Annular Pads will give a void in 'contact' with the pad.
Regards
Rex

Rex Waygood
Technical Manager
 
Hansatech EMS provides value manufacturing through engineering and
quality
 
Hansatech EMS Limited
Benson Road
Nuffield Industrial Estate
Poole
Dorset
BH17 0RY
 
+44 (0)1202 338200

 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: 25 February 2010 15:43
To: [log in to unmask]
Subject: [TN] Suggestions on Making BGA Voids

Hi gang! Ok, I have a fairly crazy request for suggestions on how to
make BGA voids.  First here is the background - Dr. David Bernard
(Dage), Dave Adams (Rockwell Collins)  and I are working on a
collaborative project to investigate the thermal cycle solder joint
integrity of BGA components. We are attempting to produce data which the
IPC JSTD 001 committee can use to revise the 25% maximum void criteria.
Despite public rumor, this current IPC JSTD 001 void requirement is
based on actual IPC Class 3 field equipment  results submitted to the
committee several years ago. However, BGAs have changed in both size,
pitch and solderball diameter since the creation of the void criteria
thus the reason for collaborative project. 
We have a test vehicle which contains BGAs at 0.5mm, 0.8mm and 1.0mm
pitch with each having a corresponding larger solderball diameter. We
have put uvias in the BGA pads to "create" voiding. Great plan, figured
we had it
made- however, after running the test vehicles thru a standard reflow
process (this effort is focused on tin/lead right now) we find that we
have an average void size in the range of 0-5%!  My production process
folks are very proud of that result but it doesn't do our voiding
investigation much good (you can imagine the look I got when I told them
they didn't make enough voids greater than 25%).  I know that a number
of the Technet community have tried to accomplish this voiding task with
only mild success (i.e. Bev Christian, Martin Wickham, etc.). 

My Technet request is - do you have any suggestions on how to increase
the solderball void size without causing a biased negative impact on the
solder joint quality? I can obviously make some huge solderball voids
(such as pouring Doug's Diet Mt. Dew on the test vehicles) but the
overall quality of the solder joint would not be representative of the
real world product.

Thanks in advance

Dave Hillman
Rockwell Collins
[log in to unmask]


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