Bev, look what you have started!
Now I have to send Ronald Bulwit's article 'A Practical Guide for Soldering to Gold' to you. A very good one, without exaggerated academic stuff, but deep enough for daily understanding.
Inge
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Fenner
Sent: den 17 januari 2008 14:21
To: [log in to unmask]
Subject: Re: [TN] SV: [TN] SV: [TN] Solderability of Tin-Gold Intermetallic
Interesting thread.
In my experience in dealing with problems of first soldering to "gold" with tin based solders, the problems have not been with the gold (it is readily soluble in tin or tin based alloys) but to the underlying surface, People rarely solder to solid gold but to a gold finished surface. Its the underlying surface which is key as that is where the solder joint is formed.
Here I am making a distinction between the process of soldering and the properties of the subsequent joint which may well have embrittlement problems etc. And I am thinking only of individual solder joints made with discrete, finite amounts of solder, not wave soldering or dipping.
ON reflowing (second soldering) a previously soldered "gold" surface the picture is muddied slightly because the solder may not flow very well or appear to wet very well because of the presence of gold tin intermetallics, amongst others, in the joint which drive up the liquidus of the solder puddle. On the second go round if there have been problems of joint formation there is no reason to believe these will have been alleviated by subjecting the surface to a [soldering] heating cycle.
As an aside with respect to below.
Gold tin solder (80Au/2Sn) MP280C is very corrosion resistant, it takes something like aqua regia to dissolve it.
Regards
Mike Fenner
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis
Sent: Thursday, January 17, 2008 9:43 AM
To: [log in to unmask]
Subject: Re: [TN] SV: [TN] SV: [TN] Solderability of Tin-Gold Intermetallic
1. It doesn't take much corrosion to reduce the solderability.
2. It's the base metal that will corrode 3. My wedding ring, after 49 years,
this year, is a lot thinner than it was. Who can say whether the wear is
purely mechanical abrasion or partially corrosion at molecular levels,
bearing in mind that potential corrosion products would probably be easier
to wear off?
4. In this country, many bronze age gold artefacts in the Cyprus Museum are
visibly corroded after being buried for 3 or 4 millennia: granted I have no
idea of the purity of the gold, but I imagine it is reasonably high from the
brilliance of the pieces.
5. Analogically, 100% pure iron does not rust. It requires an impurity, such
as an iron carbide crystal, forming an electrochemical couple, moisture and
probably CO2 to allow rusting (corrosion) to occur.
Anyway, it was just a hypothetical thought!!!
Brian
Hernefjord Ingemar wrote:
> So, a gold/copper alloy wedding ring will fall apart if your finger is
wet...hmmmm...but it will take some time, wuntit?
> /Inge
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis
> Sent: den 17 januari 2008 09:23
> To: [log in to unmask]
> Subject: Re: [TN] SV: [TN] SV: [TN] Solderability of Tin-Gold
> Intermetallic
>
>
> Can I add a wee bittie more hypothesis to the arguments? The
electrochemical potentials of gold and tin differ by 1.8295 V, which is
boooody enormous. In the presence of humidity, it is conceivable that
important corrosion currents could flow between gold-rich and tin-rich areas
on the surface...
>
> ???
>
> Brian
>
> Werner Engelmaier /* wrote:
>> Hi Inge,
>> I visited Gerd Becker twice in Swedenâ besides being a great guy, he
>> was of course Eicsson's soldering guru.
>>
>> Werner
>>
>>
>>
>> **************
>> Start the year off right. Easy ways to stay in shape.
>>
>> http://body.aol.com/fitness/winter-exercise?NCID=aolcmp00300000002489
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