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What Does It Mean To Round-off?

Printed From: PCB Libraries Forum
Category: PCB Footprint Expert
Forum Name: Questions & Answers
Forum Description: issues and technical support
URL: https://www.PCBLibraries.com/forum/forum_posts.asp?TID=1199
Printed Date: 07 Oct 2024 at 3:20am


Topic: What Does It Mean To Round-off?
Posted By: yixin
Subject: What Does It Mean To Round-off?
Date Posted: 03 Dec 2013 at 11:12pm
In the pad stack designer dialog box, on the right column roundoff parameter settings What does it mean?


Replies:
Posted By: Tom H
Date Posted: 03 Dec 2013 at 11:22pm
Here is an example:
 
Round-off is either pad to pad "C" dimension or pad size.
 
If your round-off value is set to 0.05 mm then the resulting pad dimensions will be in 0.05 mm increments and the "C" pad span could snap your pads to 0.05 mm increments.
 
The Round-off value will help you in Part Placement and manual Routing on a 0.05 mm grid system.
 
You choose the grid system that you want to use.
 
I personally use a 0.01 mm grid system so that all my pad sizes are in 0.01 mm increments and the "C" pad span is 0.01 mm and my placement grid is 0.1 mm and routing grid is 0.01 mm.
 


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Posted By: yixin
Date Posted: 06 Dec 2013 at 2:22am
If the Round-off is set to 0, to ask what does it mean?

Posted By: Tom H
Date Posted: 06 Dec 2013 at 7:45am
That means that the pad spacing and sizes will be accurate to the nearest micrometer.
 
Zero round-off is good if you are using an Enterprise CAD Tool like Expedition, Allegro, Board Station or CR-5000 and you do not use a snap grid for placement or routing. Enterprise CAD Tools are rule dependent. Enterprise CAD Tools have good shape based gridless auto-routers.
 
If you are using a PCB design tool like PADS, Altium, ORCAD PCB or CADSTAR then it's best to work with a grid system.
 
If you are using a Low End CAD Tool like Eagle, DipTrace, DesignSpark or Pulsonix then you need to work with a grid system.
 


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Posted By: jameshead
Date Posted: 09 Dec 2013 at 2:39am
Nice answers but I wouldn't say Pulsonix was a low-end system.  It's at a comparable level to PADS and CADSTAR.

Easy PC is the "low-end" package, and DesignSpark, the "free" package from the same company.  Pulsonix is defineatly aimed at the Cadstar and PADS level.

Posted By: Tom H
Date Posted: 09 Dec 2013 at 6:48am
OK, you're probably correct and I need to categorize Pulsonix as a PCB design tool.
 
It's just that I'm in the USA and I don't know any company or service bureau who uses it, so I'm totally unfamiliar with the features and GUI.
 
And you are correct that "Easy PC" and "PCB123" and "Target 3001!" are low end CAD Tools.
 


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Posted By: lsday
Date Posted: 12 Sep 2019 at 3:02pm
Is there a place to change that round off for all package types? 

I went in to the Library Expert Preferences and changed the round off for chips. 

Looked at another package and it was still at 0.01. 

Also I went and looked at the chips again and it was back from 0.05 to 0.01.

Posted By: Tom H
Date Posted: 13 Sep 2019 at 7:13am
There are 7 different Chip Sizes:
  1. 01005 and smaller
  2. 0201
  3. 0402
  4. 0603
  5. 0805
  6. 1206
  7. Greater than 1206
Each Chip size has it's own unique Toe, Heel and Side solder joint goals and Pad Size and Place Round-off. 

Of course the user has 100% control of what these values should be and you should change them per your assembly shop recommendations. 

As technology advances, minor adjustments can be made due to machine accuracy. 



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