Microstructure Formation in Reinforced Sn-Cu Lead-free Solder Alloys

234 Pages·2016·10.72 MB·English

Microstructure Formation in Reinforced Sn-Cu Lead-free Solder Alloys
Mohd Arif Anuar Mohd Salleh
B. Eng., M.B.A., M. Eng.

A thesis submitted for the degree of Doctor of Philosophy at
The University of Queensland in 2016
School of Mechanical and Mining Engineering
Abstract

Electronics manufacturers are pushing the limits in reducing the physical size of circuitry
while simultaneously increasing the number of transistors to satisfy Moore’s Law [1]. This
includes investing in new materials, and configuring new ways to manufacture complex 3D
(three dimensional) electronic packaging [1]. One key requirement of new materials and
techniques is ensuring the high reliability of the resultant products in various challenging
operating environments including thermal and mechanical extremes [2-4]. A viable method
to enhance the properties and performance of a solder joint is by incorporation of
reinforcement particles to the solder matrix, either by intrinsic or extrinsic methods. In this
thesis a series of Sn-Cu Pb-free solder alloys with extrinsic or intrinsic phase reinforcement
were manufactured and the microstructure and soldering behavior were investigated in
detail.

Additions of extrinsic reinforcement in the form of nano-sized ceramic material were made
using a microwave sintering powder metallurgy (PM) method, which is a viable method to
improve the mechanical and thermal properties of Pb-free solder materials. In addition, the
advanced processing routes ensures a homogenous distributions of reinforcement particles
is present. To investigate the performance of the reinforced bulk solders including thermal
and mechanical properties and relate this to the microstructure, samples were investigated
using techniques such as synchrotron micro-XRF, HRTEM, SEM, XPS, dilatometery, DSC
and shear and microhardness testing. A hypothesis of how reinforcement improves solder
properties is developed and discussed. Synchrotron X-ray radiography imaging (SXRI) was
used to analyse the development of microstructure and the complex interactions occurring
in the solders. Based on the properties of the fabricated solder, the microwave sintering PM
route was discussed as a promising method for the reinforcement of Pb-free solders.

The initial formation of interfacial IMC products was studied in Sn-Cu based solder alloys by
in situ experiment techniques such as SXRI and UHV-TEM. The results provide direct
experimental evidence of real-time initial Cu Sn layer development during soldering and
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also the stress creation and release events that arise due to the polymorphic transformations
of the Cu Sn phase and the associated volumetric change.
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In addition, the nucleation and growth behavior of primary intermetallics which can be
considered an intrinsic reinforcing material in solder joints was studied. Here, the nucleation
and growth behavior of primary Cu Sn and β-Sn crystals in some of the most commonly
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used solder alloys including Sn-0.7Cu and Sn-3.0Ag-0.5Cu is explained. This also includes
the effects of Ni additions for refining primary Cu Sn in Sn-Cu solder joints. Using SXRI,
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observations were made during solder joint solidification, which is difficult using conventional
methods. The initial nucleation and solidification kinetics of primary Cu Sn crystals were
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discussed.

The growth of primary and interfacial Cu Sn intermetallics after multiple reflow and
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annealing and the effect of this growth on the solder joint shear strength was studied to
understand the effect of electronic component assembly processes on microstructure
development. It was found that additions of TiO reinforcement were able to reduce the
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number and total length of primary Cu Sn particles and suppress the interfacial layer during
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multiple reflows. It is possible that TiO particles in intimate contact with the interfacial
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Cu Sn hinder the Cu dissolution paths. By reducing the undercooling, additions of TiO
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result in a lower average thickness in the interfacial IMC and a more stable growth
morphology.

The collective results of this thesis demonstrate a detailed understanding of the manufacture
of reinforced Sn-Cu Pb-free solder alloys and the mechanism of microstructure formation.
The results are of significance scientifically and have industrial relevance and implications
in controlling the microstructure and improving the performance and reliability of Pb-free
solder joints.

