2000-01-0017 Implementation of Lead-Free Solder for ... - Delphi

SAE TECHNICAL
PAPER SERIES 2000-01-0017
Implementation of Lead-Free Solder
for Automotive Electronics
Brenda B. Baney, Pascal Bezier, Michael S. Campbell, Richard D. Parker,
Pamela A. Sneller, Delbert R. Walls, Matthew R. Walsh,
Richard L. Whiteside and Gordon C. Whitten
Delphi Automotive Systems
Reprinted From: Environmental Concepts for the Automotive Industry
(SP–1542)
SAE 2000 World Congress
Detroit, Michigan
March 6-9, 2000
400 Commonwealth Drive, Warrendale, PA 15096-0001 U.S.A. Tel: (724) 776-4841 Fax: (724) 776-5760

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1
2000-01-0017
Implementation of Lead-Free Solder for Automotive Electronics
Copyright © 2000 Society of Automotive Engineers, Inc.
ABSTRACT
Lead-free solders for electronics have been actively pursued
since the early 1990’s here and abroad for environmental,
legislative, and competitive reasons. The
National Center for Manufacturing Sciences (NCMS-
US) 1 , the International Tin Research Institute (ITRI-UK) 2 ,
Swedish Institute of Production Engineering Research
(IVF-Sweden) 3 , Japan Institute of Electronics Packaging
(JIEP Japan) 4 , Improved Design Life and Environmentally
Aware Manufacture of Electronics Assemblies by
Lead-free Soldering (IDEALS-Europe) 5 , and, more
recently, the National Electronics Manufacturing Initiative
(NEMI-US) 6 have been aggressively seeking lead-free
solutions
The automotive industry has some unique requirements
that demand extensive testing of new materials and processes
prior to implementation. The specific steps taken
at Delphi Automotive Systems with lead-free solder will
be described along with the lessons learned along the
way. This includes the alloy down-selection which lead to
several interesting alloys. Product emulator builds will be
described beginning with hand-assembled units which
were used to demonstrate product viability on to production
line builds which were used to assess manufacturing
challenges. Finally, any remaining roadblocks to full
implementation will be described along with the plans to
eliminate them.
1
Project 0401RE96, National Center for Manufacturing Sciences,
3025 Boardwalk, Ann Arbor, Michigan 48108-
3266, www.ncms.org
2 ITRI Ltd, Kingston Lane, Uxbridge, Middlesex, UB8 3PJ,
UK.. www.itri.co.uk/index.htm
Brenda B. Baney, Pascal Bezier, Michael S. Campbell, Richard D. Parker,
Pamela A. Sneller, Delbert R. Walls, Matthew R. Walsh,
Richard L. Whiteside and Gordon C. Whitten
Delphi Automotive Systems
INTRODUCTION
3
Institutet för Verkstadsteknisk Forskning, Argongatan 30,
SE-431 53 Mölndal, Sweden, www.ivf.se
4 Japan Institute of Electronic Packaging, 3-12-2 NIshiogikita,
Suginami-ku, Tokyo 167-0042, Japan, www.jiep.or.jp
5 Brite/EuRam III, Project number BE95-1994, D M Jacobson
& M R Harrison, GEC J Research, 14(2), 1997,
www.cordis.lu/brite-euram/src/1994.htm
6 National Electronics Manufacturing Initiative, 2214 Rock
Hill Road, Suite 110, Herndon, VA 20170-4214,
www.nemi.org 7 See www.lead-free.org
Based on the $10 million spent on the NCMS project during
the period 1992-1996; the electronics companies are
very interested in achieving lead-free products. The goal
of that project was to develop lead-free alternatives for
electronic interconnection. A drop-in replacement for the
eutectic SnPb solder was not identified, however, many
alloy alternatives have since been investigated by electronics
companies worldwide.
In late 1997, there was renewed interest in lead-free electronics
because of European Union draft directives on
End-of-Life Vehicles (ELV) and Waste From Electric and
Electronic Equipment (WEEE) 7 . These draft directives
have specific material bans aimed at the use of lead in
both transportation and electronics. While the ELV directive
has an exemption for lead used in solder for electronics,
the pending WEEE directive proposes to ban lead
metal in electronics beginning in January 2004. Although
this deadline may be postponed, many electronics manufacturers
are pursuing lead-free manufacturing solutions.
There are numerous announcements from major
Japanese electronics manufacturers concerning the
reduction or elimination of lead from solder in the 2001
timeframe.
