Electroplating is one of the most common procedures utilized in day-to-day life, but details of which often go unnoticed. It has numerous applications in industries where a protective coating on different materials is necessary, in jewellery production and in very specialized areas such as Integrated Circuit (IC) fabrication techniques, which is the current topic of discussion. Since, this is a rather unexplored area; this article would give the readers an insight regarding the basic procedure of electroplating.
Electroplating consists of coating or rather plating a conducting metal surface with other materials of choice such as copper, gold, silver or nickel to prevent corroding and add to a better surface finish or polish. The laboratory setup for electroplating is simple and crude and consists of components such as a beaker, platinum or tungsten wire gauge (to act as the anode terminal), the electrolyte solution (containing salt solution of the material to be deposited), the material to be electroplated, heater with a magnetic stirrer bit, a constant current source and connecting wires. The setup essentially consists of two terminals, one positive known as the anode terminal and one negative, known as the cathode terminal. Here, the platinum or tungsten wire gauge acts as the anode or the positive terminal, whereas, the metal plate to be electroplated acts as the cathode or the negative terminal. The positive and negative terminals of the constant current source are attached to subsequent terminals via connecting wires. Upon passage of current, the electrolyte solution containing salt of the metal to be electroplated undergoes electrolysis to divide into its corresponding cations (positively charged ions which are attracted towards the cathode) and anions (negatively charged ions which are attracted towards the anode) respectively. The positively charged metal ions thus get attracted towards the negatively charged cathode which is nothing but the material to be electroplated and deposits on the surface whereas, the anions are attracted towards the positively charged anode, i.e., the platinum or tungsten wire gauge.
The electrolyte solution is chosen in accordance with the material to be electroplated. Potassium auro cyanide for gold electroplating, copper sulphate for copper electroplating and nickel sulphate for nickel electroplating are the respective electrolyte solutions employed in each case. A weighted amount of the salt is dissolved in deionized water and the resultant solution is heated with constant stirring using the magnetic stirrer bit to provide a uniformly distributed solution. Temperatures of the electrolyte bath may vary in accordance with the different materials to be plated. For e.g., the potassium auro cyanide bath for gold electroplating requires the solution to be maintained at a fixed temperature of 75°C throughout the duration of electroplating.
The constant current source should be maintained at a fixed value throughout the duration of electroplating. A lower current rate will result in better surface finish and smoother coating of the metal surface placed at the cathode terminal. However, this technique is highly time consuming for those cases where a thicker metal layer (more than 1 micron) is desired to be deposited. Hence for thicker electroplated layers, the current rate needs to be optimized such that a smooth surface profile is resulted within a decent amount of time spent.