JPH0421786A - Electroless plating method - Google Patents

Abstract

PURPOSE:To enable uniform electroless plating by immersing a pretreated body to be plated in water heated to a prescribed temp. and then immersing the body in a plating bath. CONSTITUTION:The surface of a body to be plated is pretreated by degreasing and washing. The pretreated body is immersed in water heated to a temp. above the temp. of a plating bath or in heated water ensuring a more rapid deposition reaction than water at ordinary temp. At the time when the temp. of the body exceeds the temp. of the plating bath, the body is taken out of the heated water and immersed in the plating bath at once and electroless plating is carried out. A plating reaction begins uniformly and the occurrence of unevenness in the thickness of a plating film can effectively be inhibited.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an electroless plating method, particularly an electroless plating method in which a plated film is formed using a high plating bath temperature.

[Conventional technology] Electroless plating is known as chemical plating that forms a metal film by reducing metal ions in a plating solution, and is contrasted with electroplating that deposits electrolytic ions through the application of an electric current. It has been pointed out that objects of similar shapes can be plated to a uniform thickness. Other technical comparisons are omitted here because they are not directly related to the gist of the present invention.

In electroless plating, a plating solution containing a reducing agent is placed in a container, and as in the case of Ni plating, the plating solution is heated to a predetermined temperature and the plating preparation is completed. It is called a bath or simply a bath, and the temperature of the plating bath in this state is called the bath temperature. Therefore, in the following description, the terms plating bath (or bath) and bath temperature will be used as appropriate.

FIG. 2 is a flowchart showing the steps of a conventional electroless plating method. As shown in the figure, in order to obtain a plated thin film using conventional electroless plating, the surface of the object to be plated is degreased with an organic solvent such as trichlene or chlorocene, and then washed with pure water, pretreated, and rinsed with water. conduct. Thereafter, plating is carried out immediately or after drying and storage, by putting it into a plating bath (immersion) and plating for a period of time until the required film thickness or film resistance value is obtained. In this case, in plating that uses a plating solution at a high temperature of 70 to 90° C., such as Ni plating, the reducing agent contained in the plating solution is not activated at lower temperatures, so no plating reaction occurs. In such plating methods, measures such as keeping the bath temperature constant, stirring the bath well, and rotating the object to be plated have been taken to obtain a uniform coating.

[Problems to be Solved by the Invention] In the conventional electroless plating method as described above, the shorter the plating time, the greater the variation in the resistance value of the plating film, making it extremely difficult to obtain a uniform thin film. Ta. The reason for this is that there is a time lag between when the object to be plated is put into the plating solution and when the plating reaction actually occurs on the surface of the object to be plated. It is caused by When an object to be plated at room temperature is placed in (immersed in) a plating solution, it will be heated by the surrounding high temperature plating solution. Then, the plating reaction proceeds preferentially from the part where the temperature at which the plating reaction occurs is reached, and the reaction is not uniform.

As a result, variations occur in the plating film.

This problem could not be solved even by keeping the bath temperature constant, stirring the liquid, or rotating the coating or coating.

The present invention has been made in order to solve the above-mentioned problems, and provides an electroless plating method that performs plating without uneven plating (variation) by inserting a step in which the time until the plating reaction occurs is constant. The purpose is to

[Means for Solving the Problems] The electroless plating method according to the present invention is such that when the object to be plated, which has been subjected to pre-plating treatment, is immersed in water at a temperature equal to or higher than the plating bath temperature or at least at room temperature immediately before plating, After being immersed in water heated to a temperature that facilitates the precipitation reaction, it is immediately immersed in a plating bath for plating.

[Function] In the present invention, immediately before plating, the material is immersed in water heated to a temperature higher than the plating bath temperature, or at least at a temperature at which the precipitation reaction proceeds more than when immersed in water at room temperature, and then taken out. Since plating is performed, the temperature of the surface of the object to be plated is higher than the plating bath temperature, so plating is performed with a constant time until the plating reaction occurs. In other words, the start of the plating reaction can be accelerated and the plating reaction can be made uniform on all plating surfaces, so that the plating reaction progresses uniformly and smoothly. Even if the temperature is not higher than the plating bath temperature, the higher the surface temperature of the object to be plated, the faster the plating reaction will start and the more uniform the plating reaction will be.

[Examples] Example 1; FIG. 1 is a flowchart showing an example of the procedure of the electroless plating method according to the present invention. First, the surface of the object to be plated is degreased with an organic solvent such as trichlene or chlorocene, and then cleaning with pure water (water washing), pretreatment, and water washing are carried out in the same manner as the conventional process shown in FIG. Thereafter, either immediately or after dry storage, it is first immersed in water (warm water) heated to a predetermined temperature higher than the plating bath temperature (warm water immersion). When the object to be plated reaches a temperature equal to or higher than the plating bath temperature by this immersion, the object to be plated is removed from the water and immediately immersed in the plating bath to perform plating. Plating is time plating as in the conventional example.

In the above procedure, a case where the object to be plated is a metal such as Cu (copper) and is plated with Ni will be described. The plating solution is a solution containing N r SO 4 as a main component, to which a predetermined amount of sodium hypophosphite (N a H 2 P 0 2 ) is added as a reducing agent. When the plating bath was an acidic bath, it was used at a pH of 5.0 and a temperature (bath temperature) of 90'.

