JPH0247550B2 - MUDENKAIDOMETSUKIEKINOKANRIHOHO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for managing an electroless copper plating solution for stably and continuously operating the electroless copper plating solution to obtain stable deposited copper.

Electroless copper plating solutions used in the manufacturing process of printed wiring boards require strict composition control in order to obtain deposited copper of stable quality. For this reason, automatic controllers are used to analyze the composition of the plating solution and replenish the consumed components.

Generally, automatic controllers measure and replenish the copper ion concentration, hydroxide ion concentration, and formalin concentration, which are the main components of electroless copper plating solution, and are used for the absorbance measurement method, glass electrode method, and sodium sulfite added glass, respectively. Measured using the electrode method. However, for formalin, measurement accuracy is poor and measurement is difficult in the high pH range. Because the reaction speed is slow, there are problems such as a large time delay in measurement and a decrease in control accuracy. In addition, as a method developed to avoid the difficulties of formalin analysis, the deposition rate of electroless copper plating solution is measured continuously or intermittently at regular intervals, and formalin is replenished according to the measurements. There is a method to do this, but this method does not necessarily keep the formalin concentration constant.

The present invention was made in view of these points, and it is not necessary to analyze formalin, and it is possible to detect the effect of a side reaction known as the Cannitzaro reaction by using two highly reliable measurements of copper ion concentration and hydroxide ion concentration. This method is characterized in that the total amount of formalin consumed, including consumption, is calculated and replenished.

The present invention provides a method for managing an electroless copper plating solution that analyzes and measures the necessary composition and parameters and replenishes them in proportion to the consumed components _. ²⁺ , and △
The method is characterized in that C _OH- is measured and formalin is replenished according to the relational expression ΔC _HCHO =2ΔC _OH- −6ΔC _Cu ²⁺ .

That is, the present invention controls the electroless copper plating solution by analyzing and replenishing the composition excluding A formalin as necessary.

B From the measured reduction in copper ions and hydroxide ions (△C _Cu ²⁺ , △C _OH- ), the reduction in formalin is determined by the relational expression △C _HCHO = 2△C _OH- −6△C _Cu ²⁺ Amount△
The electroless copper plating solution is controlled by calculating C _HCHO and replenishing formalin. The principle of calculating the formalin reduction amount, which is based on the copper ion concentration and the hydroxide ion concentration, is as follows.

The reactions of electroless copper plating solution include the following main reactions: C _u ²⁺ +2HCHO+4OH ^- →C _u ⁰ +2HCOO ^- +2H ₂ O+H ₂ ↑ (1) and 2HCHO+OH ^- →HCOO ^- +CH ₃ OH (2) It is known that there is a side reaction (Cannitzaro reaction) that proceeds separately. From equations (1) and (2), if the amount of decrease in each component is expressed as concentration change △C, then △C _Cu ²⁺ = △C _Cu ²⁺ (3) △C _OH- = 4△C _Cu ²⁺ + △ C _OH- (4) △C _HCHO =2△C _Cu ²⁺ +2△C _OH- (5). ΔC _OH- is the amount of decrease in hydroxide ions due to side reactions. Substituting equation (4) into equation (5), we get △C _HCHO = 2△C _OH- −6△C _Cu ²⁺ (6), and the total reduction of formalin including side reactions can be determined by two highly accurate measurements. It can be calculated from the amount of decrease in copper ion concentration and hydroxide ion concentration.

In the present invention, the copper ion concentration is measured by the absorbance measurement method, and the hydroxyl ion concentration is measured by the glass electrode method.
Methods such as pH measurement or neutralization titration are used. A microcomputer is also used to store measured values and calculate formalin consumption.
In the present invention, since the amount of formalin reduction is calculated by equation (6) using the copper ion concentration and the hydroxide ion concentration, it is necessary to use a microcomputer.

In the method for controlling an electroless copper plating solution according to the present invention, replenishment of formalin is controlled only by calculation, and replenishment is not stopped when a set value is exceeded, unlike other components. Therefore, the accuracy of △C _Cu ²⁺ and △C _OH-, which are the basis of calculation, is very important. Figures 1 and 2 show measurement intervals of 1
Conceptually, the difference in control accuracy due to the difference in the calculation method of △C _Cu ²⁺ and △C _OH- is the decrease in copper ion concentration and hydroxyl ion concentration in a system with a 5-minute time delay from sampling to measurement. This is shown in .

Figure 1 shows the deviation of the copper ion concentration and hydroxyl ion concentration from the set concentration by the amount of decrease in the copper ion concentration and hydroxide ion concentration, respectively △C _Cu ²⁺ , △
This figure shows the replenishment of formalin in response to changes in [C _u ²⁺ ] or [OH ^- ] when C _OH- is used. Figure 2 shows the consumption amount within a certain time interval as △C _Cu ^{2 +} , △C _OH- . As is clear from Figures 1 and 2, if there is a delay in the system,
In the method shown in Figure 1, formalin is excessively replenished,
This is an inappropriate method because it gradually accumulates, whereas in Figure 2, formalin is replenished only in response to the actually consumed [C _u ²⁺ ] (or [OH ^- ]).

