• Korean Journal of Materials Research
• /
• v.10 no.12
• /
• pp.799-806
• /
• 2000

Cu$_{6}$Sn$_{5}$-dispersed 63Sn-37Pb solder bumps of 760$\mu\textrm{m}$ size were fabricated on Au(0.5$\mu\textrm{m}$)/Ni(5$\mu\textrm{m}$)/Cu(27$\pm$20$\mu\textrm{m}$) BGA substrates by screen printing process, and their shear strength were characterized with variations of dwell time at reflow peak temperature and aging time at 15$0^{\circ}C$ . With dwell time of 30 seconds at reflow peak temperature, the solder bumps with Cu$_{6}$Sn$_{5}$ dispersion exhibited higher shear strength than the value of the 63Sn-37Pb solder bump. With increasing the dwell time longer than 60 seconds, however the shear strength of the Cu$_{6}$Sn$_{5}$-dispersed solder bumps became lower than that the 63Sn-37Pb solder bumps. The failure surface of the solder bumps could be divided into two legions of slow crack propagation and critical crack propagation. The shear strength of the solder bumps was inversely proportional to the slow crack propagation length, regardless of the dwell time at peak temperature, aging time at 150 $^{\circ}C$ and the volume fraction of Cu$_{6}$Sn$_{5}$ dispersion.> 5/ dispersion.

• Journal of the Microelectronics and Packaging Society
• /
• v.21 no.2
• /
• pp.91-97
• /
• 2014

With Pb-free solder joints containing Sn-Ag-Cu-based ternary alloys (Sn-1.0 wt.%Ag-0.5Cu and Sn-4.0Ag-0.5Cu) and Sn-Ag-Cu-In-based quaternary alloys (Sn-1.0Ag-0.5Cu-1.0In, Sn-1.2Ag-0.5Cu-0.4In, Sn-1.2Ag-0.5Cu-0.6In, and Sn-1.2Ag-0.7Cu-0.4In), fracture-mode change, shear strengths, and fracture energies were observed and measured under a high-speed shear test of 500 mm/s. The samples in each composition were prepared with as-reflowed ones or solid-aged ones at $125^{\circ}C$ to 500 h. As a result, it was observed that ductile or quasi-ductile fracture modes occurs in the most of Sn-Ag-Cu-In samples. The happening frequency of a quasi-ductile fracture mode showed that the Sn-Ag-Cu-In joints possessed ductile fracture properties more than that of Sn-3.0Ag-0.5Cu in the high-speed shear condition. Moreover, the Sn-Ag-Cu-In joints presented averagely fracture energies similar to those of Sn-Ag-Cu joints. While maximum values in the fracture energies were measured after the solid aging for 100 h, clear decreases in the fracture energies were observed after the solid aging for 500 h. This result indicated that reliability degradation of the Sn-Ag-Cu-In solder joints might accelerate from about that time.

• Korean Journal of Metals and Materials
• /
• v.48 no.11
• /
• pp.1041-1046
• /
• 2010

The reactions between a Sn-3.0Ag-0.5Cu solder alloy and electroless Ni/electroless Pd/immersion Au (ENEPIG) surface finishes with various Pd layer thicknesses (0, 0.05, 0.1, 0.2, $0.4{\mu}m$) were examined for the effect of the Pd layer on the massive spalling of the $(Cu,Ni)_6Sn_5$ layer during reflow at $235^{\circ}C$. The thin layer deposition of an electroless Pd (EP) between the electroless Ni ($7{\mu}m$) and immersion Au ($0.06{\mu}m$) plating on the Cu substrate significantly retarded the massive spalling of the $(Cu,Ni)_6Sn_5$ layer during reflow. Its retarding effect increased with an increasing EP layer thickness. When the EP layer was thin (${\leq}0.1{\mu}m$), the retardation of the massive spalling was attributed to a reduced growth rate of the $(Cu,Ni)_6Sn_5$ layer and thus to a lowered consumption rate of Cu in the bulk solder during reflow. However, when the EP layer was thick (${\geq}0.2{\mu}m$), the initially dissolved Pd atoms in the molten solder resettled as $(Pd,Ni)Sn_4$ precipitates near the solder/$(Cu,Ni)_6Sn_5$ interface with an increasing reflow time. Since the Pd resettlement requires a continuous Ni supply across the $(Cu,Ni)_6Sn_5$ layer from the Ni(P) substrate, it suppressed the formation of $(Ni,Cu)_3Sn_4$ at the $(Cu,Ni)_6Sn_5/Ni(P)$ interface and retarded the massive spalling of the $(Cu,Ni)_6Sn_5$ layer.

