Data Sheet

LABCENTER ELECTRONICS LTD.
116
Net Classes
This is the place where we configure trace and via styles and control which layers we route on
when auto-routing the board. The selector at the top allows us to switch between different net
classes and configure each separately.
Let’s start with the POWER Net class, which should be the default selection. As we discussed in
the Proteus Getting Started Guide any nets that include a power or ground terminal are
automatically assigned to the POWER net class, unless manually overridden.
We’ll set the track / trace size to 25th, not so much for current considerations but to reduce track
impedance (we’ll also place a single low impedance ground plane later to help with this). In PCB
nomenclature this corresponds to track style T25.
The neck style – if configured – specifies the track style for necking (thinning) to help the track
pass through obstacles. Together with our design rule aware routing (which knows which
objects are obstacles) this is very powerful. When set, you can hold the SHIFT key during route
placement to toggle between necked and normal track styles which is invaluable in tricky or
dense routing.
Advanced necking: The SHIFT key is held down while routing the escape from the BGA and
then released to resume routing at normal track width.