Optimal probe point placement

A method of probing an IC having a plurality of nets, comprising the steps of:

• a. retrieving from storage a layout description of the IC which defines a set of polygons separated into layers, a netlist description of the IC which defines relationships between nets and devices, and a cross-reference description of the IC which defines relationships between polygons in the layout and nets in the netlist;
• b. creating data structures which associate with each net name a list of polygons;
• c. for a selected net, breaking its polygons into segments of predetermined step size, each segment corresponding to a physical incremental net location of the IC, and computing for each segment a Cutter score which is dependent upon suitability of the corresponding net location for placing a probe point;
• d. storing a representation of the net location corresponding to a segment for which the computed Cutter score indicates an optimal location for probe-point placement;
• e. cutting a probe-point opening in the IC to make the selected net accessible at the optimal location indicated by the Cutter score;
• and
• f. probing the selected net at the optimal location indicated by the Cutter score.

Apparatus for probing at an optimal probe-point a net of an IC having a plurality of nets, comprising:

• a. means for storing a layout description of the IC which defines a set of polygons separated into layers, a netlist description of the IC which defines relationships between nets and devices, a cross-reference description of the IC which defines relationships between polygons in the layout and nets in the netlist, and a data structure which associates with each net name a list of polygons;
• b. means for breaking polygons of a selected net into segments of predetermined step size, each segment corresponding to a physical incremental net location of the IC;
• c. means for computing for each segment a Prober score which is dependent upon suitability of the corresponding net location for probing;
• d. means for evaluating whether the Prober score indicates an optimal segment exists for probing and for storing, if an optimal segment exists for probing, a representation of the net location corresponding to that segment;
• e. means for computing for each segment a Cutter score which is dependent upon suitability of the corresponding net location for placing a probe point, if the Prober score indicates no optimal segment exists for probing;
• f. means for storing a representation of the net location corresponding to a segment for which the computed Cutter score indicates an optimal location for probe-point placement;
• g. means for cutting a probe-point opening in the IC to make the selected net accessible at the optimal probe location;
• and
• h. means for probing the selected net at an optimal probe-point location indicated by the Prober score or the Cutter score.