Transcript Lead Free Keep It Simple Soldering

LEAD-FREE, KISS PROCESS
(KEEP-IT-SIMPLE-SOLDERING)
SUPERIOR FLUX & MFG. CO.
6615 Parkland Blvd.
Cleveland, OH 44139
OBJECTIVE OF LEAD-FREE
SOLDER
WEEE/RoHS and Japanese
regulations originally set July 1,
2006 as the date when
electronics assembly be LeadFree.
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Primary Reason: Landfill Lead
Leaching into Soil.
ELECTRONICS USE OF LEAD
Electronics assembly represents 0.30.5% overall use of lead*.
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With such a small use of lead, why is
electronics targeted?
Number of landfills led to this legislation;
the high profile of electronics in ‘garbage
dumps’; and the ‘wealth’ of the highly
profitable electronics market.
* Source: AlphaMetals div. of Alpha/Fry Group.
ELECTRONIC PRODUCTS
Electronics targeted for addressing
European legislation removing lead
from landfills.

A wide variety of Tin/Lead solders are
used in televisions, cell phones,
telephones, computers and monitors,
and other consumer products.
Adding electronic assemblies to
Lead-Free list continues the removal
of Lead from solder, that is now
standard for plumbing solders.
WHO HAS CONDUCTED
LEAD-FREE RESEARCH?
Primary American research has taken place at the
Department of Energy’s (DOE) Ames Laboratory
at Iowa State University, under Dr. Iver
Anderson, who has conducted research into
Tin/Lead alternatives and arrived at a patent for
the basis of the SAC alloys.
The alloy that they have patented and
recommend is a ternary alloy combination of:
Sn: 93.6%
Ag: 4.7%
Cu: 1.7%
Eutectic Melt Point: 217ºC
ADDITIONAL LEAD-FREE
‘SAC’ ALLOYS
While the previous terneray ‘SAC’ alloy is the
patented solder, new ‘SAC’ alloy solders have
been presented to the market by a number of
different metals/solder companies:
1
2
3
Sn :
96.5
95.5
95.8
Ag:
3.0
4.0
3.5
Cu:
0.5
0.5
0.7
Additional ‘SAC’ Alloy Solders are also available.
These different alloy combinations all claim a
‘Eutectic’ of 217ºC.
BINARY EUTECTIC ALLOYS
While the talk has been of ternary
‘SAC’ alloy Lead-Free solders, there
are binary options:
1
2
Sn
96.5
99.3
Ag
3.5
-Cu
-0.7
Eutectic 221ºC
227ºC
…AND STILL MORE
Additional Lead-Free Alloys Exist
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42Sn/58Bi:
138ºC Eutectic
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95Sn/5Sb:
Plastic range 232-240ºC
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96.2Sn/2.5Ag/0.8Cu/0.5Sb: 218ºC Eutectic
(AIM Castin® Solder)
91Tin/9Zinc:
and many more…
199ºC Eutectic
DEFINITION OF EUTECTIC
Eutectic: Designating or of a mixture or alloy with
a melting point lower than that of any other
combination of the same components.*
Most widely used metals in electronics solders
and metal melt-points**:
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•
•
Tin (Sn):
Lead (Pb):
Silver (Ag):
Copper Cu):
Indium (In):
Bismuth (Bi):
Antimony (Sb):
Melting Point
Melting Point
Melting Point
Melting Point
Melting Point
Melting Point
Melting Point
*Source: Webster’s New World Dictionary
** Source: Merck Index, Twelfth Edition
232ºC
327.4ºC
960.5ºC
1083ºC
155ºC
271ºC
630ºC
FACTORS IN LEAD-FREE
SOLDER COMPOSITION
The key factor in selecting a Lead-Free solder has been
driven by price, cost, and temperature requirements.
Tin price, which has increased more than 100% since
1/1/2003, rises from 63% of solder content to a minimum
of 93.6%.
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This raises price, cost, and temperature of Lead-Free
Solders.