A recent effort has been the formation of a Lead Free
Task Group within the NEMI organization with a goal to
provide a lead-free solution by 2001. The tasks were
divided into five subgroups: Industry Awareness, Components,
Solder Alloy Selection, Solder Reliability, and Environmental
Legislation Monitor. The output of the solder
alloy selection group for recommended solder replacements
will drive the component groups recommendation
to suppliers with regard to higher processing temperature
needs for electronic components. The combination of
these two groups efforts will be assessed in the reliability
subgroup including test parameters approximating automotive
environments. Preliminary results are expected
from this Task Group in the last quarter of 2000.

HISTORY
Delphi Delco Electronics Systems has been quietly pursuing
lead-free electronics since our first foray into the
field in the early 90s. We have completed a down selection
process and performed numerous manufacturing trials
with a proposed lead-free alternative. The major
obstacles to lead-free soldering; modifying current circuit
board, component, and process materials to tolerate
higher temperature exposure, along with new characterization
of manufacturing and product reliability are currently
being addressed.
In the early 1990’s, Delphi Delco Electronics began working
with lead-free solder. Initial alloy development has
been described previously. 8 During the NCMS alloy
selection activities, a hand-assembled Electric Vehicle
Power Control Module was produced which was fully
functional. In the late 1990’s, a serious effort was
focussed on a lead-free radio receiver board which has
also been described previously.
Figure 1. Lead-free Automotive Radio Receiver Board
The lead-free radio receiver boards passed all of our
product validation testing. In fact, the thermal shock testing
led to some surprising results. Thermal shock tests
which are normally applied to electronic components are
very difficult for an electronic module to survive. The differing
CTE’s of the organic laminate material and the solder/lead
often results in solder joint cracking as shown in
Figure 2. The surprise is shown in Figure 3. In this case
the Lead-free alloy showed no cracking though they both
experienced the same thermal shock. This success led
to further work in a full manufacturing environment.
8 Lead Free Solder for Automotive Electronics, G Whitten,
Design and Manufacture for the Environment (SP-1342),
SAE, 400 Commonwealth Drive, Warrendale, PA 15096-
0001, USA
2
Figure 2. Normal Eutectic SnPb Joint Following
Thermal Shock
Figure 3. Lead-free Solder Joint Without Cracks
In 1998, a joint effort was initiated with Delphi’s Texton
operation in Brittany, France. In this case, a current production
keyfob (Figure 4) was used as a test vehicle to
learn if there would be any surprises in a full manufacturing
process.
Figure 4. Lead-free Keyfob
In this case, the keyfob was manufactured on a normal
manufacturing line. The PWB surface finish was
changed, the alloy was changed, and the thermal profile
for the reflow oven was changed. Otherwise normal production
techniques were used.

The keyfob again easily passed the customers product
validation tests.
In the process of optimizing the reflow profile for the keyfob,
the profile was altered based upon study of the joints
resulting from the initial keyfob builds. Earlier work on the
NCMS Lead-free project may have been reflowed with a
profile that was too cool as suggested in the cross-section
photographs shown in Figure 5.
Figure 5. SOIC Joint With Cool Reflow Profile 9
The good news is that the reliability data from the NCMS
report may be overly pessimistic. Higher temperature
reflow profiles result in more uniform joints with less voiding
as shown in Figure 3.
COMPONENT THERMAL REQUIREMENT
As a result of this work, the need for higher temperature
qualified components has been highlighted. The melting
point of eutectic Sn 37Pb solder is 183C. The melting
point of the ternary eutectic, Sn 3.8Ag 0.7Cu alloy, which
has been selected by the NEMI members is 217C, an
increase of 34C. Component moisture sensitivity is
already a constraint with current manufacturing processes.
Higher temperatures, particularly for wave soldering
in which an organic laminate board must make
contact with a solder wave whose temperature may be as
high as 275C, is the single most important change.
ICS AND PASSIVE COMPONENTS – Most packaged
IC’s have a moisture absorption rate designation. This
designation specifies a moisture absorption rate, under
specific temperature and humidity conditions, for an IC
package style. The moisture absorbed by the IC package
encapsulant material has become critical as the
package size decreases and die size increases. The
moisture trapped in the package becomes an explosive
as the solder reflow temperature quickly increases during
a reflow process thereby turning the moisture into superheated
steam. This, in turn, leads to delamination
9 NCMS Lead-Free Solder Project Final Report, 0401RE96,
August 1997
3
between the die surface and the overmold encapsulant.
This is aggravated further for a lead-free solder reflow
process when the reflow temperature is typically 25 – 30 0
C higher than that of a eutectic SnPb reflow process.
