The user interface is carefully designed to suit the typical flow a board layout engineer would go through. The top-level graphical user interface (GUI) is composed of a menu bar, a design view area, and a message area. The menu bar contains all menu items associated with all the features this tool offers. The message area holds the messages generated during various courses of action. The design viewe area is the most important for user to understand.
In order to prepare for the calculation of the characteristic impedance for the traces of concern, the user have to collect information about:
These three aspects of the preparation are reflected in the GUI by the three "design views" as shown in the figure below
Navigation between the design views can be achieved by using the menu "Goto View".
The "Stackup View" is the most complicated among the three design views. The right half of the "Stackup View" is reserved for drawing a symbolic layer stackup when the layers are specified. The left half of the "Stackup View" contains three tabbed panes labeled as:
The material attributes, as far as board deign is concerned, are indicated by the self-explanatory labels:
Typical operations for defining material properties are illustrated below:
Click the "Add defaults" button causes the tool to load the pre-defined materials: air, FR4, and copper.
Enter a name of user's choice, choose "type", enter appropriate attributes in the text fields. Click "Add/Save" button to take effect.
Select the material to be edited from the listed names. Click "Edit material" to load the current definition of the material. Modify the attributes, then click "Add/Save" to update the changes.
Select the material to be removed from the listed names. Click "Del. material" to delete.
When the actual board consists many metal layers, say 10 or more, user is advised to break the stackup into several regions with each region composed of manageble number of metal layers. The most important decision is to set the number of metal layers. Upon clicking the "Set" button, definition of metal layers are automatically generated with initial settings. The attributes in the upper half of the pane are obvious, while the attributes in the lower half are explained below:
An important feature of this tool is to allow different units used in layer stackup ("z-" coordinates for thickness of metal and dielectric layers) and in the "x-" coordinate for trace widths and spacings. User can choose a new "z-" unit with menu "Stackup::Set Z Unit". However, after switching from one unit to another, all values will remain unchanged. The user is resposible to manually adjust the values due to conversion between units.
It is recommended to always specify the number of dielectric layers to (<number of metal layers>+1). This will assure consistency with the automatic settings of the boundary choice in the "Metal Layer" pane. For an actual board, there are (<number of metal layers>-1) dielectric layers sandwiched between the metal layers. Two more dielectric layers are the solder mask (passivation) layers above/below the top/bottom metal layers. If there is no solder mask, user can simply specify the topmost and bottommost dielectric layer to be made of "air".
This view is automatically displayed when user is ready to define or edit traces. The cross section of each trace is adequately defined by:
The position of trace matters only when there are more than one traces being analyzed. The position of a trace is determined by sepcifying the "x-" coordinate of the left edge. This "x-" coordinate can either be specified in absolute value, or in relative displacement with respect to the right edge of the last defined trace. The radio button "absolute" and "relative" can be chosen. Clicking the "Add" button cause a new trace to be entered. Once a trace is entered, it can not be modified, however, it can be removed by using the "Remove Last Trace" button. You may also decide to re-define all traces by using the menu "Traces::New Traces" to start from scratch. As mentioned earlier, this tool allows different units for "z-" and "x-" coordinates. The "x-" coordinate unit can be selected using menu "Traces::Set X Unit". However, after switching from one unit to another, all values will remain unchanged. The user is resposible to manually adjust the values due to conversion between units. There are two colors used in the "Trace View" - Red for the signal traces, and Green for the power/ground planes as well as for the grounded traces. Any metal layer associated with "Yes" in the "is plane?" in the "Metal Layers" panel is recognized as a power/ground plane and colored green automatically. Each trace is given an index starting from "1" and displayed on the canvas. Traces can be grounded by using the menu "Traces::Set Grounding Traces" to enter indices for traces to be grounded. Conversely, menu "Traces::No Grounding Traces" reset all trace to be signal traces. The effects of all grounding structures are automatically accounted for in impedance calculations. The eventual results apply to only the signal traces. The usage of the trace-grounding option is very powerful. In particular, the impedance of a co-planar structure with or without ground planes can be easily solved by first defining a group of (Ns+Ng) traces then set Ng of them being grounded, the system contains only Ns signal conductors.