JPH03291384A - Electroless plating method and apparatus - Google Patents

Abstract

PURPOSE:To control the concn. of each component in a plating soln. to the desired value independently of the area of a body to be plated by measuring the concn. of each component in the plating soln. during electroless plating, setting intervals of working time of a feeder for replenishing the component from this measurement to the next measurement and setting the amt. of the component replenished per unit time from the area of the body plated with unit amt. of the plating soln. CONSTITUTION:The concn. of each component such as metal ions, a pH adjusting agent or a reducing agent for the metal ions in a plating soln. is measured during electroless plating with Cu, Ni, Sn, Ag, etc., and intervals of working time of a feeder for replenishing the component from this measurement to the next measurement is set because the concn. of the component is reduced by a plating reaction. In the case where the area of a body to be plated varies, the amt. of the component replenished is automatically controlled according to the working time of a diaphragm pump on the basis of the area of the body plated per unit atm. of the plating soln. and the concn. of each component in the plating soln. is automatically controlled to the desired value.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for continuously using an electroless plating solution.

C. Prior Art] With use of electroless plating, metal ions and reducing agents that are reduced and precipitated are consumed, and as a result, the concentration of these components in the device liquid decreases.

An example of electroless copper plating using formaldehyde as a reducing agent is shown in the following equation.

Cu"+2GH1 (reducing agent) +40H--Cu' (plating metal)+21(!O+Hzτ+21(COO-
As is clear from the formula (1), copper ions, formaldehyde, and hydroxide ions are consumed as the plating solution is used. In order to use the electroless plating solution continuously for a long time, these consumed components must be replenished.

Further, at this time, the plating deposition rate, the characteristics of the film obtained by plating, and the stability of the plating solution are controlled by the concentration of the components in the plating solution, so it is necessary to control the component concentrations.

Therefore, based on component analysis and analysis values (component replenishment is carried out).Metal ion concentration is measured by spectrophotometry or selective ion electrode.pH adjusting component (hydroxide ion) is
Measured by H electrode, acid, and base titration methods. The reduced side is also measured using methods such as chemical analysis and ion chromatography.

These measurements are performed at regular intervals. Then, the amount of component replenishment for the period until the next measurement is determined. The amount of component replenishment is determined by the operating time of the component replenishment device with respect to the component measurement period (unit: minutes or hours).

Generally, proportional control is adopted, and when the concentration is at the control center,
The operating time is 50% of the measurement cycle, and as the concentration becomes lower than the control center concentration, the operating time increases proportionally from 50% to 1%.
Increases to 00%. Conversely, as the concentration becomes higher than the control center concentration, the operating time decreases proportionally by 50-0%. At this time, lower and upper limit concentrations are set when the operating time becomes 100% and 0% (the conventional component management device is as described above).

By the way, when a plating solution is continuously used, it is inevitable that the objects to be plated are taken in and out, and it is difficult to always keep the plating area of the objects to be plated constant. Therefore, in reality, under conditions that change the plating area of the object to be plated,
It is necessary to control the component concentration of the plating solution at a constant level.

Problems arise with the above component concentration control method for the following reasons. The relational expressions between the amount of component consumed and the amount of component replenishment are shown in (2) and (3), respectively.

Component consumption ■ Plating deposition rate x plating area - (2) Component replenishment amount = Component replenishment device operating time x replenishment amount per unit operating time - ... ) When a component is being consumed, maintaining a constant concentration requires equal component consumption and component replenishment. (2) and (
As is clear from 3), in the conventional method, when the plating area changes rapidly (for example, when the object to be plated is removed from the plating solution), the time required for the next component measurement is During this time, components are replenished based on the previous measured value, so there may be cases where the upper limit for management is exceeded.

Conversely, if the object to be plated is placed in the plating solution,
There are cases where the value falls below the lower limit of management.

This problem occurs because the amount of replenishment per unit operating time of the component replenishment device is not controlled.

[Problem to be solved by the invention]

The present invention provides a method that allows component concentrations to be controlled within a target control range even if the plating area varies.

[Means to solve the problem]

That is, the present invention is a method of continuously performing plating while controlling the concentration of components in an electroless plating solution, in which the concentration of components is analyzed, and based on the obtained analysis value, the concentration of components is The component concentration in the plating solution is determined by determining the operating time ratio of the component replenishing device, and further determining the replenishment amount per unit operating time of the component replenishing device based on the plating area for the unit plating solution amount. It is a management method.

Electroless plating solutions include copper, nickel, tin, Ag,
It can be applied to electroless plating solutions that perform plating while controlling the composition of Co, etc. Component concentration analysis is performed intermittently on a sampled plating solution at regular intervals. Then, based on this analysis value, the operating time of the component replenishing device until the next analysis time is determined. This operating time includes the following cases: For example, if the analysis time interval is 1
If the operating time of the component replenishment device is 5 minutes,
In the case of 5 minutes, this 5 minutes is divided into an analysis interval of 10 minutes on average, and this includes the case where replenishment is performed.

