Whole PCB manufacturing process explained in layman language

1. GENUS P.C.B
PLANT

3. Genus is one of the fastest emerging PCB industry in India, manufacturing
single sided, double sided, RF, metal clad and multilayer PCBs.
Cu clad laminates of 1 square metre are purchased.
We have 2 main processes - one is remove excess Cu and other is to
deposit Cu on the places where more thickness of Cu is desired.

4. 1. Shearing
Shearing of the Cu laminate as per the required size.
Stalking of the sheared Cu laminates is done.
Now the stalked laminate is sent for drilling.

5. 2.CNC Drilling
Drilling refers to making holes of different diameter in
the PCB using spindle according to the design sent by
the customer. Data related to it is fed through a
software in the drilling machine.
Parameters involved are - tool life, spindle speed, feed,
no. of holes per sec, total no of holes on the panel. This
is one of the most expensive process. Operator must
ensure that there is no missing hole, all holes are
according to the software, drill bit is properly grinned,
burrs are removed using deburring machine.

7. 3. Cleaning
It is basically a mild etching process in which Cu layer
of few micron is removed so that surface of the panel
is smooth.

8. 4. PTH (Plating through holes)
Electroless deposition of Cu through the holes as
holes are composed of epoxy initially. After Cu
deposition, panel is dipped in acid dip and anti-tarnish
solution to prevent against oxidation. It is of two types -
horizontal and vertical.
Horizontal PTH is for carbon deposition and vertical
PTH is for Cu deposition.

9. 5. PIT (Photo Image Transfer)
Cu laminate after PTH is sent to the yellow room where
initially Dry green film which is photosensitive is coated over
the Cu laminate. After this, pattern printing is done with a
help of the pattern sent by the customer which is made to
expose to UV light. Pattern is designed such that UV light
only passes through the unwanted area and this area when
exposed to UV light becomes hard and becomes resistant
to Cu and Sn plating. The panel is then passed through a
developing process, which removes all the dry film from the
soft area.
Yellow room must be made
according to CLASS 10,000

10. 6. Plating
First Cu is plated on soft area according to the
thickness required by the customer. This soft area was
the one which was not exposed to UV.
After Cu is plated, Sn is coated over it where Cu
laminate is made anode and electrolysis takes place.
Cu & Sn does not gets coated over the hard area.

11. 7. SES (Stripping Etching Stripping)
First the green dry film is stripped out and then Cu is
etched out from the hard area since Sn prevents
removal of Cu from the soft area.
After this Sn is also stripped out, as a result of which
Cu remains only on the soft area.

12. 8. Brushing
It involves Cu laminate being rinsed with chemicals in
order to prepare the surface for PISM (Photo Imaginable
Solder Mass).

13. 9. PISM
After brushing, Cu laminate is taken to PISM room where it
is coated with an ink film and then it is made to expose to
UV light such that only the area where Solder is to be
deposited(if HAL) is not exposed to the UV.
After exposure, the panel is developed to wash away the
unexposed solder mask. The mask is then cured.
PISM room must be
made according to
CLASS 100,000

14. 10. HAL(Hot Air Levelling)
It involves coating of solder over the unexposed area(area
where components are to be mounted).
Instead of solder some other material may also be deposited
according to the demand of the customer. These are :-
• ENIG is used for gold
• Lead free HAL
• Silver
• Tin
• OSP

15. 11. Legend Printing
This process refers to printing markings for the
components to be mounted later in SMT by rubbing
the ink over the Cu laminate through the pattern and
then it is made to hardened by passing it through heat
or UV exposure.

16. 12. Carbon Printing (optional)
It is preferred where the component to be mounted on
PCB needs to pressed repeatedly. Eg: Enter button
etc.

17. 13. V Cut Grooving
Grooves are made on the Cu laminate to enable easy
separation of PCBs from the panel. Eg: If the panel
consist of 8 PCBs so each PCB has to be separated
after SMT as all the PCBs are to be used separately.

18. 14. Routing
The routing process is a milling process in which a
routing bit is used to cut the profile of the desired board
contour. The panels are “pinned and stacked” as
previously done during the “Drill” process. The usual
stack is 1 to 4 panels.(This process is part of the design)

19. 15. Bare Board Testing
The purpose of an electrical test is to check the
electrical integrity of the circuit, i.e to make sure that
the circuits are complete and carry the correct
currents. Using a test fixture, which consists of a series
of pins, every circuit is tested. The pins are aligned
with the features. Current is passed between one test
point and a test point on the same track. If a signal is
detected the circuit is okay.

20. 16. Peel masking
This process involves coating peelable (blue in colour)
over the holes which is to be mounted with the
components manually after passing it through SMT
machine.
Peelable as the name suggest can be easily removed
when needed.

21. 17. FQC (Final Quality Control)
AQL - Accepted Quality limit

22. Shearing CNC Drilling PTH
PITPlatingSES

23. PISM HAL Carbon Printing
Legend Printing Routing

24. In case 4 layers PCB :-
Cu plate of 0.8mm is taken. On top and bottom of the
Cu plate, 2 layers of Prepreg are placed(each of
0.17mm). Finally two Cu layers each of 0.035 mm are
placed on top and bottom. This is compressed to
obtain 4 layer PCB.

25. Major Defects in PCB
1. Extra Short - when two paths or pads gets joined as a result of which
circuit gets short.
2. Track Out - when a path gets break down as a result of which circuit
becomes open.
3. Handling Scratch - when scratches get developed on PCB during
circulation of PCB from one process to other or may be due to
carelessness of the operators.
4. LP Shift - LP gets shifted as a result of which markings get misaligned.
5. More X Out - X out refers to PCBs which are damaged beyond being
able to be worked upon.
6. V Cut Shift
7. Dry Film Hang - It occurs when dry film fails to get stripped out during
SES

26. LP Shift is caused due to improper alignment of the printing
pattern over the Cu laminate.
Shorting and Track Cut are caused due to presence of dust,
germ, dry film on the PCB.
Dry Film Hang occurs due to improper developing during PIT.
Causes
Track Cut Extra Short

27. Main Issue
To minimise wastage of Cu laminate during Shearing and at the
end when required panel is separated from the Cu laminate.