• Proceedings of the KWS Conference
• /
• 2006.05a
• /
• pp.30-32
• /
• 2006

The interfacial reaction and reliability of eutectic Sn-Pb and Pb-free eutectic Sn-Ag ball-grid-array (BGA) solders with an immersion Ag-plated Cu substrate were evaluated following isothermal aging at $150^{\circ}C$. During reflowing, the topmost Ag layer was dissolved completely into the molten solder, leaving the Cu layer exposed to the molten solder for both solder systems. A typical scallop-type Cu-Sn intermetallic compound (IMC) layer was formed at both of the solder/Cu interfaces during reflowing. The thickness of the Cu-Sn IMCs for both solders was found to increase linearly with the square root of isothermal aging time. The growth of the $Cu_3Sn$ layer for the Sn-37Pb solder was faster than that for the Sn-3.5Ag solder, In the case of the Sn-37Pb solder, the formation of the Pb-rich layer on the Cu-Sn IMC layer retarded the growth of the $Cu_6Sn_5$ IMC layer, and thereby increased the growth rate of the $Cu_3Sn$ IMC layer. In the ball shear test conducted on the Sn-37Pb/Ag-plated Cu joint after aging for 500h, fracturing occurred at the solder/$Cu_6Sn_5$ interface. The shear failure was significantly related to the interfacial adhesion strength between the Pb-rich and $Cu_6Sn_5$ IMC layers. On the other hand, all fracturing occurred in the bulk solder for the Sn-3.5Ag/Ag-plated Cu joint, which confirmed its desirable joint reliability.

• Korean Journal of Metals and Materials
• /
• v.49 no.2
• /
• pp.180-186
• /
• 2011

Isothermal annealing and electromigration tests were performed at $125^{\circ}C$ and $125^{\circ}C$, $3.6{\times}10_4A/cm^2$ conditions, respectively, in order to compare the growth kinetics of the intermetallic compound (IMC) in the Cu/thin Sn/Cu bump. $Cu_6Sn_5$ and $Cu_3Sn$ formed at the Cu/thin Sn/Cu interfaces where most of the Sn phase transformed into the $Cu_6Sn_5$ phase. Only a few regions of Sn were not consumed and trapped between the transformed regions. The limited supply of Sn atoms and the continued proliferation of Cu atoms enhanced the formation of the $Cu_3Sn$ phase at the Cu pillar/$Cu_6Sn_5$ interface. The IMC thickness increased linearly with the square root of annealing time, and increased linearly with the current stressing time, which means that the current stressing accelerated the interfacial reaction. Abrupt changes in the IMC growth velocities at a specific testing time were closely related to the phase transition from $Cu_6Sn_5$ to $Cu_3Sn$ phases after complete consumption of the remaining Sn phase due to the limited amount of the Sn phase in the Cu/thin Sn/Cu bump, which implies that the relative thickness ratios of Cu and Sn significantly affect Cu-Sn IMC growth kinetics.

• Electronic Materials Letters
• /
• v.14 no.6
• /
• pp.678-688
• /
• 2018

The repeated-bending properties of Sn-0.7Cu, Sn-0.3Ag-0.7Cu (SAC0307), and Sn-3.0Ag-0.5Cu (SAC305) solders mounted on flexible substrates were studied using highly accelerated stress testing (HAST), followed by repeated-bending testing. In the Sn-0.7Cu joints, the $Cu_6Sn_5$ intermetallic compound (IMC) coarsened as the HAST time increased. For the SAC0307 and SAC305 joints, the $Ag_3Sn$ and $Cu_6Sn_5$ IMCs coarsened mainly along the grain boundary as the HAST time increased. The Sn-0.7Cu solder had a high contact angle, compared to the SAC0307 and SAC305 solders; consequently, the SAC0307 and SAC305 solder joints displayed smoother fillet shapes than the Sn-0.7Cu solder joint. The repeated-bending for the Sn-0.7Cu solder produced the crack initiated from the interface between the Cu lead wire and the solder, and that for the SAC solders indicated the cracks initiated at the surface, but away from the interface between the Cu lead wire and the solder. Furthermore, the oxide layer was thickest for Sn-0.7Cu and thinnest for SAC305, regardless of the HAST time. For the SAC solders, the crack initiation rate increased as the oxide layer thickened and roughened. $Cu_6Sn_5$ precipitated and grew along the grain and subgrain boundaries as the HAST time increased, embrittling the grain boundary at the crack propagation site.