As well as the time delay of the system, external noise affects the amount of decrease in copper ion concentration and hydroxyl ion concentration △C _Cu ²⁺ and △C _OH- . This is caused by air bubbles accidentally passing through the absorbance cell during absorbance measurement, or by noise caused by the operation of external equipment getting onto the signal line. Formalin replenished due to such causes still accumulates during long-term operation of the electroless copper plating solution, causing a decrease in control accuracy. In order to reduce or substantially eliminate the effects of such transient noise, △C _Cu ²⁺ , △C was calculated from the average value of measurements taken two or more times within a certain time interval (measurement interval). _OH- must be used.

In the present invention, when △C _Cu ²⁺ and △C _OH- take a negative value, they are treated as O, and when △C _HCHO calculated by equation (6) takes a negative value, it is also treated as O. shall be treated as such.

In addition, if the pH of the electroless copper plating solution is high,
pH measurement using the glass electrode method causes an alkaline error. Problems such as a shift in the pH value occur, reducing the accuracy of △C _OH- , which is the basis of calculation.
Therefore, it is necessary to determine ΔC _OH- by neutralization titration.

As a method to prevent excessive replenishment or accumulation of formalin due to measurement errors or noise, the deposition rate of the electroless copper plating solution is measured, for example, by a gravimetric method, continuously or intermittently at regular intervals, and the measured value is There is a method to stop formalin replenishment if it deviates from a defined range.

In the present invention, the necessary composition to be analyzed and measured,
The parameters are copper ion concentration,
There are hydroxide ion concentration, cyanide concentration, etc., as well as temperature, mixed potential, precipitation rate, etc.

Copper plating solutions include copper salts such as cupric sulfate,
A general plating solution is used, which consists of a complexing agent such as Lotusel's salt, a reducing agent such as formalin, and a pH adjusting agent such as alkali hydroxide.

Example C _u SO ₄・5H ₂ O 10g/HCHO (37%) 3ml/EDTA・4Na 45g/Polyethylene glycol (molecular weight 600)
20g/α,α'-dipyridyl 30mg/pH 13.0 Temperature 70°C Load 1.5dm ² /Plating solution was operated continuously for 4 hours using the controller shown in Figure 3.

In Figure 3, 1 is a plating liquid tank, 2 is a constant temperature water bath, 3 is a spectrophotometer (copper ion concentration measurement), and 4 is a
pH meter (hydroxide ion concentration measurement), 5 is a precipitation rate meter,
6 and 7 are recorders, 8 is a typewriter, 9 is a microcomputer, 10 is a meter relay, and 11 is a replenisher tank.

Controls were carried out using two methods: the method shown in the graph of FIG. 1 (Example 1) and the method shown in the graph of FIG. 2 (Example 2).

Example 1 (1) Measurement: [C _u ²⁺ ] Concentration Absorbance was measured once per minute by spectrophotometry.

[OH ^- ] Concentration Measured once per minute using the glass electrode method.

(2) Calculation method: Absorbance and
The difference between the set pH value and the measured value is defined as the amount of decrease in copper ion concentration (△C _Cu ²⁺ ) and the amount of decrease in hydroxide ion concentration (△C _OH- ), respectively, and △C is determined by equation (6) above. Asked for _HCHO . In addition, the pH setting value of the above plating solution is 13, the absorbance setting value is 0.36,
When a change in pH 0.01 is expressed as NaOH consumption, it is approximately
0.33 ml, and the change in absorbance of 0.01 is approximately 2.71 ml when expressed as CuSO ₄ consumption.

The results are shown in Figure 4. In FIG. 4, the horizontal axis indicates an arbitrary 90 minutes during measurement. As is clear from the figure, the controllability of pH and CuSO ₄ is as follows: pH 13.00
±0.07, absorbance at steady state 0.36±0.01,
It was controlled within a range of , with accuracy equal to or greater than that of general automatic controllers. In addition, the formalin concentration is 3 to 7 ml/
controlled within the range.

Note that, as is clear from FIG. 4, the formalin concentration shows a gradual increasing tendency. As explained using the conceptual diagram of FIG. 1, this is considered to be due to excessive replenishment of formalin due to a time delay in the system and measurement errors in pH value and absorbance due to external noise. Therefore, in Example 2, △C _Cu ²⁺ and △
C _OH- was defined as the difference between the previous measurement value and the current measurement value (consumption amount within a certain time interval), and each measurement value was the average value of the measurement values measured multiple times.

Example 2 (1) Measurement: [△C _Cu ²⁺ ] Concentration Absorbance was measured once per minute by spectrophotometry.

