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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