JPH0874060A - Method for controlling plating film in electroless copper plating - Google Patents

Abstract

PURPOSE: To obtain a printed board uniform in film thickness by electroless plating even if the plating rate varies from turn to turn and from batch to batch and to reduce the roughness on the surface of a plating film by adjusting the dissolved oxygen concn. in the plating soln. CONSTITUTION: In the method for electroless plating a printed board with copper, the dissolved oxygen concn. in a plating soln. is adjusted, and the copper plating reaction is stopped at the optional time to obtain a plating film having a desired thickness. Alternatively, the dissolved oxygen concn. in the soln. is adjusted, and the board is dipped in the soln. for a specified time and electroless- plated with copper. The plating films having about the same thickness are obtained in about the same time. As a result, the working time is shortened, the surface roughness of the obtained plating film is reduced to 1/3 to 1/12 of that in the conventional process, and a uniform plating film is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the thickness of a copper plating film plated by an electroless copper plating method for forming wiring on a printed circuit board.

[0002]

2. Description of the Related Art Conventionally, an electroless plating method has been used to manufacture a printed circuit board and a multilayer printed circuit board. At this time, in the factory, a series of plating operations are machine-controlled and automated in order to simultaneously manufacture a large number of printed circuit boards. However, the plating rate varies depending on the plating solution and the number of times the plating solution is used. When forming a uniform film thickness on a printed circuit board in these plating tanks having different plating speeds, the plating speed in each tank is checked in advance, and the operator takes out the substrate in each tank.

Further, as a method for carrying out plating by feeding a gas containing oxygen into the plating solution, there is used an electroless copper plating method in which plating is carried out while maintaining the dissolved oxygen concentration in the plating solution higher than the saturation value by air. A method for obtaining a stable plating film by increasing the concentration of dissolved oxygen as the concentration of reaction by-products accumulated in the plating solution increases (Patent Document 2
No. 141581) or oxygen is supplied so that the amount of oxygen supplied near the center of the plating tank is greater than the amount of oxygen supplied to the peripheral portion of the plating tank. Method to reduce precipitation or plating reaction stop
(Japanese Patent Laid-Open No. 4-376). Further, after the electroless plating of the printed circuit board, steps such as a polishing method and an etching method are added to make the surface of the plated film uniform.

[0004]

However, in order to make the film thickness of the substrate constant, the plating rate in each tank is checked in advance as described above, and when the operator takes out the substrate in each tank, It took time. Further, the roughness of the plating film of the substrate prepared by the above method is large (R _max = 8 to 23 μm).
In the case of m), the polishing method and etching method using a belt sander and the like take time and cost because these steps are added after the plating treatment.

In order to solve these problems, the present invention is designed so that even if the plating speed is different for each turn or each batch,
Make sure that a substrate with a constant film thickness is obtained when the printed circuit board is taken out of the plating solution, and adjust the dissolved oxygen concentration in the plating solution after plating to reduce the roughness of the plating film surface. Is intended.

[0006]

The invention for achieving the above object is to provide an electroless copper plating method for forming wiring by immersing a printed circuit board in an electroless copper plating solution.
By increasing the oxygen content in the gas blown into the plating solution, the dissolved oxygen concentration in the solution is increased and the plating reaction is stopped. Then, the surface roughness of the plated film is reduced by immersing it in the plating solution for a certain period of time.

For example, when a printed board is subjected to chemical copper plating with plating solutions having different plating rates, the plating rate for each tank is checked in advance, and when the target film thickness is reached,
The amount of oxygen in the blown gas is increased to increase the concentration of dissolved oxygen in the liquid and stop the plating reaction. And if the substrate is pulled up when the film thickness of the substrate in all tanks is constant,
It is possible to obtain a constant film thickness of the printed circuit boards in all tanks.

[0008]

The action of the main component in the electroless copper plating solution is a reaction in which electrons generated by the oxidation reaction of formaldehyde are incorporated into copper ions in the complexing agent using copper as a catalyst to deposit copper.

[0009]

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[0010]

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[0011]

[Chemical 3]

Therefore, when the thickness of the plating film reaches a target value, oxygen is fed into the plating solution so that the concentration of dissolved oxygen is higher than that when bubbling with air, and cuprous oxide or oxide The plating reaction is stopped by producing copper.