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Declaration by author

This thesis is composed of my original work, and contains no material previously published
or written by another person except where due reference has been made in the text. I have
clearly stated the contribution by others to jointly-authored works that I have included in my
thesis.

I have clearly stated the contribution of others to my thesis as a whole, including statistical
assistance, survey design, data analysis, significant technical procedures, professional
editorial advice, and any other original research work used or reported in my thesis. The
content of my thesis is the result of work I have carried out since the commencement of my
research higher degree candidature and does not include a substantial part of work that has
been submitted to qualify for the award of any other degree or diploma in any university or
other tertiary institution. I have clearly stated which parts of my thesis, if any, have been
submitted to qualify for another award.

I acknowledge that an electronic copy of my thesis must be lodged with the University Library
and, subject to the policy and procedures of The University of Queensland, the thesis be
made available for research and study in accordance with the Copyright Act 1968 unless a
period of embargo has been approved by the Dean of the Graduate School.

I acknowledge that copyright of all material contained in my thesis resides with the copyright
holder(s) of that material. Where appropriate I have obtained copyright permission from the
copyright holder to reproduce material in this thesis.

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Publications during candidature

Peer-reviewed journal papers
1. K. Nogita, M. A. A. Mohd Salleh, E. Tanaka, G. Zeng, S. D. McDonald, S. Matsumura,
In-situ TEM observations of Cu Sn polymorphic transformations in reaction layers
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between Sn-0.7Cu solder and Cu substrate. JOM (2016). Accepted on the 25th May
2016.
2. M. A. A. Mohd Salleh, S. D. McDonald, C.M. Gourlay, S.A. Belyakov, H. Yasuda, K.
Nogita, Effect of Ni on the formation and growth of primary Cu Sn intermetallics in Sn-
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0.7wt%Cu solder pastes on Cu substrates during soldering process, Journal of
Electronic Materials, 45 Issue 1 (2016) 154-163.
3. M. A. A. Mohd Salleh, S. D. McDonald, Y. Terada, H. Yasuda, K. Nogita, Development
of a microwave sintered TiO reinforced Sn-0.7wt%Cu-0.05wt%Ni alloy, Materials &
2
Design, 82 (2015) 136-147.
4. M. A. A. Mohd Salleh, S. D. McDonald, H. Yasuda, A. Sugiyama, K. Nogita, Rapid
Cu Sn growth at liquid Sn/solid Cu interfaces, Scripta Materialia, 100 (2015) 17-20.
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5. M. A. A. Mohd Salleh, S. D. McDonald, H. Yasuda, A. Sugiyama, K. Nogita, In-situ
soldering process technique by synchrotron X-ray imaging, Applied Mechanics and
Materials, 754-755 (2015) 508-512.
6. M. A. A. Mohd Salleh, S. D. McDonald, K. Nogita, Non-metal reinforced lead-free
composite solder fabrication methods and its reinforcing effects to the suppression of
intermetallic formation: Short review, Applied Mechanics and Materials, 421 (2013)
260-266.
7. M. A. A. Mohd Salleh, Al Bakri, A.M.M., Somidin, F., Sandu, A.V., Saud, N.,
Kamaruddin, H., McDonald, S.D., Nogita, K. A comparative study of solder properties of
Sn-0.7Cu lead-free solder fabricated via the powder metallurgy and casting methods,
Revista de Chimie, 64 (7) (2013), 725-728.

