JPH0331789B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to an apparatus for accurately stabilizing the concentration of copper ions in a chemical copper plating solution. [Prior Art] Conventionally, the concentration of the main components of chemical copper plating solutions has been controlled by trial and error. In other words, the total surface area of the object to be plated is roughly estimated, the consumption of the main component is calculated from the plating speed and the plating time based on factors created by the manufacturer, and a predetermined amount is replenished. However, a more accurate concentration control method has been to perform intermittent chemical analysis to adjust the concentration. When insulating materials such as inorganic and organic materials are coated with metal to form composite materials, chemical copper plating is a pre-treatment that uses the good electrical conductivity of metallic copper to impart conductivity to the insulating material. It was hot. In this case, there was no need to place importance on the mechanical properties of the copper plating film, and a method that was easy for the customer to manage, although less accurate than the above-mentioned control method, was sufficient. [Problem to be solved by the invention] However, recently, epoxy resins, phenolic resins,
The use of chemical copper plating to form conductors on insulating materials such as ceramics has become more common. In such cases, it is necessary to have not only electrical properties as a conductor but also mechanical properties as a metal to a certain extent. However, since the properties of the plating film are significantly affected by the concentration of the main components of the plating solution, it is natural that plating cannot be performed with good reproducibility and reliability using the trial-and-error management method described above. It is. Therefore, in order to eliminate the drawbacks of the above methods, it was considered to perform continuous automatic analysis to control the concentration. When concentration management is automated, changes in concentration must be input as changes in potential and current. Instrumental analyzers are used for this purpose, but they are generally expensive and complicated, and the coexistence of compounds, ions, etc. other than the target component causes interference and reduces accuracy. For example, the colorimetric method and equipment used to control copper ion concentration in chemical copper plating solutions are not only expensive, but also the pH of the plating solution, the concentration of compounds and ions other than copper ions, and the concentration of compounds and ions present in the plating solution. It was strongly influenced by hydrogen gas bubbles, etc., and the error was large. The purpose of the present invention was to solve the above-mentioned drawbacks in stabilizing the copper ion concentration of the conventional chemical copper plating solution. To provide a device for stabilizing copper ion concentration. [Means for Solving the Problems] In order to achieve the above object, the present invention provides means for collecting a chemical copper plating solution containing at least copper ions and a chelating agent from a plating tank at a flow rate of V, A first extraction solution containing Fe or Cu ions at a concentration Ct ₁ to form a chelate compound with a chelating agent, and a desired total chelating agent concentration nC, Cu concentration C, and Ct ₁ in the chemical copper plating solution. means for collecting the liquid from the first titrant at a speed Vt ₁ set so that Ct ₁ Vt ₁ , which is determined from the relationship between a first mixing means for mixing a first titrant; a copper ion detection cell that includes an insoluble electrode and a reference electrode and is coupled to the first mixing means; and a redox detected from the copper ion detection cell. An apparatus for stabilizing the concentration of copper ions in a chemical copper plating solution, characterized by comprising means for replenishing copper ions to the plating tank based on the electric potential. [Function] Next, copper ions of the chemical copper plating solution according to the present invention,
The concentration stabilizing device will be described. Chemical copper plating solution consists of copper ions, copper ion chelating agents, complexing agents and reducing agents, and alkali metal hydroxides as PH adjusting agents. Copper ions are chelated and complexed by copper ion chelating agents and complexing agents, and attacks are prevented by reducing agents. Copper ions are consumed during the plating reaction and must be maintained at an optimal concentration at all times. In order for copper ions to be chelated and complexed in a sufficiently stable manner, the copper ion concentration must be adjusted to a certain extent according to the stability constant between the copper ion and the copper ion chelate and copper ion complexing agent used. The above-mentioned chelates and complexing agents are added, and since these are expensive chemicals, they are generally used at a concentration of 1.5 to 5 times the copper ion concentration. The reducibility of copper ions in chemical copper plating largely depends on the copper ion concentration and the concentration ratio of copper ions, chelates, and complexing agents, that is, the stability of copper ion chelate and complex formation. Therefore, concentration control of copper ions, copper ion chelates, and complexing agents is important in obtaining a high-quality plating film.
It is extremely important. The present invention is an apparatus for stably controlling copper ion concentration with sufficient precision using the following method.
For example, when ethylenediaminetetraacetic acid (hereinafter abbreviated as EDTA), ethylenediaminepentaacetic acid (hereinafter abbreviated as DTPA), etc. are used as a chelating agent,
