Modern technology has streamlined the process of PCB fabrication. Almost
all tasks are conducted by machines. This guarantees that you get a perfect and
high functioning product each and every time. But if you have ever wondered
what exactly goes on in the fabrication process, then keep on reading because
today you are going to know about the process of creating multilayer PCB, step
by step.
Schematics
The designer of the board uses the CAD system (Computer
Aided Design) to create the schematics. CAD system uses its own internal data
format. The PCB industry had developed its own standard output format to
transfer the layout data of the manufacturer referred to as the gerber file. This
file defines the copper lines in the schematics, as well as the soder mask and
the location of the components. The designer of the schematic conducts the DFM
review after the initial design is complete. This is done to check the trace
lift widths; the space between the traces and the size of the holes to make the
design fit the manufacturing capabilities. Once this task is complete, the file
data is sent to the appropriate machines for the next step.
Photo Plotting
The laser photo plotting machines create the film that will
be used to make the PCBs in a temperature and humidity controlled darkened
environment. The data from the gerber file is converted into an image file here
and the laser photo plotter cuts it onto the film. The machine then
automatically develops the film and unloads it.
Inner Layer Lamination
This
process starts with cleaning the copper sheets. This is done in a clean
environment to make sure that no dust can get it in, because otherwise it might
cause a short or open circuit. After the cleaning, the sheet is coated with a
photo sensitive material called the photo resist. After that the previously
created film is placed in the printer. Over that the copper sheet with photo
resist is placed and the layers are precisely aligned. This time the printer
uses powerful UV lamps, which harden the photo resist on top of the copper
sheet.
Etch Strip Developing
The hardened resist remains on the copper
sheets while the rest of the resist needs to be cleaned away. A powerful
alkaline solution is used to etch away (dissolve) the unwanted copper. After
that the film, that protected the remaining copper, is stripped away. Later, to
align the inner and outer layers, holes are punched in the layer.
Automatic Optical Inspection
Flaws in the layers
cannot be detected once the PCB is assembled. That is why the AOI (Automatic
Optical Inspection) machine is used to compare the produced copper layer with
the original image created by CAD. The machine displays the flaws on the
screen. Once they have been corrected, the oxide treatment of the sheet begins.
This is done to protect the copper sheets from oxidizing. For this process the
brown or black oxide is used.
Multilayer Lamination
The multilayer lamination process starts with placing copper
foil at the base. On top of which, two prepreg sheets are placed. The copper
sheet, fresh from the oxide treatment is placed in the middle, again followed
by prepreg sheets and copper foil. However, the aluminum plate is added at the
top this time. This stack is sent to the pressing machines, where it is
laminated together using heat. The aluminum plate is placed on top to protect
the copper foils and it is later removed. The prepared panels are sent to
another machine where excess material is cut off very carefully.
Drilling
The
drilling machines are prepared with exit material, on which the panels would be
placed. On top of the panel, an aluminum plate is placed to make sure that the
panels don’t tear up during the drilling. The computer operated machine drills
precise holes in the panel according to the original schematics. The drilled
panels again go through a cleaning process to remove the excess debris. Finally
the boards are electroplated with copper and stacked automatically.
Jet Scrub Cleaning and Soder Mask Application
This is done to remove oxidation from the surface of the
copper, as well as to create topography to enhance the doer mask adhesion about
to be applied soon. The process also makes the panels go through anti tarnish.
Most boards have soder mask printed on to each side to protect the copper
surface and to prevent soder shorting between components during assembly. A
coating of soder mask is applied using machine machines to spray it on the
surface of the panel. Soder mask is also called Liquid Photo Imageabel (LPI). Afterwards,
the panel is covered with protecting platting. An inkjet printer is used to
plot the location of the components that will be placed on the board.
Electrical Testing and Inspection
The prepared panels are all tested for any open and short
circuit. Once it’s declared flaw free, the panels are rigorously tested by both
machine and human operators. Only when they have been cleared by both, are the
panels sent for final inspection and testing. The panels are tested against the
original design, and checked to see if they will fit the components and operate
within the parameters they were designed. The boards which pass each and every
test are made ready for the shipment.
If
you are interested in the fabrication process, or if you are looking for that
specializes in developing prototypeprinted circuit boards, then contact the leading PCB developers, Super
PCB right now to get a quote.
Or you can visit http://superpcb.com
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