Definition

Fanout refers to the via pattern and trace routing that connects surface component pads to vias for escape routing to other layers. Dog-bone fanout uses short traces from pads to via lands between pads, suitable for >0.8mm pitch. Via-in-pad places vias directly in the pad, required for fine pitch. Fanout strategy affects routing density, layer count, and cost. Good fanout balances via count, layer usage, and signal integrity. Complex BGAs may use multiple fanout strategies for different regions.