JPS5921386B2 - Automatic plating speed control method for electroless plating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for automatically adjusting plating speed in electroless plating.

Conventionally, the method of controlling the plating speed in electroless plating is to actually measure the thickness of the plating film formed on the surface of the substrate to be plated at appropriate intervals, and adjust the composition of the electroless plating solution based on the measured values. This is done by doing this.

However, this method has drawbacks such as the inability to automatically adjust the plating speed, which results in uneven plating films, making it difficult to perform high-speed moped plating, which consumes a large amount of electroless plating solution. Ta. In view of the above, the present invention has been made as a result of conducting various studies. After immersing a metal electrode made of the same element as the metal to be reduced and deposited in an electroless plating solution and measuring the hybrid potential of the electrode, A method of continuously and automatically controlling the plating speed by determining the potential difference between the potential difference and a preset standard hybrid potential, and then adjusting the composition of the electroless plating solution so that this potential difference becomes a predetermined value, for example, zero. The purpose is to provide The present invention will be explained in detail below.

The electroless plating solution in the present invention comprises a salt of a metal of Group IB or Group II of the Periodic Table of Elements, a complexing agent for the metal ion, a reducing agent, and a pH adjusting agent.

Examples of metals in Groups and Group II of the periodic table of elements include copper, silver, gold, platinum, nickel, cobalt, and palladium.
Examples of complexing agents for metal ions include potassium sodium tartrate and tetrasodium ethylenediaminetetraacetate for copper, and sodium citrate for nickel. Examples of reducing agents for reducing metal ions include formaldehyde or formaldehyde derivatives such as paraformaldehyde, trioxane, dimethylhydatoin, and glyoxal. Other reducing agents include alkali metal borohydrides, amine borane, morpholine borane, sodium hypophosphite, hydrazine and derivatives thereof. Examples of the pH adjuster include sodium hydroxide and ammonium hydroxide. By immersing a substrate for liquid plating in an electroless plating solution with the above composition, metal ions are reduced and deposited on the surface of the substrate to perform a plating reaction. It is thought to be due to reaction synthesis.

This local anodic reaction is a reaction in which the reducing agent is oxidized, and the local cathodic reaction is a reaction in which metal ions are reduced to metal, and these reactions are catalyzed by the plating film formed on the surface of the substrate to be plated. I'm not sure if it will react. On the other hand, when looking at this plating reaction from the viewpoint of electrical balance, the anode partial current due to the oxidation reaction of the reducing agent,
The absolute values of the cathode partial currents due to the reduction reaction of metal ions become equal. In electroless plating where such a reaction occurs, the potential of the substrate to be plated is called a hybrid potential,
This hybrid potential changes when either the local anodic reaction or the local cathodic reaction is held constant, that is, when the shape of the current-potential curve for one reaction is constant, the shape of the current-potential curve for the other reaction is As the voltage changes, the hybrid potential also changes. Therefore, since there is a proportional relationship between the plating speed and the current, it is possible to know the change in the current, that is, the change in the plating speed, by measuring the change in the hybrid potential. The present invention has been made with attention to this point, and the method will be described in detail below based on explanatory diagrams illustrating the method. In the figure, 1 is a plating tank, and this plating tank 1 contains an electroless plating solution 2 having a predetermined composition.

