Renjith, 

The BGA ball size reduction of 20% to calculate the pad size has a tolerance
range of +/- 0.05 mm. 

If the 0.80 mm pitch BGA ball size of 0.50 mm and has a 20% reduction = 0.40
mm +/- 0.05 mm tolerance.

Maximum = 0.45 mm
Nominal = 0.40 mm
Minimum = 0.35 mm

IPC-7351 specifies that the Maximum Material Condition is the best pad size
option - 0.45 mm pad (land) size

So even though 0.40 mm is 20% of 0.50 mm, IPC-7351 uses the high side of the
tolerance range for the BGA pad (land) size calculation. 

The Nominal value is safe to use if you need the room for dog-bone via
fan-out but the Maximum value is what is calculated.  

I will try to make this more clear in the upcoming IPC-7351C Land and Pad
Pattern Development Issues and Recommendations

Tom

Tom Hausherr CID+, CIT
Founder & CEO
PCB Libraries, Inc.
13730 Sorbonne Court
San Diego, CA 92128
858.592.4828 Office
858.859.5371 Cell
www.pcblibraries.com 
 

-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of
Varughese, Renjith
Sent: Tuesday, August 05, 2014 3:39 AM
To: [log in to unmask]
Subject: [DC] land size for BGA

Hello All,

As per IPC-7351B the nominal land of a BGA is 20% reduction below nominal
ball diameter for periphery collapsing ball. But when we calculate using
IPC-7351 calculators the land size is more for a .8MM pitch BGA. Does anyone
help me why there is a difference?


Thanks and regards,

Renjith Varughese



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