JPS648711B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for continuously measuring electroless plating thickness, which continuously and accurately measures the electroless deposit thickness that changes moment by moment in an electroless plating solution.

Conventionally, as a method for continuously measuring the electroless plating thickness during a deposition reaction, the sensor material is immersed in a plating solution using the electrical conductivity of the plating film.
Generally, changes in electrical conductivity are converted into changes in plating thickness and measured continuously.

FIG. 1 is a diagram showing a conventional electroless plating thickness measuring device. In FIG. 1, 1 is an electroless plating solution, 2 is an object to be plated, 3 is a metal sensor, 4 is a sensor holder, and 5 is a resistance meter.

When measuring the plating thickness using this electroless plating thickness measuring device, the object to be plated 2 and the metal sensor 3 are immersed in the plating solution 1 at the same time, and the metal sensor 3 is immersed in the plating solution 1.
The electrical conductivity changes due to the thick film deposited on the
The amount of change is converted into a plating thickness and measured using a resistance measuring meter 5. Note that various amplifiers are used in the resistance measuring meter 5 in order to increase sensitivity.

FIG. 2 shows the results of actually measuring plating thickness by the inventors using the electroless plating measuring device shown in FIG. 1. In order to completely eliminate the potential influence of the resistance meter 5, the plating thicknesses of the plated object 2 and the metal sensor 3 were measured without connecting the resistance meter 5.

In FIG. 2, characteristic A shows the relationship between the plating time and the deposited thickness of the object to be plated 2, and characteristic B shows the relationship between the plating time and the deposited thickness of the metal sensor 3. As plating conditions, plating liquid 1 contains:
Well-known electroless Ni-B bath, plated object 2 is pretreated epoxy plate, metal sensor 3 is 0.3mmφ
Nickel wire was used.

As is clear from FIG. 2 above, in the initial reaction of electroless plating, the deposition rate differs depending on the material of the object 2 to be plated and the processing conditions. For this reason,
When controlling the deposited thickness on the order of several thousand angstroms, it is difficult to accurately measure the plating thickness because the deposited thicknesses of the metal sensor 3 and the plated object 2 are different.

This invention was made to eliminate the above-mentioned conventional drawbacks, and an object of the present invention is to provide a method for continuously measuring electroless plating thickness that can minimize deposition errors at the initial stage of an electroless plating reaction. .

Embodiments of the method for continuously measuring electroless plating thickness of the present invention will be described below with reference to the drawings. Third
The figure is a perspective view of a sensor applied to one embodiment. Reference numeral 6 in FIG. 3 indicates a non-conductive material made of the same material as the material to be plated, and near both ends of one surface of this non-conductive material 6 there are connecting pads 7 for drawing out electrodes.
is provided. Reference numeral 8 denotes the mating surface between the connection pads 7 for leading out the electrodes.

The surface 8 to be plated is subjected to the same pretreatment as the object to be plated, and a first
By connecting the resistance meter 5 shown in the figure,
Plating thickness can be accurately monitored.

FIG. 4 is a perspective view of the sensor appearance after measurement when the resistance measuring meter 5 is connected between the electrode lead-out connection pads 7. In the figure, 9 indicates the electroless coating, and 10 indicates a crack in the electroless coating. .

As shown in FIG. 4, when a resistance meter is connected between the connection pads 7 for connecting the electrodes, the resistance meter will connect the connecting pads 7 for connecting the electrodes from the internal power source.
Since a current is passed between the two and the resistance value is measured from the current, it is thought that in an extremely thin film at the early stage of the electroless plating reaction, the current will destroy the film and cause cracks 10.

Actually, since the resistance measuring meter 5 has a measurement potential of 1 to 4 V, when such a sensor is used, it is necessary to use the minimum measurement potential.
Figure 5 shows the measured potential by modifying the resistance meter 5.
This data shows data measured under conditions where the voltage was lowered to 0.3V to prevent cracks from forming. Characteristic C in FIG. 5 shows the relationship between plating time and plating thickness of the plated object 2, and characteristic D
1 shows the relationship between the plating time and the plating thickness of the plating surface 8 of the sensor. The characteristics shown in FIG. 5 are similar to the data shown in FIG. 2, and it was found that the coating deposited on the sensor was thinner than the coating.

As shown in Figure 5, even if the sensor material is the same as that of the plated object, the deposit thickness may differ due to the fact that an electric potential is applied to the sensor from the outside. This is thought to occur because the redox potential of the sticking reaction is different from that of the coated material.

Therefore, in order to correctly monitor the amount of precipitation using the sensor shown in FIG. 3, there are two methods: either reduce the potential applied to the sensor as much as possible, or apply it intermittently. Of these, when the former potential is made as small as possible, an amplifier with a high amplification factor is required. Therefore, stable operation is difficult due to noise and the like.

