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PCB Manufacturing
How Is A PCB Made?
RadioTech
Design
A PCB designer first uses
special CAD software to design the circuit board.
Once the design is created,
the template is exported and examined to determine key details, such as hole
size and spacing, board edge spacing and track width.
It is then double-checked
to ensure it meets the factory’s minimum requirements before being
manufactured.
Films
Once everything is
approved, preprinting begins. PCBs are printed on a special printer called a
Plotter, which makes films of the template it’s about to print.
It first creates a plastic
sheet with a negative of the design, then develops it. Each layer of the board
and the solder mask gets its own film, all of which must correspond with each
other precisely.
To ensure the films all
line up, one or more holes is punched through them.
Inner Layers
This step is for PCBs that
have more than two layers. The film created in the previous step is a sort of
map for what the copper layer should look like.
The copper is bonded to the
substrate board beforehand, then cut away to match the pattern on the film.
After that, it’s thoroughly
cleaned to eliminate debris, so it will not affect the board.
The copper then gets a
layer of a special film called photo resist to protect it, then it’s washed and
dried again. It’s then inspected for defects by a technician.
Copper Removal
Even after the rigorous
prior cleaning, there is usually still some copper that needs to be removed.
This is done by putting the
PCB into a special copper solvent that removes any leftover copper.
After that, the board goes
into another solvent to remove the photo resist applied earlier.
Layer Alignment
Once all the layers are
ready, they are punched with a hole to make them easier to align. This is done
by a machine called an optical punch, which punches a hole in each layer in the
exact same spot.
Once all the layers are
punched, they’re all inspected again, by both human and machine. It’s then
compared to the template made beforehand.
Once each layer is
inspected, and no issues are found, the layers are cleared for bonding.
Bonding
There are two steps to the
bonding process: layering up and bonding.
In essence, the layers are
stacked and then bonded together, but they first need additional materials to
bond properly.
There are a few more layers
applied to aid the bonding process: layers of fiberglass pre-impregnated with
epoxy on top, and copper foil, which has the copper trace etchings, on the top
and bottom of the substrate layer.
The layers are all placed
together on a special table with clamps in a specific order, then a computer
handles the bonding process.
When it’s complete, a
technician removes the PCB for the next step.
Drilling
Holes are drilled into the
board to accommodate components that will be added later.
The holes must be drilled
precisely, so they are made with special drills that typically measure between
100 and 150 microns in diameter.
A special x-ray machine
helps to determine where holes should be drilled, then registration holes are
made to secure the board for additional drilling.
Before drilling starts, the
board is buffed to remove debris and prevent tearing. A computer-guided drill
system takes care of the rest.
Copper Coating and Photo
Resist
Next comes a copper
coating, which happens after the board is cleaned and soaked in a series of
chemical baths.
These baths deposit a
one-micron thick layer of copper into the newly made holes to cover them.
Afterwards, a new layer of
photo resist is added. This time, the process is different: the outer layers
are imaged with the PCB’s design.
The board is taken into a
sterile room, where the photo resist is applied. UV light is then applied to
the photo resist to harden it, and anything not hardened is cleaned off.
Plating and Final Etching
The board is electroplated
with another thin layer of copper, with the photo resist protecting everything
that does not need to be coated.
It is then coated with a
thin layer of tin, which guards the parts of the panel that need to stay
covered with copper during etching.
Exposed copper, and any
copper beneath the photo resist layer, are removed and the rest is kept as the
board’s connections and conducting areas.
The Finishing Touches
The next step is to apply
the solder mask. Before it’s applied, both sides of the board are cleaned and
given epoxy solder mask ink.
The boards are then exposed
to UV light, through the solder mask’s photo film. Anything not hardened is
removed, and the board is then baked in a special oven.
When it comes out, the
board is plated with gold or silver to aid any additional soldering. A surface
finish may also be applied, depending on what customers ask for.
Last comes the silkscreen
labeling, one last coat and a final curing.
Testing and Cutting
Before the board can truly
be considered done, it has to be given one last test to ensure it works.
How a test is done differs,
but there are two types of testing that can be done to a PCB. After tests are
complete, the board is cut from its panel.
This can either be done
with a router or a v-groove. With that, the process is complete.
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