The Manufacturing Process
The manufacturing process is carried on in a special and clean environment where the air is pure and there is no such type of pollution that could contaminate the procedure. The components are to be kept absolutely clear off any mixture of any substance that would result in any kind of failure in the production.
Steps to manufacture:
The following steps to the manufacturing of circuit boards may differ from one board to another, but these are the common procedures used in instrumentation in India. The manufacturing process of a printed circuit boards are as follows:-
Producing the surface or the substrate
First the woven glass fiber is taken and filled with epoxy resin by dripping or by spraying. This is done with the help of a process station. Then the glass fiber is rolled through a roller so that the desired amount of thickness is attained and extra resin is blotted out. The substrate material is then passed through an oven and then cut out into large panels.
The substrate gets semi-cured in the oven which makes the board hard. All the panels are then stacked in layers and where adhesives are applied on them with coverings of copper foil. The whole stack is then heated at 170 degree Celsius with pressure of 1500 PSI for over an hour so that the resins could get fully cured and the copper foil could be tightly pasted on the surface.
Drilling holes
The large substrate panels are taken and pilled up one on the other in a perfect placement so that the plates do not move. Each of the large boards can be made into several printed boards. The stacks of boards are then pinned down to avoid any movement during the cutting and drilling process. The stacks are then placed in a machine which is responsible for drilling holes and removing all excess substance that clings to the holes. Each side of the boards is covered with copper plate.
Added and Subtracted Method
The printed circuit pattern is created by two methods. These methods are the added method or the subtracted method. The added method is very simple where the copper added or plated to the surface or the substrate according to the required pattern. This leaves the other parts untouched and so only the network can be easily created.
The second method is the subtracted method where the full substrate is coated with the copper and plated thoroughly. Then the area which is not required is removed or subtracted from the board leaving the lines of copper network to remain.
The following are descriptions of the added method:
At first the substrate is degreased, then entire panel is passed through the vacuum chamber. Here layers of photo resist materials, which are positively charged, are compressed onto the surface of the foiled substrate. Photo resist materials are those materials which become soluble when ultraviolet rays fall on them. Now the vacuum ensures that no air is trapped inside the foil and photo resist. Next the designed or patterned mask is placed on the photo resist board, which is then placed under the intensity of ultraviolet light.
The designed mask is then removed and the surface is sprayed with alkaline developer which dissolves the irradiated photo resist from the printed pattern. This allows the copper foil to merge out and remain exposed on the substrate.
The whole board is then plated with electrode copper. The foil on the substrate works as a cathode in the process. The copper is plated on the exposed parts with a thickness of about 0.002 inches. The photo resist is then taken off the boards with solvent so that the substrate copper foiled material is exposed. Then the boards are sprayed with acidic solution that eats away the foiled copper. The main pattern is protected by the tin lead coating which remains unaffected by the acid spray.
