Metal Finishing Guide Book

2012-2013

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Fig. 3. Common pulse waveforms. gy, pulse-plating systems provide the opportunity to modulate the voltage or current to achieve different results. The application of gold, silver, and copper with pulse plating results in finer grain structures, higher surface densities, and lower electrical resistance. Additionally, plating times can be reduced by up to 50%. These characteristics make pulse plating attractive, if not mandatory, in the electronics industry. From an industrial standpoint, pulse plating has found a number of important applications. For example, when used in chromium plating, pulse plating will result in a harder, more wear-resistant surface. In a nickel plating application, using pulse plating may eliminate the need to add organic compounds to control stress and will result in a brighter finish with better thickness control and reduced plating times. Many plating profiles are available, including standard pulse, superimposed pulse, duplex pulse, pulsed pulse, and pulse on pulse. These waveforms can be obtained from a unipolar power supply. Other variations, possible when using a bipolar pulsing rectifier, include pulse reverse, pulse reverse with off time, pulsed pulse reverse, and pulse-on-pulse reverse. Fig. 3 illustrates a few of the many different pulse waveforms available. The pulsing profile you use will be determined by the type of plating finish desired, the makeup of the plating bath, and the type of power supply available. There are three basic types of power supply technologies employed to achieve pulsed outputs. The most common design consists of a standard SCR phase-controlled rectifier with a semiconductor switch on the output. Although this system can be successfully employed in almost all pulsing applications, there are some drawbacks, mainly the inherent limitations associated with pulse rise and fall times. 772

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