Papers about SAC
by Dr. Ning-Cheng Lee , Dr. Hong-Sik Hwang, Dr. Benlih Huang
Addition of Al into SAC alloys reduces the number of hard Ag3Sn and Cu6Sn5 IMC particles, and forms larger, softer non-stoichiometric AlAg and AlCu particles. This results in a significant reduction in yield strength, and also causes some moderate increase in creep rate. For high Ag SAC alloys, adding Al 0.1-0.6% to SAC alloys is most effective in softening, and brings the yield strength down to the level of SAC105 and SAC1505, while the creep rate is still maintained at SAC305 level. Addition of Ni results in formation of large (Ni,Cu)3Sn4 IMC particles and loss of Cu6Sn5 particles. This also causes softening of SAC alloys, although to a less extent than that of Al addition. Addition of Al also drives the microstructure to shift from near-ternary SnAgCu eutectic toward combination of eutectic SnAg and eutectic SnCu. Addition of Ni drives shifting toward eutectic SnAg. For SAC+Al+Ni alloys, the pasty range and liquidus temperature are about 4°C less than that of SAC105 or SAC1505 if the addition quantity is less than about 0.6%. Addition of Al and Ni also results in a slight decrease in modulus and elongation at break, although the tensile strength is not affected.
Ni, Al, creep resistant, compliant, soften, SAC, lead-free, solder
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Posted on 1 Jan 2009
by Dr. Ronald C. Lasky , Brook Sandy
Developing low-cost alternatives to near-eutectic SAC alloys for Pb-free assembly is crucial to continue producing affordable electronics products. Metals prices, especially silver, have been on the rise, and will likely stay at their near historic high levels. Solder alloys with lower silver content have been considered with trade-offs in performance, but are there alternatives?
There are many reasons to consider alternative Pb-free alloys to SAC305. Several new alloys have been recently introduced, while others, which had little popularity in the past, are showing more potential due to changes in the industry. The question is: how much do subtle variations in alloy composition affect the performance and process requirements of PCB assembly? This paper will compare some of these alloys side-by-side and discuss whether existing processes need to be modified for alternative alloys.
Apex 2012, SAC, pb-free, lead-free, solder alloy
[Permanent Link to this Paper ]
Posted on 14 Oct 2011
by Jason Bragg, Russell Brush, Polina Snugovesky, Blake Harper, Simin Bagheri, Dr. Ning-Cheng Lee , Dr. Weiping Liu
Board-level drop test performance was evaluated and compared for the following four different solder combinations in BGA/CSP assembly: 1) SnPb paste with SnPb balls, 2) SnPb paste with SAC105Ti balls, 3) SAC305 paste with SAC105Ti balls, and 4) SAC305 paste with SAC105 balls. The presence of Ti improved the drop test performance significantly, despite the voiding side effect caused by its oxidation tendency. It is anticipated that the voiding can be prevented with the development of a more oxidation-resistant flux. The consistently poor drop test performance of 105Ti/SnPb is caused by the wide pasty range resulting from mixing SAC105Ti with Sn63 solder paste. The effect of Ti in this system is overshadowed by the high voiding outcome due to this wide pasty range material. In view of this, the use of a SAC105 BGA with an SnPb solder paste is not recommended, with or without the Ti addition. High reflow temperatures drove the fracture to shift to the interface at the package side, presumably through building up the IMC thickness beyond the threshold value. A lower reflow temperature is recommended. The electrical response is consistent with the complete fracture data, but the complete fracture trend is inconsistent with that of the partial fracture trend, and neither data can provide a full understanding about the failure mode. By integrating the complete fracture and the partial fracture into a “Virtual Fracture”, the failure mechanism becomes obvious and data sets become consistent with each other.