Conference presentations
1. M. A. A. Mohd Salleh, C.M. Gourlay, J.W. Xian, S.A. Belyakov, H. Yasuda, S. D.
McDonald, K. Nogita, Nucleation events and growth behavior of primary Cu Sn
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intermetallic and β-Sn crystals in Pb-free solder joints, 2016 TMS Annual Meeting &
Exhibition, Nashville, Tennessee, USA, 14-18 February (2016).
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2. M. A. A. Mohd Salleh, H. Yasuda, S. D. McDonald, K. Nogita, Development of a
microwave sintered TiO reinforced Sn-0.7wt%Cu-0.05wt%Ni solder alloy, 2016 TMS
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Annual Meeting & Exhibition, Nashville, Tennessee, USA, 14-18 February (2016).
3. M. A. A. Mohd Salleh, J. Read, X. Tran, S. D. McDonald, K. Nogita, Effects of trace
additions of phosphorus in Sn-Cu-Ni-Ge solders, 2016 TMS Annual Meeting &
Exhibition, Nashville, Tennessee, USA, 14-18 February (2016).
4. M. A. A. Mohd Salleh, C.M. Gourlay, J.W. Xian, S.A. Belyakov, H. Yasuda, S. D.
McDonald, K. Nogita, In-situ synchrotron real-time imaging of soldering: Experimental
methods and post experiment analysis, 24th Australian Conference on Microscopy &
Microanalysis, Melbourne, Australia, 31 January – 4 February (2016).
5. M. A. A. Mohd Salleh, R. M. Said, N. Saud, H. Yasuda, S. D. McDonald, K. Nogita, In-
situ soldering process imaging of Sn-Cu lead-free solder systems on Cu substrate: Initial
intermetallic compound formation and its subsequent growth, 1st Electronic Packaging
Interconnect Technology Symposium (EPITS), Penang, Malaysia, 21 November (2015).
6. M. A. A. Mohd Salleh, S. D. McDonald, H. Yasuda, A. Sugiyama, K. Nogita, In-situ
soldering process imaging of Sn-Cu lead-free solder systems on Cu substrate: Initial
intermetallic compound formation and its subsequent growth. 2015 TMS Annual Meeting
& Exhibition, Orlando, Florida, USA, 15-19 March (2015).
7. M. A. A. Mohd Salleh, S. D. McDonald, K. Nogita, In-situ imaging of Sn-Cu lead-free
soldering on Cu substrates: Intermetallic compound formation and growth, EAIT
Postgraduate Conference, University of Queensland, Australia, 10 June (2015).
8. M. A. A. Mohd Salleh, S. D. McDonald, H. Yasuda, A. Sugiyama, K. Nogita, In-situ
soldering process technique by synchrotron X-ray imaging, 3rd International Conference
on Advanced Materials Engineering and Technology (ICAMET), Vietnam, 4-5 December
(2014).
9. M. A. A. Mohd Salleh, S. D. McDonald, K. Nogita, The development of Sn-Cu based
reinforced composite lead-free solder, EAIT Postgraduate Conference, University of
Queensland, Australia, 11 June (2014).
10. M. A. A. Mohd Salleh, S. D. McDonald, K. Nogita, Non-metal reinforced lead-free
composite solder fabrication methods and its reinforcing effects to the suppression of
intermetallic formation: Short review, 4th International Conference on Information
Technology for Manufacturing Systems (ITMS), Auckland, New Zealand, 28-29th August
(2013).

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Publications included in this thesis

1. M. A. A. Mohd Salleh, S. D. McDonald, Y. Terada, H. Yasuda, K. Nogita, Development
of a microwave sintered TiO reinforced Sn-0.7wt%Cu-0.05wt%Ni alloy, Materials &
2
Design, 82 (2015) 136-147. – incorporated as Chapter 3.

Contributor Statement of contribution
Author Mohd Arif Anuar Mohd Salleh Designed experiments (90%)
(Candidate) Wrote the paper (80%)
Author Stuart D. McDonald Wrote and edited paper (10%)
Author Yasuko Terada Assisted with synchrotron micro-X-ray
fluorescence (5%)
Author Hideyuki Yasuda Assisted with synchrotron micro-X-ray
fluorescence (5%)
Author Kazuhiro Nogita Designed experiments (10%)
Wrote and edited paper (10%)

2. M. A. A. Mohd Salleh, S. D. McDonald, H. Yasuda, A. Sugiyama, K. Nogita, In-situ
soldering process technique by synchrotron X-ray imaging, Applied Mechanics and
Materials, 754-755 (2015) 508-512. – incorporated as Chapter 3.

