Generally, we use 20 mil via with 10 mil drill inside BGA's with 4 mil
trace/space.  We've found that most of our fab houses handle 4 mil
traces well but have great difficulty with anything smaller.

Bonnie Brown
Sr. PCB Designer
Inter-tel Integrated Systems
Chandler, AZ 
(480) 961-9000 Ext. 21272  

-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of
Charles Gervasi
Sent: Friday, April 07, 2006 10:11 AM
To: [log in to unmask]
Subject: Re: [DC] 1mm BGA routing

It seems like the fab house ought to be able to make suggestions for
changes, since they are the ones having the problem.

I use a via with a 22 mil pad, 8 mil drill.  Even if you kept the pad
size at 20 mils, maybe a smaller drill would help.  Also 3mils, is very
small.  Are you using 3 mils so you can keep diff pairs together?  Like
Patrick said, maybe they don't need to be routed together until they're
escaped from the BGA.  

Regards,

Charles Gervasi

-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of
Steve Mariani
Sent: Thursday, April 06, 2006 5:29 PM
To: [log in to unmask]
Subject: [DC] 1mm BGA routing

I have a BGA with pin pitch of 1mm and have diff pairs routing between
pins.
Pad stack is:
18 pad with 10 hole.
Differential pair traces are 3 mil with 5 mil space.
Spacing under BGA is 5 mil from pad to trace.
20 layer board

We are having poor yeilds at the fabricator and would like to know what
others do in this situation.
Any ideas on how I can improve yeild. I have to keep the routing as is.
Does anyone play around with shaving pads?
Looking for any ideas.

Thanks

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