Hi Dave-
I had a terrible BGA voiding problem when trying to solder a BGA down to thick film solderable gold (PtPdAu) over alumina with RMA flux. Successive experiments showed that I could virtually eliminate the problem by burnishing the pads. That seemed to suggest the voids were caused by the porosity of the thick film which trapped flux constituents.
You might try having the surface of the board go partially through a lamination adhesion promotion cycle prior to finishing it off. These usually have a process designed to increase porosity in the surface.
This is similar to you microvias, but on a finer scale and a whole lot more of them.
May need to try other flux techologies.
Wayne
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Goulet
Sent: Sunday, February 28, 2010 9:59 AM
To: [log in to unmask]
Subject: Re: [TN] Suggestions on Making BGA Voids
I remember a few years ago we had a problem with BGA voids and the two major causes were the use of Indium solder paste and possibly the higher humidity in the spring. We were always within specification and Indium gave us different stories and two different variations of the same past. I don't remember if it was No-Clean/OA or even PB-free.
I do know that when we changed solder paste to Multicore, the problem disappeared.
----- Original Message -----
From: "David D. Hillman" <[log in to unmask]>
To: [log in to unmask]
Sent: Thursday, February 25, 2010 10:42:57 AM GMT -05:00 US/Canada Eastern
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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