Specifications

92
Figure 3.6.3-1: Layout of printed circuit board.
To understand the component placement better, a simulated view of the finished
product is available in Figure 3.6.3-2. Using this view, it is possible to ascertain
the types of capacitors and resistors needed. While PCB123 has several pre-
defined (and user definable) footprints, the final appearance and relative size is
not always immediately obvious. The simulated view helps in this regard. The
layout was designed using PCB123’s proprietary software, PCB123 Design
Suite. While available for free download, it creates PCB123’s own format that is
not compatible with software from other custom PCB manufacturers.
When designing this PCB, not only was space efficiency a large concern (given
our small board size), but also efficiency in routing traces was a chief concern.
Given the fact that component footprints were not as clearly defined as possible
in the PCB123 software, it is important to have a bit of flexibility in placing the
components. If the traces are too far apart, space on the board will be wasted.
However, if they are too close together, a small variation in a part could mean
that a trace becomes accidentally soldered. Several considerations were made
due to the relatively large power flows through this board, as well as the fact that
it would be handling both analog and digital signals. The need to reduce
crosstalk and other interference effects was significant. Therefore, several
conditions were observed in routing traces. Power traces were set at 32 mil,
signal traces were set at 15 mil, and signals traces were spaced 25 mil apart. In
addition, a mostly dedicated group plane was used to provide a robust ground
and to reduce unintended capacitive and inductive effects. In addition, all pin