FIG. 6 is a circuit diagram showing an electroless plating thickness measuring device applied to the electroless plating thickness continuous measuring method of the present invention. In this FIG. 6, 11 is a constant voltage circuit for applying a constant voltage to the sensor, and an operational amplifier (hereinafter referred to as an operational amplifier) 11
The inverting input end and output end of a are directly connected. The non-inverting input terminal of this operational amplifier 11a is a variable resistor VR
-1 is connected to the movable terminal. variable resistance VR
-1 is connected between the connection point between the resistor 11b and the Zener diode D and the ground. The resistor 11b and the Zener diode D are connected in series, the anode of the Zener diode D is grounded, and the resistor 1
A pulse signal P is applied from one end of 1b.

The output end of the operational amplifier 11a is connected to the sensor terminal _S1 via a resistor _R1 . The sensor terminal S ₁ forms a pair with the sensor terminal S ₂ , and the sensor terminal S ₂ is grounded. Resistor R ₂ a from both ends of resistor R ₁ ,
They are connected to the non-inverting input terminal and the inverting input terminal of the operational amplifier 12a via R ₂ b, respectively. A resistor R ₃ is connected between the inverting input terminal and the output terminal of the operational amplifier 12a.
is connected. Thus, op amp 12
A, resistors R ₂ a, R ₂ b, and R ₃ constitute an amplifier 12.

The output of the amplifier 12 is applied to the input terminal of an operational amplifier 14a of a sample-and-hold circuit 14. In addition, C ₂ is a capacitor, 5
is the resistance measuring device shown in FIG. 1, and V is the output potential. A pulse signal P from the pulse generating circuit 13 is applied to the gate G of the sample-and-hold circuit 14 and the resistor 11b of the constant voltage circuit 11. Sample and hold circuit 1
4 is provided to hold the measurement results and stably output the measurement results.

The pulse generation circuit 13 is composed of an oscillator 13a, capacitors _C1 , _C3 , and resistors _R4 , _R5 , and generates the above-mentioned pulse signal P determined by the time constant of the capacitor _C1 and resistors _R4 , _R5 . It is something to do.

Next, a method for continuously measuring electroless plating thickness according to the present invention will be explained using the electroless plating thickness measuring apparatus shown in FIG. A pulse signal P generated from the pulse generation circuit 13 is applied to the gate G of the constant voltage circuit 11 and the sample and hold circuit 14. Of these, in the constant voltage circuit 11, the ON signal of the pulse signal P enters the Zener diode D through the resistor 11b, creating a constant voltage of about 1V,
A voltage divided to 0.3V is input to the operational amplifier 11a by the variable resistor VR-1.

In the operational amplifier 11a, the low impedance
Output 0.3V to the output terminal and apply it between sensor terminals S ₁ and S ₂ through resistor R ₁ . This resistance
The purpose of R ₁ is to minimize the current flowing through the sensor,
The current that changes depending on the sensor resistance value is passed through the resistor _R1
The purpose is to generate a voltage drop across both ends of the .
In the example shown in FIG. 6, the resistor R ₁ is 10KΩ, and the maximum current flowing through the sensor is 3×10 ⁻⁵ A.

Next, the potential generated across the resistor _R1 is applied to the resistor by an operational amplifier 12a, which is the main component of the well-known amplifier 12.
R ₃ , the ratio of R ₂ a and R ₃ , i.e. R ₃ / (R ₂ a + R ₂ b)
Sample and hold circuit 1
Add to the input terminal of 4. An LF-398 or the like is suitable as the sample-and-hold operational amplifier 14a.

The input of this sample-and-hold circuit 14 inputs an external signal (i.e., the output of the amplifier 12) by turning on the gate G (“high”), and when the gate G is turned off, the input is cut off.
It holds the input signal as it is as an output voltage, and the holding time is determined by capacitor _C2 .

FIG. 7 shows a time chart of the electroless plating thickness measuring device shown in FIG. 6, where P is a pulse signal output from the pulse generator 13, and V
is the output voltage of the operational amplifier 14a. and,
15 indicates the on-time of the pulse signal P, and 16 indicates the off-time of the pulse signal P.

In this embodiment, when the on-time 15 is 1 msec and the off-time 16 is 9 msec, the output voltage V increases in steps according to the thickness of the deposit on the plating surface 8 of the sensor. The length of this step is as short as 1/100 second, so it is the same as a linear rise. Therefore, as shown in FIG. 6, the voltage applied to the sensor connected between the sensor terminals S ₁ and S ₂ can be applied in 1/10 of the time required for normal measurement.

FIG. 8 is a sectional view showing the sensor applied to the present invention attached to a sensor mounting jig;
FIG. 9 is a perspective view thereof. In both Figures 8 and 9, 6 to 8 are shown in Figures 3 and 4.
It is the same as shown in the figure, 6 is a non-conductive material, 7
8 is a connection pad for drawing out the electrode, and 8 is a mating surface.

