Advanced Microelectronic Packaging, Emerging Interconnection Technology and Pb-free Solder: Quality and Reliability of Advanced Microelectronic Packaging
Sponsored by: TMS Functional Materials Division, TMS: Electronic Packaging and Interconnection Materials Committee
Program Organizers: Christopher Gourlay, Imperial College London; Kazuhiro Nogita, University of Queensland; David Yan, San Jose State University; Mike Wolverton; Babak Arfaei, Ford Motor Company; Andre Delhaise; Mehran Maalekian, Mat-Tech; Mohd Arif Salleh, Universiti Malaysia Perlis
Monday 8:00 AM
February 24, 2020
Room: Palomar
Location: Marriott Marquis Hotel
Session Chair: Andre Delhaise , Celestica Inc.; Luke Wentlent, Universal Instruments
8:00 AM Introductory Comments
8:05 AM
Synchrotron X-ray Study of Sn Electromigration, Sn Whisker Growth, and Residual Strain Evolution in A Blech Structure: Pei-Tzu Lee1; Wan-Zhen Hsieh2; Cheng-Yu Lee3; Xiao-Yun Li2; Shao-Chin Tseng2; Mau-Tsu Tang2; Ching-Shun Ku2; C. Robert Kao1; Cheng-En Ho3; 1National Taiwan University; 2National Synchrotron Radiation Research Center; 3Yuan Ze University
Electromigration and Sn whisker growth both played key roles in microelectronic packaging reliability for past decades and a dynamic observation on these two issues are still quite lacking to date. In this study, we conducted a real-time analysis on Sn electromigration behavior and Sn whisker growth in a Blech structure via nano-X-ray fluorescence (nano-XRF) microscopy (beamline 23A, Taiwan Photon Source) and white X-ray nanodiffraction (beamline 21A, Taiwan Photon Source). The Sn depletion at the cathode and the Sn whisker/extrusion formation at the anode upon electron current stressing were in-situ characterized using nano-XRF, and the residual deviatoric strains of Sn films after electromigration were analyzed using white Laue diffraction. The knowledge would greatly advance our fundamental understandings of Sn electromigration/whiskering mechanisms. Details will be presented in this talk.
8:25 AM
Recrystallized Shallow Grains as the Whisker Growth Sites in Large-grain Sn-alloy Films: Wei-Hsun Chen1; Congying Wang2; John Blendell2; Carol Handweker2; 1ASML; 2Purdue University
Recrystallization has been reported as one of the whiskers nucleation mechanisms in Sn films. This talk focuses on the evolution of the orientation, dislocation densities, and subsurface microstructure in the defect regions via combined analysis of X-ray synchrotron microdiffraction, FIB, and EBSD before and after thermal cycling. We prepared large-grain Sn-alloy films to simplify the local stress states and observed: (1)whiskers grew from recrystallized grains at one GB, and (2)grain boundary sliding at the other GB. The elastic strain energy density and the geometrically necessary dislocation (GND) densities decreased at both GBs, indicating a dislocation-related stress relaxation mechanism. One low-angle GB formed near the sliding region with shallow grain microstructure. This work provides direct evidence of recrystallization as the mechanism for whisker formation by nucleating shallow surface grains. The local deformation showed a strong dependence on initial orientation, dislocations, and subsurface microstructure.
8:45 AM
Using Applied Pressure to Make Tin Whiskers Grow: Measurements and Analysis: Nupur Jain1; Piyush Jagtap1; Allan Bower1; Eric Chason1; 1Brown University
Tin whisker growth is often considered to be a stress-driven phenomenon. We have developed a new system to apply controlled mechanical pressure to Sn layers in order to quantify the stress-driven kinetics of whisker formation. The system is designed to fit in an SEM so that the whisker evolution can be observed in real time. A thin film force sensor is used to measure the applied pressure. We report results for the kinetics of nucleation and growth under applied pressure. Finite element analysis is used to calculate the stress evolution in the layer to relate it to the whiskering.