Several IC package styles (PLCC, SOIC, QFP) were
tested under the higher temperature conditions. Inspection
methodology for delamination between the die surface
and the encapsulant was performed per JEDEC
standard J-STD-20, using a C-mode Scanning Acoustical
Microscope (CSAM) 10 . Results revealed the QFP and
SOIC package styles survived with no delamination
between the die surface and encapsulant, and minimal
delamination between the die paddle surface and encapsulant.
The PLCC package style showed major delamination
under the die, between the bottom die surface and
the die attach epoxy as shown in cross-section in Figures
6 and 7.
Figure 6. IC Cross-Section
Figure 7. Delaminated Die to Paddle Joint
While the delamination shown in Figures 6 and 7 will not
necessarily cause an electrical failure, it certainly
increases the reliability risk, particularly in an environment
with a lot of vibration.
10 See IPC/JEDEC J-STD-035 for a description of the scanning
acoustical microscope process.

CAPACITORS AND HYBRIDS – Capacitors often contain
lead in the high dielectric constant materials. In addition,
dielectric materials in capacitors and hybrid circuits
often use lead-glass which is characterized by a low melting
point.
Alternative materials are available, however, so this
should not be a barrier in the long run.
INDUCTORS AND CHOKES – Many inductors, chokes,
and transformers, used in electronic modules contain ferrite.
Unfortunately, the higher reflow temperatures can
push the materials above their Curie temperature where
the ferromagnetic properties of the materials change dramatically.
This can effect the inductance of these components
thereby altering the resonant frequency of the
circuits. This is a recognized problem in the telecommunications
industry and will likely effect multimedia applications
in the automotive industry. This is a relatively
new problem so work must be done to adequately
address the issue.
ORGANIC LAMINATE PRINTED WIRING BOARDS –
As indicated earlier, the glass transition temperature, T g,
and the coefficient of thermal expansion, CTE, particularly
in the Z-Axis for through-hole components are two of
the most important parameters for an organic laminate. 11
Fortunately, there has been significant progress in the
last few years towards the development of good board
materials. There is a looming requirement, however, in
Europe for the elimination of the Bromine based fire
retardents that are present in today’s FR4 materials. This
means that additional work is required to qualify new
materials which do not contain the prohibited substances.
That work is in the early stages though materials are
available.
COMPONENT SURFACE FINISH
A second major hindrance to full implementation of Leadfree
solder is the lack of Lead-free component finishes.
While several component manufacturers have provided
Lead-free finish for some time, notably Nickel-Paladium,
not all components are currently available with a leadfree
coating. Eutectic SnPb has been used for some time
because it is inexpensive and solderable. Many of the
fine pitch components are electroplated in order to avoid
the non-uniform coating characteristic of dipped parts.
Electroplating new finishes is a non-trivial process development.
Plated NiPd gives good uniform plating, and has been
used for many years. Unfortunately, the volatility and
high price of Palladium makes many component manufacturers
reluctant to initiate a program with Palladium.
Thankfully, there are a number of new coating materials
including immersion tin, immersion silver, electrolytic tin,
11 Whitten, OpCitation
4
organo-silver, and organo-tin, that are being developed
which should remedy this problem.
PWBs use several types of finish today. For low density
circuit boards, Hot Air Solder Level or HASL boards are
common. With this technique, the organic laminate
boards are dipped into a molten solder bath briefly, with
the excess solder blown off with an air or nitrogen knife.
For higher density boards, the copper leads are either
electroplated with SnPb or an organic solder preservative,OSP,
is used to prevent oxidation of the copper lands.
Lead-free HASL is available and will probably be used by
low density applications. OSP can also be used, but the
higher reflow temperatures makes double pass soldering
for dual side circuit board component mounting more difficult.
Fortunately, there are other solutions developing
which may solve this problem. There has been significant
progress with very thin organo-silver layers which
protect the copper, but then become part of the solder
joint after reflow.. Pure tin is also being considered as an
alternative finish. Since both Tin and Silver are expected
to be in the alloy of choice, and since the amount of
material in the surface finish is very small, the use of
either Tin or Silver will have minimal impact on the alloy
composition.
CONCLUSION
The NEMI Lead-free Task Group has identified the qualification
of high temperature components as a major hinderance
to Lead-free solder implementation. At the
current time extensive testing and materials development
is underway in order to provide components with proper
moisture and temperature capability. Delphi Delco Electronics
began sending requests to component providers
several years ago requesting information on their Leadfree
programs. These requests along with the increased
pressure from other electronics manufacturers are beginning
to have an impact on the supply base. Lead-free
components are already available in some quarters and
we expect the entire industry to move to lead-free components
over the next few years.
