Use paste/tacky flux with ramp reflow profile.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Thursday, 25 February 2010 11:43 PM
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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