Many metal ions, including copper ions, react at a molar concentration ratio of 1:1. That is, this reaction is a chelate-forming reaction, and the reaction product is a metal chelate compound. Now, if the copper ion concentration in the chemical copper plating solution is C moles and the molar concentration of the chelating agent is n times nC moles, the copper ions will be completely chelated. For example, if an insoluble electrode such as platinum or gold is used, the gap between monovalent copper ions (hereinafter abbreviated as Cu〓) and divalent copper ions (hereinafter abbreviated as Cu〓) contained in trace amounts of plating solution as impurities As the potential of E ₍₁₎ = 0.153−0.05921og {K(n
−1) [Cu〓]}...(1) is obtained. However, K is the stability constant between Cu〓 and EDTA, and [Cu〓] indicates the molar concentration of Cu〓 in the plating solution. Now, a constant concentration of trivalent iron ions (hereinafter referred to as
Consider the case where the solutions (abbreviated as Fe〓) are gradually mixed. Trivalent iron ions form very stable chelates with chelating agents, which are more stable than many divalent metal ions. Therefore, Fe〓 from outside
As the mixing progresses, the concentration difference between Cu and the chelating agent (n-1) When the mixed amount of Fe slightly exceeds the C mole, the chelated Cu is removed from the chelating agent. Dissociates to produce free Cu〓. Therefore, the potential obtained by the insoluble electrode at this time is E ₍₂₎ = 0.153 + 0.05921og {[Cu−
〓〕／〔Cu〓〕}……(2). Furthermore, when the mixing of Fe〓 progresses and the amount of Fe〓 slightly exceeds the amount (nC mol) required to form a chelate with all the chelating agents, free Fe〓 will be present, and a trace amount of Fe〓 will be present as an impurity. The potential between the included divalent iron ions (hereinafter abbreviated as Fe〓) is E ₍₃₎ = 0.771 + 0.05921og {[Fe〓
]/[Fe〓]}...(3). In other words, the total amount of Fe when the potential changes from E ₍₂₎ to E ₍₃₎ is the total amount of chelating agent: nC
Equal to moles. The total amount of Fe when the potential changes from E ₍₁₎ to E ₍₂₎ is equal to the total amount of free chelating agent: (n-1) C moles. The difference in these amounts of Fe〓, nC−(n−1)
From C=C, the total Cu concentration (C moles) can be determined. When the principle of this potentiometric titration method is used as an automatic control method, the following method is used. Total Cu concentration: C mole, total chelating agent concentration:
A chemical copper plating solution consisting of nC moles is sampled in a constant flow path by a micropump. Next, an Fe solution slightly thicker than (n-1) C mol is sampled at the same flow rate and mixed. This mixed solution is introduced into a microcapacitance detection cell consisting of a suitable reference electrode and an insoluble electrode. The electrode potential detected here is E ₍₂₎ described above. The electrode potential measured here may be a simple equilibrium potential, or
It may be a polarized potential. If Cu〓 is consumed in the chemical copper plating reaction and the concentration is lower than C mole, we get E ₍₁₎ . Therefore, it is sufficient to replenish Cu〓 using an appropriate control device until the potential of E ₍₂₎ is detected. An Fe solution having a mole of slightly less than C is mixed into the mixed solution exiting the detection cell at the same flow rate.
This liquid mixture is introduced into a detection cell having the same configuration as the detection cell described above. The electrode potential detected here is E ₍₂₎ . If the chelating agent concentration becomes lower than nC mol because the plating solution adheres to the body to be plated and is carried out of the plating tank, E ₍₃₎ is obtained. Therefore, until the potential of E ₍₂₎ is detected,
The chelating agent may be replenished using a suitable control device. [Example] Next, the present invention will be specifically explained using Examples. Example 1 Plating liquid composition and conditions CuSO ₄・5H ₂ O: 14 g EDTA-2Na: 41.5 g NaOH: 12 g 37% formalin: 10 ml Additives: a small amount of water...the total amount is 1 Plating temperature 70℃ Plating Area 1 dm ² / Plating speed 2.5 μ/h Sampling speed 20 ml/h 1st titration, 2nd titrant composition, conditions Titrant composition Fecl ₃ : 18.1g Hcl: 10ml Water...amount with the total as 1 First titration conditions Set potential +0.28V Reference electrode Saturated Amane electrode working electrode 0.3φ platinum wire titration rate 20ml/h Second titration condition setting potential +0.54V Reference electrode Saturated Amane electrode working electrode 0.3φ platinum wire titration rate 20ml/h Above configuration The plating solution and titration solution were sampled, detected, and automatically controlled by the copper ion concentration stabilization device shown in the figure. That is, as mentioned above, the plating liquid is sampled from the plating tank 1 using the multiple tube pump 2 at a sampling rate of 20 ml/h, and first from the first titrant liquid tank 3 at a sampling rate of 20 ml/h.
The first titrant sampled at 20 ml/h was mixed in T-tube 4-1. The mixed liquid is saturated with a saturated electrode 5
The electrode potential was measured in a copper detection cell 7 consisting of a copper electrode 6-1 and a platinum electrode 6-1. The measured electrode potential is input to the copper control device 8, and the set potential of the copper control device is
When the voltage is lower than 0.28V, the solenoid valve 9-1 (a replenishment pump may be used instead of the solenoid valve) opens, and the concentrated copper ion solution is replenished from the copper replenishment tank 10 to the plating tank 1. When the electrode potential measured by the copper detection cell 7 became higher than 0.28V, the solenoid valve 6 was closed and replenishment was stopped. In the above copper ion concentration stabilizing device, the relationship between the copper ion concentration converted to CuSO ₄ .5H ₂ O in the plating solution and the measured potential was determined as shown in Table 1. At the set concentration (14 g/), the set potential (0.28 V) was obtained, and an S-shaped relationship was obtained with this as the equivalence point. When the measured potential showed 0.3V, the copper ion concentration was 14.15 g/, and when it showed 0.25 V, it was 13.75 g/. In other words, it was found that the copper ion concentration could be measured by detecting whether the measured potential was larger or smaller than the set potential of 0.28V.

