Inge,
you might be far from finding the solution, but I think you've made a big step here. If the whiskers were already there, before assembly, you can charge IBM for all the rework and recalls.
Regards,
Ioan
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Hfjord
Sent: Wednesday, September 20, 2006 1:36 PM
To: [log in to unmask]
Subject: Re: [TN] PbCO3
Hi all,
I am now confused at maximum level! I studied some CBGA samples that I got
from IBM . They have been in a plastic box for a year or two and never been
used. The Lead whiskers had started growing already!! So, it seems as the
soldering process only accelerates the process, but does not start it. The
balls are high Pb as usual for heavy CBGAs. I'm now going to check some
ditto Kyocera too see if there is a difference.
If one looks close, it seems as the whiskers start growing from microscopic
round pores in the Pb surface. I begin to wonder, if the phenomenon has
something to do with Tin starvation, as Richard proposed, because there is
nearly no Tin left in the pore areas. The whiskers do only grow where there
are pores.
Any threads? Any Solid State experts?
See Steve's wall
Inge
----- Original Message -----
From: "Hfjord" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, September 12, 2006 8:32 PM
Subject: Re: [TN] PbCO3
> Richard,
>
> thx for your interest. Bev and other specialists seem to be somewhere
> else.´
> According to von Mise's equation, the stress is predominant in the
> ceramic-to-ball interface, or, in the PWB-to-ball interface, while the
> equator ought to have the least stress! So, why on earth do the whiskers
> grow around the circumpherical part of the ball. The balls (nearly pure
> Lead) are soldered on the ceramic platform by means of a Lead/Tin alloy.
> This alloy wets nearly all the way to the equator. Can the interface
> between
> the pure Lead ball and this wetting Lead/Tin alloy cause some stress?
>
> Any hint is welcome. Is there someone from China Lake reading this? Or ERA
> Welding Institute? Or the Welding Institute in Abington? Holden Happy, who
> worked with CBGAs earlier at IBM Fishkill ?
>
> Inge
>
>
>
> ----- Original Message -----
> From: "Stadem, Richard D." <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Tuesday, September 12, 2006 3:33 PM
> Subject: Re: [TN] PbCO3
>
>
> Thanks, Reuven
> This brings me to the question of PbCO3 lead whiskers. They must be
> caused by internal stressors. If seen around the widest diameter of the
> lead balls like in Inge's case where no electro-chemical reaction would
> be the cause if the balls were actually a Pb90/Sn10 alloy, the whiskers
> are likely caused by the lateral stresses from the CTE mismatch between
> the aluminum oxide CBGA substrate and the PWB substrate the components
> are soldered to. These stresses would thus be concentrated near the
> widest part of the ball. If the balls are lead plating over some other
> metal, the lead whiskers would be from stresses due to the plating, and
> would not be focused on the equator, but distributed evenly over the
> ball.
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