The document outlines the fundamental processes involved in building a printed circuit board (PCB), detailing the materials used, such as copper clad FR4, and the essential steps including dry film lamination, copper etching, multilayer lamination, and various drilling and plating techniques. It describes the equipment used throughout the manufacturing process, emphasizing the importance of chemical treatments and air filtration. Finally, it covers the application of solder masks, component markings, and the final fabrication and testing of the boards.

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