Contributor Statement of contribution
Author Mohd Arif Anuar Mohd Salleh Designed experiments (90%)
(Candidate) Wrote the paper (80%)
Author Stuart D. McDonald Wrote and edited paper (10%)
Author Hideyuki Yasuda Assisted with synchrotron X-ray
radiography (5%)
Author Akira Sugiyama Assisted with synchrotron X-ray
radiography (5%)
Author Kazuhiro Nogita Designed experiments (10%)
Wrote and edited paper (10%)

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3. M. A. A. Mohd Salleh, S. D. McDonald, H. Yasuda, A. Sugiyama, K. Nogita, Rapid
Cu Sn growth at liquid Sn/solid Cu interfaces, Scripta Materialia, 100 (2015) 17-20. –
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incorporated as Chapter 4.

Contributor Statement of contribution
Author Mohd Arif Anuar Mohd Salleh Designed experiments (90%)
(Candidate) Wrote the paper (80%)
Author Stuart D. McDonald Wrote and edited paper (10%)
Author Hideyuki Yasuda Assisted with synchrotron X-ray
radiography (5%)
Author Akira Sugiyama Assisted with synchrotron X-ray
radiography (5%)
Author Kazuhiro Nogita Designed experiments (10%)
Wrote and edited paper (10%)

4. K. Nogita, M. A. A. Mohd Salleh, E. Tanaka, G. Zeng, S. D. McDonald, S. Matsumura,
In-situ TEM observations of Cu6Sn5 polymorphic transformations in reaction layers
between Sn-0.7Cu solder and Cu substrate. JOM (2016). Accepted on the 25th May
2016. – incorporated as Chapter 4.

Contributor Statement of contribution
Author Kazuhiro Nogita Designed experiments (50%)
Wrote and edited paper (50%)
Author Mohd Arif Anuar Mohd Salleh Designed experiments (50%)
(Candidate) Wrote and edited paper (40%)
Author Eishi Tanaka Assisted with high voltage TEM (5%)
Author Guang Zeng Wrote and edited paper (5%)
Author Stuart D. McDonald Wrote and edited paper (5%)
Author Syo Matsumura Assisted with high voltage TEM (5%)

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5. M. A. A. Mohd Salleh, S. D. McDonald, C.M. Gourlay, S.A. Belyakov, H. Yasuda, K.
Nogita, Effect of Ni on the formation and growth of primary Cu Sn intermetallics in Sn-
6 5
0.7wt%Cu solder pastes on Cu substrates during soldering process, Journal of
Electronic Materials, 45 Issue 1 (2016) 154-163. – incorporated as Chapter 5.

Contributor Statement of contribution
Author Mohd Arif Anuar Mohd Salleh Designed experiments (85%)
(Candidate) Wrote the paper (85%)
Author Stuart D. McDonald Wrote and edited paper (5%)
Author Christopher M. Gourlay Designed experiments (5%)
Wrote and edited paper (5%)
Author Sergey A. Belyakov Assisted with annealing and microscopy
observation (5%)
Author Hideyuki Yasuda Assisted with synchrotron X-ray
radiography (5%)
Author Kazuhiro Nogita Designed experiments (10%)
Wrote and edited paper (5%)

6. M. A. A. Mohd Salleh, S. D. McDonald, C.M. Gourlay, H. Yasuda, K. Nogita,
Suppression of Cu Sn in TiO reinforced solder joints after multiple reflow cycles,
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Materials & Design, 108 (2016) 418-428. – incorporated as Chapter 6.

Contributor Statement of contribution
Author Mohd Arif Anuar Mohd Salleh Designed experiments (85%)
(Candidate) Wrote the paper (85%)
Author Stuart D. McDonald Wrote and edited paper (5%)
Author Christopher M. Gourlay Designed experiments (5%)
Wrote and edited paper (5%)
Author Hideyuki Yasuda Assisted with synchrotron X-ray
radiography (5%)
Author Kazuhiro Nogita Designed experiments (10%)
Wrote and edited paper (5%)

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Contributions by others to the thesis

No contributions by others

Statement of parts of the thesis submitted to qualify for the award of another degree

None.

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