In addition, 17 is an insulating plate part of a copper-clad laminate, 18 is a metal foil plated by electroless plating using copper foil,
Reference numeral 19 indicates a plastic screw for attaching the sensor to the mounting jig so as not to affect the electroless reaction. Furthermore, 20 is a mask plate for masking the metal foil, 21 is a window for bringing the plating surface 8 of the sensor into contact with the plating liquid, and 22 is an external connection terminal.

As is clear from FIG. 8, a pad having the same shape as the connecting pad 7 for leading out the electrodes of the sensor is formed on the insulating plate part 17 using metal foil 18, and the connecting pad 7 for leading out the electrodes is secured by a plastic screw 19.
and a pad surface formed of metal foil 18 are fixed in contact with each other. In FIG. 9, external contact terminals 21 made of metal foil 18 output changes in the resistance value of the sensor.

Figure 10 shows the results using the electroless plating thickness continuous measuring device shown in Figure 6 and the sensors shown in Figures 8 and 9.
This figure compares the deposited thickness of the plated surface 8 of the sensor and the plated object 2 when the plating thickness is monitored over time. Characteristic E in FIG. 10 shows the relationship between the plating time and the plating thickness of the object to be plated. Further, characteristic F shows the relationship between the plating time and the plating thickness of the plated surface 8 of the sensor. These characteristics E and F almost match,
It can be seen that it is not affected by the potential for measurement.

As explained above, in the above embodiment, in order to use the same material as the object to be covered as the covered sensor and to minimize the influence of external potential, a pulsed voltage is applied. Since the measurement is performed with the cumulative voltage application time as short as possible, there is an advantage that the plating thickness can be measured with less error even during unstable deposition at the initial stage of the electroless plating reaction.

As described in detail above, according to the method for continuously measuring electroless plating thickness of the present invention, a sensor is constructed by attaching connection pads for drawing out electrodes to both ends of a non-conductive material made of the same material as the object to be plated, By applying a pulsed voltage to this sensor and sample-and-holding the voltage corresponding to the current flowing by applying the pulsed voltage in synchronization with the pulse, the electroless plating reaction is applied to the sensor. Since the plating thickness is continuously measured by converting the coating thickness from the resistance value of the deposited metal, the cumulative amount of voltage applied to the sensor can be minimized. Along with this, it has the advantage that deposition errors at the initial stage of the electroless plating reaction can be minimized. Furthermore, this method is a very simple method that allows continuous measurement of plating thickness without requiring special calculations.

[Brief explanation of drawings]

Figure 1 shows the configuration of an electroless plating thickness measuring device applied to the conventional continuous electroless plating thickness measurement method, and Figure 2 shows the configuration of the electroless plating thickness measuring device applied to the conventional continuous electroless plating thickness measurement method. FIG. 3 is a perspective view showing the configuration of a sensor applied to the electroless plating thickness continuous measurement method of the present invention; FIG. The figure is a perspective view showing the state in which cracks have been generated due to the application of overvoltage to the sensor in Figure 3, and Figure 5 is a graph showing the relationship between plating time, plated object, and deposits on the sensor using the sensor in Figure 3. A characteristic diagram showing the relationship between plating thickness, FIG. 6 is a circuit diagram of an electroless plating thickness continuous measurement device applied to the electroless plating thickness continuous measurement method of the present invention, and FIG. Fig. 8 is a time chart of the electroless plating thickness continuous measuring device of this invention, Fig. 8 is a cross-sectional view showing the state in which the sensor applied to the electroless plating thickness continuous measuring method of the present invention is attached to the mounting jig, Fig. 9 The figure is a perspective view showing the above sensor attached to a mounting jig, and Figure 10 is a case where the sensor shown in Figures 8 and 9 is used in the electroless plating thickness continuous measuring device shown in Figure 6. FIG. 3 is a characteristic diagram showing the relationship between the plating time and the deposition thickness of the plated object and the sensor. DESCRIPTION OF SYMBOLS 1... Plating liquid, 2... Plating object, 5... Resistance measuring meter, 6... Non-conductive material, 7... Connection pad for electrode extraction, 8... Plating surface, 11... Constant voltage circuit, 12...
Amplifier, 13...Pulse generator, 14...Sample and hold circuit.

Claims (1)

[Claims] 1. Immerse an object to be plated and a sensor consisting of a non-conductive material made of the same material as the object to be plated and provided with connecting pads for drawing out electrodes at both ends of the object, and apply the electrodes to the sensor in sequence at a predetermined period. A pulse-like first voltage is applied and a second voltage corresponding to a current flowing according to the resistance value of the sensor is applied to a sample-and-hold circuit, and the sample-and-hold circuit applies the pulse-like first voltage. sampling and holding the second voltage in synchronization with the voltage application;
A method for continuously measuring electroless plating thickness, characterized in that the plating thickness of the object to be plated is continuously measured by measuring a voltage held in the sample-and-hold circuit.