Since a particular proprietary solder, the Nihon Superior "SN100C" is in the
title of this string I will mention that it has been found that the rate of
growth of the intermetallic that is the first to form on at the interface
between copper and a high-solder, Cu6Sn5, is also affected by dopants. As I think
by now everyone knows one of the features that distinguished SN100C from
other solders was a Ni addition at a specific level. The Ni selectively
incorporates into the intermetallic so that it becomes (Cu,Ni)6Sn5. Nishikawa et al.
reported to the IPC/Soldertec Lead-free Conference in Amsterdam in 2004 that
in their experiments with droplets of SnCu solder on a copper substrate the
growth of the intermetallic reached a minimum at 0.05%Ni. That observation is
consistent with practical observations that intermetallic growth in SN100C
solder joints to copper is slower and more even than in joints that do not
contain Ni and that can have implications for reliability in long term service.
Keith Sweatman
Nihon Superior Co., Ltd.
In a message dated 25/06/2008 3:53:10 AM E. Australia Standard Time,
[log in to unmask] writes:
> Subj:Re: [LF] [TN] SN100 for Reflow Application
> Date:25/06/2008 3:53:10 AM E. Australia Standard Time
> From:[log in to unmask]
> Reply-to:[log in to unmask]
> To:[log in to unmask]
> Sent from the Internet ()
>
>
>
> Just a quick note on the intermetallic growth. It growth ALL THE TIME.
> As it's a diffusion process. Depending on the temperature the rate of
> growth will change but it never stops, so to say.
>
> Regards,
>
> Vladimir
>
> -----Original Message-----
> From: Leadfree [mailto:[log in to unmask]] On Behalf Of Pete Houwen
> Sent: Tuesday, June 24, 2008 12:59 PM
> To: [log in to unmask]
> Subject: Re: [LF] [TN] SN100 for Reflow Application
>
> Richard,
>
> There have been a few studies that suggest the IMC continues to develop
> over some period of time. I don't know that any of them have been able
> to
> definitively measure the growth/time ratio. HAST testing for lead free
> solder
> requires additional dwell time at either end of the thermal cycles for
> relaxation
> of the shear stress (measured in minutes). If their production line is
> set up to
> create mechanical stress within minutes of a thermal cycle, the joint is
> also
> still fighting thermal stress. So if Amol is having so many problems,
> and has
> the time, it certainly couldn't hurt. Anecdotally, we did find a
> reduction in
> failures by not pulling boards out of the reflow oven and depanelizing.
> Of
> course we had so many other things going on - no kid glove, but I did
> watch
> an operator wearing an oven mitt grabbing boards out of the wave machine
>
> (not even waiting for the conveyor), thumb on top, fingers underneath (I
> 'kid'
> you not), and wondering why electorlytic caps were falling off the
> boards.
>
> Pete
>
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