Journal ArticleDOI
The microstructure of Sn in near-eutectic Sn-Ag-Cu alloy solder joints and its role in thermomechanical fatigue
Donald W. Henderson,James John Woods,Timothy A. Gosselin,Jay Bartelo,David E. King,T.M. Korhonen,Matt A. Korhonen,L.P. Lehman,Eric J. Cotts,Sung K. Kang,Paul A. Lauro,Da-Yuan Shih,Charles C. Goldsmith,Karl J. Puttlitz +13 more
TLDR
In this article, the solder joint fatigue process is characterized by the recrystallization of the Sn phase in the higher deformation regions with the production of a much smaller grain size.Abstract:
During the solidification of solder joints composed of near-eutectic Sn–Ag–Cu alloys, the Sn phase grows rapidly with a dendritic growth morphology, characterized by copious branching. Notwithstanding the complicated Sn growth topology, the Sn phase demonstrates single crystallographic orientations over large regions. Typical solder ball grid array joints, 900 μm in diameter, are composed of 1 to perhaps 12 different Sn crystallographic domains (Sn grains). When such solder joints are submitted to cyclic thermomechanical strains, the solder joint fatigue process is characterized by the recrystallization of the Sn phase in the higher deformation regions with the production of a much smaller grain size. Grain boundary sliding and diffusion in these recrystallized regions then leads to extensive grain boundary damage and results in fatigue crack initiation and growth along the recrystallized Sn grain boundaries.read more
Citations
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Journal ArticleDOI
Influence of Sn Grain Size and Orientation on the Thermomechanical Response and Reliability of Pb-free Solder Joints
Abstract: The size and crystal orientation of Sn grains in Pb-free, near eutectic Sn-Ag-Cu solder joints were examined. A clear dependence of the thermomechanical fatigue response of these solder joints on Sn grain orientation was observed (Sn has a body centered tetragonal crystal structure). Fabricated joints tend to have three orientations in a cyclic twin relationship, but among the population of solder balls, this orientation triplet appears to be randomly oriented. In thermally cycled joints, solder balls with dominant Sn grains having the particular orientation with the c-axis nearly parallel to the plane of the substrate were observed to fail before neighboring balls with different orientations. This results from the fact that the coefficient of thermal expansion of Sn in the basal plane (along the alpha-axis) is half the value along the c-axis; joints observed to be damaged had the maximum coefficient of thermal expansion mismatch between solder and substrate at the joint interface, as well as a tensile stress modes during the hot part of the thermal cycle. Localized recrystallization was observed in regions of maximum strain caused by differential expansion conditions, and its connection with crack nucleation is discussed.
Journal ArticleDOI
Growth of Sn and intermetallic compounds in Sn-Ag-Cu solder
L.P. Lehman,S. N. Athavale,T. Z. Fullem,A. C. Giamis,R. Kinyanjui,Margaret Lowenstein,K. Mather,R. Patel,D.F. Rae,J. Wang,Y. Xing,L. Zavalij,Peter Borgesen,Eric J. Cotts +13 more
TL;DR: In this article, the microstructure of the Sn-Ag-Cu solder was examined by optical microscopy and scanning electron microscopy (SEM) for various compositions near the ternary eutectic for different cooling rates from the solder melt.
Journal ArticleDOI
Grain-boundary character and grain growth in bulk tin and bulk lead-free solder alloys
Adwait U. Telang,Thomas R. Bieler,J. P. Lucas,K. N. Subramanian,L.P. Lehman,Y. Xing,Eric J. Cotts +6 more
TL;DR: In this article, the effects of alloy composition variations and cooling rates on microstructural stability and deformation processes were investigated in a pure-tin ingot and a reflowed sample.
Journal ArticleDOI
Incremental recrystallization/grain growth driven by elastic strain energy release in a thermomechanically fatigued lead-free solder joint
TL;DR: In this article, a single shear lap solder joint specimen with lead-free eutectic Sn-Ag solder on copper substrates was exposed to 1500 thermomechanical fatigue (TMF) cycles between −15° (3.5) and 150°C (20min) to generate intrinsic thermal strains.
Journal ArticleDOI
The role of elastic and plastic anisotropy of Sn in recrystallization and damage evolution during thermal cycling in SAC305 solder joints
Thomas R. Bieler,Bite Zhou,Lauren Blair,A. Zamiri,Payam Darbandi,Farhang Pourboghrat,Tae-Kyu Lee,Kuo Chuan Liu +7 more
TL;DR: In this paper, a low-stress plastic ball grid array (PBGA) package design at different stages of cycling history is compared with preliminary experiments using higher-stress package designs.
References
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Journal ArticleDOI
Foreword contributions from the 50th electronic components and technology conference
Journal ArticleDOI
Experimental and thermodynamic assessment of Sn-Ag-Cu solder alloys
Kil-Won Moon,William J. Boettinger,Ursula R. Kattner,Frank S. Biancaniello,Carol A. Handwerker +4 more
TL;DR: In this paper, phase diagram data in the Sn-Ag-Cu system were measured and the location of the ternary eutectic involving L, (Sn), Ag3Sn and Cu6Sn5 phases was confirmed to be at a composition of 3.5 wt.% Ag, 0.91 wt% Cu at a temperature of 216.2±0.3°C.
Journal ArticleDOI
Effects of cooling speed on microstructure and tensile properties of Sn–Ag–Cu alloys
TL;DR: In this paper, the microstructures and tensile properties of three typical Sn-Ag-Cu alloys, Sn-30wt%Ag-05wt%Cu and Sn-39Ag-06Cu, were evaluated after casting under three different cooling conditions.
Journal ArticleDOI
Pb-free solders for flip-chip interconnects
TL;DR: In this article, a variety of lead-free solder alloys were studied for use as flip-chip interconnects including Sn-3.5Ag, Sn-0.7Cu, and eutectic Sn-37Pb as a baseline.
Journal ArticleDOI
Ag3Sn plate formation in the solidification of near ternary eutectic Sn–Ag–Cu alloys
Donald W. Henderson,Timothy A. Gosselin,Amit K. Sarkhel,Sung K. Kang,Won-Kyoung Choi,Da-Yuan Shih,Charles C. Goldsmith,Karl J. Puttlitz +7 more
Abstract: Near-ternary eutectic Sn–Ag–Cu alloys are leading candidates for Pb-free solders. These alloys have three solid phases: β–Sn, Ag3Sn, and Cu6Sn5. Starting from the fully liquid state in solidifying near-eutectic Sn–Ag–Cu alloys, the equilibrium eutectic transformation is kinetically inhibited. The Ag3Sn phase nucleates with minimal undercooling, but the β–Sn phase requires a typical undercooling of 15 to 30 °C for nucleation. Because of this disparity in the required undercooling for nucleation, large, platelike Ag3Sn structures can grow rapidly within the liquid phase, before the final solidification of the solder joints. At lower cooling rates, the large Ag3Sn plates can subtend the entire cross section of solder joints and can significantly influence the mechanical deformation behavior of the solder joints under thermomechanical fatigue conditions. In this paper, it is demonstrated that the Ag3Sn plate formation can be inhibited, an important factor in assuring the reliability of solder joints composed of these alloys.