maxFloatingArea

Specifies the maximum area for floating metal shapes on a routing layer that are not connected to a diffusion or polysilicon gate. Similar to process antenna rules, maximum floating area rules apply only to the current layer and any lower layers (that is, all layers that have been fabricated up to the layer of interest). Maximum floating area rules can be used to avoid shorts between floating and non-floating metal wires that are caused by arcing due to charge build-up during processing steps. Applies only to routing layers.

Floating metal is defined as metal on the current layer that cannot trace a path to a diffusion connection or polysilicon gate, using only same layer or lower layer metal connections.

Grounded metal is defined as metal that can connect to a diffusion connection or polysilicon gat using only same layer or lower layer metal connections.

maxFloatingArea Quick Reference

Value Type

Parameters

• floatingAreaSpacing (LayerDualArrayTblValue) specifies minimum spacing/minimum parallel length pairs by layer. The LayerDualArrayTblValue syntax is:
  

  {s_layerName i_numPairs {{f_minParSpacing f_minParallelLength}…}…}

  where
  

  s_layerName	Name of the layer.
  i_numPairs	Number of DualValue pairs for the layer.
  {f_minParSpacing f_minParallelLength}
  	The first DualValue pair for a layer must have the format {f_minSpacing 0} If the floating metal for the layer has area > maxFloatingArea, then the floating metal on the layer (and all connected lower layers when the floatingMetal parameter is CONNECTED or ALLCONNECTED) must be >= f_minSpacing away from all grounded metal on the layer or the rule fails. For other DualValue pairs for the layer, floating metal that is >= f_minParSpacing from grounded metal must have >= f_minParallelLength at the f_minSpacing distance. f_minSpacing should be > f_minParSpacing values and if more than one DualValue pair of {f_minParSpacing f_minParallelLength} is given, then the f_minParSpacing values must be decreasing in value. You use the pair for the smallest f_minParSpacing that is >= the spacing between the floating metal and the grounded metal.

• floatingMetal (StringAsIntValue) specifies how the constraint is applied as described in the following table.
  

  String	Integer Value	Constraint applies to:
  singleLayer	0	Each individual floating metal shape on the routing layer must have an area <= maxFloatingArea or meet the minimum spacing to other grounded shapes.
  connected	1	The area of floating metal shapes connected together on the layer.
  allConnected	2	The area of floating metal shapes connected together on each layer defined by the constraint

Examples

Sets the required floatingMetal and floatingAreaSpacing parameters and the maxFloatingArea constraint.

set_constraint_parameter -name floatingMetal \
  -StringAsIntValue connected
set_constraint_parameter -name floatingAreaSpacing \
  -LayerDualArrayTblValue \
  {Metal1 3  1.0 0.0  0.5 0.8  0.2 2.0  \
   Metal2 2  0.6 0.0  0.3 0.9  \
   Metal3 2  0.6 0.0  0.3 0.9  \
   Metal4 2  0.6 0.0  0.3 0.9  \
   Metal5 2  0.6 0.0  0.3 0.9  \
   Metal6 2  0.6 0.0  0.3 0.9  }
set_constraint -constraint maxFloatingArea -AreaValue 1000

LIBRARY LEF58_MAXFLOATINGAREA STRING
"MAXFLOATINGAREA 1000 CONNECTED m1 m6 
  LAYERS m1 m1 SPACING 1.0 PARSPACING 0.5 0.8 0.2 2.0
  LAYERS m2 m6 SPACING 0.6 PARSPACING 0.3 0.9 ;" ;

The following figure shows the behavior when the constraint is applied for this example.

Related Topics

Antenna Constraints