That is, in this case, in order to perform continuous plating, including when the component replenishment device is repeatedly activated for 30 seconds and stopped for 30 seconds for a total replenishment time of 5 minutes, at least metal ions and reducing agent must be replenished. Although it is necessary to do so, it also includes cases in which the replenishment time of other components is determined based on the analysis value of one type of component.

The range of plating area for unit plating solution amount is from zero to 1.
The range is 0dnf71. When the object to be plated is, for example, a plate-like object such as a printed wiring board, a predetermined number of sheets are placed in a basket, and the basket is placed in the plating solution. Therefore, the plating area is determined by the number of baskets in one plating tank. A position sensor or the like can be used to automatically detect the number of baskets. That is,
A position sensor reads the presence or absence of a car at a predetermined location. Based on the information on the plating area obtained in this way,
Determine the amount of replenishment per unit operating time of the component replenishment device. Generally, supplementary components are handled in liquid form. Therefore, a pump is used for -g as a replenishment device. In the case of a cylinder type, the amount of replenishment can be controlled by changing the number of strokes or the displacement of the piston. The most suitable pump is a diaphragm pump in which the amount of displacement of the diaphragm is controlled. An example of a commercially available product of this kind is a piezo pump manufactured by Nippon Keiki Seizo. In the case of this pump, the replenishment amount per unit time is 0.01
mJ! It can be arbitrarily selected between /min and 40GmJ/min.

Therefore, the plating area is converted into information using a position sensor that indicates the presence or absence of a car, and the replenishment amount of the piezo pump is automatically set based on this information.

〔Example〕

The composition of the plating solution and the plating conditions were as follows.

Cu S Oa ・5 Ht O-8g / IEDT
A ・4Na -40g/1pH (adjusted with NaOH) -12,3 36%HCHO=4 ml/1 addition
= Small amount of air racing -5Q m It / j,
Separating salt = 70℃ Liquid volume = 30004! Plating area
- Maximum plating area per 2 drd/11 cars = 1200 dr/number of cars that can be plated = 5 cars (Plating area under these conditions is 2 drI?/1) Automatic analysis of plating components and automatic replenishment equipment are provided by Hitachi Chemical Co., Ltd. A PDB-300 model was used. This device automatically analyzed every 7 minutes, and based on the analyzed values, the operating time of the replenishment device was proportionally controlled. Position sensors were attached to five baskets at predetermined locations in the plating tank where the baskets were placed. The replenishment device uses Ichi Nippon Keiki Seisakusho's Viezo Bump (flow rate can be electrically varied), and the amount of replenishment from the pump can be changed based on the signal from the position sensor indicating the presence or absence of the car.

On the other hand, in the conventional method as a comparative example, a diaphragm pump whose replenishment amount cannot be changed electrically was used as a replenishment device.

The plating area was varied using the above plating solution composition, plating bath conditions, and equipment conditions. The changes in the plating solution composition and the results of the plating condition at this time are shown in the table.

As shown in the results shown in the table, the conventional (comparative example) method
If the plating area changes rapidly, the component concentration will also change,
Roughness occurred on the plating surface.

In the case of the present invention, since the amount of replenishment per unit time of the replenishing device can be automatically controlled in accordance with changes in the plating area, it is possible to stably use the plating solution for a long time. Further, in this example, the case of electroless copper plating has been described, but it can be similarly applied to other electroless plating.

〔Effect of the invention〕

As explained above, according to the present invention, it was possible to provide a method excellent in controlling the concentration of each component of an electroless plating solution and an apparatus used in the method.

Claims (4)

[Claims] 1. While controlling the concentration of each component in the electroless plating solution,
In a method where plating is performed continuously, the concentration of each component is analyzed, and based on the obtained analysis value, the operating time interval of the replenishment device for each component is determined until the next analysis, and the unit plating solution is An electroless plating method characterized in that the amount of replenishment per unit operating time of the replenishing device is determined based on the plating area relative to the amount. 2. A means for measuring the concentration of each component of the electroless plating solution,
Compare each preset component and its measured results,
In a continuous electroless plating apparatus, the continuous electroless plating apparatus includes a means for replenishing a reduced component in accordance with a reduced amount, and a means for determining an operating time interval of the replenishing device in accordance with a reduced amount of the component;
1. An electroless plating apparatus, comprising means for determining the amount of replenishment according to the area of an object to be plated. 3. 3. The electroless plating apparatus according to claim 2, wherein the method for detecting the plating area includes detecting the presence or absence of the object to be plated using a position sensor. 4. 4. The electroless plating apparatus according to claim 2, wherein the component replenishment device is a diaphragm pump whose replenishment amount can be electrically varied.