Accumulation and Analysis of Cuprous Ions in a Copper Sulfate Plating Solution

We have succeeded in quantifying monovalent copper concentration in plating solution using this simple method. By quantification, monovalent copper is a parameter that anyone can use. Our research will contribute to future plating technology.

If the neutralizing and BCS solutions are prepared beforehand. Simply mix the plating solution and measure it, so even at the manufacturing site measurement of monovalent copper becomes possible. We monitor the variation of monovalent copper in the plating bath.

Which resulted in improvement of the manufacturing process. Our aim is prediction of coating quality based on optical evaluation of solution. Optical methods are extremely suitable for production sites.

It will be a key device for creating manufacturing technology to IoT. To begin this procedure add a stir bar to a 200 milliliter beaker. Pour 150 milliliters of copper sulfate plating solution into the beaker.

And leave the plating solution at room temperature for one hour. Begin the flow of nitrogen gas at a flow rate of 85 milliliters per minute. Insert the tube before the nitrogen gas into the beaker.

And deoxidize the plating solution for at least 30 minutes. Using metal scissors add a 3 millimeter thick copper plate to 9.5 centimeters by two centimeters. Add a 1 millimeter thick platinum plate to the same dimensions.

Wash both the copper and platinum plates with ethanol. And then rinse with pure water. Use nitrogen gas to dry the plates.

Attach the plates to the fixing jig. Insert the jig inside the beaker and fix it in place. Connect the electrode of the copper plate to the positive end of the power supply.

And connect the electrode of the platinum plate to the negative end. Turn on the power supply at a constant current of one ampere. After 10 minutes turn off the power and stop the stirrer.

Let the solution rest for approximately 10 minutes to let the particles settle. Set out two absorption measurement cells and add a stir bar to each. Then pour in 2.5 milliliters of neutralization solution.

And 219 microliters of BCS solution. Prepare two cells for sample and reference. Mix in 22 microliters of plating solution sample and stir for 20 minutes.

The neutralizing solution will develop an orange color. Mix the non-electrolysis plating solution with the reference. The color of this solution will be blue.

Use a UV-Vis Spectrophotometer to measure the absorption spectra of the sample solution in the wave length range of 400 to 600 nanometers. Use a UV-Vis Spectrophotometer with a time measurement function of more than 20 minutes for injection measurement. The spectrophotometer should have a sample chamber cover with a syringe port.

And a thermostat cell holder with a stirrer. Prepare a neutralizing solution and a BCS solution in a cell containing a stirrer bar. Set the cell in the holder and turn the stirrer rotation speed to maximum.

In the time measurement mode, set the measurement time to 1270 seconds at 485 nanometers and start recording. One minute after starting use a pipette to inject 22 microliters of the plating solution sample from the syringe port of the chamber cover. Acquire reaction curves for copper one and BCS.

The concentration of copper one in the plating solutions can be determined from the absorbance of the copper one to BCS key laid at 485 nanometers. The absorption spectra of representative plating solutions are shown here. The copper one concentration tends to increase from zero minutes to 10 minutes depending on the electrolysis time.

A curve simulating the change and the absorbance of the color reaction of the electroplating solution is shown here. From the simulation the parameters related to copper one accumulation are quantified. Then the simulation value of the component that reacts instantaneously, A zero in the plating solution that was electrolyzed is plotted.

While the value of A0 did not change significantly until after four minutes of electrolysis, an increase corresponding to electrolysis time is seen between six and 10 minutes. Each electrolysis solution is plated onto copper plates to investigate the influence of copper one on the quality of copper plating such as roughness and shape. From the SEM images, the coating surface structures from using the zero minute and four minutes electrolysis solutions are nearly indistinguishable.

After six minutes of electrolysis plating some swelling on the surface can be seen. While after 10 minutes there is a large chunky roughness. Compared with general color reaction it takes time to form a complex or monovalent copper and BCS or accurate measurement still for at least 20 minutes.

The injection method is used for more accurate determination. Along with the time response of the color reaction. It's also possible to analyze the retention component of monovalent copper.

Traditionally it has been thought that monovalent copper does not exist stably in liquid solution. We made the monovalent copper in the plating solution visible.