thank you very much!
Gaby
> -----Original Message-----
> From: Carey Pico [SMTP:[log in to unmask]]
> Sent: ג אוקטובר 19 1999 0:56
> To: [log in to unmask]
> Subject: Re: [TN] TIN/GOLD alloy
>
> There are many practical problems in discussing solder compounds: 1) when
> does one talk about "equilibrium" compositions/phases when one has
> nonuniform thermal processing (heat/cool), 2) interface metals not fully
> dissolved, 3) gaseous and liquid (flux) impurities, and 4) reliable aging
> tests.
>
> That said, here is my comments on tin-gold:
> The issue with using gold is the occurance of the crystal structure of the
> AuSn4 phase depending on the solder mix, about 220C melting/liquidus/phase
> change point. Above a critial value (approximately 5% Au for Pb37-Sn63 wt%
> or ~10% Au for pure Sn), the crystal structure becomes large grained. The
> the poor interfacial properties between AuSn4 crystals tend to dominate
> the
> mechanical strength, leading to embrittlement. (For the record, at lower
> percentages of Au, you still have AuSn4 crystals, only that they are
> fine-grained and are dispersed in the Pb-Sn mix. In fact, they can
> increase
> the quality of the joint by "pinning" the Pb-Sn grains from moving without
> much plastic flow). So soldering to pure Au with Pb-Sn (or pure Sn) is
> going to get you into trouble. Track down some of the past work on TAB
> bonding to Au-bumped Si substrates (sorry, I don't have any references to
> start you on).
>
> Still I'm confused about the original memo (below in a mail response). If
> you are soldering to gold, you are starting from the worst alloy in using
> AuSn4, the most brittle form of Au-Sn. If you want to solder to gold, use
> a
> gold-dominated solder (e.g. Au5Sn). But these are in the 400C+ melt
> region.
> These are typically used as initial/tack-down solder step or in packaging?
> If so, then they can go through a secondary soldering (Pd-Sn) step at 200C
> without
> noticeable damage (assuming the Pd-Sn is not applied to the Au area).
>
> Any comments from the peanut gallery?
> Carey
> -----Original Message-----
> From: Jack Crawford <[log in to unmask]>
> To: [log in to unmask] <[log in to unmask]>
> Date: Sunday, October 17, 1999 3:06 PM
> Subject: Re: [TN] TIN/GOLD alloy
>
>
> >Gaby, et al
> >
> >Don't forget that IPC also has a leadfree website http://www.leadfree.org
> and we are
> >hosting a leadfree e-mail forum (like technet) also. More info on that
> website.
> >jack
> >
> >>>> Gabriela Bogdan <[log in to unmask]> 10/17/99 03:00PM >>>
> >Dear TechNetters!
> >Please could you comment on the use of Tin/Gold 90/10 solder ?
> >The application is for microwave applications when soldering to gold.
> >Its melting temp. is 217C .
> >I have the following questions:
> >How does this composition correlate with the maximum gold content in a
> >solder joint?
> >Would it be possible to pass such a subassembly through a secondary
> >reflow with 63/37 Tin/Lead?
> >Is it recommended ONLY for soldering to gold?
> >It must be very expensive too??!!
> >Paul, Werner, my apologies.
> >Thank you
> >Gaby
> >
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