Dave,
Thanks for the pointer, I'll look for the text. Sorry to be so
vague, it wasnt deliberate!
One of the guys in another plant has asked some pretty vague
questions as to why the two alloys should behave differently, and
which would be better, and as the metallurgist within the group I get
to look at the microstructure and alloy composition, and comment.
This is an open statement and any response or comment is welcome.
Im assuming that the 95/5 will form a standard particle hardened
binary structure (eutectic dispersion in the Pb) but when we tried to
look at the microstructure itself we drew a blank, and cant get to
resolve anything, and certainly cant find the grain size of the Pb
phase.
Meanwhile the 10/88/2 will most likley from a ternary structure
with the Pb as the alpha, and isolated islands of the Sn with Ag in
solution as well as precipitating in small amounts. Again analysis is
drawing a blank.
As both materials age, it is certain that grain growth will occur,
and any dispersion will get coarser. In view of this, I would
estimate the 95/5 would have a better fatigue life and ageing response
than the 10/88/2 which will have a lower grain boundary density,
and the hardening effect of the initialy course "phase seperation"
will reduce. It is also likely that the grain boundary junctions will
begin to precipitate particles from solution, which will also reduce
strength. Meanwhile, the 95/5 will also undergo grain growth in the
Pb. The second phase will coarsen, (Ostwald ripening etc), but the
initial dispersion size will mean this takes a fair bit longer than
for the 10/88/2, also the chance of further precipitation is low. Even
if the particle spacing is greater than the critical value, the
structure should be stronger due to the normal dislocation pinning,
econd phase hardening etc.
Anyway thats what I thinks happening, and as we are drawing a blank
in analysing actual parts, I wondered if anybody out in the real world
has either read a paper on this for either alloy, has done similar
work, and feeling brave, or have any advice on analysis techniques
we've tried SEM/EDX, metallography and even had a look with auger.
Thanks again for anything you may offer
Roger
______________________________ Reply Separator _________________________________
Subject: Re: [TN] Solder Metallurgy
Author: "David D Hillman" <[log in to unmask]> at #email
Date: 08/01/99 06:57
Hi Roger - your question is very open ended but I'll take a stab at giving
you an answer. First, if you are just looking for basic solder alloy
information contact any of the solder alloy manufacturers (e.g. Kester,
Multicore, Indium, Alpha, Arconium, and the remaining cast of thousands) -
they will have some material properties, use environments, forms etc types
of information. Second, if you are going for more detailed information
find a copy of the following book - "Solder Mechanics: A State of the Art
Assessment", edited by Frear, Jones, Kinsman, ISBN # 0-87339-166-7. This
book isn't organized in the most user friendly manner but does contain a
host of references to the specific alloys of interest to you. Good Luck.
Dave Hillman
Rockwell Collins
[log in to unmask]
Roger Massey-G14195 <[log in to unmask]> on 01/08/99
05:50:17 AM
Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
to Roger Massey-G14195 <[log in to unmask]>
To: [log in to unmask]
cc:
Subject: [TN] Solder Metallurgy
Happy New Year to all "netters"
Dont know if this has been asked before, but can anybody point me
towards some metallurgical information on the standard 10Sn/88Pb/2Ag
solder alloy and its equally popular friend 95Pb/5Sn.
Any help greatly appreciated
Roger
Motorola UK
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