Hi Jesse - yes, under ideal conditions if the supply of tin was the only
variable in determining the thickness of the intermetallic then your
assumption would be right. But there a a large number of diffusion issues
(kinetics) and composition issues (thermodynamics) that change things
(remember how the ideal gas law worked great in school but not in the real
world!).  Dr. Chris Hunt gave a very good paper at the 1996 SMI Conference
which contains some experimentally derived diffusion coefficients that you
can use for approximating intermetallic growth/thickness that work pretty
well. Have fun.

Dave Hillman
Rockwell Collins
[log in to unmask]





"Martin, Jesse" <[log in to unmask]> on 02/17/99 05:16:51 PM

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
      to "Martin, Jesse" <[log in to unmask]>

To:   [log in to unmask]
cc:
Subject:  Re: [TN] Intermetalics




From this would you expect that (holding all other varaibles constant) you
would get a thicker IMC layer on the final solder joint with thin HAL
boards
than with more normal, thicker HAL?

> -----Original Message-----
> From: [log in to unmask]
> [SMTP:[log in to unmask]]
> Sent: Wednesday, February 17, 1999 11:59 AM
> To:   [log in to unmask]
> Subject:      Re: [TN] Intermetalics
>
>
> It would not be at all unexpected to observe a higher relative
> concentration of tin in an area determined to have a  "thin" HAL deposit.
> The XRF is responding to the ratio of tin to lead, and given you are
> approaching the copper/solder interface, and more specifically the
> tin/copper interface, it would be naturally preferential to tin
> concentration.
>
> Sounds like you are within expected conditions, other than the thin
solder
> deposits. May I assume they are on larger ground areas? There is a direct
> correlation between deposit thickness and area size under given
conditions
>
> Hope this helps!
>
> Joseph Webb
> TET/Halco
>
> ################################################################
>

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