8/8/2019 Pcb Manufacture
1/38
Printed Circuit Boards
8/8/2019 Pcb Manufacture
2/38
PRINTED CIRCUIT BOARDS
Format of Course
A series of 10 one hour long lectures / tutorials
Delivered by
Dr Gary J Callon
Dr Graham Berry
8/8/2019 Pcb Manufacture
3/38
PRINTED CIRCUIT BOARDS
Course Content
History of PCB Development
The rapid advancements during the 50s and 60s
Developments up to the modern day
Materials choices, properties of substrates, solders, metal
interconnects, chip and component packages etc.
8/8/2019 Pcb Manufacture
4/38
PRINTED CIRCUIT BOARDS
Course Contenturface Mount Technology
Multi layers associated technology, interconnecting layers,
vias, electroless & electroplating etc.
Future Trends in PCB Manufacture
8/8/2019 Pcb Manufacture
5/38
PRINTED CIRCUIT BOARDS
The PCB
Basically consists of a planar (flat) substrate which has
electronic components mounted on it that are interconnected
by conductive tracks.
8/8/2019 Pcb Manufacture
6/38
PRINTED CIRCUIT BOARDS
The PCB
Obvious Advantages
Large number of components can be fitted and connected
together on a small, flat substrate aided by advancements
in component reduction, thin line widths of interconnects.
Multi layer possibilities allows more complex circuitry
without taking up more room.
Mass production high volume throughput, reduces cost to
customer.
8/8/2019 Pcb Manufacture
7/38
PRINTED CIRCUIT BOARDS
HISTORYLate 1890s Great Advancements in Telephony
Early 1900s Great Advancements in Wireless Radio
Wiring becoming more and more complex as more components
being used.
High error rate as more and more wires needed to connectcomponents improvement needed
8/8/2019 Pcb Manufacture
8/38
PRINTED CIRCUIT BOARDS
HISTORYAlternative concept of using a planar substrate with mounted
components and patterned interconnects dates back to early 1900s
In 1903, Albert Hanson, from Berlin, filed a printed wire patent
based on stamped or cut out brass or copper foil adhesively bonded
to paraffin paper.
Included the concept of a double sided board with interconnections
between top and bottom layers. Interconnects basically crimped!
Also suggested the use of conductors deposited from conductive inks
and electrodeposition
8/8/2019 Pcb Manufacture
9/38
PRINTED CIRCUIT BOARDS
HISTORY
Edison had also been asked by the Sprague Electrical Co. how to
draw conductive traces on paper.
He suggested [1] applying glue or polymer and dusting with conductive
powder. [2] Patterning a dielectric with silver nitrate solution and
decomposing the salt to the metal. [3] applying gold foil to the
adhesive.
[1] and [2] can basically be applied as printing techniques Edisonrealised the importance of mass production!
8/8/2019 Pcb Manufacture
10/38
PRINTED CIRCUIT BOARDS
HISTORY
Edison could have pondered further and included vacuum deposition
technology and copper plating.
Americas most prolific inventor had patented these!
NOTE Edisons suggestions were ADDITIVE techniques
Putting material only where it is needed.
8/8/2019 Pcb Manufacture
11/38
PRINTED CIRCUIT BOARDS
HISTORY
Early circuitry generally ignored Subtractive techniques & favoured
Additive.
Generally conductive interconnects today are made via subtractivetechnology i.e. cover whole substrate with copper and etch or mill
away unwanted material.
There is considerable interest at the moment in being able to return to
additive technologies. Less waste, effluent, chemicals etc.
8/8/2019 Pcb Manufacture
12/38
PRINTED CIRCUIT BOARDS
HISTORY
In 1913, Arthur Berry filed for a patent which described
a method of manufacturing circuits for electric heaters,
in which metal was etched away. His patent described
the process of coating metal with a resist prior toetching, an improvement over die-cutting, which left
stress-concentrating sharp corners. Later, Littlefield
described a similar methodology.
Bassist also described a photoengraving process verysimilar to print plate production.
8/8/2019 Pcb Manufacture
13/38
PRINTED CIRCUIT BOARDS
HISTORY
The next inventor to rise to the occasion was
Charles Ducas, whose patent described both
etching and plated-up conductors. One version
involved electroplating a copper, silver, or gold
pattern onto a low-temperature metal alloy
through a contact mask.
