JPS6317906B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to the composition of an electroless plating bath and a continuous plating method using the plating bath, and in particular, its purpose is to consistently maintain stable bath management using inexpensive equipment and simple operation, and to obtain a high-quality deposited film. . Originally, electroless plating technology is widely used as a method for forming conductors on insulators in printed wiring boards, etc., but it is difficult to control the deposition reaction and consistently obtain a high-quality deposited film. had difficulties. For example, one method of controlling precipitation reactions is generally to control bath components, and volumetric analysis and instrumental analysis are applied, but bath component control using volumetric analysis is effective only in batch operations. Therefore, continuous bath component management cannot be performed. Furthermore, in the case of continuous automatic bath management using mechanical analysis, the equipment becomes expensive and maintenance costs increase. That is, according to conventional methods, component management of electroless plating baths was initially carried out in a batch manner, but later a continuous automatic control method using an automatic analyzer was adopted. However, the batch control method requires complicated analysis work by skilled analytical workers, and it takes a long time from the end of plating to the end of bath composition adjustment, and in the case of thick electroless plating, During the required time of ~10 hours, if the material to be plated is added in the middle, the plating thickness will vary, and the amount of reducing agent and PH adjuster added is theoretically calculated, so oversupply may occur during the actual reaction. This has disadvantages such as a shortage resulting in bath decomposition and reaction inhibition. On the other hand, the automatic control method improves this, but it has disadvantages such as the equipment is expensive, the installation location is often in an unfavorable environment for equipment maintenance, and depreciation is expensive. . The present invention eliminates the drawbacks of the above-mentioned conventional methods, and provides an electroless plating bath composition and electroless plating bath that enables metal ion control without the use of special measuring instruments and automatic control using inexpensive equipment. This provides a continuous plating method. Hereinafter, one embodiment of the present invention will be described based on the drawings. First, the bath components according to the embodiments of the present invention include cupric hydroxide, ETA.2Na.2H ₂ O. formalin, caustic soda, and others, but the gist is not limited to this combination. Further, FIG. 1 shows an example of the configuration of a plating device, and the plating liquid in the plating tank 12 is supplied to the metal ion source tank ₁ by a circulation pump P1.
After passing through a filter 8, the liquid is refluxed to a plating tank 12. This metal ion source tank 11
Cupric hydroxide particles are placed on the liquid supply side and are stirred by a stirrer _M1 . Here, the cupric hydroxide grains that have come into contact with the plating solution partially form a complex with ETA and are dissolved in the plating solution, and after passing through the filter 8, reach the plating tank 12. The copper complex ions are removed from the liquid phase by a precipitation reaction in the plating tank 12. This reaction continues as long as the cupric hydroxide grains are present. In addition, a portion of cupric hydroxide changes to copper oxide, but forms a complex with ETA ions and eventually dissolves. Further, the copper ion concentration fixed by this plating device is determined by the amount of precipitation reaction and the amount of complex formation reaction. If the capacity of the metal ion source tank 11 is small, the copper ion concentration is maintained at a low value, but if the capacity is sufficiently large, it is maintained at a value slightly lower than the initial ETA concentration regardless of the area to be plated. . Here, the change in copper ion concentration in the plating tank 12 was measured as shown in FIG. 2 after the cupric hydroxide grains were introduced using the above plating apparatus. Under the conditions of this measurement example, if the difference between the initial ETA concentration and the copper ion concentration is 0.005 mol/l or more, a fast complex formation reaction rate of 0.001 mol/l can be obtained. This indicates that the initial copper ion concentration is
The concentration will be maintained constant at 0.005M lower than the ETA concentration, while the PH will be adjusted using the glass electrode unit 3.
This is performed by the recording type PH indicator controller 4, control unit 5, metering pump _P3 , and PH adjusting agent from the tank 10. Continuously, the metering pump _P2 is driven to discharge formalin from the reducing agent tank 9. are additionally supplied, these supply ratios can be adjusted by adjusting pumps P ₂ and P ₃ , and the concentrations of these supply liquids are set so that the total supply liquid volume and the plating liquid evaporation amount cancel each other out. determined. Generally, the glass electrode 3 is affected by temperature and coexisting ions, but in the present invention, the absolute value of PH is not required. This can be resolved by keeping the However, the effect of increase or decrease in coexisting ions appears as an effect of accumulation of sodium formate as the precipitation reaction progresses, and the pH value becomes lower than the actual pH. For this reason, it is generally necessary to lower the control point for pH adjustment in accordance with the additional supply amount of caustic soda, but in the case of the example, as in the bath composition example of the present invention, by using cupric hydroxide. The amount of caustic soda supplied can be reduced by about half,
The frequency of adjustment of control points can be reduced. Next, using the following plating bath composition, apply the first plating bath described above.
When the change in copper ion concentration over time was measured using the plating device shown in the figure, the values shown in Table 1 were obtained.
The copper deposition rate at this time was 4μ/hour, and a final film thickness of 12μ could be obtained.