[OH ^- ] Concentration Average value of values measured 8 times per minute using the glass electrode method.

(2) Calculation method: The consumption amount (previous measurement value - current measurement value) within a certain time interval is calculated as the amount of decrease in copper ion concentration (△C _Cu ²⁺ ) and the amount of decrease in hydroxide ion concentration (△C _{OH )} , △C _HCHO was calculated using the above equation (6). The set values of the plating solution, the amount of NaOH consumed with respect to a change in pH of 0.01, and the amount of CuSO ₄ consumed with respect to a change in absorbance of 0.01 are the same as in Example 1 above.

(3) pH correction: When replenishing CuSO ₄ and formalin,
The pH associated with the replenishment decreases. Therefore, in this example, in addition to replenishing the amount of NaOH consumed by the plating reaction, an amount of NaOH to compensate for the decrease was added.
Add _CuSO4 and formalin at the same time when supplementing. However, the amount of NaOH for pH correction is not used in calculating formalin consumption.

The results are shown in FIGS. 5 and 6. Here, the fifth
Time "0" in the figures and FIG. 6 indicates the time at which the measurement starts. Moreover, FIG. 5 shows the relationship between pH change, amount of formalin input, and concentration, and FIG. 6 shows pH change and absorbance change over the entire measurement time.

As is clear from the figure, the controllability of pH and CuSO ₄ is as follows: pH is 13.00±0.07, absorbance is 0.36±
It is controlled in the range of 0.02, and
Formalin concentration was controlled within the range of 3-4 ml/ml.

In this example, the amount consumed within a certain time interval is the amount of decrease in copper ion concentration (△C _Cu ²⁺ ) and the amount of decrease in hydroxide ion concentration (△C _OH- ), and the influence of external noise is removed. and pH correction, formalin is not excessively replenished as explained in the conceptual diagram of FIG. Therefore, Example 1
Formalin replenishment was carried out with higher precision.

Conventional automatic controllers must analyze formalin, and furthermore, measurement is difficult in the high pH range where formalin measurement accuracy is poor.
There were problems such as slow reaction speed, large measurement time delay, and reduced control accuracy.

However, as explained above, according to the method of the present invention, it has become possible to control formalin without analyzing it.

[Brief explanation of drawings]

FIGS. 1 and 2 are graphs showing formalin replenishment amounts based on different calculation methods for the decrease in copper ion concentration and hydroxide ion concentration, and FIG. 3 is a system diagram of the controller. Figure 4 shows pH, NaOH input amount, absorbance, and CuSO ₄ input amount when the difference in copper ion concentration and hydroxide ion concentration from the set value is defined as the decrease in copper ion concentration and the decrease in hydroxide ion concentration, respectively. , a graph showing the relationship between formalin input amount and concentration. Figure 5 shows the pH change and formalin when the consumption amount of copper ion and hydroxide ion within a certain time interval is taken as the decrease in copper ion concentration and hydroxide ion concentration. Graph showing the relationship between input amount and concentration, Figure 6 is pH
and a graph showing changes in absorbance. Explanation of symbols, 1 is a plating liquid tank, 2 is a constant temperature water tank,
3 is a spectrophotometer, 4 is a pH meter, 5 is a precipitation rate meter,
6 and 7 are recorders, 8 is a typewriter, 9 is a microcomputer, 10 is a meter relay, and 11 is a replenisher tank.

Claims (1)

[Claims] 1. A method for managing an electroless copper plating solution in which necessary compositions and parameters are analyzed and measured, and replenishment is performed in accordance with consumed components, in which the amount of decrease ΔC in copper ion concentration and hydroxide ion concentration is A method for managing an electroless copper plating solution, which comprises measuring _Cu ²⁺ and ΔC _OH- and replenishing formalin according to the relational expression ΔC _HCHO =2ΔC _OH- −6ΔC _Cu ²⁺ . 2. The method according to claim 1, wherein the measured reduction amounts ΔC _Cu ²⁺ and ΔC _OH− in the copper ion concentration and hydroxide ion concentration are the consumption amounts of copper ions and hydroxide ions within a certain time interval. How to manage electrolytic copper plating solution. 3. The electroless method according to claim 2, wherein the decrease amounts ΔC _Cu ²⁺ and ΔC _OH− in the copper ion concentration and the hydroxide ion concentration are average values of measured values measured two or more times within a certain time interval. How to manage copper plating solution. 4. A method for managing an electroless copper plating solution according to claim 1, 2, or 3, characterized in that the amount of decrease in hydroxide ion concentration ΔC _OH- is measured by a neutralization titration method. . 5. Measuring the deposition rate of the electroless copper plating solution continuously or intermittently at regular intervals, and stopping formalin replenishment when the measured value deviates from a predetermined range. A method for managing an electroless copper plating solution according to any one of claims 1 to 4.