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• 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

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

Constraint Manager Basic

The constraints are separated in different

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

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”

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

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:

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

Constraint Manager Example

Define a name for the Physical Constraint Set, example Power:

Change the value in the constraint set:

Constraint Manager Example

Reference the POWER Constraint set to the SENSE Net:

Constraint Manager Example

When starting to route the “sense” line, the line width which is defined

in the constraint manager, is chosen:

Constraint Manager Example

When for some reason the line width is smaller than the 0.2mm, a

DRC marker appears:

Constraint Manager net class

Constraint set’s can also be referenced to a net class (group of nets):

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

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:

• Line Width – Min: Minimum line width

• Line Width – Max: Max line width, when value= 0, the field is

ignored

• Differential Pair: separate chapter

• Neck min Width:

• Neck Max Length:

• Vias: define the default via

Min line width Neck min width

Neck max length

• 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

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

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:

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 !!

!! Each constraint can be enabled/disabled in

the analysis mode !!

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

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

Minimum Line Spacing

- 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!

Differential Pairs constraints can be defined in the Electrical or in the

physical category Which should I use?

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:

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:

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 !!

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:

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

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

Electrical Constraints: Total Etch length

• With Allegro PCB Designer license, you get a graphical feedback

within an extra window

• 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

• 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

• 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

• Each DRC is listed separately

• Each DRC can be waived, selected in this table in the right mouse

button menu

When you’re searching a special net or pin just enter the name in the

field marked with an * in the top row

Colouring nets are marked in CMGR

Colouring nets in the color dialog:

Net is marked in the Constraint Manager:

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

Searching a net in the CMGR

When selecting a net in the layout and the constraint manager is open,

the net is automatically selected

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

• Constraints can be exportet/imported in the Constraint Manager:

• Define a board template with your desired colors, layers and basic

constraints

• 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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