Once you have imported or synthesized your die, FA4ST can create as many power and ground rings as needed. The dialog allows the designer to quickly specify each ring, its width, type and parameters such as chamfers or fillets.
The user interface is especially clean. Unlike other AutoCAD tools, the dialog box floats above the display. Upon hitting Apply your input is realized instantly in the AutoCAD display window. This is an extremely interactive approach - you can try out different parameters almost in real time.
The user can define as many rings as needed. Each ring can be of a different type.
Using the parameters above, FA4ST generated four filleted rings for a HPBGA (this is a cavity down package with two levels - each level has two rings and a row of fingers.) The rings are 350 um wide with only 150 um spacing. The fillet radius in the corners is 500 um.
For a conventional PBGA one uses a chamfered ring for ground and a arc for the power downbonds. The radius of the arc is controlled by the difference between the minimum spacing and the maximum spacing. Generally you set the minimum spacing based on your etching rules and your maximum spacing is determined by the space you need to place one or more vias between the rings.
To generate a chamfered BGA style ring, use the parameter "chamfer" option for the inner ground ring and use the parameter "arc" for the outer power ring.