Bev,
1) take 63 and divide it by atomic weight of tin
2) take 37 and divide it by atomic weight of lead
calculate the ratio of (1) to (2) and this will give you the answer why
everyone is talking about eutectic composition of 63/37
Edward
Edward Szpruch
Eltek , Manager of Process Engineering
P.O.Box 159 ; 49101 Petah Tikva Israel
Tel ++972 3 9395050 , Fax ++972 3 9309581
e-mail [log in to unmask]
> -----Original Message-----
> From: Bev Christian [SMTP:[log in to unmask]]
> Sent: д аевеси 02 2001 14:21
> To: [log in to unmask]
> Subject: Re: [LF] Eutectic alloys?????
>
> Kay,
> As a fluorine chemist and not a metallurgist, I did not know this! I was
> so
> shocked that I even went and checked the phase diagram in an ASM book. So
> please enlighten us further on why everyone (well almost everyone) insists
> on calling 63/37 the eutectic.
>
> regards,
> Bev Christian
> Research in Motion
>
> -----Original Message-----
> From: Kay Nimmo [mailto:[log in to unmask]]
> Sent: August 1, 2001 3:31 AM
> To: [log in to unmask]
> Subject: Re: [LF] Eutectic alloys?????
>
>
> And as all metallurgists know, 63/37 is not the eutectic point of the
> SnPb phase diagram in any case.....its 61.9/38.1
>
> Kay
>
> +++++ Visit our lead-free.org website +++++
> Soldertec at Tin Technology Ltd, Kingston Lane,
> Uxbridge, Middx, UK, UB8 3PJ
> tel: +44 (0)1895 272406 fax: +44 (0)1895 251841
> [log in to unmask], http://www.lead-free.org
> *****************************************************************
> -----Original Message-----
> From: Andrew Hoggan [mailto:[log in to unmask]]
> Sent: 01 August 2001 08:17
> To: [log in to unmask]
> Subject: Re: [LF] Eutectic alloys?????
>
>
> Thanks Harvey,
>
> nicely put.
>
> So to phase diagrams - lies, damn lies, statistics and phase diagrams!
>
> OK I'll admit it I'm an organic chemist not a metallurgist (this'll make
> some friends happy), I thought the 63/36 phase diagram was a map of
> Bourgogne till I followed it and ended up in New Jersey.
>
> I don't know, I've never taken the decade off paying the mortgage to
> carry
> out the work (wife wouldn't let me) to confirm the results of 63/37 as
> manufactured by .... sorry I lost count I don't have enough fingers to
> count
> up the number of suppliers out there. Never mind their all using virgin
> tin
> so I'm sure the analysis will be spot on.
>
> In operation, lets see the 63/37 is contaminated with copper, silver,
> palladium, gold (not sure of the rest - wait a minute forgot nickel and
> good
> old pasty 60/40)- take account of throughput rate, drag out and
> replenishment, we get equilibrium. Then someone changes the board cycle
> (lucky buggers got a new account) so that screws that up , but then gosh
> (with a little bit of luck) equilibrium is achieved again, but wait,
> isn't
> the composition different from the previous run - could be! How does
> that
> effect the performance, but hehe, we've 4000 years of using tin lead
> behind
> us with absolutely noooooo problems, so that's OK. Anyway we analyse the
> pot
> every month, 3 months, 6 months, 12 months, pot analysis?
>
> Heh, that's good old 73/36, that could never be the case with other
> alloys
> could it?
>
> Tell you Harvey, you have some points but you're pointing in the wrong
> direction. The issue won't be the pasty range of the alloys, I've seen
> some
> nasty, nasty differentially cooling 62/36/2, I don't see planes trains
> or
> auto's falling out of the skies any more than they do now - for that
> reason.
>
> What really worries me is the research (yeah, these guys weren't
> married,
> didn't have mortgages) that indicates the so called improvement in
> strength
> by utilising lead-free alloys ShOuTeD quietly from the rooftops by other
> researchers (no names, no embarrassment, no litigation....) is
> conditional,
> not absolute.
>
> In other words, the initial testing carried out was limited it indicated
> (specific) lead-free alloys gave improvements in physical performance
> over
> tin lead (63/37) alloy. Unfortunately (and this is the really worrying
> part)
> if you were to take the same alloys and run the testing past the 1000
> hours
> or change the cycle rate or change the stress and/or the frequency
> applied,
> the results don't indicate performance improvements........!
>
> Now that scares me when I'm driving my Merc 230K at 140mph, worst still
> it
> scares when someone else is driving by my kid at 30mph......
>
> But look Ford have approved lead-free alloys after a three year
> programme so
> it must be OK.
>
> Seriously though, do some research, get surfing. Check out a couple of
> the
> links on my website (I built it, it's mine!!!!).
>
>
> Best regards,
>
> Andrew Hoggan
> BBA Associates Ltd
> www.bba-associates.com
>
>
>
>
>
> -----Original Message-----
> From: [log in to unmask] [mailto:[log in to unmask]]
> Sent: 01 August 2001 04:29
> To: [log in to unmask]; [log in to unmask]
> Cc: [log in to unmask]
> Subject: Re: [LF] Eutectic alloys?????
>
>
> Andrew Hoggan
> I am sure that you were never even on a banana boat on the River
> Clyde.
> And I thank you for pointing out that under- hood and airframe
> electronics
> are important niches where high temp alloys do fit. Also, it occurs to
> me
> that they use ceramic packages/packaging substrates that start out with
> Level
> 1 moisture sensitivity. So maybe they degrade a level or two, they are
> probably reliable enough. But all this would not apply to the passenger
> compartment electronics. I do want to check with friends at Rockwell
> Collins
> before conceding.
>
> Re pure ____ for 63-37, I note from phase diagrams that the pasty
> zone
> is
> much smaller and well-contained than it is for the SnAg, SnCu, and
> SnAgCu
> alloys when composition deviates from eutectic. I am still trying to
> understand the effects on production throughput, disturbed joints, and
> ____
>
> Also will the higher surface tension of lead-free alloys affect
> lead,
> solder ball, and flip chip package self-location. Tin lead works so
> well.
> Anyone?
>
> I am certainly willing to agree that lead-free has a place, not
> because
> itis free of lead, but because of other characteristics conferred. But,
> when
> all the shouting is over, in 2010, SnPb will dominate.
>
> By the way, would you want to be defibrillated lead-free?
>
> Harvey Miller
>
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