• Journal of the Microelectronics and Packaging Society
• /
• v.16 no.2
• /
• pp.27-31
• /
• 2009

Sn whiskers can grow from the pure Sn and high Sn-based finish and cause the electrical shorts and failures. Even with the wealth of information on whiskers, we have neither the clear understanding of whisker growth nor methods for its prevention. In this study, the whisker grain roots which connected with intermetallic layer were analyzed by high-resolution transmission electron microscopy (HR-TEM). In the Sn-Cu plated leadframe (LF) that was stored at ambient condition for 540 days, filament-shaped whiskers were grown on the Sn-plated surface and ${\eta}'-Cu_6Sn_5$ precipitates were widely distributed along the grain boundaries at the Sn matrix. The measured of the lattice fringes at the ${\eta}'-Cu_6Sn_5$ was $4.71{\AA}$ at the coarse grain and $2.91{\AA}$ at the fine grain. The $Cu_3Sn$ which generates the tensile stresses was not observed. The formation of $Cu_6Sn_5$ precipitates and intermetallic layer were strongly related to whisker growth, but, the whisker growth tendency does not closely relate with the geometric morphology of irregularly grown intermetallic compound (lMC).

• Korean Journal of Materials Research
• /
• v.13 no.2
• /
• pp.133-136
• /
• 2003

Sn-2.5Cu alloy layers were deposited on the Alloy 42 lead-frame substrates by the electroplating method, and their microstructures, adhesion strength, and electrical resistivity were measured to evaluate the applicability of Sn-Cu alloy as a surface finishing material of electronic parts. The Sn-2.5Cu layers were electroplated in the granular form, and composed of pure Sn and Cu$_{6}$Sn$_{5}$ intermetallic compound. Surfaces of the electroplated Sn-2.5Cu layers were rather rough and also the thickness variance was large. The adhesion strength of the Sn-2.5Cu electroplated layers was highly comparable to that of the electroplated Cu alloy layer and the electrical conductivity was about 10 times higher than the pure Sn. After the 20$0^{\circ}C$ 30 min. annealing of the electroplated Sn-2.5Cu layers, the surface roughness was reduced, and adhesion strength and conductivity were improved. These results showed the Sn-Cu alloys can be used as an excellent surface finishing material.ial.

• Journal of Korea Foundry Society
• /
• v.22 no.2
• /
• pp.89-96
• /
• 2002

This study examined the effects of adding Zn to Sn-3.5Ag solder on the microstructure changes and behavior of interface reaction of the solder joint with Cu substrate. The solder/Cu joints were examined with microscope to observe the characteristics of microstructure changes and interfacial reaction layer with aging treatment for up to 120 days at $150^{\circ}C$. Results of the microstructure changes showed that the microstructures were coarsened with aging treatment, while adding 1%Zn suppresses coarsening microstructures. The Sn-3.5Ag/Cu had a fast growth rate of the reaction layer in comparison with the Sn-3.5Ag-1Zn at the aging temperature of $150^{\circ}C$. Through the SEM/EDS analysis of solder joint, it was proved that intermetallic layer was $Cu_6Sn_5$ phase and aged specimens showed that intermetallic layer grew in proportion to $t^{1/2}$, and the precipitate of $Ag_3Sn$ occur to both inner layer and interface of layer and solder. In case of Zn-containing composite solder, $Cu_6Sn_5$ phase formed at the side of substrate and Cu-Zn-Sn phase formed at the other side in double layer. It seems that Cu-Zn-Sn phase formed at solder side did a roll of banrier to suppress the growth of the $Cu_6Sn_5$ layer during the aging treatment.

• Journal of the Microelectronics and Packaging Society
• /
• v.14 no.4
• /
• pp.27-36
• /
• 2007

In this study, we investigated the interfacial reactions between various Sn-Ag-Cu(SAC) solder alloys and ENIG(Electroless Ni Immersion Gold) and Cu-OSP(Organic Solderability Preservative) pad finish. In the case of the interfacial reaction between Sb added SAC solder and ENlf thinner P-rich Ni layer was formed at the interface. In the case of the interfacial reaction between Ni added SAC solder and Cu-OSP, the uniform $Cu_6Sn_5$, intermetallic compounds(IMCs) were formed and $Cu_6Sn_5$ grain did not grow after multiple reflows. Thinner $Cu_3Sn$ IMCs were farmed at the interface between $Cu_6Sn_5$ and Cu-OSP after $150^{\circ}C$ thermal aging.