Guidance notes for Structure Layer Properties
Application Note AP559

Guidance notes for Structure Layer Properties

It is often convenient to base a new design on an existing stackup and then add or remove electrical layers to create the new stack, leaving the previous existing structures intact or to switch between layer types (Signal, Plane, Mixed, Hatched) without removing structures.

Speedstack allows the designer to retain and re-allocate structures when changes are made to the electrical layers of the stackup. This enables reallocation of structures after the following stackup changes:
  • Adding foils and/or cores – increasing the layer count
  • Deleting foils and/or cores – reducing the layer count
  • Moving foils and cores up and down, even beyond another copper layer
    – maintaining the layer count but, for example, exchanging two different thickness cores within the stackup
  • Copying and pasting foil or core – increasing the layer count
  • Changing layer type – signal to plane, plane to signal, mixed to signal or plane, signal to hatch, hatch to signa
  • Deleting a rigid core and adding a flex core – to maintain layer count but swapping material type
  • Deleting a rigid core and adding two foils – to maintain layer count but switching to an HDI type build

For the following example, consider the stack below.

Switching layer types and reallocating structures

Switch signal layer 2 to a plane layer and plane layer 3 to a signal layer. Speedstack issues a warning indicating that continuing with the change will require the existing structures to be re-allocated.

Select Yes to confirm the change to the stackup. The stack editor reflects the change in the stackup, layer 2 is a plane layer and layer 3 a signal layer.

Speedstack also displays a flashing Rebuild indicator; due to the changes to the stackup it is necessary to refresh the structures.

 Click the Rebuild and Recalculate icon – Speedstack displays an information dialog indicating which structures need re-allocating.

Click OK then click the Structure Layer Properties icon to reallocate the structures to the correct signal and plane layers.

The Structure Layer Properties dialog includes two layer columns, the Current layer column and the New layer column. The Current column shows the Signal / Plane stackup layers assigned to the structure before the stackup was changed.

In this case, note the Upper Plane Layer is changed from layer 3 to layer 2.

In many cases multiple structures will have the same Signal / Plane layer assignments. In the example above Speedstack indicates that there are two structures affected. Click the Move All check box to re-allocate all matching structures in a single operation then click Apply.