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PCB Design Documentation

For an example of our online documentation, please
visit this page - then the words below will probably make a lot more
sense!
The really critical documentation items for an electronics
design are the circuit diagram, PCB overlay, and Bill-Of-Materials (BOM,
or parts list) and Gerber files. Without a circuit diagram it is difficult to
work on a board - either for modification or repair. A competent electronics
person can take a board and make a circuit diagram from it - but it takes a lot
of work, and accuracy is not guaranteed.

The PCB overlay diagram shows the components and tracks on the PCB,
colour coded. If you have a sample board in front of you, the overlay diagram is
less essential - because you just look at the sample as your reference. Not
all the text may be as easily readable. If you do not have a sample board,
an overlay is essential - there is no other way to see how it all fits
together.

The Bill-Of-Materials is a parts list, telling you what parts are
needed to make the board. There are usually some notes associated with the BOM -
such as "R1: do not fit this part". Again, a competent electronics person can
take a board and generate a BOM from it, but it will certainly not be accurate -
and it will take a lot of work. Many surface mount parts do not contain
complete labelling, and finding what parts were used for surface mount is
difficult.

The Gerbers are the manufacturing files used to make the etched base
laminate of the PCB. Without these, you can't make new PCBs. It is possible to
generate the Gerbers from the original CAD files - otherwise you need to remake
the Gerbers. To remake Gerbers from the original PCBs is a difficult job but
it is one that AirBorn Electronics can assist with - we scan the board and then
use it as a backdrop for our CAD package, laying out the new PCB on top of an
image of the old PCB - assuring the result is identical to the sample
board.

There is a host of other information that is really quite necessary for a PCB
design - such as the PCB size and the mounting holes, any revisions and notes,
the date of the PCB design, and some explanation about what it actually does -
but the four element above are the critical bits.

Most electronics designers will supply you with two seperate things - a
PDF file containing the circuit and overlay, (and possibly the BOM) and a
zip file containing the Gerbers, (and possibly the BOM). We put
the BOM in with Gerbers - it can always be deleted when sending the file out for
PCB laminate manufacture, but by having it in with the Gerbers it makes it
possible to send just one file for subcontract PCB assembly manufacture, and the
BOM will always match up with the gerber.

We put up a web page for our clients so they can get information on their
board whenever they need it, and whereever they are. The webpage includes the
extra information outlined above - things like a description, notes and project
status are attached - and the parts list links off to distributors websites to
make it easy to kit up boards for production. Words don't describe it well,
actually, it is better to look at examples.

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©2013 AirBorn - Last updated 01 May 2013