Auto routing

Dear all,

In auto router, I am unable to get clean routes.

I’ve shown that in the attachment.

When I try manually, I can able to come out of the BGA with no criss-crosses.

But then why it fails in auto routing?What should we do to control this atleast to a certain extent.

Am I missing any set-up rules. Please help me out. Really want to wrap up this board

in a couple of days.

Thanks.

There's a few different things to take into account - it's very rare that an auto-routed design will exactly match a hand routed design.

Are you using a specific do file, or just generic smart-route?
How many passes did you give the router?
How many routing passes - any clean passes?
What sort of constraints are you using?

Have you applied any tax or cost rules to crosses in the auto-router?

The above are a list of things you could look into - from the posts you've made I'd guess you are trying to teach yourself how to use the auto-router. You should possibly consider some training on the tool, or at least going through the online tutorials that are available

Here, i've not used any specific do file.am usng Autoroute --------->Route------------->Basic
In that I gave proper values for passes.
The constraints i use is layer constraint and length matching.

I couldn't get your point "Have you applied any tax or cost rules to crosses in the auto-router?
"
Yes,i really want to attend the cadence training but meanwhile i am going through the tutorials to work out this as i was assigned to finish this task.

May be my questions would be very basic. sorry. kindly bear with me.

The Auto-Router tries to route a design using a series of passes - there are a number of different types of passes:-

bus
fanout
route
clean

to name a few. Typically what happens is you use either the Smart-Router, which runs a predefined set of passes, or you define your own set of passes in a .do file. In using the Basic route command from inside the Router you are just running a set of routing passes (probably 25 if you've stuck with the default values). This isn't too much guidance for the router to get by on, which is probably why there are cross overs. You'd probably be better off using the Smart Router (available in the same window on the right) to try and route the design.

Cost and Tax are 2 settings which the Router uses to guide itself - the Router has predefined settings for Cost and Tax which guide it when routing a design and it's ability to put conflicts in. As a design routes further the Cost and tax values typically get stricter which in turn means less conflicts. Tax either makes the default settings stricter or easier, depending on the Tax value - Cost is an absolute value applied which overrides the predefined settings. Tax is preferable rather than cost unless you really know what you are doing.

The level on settings you need to apply will depend on which host PCB system you re using - for example if you are using Allegro PCB then the constraint set there are passed to the Router, which means that less setup is involved - either manually or via a do file. There's normally not one do file or routing strategy that will work for all designs - most designs are unique so need a different strategy to auto-route.

Can you post your board? It might be easier to address. If you would rather send it privately then provide your contact info.