〔Effect of the invention〕

As described above, the device for stabilizing the copper ion concentration of a chemical copper plating solution according to the present invention has the effect of being able to manage stabilization more easily and accurately at a lower cost than the conventional technology.

[Brief explanation of the drawing]

The figure is a diagram showing the configuration of a device for stabilizing the copper ion concentration of a chemical copper plating solution according to the present invention. 1... Plating tank, 3... First titrant tank, 5-
1, 5-2...Saturated sweet electrode, 6-1, 6-2...
...Platinum electrode, 7...Copper detection cell, 8...Copper control device, 10...Copper supply tank, 11...Second titrant tank,
12...Detection cell, 13...Chelating agent control device, 14...Chelating agent supply tank.

Claims (1)

[Claims] 1 Means for collecting a chemical copper plating solution containing at least copper ions and a chelating agent from a plating tank at a flow rate V, containing Fe〓 or Cu〓 ions at a concentration Ct ₁ to form a chelate compound with the copper ion chelating agent. _Ct 1 Vt 1, which is determined from the relationship between the first extraction solution to be used, _the desired total chelating agent concentration nC, Cu concentration C, and Ct ₁ in the chemical copper plating solution, slightly exceeds (n-1) CV. means for collecting a liquid from the first titrant solution at a speed Vt ₁ set as such, a first mixing means for mixing the collected pickling solution and the sampled first titrant solution, an insoluble electrode and a reference. a copper ion detection cell having an electrode and coupled to the first mixing means; and means for replenishing the plating tank with copper ions based on the redox potential determined from the copper ion detection cell. A device for stabilizing copper ion concentration in a chemical copper plating solution, characterized by: