Ho!
I just love the reverse symmetry of this question....
First I refer you to one of Dr Lee's papers on voiding, the one which starts
with an illustration of 2 voided joints, identically processed. One has the
void at the top of the joint and the other at the bottom. In other words
void production to order might be difficult. Yu might have to make a lot to
get enough to select for your point!
As voiding is at least partially a function of poor solderability, you could
do worse than messing that up in a controlled progressive way. An
appropraite messing up process would also pump the PCBs with moisture - so
many hours of H and RH -which would also be a handy contributor to
production.
If this worked you could then pass to purchasing for a bonus cost saving
project - buy boards as bad as this!
Regards
Mike
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Thursday, February 25, 2010 3:43 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
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