UCLA-Materials Science

Electronic Thin Film Lab at UCLA









Organize by EPA Centre, University of California, Los Angeles, City University of Hong Kong


Training Course on

Reliability of Pb-free Solder Joint

in Advanced Electronic Packaging Technology



The rapid growth in wireless, portable, and multi-functional devices has enhanced the development of electronic packaging technology.?There is a greater demand of flip chip assembly in advanced packaging, especially the use of?Pb-free solder joints.?European Union Congress has a ban on Pb-based solders in consumer electronic products on July 1st, 2006.?The reliability of Pb-free solder joins is of concern in manufacturing industry.?For example, the reflow of Pb-free solder paste produces many more residue voids than SnPb solder paste.?This one-day course will start from the trend in electronic packaging technology.? It will be followed by the analysis of solder reactions in wetting and in solid state aging.?The unique reliability behavior of spalling of intermetallic compounds in thin film under-bump-metallization and the formation of Kirkendall voids in thick under-bump-metallization will be discussed.? Next, electromigration induced failure in flip chip solder joints will be analyzed.?The unique failure mode of electromigration in flip chip solder joints will be explained on the basis of current crowding.?Joule heating that leads to melting of flip chip solder joints will be discussed.?Thermomigration in solder joints will be covered.?Then, mechanism and prevention of spontaneous Sn whisker growth on Pb-free finish will be presented.?Spontaneous Sn whisker growth is an irreversible process, in which there are two atomic fluxes driven by two driving forces.?We must decouple the two driving forces or the two atomic fluxes in order to prevent Sn whisker growth.? Due to accidental and frequent drops of portable devices to the ground, impact test has recently received much attention from the point of view of reliability of handheld and portable devices?A mini impact test machine which has been built to detect the ductile-to-brittle transition in ball-grid-array solder joints will be described.? Finally, the trend of miniaturization and the prospect of using nano structured materials in future electronic packaging technology will be discussed.


Course Content:


*          Introduction - Trend of electronic packaging technology

*          Solder joint reactions

*          Electromigration in flip chip solder joints - I

*          Electromigration and thermomigration in flip chip solder joints -II

*          Spontaneous Sn whisker growth

*          Impact test of ductile-to-brittle transition in solder joints

*          Conclusion ?Nanostructured materials for electronic packaging









Course Fee:

3 January 2006 (Tuesday)

9.00am ?5.30pm

G6302, 6/F, Lift 7,Academic Building, City University of HK,

83 Tat Chee Avenue,

Kowloon Tong, Hong Kong


HK$800 per person



Speaker: Professor King-Ning Tu received his Ph. D. degree in Applied Physics from Harvard University in 1968.?He spent 25 years at IBM T. J. Watson Research Center as Research Staff Member in Physical Science Department.?During that period, he also served as Senior Manager of Thin Film Science Department and Materials Science Department for 10 years.?In September 1993, he joined the Dept. of Materials Science and Engineering at UCLA as full professor.?He was chairman of the Department for six years from 1998 to 2004.?He is a Fellow of American Physical Society, The Metallurgical Society (TMS), and an Overseas Fellow of Churchill College, Cambridge University, UK.?He was president of Materials Research Society in 1981. He received the Application to Practice Award from TMS in 1988, and Humboldt Award for US Senior Scientists in 1996.?He has been elected a member of Academia Sinica, Republic of China in 2002.? He has over 350 journal publications, edited 13 proceedings, and co-authored a textbook on “Electronic thin Film Science,?published by Macmillan in 1992.?His research interests are in metal-silicon reactions, solder reactions, nanoscale reactions, polarity effect of electromigration on interfacial reactions, and kinetic theories of interfacial reactions. His website is http://www.seas.ucla.edu/eThinFilm/.