9:05 AM
Tin Whisker Growth on Pb-Free, Bi-containing Solder Alloys after Ambient Temperature, High Humidity Storage: Andre Delhaise1; Zohreh Bagheri1; Stephan Meschter2; Jeffrey Kennedy1; Polina Snugovsky1; 1Celestica; 2BAE Systems
With the introduction of environmental legislation, lead (Pb)-free materials have made their way into the electronics manufacturing industry. Pb-free solder alloys can initiate and grow tin whiskers under specific conditions, which may cause in-field failures in many high-reliability applications such as aerospace, automotive, and medical.Bismuth (Bi) has been considered for inclusion in Pb-free solder alloys to replace the current tin-silver-copper (Sn-Ag-Cu, or SAC) industry standard. In this study, we discuss whisker formation after ambient temperature, high humidity (25°C/85% RH) storage, on small outline transistor (SOT) and chip capacitor components assembled with Bi-bearing alloys. Four alloys were considered – SAC 305 (Sn-3.0Ag-0.5Cu), Violet (Sn-2.25Ag-0.5Cu-6.0Bi), Sunflower (Sn-0.7Cu-7.0Bi), and Senju M42 (Sn-2.0Ag-0.7Cu-3.0Bi). The boards were finished with either electroless nickel immersion gold (ENIG) or immersion tin (ImmSn), and half of assemblies were intentionally contaminated with sodium chloride (NaCl) to study the impact of corrosion on Sn whisker formation.
9:25 AM Break
9:45 AM Invited
Micro Interconnect Mechanical Stability in Cryogenic Temperature Environments: Ande Kitamura1; Ruben Contreras1; Tae-Kyu Lee1; 1Portland State University
Recent application in quantum computing and extreme environment end-use conditions pushed the temperature limit for an electric component to an unprecedented low temperature. Although the performance of those components are those temperature range are extensively studied, the interconnections which are still mainly Sn based and needs a thorough observation and assessment to support the mechanical and electrical stability at those low environments. Sn based solder interconnects are subjected to be shear tested at various temperatures between 150°C and -196°C. The isothermal aging impact and the testing temperature reveals a variation of mechanical response, which will be discussed. The shear region between the intermetallic phase and solder interface show a dynamic chemical gradient with different aging conditions and surface finish combination, which reveal a specific degradation mechanism.
10:05 AM Invited
Comparison of Corrosion Resistance between Electroless and Electroplating Ni/Pd/Au Surface Finish on PCB: Albert T. Wu1; Yi-Ting Shen1; Nico Li2; Freeze Wang2; Chih-Yuan Hsiao2; 1National Central University; 2Taiwan Uyemura Co.
Corrosion resistance of electroplating Ni/Pd/Au is in comparison with electroless Ni/Pd/Au (ENEPIG) surface finishes. Both surface finishes were plated on Cu pad in automobile printed circuit board (PCB). Each layer and different combination of the double layers were also investigated to study the corrosion properties of the materials. The samples were placed in a chamber of 100% RH (relative humidity) and an ambient of 15 ,150 and 1500 ppm of SO2.The morphology of corrosion products formed on the surface were studied by scanning electron microscopy (SEM), and the elements of corrosion products were analyzed by energy dispersive X-ray spectroscopy (EDS). Grazing incident X-ray diffraction (GIXRD) was applied to characterize the crystal structure of the corrosion products. The results reveal that the electroplating Ni/Pd/Au has better corrosion resistance than the ENEPIG. A mechanism is proposed to discuss the corrosion behaviors for the surface finishes.
10:25 AM
Chlorination and Power Cycling Characteristics of Fine Au/Pd Coated Copper Wire
: Che-Hao Chang1; Fei-Yi Hung1; 1National Cheng Kung University
In this research, gold and palladium layers are electroplated on the surface of copper wire to improve corrosion resistance and to enhance oxidation resistance. Chlorination test and power cycling test are conducted to discuss the difficulties in practical application and to reveal their deterioration mechanism. In chlorination test, both tensile strength and elongation decrease since chloride ions attack the surface of wires. However, if comparing Au/Pd-coated wires to those of pure copper, the coating layer still has a significant impact on the improvement of corrosion resistance. In power cycling test, voids appear on the interface of Pd layer and copper matrix. As the number of cycle increases, grain growth are induced by Joule’s heat, which is produced by high current density. Besides, repeated thermal expansion effect results in fatigue which makes the whole system fail.
10:45 AM
Electromigration in 2μm Nano-twinned Cu Redistribution Lines: Hung-Hsuan Li1; Chih Chen1; 1National Chiao Tung University
As the development of high end technology devices, it requires much more transistors under the same dimension than before, which leads to narrower and thinner Cu redistribution lines (RDLs). Consequently, the electromigration reliability issue becomes an important issues. In previous studies, the columnar nano-twinned Cu has highly <111>-oriented surface, which has better performance for resisting oxidation while comparing to random-oriented Cu. Also, the surface electromigration could be inhibited by the triple junctions which consisted of twin boundaries and the free surface. In this study, we successfully prepare 2μm wide and 2μm thick nano-twinned Cu lines covered with PI passivation layer, and apply 10^6 A/cm^2 at 180℃ for electromigration tests. The results show that the nano-twinned Cu lines possess a higher electromigration lifetime than the regular Cu lines.