if the uVias had been plated heavy at the knees (so that the top was 
smaller than the bottom of the via) you would have had spectacular voids.


At 07:42 AM 2/25/2010, David D. Hillman wrote:
>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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