The microstructure, mechanical response, and failure behavior of lead free solder joints in electronic assemblies are constantly evolving when exposed to isothermal aging and/or thermal cycling environments. Over the past several years, we have demonstrated that the observed material behavior variations of Sn-Ag-Cu (SAC) lead free solders during room temperature aging (25 C) and elevated temperature aging (50, 75, 100, 125, and 150 C) were unexpectedly large and universally detrimental to reliability. The measured stress-strain data demonstrated large reductions in stiffness, yield stress, ultimate strength, and strain to failure (up to 50%) during the first 6 months after reflow solidification. In addition, even more dramatic evolution was observed in the creep response of aged solders, where up to 100X increases were found in the steady state (secondary) creep strain rate (creep compliance) of lead free solders that were simply aged at room temperature. For elevated temperature aging at 125 C, the creep strain rate was observed to change even more dramatically (up to 10,000X increase). There is much interest in the industry on establishing optimal SAC-based lead free solder alloys that minimize aging effects and thus enhance thermal cycling and elevated temperature reliability. During the past year, we have extended our previous studies to include several doped SAC alloys (SAC-X) where the standard SAC alloys have been modified with small percentages of one or two additional elements (X). Materials under consideration include SAC0307-X, Sn-.7Cu-X, SAC305-X, SAC3595-X and SAC3810-X. Using dopants (e.g. Bi, In, Ni, La, Mg, Mn, Ce, Co, Ti, etc.) has become widespread to enhance shock/drop reliability, and we have extended this approach to examine the ability of dopants reduce the effects of aging and extend thermal cycling reliability. In the current paper, we concentrate on showing results for SACX™, which has the composition Sn-0.3Ag-0.7Cu-X with X = 0.1Bi. We have performed aging under 5 different conditions including room temperature (25 C), and four elevated temperatures (50, 75, 100 and 125). We have also extended the duration of aging considered in our experiments to up to 12 months of aging on selected alloys. Variations of the mechanical and creep properties (elastic modulus, yield stress, ultimate strength, creep compliance, etc.) have been observed. We have correlated the aging results for the doped SAX-X alloy with our prior data for the “standard” lead free alloys SACN05 (SAC105, SAC205, SAC305, SAC405). The doped SAC-X alloy shows improvements (reductions) in the aging-induced degradation in stiffness, strength, and creep rate when compared to SAC105, even though it has lower silver content. In addition, the doped SAC-X alloy has been observed to reach a stabilized microstructure more rapidly when aged. Mathematical models for the observed aging variations have been established so that the variation of the stress-strain and creep properties can be predicted as a function of aging time and aging temperature.
Skip Nav Destination
ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems
July 6–8, 2011
Portland, Oregon, USA
Conference Sponsors:
- Electronic and Photonic Packaging Division
ISBN:
978-0-7918-4462-5
PROCEEDINGS PAPER
The Effects of Dopants on the Aging Behavior of Lead Free Solders
Jeffrey C. Suhling,
Jeffrey C. Suhling
Auburn University, Auburn, AL
Search for other works by this author on:
Michael J. Bozack
Michael J. Bozack
Auburn University, Auburn, AL
Search for other works by this author on:
Zijie Cai
Auburn University, Auburn, AL
Jeffrey C. Suhling
Auburn University, Auburn, AL
Pradeep Lall
Auburn University, Auburn, AL
Michael J. Bozack
Auburn University, Auburn, AL
Paper No:
IPACK2011-52184, pp. 733-748; 16 pages
Published Online:
February 14, 2012
Citation
Cai, Z, Suhling, JC, Lall, P, & Bozack, MJ. "The Effects of Dopants on the Aging Behavior of Lead Free Solders." Proceedings of the ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems. ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems, MEMS and NEMS: Volume 2. Portland, Oregon, USA. July 6–8, 2011. pp. 733-748. ASME. https://doi.org/10.1115/IPACK2011-52184
Download citation file:
8
Views
Related Articles
Creep Analysis of Wafer Level Chip Scale Package (WLCSP) With 96.5Sn-3.5Ag and 100In Lead-Free Solder Joints and Microvia Build-Up Printed Circuit Board
J. Electron. Packag (June,2002)
Investigation of Effect of Creep Strain on Low-Cycle Fatigue of Lead-Free Solder by Cyclic Loading Using Stepped Ramp Waves
J. Electron. Packag (December,2010)
The Effects of Temperature Cyclic Loading on Lead-Free Solder Joints of Wafer Level Chip Scale Package by Taguchi Method
J. Electron. Packag (March,2008)
Related Chapters
Back Matter
Analysis of ASME Boiler, Pressure Vessel, and Nuclear Components in the Creep Range
Polycrystalline Simulations of In-Reactor Deformation of Zircaloy-4 Cladding Tubes during Nominal Operating Conditions
Zirconium in the Nuclear Industry: 20th International Symposium
Advanced PWR Cladding Development through Extensive In-Reactor Testing
Zirconium in the Nuclear Industry: 20th International Symposium