Add [Table].

[Table] **...At the time of inputting the material to be plated As a result, by supplying a large excess amount of cupric hydroxide as a metal ion source, the copper ion concentration during the plating process was not affected by changes over time.
It can be seen that it is maintained approximately constant. As described above, the present invention provides a metal ion source,
In an electroless plating bath consisting of a reducing agent, a complexing agent, a pH adjuster such as caustic soda, and additives such as a bath stabilizer and a precipitation improver, supplying a large excess amount of cupric hydroxide, for example, as a metal ion source. This makes it possible to create a plating bath that can maintain a constant metal complex ion concentration, that is, copper complex ion concentration during the plating process. That is, the metal ion concentration control of the present invention uses one or more of metal salts, metal oxides, and metal hydroxides, which are dissolved only in the presence of a complexing agent, as a metal ion source in the plating bath. It is established by using it. The metal ion source supplied in a large excess amount rapidly dissolves in the plating bath due to the large presence of the complexing agent, but as the metal complex ion concentration increases, the dissolution rate decreases, and the coordination site of the complexing agent decreases. The dissolution reaction stops when all metal ions are occupied, and the concentration becomes constant. If this dissolution reaction and the decrease in metal ion concentration due to precipitation reaction compete with each other, the metal ion concentration can be maintained at a constant value slightly lower than the complexing agent concentration. Another improvement of the present invention is that the reducing agent concentration is controlled in conjunction with the PH adjuster control. That is, taking formalin as an example of a reducing agent, the reaction ratio of formalin and hydroxide ions in the plating precipitation reaction is 1:2,
2:1 in Cannitzaro reaction as a side reaction
becomes. Furthermore, the reaction amount ratio of both reactions is a value determined by the area to be plated per unit amount of plating liquid. Focusing on this value, formalin is supplied in conjunction with PH control based on the supply ratio of formalin and PH adjuster, which is empirically determined for each area to be plated per unit amount of plating liquid, and the reducing agent concentration is maintained at a constant level. can be done. As explained above, the present invention makes it possible to control bath components using a simple method, but when particularly accurate analytical values are required, the analytical method used in the batch control method can be applied. In that case, if the analysis is performed after the start of plating, it can be done without reducing work efficiency.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a main part of a plating apparatus showing an embodiment of the present invention, and FIG. 2 is a curve diagram showing the state of dissolution of cupric hydroxide in a plating solution. In the figure, P ₁ is a circulation pump, P ₂ and P ₃ are variable metering pumps, M ₁ and M ₂ are stirrers, 1 is a heater, 2 is a resistance temperature detector, 3 is a glass electrode unit,
4 is a recording type PH indicating regulator, 5 is a control unit, 6 is a temperature regulator, 7 is a valve, 8 is a filter, 9 is a reducing agent tank, 10 is a PH adjusting agent tank, 11 is a metal ion source tank, 12 is a Metsuki tank.

Claims (1)

[Claims] 1. In an electroless plating bath, a container that is provided separately from the plating tank and in which the plating solution is circulated through a filter is used as a metal ion source that is insoluble in water and an alkaline aqueous solution. A continuous plating method using an electroless plating bath characterized by adding one or more of metal oxides and metal hydroxides to prevent insoluble substances from being brought into the plating bath. 2. When additionally supplying reducing agent in conjunction with PH value control to adjust the reducing agent concentration, the supply ratio of reducing agent and PH adjuster is determined by the consumption ratio of reducing agent and PH adjusting agent due to precipitation reaction and side reaction. Decided according to
A continuous plating method using an electroless plating bath according to claim 1, characterized in that additional supply is performed based on this ratio. 3. In an electroless plating bath composition consisting of a metal ion source, a reducing agent, a complexing agent, a PH adjuster such as caustic soda, a precipitation improver, a bath stabilizer, and other additives, a metal ion source that is insoluble in water and an alkaline aqueous solution is used as a metal ion source. 1. An electroless plating bath composition characterized in that it uses cupric hydroxide which can easily form a complex with a complexing agent.