8/8/2019 Pcb Manufacture
14/38
PRINTED CIRCUIT BOARDS
HISTORY
Another Ducas process involved forming
grooves in dielectrics such as wax and filling
them with conductive paste, which was thenelectroplated. Both sides of the dielectric could
be circuitised, and Ducas went on to describe
multilayer circuits and a means of
interconnecting the layers.
8/8/2019 Pcb Manufacture
15/38
PRINTED CIRCUIT BOARDS
HISTORY
Frenchman Cesar Parolini disclosed
improvements in additive processing when he
patented the printing of patterns with adhesiveonto dielectric, followed by applying copper
powder to the wet ink. This was Edison's basic
concept and one of Ducas's methods, but
Parolini implemented it fully and added theconcept of jumper wires
8/8/2019 Pcb Manufacture
16/38
PRINTED CIRCUIT BOARDS
HISTORY
1920s and 30s many other inventors exploit
print and plate technologies.
E.G. In 1933, Franz added conductive carbon
particles to polymer ink for printing on
cellophane or similar lamina and, perhaps aware
of Parolini's earlier work, added a copper platingstep.
8/8/2019 Pcb Manufacture
17/38
PRINTED CIRCUIT BOARDS
Introducing the Father of the PCBPaul Eisler Born in Austria in 1907
In early 1930s worked for HMV improving radio reception on
trains.
Life was difficult being Jewish in Austria/Germany at the time
Escaped to England, eventually interned as an enemy alien butReleased in 1941
Used his creativity to aid the defeat of the Nazis
8/8/2019 Pcb Manufacture
18/38
PRINTED CIRCUIT BOARDS
Introducing the Father of the PCBIn late 30s in England, Eisler took a radio he had made to bits and
took it apart and replaced all the wire-to-wire connections with
flat circuitry he made from strips of copper foil varnished on
Bakelite-backed paper.
Nearly sold the idea to Plessey in 1936 but production staff turned
it down women labour was cheaper and more flexible!
By 1943, The US Army were applying some of the techniques
Developed by Eisler in the production of rugged &
robust radio sets.
8/8/2019 Pcb Manufacture
19/38
PRINTED CIRCUIT BOARDS
Introducing the Father of the PCBAt the end of the war, Eisler and his wife were
making electrodeposited copper foil on planar
substrates and etching it with ferric chloride.
Founded Technograph Printed Circuits Ltd and
filed many patents for printed heating and
electrical interconnect circuitry.
His most important patents dealt with etching
8/8/2019 Pcb Manufacture
20/38
PRINTED CIRCUIT BOARDS
Introducing the Father of the PCB
Etching had been perfected by the printing industry
hundreds of years before in plate making.
An etch resist was used that was mechanically scraped
away
During the 1800s, photosensitive coatings were perfected
that enable the widespread use of photoengraving.
8/8/2019 Pcb Manufacture
21/38
PRINTED CIRCUIT BOARDS
Introducing the Father of the PCB
Eislers technique however was different
Printers generally etched into a layer of thick copper
Eisler used thin, electrodeposited copper foil and therefore
Etched completely through the metal to isolate conductors.
He became embroiled in legal patent arguments in US
because British patents had constantly referenced as used
in the printing industry
8/8/2019 Pcb Manufacture
22/38
PRINTED CIRCUIT BOARDS
The Rise of the PCB in the 1950s
PCB becomes commonplace in consumer products
Aided strongly by US releasing invention for
common use in 1948
Eisler therefore unsuccessful with US patentattempts
8/8/2019 Pcb Manufacture
23/38
PRINTED CIRCUIT BOARDS
The Rise of the PCB in the 1950s
In the 1950s, every electronic component generally had wire
leads, and the PCB had holes drilled for each wire of each
component.
The components were then soldered to the PCB. This
method is called through-hole construction.
This could be done automatically by passing the board over
a ripple, or wave, of molten solder in a wave-soldering
machine.
8/8/2019 Pcb Manufacture
24/38
PRINTED CIRCUIT BOARDS
The Rise of the PCB in the 1950s
Through-hole mounting is still useful in attaching
physically-large and heavy components to the board.
However, the wires and holes are wasteful. It costs money to
drill the holes, and the wires are merely cut off.
