It's believed to be Tin/Bismuth directly on Copper (beware) and a 
extraordinary thick solder mask.  I'll take a closer look 2morrO.
Inge

----- Original Message ----- 
From: "David D. Hillman" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, September 03, 2009 9:24 PM
Subject: Re: [TN] BGA Pb-free, this is what I feared: Tin whiskers


> Hi Inge - what is the pwb finish?
>
> Dave Hillman
> Rockwell Collins
> [log in to unmask]
>
>
>
> Inge <[log in to unmask]>
> Sent by: TechNet <[log in to unmask]>
> 09/03/2009 02:15 PM
> Please respond to
> TechNet E-Mail Forum <[log in to unmask]>; Please respond to
> Inge <[log in to unmask]>
>
>
> To
> [log in to unmask]
> cc
>
> Subject
> [TN] BGA Pb-free, this is what I feared: Tin whiskers
>
>
>
>
>
>
> We have HASL and via-in-pad. Electrical issues, disturbed signals. There
> were hundreds of Tin whiskers on inside of the unfilled vias, and even
> whiskers from solder pads circumperiphery, pointing at the nearby solder
> pads. I suspect that the signal failures are caused by CAFs. Have any of
> you
> seen a connection between the presence of Tin whiskers and CAF growth?
>
> All BGA via-in-pads are solder mask defined. If you want photos, I can
> send
> a couple to the PA immigrant.
>
> /Inge
>
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