-based alloys, the ratio of chlorate / hydrogen chloride / ferric chloride is 1 equivalent / 6.6 to 7.7 mol / 4.0 to 6.5 mol; iron, nickel, chromium , Stainless steel, 4,2-
1 equivalent / 6.6 to 7.7 mol / 5 to 12 mol for alloys or other alloys mainly composed of iron or nickel.

If 6 mol or more of hydrogen chloride is not used, the chlorate becomes excessive and remains in the etching solution, and sludge is generated, which is not preferable, and if used in a too large amount, undercut proceeds. Further, when the amount of ferric chloride is small, the etching rate is low, and when it is large, the utilization rate is low, the drainage is large, and the cost is high.

In the present invention, the specific gravity of the etching solution should be maintained at 1.30 to 1.45, preferably 1.33 to 1.43, by supplying an appropriate amount of water. If the specific gravity is less than 1.30, the undercut tends to increase, and if it exceeds 1.45, the etching speed tends to decrease. In addition, the concentration ratio of ferrous ion and ferric ion in the etching solution is Fe ⁺⁺ / Fe ⁺⁺⁺ = 0.15 to 0.50, preferably 0.15 to 0 by appropriately supplying chemicals.
It is preferable to maintain the concentration at 40, and the ferric ion concentration in the etching solution at 40 g / or higher, preferably 55 g / or higher. By maintaining in this way, a high etching rate can be maintained and high-performance etching with less undercut can be performed.

Further, in the conventional copper etching method using ferric chloride, the etching speed was significantly reduced when the copper ion concentration in the etching solution became 65 to 70 g /, and the etching had to be effectively stopped, According to the etching method of the present invention, the copper ion concentration in the etching solution is 90 ~
Even if it is as high as about 100 g /, it is possible to maintain the same etching speed as when copper ions are not included.

An apparatus suitable for carrying out the etching method of the present invention will be described below with reference to FIG.

FIG. 1 shows one example for carrying out the method of the present invention, in which the etching solution is pumped from the etching tank (1) (10).
It is supplied to the control tank (2) through the circulation pipe (101) by 0) and is returned to the etching tank (1) through the circulation pipe (102) by the pump (103) (which may be omitted) to be cycled. It The control tank (2) is a storage tank for analyzing or detecting the composition of the etching solution in the etching tank (1). As shown in FIG. 1, the detecting section (3 ') is provided in the etching solution, and the detecting section (3') is provided. (3 ')
A specific gravity detector (3) and a detection unit (4 ') that generate an electric signal from (for example, a float type, an electromagnetic type, a specific electric conductivity type, etc. as a control signal satisfying a setting condition) in an etching liquid are used. And controlling the electric signal related to the ferrous ion concentration from the detector (4 ′) (for example, redox potential difference type, constant voltage current value type, phototube type, etc., not particularly limited) satisfying the setting condition. A detection unit (3 ') (4') of a ferrous iron ion detector (4) generated as a signal is provided, or the specific gravity of the liquid in the control tank (2) is measured by a densitometer, and the control tank ( A part of the solution in 2) is sampled and titrated with a potassium permanganate standard solution or the like, so that the composition of the etching solution can be analyzed or detected constantly, regularly or at any time.

In the etching tank (1), mixed supply pipes (5, 5 ', 6) of ferric chloride aqueous solution and hydrochloric acid aqueous solution (may be supplied separately), chlorate aqueous solution supply pipes (7, 7') ( Do not mix with ferric chloride or hydrochloric acid aqueous solution before supplying to etching solution), water supply pipe (8) is open.

Each supply pipe is connected to each tank [ferric chloride aqueous solution tank (105), hydrochloric acid aqueous solution tank (106), chlorate aqueous solution tank (107)] and an output terminal (A) of the ferrous ion detector (4). ) And a pump electrically controlled by the output of the detector (4) [ferric chloride aqueous solution pump (11
5), hydrochloric acid aqueous solution pump (116), chlorate aqueous solution pump (117)] or output terminal (B) of specific gravity detector (3)
And a water pump (118) electrically coupled to and controlled by the output of the detector (3).

In practice, it is preferable to use the cushion tanks (125, 126, 127) for chemicals other than water as shown in FIG.

Further, the etching tank (1) is provided with an overflow pipe (109) for taking out the overflowed etching waste liquid.

As a modified example of the example shown in FIG. 1, the ferric chloride aqueous solution cushion tank (125) and the hydrochloric acid aqueous solution cushion tank (126) may be used in the same cushion tank. You may use the cleaning drainage of the to-be-etched object.

Further, each detector and pipe may be directly provided in the etching tank (1) without providing the special control tank (2), but it is preferable to provide the control tank (2) in practical use.

[Examples] Example 1 A copper clad laminate for a printed circuit board was etched under the following conditions, basically using the apparatus shown in FIG.

Shower type etching machine as an etching tank (effective etching distance of 3 m, etching circulating fluid amount 800
) Using a specific gravity detector (Fuji Electric Co., Ltd.) and a redox potential detector (Fox UK redox potential detector)
The control tank equipped with was used.

Copper clad laminate for printed circuits (copper foil thickness 35μ, single-sided board,
The average removal rate of copper is 50%), the etching solution temperature is 55 ° C, the conveyor line speed is 3.3m / min, and the chemical is 40 ° Be ′.
Ferric chloride aqueous solution, 35 wt% hydrochloric acid, 38 wt% sodium chlorate aqueous solution, the potential of the oxidation-reduction potential detector is 510 ± 10 m
It was supplied so as to be 4.7: 7.1: 1 (molar ratio) while being automatically controlled to be v.

