This is a presentation that I put together that explains the basic manufacturing process for printed circuit boards. There are many different ways to build a board. This presentation explains the basics of the most common operations. This is a general overview. For more information on the subject visit www.pcbdesignschool.com

2. PCB 101
The Basics of Building a Printed Circuit Board.
Presented by
David Duross
Engineering Director

3. Inner Layer Process.
● Starts with copper
clad FR4.
● FR4 is a composite
material of woven E-
glass and epoxy
resin.
● Referred to as a core
or C-stage.

4. Dry Film Lamination
● Core is chemically
cleaned to remove
process residue or
contaminates.
● Core is laminated with
Dry Film Photo-resist.
● Cleaning operation
promotes dry film bond
to copper surface.

5. Dry Film Laminating Equipment
● The dry film is
laminated onto the
core by use of a cut
sheet vacuum
laminator.
● Conveyorized
processing allows any
thickness material to
be laminated.

6. Dry Film Expose
● Artwork is placed
against the dry film.
● The surface is
exposed to high
energy UV light.
● The circuit pattern is
exposed to UV light.

7. Exposure Equipment
● Automated equipment
allows a hands free
operation.
● System automatically
aligns artwork front to
back for accurate
registration.
● Interior of unit has
hepa air filtration.

8. Dry Film Develop
● The exposed dry film
is chemically
developed and made
permanent.
● Undeveloped dry film
is rinsed away.
● The dry film forms the
circuitry pattern.

9. Copper Etch
● The copper we don't
want to keep is
chemically etched
away.
● The dry film acts as
an etch resist
protecting the copper
we want to keep.

10. Dry Film Strip
● The dry film photo-
resist is chemically
removed.
● The inner layer
circuitry pattern is
now formed.

11. Post Etch Punch and AOI
● Post etch punch
automatically adds
mechanical alignment
positions to the core in the
form of four slots.
● Provides accurate alignment
for multiple cores.
● Panels are then inspected on
a system known as an AOI.
● AOI is short for Automatic
Optical Inspection.

12. Oxide Treatment
● Copper is a very smooth
surface.
● The copper surface needs
to be roughened up to
promote bonding to epoxy
resin later on. Oxide
treatment does this.
● FR4 after copper etch is
rough enough to provide a
good bonding surface.

13. Multilayer Lamination
● The core forms the inner
layers.
● Sheets of pre-preg (B-
stage) are placed against
the core.
● Copper foil is then placed
against the pre-preg.
● The copper foil forms the
outer layers of the printed
circuit board.

14. Lamination Press Equipment
● Vacuum lamination systems
evacuate air from the system
under light pressure.
● When the temperature
increases beyond a control
point the system applies high
pressure.
● Press cycles are controlled
by a computerized system.
● Multiple process panels are
pressed at the same time in
what is referred to as a
lamination book.

15. Multilayer Lamination
● The core, pre-preg and
copper foil are pressed
together under a vacuum
with high pressure and heat.
● The pre-preg liquefies, flows
and encapsulates the oxide
treated copper.
● The pre-preg solidifies as
temperature increases.
● The stack is then allowed to
cool.

16. Primary Drill
● Holes are drilled into the pressed panel
intersecting copper features on the
inner layers.
● Drilled holes are non-conductive.
● Copper burrs at the edge of the hole
are mechanically removed.
● Drilling leaves an epoxy smear over
the inner layer copper exposed by the
drilling process.
● The epoxy smear is chemically
removed to ensure that the inner layer
copper is exposed.
● Note the location of the two holes.

17. Hole Formation
● Drilling is done on an
automated CNC drilling
system.
● De-smear is either done with
a plasma etch system or with
a chemical process line.

18. Copper Deposition / Direct
Metalization
● Copper deposition or
direct metalization is
applied to non-copper
surfaces.
● Material applied is very
thin but conductive.
● The conductive material
provides the electrical
pathway for electroplated
copper later on.

19. Copper DepositionDirect
Metalization
● Direct metalization coats only the
epoxy and glass.
● Copper deposition coats
everything.
● Both can be processed vertically or
horizontally.

