Accelerate from Making to Manufacturing - Building Open Source Hardware - page 205

The layout of the traces is then redrawn to reduce the number of vias, length of traces,
and overall complexity of the circuit. Parts of the schematic are exchanged to maintain the
functionality of the circuit while lowering the cross-routing of traces.
Thickness of the board is an important consideration. A thinner board can be cheaper
to ship in large quantities and easier to pack into an enclosure. A thicker board, however,
will provide greater rigidity. Board thickness will affect how the board is handled through
the manufacturing process (stenciling, pick and place, reflow) as well as testing and in-
spection. Radio frequency (RF) performance is also drastically affected by board thick-
ness, so these tradeoffs need to be considered and discussed with the circuit designer to
make sure a manufacturing decision doesn't negatively affect the end product.
Next, the silkscreen on the board is reviewed to confirm that it can be printed clearly
and repeatedly by any PCB fabricator. Labels are added and updated to make board con-
nections as easy as possible to understand. A common example is adding “on/off” indicat-
ors to switches, LED meanings, and any important instructions for use of the board, such
as “5V DC only!”
Smaller PCB designs are often multiplied into a larger panel. This process, called pan-
elization , requires someone close to the manufacturing process to think through how the
board will be handled during the manufacturing process. The most common pitfall is hav-
ing connectors on the edge of a board that will interfere with components on the neighbor-
ing copy of the board. Bigger panels are not always better. You may want a smaller panel
if you are stenciling the PCBs by hand. If you are placing components by hand, the solder
paste on a large PCB may begin to dry out before you are able to get all the parts placed.
Although those are the most important DFM considerations to make, other details to
consider include the following:
Consider adding fiducials for ease of repeatable manufacturing and automated op-
tical inspection (AOI). Fiducials are tiny metal dots found on the edge of the
board and sometimes the panel.
Consider adding side bars to aid in handling the board in panel form with mouse
bites . Mouse bites are small perforations used to hold the side bars to the boards
and can be easily snapped off in postproduction.
Consider the user experience versus the cost of manufacturing. For example, dif-
ferent LED colors are better for user experience, but using all red LEDs is cheaper
in terms of cost and placement than sourcing multiple LED colors.
Stenciling solder paste by hand requires a smaller panel versus an automated sten-
ciling machine capable of larger panels.