Myeong-Hyeok Jeong

Effect of Cu–Sn intermetallic compound reactions on the Kirkendall void growth characteristics in Cu/Sn/Cu microbumps

Growth behaviors of intermetallic compounds (IMCs) and Kirkendall voids in Cu/Sn/Cu microbump were systematically investigated by an in-situ scanning electron microscope observation. Cu–Sn IMC total thickness increased linearly with the square root of the annealing time for 600 h at 150 °C, which could be separated as first and second IMC growth steps. Our results showed that the growth behavior of the first void matched the growth behavior of second Cu6Sn5, and that the growth behavior of the second void matched that of the second Cu3Sn. It could be confirmed that double-layer Kirkendall voids growth kinetics were closely related to the Cu–Sn IMC growth mechanism in the Cu/Sn/Cu microbump, which could seriously deteriorate the mechanical and electrical reliabilities of the fine-pitch microbump systems.

Effects of Temperature and Current Stressing on the Intermetallic Compounds Growth Characteristics of Cu Pillar/Sn--3.5Ag Microbump

The mechanical and electrical reliability of Cu/Sn–3.5Ag microbumps under both annealing and current-stressing conditions were systematically evaluated. Intermetallic compound (IMC) growth was controlled by a diffusion-dominant mechanism and a chemical reaction-dominant mechanism with annealing and current-stressing time, respectively. The transition time for IMC phase change had an inverse relationship with current density because of the electron wind force under current stressing conditions. The shear strength and IMC thickness increased monotonically with annealing time at 150 °C, while the amount of solder decreased. It was clearly revealed that strong correlations exist between IMC growth kinetics, shear strength, and fracture modes in Cu/solder microbumps.

Effect of Interfacial Microstructures on the Bonding Strength of Sn–3.0Ag–0.5Cu Pb-Free Solder Bump

The effect of interfacial microstructures on the bonding strength of Sn–3.0Ag–0.5Cu Pb-free solder bumps with respect to the loading speed, annealing time, and surface finish was investigated. The shear strength increased and the ductility decreased with increasing shear speed, primarily because of the time-independent plastic hardening and time-dependent strain-rate sensitivity of the solder alloy. The shear strength and toughness decreased for all surface finishes under the high-speed shear test of 500 mm/s as a result of increasing intermetallic compound (IMC) growth and pad interface weakness associated with increased annealing time. The immersion Sn and organic solderability preservative (OSP) finishes showed lower shear strength compared to the electroless nickel immersion gold (ENIG) finish. With increasing annealing time, the ENIG finish exhibited the pad open fracture mode, whereas the immersion Sn and OSP finishes exhibited the brittle fracture mode. In addition, the shear strength of the solder joints was correlated with each fracture mode.

Effects of surface finish conditions on interfacial reaction characteristics and mechanical reliability of novel Sn-1.2Ag-0.7Cu-0.4In solder bump

The effect of interfacial microstructures on the bonding strength of Sn-1.2Ag-0.7Cu-0.4In Pb-free solder bumps with respect to the loading speed, annealing time, and surface finish was investigated. The shear force increased and the ductility decreased with increasing shear speed, primarily because of the time-independent plastic hardening and time-dependent strain-rate sensitivity of the solder alloy. The shear force and shear energy decreased for each surface finish under the high-speed shear test of 1000 mm/s as a result of increasing intermetallic compound (IMC) growth and pad interface weakness associated with increased annealing time. The organic solderability preservative (OSP) finish showed lower shear force compared to the electroless nickel immersion gold (ENIG) finish. With increasing annealing time, the ENIG finish and OSP finishes exhibited the pad open fracture.

Comparisons of mechanical reliabilities of Sn-3.0Ag-0.5Cu solder between ENIG and immersion Sn pad finishes

The effects of electroless nickel immersion gold (ENIG) and immersion Sn pad finishes on the shear strength of Sn-3.0Ag-0.5Cu solder joints were investigated under the various loading speeds of 0.2∼1,000 mm/s. shear strength increased with increasing shear speed, while ductility and toughness decreased, while immersion Sn finish showed lower shear strength rather than ENIG finish. Overall, ENIG finish showed ductile to brittle fracture mode transition with increasing shear speed while immersion Sn finish only showed increasing brittle fracture mode ratio. Therefore, strong interfacial adhesion of ENIG finish rather than immersion Sn finish seems to be related to stronger bonding strength and also higher toughness of ENIG finish.

Interfacial microstructure and mechanical reliability of Cu pillar/Sn-3.5Ag bump for 3D packages

Interfacial microstructure and mechanical reliability of Cu pillar/Sn-3.5Ag microbumps during annealing conditions were systematically and quantitatively evaluated. The IMC growth followed a linear relationship with the square root of the annealing time, which means that the IMC growth was controlled by a diffusion mechanism. The shear strength and IMC thickness increased quadratically with annealing time at 150°C, while the amount of solder decreased. It was clearly revealed that there exist strong correlations among IMC growth kinetics, shear strength, and fracture modes in Cu/solder microbumps.

Current stressing effects on the reliability of Cu pillar bump with shallow solder

The intermetallic compound (IMC) growths of Cu pillar bump with shallow solder (thin Sn thickness) were investigated during annealing or current stressing condition. After reflow, only Cu6Sn5 was observed, but Cu3Sn formed and grew at Cu pillar/Cu6Sn5 interface with increasing annealing and current stressing time. The kinetics of IMC growth changed when all Sn in Cu pillar bump was exhausted. The complete consumption time of Sn phase in electromigration condition was faster than that in annealing condition. Under current stressing condition, intermetallic compound growth was significantly enhanced mainly due to the joule heating effects. Kirkendall void was observed at the interface of Cu pillar/Cu3Sn and it affected the mechanical reliability of Cu pillar bumps, which was estimated by die shear test.

Effect of Bonding Process Conditions on the Interfacial Adhesion Energy of Al-Al Direct Bonds

【3-D IC integration enables the smallest form factor and highest performance due to the shortest and most plentiful interconnects between chips. Direct metal bonding has several advantages over the solder-based bonding, including lower electrical resistivity, better electromigration resistance and more reduced interconnect RC delay, while high process temperature is one of the major bottlenecks of metal direct bonding because it can negatively influence device reliability and manufacturing yield. We performed quantitative analyses of the interfacial properties of Al-Al bonds with varying process parameters, bonding temperature, bonding time, and bonding environment. A 4-point bending method was used to measure the interfacial adhesion energy. The quantitative interfacial adhesion energy measured by a 4-point bending test shows 1.33, 2.25, and

Effects of annealing and current stressing on the intermetallic compounds growth kinetics of Cu/thin Sn/Cu bump

6.44\;J/m^2

Correlations between interfacial reactions and bonding strengths of Cu/Sn/Cu pillar bump

for 400, 450, and