8/8/2019 Pcb Manufacture
25/38
PRINTED CIRCUIT BOARDS
1960s and Onwards
Surface Mount Technology Developed
Components made with small contact pads that are
physically held by solder to the conductors.
Solder paste generally applied by screen printing process
and components mounted on. Solder paste also acts astemporary adhesive.
PCB passed through IR oven to cure solder
8/8/2019 Pcb Manufacture
26/38
PRINTED CIRCUIT BOARDS
1960s and Onwards
Surface Mount Technology Developed
8/8/2019 Pcb Manufacture
27/38
PRINTED CIRCUIT BOARDS
Advantages of Surface Mount
smaller components
no need to drill holes through abrasive boards
simpler automated assembly
small errors in component placement are corrected
automatically as the molten solder pulls the component
into place by surface tension
components can be fitted to both sides of the circuit
board
8/8/2019 Pcb Manufacture
28/38
PRINTED CIRCUIT BOARDS
1960s and Onwards Copper Foil Bonding
Subtractive technique of copper foil bonding to wholesubstrate and removing unwanted metal becomes
generally adopted. Copper foil is typically 10s of
microns in thickness.
Substrates developed that are compatible with thistechnology. Generally matted glass fibres with epoxy
based e.g. FR4, FR5 etc.
Patterned Conductive Interconnects
8/8/2019 Pcb Manufacture
29/38
PRINTED CIRCUIT BOARDS
1960s and Onwards Copper Foil Bonding
Copper foil is generally pressed while heated onto the
substrate with adhesive
Substrates developed which are made of epoxy and glassfibres to which this process can be done Bonding aided by
Tg of the epoxy. Substrates such as FR4 become prominent.
8/8/2019 Pcb Manufacture
30/38
PRINTED CIRCUIT BOARDS
1960s and Onwards Copper Patterning
Unwanted copper etched away with ferric chloride remember Eisler!Photolithography exploited and developed further to produce
patterns
Light sensitive photoresists used as patternable barriers for etch
Design technology developed to produce circuitry as exposable
medium for transfer into photoresist e.g. photomask clear
acetate with dark emulsion as opaque regions
8/8/2019 Pcb Manufacture
31/38
PRINTED CIRCUIT BOARDS
Copper clad substrate covered with photoresist
Photomask placed over photoresist during exposure
Photolithography with a Photomask
8/8/2019 Pcb Manufacture
32/38
PRINTED CIRCUIT BOARDS
Photolithography with a Photomask
After exposure, photoresist developed
Copper left exposed in regions to be removed
8/8/2019 Pcb Manufacture
33/38
PRINTED CIRCUIT BOARDS
Photolithography with a Photomask
Exposed copper etched away with ferric chloride
Photoresist then removed
8/8/2019 Pcb Manufacture
34/38
PRINTED CIRCUIT BOARDS
Photolithography with a Photomask
A basic photomask for a simple PCB can be made today with
an inkjet transparency and a printer. Circuit design made on pc.
Photoresist covered, copper clad FR4 can be bought from RS etc
A light box can be easily made for exposing
Of course in industry much more sophisticated equipment is used!- much better resolution and quality.
Photomask acetates designed on CAD packages and printed
8/8/2019 Pcb Manufacture
35/38
PRINTED CIRCUIT BOARDS
Techniques also developed since the 1960s to screen print resist
onto copper layer no exposure undertaken.
Resolution not as good as photolithography in terms of resolved
feature sizes but a good method for mass production of low cost
boards.
Alternatives for Patterned Resist
8/8/2019 Pcb Manufacture
36/38
PRINTED CIRCUIT BOARDS
A milling tool can be used to cut away the unwanted copper to
leave a desired pattern.
This requires sophisticated plotting equipment in either X,Y or
X, Y, Z axis control.
This is another Subtractive Method
Alternative for Patterning Copper
8/8/2019 Pcb Manufacture
37/38
PRINTED CIRCUIT BOARDS
Simple Schematic for Producing a 1 layer PCB
8/8/2019 Pcb Manufacture
38/38
PRINTED CIRCUIT BOARDS
Some of the Areas of Interest for the Rest of the Course
Development of Substrate Materials properties etc.
Development of Solders
Development of Components e.g. reduction in size etc.
Multilayers PCBs with up to 24 layers interconnecting layers
& electroplating, chemistry etc.
Problems with PCBs and measures to overcome them, etc.