Keep board design, component layout, and
conductor traces as simple as possible. Avoid
odd shaped boards, multi-axis component
arrangements, and complicated conductor paths.
Attempt to restrict the maximum board
area to a size that will fit evenly into a 18 X
24 inch panel when manufactured and keep the
board outline dimensions as nearly rectangular
as possible. i.e. an 8X10 board will fit evenly
4 times into an 18X24 standard panel with the
required clearances and tooling needs of the
manufacturer being met.
Use a standard grid as large as possible
to define the locations of features and
Keep conductor traces as short as
Use 45 degree angles where ever
possible, Avoid 90 degree angles or Acute
angles for traces.
Run long conductors with the long
dimension of the board.
Keep conductors away from the edges of
the board at least .025 inches.
When wave soldering break up ground
planes on the bottom side of the board to avoid
warping or blistering of the board.
Keep terminal pads a minimum of .05 away
from board edges
Keep the number of hole sizes to a
Identify each layer of the board in the
margins just outside the board outline.
Indicate polarity and component
Place components that have adjustable
features like pots or switches or variable
capacitors, in areas of the board that they can
be accessed while mounted in the equipment.
Make sure that test points are
accessible and on a .100 inch grid for
automated bed of nails testers.
All components dissipating more than 1
Watt of heat energy should be mounted in such a
way as to not allow the body to come in contact
with the board surface. This protects the epoxy
laminate from degrading due to exposure to heat
beyond it’s rated temperature specifications.
Place components that must dissipate
more than 2 Watts of energy directly on a heat
sink or attached to the chassis to conduct the
heat away from contact with the board.
Take note of mechanical support for
heavier components, placing them near the board
Be aware of the potential to entrap
moisture under components and make provision
for cleaning the boards after assembly.
Use the minimum number of layers needed
to make your printed circuit. Always use a
symmetrical layer stack up with evenly
distributed copper on the layers.
Use standard board thicknesses where
possible, beware of the costs involved in
Components weighing more than ¼ oz. per
component lead should be mounted with a clamp
or some restraining device to prevent over
stressing the solder joints under vibration.
The solder joints should not be the sole
support for heavier components.
Do not rely on solder mask material as
an insulation device.
Before the board outline
can be defined, the following considerations
must be taken into account:
Type of housing the board will fit into
Maximum 3 dimensional space available
for the board
Mounting, fastening, clamping method to
Electrical cables, connectors,
terminals, and adjustable components that need
Type, thickness, and material to be used
Surfaces of the board to me used for
Method of assembly to be employed, Hand
assembly, wave solder, reflow solder for
surface mounting, through hole assembly with
automated equipment… etc.
Addition of any tooling holes
Before beginning a Printed
Circuit board layout the end use of the product
that the board must reside in must be known.
What sort of environmental conditions will the
assembly be exposed to? Conditions that can
affect the performance of the design must be
Shock and Vibration
EMI/EMC or electrical fields
Chemicals or corrosives
The designer needs to have
a schematic, a bill of materials or parts list,
and all the specifications for the components
to be mounted and connected on the board. From
this information the designer will develop the
layout and master pattern for the printed
circuit board. The designer will compile the
information on all components including the
physical size, lead pattern and spacing,
special mounting data required hole and
terminal sizes and electrical and thermal
The following process
describes the sequence of events that must take
place in order to develop a board layout.
Study the final schematic diagram
Understand all symbols, reference
designations, and component specifications.
Using the component specification sheet,
determine component body configuration, size ,
mounting options, land pattern, and any other
specific requirements for assembling and
testing the part.
Take note of any polarity requirements
for polarized components. Identify the Cathode
end of diodes, emitter for transistors, and
polarity for capacitors, Pin one for IC’s and
connectors, and polarity for windings of
transformers, and wire wound chokes where
Group components according to common
connections, logical function or specific
Determine grounds and supply voltage
requirements for components and IC’s and place
decoupling caps near the voltage pins as
required by the design. Observe the wattage
requirements and if using distributed power and
ground traces take note of the conductor widths
and lengths to minimize voltage drop or noise
or thermal heating of traces.
Establish heat sinks, ground planes or
other special conductor geometries as needed.
Understand connection requirements, bus
and high speed data needs, locations of clock
lines, and terminating resistors, EMI/EMC
requirements, isolation of susceptible circuits
from noisy circuits, etc.
Look for human engineering needs,
accessibility of adjustments, connectors,
switches, card guides, ejectors, protection
from high voltages, indicators and lights
located where they can be seen in the
equipment, test points, probe points, and
manufacturing registration guides and supports
Layouts should be viewed from the
PRIMARY or COMPONENT side.
Parts should be placed by their level
of critical importance in the circuit, fixed
features that interface with the chassis, or
enclosure first like connectors, switches,
lights or LED’s, displays, mounting hardware,
clamps, standoffs, screws, cables, etc. Next
larger Integrated Circuits or IC’s with their
associated decoupling capacitors located as
close as possible to the power pins, or special
high speed digital or analog or RF parts with
special features that must be incorporated into
the design copper for electrical or signal
performance reasons. These are usually laid out
in groups that can be associated with each
other and moved as a unit to their location in
the design keeping their important
relationships established at all times. If a
particular component is connected to more
components than any other component on the
board, that is the best one to start with and
build around. Try not to use odd axis mounting
of components unless absolutely necessary, as
this may require hand assembly rather than
machine assembly of those components.
