Basic Multilayer PCB Manufacturing Training Module

PCB Process Training
Module
Prepared by: Kim Bilugan
Supplier Quality Development
January 19, 2024

2
Advanced Energy Confidential Information
© Advanced Energy Industries 2023
SCOPE:
▪ Brief PCB definition
▪ PCB Base Materials
▪ Classifications of PCB
▪ PCB Process Flow
▪ Reliability Tests for PCB

3
PCB / PWB (Printed Circuit Board / Printed Wiring Board)
Purpose of PWB:
Mechanically supports and electrically connects electronic
components or electrical components using conductive tracks, pads and
other features etched from one or more sheet layers of copper laminated
onto and/or between sheet layers of a non-conductive substrate.
Components are generally soldered onto the PCB to both
electrically connect and mechanically fasten them to it.
PCB History
● Before the development of printed circuit boards electrical
and electronic circuits were wired point-to-point on a chassis.
● The Austrian engineer Paul Eisler invented the printed
circuit as part of a radio set while working in the UK around
1936. In 1941 a multi-layer printed circuit was used in
German magnetic influence naval mines.
PWB PCB
1948 Motorola VT-71 7" television
PCB INTRODUCTION

4
Pre-preg ( P.P. )
A sheet material usually made of glass fiber and resin (Epoxy, phenol, polymide), that is used as
an insulator and bonding material in constructing Multilayer boards.
Pre-preg = Pre + Impregnated
Prepreg can be classified into many categories:
1). Based on glass fiber cloth: 106, 1080, 2112, 2116, 1500, 7628;
2). Based on applied resin and its performance: POLYCLAD Turbo 254/226, ISOLA
FR402/FR406, ITEQ IT180, Sheng Yi S1141-140/170
3). Based on Glass Transition (Tg): Normal Tg, Mid Tg, High Tg, Ultra High Tg
Pre-preg Process Flow
Diagram
+
+
+
Epoxy
Blending
Glass
Fiber
°Ç °Ç
Oven
Resin
Pre-preg
Magnified view of glass fibers
The glass fiber and resin content define
the thickness of Prepreg sheet.
Tg is the temperature where the solid
resin becomes liquid.
Cutter
BASE MATERIALS

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Copper Foil
The copper conductive material that
covers one side or both sides of the
base material and is intended for
forming conductive pattern
Unit of measurement: ounce per ft2
Bath Side - rough
Drum Side - smooth
Copper foil roll on a cutting machine
The bath side of the copper foil is the side to
be laminated to the pre-preg.
Magnified view of copper foil surface
Bath Side
BASE MATERIALS

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Cu
Foil
Cu
Foil
Pre-preg Roll
Entrance Drum Exit Drum
Pre-preg Roll
Pressure Cushion
Pressure Cushion
Heat &
Pressure
Heat &
Pressure
Cutter
Copper Clad Laminates ( CCL )
: Prepreg + Copper Foil
Some CCL Maker are Isola, Nanya, Doosan, Shengyi, Hongtai, TUC, LKMC (metal core).
CCL Process Flow Diagram
cross-section of Prepreg
CCL is Prepreg or wood pulp paper as reinforcing material, laminated with copper
foils on 1 or both sides.
CCL
Epoxy
Glass Fiber
BASE MATERIALS

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BASE MATERIALS
Soldermask
A thin lacquer-like layer of polymer that is usually applied to the copper traces of a printed
circuit board (PCB) for protection against oxidation and to prevent solder bridges
from forming between closely spaced solder pads.
Some of the main consideration for choosing soldermask are:
• Application voltage and current
• Hardness or resistance to scratch
• Resistance to soldering heat
Before and after soldermask application
• Resistance to chemicals (e.g. surface finishes, flux)
• Resistance to moisture
• Appearance (Glossy or Matte)
Glossy Matte
More aesthetic Easier to inspect
Wear are less prominent Imperfection is more obvious
Better resistance to scratch Solder ball reduction
Soldermask is usually colored green because green color is eye friendly and has a good
contrast to brown copper color to make defects more detectable.

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PCB CLASSIFICATIONS – BY LAYER COUNT
▪ Single Side PCB ( S/S )
A printed board with conductive pattern on one side only.
Generally used for low-cost, high volume, & low functionality boards.
copper foil on
one side
substrate
▪ Double Side PCB ( D/S )
A printed board with conductive pattern on both sides.
copper foil on
both sides
substrate
▪ Multi-layer PCB ( MLB )
A product consisting of layers of electrical conductors separated from each
other by insulating supports and fabricated into a solid mass.
By definition, MLB’s have 4 or more circuit layers.
▪ Pre-preg suppliers also manufacture copper clad laminates
(CCL).
▪PCB layer requirement generally increases as the application
become more complex.
Pre-preg
copper foil
layers

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PCB CLASSIFICATIONS – BY TECHNOLOGY
Surface mount components,
including resistors, transistors
and an integrated circuit
Through-hole (leaded)
resistors
Through-hole devices mounted
on a PCB (component side)
Solder side of PCB showing
leads component mounted
from the other side
Cross section of a via hole
of a 4 layer PCB
Bare PCB showing SMT pads
▪ Through-hole technology ▪ Surface-mount technology
The first PCBs used through-hole technology,
mounting electronic components by leads inserted
through holes on one side of the board and soldered
onto copper traces on the other side.
Components were mechanically redesigned to have
small metal tabs or end caps that could be soldered
directly onto the PCB surface, instead of wire leads
to pass through holes.

