PCB layout
Preparation:
According to the information provided with the session sheet, firstly, the PCB schematic was transformed to the Ultiboard, which was going to be used to produce the PCB layout. Then there were changes in track width, spacing and via diameter as state below:

The track was set to 20mil with the minimum track of 10mil and the maximum of 100mil to avoid the track too small to be manufactured as the manufacturing process could not be very precise. A range of uncertainty is needed.
The spacing was set to 10mil.
The pad diameter and the drill diameter in via diameter were set to 1.6mm and 0.8mm respectively.

Next, the through hole pad annular ring for the top inner and bottom was changed to 0.3mm.
Fourthly, Power lines were set to 50mil. The thickness is relatively large as the power lines are going to support the main current of the circuit, the thicker the power lines are, the less the chance they could be melted. The size of footprint for IC’s was change to a pad diameter of 1.6mm and drill diameter of 0.8mm; all the others are change to 2mm for the pad diameter and 1mm for the drill diameter.
Finally the board size was set to 75mmX95mm(Y-X), two holes were placed on the board. The coordinate of first hole was 30mm(Y)-32mm(X), the second one was 43mm(Y)-75mm(X), both of them with a diameter of 3.5mm and a clearance of 6mm. This is a very important process as fail to do it would cause problem in PCB manufacturing.
To start design the PCB layout, all components were placed onto the board according to the component position in PCB schematic.
Then the changes of position and