Therefore, in the plating method of this embodiment, the object to be plated is immersed in hot water at 90' to 100°C immediately before plating, and then immersed in the above-mentioned 90°C plating bath, thereby proceeding with plating. The plating film becomes thicker as the bathing time increases.

In this way, N a H2P O2 is used as a reducing agent.
Strictly speaking, the Ni film obtained when using the above method is an N1-P alloy film that has excellent corrosion resistance and high hardness.

As described above, by immersing the object to be plated in hot water immediately before plating and warming the temperature of the object and its surface to a temperature higher than the plating bath temperature, the plating reaction starts uniformly.
Thereby, it is possible to effectively suppress unevenness in the thickness of the plating film, that is, variations. In the examples, the object to be plated is a metal and Ni plating is performed in an acidic bath. However, the present invention is not limited to this. It is also fully applicable to metal plating other than Ni plating, such as plastic.

Example 2: In this example, Ni plating was performed on the surface of an insulator using the electroless plating method according to the present invention, and the results of evaluating the resulting plating film will be described.

If the insulator is, for example, plastic, it is necessary to perform a pretreatment different from the usual pretreatment performed on metal objects to be plated (see FIG. 1), although this is a well-known technique. FIG. 3 is a flowchart showing the sub-steps of the pre-treatment step when performing electroless Ni plating on plastics. As shown in the figure, the pretreatment is completed by repeating the manual process three times, each consisting of a series of sub-steps of sensitization, water washing, activation, and water washing. That is, in the initial sensitization (catalyst application also called sensitizing), the plastic was immersed in Sn in 1 p of a lee/it aqueous solution of hydrochloric acid.
Immerse for 1 minute in a solution containing 21 g of CΩ. Next, wash with water for 1 minute, and further add O, L cc/g hydrochloric acid aqueous solution 1ρ
One step A is completed by immersing it in a solution containing 120.1 g of Pd for 1 minute to activate it, and then washing with water for 1 minute.

By repeating this step A three times, Pd (palladium) is deposited on the surface in the form of a film, and the pretreatment is completed.

The object to be plated having the Pd base formed in this way is immersed in a plating solution at 75 to 90°C to perform electroless plating of Ni, and a NiP plating film is formed on the Pd base formed on the surface. Ru. The plating solution used is Nimden HDX (
It is an electroless NiP plating solution called (trademark: Nikamimura Kogyo Co., Ltd.). In this case, in the plating method according to the present invention, as in Example 1, the pretreated plastic is immersed in water heated to a temperature higher than the plating bath temperature, and then removed from the water and immersed in the bath. By performing plating, a strong plating film with little variation can be obtained.

FIG. 4 is a diagram showing the results of a confirmation experiment in which variations in film quality were examined as an evaluation of plating films on plastics. In the figure, the horizontal axis shows the plating (immersion) time, and the vertical axis shows the variation of the sheet resistance (Ω/hole) of the obtained Ni film from the maximum value to the minimum value 1. In this case, the objects to be plated (plastic) were of the same shape, and experimental results were shown for the conventional plating method (data marked) and the plating method of the present invention (data marked ■). In this case, variations in the sheet resistance of the plated film directly correspond to variations in the thickness of the plated film. The plating film was evaluated using the conventional method (Fig. 2) of the plated object in a dry state at room temperature and the present method (Figs. 1 and 3) of the plated object heated above the plating bath temperature. Each was immersed in a bath for a certain period of time to perform plating, and the variations in sheet resistance values of the resulting films were determined and compared.

From the experimental results shown in FIG. 4, it can be seen that the electroless plating method according to the present invention has smaller variations in the plating film than the conventional method. In particular, this tendency is remarkable when a plating thin film is formed within 2 minutes, and can be said to support the effectiveness of the method according to the present invention.

[Effects of the Invention] As described above, according to the present invention, the temperature of the object to be plated is raised to a temperature higher than the plating bath temperature immediately before plating, or at least to a temperature at which the precipitation reaction proceeds more than when immersed in water at room temperature. Since it was immersed in water and then immersed in a plating bath for plating,
The following effects can be obtained.

(a) It is possible to obtain uniform plating film thickness and film resistance value.

(b) Since the plating reaction starts uniformly and immediately after immersion in the bath, by using this method, it is possible to form a highly precise thin plating film by precisely controlling the plating time. I can do it.

[Brief explanation of the drawing]

Fig. 1 is a flowchart showing an example of the procedure of the electroless plating method of the present invention, Fig. 2 is a flowchart showing the procedure of the conventional electroless plating method, and Fig. 3 is electroless plating on plastic. FIG. 4 is a flowchart showing the sub-steps of the pretreatment step in this case, and FIG. 4 is a diagram showing the results of an experiment comparing the evaluation of the plating film with respect to the variation in the quality of the plating film with respect to the plating time. Mezu A1 Diagram of Saimo Water Plating Diagram Pretreatment Glue Diagram 3

Claims (1)

[Claims] The object to be plated, which has undergone plating pretreatment, is immersed in water heated to a temperature higher than the bath temperature of the plating solution, or at least to a predetermined temperature at which the precipitation reaction proceeds more than when immersed in water at room temperature. An electroless plating method characterized in that: and then plating is performed by immersion in the plating solution.