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BGA Pad Size Calculation
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lalexman View Drop Down
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    Posted: 03 Oct 2012 at 8:57am
Hi,
 
How is the size of the BGA pad calculated?
 
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Tom H View Drop Down
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Most BGA's are Collapsing Balls. In the "PCB Footprint Expert" in "Setup > User Preferences > Terminals > BGA Collapsing Ball" you will see Ball Sizes in the first column and the "Pad Size Reduction" in the second column. The Adj% = the Pad Size Reduction from the Ball Size.
  
 
 
Example: the first Ball Size in the table is 0.60 mm and the Pad Size Reduction calculation is 25%. So 25% of 0.60 mm = 0.45 mm nominal.
 
However, IPC-7351 specifies a tolerance range of +/-0.05 mm so the tolerance range is
  • 0.40 mm Minimum Pad Size
  • 0.45 mm Nominal Pad Size
  • 0.50 mm Maximum Pad Size

The IPC-7351 standard always uses the "Maximum" material condition, so the 0.60 mm Ball Size would require a 0.50 mm Pad Size.

The "PCB Footprint Expert" automatically performs all these calculations for the user.
 
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lalexman View Drop Down
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Thanks Tom.
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DaveCowl View Drop Down
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Points: 161 		Post Options Post Options   Thanks (1) Thanks(1)   Quote DaveCowl Quote  Post ReplyReply Direct Link To This Post Posted: 18 Oct 2012 at 1:44pm
I was wondering about that.

In fact I got to this page because I was trying to find out why the LP Wizard threw out .35 mm pads for my 0.8mm .4mm ball BGA where everyone else says Nominal would be 0.3mm.

In any case I am excited to see this product listed and will give it a try for sure!

Cheers!
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DaveCowl View Drop Down
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Points: 161 		Post Options Post Options   Thanks (0) Thanks(0)   Quote DaveCowl Quote  Post ReplyReply Direct Link To This Post Posted: 18 Oct 2012 at 2:16pm

Ok I have been playing with the software and I have a couple of questions:

My BGA is 18x18 0.8mm pitch with 0.4mm balls

1) It seems to output 0.35mm pads for all of L, N and M - does that make sense?

2) Looking at the table above there is no entry for 0.4 - I tried to add one but to no avail - does it just use the same settings for all sizes 0.35 - 0.45?

3) Did you know that text based HKP files are no longer supported by Mentor Library software? Do you have any fixes for that?

Thanks!
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Tom H View Drop Down
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Points: 5763 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Tom H Quote  Post ReplyReply Direct Link To This Post Posted: 29 Dec 2012 at 12:33pm
The BGA "Pad Size" calculation is 1-Tier, but the Silkscreen Line Width, Ref Des Height and Local Fiducial Size are 3-Tier environment per the upcoming IPC-7351C standard.
 
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