Operating Condition Copper Pyrophosphate

The bath is usually operated between 50 and 60oC. Temperatures greater than 60oC can lead to the rapid formation of orthophospate. Current Density Cathode current density is a function of the temperature and agitation of the plating bath. However, under standard operating conditions a current density of 1 to 9 A/dm2 is appropriate.

The anode current density is fairly critical and should be kept between 2 and 4 A/dm2. At too high and anode current density, an insoluble oxide tends to form. If the anode current density is too low, the anode efficiency exceeds 100%. The operating current density range may be increased by ultrasonic, current interruption on reversal, and by increased metal concentration. Agitation Copper pyrophosphate solutions are among those which must be most vigorously agitated. Without sufficient agitation, a brownish deposit is obtained and the operating current density range is drastically lowered.

A solution can be continuously agitated by either one or a combination of three methods; air, mechanical movement of the cathode, or ultrasonic. When air agitation is used, the air should be supplied by a low pressure blower because compressed air can contain oil. Ultrasonic agitation can reduce anode and cathode polarization and permits a 4 to 4.5 times increase in the deposition rate over that obtained with intensive mechanical agitation. The combination of ultrasonic and periodic reverse current increased current efficiency and allowable anode current density. Many process plated over zinc die castings showed that ultrasonic agitation of copper pyrophosphate solutions displaced air or hydrogen gas from blind pockets and resulted in more uniform deposits than could be obtained with copper cyanide strikes. Treatment before Plating Conventional cleaning is used for parts to be plated in pyrophosphate solutions. For ferrous metals, a cyanide or copper pyrophosphate strike before plating is needed to ensure good adhesion. Zinc die castings are normally given a cyanide strike before copper pyrophosphate plating.