I have sent some photos to Steve for you. I avoid to put any name on the
phenomenon, as that seems to start fruitless debates. Instead I focus on
what we found. The balls lifted after tempcycling, as like you lift your
fried egg from the pan. When you look at the underside of the egg, there is
a smooth and even surface, supposed you got oil or butter in the pan.
Likewise, when we looked at the separation faces on these superBGAs, we saw
a flat, smooth and even surface, as if the balls had been solidified on a
glass plate. Nearly no microjoints at all, except a little arount the
perifphery. This smooth surface was nanometer thick (still BGA balls) and
behind that, a micrometer thick layer of extremly crystalline Tin-Nickel
layer. Experts from Ericsson determined that layer as caused by overheated
IMCs. We tried to examine the nanometer smooth layer, which was the very
sort of separation interface, but the result was hard to interprete, and
there was no further investigation. We cooperated with Xilinx, who made
several microscopic surveys, but we never got to know if the failure was
related to Xilinx or the boards or to our process, because one day the
problem disappeared. We had lost lots of boards an we were of course happy,
but myselft, I am still curious and wonder who was the murderer.
Inge
----- Original Message -----
From: "Paul Edwards" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, October 28, 2010 5:06 AM
Subject: Re: [TN] AW: [TN] Cracks in BGA solderjoints - Found word(s) list
error in the Text body
Gunter,
I would also look at the possibility that the PCB had some organic
contamination embedded in the Au... This could explain the micro-voids at
the Ni-Au interface and just above it...
We have found organic contaminates in the Au surface of ENIG PCBs due to the
surface roughness of the Au... These subsequently were trapped by the
surface tension of the flux and later by the solder's surface tension... The
volume of the contaminating material was too small to develop sufficient
buoyancy to migrate along or from the surface through the solder...
Is this PCA assembled with W/S solder paste with a relatively fast cool-down
rate OR is it a thick PCB with a relatively thin BGA soldered to it??
Paul
Paul Edwards
Surface Art Engineering
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Grossmann, Guenter
Sent: Wednesday, October 27, 2010 5:51 AM
To: [log in to unmask]
Subject: [TN] AW: [TN] Cracks in BGA solderjoints - Found word(s) list error
in the Text body
Dear Colleagues
Thanks a lo for the first answers.
- No, the BGAs have not been reworked
- Most failures occur in the field, some are found after production
- We didn't find any separations after only printing solderpaste and
soldering.
- It's not only the corner balls, the defects are found statistically in the
array
Günter
>-----Ursprüngliche Nachricht-----
>Von: TechNet [mailto:[log in to unmask]] Im Auftrag von Joyce Koo
>Gesendet: Mittwoch, 27. Oktober 2010 13:26
>An: [log in to unmask]
>Betreff: Re: [TN] Cracks in BGA solderjoints
>
>Spalling of the IMC? Are those reworked?
>--------------------------
>Sent using BlackBerry
>
>
>----- Original Message -----
>From: Inge [mailto:[log in to unmask]]
>Sent: Wednesday, October 27, 2010 07:17 AM
>To: [log in to unmask] <[log in to unmask]>
>Subject: Re: [TN] Cracks in BGA solderjoints
>
>I think it's not cracks in the BGA, but snacks in the BGA. At least what
>I
>found once
>/Inge
>
>
>----- Original Message -----
>From: "Grossmann, Guenter" <[log in to unmask]>
>To: <[log in to unmask]>
>Sent: Wednesday, October 27, 2010 9:36 AM
>Subject: [TN] Cracks in BGA solderjoints
>
>
>Hi Technetters
>
>I have an effect in BGA solder joints that I have never seen before.
>In microsections and in FIB preparations I see cracks between the IMC
>and a
>slightly darker region towards the Ni which I assume to be a P enriched
>zone
>of the Ni. However, the cracks are somewhere in the width of the solder
>joint and they are quite short running out to a row of pores that look
>somehow like Kirkendall voids.
>Is there still a possibility to place one or two pictures? Kim's IPC
>site
>doesn't work.
>
>Best regards
>
>Günter
>
>
>
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