The electroless plating solution 2 that has not been taken out from the side wall of the plating tank 1 is circulated through a pump 3 to an electrode potential measurement tank 4.6 Also, the electrode potential measurement tank 4 contains the metal to be reduced and deposited. A metal electrode 5 and a Kanagai electrode 6 made of the same element are provided. When the substrate to be plated is immersed in the plating tank 1 and electroless plating is performed, the composition of the electroless plating solution 2 changes as the plating reaction progresses.
It becomes impossible to obtain a constant plating speed. Therefore, the electroless plating solution 2 whose composition has been changed is introduced into the electrode potential measuring tank 4,
Here, while stirring with a stirrer (not shown), a chemical reduction plating reaction is carried out on the surface of the metal electrode 5 provided as a model of the substrate to be plated. The mixed potential of the metal electrode 5 in this state is measured using the measuring device 7 with the Kanaga electrode 6 as a reference. This measured value is recorded on the recorder 8 so that changes in the plating speed can be known. On the other hand, in measuring device 7,
The potential difference between this measured value and a standard hybrid potential set in advance corresponding to a predetermined plating speed is determined, and after this potential is amplified by an amplifier 9, the pump is pumped until this potential difference reaches a predetermined value, for example, zero. Activate 10. The plating speed is controlled by supplying the component solution 2a that forms the electroless plating liquid 2, which is put into the tank 11, into the plating tank 1 using the pump 10 and adjusting the composition of the electroless plating liquid 2 to a predetermined ratio. This is what we do. In addition, in the above control method, when the shape of the current-potential curve in the local cathode reaction is kept constant, that is, when the concentration of the solution containing metal ions among the component solutions forming the electroless plating solution 2 is kept constant, the tank The component solution 2a supplied from 11 is a reducing agent or a pH regulator. Furthermore, when the shape of the current-potential curve in the local anode reaction is constant, that is, when the concentrations of the reducing agent and the PH regulator are constant, the tank 11
The component solution 2a supplied from is a solution containing metal ions. Although the explanatory diagram shows the metal electrode 5 and the Kanagai electrode 6 installed in the electrode potential measuring tank 4, which is provided separately from the plating tank 1, it is important to note that the metal electrode 5 and the Kanagai electrode 6 are installed in the electrode potential measuring tank 4, which is provided separately from the plating tank 1. It may also be attached to.

Next, examples of the present invention will be described.

Example 1 Using an apparatus as shown in the figure, 100 ml of electroless plating solution 2 having the following composition was placed in a plating tank 1 in advance, and a phenol plate with an active metal adhered to the surface in advance was used as a substrate to be plated. Electroless copper plating was performed by immersing the steel.

Electroless plating solution composition and electrode potential measuring tank 4 with a capacity of 0.11 have a diameter of 1 m1.
, length 10m1! A metal electrode 5 made of L-sized copper wire and a Kanaga electrode 6 are attached to the metal electrode 5 while supplying electroless plating solution 2 into the electrode potential measuring tank 4 at a rate of 0.51/min. Measure the hybrid potential of

On the other hand, a standard hybrid potential set in advance to -0.615m,
The potential difference with the measured hybrid potential was determined, and the pump 10 was operated until this potential difference became zero, and formaldehyde was supplied from the tank 11 into the plating tank 1 to control the plating speed. In this way, while keeping the shape of the current-potential curve constant in the local cathode reaction, that is, the oxidation reaction of copper ions, and controlling the plating rate by the amount of formaldehyde added,
When 8 m2 of copper was plated at a thickness of 3 microns per day, the plating speed could be continuously and automatically controlled in the range of 8.0 to 8.5 microns/hour.

Example 2 In the above Example 1, the electroless plating solution had the following composition, the local anode reaction was kept constant, and the plating rate was controlled by the amount of copper sulfate added.

Electroless plating solution composition As a result, it was possible to control the plating rate from 8.0 to 8.5 μ/hour in copper plating of 8 m 2 with a thickness of 3 μ per day.

Example 3 In Example 1 above, the electroless plating solution had the following composition, and the plating speed was controlled by varying the amount of sodium hydroxide.

In this way, by adjusting the pH of the plating solution by changing the amount of sodium hydroxide added, the local anodic reaction of formaldehyde can be controlled. Electroless plating solution composition ＼ 口 偵 As a result, when 8 m2 of copper was plated with a thickness of 3 μ per day, it was possible to control the plating speed within the range of 7.5 to 8.5 μ5/hour. did it.

As explained above, according to the method for automatically controlling the plating speed of electroless plating according to the present invention, the plating speed can be continuously and automatically controlled by an extremely simple method, and in particular, the consumption of the electroless plating solution is reduced. It has remarkable effects, such as being suitable for intense high-speed thick plating methods.

[Brief explanation of drawings]

The drawing is an explanatory diagram showing an outline of the apparatus in the method of the present invention. 1... Plating tank, 2... Electroless plating solution, 2a... Component solution, 4... Electrode voltage measurement tank, 5...・Metal electrode, 6... Kanaga electrode, 7... Measuring device, 11... Tank.

Claims (1)

[Claims] 1. After immersing a metal electrode made of the same element as the metal to be reduced and deposited in an electroless plating solution and measuring the hybrid potential of the electrode, determining the potential difference between this hybrid potential and a preset standard hybrid potential, An automatic plating speed control method for electroless plating, characterized in that the plating speed is controlled by adjusting the composition of the electroless plating solution so that the potential difference becomes a predetermined value.