A Short Course

"Diffusion and Reactions in Thin Films"

K. N. Tu
Dept. of Materials Science & Engineering, UCLA
Los Angeles, CA 90095-1595
(website: http://www.seas.ucla.edu/eThinFilm/)

1.     Basic Diffusion in Thin Films

2.     Applications

a. Electromigration in VLSI Interconnect

b. Silicide Formation in Metal Contact to Si

c. Solder Reaction in Flip Chip Technology

Basic Diffusion in Thin Films

K. N. Tu
Dept. of Materials Science & Engineering, UCLA
(3 hours)

1.     Macroscopic picture of diffusion:
Flux equation, continuity equation, growth equation

2.     Microscopic picture of diffusion:
Exchange frequency of vacancy jumps
Activation enthalpies
Pre-factor in diffusion coefficient

3.     Driving forces of diffusion:
Various chemical potential gradients

4.     Diffusion in a man-made superlattice
a. Homogenization of a periodic structure
b. Cahn and Hilliard's 4th order diffusion equation and solution

5.     Grain boundary diffusion
a. Fisher's solution
b. Whipple and Suzuki's solutions
c. GB penetration by IMC formation
d. Diffusion along a moving GB: DIGM

Go Back to the Top

Electromigration in VLSI Interconnect

K. N. Tu
Dept. of Materials Science & Engineering, UCLA
(3 hours)

1.     Introduction - Historical events

2.     Electron wind force on atomic diffusion

3.     Kinetics of electromigration

4.     Effect of stress on electromigration

5.     Effect of solute on electromigration

6.     Effect of current crowding on electromigration

7.     Polarity effect of electromigration on contact reaction at cathode and anode

8.     MTTF in Al and Cu metallization

9.     Electromigration in solder alloys and flip chip solder joints

Go Back to the Top

Silicide Formation in Metal Contact to Si

K. N. Tu
Dept. of Materials Science & Engineering, UCLA
(3 hours)

1.     Introduction - Historical development of back-end-of-line

2.     Metrology of silicide formation

3.     A survey of metal-Si reactions
a. Near-noble metal silicides
b. Transition metal silicides
c. Rare-earth metal silicides
d. Silicide formation on SOI

4.     Kinetics of metal-Si reactions
a. Diffusion-controlled and interfacial-reaction-controlled growth
b. Single phase formation
c. Solid phase amorphization

5.     Electrical properties of silicide
a. Schottky barrier on n-type and p-type Si
b. Conductivity
c. Contact resistance

Go Back to the Top

Solder Reaction in Flip Chip Technology

K. N. Tu
Dept. of Materials Science & Engineering, UCLA
(3 hours)

1.     Introduction - IBM C4 flip chip technology

2.     Metallurgical reliability issues in direct chip attachment to organic substrates

3.     Wetting reaction on bulk and thin film Cu
a. Ripening-controlled reaction
b. Spalling of IMC
c. Wetting along V-grooves

4.     Comparison of wetting reaction and solid state aging between SnPb solder and Cu
a. Ternary phase diagrams of SnPbCu
b. Morphology of IMC formation
c. Kinetics of IMC formation

5.     Wetting reaction and solid state aging on bulk and thin film Ni, Pd, and Au
a. Electroless Ni(P) & Cu/Ni(V)/Al UBM
b. Ultra-fast IMC formation on Pd
c. Ultra-fast dissolution on Au

6.     Pb-free solder - UBM reactions

7.     Morphology and kinetics of growth of Sn whiskers

Go Back to the Top

The objectives of this course are to offer

1. Basic understanding of atomic diffusion and diffusion related phenomena in thin films.

2. Kinetic analysis of microstructure changes in thin films under multiple driving forces.

3. Insight into yield and reliability issues in Al and Cu interconnects, silicide contacts, and flip chip solder joints.

Part of this short course has been given at MRS meetings (11/91, 11/93), Hong Kong University of Science and Technology (11/96), Max-Planck Institute of Microstructure Physics at Halle (7/97), National University of Singapore (1/98), Helsinki University of Technology (8/00).

Go Back to the Top

Web Design & Maintenance: Fanyi Ouyang;  Strategy: D.W. Zheng