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September 2012

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From:
Mike Fenner <[log in to unmask]>
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Date:
Mon, 17 Sep 2012 21:14:22 +0100
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Forgot to say [For completeness]: 

The place of solid/liquid dross blankets has effectively been taken by
nitrogen injection. 
Insert this wherever you think appropriate! Probably near the bit where I am
blathering on about pot covers and no clean fluxes.


Regards


Mike 


 


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Fenner
Sent: Monday, September 17, 2012 8:57 PM
To: [log in to unmask]
Subject: Re: [TN] Recycled solder?

Hmm
IN days of yore this area is one I used to josh back and forth with other
suppliers in conference hotel bars (amongst more interesting stuff of
course).
It was a pleasantly pointless discussion as we were unhampered by actual
data but had plenty of anecdotal stuff to support any view we wanted to take
for the purpose of having a good chat.
Yes processed bars made less dross and in those days was evidence of a good
overall quality. See this in context: In those early days of our industry
electronic soldering was a minor usage of tin/lead products. Major was
industrial soldering, cabling/plumbing, type metal and so on. This was all
based largely on recycled metal. Virgin grade was more literal term then.
Fast forward to present. Those industrial uses are largely gone, if you see
type metal its usually as bygones in a trivia collectables shop. Electronic
solder is a significant user segment. It's easier to source high purity
clean metal and it's pretty much a given, at least in North America/Europe.
The pendulum now has swung from solders as pure as driven snow to the
opposite: load the solder with specialized additives to improve performance!

In a wave soldering machine the dross makers are turbulent wave, movement in
the pot, overzealous skimming. Surface oxides on bar, boards and so forth.
Pot covers, oil injection and all that type of stuff as in the olden days
doesn't sit well with no clean chemistry.
The dross reducers are not skimming/dross cover and the pumping of the wave
which will bring particulates from main body of pot up in the wave to pot
surface where they will float out on re-entry. Which is dominant/more
important? .. wait for it.. it depends... on individual applications. 
The actual pot content analysis of metal and oxides will eventually steady
state according to the inputs and outputs, generally I would expect a high
oxide containing solder to pump cleaner, but steady state higher than a pot
being replenished by low oxide content bar.
In either case  this is independent of the metallic impurities which will
also steady state, using different mechanisms. You just need that to be at a
level below which you need to change your pot. 
The effect of microscopic or smaller to nano-particles of dross/oxides is a
good area for debate as above. Some of the earliest work on nano-particles
in solder was done decades ago when looking at the effect of very fine oxide
particles. It was thought positive, the particles acting as centres of
nucleation to modify the solder joint structure. (all this from memory, so I
could be slightly off.) Whether very small particles would stay in
suspension or float out I have no idea. This is probably a good area for
someone to look at. Maybe as a thesis.
Dross will be tin rich as tin is more reactive than lead, so this can tin
deplete the pot especially if frequently over-skimmed. Possibly other metals
like copper will be higher in the dross also. The actual impurity level
range will be lower as said with high purity additions.
As to costs: Solder price is based on LME (London Metals Exchange) pricing
which officially changes twice a day morning and afternoon. New solder
processed into bar will sold over metals for processing and so on costs.
Used metals will be priced under. The spread is the cost, in this case of
buying higher priced bar and selling it back as low priced dross. How much
that is depends on amount of material taking into account individual batch
analysis and shipping costs. Too many variables in other words to make as
precise a statement as "it depends". IOW you can make your sums say whatever
you need them to say.




Regards


Mike Fenner

Bonding Services & Products
M: +44 [0] 7810 526 317
T: +44 [0] 1865 522 663
E: [log in to unmask]

 


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis
Sent: Monday, September 17, 2012 4:36 PM
To: [log in to unmask]
Subject: Re: [TN] Recycled solder?

A couple of Eurocents worth and, here, I'm talking Sn/Pb as I have no 
experience of other alloys.

Alpha went to great lengths with Vaculoy, Multicore with Extrusol etc. 
What were these bars all about? Both processes were to reduce the dross 
in the bars to near-zero. When you first filled a pot with either, there 
was a minimal quantity of dross floating on the top. The wave was clean 
and stayed that way for quite some time. If you used either injected or 
surface water-soluble oil, you could stay almost dross-free for months 
(OK you had to skim the polymerised oil/dross residues, but very little 
solder was lost). Then, quite suddenly, dross quantities increased and 
the Sn:Pb ratio dropped. If you used a poor quality cast solder bar, 
with metallic impurities well within specs, you would get much larger 
dross quantities on both the first melt and in daily service.

So, what am I saying? It is my belief that dross begets dross or, to put 
it less biblically, microscopic dross particles in suspension in the 
solder, when they see oxygen, will cause the dross formation to 
accelerate. I speculate that there is a threshold effect, possibly 
dependent on the size of the suspended dross particles. This is not a 
scientific theory but an observational hypothesis.

Dross is a mechanical mixture of tin oxide and solder. Metal reduced 
from dross is tin-rich, which is why the pot is tin-poor after much 
removal of dross. IMO, metal recovered from dross should ideally be 
refined to virgin elements and re-alloyed before re-use.

The point I wish to make is that re-using the metal recovered from dross 
may contain more suspended dross than the pot and thus may be the cause 
for an acceleration of dross formation. It will probably be cheaper to 
send dross for true refining, rather than to reuse metal extracted from it.

That's 4 eurocents, not 2.

Brian



On 14/09/2012 16:56, Pete wrote:
> My understanding is that they will do the recycling themselves, on site.
They said the recycling would be mechanical, not chemical, so maybe it is
just squeezing out the droww.  They also said it was an effort to be
environmentally conscious, but they are in China, so I'd think it's really
cost.
>
> We are among their smaller customers, so I can't make a lot of demands.
They asked if we would accept boards made with recycled solder.  I suppose
the best I can do is reply with a list of concerns and ask for test results.
>
> Thanks!
>
> Pete
>

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