Basic working principle of pulse electroplating power supply
Publisher: Administrator Date：2021-03-05
Pulse electroplating is a powerful means to improve the quality of the coating through the control method outside the tank. Compared with the ordinary DC electroplating coating, it has more excellent properties (such as corrosion resistance, wear resistance, high purity, conductivity, welding and resistance It can be changed * can be better, etc.), and can greatly save rare and precious metals. Therefore, it is better used in functional electroplating. At present, square wave pulses are mostly used in pulse electroplating.
The pulse electroplating power supply can generate a square wave pulse current. It cannot obtain an ideal square wave when used in electroplating, but a waveform similar to a trapezoid, which will affect the full play of the beneficial effects of the instantaneous high potential of the pulse electroplating. The pulse frequency will also have a greater impact on the crystallization of the coating. If the frequency is too low, the effect is not obvious; if the frequency is too high, the degree of waveform distortion will be large, and even the pulse current will become a direct current. The correct use of pulse electroplating power (such as equipment installation, equipment selection, parameter selection, etc.) has an important impact on the pulse waveform, equipment reliability, and normal use of the superiority of pulse electroplating.
The digital pulse power supply of Shenzhen Rongdaxin Power Co., Ltd. has the following multiple waveforms: DC; positive pulse; negative pulse; positive and negative pulse; negative DC; DC superimposed pulse.
1. The basic principle of commutation pulse electroplating
During the pulse electroplating process, when the current is turned on, the electrochemical polarization increases, the metal ions near the cathode area are fully deposited, and the plating layer is fine and bright; when the current is turned off, the discharge ions near the cathode area return to the initial concentration. Elimination of concentration polarization.
Commutation pulse electroplating is customarily called double (ie, two-way) pulse electroplating. It introduces a set of reverse pulse currents after outputting a set of forward pulse currents. The duration of the forward pulse is long. The duration of the reverse pulse is short, large and short. The highly inhomogeneous anode current distribution caused by the time reverse pulse will cause the coating convexity to be strongly dissolved and leveled. The typical periodic commutation pulse waveform is shown in the figure below.
Typical periodic commutation pulse waveform
2. The advantages of periodic commutation pulse electroplating
1. The reverse pulse current improves the thickness distribution of the coating, the thickness of the coating is uniform, and the leveling is good.
2. The anode dissolution of the reverse pulse causes the metal ion concentration on the cathode surface to rise rapidly, which is conducive to the use of high pulse current density in the subsequent cathode cycle, and the high pulse current density makes the formation rate of crystal nucleus faster than the growth rate of crystal. Therefore, the coating is dense, bright, and low in porosity.
3. The reverse pulse anode stripping greatly reduces the entrapment of organic impurities (including brightener) in the coating, so the coating has high purity and strong discoloration resistance, which is particularly prominent in cyanide silver plating.
4. The reverse pulse current oxidizes the hydrogen contained in the coating, which can eliminate hydrogen embrittlement (for example, reverse pulse can remove co-deposited hydrogen during electrodeposition of palladium) or reduce internal stress.
5. The periodic reverse pulse current keeps the surface of the plated part in an activated state, so that a coating with good bonding force can be obtained.
6. The reverse pulse is beneficial to thin the actual thickness of the diffusion layer and improve the cathode current efficiency. Therefore, proper pulse parameters will further accelerate the deposition speed of the coating.
7. In the electroplating system where additives are not allowed or allowed in a small amount, double-pulse electroplating can obtain a fine, smooth and smooth coating.
Therefore, the temperature resistance, wear resistance, welding, toughness, corrosion resistance, electrical conductivity, discoloration resistance, smoothness and other performance indicators of the coating are doubled, and rare precious metals (about 20%-50%) and additives (such as Bright cyanide silver plating is about 50%-80%).
3. Periodic commutation pulse current waveform
1. Single pulse commutation on the off time.
That is, a forward pulse related to the off time is followed by a reverse pulse related to the off time. This waveform has the advantages of pulse and commutation, but the disadvantage is that the pulse commutation function is imperfect.
2. Single pulse commutation without interruption time.
That is, a forward pulse with no interruption time is immediately followed by a reverse pulse with no interruption time. This waveform has a more obvious effect on improving the thickness distribution of the coating, but the effect of improving the crystallization of the coating is not ideal, and it is generally not suitable for precious metal electroplating.
3. Pulse commutation
That is, a group of forward pulses is followed by a group of reverse pulses (Note: both forward and reverse pulses are group waves rather than single waveforms). This waveform is a typical periodic commutation pulse waveform, and it also improves the thickness distribution of the coating It has the dual effect of improving the crystallization condition of the coating and is the most widely used in functional electroplating.