We have experienced voiding with via in pad, I know
it ws stated that the pads don't have vias in them but if they did they can
somtimes gass through the plating, its not the air traped by the paste. I have
investigated this with my old outgassing oil test which showes up the problem
and will contribute to voiding.
Bob Willis
----- Original Message -----
Sent: Friday, November 16, 2001 8:52
AM
Subject: Re: [TN] BGA voids
Hi, Peter,
I was at a seminar earlier this year where
BGA's and their solder joints
were discussed at some length. The received
wisdom is that voids in solder
joints are not of themselves a 'defect'
unless they break out through the
side of the ball. In fact, they make the
joint more "flexible" - better
able to withstand creep fatigue - so are
beneficial, up to a point.
What causes them is often outgassing of
volatiles in the solder paste flux
during the reflow process, though the
size and shape of voids increases and
changes when there are via-in-pad
features as well. About the only way to
detect them is by X-ray, and to
judge from previous TechNet postings, there
are some pretty fancy machines
around now that can give you a very much
clearer view of the balls than is
normally the case ... if you have cash to
splash!
Peter
Duncan
Peter
Lee
<ppwlee@YAHOO
To: [log in to unmask]
.COM>
cc: (bcc: DUNCAN Peter/Asst Prin
Engr/ST
Sent
by:
Aero/ST
Group)
TechNet
Subject: [TN] BGA
voids
<[log in to unmask]
ORG>
11/16/01
04:25
PM
Please
respond
to
"TechNet
E-Mail
Forum."
Hello,
I am
encountering voids after reflow on several micro BGAs on one PCA
product.
The voids that I $B!G (Bve observed (with Xray) contribute to as high
as
60-70% of the joint area. My reflow profile was designed by running
a
sample board with dummy components and thermalcouples attached right at
the
joint. I also inspected the PCB lands and didn $B!G (Bt see any via on
pad.
Does anyone know the possible reasons for voids
formation in BGA (micro)
reflow?
In general, in step
by step how would one trouble shoot such a
defect?
Rgds,
Peter
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