Double sided printed circuit boards are used where a complex circuit with more number of ICs is to be accommodated. For preparing double sided PCB, base material has copper-clad on both the sides. The connection from one side of the board are taken to the other side using a plated through holes. Thus, the difference in processing a double sided PCB is processing of plated through hole. Initially base material is selected as copper clad and pre drilling is necessary. The copper clad is coated with photo resist. The positive of the artwork is kept pressed with copper clad and exposed to ultra violet light. This process protects part of the board from being plated. This process is known as masking. The exposed unwanted part of the artwork forms precipitate. Plating should be done through holes and around them on both sides of the boards. The exposed board is cleaned with various acids, and then dipped in SnCl₂ activation solution. The unexposed part is activated. The board is tinned by electrolysis. The holes and track are tinned. Then the board is developed in developer to remove the precipitate on the unwanted part. Final finish is then gives to the board by cutting it in required shape.