Also, water was automatically supplied so that the specific gravity became 1.36 ± 0.005.

When the ferrous ion concentration in the etching solution was measured hourly by titration with potassium permanganate (1/10 N), it was about 4.5 ml and the ferrous ion concentration was about 25 g / around.

On the other hand, the hourly chemical analysis value of total iron ions in the etching solution was 98 to 100 g /, so the amount of ferric ions was 73 to 75 g /, and Fe ⁺⁺ / Fe ⁺⁺⁺ = 0.33 It was maintained at ~ 0.34.

The copper ion in the etching solution during continuous operation is 90 to 100 g.
Although the concentration of / was high, the etching speed was continuously maintained at the original line speed of 3.3 m / min.

With this etching, about 90m ² of printed circuit board per hour can be continuously operated for an average of 8 hours a day for 3 months or more without any problems, the etching condition is good, and sludge is generated during etching. Moreover, cleaning after etching was extremely easy.

Comparative Example The same etching bath as in Example 1 was used, and etching was carried out using an aqueous solution of ferric chloride at 40 ° Be ′ containing a small amount of hydrochloric acid and no additional chemicals.

Initially, the conveyor line speed was 3.3 m / min, but as the copper ion concentration increased, the etching speed decreased, and after 6 hours the copper ion concentration was 70 g / and the line speed was 1.6 m / min. I canceled it.

With this etching, only a printed circuit board of about 65 m ² could be etched on average per hour, and the quality was rather unstable.

Sludge was generated in the etching solution, and the printed substrate after etching required sufficient cleaning.

Example 2 Using the same etching machine as in Example 1, a thin piece of stainless steel 316 was continuously etched at a liquid temperature of 45 ° C.

As the chemicals, 40 ° Be ′ ferric chloride aqueous solution, 35 wt% hydrochloric acid, 38 wt% sodium chlorate aqueous solution are automatically controlled so that the potential of the redox potential detector is 530 to 540 mv 9.0: 7.1. : 1.0 (molar ratio).

Also, water was automatically supplied so that the specific gravity became 1.38 to 1.40.

When the ferrous ion concentration in the etching solution was measured every one hour by titration with potassium permanganate (1/10 N), it was about 4.5 ml and the ferrous ion was about 25 g / around.

On the other hand, since the chemical analysis value of the total iron ions in the etching solution per hour was around 120 g /, the ferric ion concentration was 9
It was around 5g /, which means that Fe ⁺⁺ / Fe ⁺⁺⁺ = 0.26 was maintained.

The etching speed during continuous operation is 26 μm / min.
(Total on both sides, 13 μm on one side), no sludge was generated, and the etching state was good.

[Effects of the Invention] The effects of the present invention are that the equipment cost and the operation cost are relatively low, the etching rate is fast, and can be maintained constant, and as a result, a printed circuit board of constant quality can be manufactured with high productivity. It is intended to provide a continuous etching method for copper or the like with a ferric chloride solution.

[Brief description of drawings]

FIG. 1 shows an example of an apparatus for carrying out the present invention. In the figure: 1 ... Etching tank, 2 ... Control tank, 3 ...
… Specific gravity detector, 3 ′… detector, 4 …… ferrous iron ion detector, 4 ′ …… detector, 5,5 ′, 6 …… mixed supply pipe of ferric chloride aqueous solution and hydrochloric acid aqueous solution, 7, 7 '... Chloric acid aqueous solution supply pipe, 8 ... Water supply pipe, 100 ... Pump, 101, 10
2 ... Circulation pipe, 103 ... Pump, 105 ... Ferric chloride aqueous solution tank, 106 ... Hydrochloric acid aqueous solution tank, 107 ... Chloric acid aqueous solution tank, 109 ... Overflow pipe, 115 ... Ferric chloride Aqueous solution pump, 116 …… Hydrochloric acid solution pump, 117 ……
Chlorate solution pump, 118 …… water pump, 125, 126, 1
27 …… Cushion tank.

Claims (3)

[Claims] 1. A method for continuously etching a metal with a ferric chloride solution, wherein 6 to 9 mol of hydrogen chloride and ferric chloride are added to 1 equivalent of a chlorate selected from sodium chlorate, potassium chlorate and calcium chlorate. An etching method characterized in that an aqueous solution containing diiron 2.5 to 15 mol is supplied as a chemical. 2. The specific gravity of the etching solution is 1.30 to 1.45, and the concentration ratio of ferrous ions and ferric ions in the etching solution is Fe.
The etching method according to claim 1, wherein the concentration of ferric ion in the etching liquid is maintained at 40 g / or more, with ⁺⁺ / Fe ⁺⁺⁺ = 0.15 to 0.50. 3. An etching bath and a control bath in which the etching bath and the etching liquid are movably provided,
The specific gravity and the ferrous ions formed in the control tank were measured or detected chemically or physically, and a chlorate-containing aqueous solution, a hydrochloric acid aqueous solution and a ferric chloride-containing aqueous solution were provided in an etching tank, a control tank or separately. The etching method according to claim 2, wherein a device for supplying the cushion tanks individually or by mixing a part thereof is used.