[0013]

Embedded image 2Cu + H ₂ O + O ₂ + 2e ⁻ → Cu ₂ O + 2OH ⁻ (Chemical formula 4)

[0014]

[Chemical Formula 5] Cu ₂ O + H ₂ O + O ₂ + 2e ⁻ → 2CuO + 2OH ⁻ (Chemical formula 5) Since this work does not add a step after the plating process and only increases the amount of oxygen to be blown, compared to the conventional method. It seems that it does not take time and cost. Further, changing the copper concentration or the formaldehyde concentration can be considered as a means for making the plating rates the same, but it takes time and the work is difficult to increase or decrease these concentrations. On the other hand, in the present invention, since the oxygen concentration is only increased, the work itself can be promptly performed.

[0015]

【Example】

Example 1 An electroless copper plating solution having the following electroless copper plating solution composition was used.

(Electroless Copper Plating Solution Composition) Copper Sulfate Pentahydrate 10 g / l Ethylenediaminetetraacetic Acid 60 g / l Formalin (37% by Weight) 3 ml / l Polyethylene Glycol (Mw1000) 2 ml / l Germanium Oxide 60 mg / l pH (Adjusted with NaOH) 12.5 Liquid temperature 70 ° C Gas flow rate 0.5 l / (plating liquid) l / min The gas blown into the plating liquid is nitrogen and oxygen such that the dissolved oxygen concentration in the plating liquid is 4 ppm. A mixed gas was used. Then, 6 hours and 30 minutes after the start of plating, the mixed gas was adjusted so that the concentration of dissolved oxygen in the plating solution was 15 ppm. The plating rate at this time was 4.8 μm / h.

As the printed board, a board made of epoxy resin containing glass fiber and having a plating resist formed on portions other than the circuit forming portion was used.

Under the above conditions, a plating process was performed for 7 hours to form a wiring pattern.

Example 2 Under the conditions of Example 1, the formalin concentration in the plating solution was adjusted to a plating rate of 5.2 μm / h, and the adjustment time of the mixed gas blown from the start of plating was 6 hours 1
All were the same except that they were changed after 0 minutes.

Comparative Example 1 Under the conditions of Example 1, air was used instead of the mixed gas, and the composition of the gas was not changed during the plating treatment time. Except for the above, all were the same as in Example 1.

The plating treatment was performed as described above, and the plating film deposited on the substrate was examined under the following observation conditions. The results are shown in Table 1.

(Observation conditions) Plating film thickness measurement (plating speed measurement): The copper plating deposited on the copper plate placed in the plating tank was measured by a gravimetric method. The plating rate was calculated from the plating film thickness deposited 3 hours after the start of plating.

Dissolved oxygen concentration: When a part of the plating solution is taken from a plating tank, a rubber stopper is provided to shield the air from the air, and the solution is cooled with running water. , Dissolved oxygen is measured by a dissolved oxygen concentration meter.
The measurement time was measured after changing the composition of the mixed gas flowing in.

Plating bath stability: It was defined as stable because no copper was deposited in the plating bath.

Surface roughness of plating film: Measured with a stylus surface roughness meter.

[0026]

[Table 1]

[0027]

As described above, even if plating is performed in plating tanks having different plating rates, by adjusting the dissolved oxygen concentration in the plating solution according to the present invention,
It was found that plating films having almost the same film thickness can be obtained at the same time. Therefore, it is considered that the work process time can be shortened.

The surface roughness of the obtained plating film was about 1/3 to 1/12 that of the conventional one, and a uniform plating film was obtained.

Claims (2)

[Claims] 1. A method for electroless copper plating in which a printed circuit board is dipped in an electroless copper plating solution to plate copper to form wiring, and the composition of gas blown into the plating solution is changed to change the dissolved oxygen concentration in the solution. A method for controlling a plating film thickness in an electroless copper plating method, which comprises adjusting and stopping a copper plating reaction at an arbitrary time to obtain a plating film having a desired film thickness. 2. A method for controlling a plating film thickness in an electroless copper plating method according to claim 1, wherein the substrate is immersed in the solution for a certain period of time after adjusting the dissolved oxygen concentration in the solution.