SAC305, solder paste, SAC105Ti, SAC, solder sphere, lead-free, drop test, Apex 2012
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Posted on 14 Oct 2011
by Dr. Ning-Cheng Lee
In general,
new lead-free solder alloys with the following characteristics are desired in order to enable the continuation of miniaturization trend: (1) alloy with a reduced melting temperature, (2) alloy with a better solder spread, (3) alloy with a slower wetting speed at melting temperature, (4) a softer alloy, or alloy with a reduced voiding tendency or greater ductility, (5) alloy with a refined grain size, (6) alloy with low tendency to form large IMC plate, (7) alloy with a higher resistance toward corrosion and electrochemical migration, (8) alloy with a greater oxidation resistance. On the other hand, no-clean fluxes with the following features are needed: (1) reduced volatile, (2) halide-free, (3) greater fluxing
capacity, (4) higher residue resistivity, (5) more resistant to oxidation and charring, (6) more efficient oxidation barrier, (7) lower activation temperature, (8) slower wetting speed when solder begins to melt, (9) less spattering, (10) higher probe penetratability, (11) capability of inducing nucleation of solder upon cooling, and (12) greater resistance against slump.
SAC, solder joint, soldering, flux, solder alloy, lead-free
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Posted on 4 Mar 2010
by Eric Bastow , Timothy Jensen
The advent of the EU’s RoHS law has encouraged a significant amount of research to find an alloy, for electronic assembly that will satisfy RoHS’s lead-free requirement and have optimum process ability and field reliability. The resulting research, much of it lead by iNEMI, resulted in the near eutectic tin-silver-copper alloy SAC387 (Sn95.5Ag3.8Cu0.7) as an initial favorite to fill this need in the early 2000s. By 2004 or so, many people were using SAC305, partially because of its greater resistance to tombstoning. It appeared that SAC305 would become the de-facto lead-free standard alloy for RoHS compliant electronic assembly. However, with the dramatic increase in silver prices in the last few years, SAC105, having 2% less silver was being evaluated and used for its obvious cost savings. Reliability testing of SAC105 also showed that although it did not perform as well as SAC305 in thermal fatigue cycle testing, it was better than SAC305 in drop shock tests. The explosive growth of mobile phone sales, over 1 billion per year, made SAC105’s superior drop shock performance attractive for these and other portable devices.
In addition to research relating to SAC305 and SAC105, much work has been performed on the study of the effects of small quantities (<0.1%) of alloying metals on lead-free alloys’ process ability and reliability performance. These "dopants" can dramatically affect an alloy’s performance.
All of the above work has resulted in what many are calling lead-free alloy proliferation as more and more alloys are being considered for implementation. This proliferation drives up solder paste cost as manufacturers cannot achieve economies of scale. In addition, with so many alloys to consider, it is difficult for researchers to develop extensive data bases of process and reliability performance.
This paper is an overview of this lead-free alloy proliferation and an outlook on how alloy convergence might occur.
solder, SAC, pb-free, dopants, Reliability, thermal cycling, drop testing
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Posted on 15 Oct 2009
by Paul Bachorik, Dr. Ning-Cheng Lee , Dr. Weiping Liu
SAC-Ti alloys exhibited significantly improved drop test performance over not only SAC alloys, but also 63Sn37Pb for ENIG/OSP, NiAu/OSP, and OSP/OSP surface finish systems. The superior performance is attributed to (1)the increased grain size and dendrite size, therefore reduced hardness of solder, (2) inclusion of Ti in the IMC layer, and (3) reduced IMC layer thickness. DSC data indicate that the melting temperature and range were not affected by Ti, but the undercooling was almost completely suppressed. The creep properties of SAC-Ti alloy were comparable with those of SAC alloy, strongly suggesting the gain in drop test performance was not achieved by compromising the thermal fatigue performance. SAC-Mn alloys were also found to outperform SAC alloys and Sn63 for the X/OSP finish combinations studied. In general, SAC-Ti performed equally to or better than SAC-Mn alloys.
fragility, drop test, SAC, tin-silver-copper, lead-free, solder
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Posted on 10 Mar 2010
