Papers by Keyword: Solder Alloys

Abstract: Lead containing solders (SnPb eutectic alloys) are widely used in electronic devices due to their good mechanical properties and low manufacturing cost. However, two European Union regulations (Waste from Electrical and Electronic Equipment and Restriction of Hazardous Substances) banned the use of lead in electrical and electronic equipment because of the toxic effect on human health and the environment. Nowadays, it is particularly important to find replacements for Pb containing solder materials. In that respect, copper is used as an alloying element and the composition Sn-0.7wt%Cu is of particular interest. Small Ni additions can be interesting since they would be included into the composition of the commercial solder SN100 and can also avoid the presence of coarse and deleterious Cu₆Sn₅ particles for Sn-Cu alloys in the hypoeutectic range of compositions. In the present investigation, growth rate, cooling rate, interfacial heat transfer coefficient (h_i), the scale of the microstructure and morphologies, ultimate tensile strength and elongation have been experimentally determined for Sn-0.7wt%Cu and Sn-0.7wt%Cu-0.1wt%Ni alloys solidified in a water-cooled vertical upward unidirectional solidification system. Further, interrelations of thermal parameters, microstructure and tensile properties may be established. A higher time-dependent h_i profile was found for the Sn-0.7wt%Cu-0.1wt%Ni alloy which seems to indicate that a higher fluidity was obtained with small Ni addition. Higher fluidity values may characterize better physicochemical affinity between the melt and the mould surface. The modified Sn-Cu alloy propitiates higher ultimate tensile strength values to be obtained. This may be due to the prevalence of eutectic two-phase cells along the casting associated with fine Cu-rich particles close to the water-cooled surface.

Abstract: Solder joints are strongly dependent on how well the solder alloy can wet the substrate. One of the parameters which can be used to characterize the wettability of solder alloys on a substrate is the heat transfer coefficient at the interface alloy/substrate, h_i. This study focus on the effect of the surface roughness of the substrate on the interfacial heat transfer coefficient during solidification of solder alloys. A comparative study is carried out with two lead-free solders alternatives and the traditional Sn-Pb solder (Sn 0.7wt%Cu, Sn 3.5 wt%Ag and Sn 38wt%Pb, respectively). These alloys were directionally solidified using a solidification apparatus having a water cooled bottom made of low carbon steel with two different surface finishing: machined and polished. The experimental thermal data collected by thermocouples positioned along the casting length were used as input information into an Inverse Heat Transfer Code implemented in this work in order to determine the h_i variation in time. A power–law function given by (where a and m are constants which depend on the alloy composition, substrate and melt superheat and t is the time) which is based on both theoretical and experimental analyses is proposed. The transient h_i profile has a typical drastic reduction from a high initial value due to the development of an air gap, followed by a recovery to an essentially constant value. The literature generally reports a decrease in h_i with increasing surface roughness. However, in the present work an opposite behavior has been detected, which is explained based on contact interactions between alloy and substrate that are subjected to thermal contraction and thermal expansion during the soldering process, respectively.

Abstract: In the paper, the Sn2.5Ag0.7Cu solder alloy is selected out by comprehensive comparison. Minute a mount of rare earth (RE) was added into Sn2.5Ag0.7Cu solder aiming at examining the effect of different a mount of RE on microstructure,the physical properties and mechanical properties of Sn2.5Ag0.7Cu solder.the aim is to define the optimization range of the RE addition.

Abstract: The past years have triggered considerable scientific efforts towards the predictive analysis of the reliability of solder connections in micro-electronics. Undoubtedly, the replacement of the classical Sn-Pb solder alloy by a lead-free alternative constitutes the main motivation for this. This paper concentrates on the theoretical, computational and experimental multi-scale analysis of the microstructure evolution and degradation of the conventional solder material Sn-Pb and its most promising lead-free alternative, a Sn-Ag-Cu (SAC) alloy. Special attention is given to the thermal anisotropy of bulk SAC and the interfacial fatigue failure of SAC interconnects.