This application claims the benefit of the filing date under 35 U.S.C. §119(a)-(d) of Chinese Patent Application No. 201610018003.7, filed on Jan. 12, 2016.
The present invention relates to chemical plating, and more particularly, to quantifying the activity of a chemical plating solution.
During chemical plating, the activity of a chemical solution plays a crucial role in the quality of the resulting chemically plated product. The activity of the chemical solution determines the starting time of the chemical plating and the adjustment of the operation parameters in the production process. A starting time that is too early or too late will result in not only products with defects, due to issues such as skip plating and overflow plating, but also low productivity. Additionally, during the production, the operation parameters, such as the chemical composition, the temperature, the pneumatic blending, and the like, must be adjusted according to the solution activity. It has been shown in practice that wrong estimation of the activity during production not only results in a high proportion of defective products but also shortens the life-time of the chemicals.
Generally, a higher activity corresponds to a faster reaction. At present, the bubble observation method is used as the traditional method for estimating the solution activity in the production process. More bubbles at the surface of the reaction represent a higher solution activity. This estimation method is subjective and crude, depending primarily on the production experience of the operator to estimate and adjust the solution activity, lacking objectivity and the ability of quantitative measurement. Hence, traditional methods often result in wrong estimation and product defects. Although generally a weighing method is used in the lab to estimate the average rate of the chemical reaction of a solution during a period, it takes a relatively long time and has no real value in the production. There is still no method that can quantitatively measure the instant activity of a solution on the production line, and there is still no method or apparatus that can quantitatively measure the instant activity of a chemical plating solution on the production line to control the production process. There is therefore a need for a method and an apparatus that can measure the activity of a chemical plating solution in industry rapidly and accurately.
Electrochemical impedance spectrum (EIS) is an electric measurement method which uses the potential of a small amplitude sine wave as a perturbation signal. In EIS, the interference is small, information for the interface state and process is provided, the process of data analysis is relatively simple, and the results are reliable.
CN102227628A proposes a method for controlling the concentration of a stable additive in an electrolyte solution for the electroless plating of a metal and metallic alloy by using a voltammetric measurement. Results from the electrochemical impedance spectrum (EIS) of the EDTA-based electrolyte solution for the electroless plating of copper and the constant-coulomb-measurement are provided (J. Electrochem. Soc. 135 (1988) 1645-1650). The concentration of the stable additive 2-mercaptobenzothiazole on the platinum electrode was measured by evaluating the double layer capacitance and the polarization resistance.
CN101831641B proposes an acidic zincating solution and zincating method for a magnesium-aluminum alloy. The EIS measurement is performed for that system, and an equivalent circuit, which comprises the solution resistance, the membrane capacitance, the membrane resistance, the double layer capacitance at the solution/electrode interface, and the electrochemical reaction resistance, is obtained by fitting. According to the analysis of each element of the equivalent circuit, the corrosion resistance of the substrate is estimated.
No method for characterizing the activity of a chemical plating solution by means of the charge transfer resistance value in EIS is described in the prior art.
An object of the invention, among others, is to provide a method and apparatus for rapid and accurate measurement of the activity of a chemical plating solution. The disclosed method comprises performing an electrochemical impedance spectrum (EIS) measurement on one or more chemical plating solutions in the chemical plating system, processing data for each EIS measurement result to obtain a corresponding charge transfer resistance value, obtaining a correspondence between the activity and the charge transfer resistance value in each chemical plating solution, and quantifying the activity of each chemical plating solution in the chemical plating system using the correspondence to the charge transfer resistance value.
The invention will now be described by way of example with reference to the accompanying Figures, of which:
Exemplary embodiments of the present disclosure will be described hereinafter in detail with reference to the attached drawings, wherein like reference numerals refer to like elements. The present disclosure may, however, be embodied in many different forms and should not be construed as being limited to the embodiment set forth herein; rather, these embodiments are provided so that the present disclosure will be thorough and complete, and will fully convey the concept of the disclosure to those skilled in the art.
The present invention provides a quantification method of the activity or deposition of a chemical plating solution. The quantification method quantifies the activity of a chemical plating solution by the charge transfer resistance value calculated from the result obtained from an EIS measurement performed in the chemical plating solution. The quantification method of the present invention will be described with reference to an exemplary embodiment shown in
A system performing an EIS measurement according to the invention is shown in
In the EIS measurement, a three-electrode system is used with a working electrode, an auxiliary electrode and a reference electrode as shown in
The three electrodes are immersed in the chemical plating solution as shown in
Meanwhile, in the embodiment shown in
The EIS calculations are performed on the Computer shown in
Specifically, impedance data and the Nyquist diagram at different alternative frequencies can be obtained from the EIS measurement. According to the Nyquist diagram, the equivalent circuit of the electrochemical system is fitted, and thus the charge transfer resistance can be derived. The above-mentioned data processing process for the EIS measurement result is performed generally by using computer software stored in a non-transitory computer readable medium on the Computer. The impedance data are inputted to the computer software, then the equivalent circuit diagram matching the Nyquist diagram is chosen, and thereby the value of each circuit element (including Rct) therein can be calculated by the software. An example of the computer softwares that may be used in the present invention is ZSimpWin Demo provided by the Echem Software company.
