| PCB layout tutorial |
PCB layout tutorial
an overview, information, tutorial about PCB layout, PCB CAD and PCB
software for designing printed circuit boards.
Today, PCB CAD design systems offer a tremendous advance
since the days many years ago when PCB design was undertaken using tape on a
translucent sheet. Now PCB layout software enables printed circuit boards to be
designed in a far more efficient way. It is possible to PCB designs to be made
using huge numbers of very small components. In addition to this very high
levels of track density may also be present, and this would not have been
possible using manual PCB design techniques.
NOTE: Further information on PCB layout can be found
on additional pages given in the related articles list that can be seen below
the main menu.
PCB layout steps
There are a number of steps that should be followed in any
PCB design:
- Set up initial settings This stage of the PCB design
involves setting up the snap and visible grids. At this stage the default
track and pad sizes should also be determined and set.
- Set up the mechanical elements of the PCB design It is
necessary to import the details for the printed circuit board outline into
the PCB layout software programme as soon as possible. It is also necessary
to set up any reference marks and holes. These may be required for pick and
place machines, or test fixtures during the production process.
- Put all components onto the board At this stage of the
PCB layout, the components need to be placed onto the printed circuit board
so that they are available to be moved and set in place later.
- Create functional building blocks At this stage of the
PCB layout, the components should be moved into their functional blocks so
that associated components are close to each other and the circuit can be
routed easily later.
- Identify and route layout critical tracks Any tracks
that are layout critical should be identified and then routed as they are
required. By routing these tracks at this stage, then the remained of the
design can be implemented around these tracks rather than trying to resolve
problems later in the PCB layout.
- Route power and earth rails Often the earth and power
rails may be included as planes, occupying a complete layer of the printed
circuit board. This has significant advantages not only in terms of enabling
the higher levels of current to be routed easily, but it also significantly
reduces any problems with interference on the printed circuit board.
- Route the remaining lines usually it is necessary to use
the auto-route function on the PCB layout software. Although there are
manual routing options on PCB layout software, it is normal to use the
auto-route function as this may save many days trying to route the PCB
layout manually. The auto-route functions have been very well developed in
recent years and normally provide very good results. It is possible to set
up various parameters to ensure the PCB layout software routes the circuit
according to the requirements.
- Manually route any final lines on the PCB layout After
the PCB layout software has completed the auto-routing, there may be a few
tracks that would not route. These can often be routed manually.
Alternatively if the design has become too complicated for the space and the
available number of layers, it may be necessary to make some fundamental
changes to the board.
- Undertake final tidy up Once all the lines have been
routed, it is complete any small items that may need completing at this
stage.
- Complete a design rule check While all the design rules
should have been followed during the design, it is necessary to do a final
check. It is better to catch any problems at this stage rather than once a
prototype PCB has been made.
- Have the work checked by an independent party However
much care has been taken designing using the PCB layout software, there is
always room for possible errors. These are not easy to spot having worked
intimately with the job. It is therefore always good practice to have the
work checked by an independent party who has not been involved on the PCB
layout in question.
- Release the design for prototype PCB manufacture With
the PCB layout complete and checked, it is necessary to send it to the PCB
manufacturer for the manufacture of the bare prototype PCB. At this stage it
is necessary to ensure that all the correct files are sent. In order to
ensure that there is no confusion, the files should be formally released.
Although many design checks will have been carried out, it is still
necessary to undertake the manufacture of a prototype PCB because there is
always the risk of an unforeseen problem. Committing to large quantities of
PCBs could be costly is a problem is found and as a result it is always wise
to undergo a prototype PCB stage.
PCB layout summary
PCB layout and design should be a relatively straightforward
process in terms of the steps to take. The real challenges can test the PCB
layout engineer in terms of achieving a layout that works well first time, and
one that fits within the given mechanical constraints. If the process is
correct, then this will enable the PCB layout engineer to focus on what is
important and where his skills really lay.
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