Other alloys, such as bismuth and indium, used in fusible
alloys, have too low a melt-point for reliability and stability
of finished products; are too weak as solder alloys and may
yield unreliable field dependability; or too expensive due to
limited global supply.
Antimony, long used in industrial applications, has been
kept from electronics applications for many years due to a
high temperature requirement, and, if too much antimony is
used, yield a weak joint that may peel over time and cause
electric failure.
WITH SO MANY LEAD-FREE
SOLDERS TO CHOOSE FROM,
WHY IS IT SO DIFFICULT?
The Eutectic melt-point of 63Tin/37Lead alloy is 183ºC.
The lowest melt Eutectic Lead-Free alloys used
primarily as fusible alloys, 48Sn/52In is 118ºC and
42Sn/58Bi is 138ºC, are too low for stable and
dependable life-cycle reliance use in a vast majority of
applications.
91Sn/9Zn is 199ºC, currently used in aluminum
soldering applications, is closer to the 183ºC base-line
melt-point of the current industry standard , but the
alloy is too corrosive for electronics applications.
WHICH FOCUSES THE
ALLOY BASE TO…
This leads to the Tin-Based Alloys,
which include:
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100Sn:
Melt-point of 232ºC
99.3Sn/0.7Cu: Eutectic of 227ºC
96.5Sn/3.5Ag: Eutectic of 221ºC
‘SAC’ Alloys: claim Eutectic of 218ºC
Actual plastic phase of 218-220ºC
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AIM Castin® Alloy: Eutectic of 218ºC
Kester SAF-A-LLOY: Plastic 219-235ºC
TIN PROPERTIES
All Lead-Free alloys, that meet the requirements for
electronics applications, are high tin-content alloys.
All melt-points with these alloys are, a minimum, of
34ºC above the Eutectic Tin/Lead Solder.
Tin, by itself, is a corrosive metal that requires
changes in the solder pots or lining of solder baths
used for wave soldering or solder dip applications.
Post-solder tin-based alloys must be watched for “Tin
Whiskers” that occur over time as the alloy ‘settles’
and forces out tin spikes from a previously flat
surface.
Tin reacts with copper and creates tin/copper
Intermetallics that can cause metal cracking or
embrittle the alloy.
‘BACK TO THE FUTURE’
While legislation from Europe and the Far East is leading to the
removal of Lead from the electronics assembly process:
Lead-Free soldering is not new!
When surface mount technology (SMT) reflow soldering was
introduced, double- sided boards were reflowed in a two step
process:
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Step One: 96.5Sn/3.5Ag with 221ºC reflow was the first side.
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Step Two: 63Sn/37Pb with 183ºC reflow was the second side.
The dual alloy process was incorporated to create a 38ºC
temperature difference between the Eutectic Melt-points of the
solders. This included stability in alloys that allowed the dual
reflow process to take place that did not displace or cause any
alterations to the first process step that incorporated the Sn/Ag
alloy. At the time, metallurgical properties included an alloy that,
today, can be used as a Lead-Free alloy with a proven track record.
When US Mil Standards were used to establish which alloys were
acceptable in SATCOM and Aerospace applications, the only LeadFree alloy that was proven and, therefore, specified, was
96.5Sn/3.5Ag, meeting specification QQ-S-571.
KISS LEAD-FREE
Given the variety of different Lead-Free Solders,
Binary: 96.5Sn/3.5Ag, 99.3Sn/0.7Cu
Ternary SAC Alloys: 93.6Sn/4.7Ag/1.7Cu,
96.5Sn/3.0Ag/0.5Cu, 95.8Sn/3.5Ag/0.7Cu,
95.5Sn/4.0/Ag/0.5Cu, and others.
Quad Alloys: 96.2Sn/2.5Ag/0.8Cu/0.5Sb
Five or more alloy solders: Include Tin,
Copper, Silver, Bismuth, Indium, and other
combinations
A number of critical factors must be considered,
but all lead to:
KEEP-IT-SIMPLE-SOLDERING!!!
