Werner,
Thanks for the posting with declarations and illustrations of IMC impact on
solder ductility etc.
I'm not a chrystallography guy, nor a thermodynamic freak, so I need some
further explanation. Have patience with me, please. At my age, the brain is
not so quick any longer.
If one gradually increases the Au percentage in SnPb, the size and number of
IMC platelets undergo a increase. The forbidden level is assumed to be when
you pass 4 wt%. Over that level you get to brittle solder joints. That's
clear.
If one lowers the Lead content gradually, I've seen that the size and number
of IMC platelets undergo a decrease until, finally, they vanish completely.
With other words, if you have just Sn, you can increase the Au percentage
until you get the much used 80AuSn. In this case you get an extremly fine
grade, dense and IMC-free solder joint. How come that no AuSn IMCs are grown
now? Is the reason for IMC growth in SnPb that you have a binary situation?
I'll send a diagram to Steve. An old one which I have been using for 20
years when speaking to colleagues. Are the figures still actual or do you
use different data today? From these graphs, I used to tell people, don't
feel too safe about the 4wt% rule, things happen to the solder joint before
that level.
(The diagram is from Dr Willy Beckers at Ericsson, retired since many
years. He was our solder guru. There is none of his kind today at Ericsson)
Inge
PS. I forwarded your excellent report to RUAG Space analysis lab. They
found it to be a gold coffin of comprehension.
----- Original Message -----
From: "Inge" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, November 24, 2010 12:01 AM
Subject: Re: [TN] Ductile to Brittle transition
> In fig 14 and 15 you say that IMCs are sticking out , and as I can see it,
> they are needles.
>
> Inge
>
>
>
>
> Hi Inge,
> 1. Not a good simile—the steel in concrete only adds strength in tension,
> not compression, it is not brittle, and it is round; IMCs are NOT
> needles—they only appear that way when the platelets are sectioned at
> acute angles; the adhesion of the concrete to steel is very high, not so
> solder to IMC.
> 2. Crystal growth at times appears [at least] chaotic.
> 3. I think it is the basic material properties—similar to all crystal
> structure—high modulus and little ductility.
> 4. Certainly the presence of the constituent metals is required—Margareta
> Nylen in Sweden has shown that when all the Sn was used up in forming
> IMCs, no more dissolution took place—elegant experiment; solidification
> speed certainly would have an impact, I would think impurities as well.
> Skoal,
> Werner
>
>
>
>
>
>
> ----- Original Message -----
> From: "Inge" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Tuesday, November 23, 2010 10:28 PM
> Subject: [TN] Ductile to Brittle transition
>
>
>> Hi,
>> have a few questions on Konstantina's and your report.
>>
>> 1. If you place steel bars or steel nets in the concrete, the strength
>> will increase significantly, but the IMC plates and needles in the
>> sollder joint do the opposite. How com?
>>
>> 2. Why are so many geometries created? Large plates, small plates,
>> needles, bars, all in a chaotic oder.
>>
>> 3. What causes the predominant brittleness, size of IMCs or geometric
>> form or anything else?
>>
>> 4. What is the major driving force to build up the IMC structure,
>> percentage of xx in the solder, or solidification speed or what?
>>
>> Inge
>>
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