Test data requirements for assessment of alternative Pb-free solder alloys
Test data requirements
for assessment of alternative
Pb-free solder alloys
by Helen Holder, Gregory Henshall, Aileen Maloney, et al*, Hewlett-Packard Company
introduction
life.
[25-28]
Since the implementation
The standardization on near-eutectic
A range of tests has been included in
of EU RoHS in 2006, the
SnAgCu alloys for Pb-free electronics was in-
this protocol in order to provide a balanced
electronics industry has seen a
strumental in enabling the electronics indus-
assessment of potential alloys. If widely
try to meet the requirements of EU RoHS
proliferation of Pb-free alloys
adopted, the standardized test protocol
legislation by 1 July 2006. The SAC family
for wave soldering, mini-pot
presented in this paper would help bridge
of alloys, which includes Sn-3.0Ag-0.5Cu,
the gap between the specialized data gener-
rework, BGA and CSP solder
Sn-[3.5-3.6]Ag-[0.7-0.9]Cu (eutectic), Sn-
ated on materials optimized for particular
balls and, more recently,
3.9Ag-0.6Cu (iNEMI) and Sn-4.0Ag-0.5Cu,
attributes and the data required for assessing
solder pastes for mass reflow. has proven to be an acceptable, working
the suitability of alloys for general use. This
New alloys may help reduce solution for a broad range of applications.
test protocol does not completely eliminate
cost; however, the risk of
Nevertheless, it is clear that these
validation tests needed for special applica-
reduced thermal fatigue life,
materials, while functional, are not ideal.
tions; however, it should significantly reduce
improper soldering with high
The short RoHS transition period did not
duplicate testing and improve the quality of
melting point alloys, laminate
allow sufficient time for systematic alloy
the primary reported data for new materials.
damage due to high solder pot
design and testing to identify optimal SnPb
replacements.
temperatures and other poten-
accepteance criteria
When screening began in earnest to
tial negative effects present
This assessment approach only establishes
find Pb-free alloys to meet the RoHS dead-
the tests and data reporting, not the ac-
challenges and possible field
line, many alternatives to SnPb had already
ceptance criteria for alloys. This point is
reliability risks for OEMs.
been developed both in universities and
important because pass/fail criteria may
The authors have defined in industry. However, the long dominance
vary by industry segment, by company and
a set of tests that can be used of SnPb meant that many of the widely
by product. However, the underlying data
for assessing new SnAgCu,
available alternatives were specialty alloys
needed to evaluate new alloys are likely to be
SnAg and SnCu alloys for
developed for applications where SnPb was
similar in most cases. Thus, the assessment
general use in electronics.
inappropriate, rather than replacement
method provided in this paper is believed
The goal of this protocol is to
technologies intended to surpass SnPb
to be relevant across the entire electronics
standardize the test methods,
performance.
[1-4]
industry.
In the years since the RoHS deadline,
test parameters, test vehicles
the industry has had an opportunity to
and control samples so that
controls
revisit the formulations of Pb-free solders,
Most tests in this protocol have an alloy or
the performance of each new
and a wide range of new alloys has been
combination of alloys specified as controls.
alloy can be properly and
developed.
[5-24]
These controls have been selected to allow
fairly assessed relative to A significant obstacle to useful, data-
for ordered ranking against currently ac-
previously studied materials. driven assessments of alternate Pb-free cepted materials. By bounding the perfor-
These tests represent the
alloys has been the inconsistent testing that
mance of new materials with the current
minimum data required,
has been performed on the materials. The
and historic materials of SAC alloys and
and additional tests may be
data from experiments conducted on these
SnPb, appropriate pass/fail criteria are often
needed for special applications.
newer materials, while valid on their own,
apparent.
are often not comparable in any meaningful
For example, both SAC305 and SnPb
way to data from other equally valid experi-
controls are required in accelerated thermal
ments due to the choice of test conditions,
cycling (ATC). It is possible that low silver
Keywords: Pb-Free Solder
controls, or other parameters. Also, alloys
alloys may not perform as well as high
Alloy, SAC Family, Thermal formulated to meet specific goals, such as
silver alloys in ATC, however, some may be
Fatigue Life, Field Reliability improved mechanical shock resistance,
comparable to or better than SnPb. If low
have not always been tested to determine
silver alloys were only compared to high
This paper was originally presented
suitability for general use by assessing other
silver SAC alloys, they might be rejected
at SMTAI 2008.
performance aspects, such as thermal fatigue
due to the unfavorable comparison in ATC
12 – Global SMT & Packaging – November 2008
www.globalsmt.net
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