Thanks, Wayne. Yes, I know there is no dissolution (IMF) taking place during the periods of solidus, but going back to Werner's comments on this forum regarding reflow of SAC105 and many people reflowing at too low of an MRT, I began to wonder just what happens to a given alloy such as 63/37 and SAC305 and SAC105 when they are held close to the eutectic point, where perhaps it can oscillate back and forth between solidus and liquidus for a period of 45 seconds or so. It sounds like you have sectioned some SJs that have done this. Care to post them on Steve's Wall of Honor? If so, email to [log in to unmask] I and others would be very interested in seeing what they look like.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer
Sent: Wednesday, May 23, 2007 1:13 PM
To: [log in to unmask]
Subject: Re: [TN] SV: [TN] Definition of Eutectic Solder
Reflow at the eutectic point? It may be liquid, but it will probably not wet very well unless you give it infinite time in an inert environment.
Something missing from the discussion of eutectics is the metalurgical beauty of the grains of the alloy: At the eutectic point, the molecules of the constituents line up in these thin planes within each grain of the alloy. If you section and etch a bit, the makeup is pretty clear. Get just a tad either side of that point, and you see a grain of the primary material which envelops the grains of the lesser constituent. Very close to the eutectic point, you get some grains which have switched to the "thin planes" and some which have the other structure.
Wayne Thayer
>>> [log in to unmask] 5/23/2007 1:36:02 pm >>>
Not worried about them, just curious about the effects of sustaining a reflow profile right at the eutectic point of a given alloy.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Hfjord
Sent: Wednesday, May 23, 2007 11:57 AM
To: [log in to unmask]
Subject: [TN] SV: [TN] Definition of Eutectic Solder
Don't you all make this very academic and complicated. In my simple world water is a liquid and ice is a solid. And there is nothing in between. So, when the researchers down the South Pole pee at -60 Centigrades, they can see how liquid changes to solid in a second.
Inge
-----Ursprungligt meddelande-----
Från: TechNet [mailto:[log in to unmask]] För Brian Ellis
Skickat: den 23 maj 2007 18:04
Till: [log in to unmask]
Ämne: Re: [TN] Definition of Eutectic Solder
The range is theoretically 0°C for a perfect eutectic alloy.
Brian
Stadem, Richard D. wrote:
> Dave/Werner,
> In all of these discussions of the term eutectic alloy, I always
> wondered if there was a concrete definition of eutectic. Is there a
> specification or standard that determines the plus/minus temperature
> range over which an alloy transcends through the completely liquified
> stage to the completely solidified stage in order to be called
> "eutectic"?
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
> Sent: Wednesday, May 23, 2007 8:36 AM
> To: [log in to unmask]
> Subject: Re: [TN] Definition of Eutectic Solder
>
> Hi Werner! Here is the definition from the American Society for Metals
> (ASM) Metals Handbook, 2nd Edition:
>
> "Eutectic. (1) An isothermal reversible reaction in which a liquid
> solution is converted into two or more intimately mixed solids on
> cooling, the number of solids formed being the same as the number of
> components in the system"
>
> Now, your definition is perfectly correct too and I agree with it.
> However, using the terms Liquidus and Solidus are necessary in the
> definition. Most folks struggle a bit with the terms Liquidus or
> Solidus and I didn't want to get too deep in the metallurgy (Mr. Pauls
> has such a hard time understanding metals and the English language in
> general (if folks haven't noticed, Doug and I are making fun of each
> other today).
>
> Lots of fun metallurgy discussions to start the day! Very cool.
>
> Dave
>
>
>
> Werner Engelmaier <[log in to unmask]> Sent by: TechNet
> <[log in to unmask]>
> 05/23/2007 08:03 AM
> Please respond to
> TechNet E-Mail Forum <[log in to unmask]>; Please respond to
> [log in to unmask]
>
>
> To
> [log in to unmask]
> cc
>
> Subject
> Re: [TN] Definition of Eutectic Solder
>
>
>
>
>
>
> Hi Dave,
> Sorry, I must disagree; your definition of "1) Eutectic: when a metal
> alloy transforms from a liquid state into a single solid state" is
> wrong.
> A eutectic alloy composition is by definition that composition where
the
>
> alloy's Solidus and Liquidus temperatures coincide and having the
lowest
>
> melting
> temperature among all other alloy compositions of the same materials.
>
> Werner
>
>
>
> **************************************
> See what's free at http://www.aol.com.
>
>
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