Analysis of trivalent chromium using in PCB electroplating
There are still many weakness of trivalent chromium electroplating , such as unstable plating, sensitivity to impurity, high cost, dark color of film and so on. These must be consider except especially in the following aspects.
1. Difficulty in thickening of plating.
The thickness of trivalent chromium plating just be few microns normally, it only apply to ornamental plating. This is mainly due to that the electroplating condition being change as the time of electroplating. During electroplating, cathode current density and the time could be controlled, while the solution PH and temperature does not. So the solution PH and temperature are the main reason why the plating can not be thickened.
2. Difficulty in anode choosing.
Because of unstable plating and sensitivity to impurity, the solubility material usually can’t be chosen for anode. But trivalent chromium is easy to be oxidized to hexavalent chromium by the insolubility anode .It cause the plating change accelerates. At present, the study about trivalent chromium in China almost use the graphite as anode. The following is the graphite’s disadvantage:
(1). The electrode being oxidized to carbon dioxide because that the unstable in the bath solution.
(2). The plating solution could be polluted by the carbon residue which from the anode collapsing
(3). After oxidizing, anode thinning causes that the internal resistance rises and the distance between anode and cathode increases.
3. Complicated solution composition.
Domestic scholars proposed a new electroplating system—Oxalic acid salt – ethylenediamine tetraacetic acid system. It’s a complicated formula of the system, with the disadvantages such as small range of the temperature and current density, the graphite anode. During the actual process, it is difficulty to management and maintenance due to complicated composition.