You can try to reduce the soak time to maximize flux amount at reflow zone.
Also, you could try to reflow boards multiple times. The trapped flux inside voids tends to expand further during subsequent reflows making them even larger.
Date: Sun, 28 Feb 2010 14:58:34 +0000
From: John Goulet <[log in to unmask]>
Subject: Re: Suggestions on Making BGA Voids
I remember a few years ago we had a problem with BGA voids and the two maj=
or causes were the use of Indium solder paste and possibly the higher humi=
dity=C2=A0in the spring. We=C2=A0were always within specification and Indi=
um gave us=C2=A0different stories and two different=C2=A0variations of the=
same past. I don't remember if it was No-Clean/OA or even PB-free.=20
I do know that when we changed solder paste to=C2=A0Multicore, the problem=
disappeared.=C2=A0=20
----- Original Message -----=20
From: "David D. Hillman" <[log in to unmask]>=20
To: [log in to unmask]
Sent: Thursday, February 25, 2010 10:42:57 AM GMT -05:00 US/Canada Eastern=
=20
Subject: [TN] Suggestions on Making BGA Voids=20
Hi gang! Ok, I have a fairly crazy request for suggestions on how to make=20=
BGA voids. =C2=A0First here is the background - Dr. David Bernard (Dage), =
Dave=20
Adams (Rockwell Collins) =C2=A0and I are working on a collaborative projec=
t to=20
investigate the thermal cycle solder joint integrity of BGA components. We=
=20
are attempting to produce data which the IPC JSTD 001 committee can use to=
=20
revise the 25% maximum void criteria. Despite public rumor, this current=20=
IPC JSTD 001 void requirement is based on actual IPC Class 3 field=20
equipment =C2=A0results submitted to the committee several years ago. Howe=
ver,=20
BGAs have changed in both size, pitch and solderball diameter since the=20=
creation of the void criteria thus the reason for collaborative project.=20=
We have a test vehicle which contains BGAs at 0.5mm, 0.8mm and 1.0mm pitch=
=20
with each having a corresponding larger solderball diameter. We have put=20=
uvias in the BGA pads to "create" voiding. Great plan, figured we had it=20=
made- however, after running the test vehicles thru a standard reflow=20
process (this effort is focused on tin/lead right now) we find that we=20
have an average void size in the range of 0-5%! =C2=A0My production proces=
s=20
folks are very proud of that result but it doesn't do our voiding=20
investigation much good (you can imagine the look I got when I told them=20=
they didn't make enough voids greater than 25%). =C2=A0I know that a numbe=
r of=20
the Technet community have tried to accomplish this voiding task with only=
=20
mild success (i.e. Bev Christian, Martin Wickham, etc.).=20
My Technet request is - do you have any suggestions on how to increase the=
=20
solderball void size without causing a biased negative impact on the=20
solder joint quality? I can obviously make some huge solderball voids=20
(such as pouring Doug's Diet Mt. Dew on the test vehicles) but the overall=
=20
quality of the solder joint would not be representative of the real world=20=
product.=20
Thanks in advance=20
Dave Hillman=20
Rockwell Collins=20
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