JPH0518057B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a method for measuring changes in metal corrosion rate due to changes in liquid composition in a corrosive liquid, and an apparatus therefor.

(b) Conventional technology Conventionally, metal corrosion rates in metal-corrosive liquids have been measured by immersion measurement by observing changes in weight and appearance of the metal to be inspected (test metal), or by polarization of non-dissolving metals. There are electrochemical measurement methods that measure oxidation and reduction changes in a specific fluid as the dissolution rate of the metal being tested using the electrical potential difference (ORP) generated during the test. Similarly, devices using these measurement methods have been used for etching.

The etching process is a process in which copper is removed from areas other than those protected by the etching resist using a liquid (etching solution) that corrodes the copper. Only after this process is the printed wiring board completed, is the etching process completed. Printed circuit boards have become indispensable in the current social movement that demands electronics, and the role of the etching process in the manufacture of printed circuit boards as electronics progresses. It's getting better. As the demand for printed circuit boards increases, etching methods shift from batch etching to automatic control that allows for continuous operation. Against this background, the etching solution itself has shifted to one that can be used continuously. In order to use the etching solution continuously, it is important to keep the solution composition constant.

〔As an example〕

In case of cupric chloride etching solution Cu＋CuCl ₂ →2CuCl…… (1) 2CuCl＋2HCl＋H ₂ O ₂ →2CuCl ₂ +2H ₂ O…… (2) In case of alkaline etching liquid Cu＋Cu(NH ₃ ) ₄ Cl ₂ →2Cu( NH ₃ ) ₂ Cl... (1) 2Cu(NH ₃ ) ₂ Cl+2NH ₄ Cl+2NH ₄ OH+1/2O ₂ →2Cu(NH ₃ ) ₄ Cl ₂ +3H ₂ O... (2) Equation (1) shows the etching process. show. Copper corrodes into divalent copper and changes to monovalent copper. Equation (2) shows the regeneration process. The liquid quality changed to monovalent copper is regenerated into divalent copper by adding each regeneration aid.

If the etching process and regeneration process are always constant, the etching solution can be used continuously. By measuring the corrosion rate of copper or the like as the composition of the etching solution changes, it becomes possible to keep the composition of the etching solution constant.

Conventional methods for controlling the composition of etching solution include: determining the corrosion state of the product and the chromaticity of the etching solution using human vision; controlling changes in the liquid composition due to PH with a PH meter; and controlling changes in liquid composition due to specific gravity. A method to control liquid composition changes due to chromaticity using a hydrometer, a method to control liquid composition changes due to chromaticity using a suitability test, and a method to control liquid composition changes due to oxidation and reduction potential using an ORP meter. Control methods were used.

(c) Problems to be Solved and Used by the Invention The immersion measurement method for measuring the metal corrosion rate in a specific fluid requires time to judge the results and is not suitable for continuous measurement. Measuring the oxidation/reduction potential in a fluid, which is an electrochemical measurement method, is affected by PH and temperature changes in the fluid, and is subject to current conditions.
Measuring the dissolution rate of the metal under test with an ORP electrode requires a narrow measurement range, and continuous measurement results in a large error range. Since the ORP electrode is not a soluble metal, it is difficult to directly sense the potential difference that occurs in the fluid. Furthermore, the method of determining the liquid composition control of the etching solution using human vision causes errors depending on the physical condition of the person at the time, and it is not possible to always set a constant standard. Control using a PH meter allows control within the measurement range, but in actual equipment the value is outside the measurement range of the PH meter. Although it can be measured by operations such as dilution, it takes time for continuous measurement and is not suitable. Control using a hydrometer is possible if the etching solution has a single composition, but errors occur if the etching solution has a complex composition. In control using an optical meter, the concentration can be determined based on the shade of color, so any colored substance (such as a solution) is sufficient, but if the substance is colorless and transparent (such as a liquid solution), an error will occur. Control by suitability tests provides the best judgment for knowing the liquid composition, but it is not suitable for continuous measurement because it takes time to make judgments. Control by ORP meter is
Since it measures the ratio of oxides and reduced substances, the measurement range is narrow, and it is affected by pH and temperature changes, resulting in errors during continuous measurements. Due to the nature of ORP, it can be measured by chloride etching, but with strong oxidizing power, no potential difference is observed, making it difficult to see a correlation, which puts restrictions on its use. because,
Since the current ORP electrode is not a soluble metal, it is difficult to directly sense the potential difference that occurs in the etching solution. For example, although control accuracy is improved, the scale and cost of the control system increase, and the system becomes quite complex, requiring careful attention and skill each time it is used. Since the above control method fundamentally does not involve direct measurement or is difficult to measure continuously, it is difficult to use it as a control value for control in corrosive fluids such as etching solutions, and it is only one standard or guideline.

When controlling the liquid composition using various measuring instruments in the actual equipment, the measurement state due to changes in the concentration of the etching liquid will appear to be the same as the stable liquid composition of the etching liquid according to the set value (value when etching is good). However, in the etching process of a precision board where many conductors are arranged with a width of about 0.1mm, direct measurement is not possible.
Alternatively, slight errors caused by difficulty in identifying continuity may cause excessive addition of regeneration aid, worsening the etch factor, easily causing corrosion conditions such as thinning of the conductor width, and causing over-etching and poor etching. .

This invention directly detects changes in etching speed due to changes in the composition of the etching solution as changes in the dissolution current of a sample electrode made of the metal to be etched,
It is an object of the present invention to provide an etching control device that can adjust the composition of an etching solution based on this.

