EMS1EP Lecture 3
Intro to Soldering
Dr. Robert Ross
Overview
(what you should learn today)
• What are Printed Circuit Board (PCB’s)
– How PCB are made
– Different types of PCBs
• What is soldering
• How to solder
What are Printed Circuit Boards
• PCBs consist of a surface
which is plated with a
conductive material (like
copper)
• Components can be soldered
directly onto the conductive
material
– This supports components and
connects them to each other to
form a circuit
Some PCB terms
• Track: the copper traces
between pads
• Pad: what components are
soldered to
• Via: an electrical connections
between different layers of the
board
• Footprint: the mechanical
relationship between the pads
for a specific component
• Plane: not just traces but
whole regions which connect
pads together
How PCBs are made
Several different techniques, most common are:
• Silk screen
• Photo engraving
• PCB milling
As part of the process a drill is then used to
create all the holes to put components and
screws through
Silk Screen PCB
• Board (typically fiberglass
FR4) is covered with a
thin layer of copper foil
• Any tracks and pads
(copper we want to keep)
is covered in etchresistant ink
• The remaining copper is
then chemically etched
away
Photoengraving
• Copper layer on board is
covered with a light-sensitive
ink
• A photomask is placed onto
the board and the board is
exposed to UV light
• The remaining copper is then
chemically etched away
• Finer resolution compared to
silk screening process
PCB Milling
• A 3-axis mechanical milling
machine is used to cut away
unwanted copper
• High speed motor drives a
cutting bit which cuts away
the copper
• Not as accurate and trickier
for multi-layer PCBs
• Automates hole drilling
Solder Mask
• Any part of the exposed
copper can be soldered
• Generally we only want
to solder where we
attach components
• A solder mask (nonconductive layer) is added
to the board leaving the
solder pads exposed
• Prevents oxidation and
solder bridges between
close tracks
Overlay
• An overlay can be applied
over the solder mask
• This is the writing which
is useful for humans to
read for assembly and
maintenance
• Generally using a
silkscreen (white is the
most common overlay
colour)
Multilayer PCBs
• A single piece of fibreglass can be coated on the front and back with
copper – this is a 2-layer PCB
• For more layers boards can be made separately and laminated together
• This gives more layers that tracks can be mounted on
• Often whole layers are selected as ground layers which improves noise
performance
• Vias connect between the different layers
• 4 and 6 layer boards are common, can go up to around 38 layers
How PCBs are designed
• Design schematic in CAD
software (we use Altium)
• Layout and route board
in CAD software (Altium)
• Many different routing
possibilities
• Auto routing
• Guidelines:
– Ground plane (avoid large
loops)
– Wider tracks for power
– Avoid right angles
What is soldering
• Soldering is a way of making electrical
connections
• It involves melting solder (an alloy of tin and
lead) to form a bond between the conductors
on different components
Soldering Precautions
• Never touch the hot end of
the soldering iron (~370oC)
• If you do get burnt run
your finger under cold
water for 5 minutes
• Don’t burn the table, the
power leads, keyboards,
your classmates
• Don’t melt anything except
solder
• When not in use put the
soldering iron back on the
stand (not on the table)
Soldering Precautions
• Wear safety glasses,
solder can flick into
your eye
• Wash your hands
well after soldering
(solder is 40% lead)
• Use the fume
extractors and don’t
breath in the solder
fumes
How to solder
• Hold the soldering
iron like a pencil
• Clean the soldering
iron (wet sponge or
brass strands)
before you use it (if
it hasn’t be used for
more than 60
seconds) – it should
look shiny
How to solder
• Hold the tip on the
component lead and
pad
• Add solder and let it
flow into the joint
• Remove the solder
• Remove the soldering
iron and allow joint to
cool (5 sec) before
moving anything
Soldering Video Demo
• http://www.youtube.com/watch?v=euw9tkxBgus
Soldering inspection
Through-hole/Surface Mount
• 2 types of components:
– Through hole: have leads
which pass through holes on
the PCB and are soldered on
other side
– Surface Mount (SMT) soldered
onto the same side of the PCB
that the component is on
• SMT tends to be much
smaller allowing greater
miniaturisation of
electronics
Desoldering
• If something goes wrong –
don’t worry solder will remelt
• Techniques to removing
components:
– Reheat and pull component out
– Desoldering braid (braid draws
solder away from joint)
– Desoldering gun (sucks hot
solder from joint)
– Hot air (heats all the pads using
hot air)
Summary
(What you learnt in this session)
• Printed Circuit Boards (PCBs) are the most
common method used to implement
electronic circuits
• Soldering is how we make the electrical
connections between components and the
PCB