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FastCap Partition Editor

For FastCap, conductor surfaces and dielectric interface planes are partitioned into rectangles. Each partition rectangle serves as a container for the charge and polarization accumulation for that region. For greatest accuracy, one should use a fine decomposition, at least in regions with high field gradients. However, increasing the number of partition rectangles increases FastCap execution time.

The initial partitioning is applied to the top and bottom surface of all conducting objects, to the ``vertical'' edges of the conductors and vias, and to the interface planes that separate dielectrics. The "vertical" partitions are created internally and are not editable. Their width is the film thickness, and length is limited by FcEdgeMax. For conductor top and bottom surfaces, the via areas are first subtracted, and the resulting polygons decomposed into boxes. The boxes are split along projected edges from the current object, and along overlapping edges from other objects. Each box is split further if a side is larger than the FcPartMax value. Unlike the FastHenry partitioning, there is no constraint on where divisions of the rectangles can occur. For simplicity, the same partitioning is used on the top and bottom of conductors. The space left for a via on the opposite side is automatically filled in. At each outside edge of each rectangle, an additional, thin, edge partition is created. This will have width (normal to the edge) given by the FcThinEdge value. The edge partitions account for the greater charge accumulation near edges. Dielectric interfaces are initially partitioned in an analogous manner.

At this point, the partitioning may be quite rough, and FastCap accuracy would be poor, with a high potential for matrix malformation errors. The partitioning may require further refinement to improve accuracy. One way to accomplish this automatically is to set FcPartMax to a small value, however this often becomes impractical due to memory and execution time limitations. The FastCap partition editor allows the user to refine the partition only where necessary. The partition panels should be small where field gradients are large. Using the partition editor requires some intuition about E&M, and experimentation will aid the user in developing the art.

When the partition editor starts, the partitioning of all objects is shown. Clicking on a conducting object will change the display to show only the partitioning for that object, which will be termed the ``current object''. Clicking on another object will change the display to show the new object's partitioning, and make it the current object.

With the current object defined, clicking on or dragging over the partition panels will refine each of those panels into four new panels. The process is repeated to provide sufficiently small panels where necessary.

The layer-specific mode can be used to limit object selection to specific layers. This is often necessary to ensure that the button presses apply to the current object, rather than selecting another object at the same location (or vice-versa).

It is presently not possible to ``un-refine'' a partition box. However, pressing the Delete key will, for the current object, destroy all partitioning, and recreate the initial partitions.

If `c' is pressed, cut mode is enabled. A vertical or horizontal line is attached to the pointer. Pressing `/' will switch the orientation. Clicking on a panel will divide the panel along the line. Dragging over multiple panels will cut each panel dragged over. Press `c' again to exit cut mode.

The interface planes are associated with layers, and not objects. These may also require refinement. The interface plane partitioning is invisible until the user switches to interface edit mode by pressing the `i' key.

The interface that is shown, and can be edited, is determined by the current layer selection in the layer menu. If a conducting layer is selected, the interface plane is the one located at the bottom surface of that layer. Selecting a via layer will display the interface at the top surface of that layer. Selecting the passivation layer will display the interface at the top surface of the passivation. These partitions are refined using the same technique as for conductors. Pressing `i' again exits the interface editing mode, and the interface partitioning becomes invisible.

The partitioning is remembered between invocations of the partition editor, until the interface is cleared, reset, or a new object is saved. The partitioning can be saved with the Dump Saved button in the RLC Extraction panel.


next up previous contents index
Next: The RLC Extraction Panel Up: The FastCap/FastHenry Interface Previous: FastHenry Partition Editor   Contents   Index
Stephen R. Whiteley 2006-10-23