20. Outer Layer Dry Film Lamination
● Panel is chemically cleaned
to remove process residue or
contaminates.
● Panel is laminated with Dry
Film Photo-resist.
● Cleaning operation promotes
dry film bond to copper
surface.
● Cleaning is typically done
prior to the copper deposition
/ direct metalization process.

21. Outer Layer Dry Film Expose
● Artwork is placed
against the dry film.
● The surface is
exposed to high
energy UV light.
● The circuit pattern is
prevented from being
exposed to UV light.

22. Outer Layer Dry Film Develop
● The exposed dry film is
chemically developed and
made permanent.
● Undeveloped dry film is
rinsed away.
● Openings in the dry film form
the circuitry pattern.
● Note that one of our two
drilled holes is covered by
the dry film.

23. Copper Plate
● The dry film acts as a plating resist.
● The dry film covers copper we
don't want to keep.
● Additional copper is electro-plated
onto exposed surfaces not covered
by the dry film.
● Copper is plated in the hole not
covered by dry film.
● Approximately .001” (0.0254 mm)
of continuous copper is plated in
the hole.

24. Tin Plate
● Electro-plated tin is plated
directly onto the electro-
plated copper.
● The tin also plates into
holes not covered by dry
film.
● The tin protects the copper
we want to keep.
● The plated tin is very thin.

25. Outer Layer Dry Film Strip
● The dry film is chemically
stripped away from the
panel.
● Note that the hole in the
center of our sample is
tin plated.
● The hole on the right
side is not plated with tin.

26. Copper Etch
● The tin acts as an etch resist.
● Copper not plated with tin is
chemically etched away.
● The hole plated with tin is
protected.
● The hole on the right was not
copper or tin plated due to the dry
film that covered it.
● The copper deposition / direct
metalization in the hole on the right
is removed in the copper etching
process.

27. Tin Strip
● The thin layer of electro-
plated tin is chemically
removed.
● The tin is also removed
from the center hole.
● All exposed electrical
conductors are now bare
copper.

28. Photo Image-able Solder Mask
Application
● A thin layer of liquid photo
image-able solder mask is
applied to all exposed surfaces.
● The mask may be applied either
by spraying or with a
screen/squeegee.
● The mask is a thin polymer
coating roughly .004”
(0.102mm) thick when wet.
● The mask is tack dried for
handling purposes.

29. Mask Expose, Develop and Cure
● Artwork is placed against the tack
dried solder mask ink.
● Solder mask not covered by an
artwork image is exposed to high
energy UV light.
● Exposed mask is chemically
developed and made permanent.
● Unexposed mask is washed away.
● The solder mask is then thermally
cured.
● Cured mask shall be approximately
.001” (0.0254mm) thick.

30. Hot Air Solder Leveling
● Panels are coated with solder flux.
● For vertical processing panels are
dipped into a large solder pot.
● For horizontal processing panels are
passed through a solder fountain.
● Excess solder is shaved off of the
process panel with hot blowing air
knives.
● Solder is typically 200 micro-inches in
thickness minimum.
● Solder-ability is the acceptance criteria.

31. Component Markings
● Component markings are
applied with non-conductive
inks.
● Markings can be any color.
White is the most common.
● Inks can be applied by a
screen/squeegee set-up or
with an ink-jet printer.
● Markings typically indicate
component placement and
orientation.

32. Marking Equipment
● Ink jet printing applies a white
epoxy ink sprayed as a final image
and UV tack dried as the ink is
applied.
● Silkscreening relies on pulling a
squeegee across a mesh.
Openings in the mesh match the
marking features.
● Both techniques require the ink to
be baked to ensure final cure.
● UV cure-able inks are available as
well.

33. Final Fabrication
● Individual boards are routed and or
scored free from the process panel.
● Specialty milling such as counter bores
and sinks may be added at this step.
● Boards are rinsed free of process
debris and dried.

34. Electrical Test
● Boards are electrically tested
for opens and shorts.
● Testing is done on a dedicated
fixture or with a robotic system
referred to as a flying probe
tester.

35. Final Inspection
● Boards are visually inspected to either
customer requirements or industry
standards.
● Boards are measured for dimensional
accuracy.
● Boards are tested for ionic
contamination.

36. End