Papers by Keyword: Cu₆Sn₅

Abstract: Thin layers of intermetallic (IMC) were prepared using Solid-Liquid Inter-Diffusion (SLID) process. 3μm of Tin was deposited on SiC dice, then soldered on a copper substrate at different temperature: 250-300-330-370°C and different soldering times: 5sec-300 sec - 15 min - 1h. The composition of the IMC was identified using energy dispersive X-Ray spectroscopy (EDX). Two types of intermetallic layers were identified: Cu₃Sn and Cu₆Sn₅. The samples were tested using die shear test. Then the internal stress was measured by X-Ray Diffraction (XRD). XRD spectrum obtained spotted only pure copper present underneath the intermetallic layer. The results showed that the level of residual stress is related to the amount of voids in the solder.

Abstract: Sn-0.7Cu-0.05Ni is a widely used Pb-free solder that solidifies into a near-eutectic microstructure and a small fraction of primary Cu₆Sn₅. This paper overviews in-situ time-resolved imaging experiments on the solidification of Sn-0.7Cu-0.05Ni solder under three conditions: (i) directional solidification, (ii) continuous cooling in a near-uniform thermal field, and (iii) solder joint solidification on a Cu substrate. Primary Cu₆Sn₅ grow as rods along [0001] in each case but can also grow as X-shaped crystals in (iii). There are significant differences in eutectic growth due to nucleation difficulties for tin in conditions (ii) and (iii).

Abstract: Extending the use of the Sn-Cu system to high-temperature solders poses additional challenges as the necessary high Cu content is in a region of the binary phase diagram which is dominated by the peritectic reaction and has the intermetallic compound (IMC) Cu₃Sn as the primary phase, which is known to have negative effects on soldering properties. Minor additions of nickel (Ni) have been reported to suppress the formation of Cu₃Sn in low Cu content Sn-Cu solder alloys though higher Cu content alloys have not been investigated. As such, the objective of this paper was to investigate the effect of more significant concentrations of Ni on the microstructure of a Sn-30wt%Cu alloy. An initial addition of 2wt%Ni greatly reduced the volume fractions of Cu₃Sn and the amount of eutectic present whilst significantly increasing the volume fraction of Cu₆Sn₅; however, further additions of Ni had a less pronounced affect. The Sn-30wt%Cu morphology was changed from a plate-like structure to a dendritic structure by adding Ni, which would improve solder performance by decreasing the possible crack plane length.

Abstract: This research examines the relationship between Cu and Ni concentration and the formation of primary Cu₃Sn in high Cu containing Sn-Cu solder alloys. Through thermal analysis and optical microscopy, it was determined that Ni additions still have a significant effect in minimising or eliminating Cu₃Sn for Cu concentrations as high as 30wt%. In addition, it is clear that a relationship exists between Cu concentration and the effect of Ni addition and the volume fraction of Cu₃Sn increases as the Cu content increases. It is likely that the Ni addition has a significant effect on the interdiffusional coefficients of the diffusing species of Cu₃Sn and Cu₆Sn₅, slowing the growth of Cu₃Sn and encouraging primary Cu₆Sn₅ nucleation.

Abstract: The solidification of Sn-3Ag-0.5Cu and Sn-0.7Cu-0.05Ni are overviewed and compared. In joints on Cu substrates, both solders begin solidification with primary Cu₆Sn₅ growing in the bulk liquid prior to tin nucleation. In freestanding balls and joints, SAC305 generally solidifies with a single tin nucleation event and exhibits a mutually-twinned tin grain structure. In contrast, SN100C BGA balls and joints exhibit multiple independent tin grains that grow as a columnar array in joints.

Abstract: This study investigated the effect of Ni addition on intermetallic formation in the Sn-8Zn-3Bi solder under liquid state aging. The intermetallic compounds were formed by reacting the solder alloy with copper substrate. Different reflow time was used at temperature 220°C. Morphology of the phases formed was observed using scanning electron microscope (SEM) and in order to determine elemental compositions of the phases, energy dispersive x-ray (EDX) was used. The formation of the reaction layer led by Cu₅Zn₈ intermetallic and then followed by Cu₆Sn₅ and Cu₃Sn when reflow time increases. Keywords: lead free solder, intermetallic, Cu₅Zn₈, Cu₆Sn₅, liquid state aging.

Abstract: This paper demonstrates how recent progress for real-time solidification observation at SPring-8 synchrotron has contributed to the development of Sn-7wt%Cu-0.05wt%Ni high temperature lead-free solder alloys. Lead-free solder alloys in the composition range Sn-0.7 to 7.6wt%Cu that consist of primary Cu₆Sn₅ in a eutectic Sn-Cu₆Sn₅ matrix have been proposed as solders for application at temperatures up to 400°C for the assembly high current semiconductors. It is shown that trace levels of Al have a marked effect on the solder microstructure and refine the size of the primary Cu₆Sn₅. The solidification pathway that leads to the refinement was observed in real-time using X-ray synchrotron observations.

Abstract: The morphology and growing behavior of Cu₆Sn₅ intermetallic compound (IMC) of low Ag content Sn-2.5Ag-0.7Cu-0.1RE/Cu solder joint interface are investigated by adopting the X-ray diffraction, JSM-5610LV scanning electronic microscope and energy spectrum analysis. The results show that the cross-section morphology Cu₆Sn₅ of the solder joint interface is scallop-like and its section morphology is circle-like grain. With the aging time increasing, the cross-section Cu₆Sn₅ morphology of the solder joint interface can be changed from the scallop-like to the shape-layer, and the growing kinetics is coincidence with the law of parabola and its growing behavior is controlled by diffusion. With adding a small amount of rare earth elements in the Sn-2.5Ag-0.7Cu solder alloy, the growing rate of the Cu₆Sn₅ can be reduced.

Abstract: Sn-Ag-Cu-Ni-Ge solder alloy has been developed to improve the mechanical properties of the Sn-Ag-Cu base solders and prevent oxidation of those solders. In this paper, an interfacial reaction and microstructure between the solder and a Cu electrode were investigated under heat exposure conditions. It was found that intermetallic compounds growth at the interface of the solder and the Cu electrode was greatly affected by amounts of added elements. Adding Ni in the solder can suppress the formation and growth of intermetallic compounds (IMCs) such as Cu-Sn and decreasing the amount of adding Ag in the solder can prevent the formation and growth of Ag3Sn. Moreover, it was found that there was an effect of suppress the growth of the Cu3Sn formed on the interface of Cu and (Cu,Ni)6Sn5 by adding Ni from analysis results of EDX and TEM.

Abstract: Effect of rare earth content on microstructure and interfacial reactions of low Ag content SnAgCu solder is researched by adopting the X-ray diffraction, JSM-5610LV scanning electronic microscope, energy spectrum analysis and JEM2100 ultrahigh resolution electron microscopy. The results show that proper quantities of rare earth (0.1%) can refine the eutectic microstructure of the solder alloy; and petal-like rare earth compound can be found in the solder alloy while the rare earth addition is 0.5%. The growing rate of the interfacial intermetallic compound can be reduced during the soldering with adding 0.1% rare earth in the Sn2.5Ag0.7Cu solder alloy.