Datasheet

Properties of Alloys, August 2007
LEAD FREE ALLOYS
printed circuit boards.) This erosion is between 50 and
100 times slower at normal soldering temperatures when
Savbit alloy is used.
Lead-free soldering is now EU law. The WEEE and
RoHS Directives were published by the EC in 2003 for
implementation by July 2006. All EU countries will
have, with few exempted electronics applications, to
comply with the elimination of lead in their production.
HMP SOLDER
The presence of 1.5% silver substantially improves
strength and wetting power compared to 5/95 Sn/Pb
solder. Multicore 96SC (SAC387) and 97SC (SAC305): Since
Multicore 96SC and 97SC are the universally accepted
lead-free alloys for SMT reflow, it is obvious that
96SC/97SC alloys ensure perfect compatibility when re-
working SMT assemblies originally soldered with these
alloys. These alloys perform the closest to traditional
Sn/Pb alloys.
Applications
Making nearby soldered joints: A useful application of
a high melting point alloy is the soldering of joints close
to each other in such a way that the first joint is not re-
melted while the later joint, or joints, are being made.
The first joint is made with HMP alloy (296-301°C) and
the further joints are made with successively lower
melting point alloys, for example - 60/40 tin/lead alloy
(183-188°C) and good control of soldering temperatures.
Multicore 99C: This is the standard lead-free alloy for
hand soldering and rework: Due to the fact that
temperature dynamics of rework can be less controlled
than reflow processes, it is safe to use 99C alloy for all
lead-free hand soldering and rework applications. There
is a considerable cost advantage also. 99C has superior
wetting and capillary filling characteristics and is also
used for plumbing applications.
Service at high temperatures: The maximum safe
service temperature for any solder alloy subjected to
stress is about 40°C below the solidus melting
temperature, HMP alloy can therefore be relied upon in
service up to about 255°C compared with about 145°C
for the common tin/lead alloys. HMP alloy is
consequently particularly suitable for soldering electric
motors, car radiators, high temperature lamps and other
products which are likely to meet relatively high
temperatures during their working life.
Multicore 96S: This alloy is the pure tin/silver eutectic
alloy; like pure tin, it is bright, hardly tarnishes, is lead-
free and non-toxic, but unlike pure tin it is relatively
strong.
It has higher electrical conductivity than other soft
solders and a melting point approximately 40°C higher
than either 60/40, 63/37 or LMP alloys. For one or more
of these reasons it finds uses, despite its higher cost, in
the form of Multicore Solder Wire usually in Electronics
applications. The alloy itself is however used more
extensively for non-electrical applications in the form of
Multicore ARAX Acid-cored Solder, particularly for
soldering stainless steel.
If HMP is used to solder tin/lead coated components, the
resulting soldered joint will be a new alloy with a lower
melting point than HMP alloy. This will depend on the
thickness and composition of the coating. The coating
itself could therefore be HMP alloy if necessary.
Service at very low temperatures: Tin/Lead alloys
containing more than 20% of tin become brittle at
temperatures below about -70°C. The HMP alloy
containing 5% of tin remains ductile (non-brittle) down
to below -200°C. Multicore HMP alloy is also
recommended therefore for service in extremely cold
conditions.
96S has better wetting power on stainless steel than other
solders. Note the silver in 96S does not suppress
absorption of silver from silver plated surfaces or
metallisations into the solder, so 96S is not suitable for
soldering to such surfaces.
Creep strength of HMP alloy: From information
supplied, it is clear that an outstanding feature is its very
great improvement in resistance to creep by comparison
with the tin/lead solders, both at normal and at elevated
temperatures. At 150°C for example, a 50/50 tin/lead
solder will fail under a load of 0.7 N mm-2 in
approximately 10 hours. The following results were
obtained with HMP alloy at the same temperature.
95A - Lead-free high temperature solder: 95A is a
high melting point solder suitable for general purpose
soldering where a lead-free alloy is require
Sn62 SOLDERS
Applications
Load (N mm-2) Time to failure
3.4 150 hours
1.7 about 1 year
0.7 no creep
Soldering silver-plated surfaces: The presence of the
2% silver in Sn62 alloys suppresses absorption of silver
from silver-plated surfaces into the solder. A good joint
is thus obtained. If an ordinary tin/lead alloy is used on
silver-plated surfaces, the silver can be lifted from the
surface and dissolved into the solder so that a good joint
is unlikely. The attachment of terminations in the
manufacture of silver ceramic capacitors is a typical
application.
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