ARE THE ALLOYS PROVEN
FOR ELECTRONICS?
The only alloy which meets military specifications and
has been subjected to life tests that meet SATCOM
requirements is 96.5Sn/3.5Ag binary Eutectic alloy of
221ºC.
 The fewer metal elements in any solder alloy make
for a more reliable, dependable solder and are
similar to the 63Sn/37Pb in terms of binary
formulation, solder stability, and Eutectic
consistency.
The IPC, to date, has not written any specifications
under the ANSI-J-STD 004, 005, 006 Standards for
Lead-Free alloys.
Potential patent infringement has led to the variety of
different ‘SAC’ Alloys all claiming to be Eutectic. This
has led to a re-definition of Eutectic to include a
plastic range of 218-220ºC as ‘Eutectic’.
WHAT DOES LEAD-FREE SOLDER
CONNECT WITH BEST?
Silver Immersion is recommended for
PCB coating over HAL, Gold, OSP and
other PCB finishes.

The Lead-Free solders that are emerging
as ‘the choice’ are generally a
combination of alloys containing Silver.
Having a like-to-a-like in the Silver
Immersion PCBs and the Solders
ensures a better fusion of solder to PCBs
in assembly processes.
SHEAR STRENGTH VS. DUCTILITY
In all tests conducted to prove a Lead-Free Solder can be
used to replace Sn/Pb, the ‘strength’ of the solder,
defined by Shear Strength, is the factor employed to
determine how reliable a solder will be.
Tin/Lead solder will always lose to the Lead-Free alloys,
which have greater shear strength.
 However, the ductility, or ability to be forgiving, is
overlooked as the true strength for the Tin/Lead
solders that have been the industry standard for more
than 50 years.
 The Lead-Free Alloys, with high tin-content are more
prone to:
Cracking than tin/lead, due to the tensile strength
and lower ductility.
Tin Whiskers in the event that the alloy-balance is
altered by metals content and fluctuation over
time.
Tin/Copper Intermetallics developing between the
tin and copper reaction.
PCB ASSEMBLY PROCESS
SMT Reflow (Recommended alloys: 96.5Sn/3.5Ag, SAC Alloys)
Higher temperature and longer time profiles are necessary to
accommodate the higher melt-point of Lead-Free alloys.
Components, sensitive to high temperatures, must be carefully
monitored to ensure that over-heating does not affect reliability.
Once established, thermal profiling must be strictly adhered to, to
ensure consistent PCB output
Wave Soldering (Recommended Alloy: 99.3Sn/0.7Cu*)
Solder pots formulated for Tin/Lead solders must be replaced or
retrofit with a special lining to ensure that the tin does not
corrode, or ‘eat-away’, at the metal-lining of the pot and corrupt
the solder.
Solder temperature must be raised from 235-250ºC to 260-290ºC
(or higher) to create similar flow action to the tin/lead solder
onto, and up into, the PCB leads and joints.
Higher solder temperatures create greater dross than the lower
temperature of the Tin/Lead solders.
The use of nitrogen on the solder bath can greatly improve flow
and reduce dross content on the solders.
*Ask Superior Flux about this alloy vs. SAC and other alloy recommendations.
SOLDER PASTES AND FLUXES
SMT REFLOW
Conventional solder paste mediums can, and should be used,
for all Lead-Free solder alloys and provide:
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No slumping.
No tomb-stoning
No white residues on PCBs
Non-halide Activation system
Consistent rheology, thixotropy, and viscosity.
Clear, pin-testable residues with all No-Cleans.
WAVE SOLDERING
Fluxes
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When going Lead-Free, consider a VOC-Free/Lead-Free operation
for workplace and environmental safety.
No-Clean fluxes require more activity to meet the higher
temperature requirements of the Lead-Free Solder process.
Water-Soluble fluxes, with higher solids contents and activity
levels, can be used as drop-in fluxes.
VOC-Free and Alcohol-based fluxes all meet the process and
performance requirements for Lead-Free applications in watersoluble and No-Clean formulations.
