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Purpose of No Probe Top and DFA Top

Printed From: PCB Libraries Forum
Category: Training / Events
Forum Name: PCB Design Basics
Forum Description:
Printed Date: 08 Feb 2023 at 4:14pm

Topic: Purpose of No Probe Top and DFA Top
Posted By: ANANDT
Subject: Purpose of No Probe Top and DFA Top
Date Posted: 27 Jun 2022 at 9:13pm

I'm currently working with Allegro, please explain the purpose of No probe TOP why do we need to add one for our footprint. 

Next if we create a standard footprint using Allegro Footprint wizard it creates Place Bound Top along with DFA Top how one differs from another and purpose of it. 

Please explain.

Posted By: Tom H
Date Posted: 28 Jun 2022 at 8:35am
I'm not an expert on the Allegro CAD tool, but I am familiar with the terms. 

You would use a "No probe TOP" feature if you're using Test Points. They cannot be placed under a footprint because they need to be Probed. The No probe TOP feature throws a DRC error if a Test Point is in the No Probe area. Also, Allegro has a feature for auto-placing test points. That feature will avoid all No probe TOP areas. 

Place Bound Top is used to establish a part placement area. You set spacing rules for each component footprint. If you violate the Place Bound spacing rules Allegro throws a DRC error. Other CAD tools that have less features use a Placement Courtyard boundary outline as a guide for part placement. 

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