Almost certainly, a partnership with automotive manufacturers
will be required in the early stages of lead-free solder
implementation. We are proceeding systematically
towards the goal of lead-free products. We expect passenger
compartment solutions to be first. Engine compartment,
Transmission, and ABS applications, however,
have much to gain from the higher melting point of the
lead-free solder.
While regulatory pressure is a current driver, market
pressure may soon bypass it as the principal driver. A
recent experience by a Japanese supplier illustrates this
well. Market share in Europe for an audio CD player
jumped from 4% to 19% almost immediately after the CD
player was converted to lead-free solder.

ACKNOWLEDGMENTS
The authors gratefully acknowledge contributions from
many of the supporting staff at Delphi Delco Electronics.
Their assistance was essential to the work described
here.
REFERENCES
1. “Lead Free Solder Project Final Report," NCMS
Report 0401RE96, 1997, National Center for Manufacturing
Sciences, 3025 Boardwalk, Ann Arbor
Michigan 48108-3266
2. R. J. Klein and Wassink,” Soldering in Electronics," II,
Electrochemical Publications LTD, Asahi House, 10
Church Road, Port Erin, Isle of Man, British Isles,
1994, ISBN 0 901150 24 X
3. BP Richards et al, “Lead-free Soldering”, Department
of Trade and Industry, UK
4. www.leadfree.org, a site maintained by IPC
5. www.lead-free.org, a site supporting the ITRI
work(UK)
CONTACT
Gordon Whitten is currently in Advanced Engineering at
Delphi Delco Electronics Systems. He has 15+ years
experience in electronic packaging including semiconductor,
thin film magnetic R/W head, and multi-chip module
development. He is the Reliability Chairman of the
NEMI Lead Free Task group. His career has included
teaching in Physics and Engineering at Olivet Nazarene
University. Dr Whitten has B.S(Engineering Physics with
Electrical Engineering Minor), M.S and PhD(Physics)
degrees awarded by the University of Maine at Orono.
He can be reached at gordon.c.whitten@delphiauto.com
DEFINITIONS, ACRONYMS, ABBREVIATIONS
ABS: Anti-lock Brake System
Ag: Chemical symbol for Silver
Al 2 O 3 : Chemical symbol for Aluminum Oxide or Alumina,
a commonly used substrate material for resistors.
BaTiO 3: Chemical symbol for Barium Titanate, a commonly
used substrate material for capacitors.
BGA: Ball Grid Array package
CD: Compact Disc
5
CSP: Chip Scale Package
CTE: Coefficient of Thermal Expansion, DL/L o C
Cu: Chemical symbol for Copper
EIA: Electronic Industries Association
ELV: End of Life Vehicle directive. European regulation
requiring vehicle manufacturers to accept vehicles at end
of life without charge.
Eutectic: Alloy which has a single liquidus to solidus
melting point, that is, no pasty range
FC: Flip Chip method of IC attachment which eliminates
the IC package. Die is attached directly to the circuit
board
FR4: Fire Retardant #4, a common composite printed
wiring board material
In: Chemical symbol for Indium
ITRI: International Tin Research Institute (UK)
IVF: Swedish Institute for Production Engineering
Research
JEDEC: Joint Electron Device Engineering Council(EIA)
JIEP: Japanese Institute of Electronic Packaging
LCCC: Leadless Ceramic Chip Carrier
Mp: Solder Alloy Melting Point
Pb: Chemical symbol for Lead
PLCC: Plastic Leaded Chip Carrier
PWB: Printed Wiring Board. A typically planar structure
used to hold electronic components physically while connecting
them electrically with photo imaged wiring.
QFP: Quad Flat Pak, a chip package.
NCMS: National Center for Manufacturing Sciences
NEMI: National Electronics Manufacturing Intiative
Sb: Chemical symbol for Antimony
Sn: Chemical symbol for Tin
Sn3.8Ag0.7Cu: Ternary eutectic composition recommended
for SnPb replacement by NEMI
SnPb: Tin Lead Solder, usually eutectic
SOIC: Small Outline Integrated Circuit Package
Tg: Glass transition temperature. The temperature at
which an organic material transitions from solid-like
behavior to viscous liquid-like behavior.
TSOP: Thin Small Outline Package: IC Package
WEEE: Waste from Electric and Electronic Equipment
directive from the European Union which requires recycling
of equipment in order to minimize landfill expansion
1206: A resistor or capacitor package which is 120 x 60
mils or 3 x 1.5 mm