For the chemical plating system shown in the exemplary embodiment of
The fitted numerical values of the Rct in the circuit diagram by the software are recorded, and the fitting results from the exemplary embodiment of
The activity of a chemical plating solution, according to the invention as described above, can consequently be characterized by the charge transfer resistance Rct value in the chemical plating solution equivalent circuit, which is, after the chemical plating solution has been subjected to the EIS measurement, obtained from the results of the measurement. Specifically, for a chemical plating solution system, when the activity of the solution is changing, the Rct value thereof will change therewith, and the Rct value corresponds to the solution activity one-to-one. Many factors, such as the composition, the temperature, the flow of the solution, or the like, can affect the activity of the chemical plating solution in the process of the chemical plating. However, as long as the solution activity is constant, the Rct value, to which the activity corresponds, is constant. That is to say, the same Rct value represents the same solution activity provided the same chemical plating system.
During the plating of a sheet, operation parameters of the plating, such as the aforementioned composition, the heating temperature, the stirring speed, and the degree of pneumatic blending of the chemical plating solution are read by the Computer and adjusted by the Computer according to the determined Rct value representing the solution activity to optimize the activity and properly plate the sheet. Furthermore, based on the determined Rct value, a starting time of the chemical plating can also be determined and initiated by the Computer.
The correspondence between the activity and the charge transfer resistance value of a chemical plating solution, or in particular, the correspondence between the deposition rate and the charge transfer resistance value of the chemical plating solution, can be represented in various forms. For example, their relationship may be represented graphically by plotting and fitting. Alternatively, their functional relationship can be obtained by fitting via functions. The correspondence also can be listed as a numerical table, or be stored as a database that can be used by a computer.
Those skilled in the art can understand that such a quantification method exhibits various implementations in practice. For example, when an operator has a first chemical plating solution having an ideal deposition rate or activity, the charge transfer resistance value representing this ideal activity can be obtained by the quantification method. Further, whether the charge transfer resistance value of a second solution having an unknown activity in the same system deviates from this value corresponding to the ideal activity is used to estimate whether the second solution has an ideal activity. The charge transfer resistance values of two solutions in the same system can be compared to determine whether the respective activities of the two solutions are essentially the same.
The correspondence between the activity and the charge transfer resistance value of the chemical plating solution is represented by the correspondence between the deposition rate and the charge transfer resistance value of the chemical plating solution. This correspondence may be obtained by performing the EIS measurement and the weighing method for the chemical plating solution at the same time during the deposition process. As mentioned above, typically, the charge transfer resistance decreases, as the reaction activity increases. That is to say, the charge transfer resistance decreases, as the deposition rate increases.
In addition to serving as criteria for a single point, correspondences between a plurality of activities and charge transfer resistance values can be used for establishing a quantitative description of the chemical plating system as a whole. A charge transfer resistance value exhibits essentially a trend of monotonical decreasing as the activity increases. Therefore, for example, given the charge transfer resistance values to which two activities correspond, respectively, it can be estimated that a solution having a charge transfer resistance value between these two values in the same system would also essentially have an activity between these two activities. If sufficient quantification measurement points are obtained in the system, for those skilled in the art, the binary correspondence can be shown graphically by a graph, be shown as a function by function fitting, or be shown as a numerical table or a database, for various uses relating to the specific value of the activity.
In another aspect, the present invention provides a method for quantitatively measuring the activity of a chemical plating solution in a chemical plating system. The method comprises obtaining previously the correspondence between the activity and the charge transfer resistance value of a chemical plating solution, which is in the same chemical plating system as the chemical plating solution to be measured; performing an EIS measurement on the chemical plating solution to be measured, and performing a data processing, to obtain the charge transfer resistance value; and comparing the charge transfer resistance value of the chemical plating solution to be measured with the correspondence, to quantitatively measure the activity of the chemical plating solution to be measured.
An apparatus for quantitative measurement of the activity of a chemical plating solution according to the invention is shown in
The comparison-output module compares the charge transfer resistance value obtained from the data processing module with an existing correspondence between the activity and the charge transfer resistance value of the chemical plating solution, and outputs the activity of the corresponding chemical plating solution. Generally, in the comparison-output module, the existing correspondence between the activity of a chemical plating solution and the charge transfer resistance value can be stored as a form that can be treated by a computer. The comparison-output module also adjusts the operation parameters of the plating based on the determined activity, including adjusting the composition, the heating temperature, the stirring speed, and the degree of pneumatic blending of the chemical plating solution, to optimize the activity. The comparison-output module also determines and initiates a starting time of the chemical plating.
Advantageously, in the method and apparatus for measuring the activity of a chemical plating solution according to the invention, the charge transfer resistance value obtained from the EIS measurement can be used to determine the activity of a solution. The EIS measurement and the data processing take a very short time, and therefore, the method and apparatus according to the invention can trace the state of the activity of the solution during the production efficiently and conveniently. After obtaining the relationship between the charge transfer resistance value and the deposition rate by using the EIS measurement and the weighing method at the same time, the corresponding deposition rate can be directly known from the charge transfer resistance value obtained by the EIS measurement and the data analysis of other solutions. By contrast, previous quantification methods for the activity of a solution are mainly non-instant measurement methods, such as the weighing method which requires removing the plated substrate from the solution, which takes a long time and interrupts production.
Number | Date | Country | Kind |
---|---|---|---|
201610018003.7 | Jan 2016 | CN | national |