Title of Presentation - iNEMI

iNEMI
Tin Whisker
Project:
Overview
Carol A. Handwerker
CARE Innovation 2010
Vienna - 9-11-2010

iNEMI Pb-Free Assembly Project – 1999-2002
1

Tin Film on Copper
• Compressive stress in electrodeposited Sn film
• Intermetallic Growth (IMC) growth increases compressive stress
• Various stress relief mechanisms depending on creep, grain
structure, IMC, …

Consistent cross-section
(column)
Whisker Examples
Striations Rings

Tin Whisker Formation in Electronic Circuits
Information from:
Tin-Plated Connector Pins after 10 years
Courtesy of NASA - Goddard Space Flight Center
http://nepp.nasa.gov/whisker/index.html and http://www.klabs.org/richcontent/General_Application_Notes/tin_whiskers_ak.doc

Split into Three Tin Whisker Teams
• To address different critical aspects of tin whisker risk
mitigation
– Three tin whisker teams formed in 2001:
• Surface Finish Users Group – Joe Smetana, Alcatel-Lucent
• Tin Whisker Test Group – Heidi Reynolds, HP
• Tin Whisker Modeling Group – George Galyon, IBM,
Maureen Williams, NIST
• In 2007, single team recombined from three teams
– To address open questions of
• Tin Whisker Fundamentals Group – Rich Parker, Delphi
5

Yes, there are tin whisker problems!
• Most consumer electronics companies have decided that the
tin whisker problem has been solved by the supply chain.
• Aerospace, military, medical, and automotive industries have
been in denial…
Tin whisker on flex tab side of a
ZIFF socket connector
6

More Whiskers – Mechanical Parts, Too!
Tin whiskers on a steel tin plated bracket
Steel- tin plated Bracket
Tin Whisker shorting the connector…
where did it come from?
Movie of tin whisker “blowing in the wind”.
On iNEMI website
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Tin Whisker Project: Seven Phases
• iNEMI proposed Tin Whisker Test Document (2001-2003)
– Phase 1 & 2 tested temperature and humidity exposure
– Evaluated multiple test conditions. Only short test durations were
used (1 month for storage tests).
– DOE1 investigated bright Sn on brass substrates.
– DOE2 investigated matte Sn on Cu substrates.
– Established testing and inspection protocol, which was integrated
into JEDEC standard JESD22A121 (Released May 2005)
• Phase 3 Evaluations (2003-2004)
– Validated and proposed test methods
– Compared short-term (1 month) vs. long-term (1 year) testing
– Results of Phase 3 evaluation combined with other industry
studies provided input for the JEDEC tin whisker standards
• JEDEC standard JESD22A121 - Test Methods (May 2005)
• JEDEC standard JESD201 - Acceptance Criteria (March 2006)
8

