SU1486764A1 - Method and apparatus for monitoring thickness of electroplating coating - Google Patents

Description

The invention relates to an instrumentation technique and can be used to control the thickness of electroplated coatings of objects by a non-destructive method. The purpose of the invention is to improve the accuracy in measuring objects placed in a galvanic bath by excluding

with

1486764

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1 486764

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effect of the electrical resistance of conductive material on the measurement result. Before switching on the current through the electrolyte, the readings of the indicator 5 are equal to zero, since model resistance 3 and the resistance of the controlled object 6, as well as the currents of the sources 1 and 2 of the current are equal to each other. As the plating metal is deposited, the resistance of the object to be monitored 6 compared to the reference resistance 3 insulated by the dielectric decreases. The controlled resistance of the electroplated coating of an object is inversely proportional to the measured voltage. According to the indications of the indicator, the known width and length of the conductor (controlled resistance) determine the thickness of the electroplated coating in the process of its buildup. The currents and the interfering electromagnetic fields equally affect the controlled object 6 and the sample resistance, which release the same voltage, since both are connected to the cathode of the galvanic bath. Therefore, the indicator readings reflect only the change in the resistance of the object due to the galvanic buildup of the metal. 2 sec. f-ly, 1 ill. /

The invention relates to measuring technique and can. be used to control the thickness of electroplated coatings of objects by a non-destructive method, in particular, in the manufacture of printed circuit boards'.

The goal is to improve accuracy at iz-. measurement of objects placed in a galvanic bath by eliminating the influence of the electrical resistance of the conductive material on the measurement result.

The method of controlling the thickness of the electroplated coating is ^ 5

that a dielectric protective coating is applied to the reference sample, the controlled and reference samples are immersed in an electroplating bath, the resistance of the reference and controlled samples is measured, and the thickness of the coating is calculated.

The drawing shows a block diagram of a device implementing the method.

The device contains sources I and 2 currents, a reference resistance 3, a differential amplifier 4, an indicator 5 and terminals (not shown) intended for connection with the object to be monitored 6.

The device works as follows.

Before switching on the current through the electrolyte, the readings of the indicator 5 are equal to $ 5

zero, since the resistances of the sample and the monitored object and the current of sources 1 and 2 are equal to each other.

As the deposition of metal gal-. The resistance of the controlled object 6 compared to the standard resistance 3, which is insulated by a dielectric, decreases and the voltage of the amplifier defined by the expression

& and = ι „(κ„), (Η

where Ι _ο

^{and l} about ^to x

- current sources 1 (2) current;

- resistance 3 to the deposition of electroplating;

- resistance of the coating material.

From the expression (1) it follows that the controlled resistance of the electroplated coating B. * of the object is inversely proportional to the measured DC voltage and is determined by the expression

The indicator 5, the known width and length of the conductor (controlled resistance) determine the thickness of the electroplating · coating in the process of its extension.

Since the controlled object 6 and the exemplary resistance 3 (conductors) are in close proximity to one another and both are connected to the cathode of the plating bath, the currents and interfering electromagnetic fields equally affect the controlled object 6 and the exemplary

five

resistance 3 and the same voltage is released on them at any time, which is suppressed by differential amplifier 4. Thus, the readings of indicator 5 reflect only the change in resistance of object 6 due to galvanic metal buildup.

The proposed method due to the possibility of controlling the thickness in the process of electroplating allows you to control the technological process, therefore, to improve the quality of the coating.

Claims (2)

Claim one . The method of controlling the thickness of the galvanic coating, which consists in measuring the resistances of the reference and controlled samples and calculating the thickness of the coatings, characterized in that, in order to improve accuracy when measuring objects placed in a galvanic bath, a dielectric protective is applied to the reference sample I486764 6 the roof and immersed in a galvanic bath. 2. A device for controlling the thickness of the electroplated coating, containing a four-shoulder bridge connected in series, two current sources in which are the first and second arms, the exemplary resistance by the third shoulder, and the terminals of the fourth shoulder are intended for connection to the object being monitored, a differential amplifier and an indicator , free resistance terminals are connected to the output terminals of the current sources and the inputs of the differential amplifier, characterized in that, in order to improve the accuracy in the measurement 20 objects placed in a galvanic bath, exemplary resistance is made with a dielectric applied to the surface, the common terminal of current sources, the third, and fourth The 25 arms and the differential amplifier are designed to be connected to the cathode of the plating bath.