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FlowCAD Webinar
Constraint Manager
Tips and Tricks
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Overview
• Constraint Manager Basic
• Physical Constraints
• Spacing Constraints
• Analysis Mode
• Differential Pair
• Total Etch length
• Constraint Regions
• This & That
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Constraint Manager
• Clearly arranged in different categories
• All the constraints are defined in one place
• Constraints can be reused
• Online Design Rule Check (DRC)
• Scalable for all future needs
• The defined constraints are used by the auto router
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Constraint Manager
Because the Constraint Manager is scalable within the different tiers,
you may have more rules which can be set. Don’t worry, the process is
always the same.
This presentation is based on a OrCAD PCB Professional 16.5 license
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Constraint Manager Basic
The constraints are separated in different
categories:
- Electrical
- Physical
- Spacing
- Same Net Spacing
- Properties
- DRC (Design Rule Check)
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Constraint Manager Basic
Each category contains two main folders:
- A Constraint set with the different parameters which can be set
- A list of all nets in the design
Some categories contains as well:
- Regions, for region rules
- Net Class, for Net class to net class rules
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Constraint Manager Basic
Function of the Constraint Manager:
- Define a constraint
- Associate the constraint to a net
- Route the design
- When a rule is not maintained, an Error will be displayed
“a DRC Marker appear”
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Constraint Manager Example
Each net has the DEFAULT constraint set associated
How to define a user defined line width on a specific net:
- The Sense net needs a minimum line width of 0.2mm
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Constraint Manager Example
There are two ways to define constraints. First we show how to define
constraints for one single net by the “override” method.
For the “sense” net, the line width is changed to 0.2000mm. Each
value which was changed manually, change the font color to blue and
get’s bold:
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Constraint Manager Example
The second method is to create a constraint set. This rule set can be
associated to a net or to a class of nets.
To create a constraint set, select in the left panel the “Physcial
Constraint Set” Folder
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Constraint Manager Example
Define a name for the Physical Constraint Set, example Power:
Change the value in the constraint set:
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Constraint Manager Example
Reference the POWER Constraint set to the SENSE Net:
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Constraint Manager Example
When starting to route the “sense” line, the line width which is defined
in the constraint manager, is chosen:
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Constraint Manager Example
When for some reason the line width is smaller than the 0.2mm, a
DRC marker appears:
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Constraint Manager net class
Constraint set’s can also be referenced to a net class (group of nets):
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Constraint Manager net class
You can define a netclass as described below:
- Select the desired nets
- Click right mouse button -> create -> class
- Define a net class name
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Constraint Manager net class
Another way to create a netclass is:
- Select Objects in the Constraint manager
- Select create-> Class
On an existing netclass, a net can be added or removed as described
below:
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Physical Constraints
• Line Width – Min: Minimum line width
• Line Width – Max: Max. line width, when value= 0, the field is
ignored
• Differential Pair: separate chapter
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Physical Constraints
• Neck min Width:
• Neck Max Length:
• Vias: define the default via
Min line width
Neck min width
Neck max length
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Physical Constraints
• BB Via Stagger: Staggered vias are two pins or vias on the same
net with a single connect line connecting them on a particular layer.
The stagger distance is the distance from the connect point of one
pin or via (x,y location) to the connect point of another.
• Allow - Etch: defines if a connect line is allowed on a specific layer
or not.
• Allow – T’s: Specifies whether T-junctions of cline segments are
allowed and where they may form (pin, via, cline).
• Allow - Pad-Pad Connect: Specifies whether a pin/via whose
connect point lies within the extents of another pin/via forms a direct
connection without the presence of an intermediate cline.
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Spacing Constraints
Define the distance between all the different elements. When selecting
the “line” under the spacing category, you see on the right side the
table with all the spacing between line and the other objects.
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Net class to Net class spacing
It is possible to define different spacing for nets in net classes. For
such cases the Net Class to Net class spacing can be defined:
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Net class to Net class spacing
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Same Net Spacing Constraints
Define the distance between all the different elements of the same net.
The behavior is similar as in the spacing constraints.
!! Don’t forget to enable the Same net Spacing under Options !!
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Analysis Mode
!! Each constraint can be enabled/disabled in
the analysis mode !!
Useful:
- For performance reason, constraints can be disabled
- constraints can be turned off temporarily
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Analysis Mode
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Analysis Mode
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Analysis Mode
Set Design Options constraints | enable/disable Design Constraints
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Differential Pair
Process how to set up differential pairs:
- Define Differential pairs in the Constraint Manager
- Define Constraint Set for Differential pairs in the Constraint
Manager
- Reference the constraint set to the desired differential pairs
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Differential Pair
Creating Differential Pairs in Constraint Manager
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Differential Pair
Auto Creation of Differential Pairs:
1. In the Net > Routing > Differential Pair of Constraint Manager,
select Objects > Create > Differential Pair.
