Hardware Reference
In-Depth Information
for making open source hardware. The layout phase is where you focus on how all of your
parts will physically be arranged and connected on your printed circuit board. During this
phase, you'll want to think about all of the manufacturing rules that Matt will explain in
more detail in Chapter 12 , and you'll want to conclude this phase with a layout review . If
you do not work at a company with a formal design review process, ask a friend in your
field to review your board or make friends with your local hackerspace. If you can't phone
a friend, many PCB fabricators and assembly houses provide design for manufacturing
rule-checking services to flag errors in your final layout.
Finally, to get to your next prototype and have your ultimate design output, you'll need
to generate Gerbers (board fabrication files that describe the layout of your board layers
in a vector format). Your Gerber package (also called “artwork” or “PCB prints”) will in-
clude a file for each physical layer of the board design. For a two-layer PCB, typical files
are as follows: top copper (sometimes called the component-side copper); bottom copper
(sometimes called the solder-side copper); top and bottom solder mask; top and bottom
silkscreen; and top and bottom solder paste mask. The NC drill file contains the center co-
ordinates for drill holes and the dimensions for each drill. Send your Gerbers off to a PCB
fabricator, order your specific parts using the bill of materials as a guide, and, when
everything comes back, assemble and test your PCB!
To avoid spending huge amounts of money on a single iteration, try to build a small
number of prototypes for each design cycle (5 to 10 pieces). That way, you have enough
samples for testing but not so many that you're broke. Each pass through the design cycle
checks that your BOM is correct and your CAD library is correct. Lather, rinse, and repeat
until you are happy with the final prototype.
Managing Constant Iteration
Managing iteration is just a matter of keeping track of the details. Every time you go
through a design cycle, maintain an archive of the following:
A copy of the parts library, schematic, and layout files
A copy of the BOM
A copy of the build package (Gerbers, drill files)
Purchasing records for parts and PCBs
Test notes (on both test procedures and test data)
A bug tracker for new issues (and old)
Each iteration of the design cycle should generate a new “version” of your design, so
you can keep track of what happened with MyThing v1.1 versus MyThing v1.25. If you
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