10
PCB CLASSIFICATIONS – BY COPPER THICKNESS
▪ Heavy Copper PCB
Heavy Copper PCB are printed circuit boards with 3 or
more ounces of finished copper in the inner and/or outer
layers. This is used in high current applications (e.g.
Military, aerospace).
Metal Core /
Inner Layer
Pre-preg
copper foil on
both sides
Some benefits of boards with higher copper density
• Increased endurance to thermal stress.
• Can survive repeated thermal cycling.
• Increased current carrying capacity.
• Increased mechanical strength at connector sites and in plated
holes.
Example of PCB used on car tail
lights. Core is 12oz copper
▪ Metal Core PCB
Metal core PCB uses a solid metal instead of the
conventional CCL as a core.
The metal core is like a built-in heat sink.
▪ Insulated Metal Substrate (IMS) PCB
Somewhat similar to metal core technology but the heat
sink material- usually aluminum, copper or stainless steel –
is at the bottom layer, and uses dielectric materials with
high heat conductivity.
The substrate is 28oz copper
Sample featuring 2oz, 10oz, 20oz, and 30oz copper on the same layer.

11
MLB Manufacturing Process Flow
SHEARING
I/L DRY FILM
I/ L ETCHING & AOI
BROWN OXIDE
LAY-UP & HOT PRESS
BREAKDOWN, HALF-CUT,
X-RAY TARGET DRILLING
DRILLING
COPPER PLATING
O/L DRY FILM
OUTER LAYER A.O.I.
OUTER LAYER ETCHING
SOLDERMASK
LEGEND MARKING
FABRICATION
BARE BOARD TESTING
FINAL VISUAL
INSPECTION
QUALITY ASSURANCE
PACKAGING
SURFACE FINISH
Actual process flow may differ depending on PCB design, supplier
preference and machines / technology.

12
SHEARING - cutting the copper clad laminate (CCL) into working size.
CCL
Cutter
Blade
Panel size
Unit
Unit
Unit
Unit
1030
1240
512
410
: Panel Size ~ 462 x 609, 512 x 410, 512 x 610, etc.
CCL Sheets Panels ~ Working Sizes
e.g. 1030 x 1240 512 x 410 mm
Laminate Size Panel Size

13
DRY FILM LAMINATION - A process of transferring the image ( circuit design ) from an
artwork film onto a photo sensitive film.
Dry Film
CCL
Sample artwork design
2.1. Lamination - Application
of Dry film on the CCL using a
laminator machine.
2.2. UV Exposure - Transferring of image from an artwork
film to the laminated panels by exposing it to UV light.
Artwork film
( Negative Film )
Polymerized
Dry film
Actual UV exposure process

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INNER LAYER D.E.S.
3.1 Developing
▪ Removal of the unpolymerized or the unexposed
part of the dry film through chemical reaction
(Na2CO3).
Spray
Nozzle
CCL
(Unwanted
Copper)
Exposed
Dry Film
3.2 Etching
▪ Removal of the unwanted copper leaving the desired
pattern or image required through chemical reaction
(HCl & H2O2).
Spray
Nozzle
Epoxy
Resin Exposed
Dry Film
3.3 Stripping
▪ Removal of the remaining exposed dry film through
chemical reaction (NaOH).
Spray
Nozzle
Epoxy
Resin
Copper Image

15
BROWN OXIDE Micro-etching on the imaged copper
surface of inner layer and treat with chemical that will enhance
bonding capability between copper and pre-preg.
Input Output
Chemical Treatment
BEFORE AFTER
Copper
Laminate
Copper
Laminate

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5.1 LAY-UP - Stacking the processed thin core ( L2 & L3 ) to the
insulating pre-preg and copper foil (L1 & L4).
5.2 HOT PRESS - Application of High
Temperature & Pressure to bond the Pre-preg,
Copper foils & CCL.
Actual CCL that has
undergone Brown oxide
process
CCL + Prepreg CCL + Prepreg +
Copper foil
Add insulating sheets +
steel plates
Laminating multiple stacks of
boards at the same time

17
CNC - DRILLING To produce an opening through the board to give
way for the formation of electrical connection between top, bottom, and
intermediate conductor pathways.
CNC: Computer Numerical Control
Trimming, Stacking and Taping
CNC Drilling Machine
Drilling
▪ Drilling holes to the board using drill
data by the CNC machine.
▪ Preparation of boards to be drilled.
Drill Bits are made of
Tungsten Carbide
Board after drilling

18
COPPER PLATING deposition of copper to the drilled holes
and panel surface thru the combination of electroless and
electrolytic plating to provide interconnection between all layers.
Smear is burned resin in the hole wall created by heat during drilling.
Deburring and Desmearing
▪ Cleaning and conditioning of hole walls before copper
plating process
Electroless Copper Plating
▪ Deposition of thin layer of copper on the hole wall of the
panels by means of chemical reaction.
Electrolytic Copper Plating
▪ Deposition of copper to the holes and surface by the use of high current DC.
Electrolytic Plating
After Drilling Electroless Plating
Before Drilling

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OUTER LAYER D.E.S.
▪ Copper tracks will be created on the outer layer by repeating dry film lamination and DES process.

