Solder voids that large are not normal. They were normal for some solder
paste formulas. But, the paste companies reformulated the paste and
minimized the problem. 
So, you will need to have some special paste made or induce the voids. I saw
a video produced by Phoenix X-ray. They induced voids by extending the time
above melt. It took about 10 minutes but the voids were pretty spectacular. 

Guy

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Thursday, February 25, 2010 10:43 AM
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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