REFLOW OPTIONS
Vapor Phase
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Can use a fixed temperature of 230ºC
with the Lead-Free Alloys, but must
maintain consistent process time at
temperature phases.
Convection
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Recommended temperature is 245250ºC and must maintain 45-60 seconds
at temperature.
LEAD-FREE REFLOW PROFILE
4ºC does not make a difference in Reflow
Profiles for the Lead-Free alloys.
PRICE OF SOLDER AND
COST OF OPERATIONS
Question anyone who tells you that the Lead-Free conversion
only costs ‘tenths of a penny per PCB joint’. Lead-Free alloys
are more expensive than Tin/Lead and the costs of the joints
add up. But this is not the sole cost added in the conversion:
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Engineering costs and the time invested in establishing and
developing a consistent process adds rapidly.
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Higher melt point of solders require hotter ovens and solder
pots, which increase capital equipment operations and
maintenance costs.
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Potential for using nitrogen, an additional consumable,
increases in Lead-Free wave solder applications to reduce
dross and extend solder life.
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Capital equipment costs, such as hotter ovens for reflow and
retrofitted or new solder baths for wave soldering add-up.
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Rework and repair will likely increase at the outset of any
operation/process change.
SUMMARY OF LEAD-FREE
SOLDERING
The new Lead-Free solders are meeting legislation, not
metallurgical/scientific discovery.
If Lead-Free soldering offers so many advantages, and
Lead-Free solders have been used in many applications for
many years, why was it not chosen as the base alloy until
legislation forced it upon the electronics industry?
All Lead-Free alloys will be more costly than the Tin/Lead
solder, as will operation and process costs.
All Lead-Free alloys that are being touted as the ‘best
choice’ have a higher melt point than 63Sn/37Pb solder.
Higher solder temperature will push the semiconductors
and components to the edge of performance.
Multiple alloys are developing as the standard for SMT and
Wave Soldering, but the industry, as a whole, have not
formulated a global standard for the solder alloys and
performance characteristics.
CONCLUSION
KEEP-IT-SIMPLE- SOLDERING
SMT Reflow
The sole long proven alloy that meets Lead-Free requirements is
96.5Sn/3.5Ag. It is a binary alloy with a true Eutectic of 221ºC.
If a SAC Alloy is the specification that must be met, the closest
alloy to the Tin/Silver Eutectic is 96.5Sn/3.0Ag/0.5Cu. The melt
point falls in the 218-220ºC range and is not different, in terms of
setting process guidelines, than the Tin/Silver. However, with
copper as part of the solder, potential tin/copper Intermetallics
and/or whiskers must be investigated.
Wave Soldering
A 99.3Sn/0.7Cu, due to cost and a wider process window
available in this process, make this 227ºC Eutectic alloy the
preferred choice. However, with copper as part of the solder,
potential tin/copper Intermetallics and/or whiskers must be
investigated.
Again, if a SAC alloy is specified, the 96.5Sn/3.0Ag/0.5Cu is
recommended to maintain consistency of boards used in Reflow
and Wave soldering. With copper as part of the solder, potential
tin/copper Intermetallics and/or whiskers must be investigated.
CONCLUSION
KEEP-IT-SIMPLE- SOLDERING
SMT Reflow and Wave applications actually show that there
may be alloys that meet the specific Lead-Free soldering
processes, while maintaining a simple process approach to
the Lead-Free conversion.
The assembly processes must be evaluated from a number
of different angles, and the final process must bring these
elements together. This includes:
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Metallurgical
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Chemical
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Temperatures
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Timing
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Acceptable output levels
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How to minimize rework and repair
All PCBs must be given extended time, after initial process
evaluations have been conducted, to ensure stability, longlife, and dependability of the PCBs that have been
converted to the Lead-Free alloys.
LEAD-FREE, KISS PROCESS
(KEEP-IT-SIMPLE-SOLDERING)
SUPERIOR FLUX & MFG. Co.
6615 Parkland Blvd.
Cleveland, OH 44139