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PHOTO SOLDER RESIST / SOLDER MASK –
A process of coating the bare copper traces with a lacquer-like layer of polymer that
provides a permanent protection against solder and contamination.
Printing – Application of ink on both sides of the panel to completely cover the copper traces.
Pre-Curing – Partial drying of ink prior to UV exposure.
Exposure – To transfer the solder resist pattern by aligning an artwork film and exposing it using UV light.
Developing – To remove the unwanted solder resist / unexposed part by the use of mild alkali solution
Post-Curing – Final or full curing of ink to attain required hardness & adhesion.
After DES After Printing After Exposure After Developing
During Exposure
Actual Printing

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SURFACE FINISH Application of coating on the copper surface to ensure
solderability, and to protect the exposed copper from contamination.
Hot Air Solder Levelling (HASL and Lead-free HASL)
The PCB is dipped into a bath of molten solder so that all exposed copper surfaces are covered by
solder. Extra solder is removed by passing the PCB between high pressured hot air blowers.
Solder finish has metallic shiny appearance.
Pros:
• Low-cost
• Easy to repair
Cons:
• Uneven surfaces
• Not good for fine pitch components
• Can clog PTH
• Poor wetting
HASL Process Flow

22
Electroless Nickel Immersion Gold (ENIG) consists of electroless nickel plating covered wi
th a thin layer of immersion gold, which protects the nickel from oxidation.
Pros:
•Good conductivity
• Excellent corrosion resistance
• Flat surfaces
• Lead Free
Cons:
• Expensive
• Hard to repair
Cu
Ni
Au
Ni : 3.0 ~ 7.0 m / Au : 0.05 ~ 0.10 m
ENIG Process Flow
Nickel prevent the IMC (Intermetallic
compound) formation between the gold and
copper layer.
IMC is the bonding reaction
of 2 different metals.
ENIG has matte yellow appearance
SEM picture of IMC

23
Hard Gold - Hard Electrolytic Gold is gold plated over nickel thru high current DC. Hard
gold is extremely durable, and is most commonly applied to high-wear areas such as edge
connector fingers and keypads.
Ni : 3.0 ~ 5.0 m / Au : 0.80 ~ 1.5 m
OSP (Organic Solderability
Preservative) - OSP is a water-based,
organic surface finish that bonds to copper
and protects it from oxidation.
Pros:
• Simple process
• Easily reworkable
• Environmentally friendly
• low equipment maintenance
Hard Gold has shiny
yellow appearance
OSP has matte pinkish
brown appearance
Pros:
• Very durable
• Best conductivity
Cons:
• Complicated to process
• Very expensive
• Poor solderability
Cons:
• Short shelf life
• Sensitive to handling
• Difficult to inspect

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Immersion Tin - Immersion Tin (ImmSn) is a metallic ﬁnish deposited thru a
chemical reaction that is applied directly over the copper surface to protect from oxidation.
Pros:
• Flat Surface
• No Pb
• High solder reliability
•Top Choice for Press Fit Pin Insertion
Cons:
• Sensitive to handing
• Could damage soldermask
• Exposed Tin on Final Assembly can Corrode
• Tin Whiskers
• Not Good for Multiple Reflow/Assembly
Processes
• Difficult to Measure Thickness
Immersion tin has matte
white appearance.
Immersion Tin Process

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FABRICATION - Final process where panels are cut into
delivery sizes according to customer’s drawing.
Routing - Cutting the boards using a router
machine and router bit.
Punch Press - Process of forming the PCB to
required shape and sizes and bore holes using
a die-set.
V-Cutting - Producing a break away guide on
the board by cutting a V- groove.
Cutter
PCB
Routing in process
Router bits
Before punching After punching
Cross section of v-cut

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Automatic Optical/Visual Inspection
(AOI/AVI) Loaded with gerber data and compares
with the actual captured image to detect PCB
anomalies.
WIP
SCANNER
MONITOR AOI for inspecting
copper traces
AVI for inspecting
finished PCB
Electrical Test Machine – Checks if there is
open or short trace by applying current to the PCB
Test fixtures Test pins

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PACKAGING - packaging of boards based on the approved
packing requirement and delivery.
VACUUM SEALING
Sealing a certain board quantity
before placing them to carton box.
CARTON PACKING
Placing the vacuum sealed boards
into the carton box.
PACKING INSPECTION
Inspection on the packing condition
and contents prior to carton sealing.

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References:
• Daeduck Philippines Inc.
• Wikipedia.org
• www.epectec.com
• www.raypcb.com
• www.pcbcart.com
• blog.optimumdesign.com
• www.pcbcuttingmachine.com
• www.circuitdomain.com
• Youtube.com
• https://madpcb.com/glossy-or-matte-solder-mask/

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