Time-Lapse Imaging of Ag3Sn Thermal Coarsening in Sn-3Ag-0.5Cu Solder Joints

Abstract

The coarsening of Ag3Sn particles occurs during the operation of joints and plays an important role in failure. Here, Ag3Sn coarsening is studied at 125°C in the eutectic regions of Sn-3Ag-0.5Cu/Cu solder joints by SEM-based time-lapse imaging. Using multi-step thresholding segmentation and image analysis, it is shown that coalescence of Ag3Sn particles is an important ripening process in addition to LSW-like Ostwald ripening. About 10% of the initial Ag3Sn particles coalesced during ageing, coalescence occurred uniformly across eutectic regions, and the scaled size distribution histograms contained large particles that can be best fit by the Takajo model of coalescence ripening. Similar macroscopic coarsening kinetics were measured between the surface and bulk Ag3Sn particles. Tracking of individual surface particles showed an interplay between the growth/shrinkage and coalescence of Ag3Sn.

A multi-scale approach to microstructure-sensitive thermal fatigue in solder joints

“…Among all 24 joints in the M rows from the two packages, only three were single β-Sn grain joints and were at positions M6 in package 1 and M8-M9 in package 2. Eutectic particle size measurements were conducted on BSE images from these joints using an image segmentation method (Xian et al, 2021). The intermetallic particle size distribution was studied in M8 and M9 and was highly similar with mean, standard deviation, median of 0.52, 0.28, 0.44 µm for M8 and 0.54, 0.29, 0.45 µm for M9.…”

The role of microstructure in the thermal fatigue of solder joints

“…1 . There was also strong localised accelerated Ag 3 Sn coarsening near the top interface, as is common in thermally cycled Sn-3Ag-0.5Cu joints 12 , 25 , 33 due to coarsening with both a thermal 34 – 36 and strain-enhanced 12 , 37 , 38 component and further due to faster diffusion along recrystallised grain boundaries once recrystallisation has begun 12 . Here, these accelerated coarsened Ag 3 Sn particles exceeded 2μm (Supplementary Fig.…”

“…The collected images were then stitched into a single image in ImageJ. Fine Ag 3 Sn and Cu 6 Sn 5 particles were segmented using the in-house MATLAB image processing algorithms published in 36 . The eutectic Ag 3 Sn particle spacing was found from a Delaunay triangulation in MATLAB, using the centroids of all detected Ag 3 Sn particles as the vertices of the triangulation.…”

Multi-scale plasticity homogenization of Sn–3Ag-0.5Cu: From β-Sn micropillars to polycrystals with intermetallics

“…The IMC size within a given solder alloy is physically determined by the undercooling reached prior to -Sn nucleation during the solidification process [14,51,52], and coarsening during isothermal aging and thermal cycling in service [2,53,54]. The representative average IMC radius (equivalent circular radius, ECR) for SAC305 BGA joints [53,54] are estimated as 0.11 𝜇𝑚 < 𝑟̅ 𝐼𝑀𝐶 < 1.88 𝜇𝑚…”

“…While the IMC size range relevant to the tests was not reported, it is likely to be consistent with the range selected ( 𝑟̅ 𝐼𝑀𝐶 =0.11 µm and 𝑟̅ 𝐼𝑀𝐶 =1.88 µm). The upper and lower extremes shown for each temperature correspond to these two IMC sizes which are relevant to the temperature conditions considered [54]. The predicted curves are obtained by utilising knowledge of the IMC size range (see Eqn.…”