Component placement is everything! Good
component placement will almost always result
in good board performance. There are four
basic component placement strategies that can
be used independently or in combination:
Central component placement
Fixed array placement
The most basic concept of schematic orientation
is used on medium to low density analog boards.
This works especially well when the input is at
one end of the circuit and the output is at the
opposite end. Peripheral placement is used when
board edge connectors or off board mounting or
components with a fixed board edge locations
are employed. These components should be
positioned first and then subsequent components
can be placed radiating inwards towards the
center of the board. Central component
placement usually involves a one or more large
BGA or FPGA components place centrally in the
board with parts being places around their
periphery in sequence until the board is
placed. The Fixed array concept is used for
large digital designs that use many large chips
of the same style with an equal spacing on a
grid pattern and are typically machine routed.
DFM or design for Manufacturing is a set of
guidelines that are used by designers to
improve the machine assembly of designs. If the
board is going to be a high volume product it
is mandatory that the designer understand and
employ these rules in their designs. Components
must be oriented in like fashion with 90 degree
two-axis locations relative to the board long
dimensions… targets or fiducials are required
to register the board with the pick and place
machines or auto insertion machines that
populate the board with components by robotic
assembly. Lower volume products may be hand
assembled and not require these features.
Typical applications for Printed Circuits are as follows:
Class 1 - General Electronics Products -
Class 2 - Dedicated Service Electronics -
Class 3 – High Reliability Electronics -
See if you can classify the following product categories:
Consumer Electronics – Digital Wrist Watch, CD Player, Am/FM/Radio/Alarm Clock, Television, Calculator, Digital Coffee Pot, Microwave Oven, Home Alarm Systems, Cellular Telephone, Home Computer, Home Theater/Stereo Surround Sound System, Cable Television Converter Box, Hand Held Video Games, Remote control electronic toys… LOJACK auto recovery system…etc.
Telecommunications – Point to Point Microwave Transceivers, Police/ Fire/ Rescue Radios, Digital Network Equipment, SatCom transceivers, Commercial and Private Aircraft Radios and Instrumentation, Cell Telephone Relay Stations, CB Radio/2 Way Walkie Talkies, etc…
Industrial Electronics and Instrumentation – Weather Radar and Weather related Telemetry, Oscilloscopes, Network Analyzers, Ohm Meters, Temperature meters, Strain Gauges, Environmental Chambers and Ovens, Spectrum Analyzers, Solar Photovoltaic Power Cogeneration equipment, DC to AC Power Inverters, Switcher Power Supplies, CCD Telescopes…
Military Electronics – IFF transponders, IR detectors, Night Vision Goggles, Military grade Computers with encryption, Fire Control circuits, Satellite Navigation instrumentation, Encrypted Frequency Hopping VHF Radios, Direction Finding Equipment, Missile Guidance Systems, FLIR Pod Test equipment, etc…
Aerospace Electronics – Satellite systems, Space Shuttle controls and system, Aircraft communications and controls, etc…
Automotive Electronics – Automotive Ignition Controls, Emission monitoring and controls, Fuel Air Mixture, Fuel Injection, Climate controls, Dash Instrumentation, Radio/TV entertainment accessories, etc…
Medical Electronics – Heart Monitors, Automated Medicine dispensing equipment, Breathing machine, Dialysis machine, Laser assisted tooth whitening machine, Laser optical corrective surgery machine LASIX, X-ray or CAT Scan equipment, MRI Imaging equipment, etc…
According to IPC-2221 1.6 Printed board assemblies are classified by intended end item use. The Performance Classes are listed as follows:
Class 1 - General Electronics Products - Includes consumer products, some computer and computer peripherals, as well as general military hardware suitable for applications where cosmetic defects are not as important, and the major requirement of the board is its functionality.
Class 2 - Dedicated Service Electronics – Includes Communication Equipment, sophisticated business machines, instruments and military equipment where high performance and extended life are required, and for which uninterrupted service is desired but not critical. Certain Cosmetic imperfections are allowed.
Class 3 – High Reliability Electronics – Includes Military and Commercial equipment where continued performance or performance on demand is critical. Equipment failure or down time is not tolerated and must function when required in the case of life support systems, or critical weapons systems. For applications where high levels of assurance are required and service is essential.
Level A – General Design Complexity - preferred
Level B – Moderate Design Complexity - standard
Level C – High Design Complexity – reduced
Type 1 – Single Sided PCB
Type 2 – Double sided PCB
Type 3 – Multilayer without Blind or Buried vias
Type 4 – Multilayer With Blind and/or Buried vias
Type 5 – Multilayer Metal Core board without blind and/or buried vias
Type 6 – Multilayer Metal Core board with blind and/or buried vias