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solder fatigue properties retry


Glen Walpert

Jan 1, 1970
There should now be a couple of pages from a SMT magazine article on ABSE.

Posted in response to Phil's post in the voids in solder joint thread:

This reference:

suggests that a fractional strain of 1% gives a fatigue life of 1000
cycles to failure with PbSn eutectic, and that the lifetime goes as
1/(epsilon**2). Lead-free solder has about a quarter of the fatigue life
of PbSn.

A single test showing separation of the solder from the pad is hardly
justification for the conclusion that "Lead-free solder has about a
quarter of the fatigue life of PbSn."

Solder joint reliability is a complex phenomenon involving surface
finish, processing parameters, solder creep and fatigue properties, etc.
The only test that matters is a test of your particular processed
assemblies, usually thermal cycling. The most challenging connection to
make reliably is usually large BGAs, where the corner balls are most
highly strained by thermal cycling. While I can't find them now, I have
seen a few published test results comparing different lead free solders
with tin-lead solders in large BGA thermal cycle to failure tests, and in
these tests some lead-free solders underperformed tin-lead by about 20%,
and some outperformed it by over 50% (not the cheap ones of course).

High reliability soldering is a complex issue, and if you want to
understand it you should follow a few of the manufacturing trade rags
like SMT.

While searching for the BGA test results I also happened to notice that
the EMS division spun off by IBM has folded. Too much effort "proving"
the unsuitability of lead-free and not enough time developing processes
that work well, perhaps. All of the surviving large EMS companies have
reported improvements in yield and reliability accompanying the
conversion to lead-free, and virtually all exempt high-rel manufacturers
are in the process of qualifying lead-free materials and processes, not
because of any need to comply with ROHS but because these materials offer
significantly improved reliability when selected and used in an optimal

Tin-lead is still easiest to use, and I would not suggest that small
exempt manufacturers convert due to the high cost of qualifying new
processes. But those who have done the work are achieving excellent

Glen Walpert

Jan 1, 1970
I used to work in the packaging research department of IBM Watson, and I
know the inventors of both the plated and injection moulded solder
processes. (We filed a few patents together on the creative use of
solder for optical alignment--see

Your characterization of IBM's effort couldn't be further off base--a
lot of very smart people spent over a decade getting lead-free right,
well ahead of the rest of the industry. A huge waste of time, effort,
and talent, due to idiotic bureaucrats solving a non-problem. (Heavy
metals don't go anywhere in landfills, due to extremely strong ion
exchange with clay minerals.)


Phil Hobbs

I don't doubt that a lot of great R&D was done by IBM, and that the real
reasons that they are no longer the leader in electronic manufacturing
that they once were has nothing to do with lead-free. Bad management
caused by the replacement of engineers with bean counters is more likely;
when the failure of a company appears to be due to something other than
bad management, it was managements job to deal with those other issues.
I did say "perhaps", and was really attempting to comment on the general
attitude towards lead-free displayed by you and other regulars on this NG,
who insist, against all evidence, that tin-lead is inherently more
reliable than lead free. It was the poor fatigue performance of tin-lead
solders that initially drove the development of lead free solders, not
ROHS, and virtually every large EMS reports better performance under
shock, vibration and thermal cycling with optimized lead-free processes
than with equally optimized tin-lead manufacturing processes.

While clay minerals do greatly slow the transport of heavy metals, and
while the problem may well not have been severe enough to justify the
money spent, lead has been found in the leachate of some landfills, some
electronics does go into incinerators, and the claim that heavy metal
poisoning is not a problem is contradicted by legitimate testing of lead
in the blood of persons near lead processing facilities. And when has
any real cost-benefit analysis been a part of any political process?