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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