(d) Means for Solving the Problems This invention provides a liquid tank in which an etching solution is stored or distributed, a first electrode made of a metal to be etched that is immersed in the etching solution, and a non-corrosive second electrode. An electrode, an ammeter or voltmeter that electrically couples these to measure the current flowing between the two electrodes or the potential difference between the two electrodes, and detects the components of the etching solution based on the detected value of the ammeter or voltmeter. It is characterized by comprising a replenishment means for replenishing.

(e) Operation In the etching control device of the present invention, a first electrode made of the metal to be etched and a non-corrosive second electrode are immersed in an etching solution. As the non-corrosive electrode, platinum, gold, carbon, titanium, tungsten, tantalum, etc. can be used.
The first electrode is corroded by the etching solution and dissolves into the solution. The first electrode and the second electrode are electrically connected by an ammeter or a voltmeter. Therefore, the ammeter or voltmeter detects a current/voltage proportional to the amount of corrosion of the first electrode.
That is, since the corrosion of metal by the etching solution is several hundred times faster than normal corrosion, this can be detected simply by connecting an ammeter or voltmeter between the electrodes. Furthermore, since the first electrode is made of the metal to be etched, the current/voltage generated is exactly proportional to the etching speed.
No conversion is necessary. The replenishing means replenishes the components of the etching solution based on the detected current/voltage values. In the case of a cupric chloride etching solution, the components of the etching solution include hydrochloric acid, hydrogen peroxide, water, and the like. When the etching ability decreases, cupric chloride is reduced and the etching ability is restored by replenishing hydrochloric acid or hydrogen peroxide. This control is possible only by measuring the current/voltage between the electrodes.

Furthermore, if the concentration of the etching solution increases and the specific gravity increases, water may be replenished to maintain the concentration within a predetermined range.

This makes it possible to accurately measure the etching rate under any conditions and control the etching rate to be constant based on this measurement.

(f) Embodiment FIG. 1 is a diagram showing the configuration of an etching control device according to an embodiment of the present invention. In the drawing, A indicates an etching machine. Etching liquid 1 is stored in liquid tank B. The liquid tank B is provided with a metal to be inspected (copper) electrode 2 and a comparison substance (carbon, etc.) electrode 3.
These are connected to an ammeter/voltmeter 4. A printed circuit board with a pattern resist is carried by a conveyor C, and an etching liquid nozzle is provided on the conveyor C. Etching liquid 1 sent via pressure pump 5 is discharged from this nozzle. This etching liquid 1 corrodes the substrate. The etching solution 1 that has passed through the conveyor C returns to the solution tank B, but due to the corrosion of the copper on the substrate, divalent copper changes to monovalent copper. As this cycle progresses, the etching solution 1 in the bath B gradually changes from divalent to monovalent copper. As the metal 2 to be inspected in the etching solution 1 corrodes, the ammeter/voltmeter 4 comprising the comparison substance 3 shows respective measured values, and as the etching power of the etching solution 1 decreases, the measured values also change. The ammeter/voltmeter 4 reads changes in current and voltage values as the etching ability changes. In accordance with such changes, the ammeter/voltmeter 4 drives the regeneration aid injection pump 7 to add the regeneration aid 6 into the liquid tank B. That is, this ammeter/voltmeter 4 is a device that also has a control function.

For the ammeter/voltmeter 4, add HCl or H ₂ O ₂ (FeCl ₃ in the case of an alkaline etching solution) and add the etching solution 1 with specific gravity adjustment water so that the current/voltage value becomes the predetermined value. Adjust the specific gravity.

Based on the measurement results of actual equipment that performs such control, it is possible to manage the composition of the etching solution, stabilize the etching process, improve product quality, reduce defective rates, increase production volume, prevent excessive addition of regeneration aids, and improve production. This demonstrated the effect of reducing costs.

In addition, although copper was used as the metal to be tested in the etching that corrodes copper, the metal to be tested, that is, the sample electrode, can be used for all metals for which the metal corrosion rate is to be measured. Although a carbon rod was used, it can be used as a comparison material for any current-carrying material that can serve as a counter electrode. In Figure 1, the metal to be inspected and the comparative substance are individually immersed in the etching solution for measurement, but the metal to be inspected and the comparative substance can also be integrated into one electrode, and the calculation display section is performed by a computer and displayed. It is also possible to increase the speed and set each condition using a program.

(g) Effects of the Invention As described above, according to the present invention, it is possible to directly and accurately measure the corrosion rate of any metal in any metal-corrosive liquid and any metal to be inspected. Therefore, by applying this invention, even when etching a precision substrate in which a large number of conductors are arranged with a width of about 0.1 mm, the etching process can be performed using a stable liquid composition, and the addition of regeneration aid can be avoided due to etching defects and over-etching. It has the effect of keeping the amount constant.

Furthermore, since the device has a simple structure, it can be installed anywhere, and can be installed on existing equipment without damaging existing equipment.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an etching control device according to an embodiment of the present invention. A...Etching machine, B, C...Liquid tank, conveyor, 1...Etching liquid, 2...Metal to be inspected, 3...
Comparative substance, 4... Ammeter and voltmeter, 5... Pressure pump, 6... Regeneration aid, 7... Regeneration aid injection pump.

Claims (1)

[Claims] 1 A liquid tank for storing or distributing etching liquid;
A first electrode made of a metal to be etched and a non-corrosive second electrode are immersed in the etching solution, and these are electrically coupled to measure the current flowing between the two electrodes or the potential difference between the two electrodes. An etching control device comprising: an ammeter or a voltmeter; and a replenishing means for replenishing the components of the etching solution based on the detected value of the ammeter or voltmeter.