2. In the Create Differential pair dialog, click Auto Setup.
3. Enter Prefix and +/-Filter as desired
4. Select Create to create the differential pairs automatically.
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Differential Pair Line Spacing
Primary Gap
Coupled Tolerance (+)
Coupled Tolerance (-)
Minimum Line Spacing
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Differential Pair
- Differential Pairs can be defined in the Physical worksheet
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Differential Pair
If you need to control the length of Differential Pairs, several options
are available:
- Total Etch length (Next chapter)
- Static phase tolerance (Allegro PCB Designer License)
The phase is checked over the entire
net from Driver to Receiver.
- Dynamic phase tolerance
(Allegro PCB Designer + High Speed Option)
This rule checks, that even in the entire
line section the two nets are always in phase!
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Differential Pair
Uncoupled length
The maximum length of the two nets of a differential pair, where they
can run uncoupled can be defined with the “max uncoupled length”
constraint.
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Differential Pair
Differential Pairs constraints can be defined in the Electrical or in the
physical category. Which should I use?
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Differential Pair
Use Electrical Category:
When you need to use phase control (static/dynamic)
(Allegro PCB Designer/+High Speed Option)
When you need to control the uncoupled length
Use Physical Category:
When different line width for each layer are required
Advise:
- Define the Differential pairs constraint only in one of the two
categories to prevent confusing.
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Electrical Constraints: Total Etch length
• The Total Etch constraint is used to specify the minimum and
maximum etch requirements for Xnet or Net.
• Following DRC appears when Constraint doesn’t match:
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Electrical Constraints: Total Etch length
• Constraints can be entered in the CMGR -> Electrical Etch Length
• The Units are the same as in the board layout
• Don’t forget to enable the Rule in the analysis Mode !!
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Electrical Constraints: Total Etch length
• During routing you get graphical feedback if the constraint is
maintained.
• A dashed line in the trace means, the min/max rule isn’t obtained:
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Electrical Constraints: Total Etch length
• If the connect line is to short, the line has to be extended
• To extend the line length, you can use the Route-> Delay Tune
command
• Define the style in the options window
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Electrical Constraints: Total Etch length
• Just add the extension until the dashed line disappears.
Cline length is smaller then
min. Etch length
Cline matches the constraint
Cline is longer then max. etch
length
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Electrical Constraints: Total Etch length
• With Allegro PCB Designer license, you get a graphical feedback
within an extra window
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Constraint Regions
• Constraint regions can be used to define areas on your pcb where
other constraints are valid then otherwise defined. For example on
a placed BGA component, you may have to allow smaller connect
lines that they can pass the pins.
• On a constraint region different spacing rules, physical rules or both
can be defined.
• A constraint region can be defined on a single layer or through the
entire stack-up.
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Constraint Regions
Constraint Region
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Constraint Regions
• Use the add shape command to design a new constraint region
• Define “Constraint region” as class
• Chose the desired subclass to define on which layer the region
should be placed.
• Define a name for the region
• Draw the region on your PCB
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Constraint Regions
• Create a physical constraint set
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Constraint Regions
• Define the physical constraints in the BGA_DEMO constraint set as
desired:
• Assign constraint set to the region
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Properties Worksheet
• For each net different properties can be set
• Example: When the “No Rat“ property is set to on, no ratnet is
displayed for this specific net
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Properties Worksheet
• A lot of Component and Pin properties can be set in this
Worksheet.
• Example: For each pin, the thermal connection within a shape can
be defined manually
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DRC Worksheet
• Each DRC is listed separately
• Each DRC can be waived, selected in this table in the right mouse
button menu
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Filter Options
When you’re searching a special net or pin just enter the name in the
field marked with an * in the top row
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Colouring nets are marked in CMGR
Colouring nets in the color dialog:
Net is marked in the Constraint Manager:
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Searching a net on the board
When selecting a net chose the “Select and Show Element” command
in the right mouse button. The net will be highlighted.
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Searching a net in the CMGR
When selecting a net in the layout and the constraint manager is open,
the net is automatically selected.
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How to change the value in an entire row?
When selecting a net in the layout and the constraint manager is open,
the net is automatically selected.
1.Select one entire row:
2.Change one value and all the selected field gets the same value
3.All the value are changed
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Constraint “Reuse”
• Constraints can be exportet/imported in the Constraint Manager:
• Define a board template with your desired colors, layers and basic
constraints.
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Outlook
• The constraint Manager is really powerful. You can use it to define
relative propagation delay, control wires topology ( ex. Daisy chain),
and much more. Requires Allegro PCB Designer License!
• You can even define your own formulas in the constraint manager!
Requires Allegro PCB Designer License!
• For more detailed information, please look at the Allegro
Constraint Manager User Guide or contact FlowCAD.
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Ende
Besten Dank für Ihre Teilnahme und für Ihr
Interesse!
Für Fragen, Anregungen oder
Bemerkungen erreichen Sie mich unter:
Tel.: + 41 (0) 56 485 91 91
E-Mail: [email protected]
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