Sigrity - Tip of the week: Improving the S-parameter result on trace and pad junctions that have fillets

You might have encountered BGA pads which are connected to the traces using fillets.

Shown below are two BGA pads with fillets which are marked.

These trace-pad junctions with fillets are potential points that lack reference planes.

 If you look into the Output pane that shows errors and warnings, the both the junction node gives an error about the reference not being found.

The resulting S-parameter can show poor result where the reflection is showing high impedance and indicates an open circuit. 

In such cases, the trace fillet junction has a see-through hole with no good reference. 

As an alternative, if you add a bottom floating patch using Tools > Options > Special Handling > Add Bottom floating patch at a distance of 0.5mm, the reference is set.

The options in the tool is shown below

With this,  the low frequency result is drastically improved. 

If you enable such floating plane either on top or on bottom, please read the limitation notes and warning that is clearly mentioned below the options in the above image.