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| 22. |
- Andersson, Cristina, 1969
(författare)
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Reliability, fatigue and mechanical characterization of lead-free solders for electronic packaging applications
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The ever increasing amount of electronic waste, most of which ends up in landfills, has become a serious worldwide concern. In addition to this, the fact that Pb is highly toxic and harmful to humans has lead to the ban of this element from the electronics industry. The main objective of this thesis is to give a better insight into some important issues in the field of lead-free solders reliability. Particularly, to understand how some of the most common lead-free solders behave in different conditions, both thermal and isothermal, in tensile, fatigue and shear modes, and both as bulk materials and solder joints. Moreover, facts like microstructure, crack initiation and propagation, and the effect of IMCs are also investigated in the context of this work. Different test methodologies and fatigue prognostic methods are also evaluated. A new lower cost alloy composition where the expensive silver was replaced by cobalt was also developed and mechanically characterized.The results show that all the lead-free solders tested performed somewhat better in LCF compared to the eutectic Sn-37Pb, except for the Bi and Zn containing alloys, which proved to have a very poor LCF behavior, mainly due to their higher strength and brittle failure mode behavior. Corrosion affects negatively the fatigue behavior of SAC solder joints and is more detrimental than both high temperature and humidity. Concerning the comparison between test methods, the data acquired from bulk fatigue tests can not be directly applied to solder joints as a result of the fatigue behavior being strain dependent and solder joints depicting lower fatigue lives at higher strains and higher fatigue lives at lower strains compared to bulk solders. Regarding the investigated fatigue prognostic models, is more accurate to use the energy based Morrow’s model since it accounts for both stress and strain and therefore can also account for the cross sectional area decrease resulting from crack propagation during fatigue testing. Moreover, since both the plastic strain range and the energy density change as a function of number of cycles, it is more accurate to take in to account all the cycles in the test when calculating the average value of these units. Subjecting lead-free SAC 388PBGA packages to thermal cycling results in random crack initiation and propagation. Moreover, the crack pattern in the solder ball array did not follow the DNP theory. The effect of two thermal fatigue profiles was also analyzed. The harsher profile resulted in earlier crack initiation and faster crack propagation rate. Finite element modeling corroborated the experimental results as the highest creep strain was measured in the solder balls situated in the middle of the PBGA package. Microstructural coarsening during thermal cycling was observed for both SAC and Sn-Ag alloys, however, only the SAC alloy showed an increase of IMC layer thickness. Furthermore, it was found that the shear strength of solder joints, subjected to thermal cycling, is a result of both microstructural changes and crack initiation and propagation. Shear strength measurements were found not to be a good measurement tool to indicate when failure takes place.The new developed alloy has a eutectic composition of Sn-0.4Co-0.7Cu and a melting temperature of 224 °C. The tensile strength of this bulk alloy was lower compared to both SAC and Sn-37Pb alloys. The elastic modulus was lower than the SAC, however, higher than the Sn-37Pb. This alloy showed, however, a stable microstructure, composed of large Sn-rich dendrites with dispersed CoSn2 and Cu6Sn5 IMCs.
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| 23. |
- Andersson, Cristina, 1969, et al.
(författare)
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Tensile properties and microstructural characterization of Sn-0.7Cu-0.4Co bulk solder alloy for electronics applications
- 2008
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388. ; 457:1/2, s. 97-105
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Tidskriftsartikel (refereegranskat)abstract
- The ternary Sn–Cu–Co system eutectic composition was obtained by means of CALPHAD (CALculation of PHAse Diagram) methodology and it was found to be 0.4% Co and 0.7% Cu (wt%) with a melting point of 224 ◦C. The tensile behavior of this alloy was investigated at different strain rates (10−5, 10−4 and 10−3 s−1) and compared to both Sn–37Pb and Sn–4.0Ag–0.5Cu. The Sn–4.0Ag–0.5Cu alloy depicts the highest ultimate tensile strength (UTS) followed by the Sn–37P and finally the Sn–0.7Cu–0.4Co system. The elastic modulus was also higher for the Sn–4.0Ag–0.5Cu followed by the Sn–0.7Cu–0.4Co and last the Sn–37Pb. The microstructure of the Sn–0.7Cu–0.4Co alloy is composed of two types of intermetallic phases, (Cu,Co)6Sn5 and (Co,Cu)Sn2 dispersed in a Sn-rich matrix. The microstructure of this alloy proved to be very stable, after aging at 150 °C for 24 h. The eutectic Sn–0.7Cu–0.4Co solder alloy can therefore be a very good alternative for theSACalloys for surface mount technology applications.
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| 24. |
- Bailey, C., et al.
(författare)
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Coffin-Manson constant determination for a Sn-8Zn-3Bi Lead-Free Solder Joint
- 2006
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Ingår i: Soldering and Surface Mount Technology. - : Emerald. - 1758-6836 .- 0954-0911. ; 18:2, s. 4-11
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Tidskriftsartikel (refereegranskat)abstract
- Purpose To determine the Coffin-Manson (CM) equation constants for fatigue life estimation of Sn-8Zn-3Bi solder joints, since Sn-8Zn-3Bi solder has a melting temperature of around 199°C which is close to that of the conventional Sn-Pb solder which has previously been used in the electronics assembly industry. Design/methodology/approach Three dimensional finite element (FE) simulation analysis was used for comparison with the experimentally measured data and to determine the CM constants. Low cycle fatigue tests and FE simulations were carried out for these lead-free solder joints, and eutectic Sn-37Pb solder was used as a reference. Findings The CM equation for Sn-8Zn-3Bi solder joints was fitted to the lifetimes measured and the shear strains simulated. The constants were determined to be 0.0294 for C, the proportional constant, and for the fatigue exponent, β, −2.833. Originality/value The CM equation can now be used to predict the reliability of Sn-8Zn-3Bi solder joints in electronics assembly and the knowledge base for the properties of the Sn-Zn solder system has been increased.
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| 25. |
- Carlsson, Lena M S, 1957, et al.
(författare)
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Long-term incidence of serious fall-related injuries after bariatric surgery in Swedish obese subjects.
- 2019
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Ingår i: International journal of obesity (2005). - : Springer Science and Business Media LLC. - 1476-5497 .- 0307-0565. ; 43:4, s. 933-937
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Tidskriftsartikel (refereegranskat)abstract
- Obesity increases risk of falling, but the effect of bariatric surgery on fall-related injuries is unknown. The aim of this study was therefore to study the association between bariatric surgery and long-term incidence of fall-related injuries in the prospective, controlled Swedish Obese Subjects study. At inclusion, body mass index was ≥ 34 kg/m2 in men and ≥38 kg/m2 in women. The surgery per-protocol group (n = 2007) underwent gastric bypass (n = 266), banding (n = 376), or vertical banded gastroplasty (n = 1365), and controls (n = 2040) received usual care. At the time of analysis (31 December 2013), median follow-up was 19 years (maximal 26 years). Fall-related injuries requiring hospital treatment were captured using data from the Swedish National Patient Register. During follow-up, there were 617 first-time fall-related injuries in the surgery group and 513 in the control group (adjusted hazard ratio 1.21, 95% CI, 1.07-1.36; P = 0.002). The incidence differed between treatment groups (P < 0.001, log-rank test) and was higher after gastric bypass than after usual care, banding and vertical banded gastroplasty (adjusted hazard ratio 0.50-0.52, P < 0.001 for all three comparisons). In conclusion, gastric bypass surgery was associated with increased risk of serious fall-related injury requiring hospital treatment.
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