Tin Whisker Project: Seven Phases, continued
• Phase 4 Evaluations (2005)
– Effects of electrical bias on the susceptibility of tin finishes to
form and grow whiskers on tin plated components assembled
with both lead-free and tin/lead solders. Bright, semi-bright,
and matte Sn finishes were used.
– Two storage test conditions were used (30ºC/60%RH and
60ºC/85%RH).
– Electrical bias did not show apparent effects in acceleration of
whisker growth.
– Proved that reflow soldering does not prevent further tin
whisker growth
– Third and fourth iNEMI Sn Whisker Workshops were held with
ECTC in 2005 and 2006.
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Oxidation/Corrosion: Another Origin of Whiskers
(it’s not just from the surface finish anymore)
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Tin Whisker Project: Seven Phases, continued
• Phase 5 (2004 – 2007) Investigated the effects of temperature
and humidity over a wide range of conditions on tin whisker
growth
– Matte Sn over Cu leadframes (C194). Multiple thicknesses (3 & 10 mm)
and reflow conditions were included. 13 sample sets in total.
– 10 Conditions: Tested 30 o C to 100 o C & 10% to 90% Humidity Storage
– Durations Tested were up to 13000 hours for certain conditions.
– Models are proposed for corrosion incubation, whisker incubation, and
whisker growth rates.
– Results were presented at 57th ECTC(2007)
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Experimental Design - Phase 5
• Large experimental matrix of test conditions and tin
platings
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Phase 5: Conclusions
• Whisker presence and the initiation of corrosion can be represented by a
function of temperature and humidity.
• The iNEMI tests can be used to indicate behavior at other
temperature/humidity points that could be relevant storage or service
conditions within the limits of the whisker and corrosion (incubation)
acceleration functions developed in this study.
• Whisker formation differs in corroded and non-corroded regions, but it
appears that the incubation times for both regions can be modeled.
• 60C/87%RH appears to be the optimal high temperature/high humidity
test condition at this time for Sn over Cu substrates
• Two temperature/humidity test conditions were not necessary.
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Phase 5 Publications
• Results were presented at the 57 th ECTC -2007 conference
(by Heidi Reynolds)
• Two papers were written to summarize the Phase 5 project
work during 2008 and 2009.
– IEEE Transactions On Electronics Packaging Manufacturing
• Papers were published in January 2010 in volume 33
– Tin Whisker Test Development – Temperature and Humidity
Effects Part I: Experimental Design, Observations, and Data
Collection
– Tin Whisker Test Development – Temperature and Humidity
Effects Part II: Acceleration Model Development
» Authors: J.W. Osenbach, H.L. Reynolds, G. Henshall,
R.D. Parker, and P. Su
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• Objectives
Phase 7 – Microstructure Evolution
– The hypothesis for Phase 7 is that the crystallographic orientations of the Sn
grains have an impact on tin whisker nucleation and growth, which leads to
whisker growth at certain locations of the finish.
– Grain orientation was analyzed with two techniques; EBSD (Electron backscattered
diffraction) (local change) and X-ray diffraction (global change).
– Attempts were made to correlate the locations of whiskers after growth tests
to the orientation information of surrounding grains prior to tests.
– The ultimate goal is to define what texture a plating finish would have for a
lower propensity of whiskers.
• Whisker Growth Tests
– AATC (standard at - 40 o C to 85 o C)
– Storage test (50 o C/50%RH)
Sn unit cell (body centered tetragonal) Matte Sn after FIB Whisker after AATC
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Impact of Microstructure, cont.
• NIST supplied the tungsten substrates with sputtered Sn as a seed layer for plating
• RamChem (Hong Kong Lab) performed the plating of the brass and tungsten
coupons (03-2009)
• Boeing did preliminary EBSD (Chris Meyers & Tom Woodrow) to develop the
techniques needed for the 3 plating finishes.
• Boeing and HP performed stress tests
• Boeing and NIST (Maureen Williams) performed EBSD to quantify the tin grain
structure
• Purdue (Pylin Sarobol, Aaron Pedigo, Michael Jablonski) performed X-ray texture
and EBSD measurements
Raw Image and Normal Direction Inverse Pole Figure
EBSD Scan: 25 X 25 µm, 0.1 µm step size:
C. Meyer; Boeing
Matte tin on brass #5, NIST EBSD; M. Williams
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Example of Effects of Electroplating Parameters:
Sn-Cu Grain Structure with Varying Current Density
4 mA/cm 2
80 mA/cm 2
16 mA/cm 2
120 mA/cm 2
Coutesy of Aaron Pedigo, Purdue
32 mA/cm 2
160 mA/cm 2
5 mm
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EBSD Measurements – Grain Orientation
Test coupons in “as received” condition:
EBSD
Bright on Brass
XRD
Bright on Brass
Bright on Tungsten*
Matte on Tungsten*
XRD
Satin on Brass
Satin on Tungsten
EBSD
Satin on Brass
Matte on Brass*
Bright on Tungsten*
Satin on Tungsten
Matte on Tungsten*
115
113
213
212
312
105 302
XRD
Matte on Brass*
Matte on Tungsten*
610
Courtesy of Pylin Sarobol; Purdue
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#
Summary of Texture Measurements
Test coupons in “as received” condition:
Sample Finish Substrate
error
RW%
Max MRD value
Pole
figure
Inverse
pole
figure
Preferred Texture
from Area Detector
XRD
Preferred Texture
from EBSD
B5B
B6B Bright Brass
20 12
16
23
16
Near 112 and Near
113
113
S5B
S1B Satin Brass
30 19
17
21
17
001 001
M14B
M13B Matte Brass
28 27
20
63
20
Near 105
primary 001
secondary 110
B6W
B7W Bright Tungsten
20 11
12
36
11
Near 115
primary 001
secondary 302
S1W
S7W Satin Tungsten
19 14
26
17
26
001 primary 001
M3W
M14W Matte Tungsten
19 35
33
50
33
Near 105 and Near 115 primary 001
* The data may not be reliable because the error value is >30%.
Measured Texture by Area Detector XRD at Purdue University
Measured Texture by EBSD at Boeing (grain by grain) Courtesy of Pylin Sarobol, Purdue
(Post stress test XRD still being conducted)
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Completion of Project: Open Questions
• There is still plenty of work to be done to understand the
nucleation and growth mechanisms for Sn whiskers and
the necessary and sufficient conditions for Sn whiskers
– Role of stress
• Global vs. local stresses
– Measurements difficult
– Fundamental growth mechanisms
• Stresses (excess energy): Necessary but not sufficient condition
for whisker growth?
– What are the whisker nucleation and growth mechanisms?
– What other processes are involved?
– Re-crystallization and growth: What are the details of these
processes?
– Impact of assembly processes
– Test method improvements (reduce time and cost)
– Better mitigation methods
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Recognition of Phase 7 Team Members
• Aaron Pedigo aepedigo@purdue.edu
• Bob Hilty bob.hilty@tycoelectronics.com
• Carol Handwerker handwerker@purdue.edu
• Christopher A Meyer christopher.a.meyer2@boeing.com
• David Godlewski dgodlewski@inemi.org
• Earl Miller tokoba1@verizon.net
• Greg Henshall greg.henshall@hp.com
• Heidi Reynolds heidi.reynolds@tycoelectronics.com
• Jim Arnold jim.arnold@rissastudios.com
• Joe Smetana joseph.smetana@alcatel-lucent.com
• John Osenbach john.osenbach@lsi.com
• Maureen Williams maureen.williams@nist.gov
• Peng Su pensu@cisco.com
• Pylin Sarobol psarobol@purdue.edu
• Rich Parker richard.d.parker@delphi.com
• Sarika Pokharel sarika.pokharel@microchip.com
• Tom Woodrow thomas.a.woodrow@boeing.com
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www.inemi.org
Email contacts:
Bob Pfahl
bob.pfahl@inemi.org
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