In single sided PCB the conductor tracks run only on one side of copper clad board. Thus crossing of conductors is not permitted. Base material is chosen as per the application. It is mechanically and chemically cleaned. Then the photo resist solution is evenly applied. Photo resist is a organic solution, which when exposed to light of proper wavelengths, change their solubility in the developers. There are two types of photo resist (1) Negative acting photo resist. (2) Positive acting photo resist. Negative acting photo resist is a mixture of which is initially soluble in its developer but after exposure to light, it is not soluble. So the unexposed soluble is selectively dissolved and washed away, leaving the desired resist pattern on the copper clad laminate. Coating of photo resist is done by
(1) Spray coating
(2) Dip coating
(3) Roller coating
The coated copper-clad laminate and film negative are kept in glass frame in intimate contact with each other. The assembly is exposed to ultra violet light for 3 minutes. The exposed board is rinsed in the developer tank. Proper developer has to be taken and used for a particular photo resist. Then the PCB is coloured in a tray. The dye revels the faults due to contrast. The faults are then separated by retouching. Etching eliminates the unwanted copper. Spray etching gives best results. Ferric chloride or cupric chloride is used as etching materials. Cupric chloride is regenerative and is thus preferred to ferric chloride. The etching solution is kept agitating by circulating low pressure air nozzles. Than the board is washed with water and dried. The board is then drilled with high speed drilling machine. The drill sizes range from 0.5mm to 1.8mm. Centring of hole on the land pad is done automatically.