Comparative Study on Solid-State and Metastable Liquid-State Aging for SAC305/Cu Joints

Abstract

In order to study the influence of the physical state of solder on the interfacial reaction of dip-soldered Sn-3.0Ag-0.5Cu/Cu system, two kinds of experiments were designed, including: (1) solid-state aging between the solder and Cu substrate; (2) liquid-state aging between the metastable supercooled liquid-state solder and Cu substrate. The aging times were 30, 60, 120 and 180 min, respectively, and the aging temperature was 8°C lower than the melting point of the Sn-3.0Ag-0.5Cu (SAC305) alloy (217°C). The experimental data revealed that the physical state of the solder obviously affected the formation of the intermetallic compound (IMC), and resulted in the difference in the diffusion of atoms on the interface between the SAC305 solder and Cu substrate. The IMC interface after aging for 30 min presents unique characteristics compared with that of the sample after dip soldering. The IMC interface of solid-state aged SAC305/Cu couple is relatively planar, while the IMC interface under metastable supercooled liquid-state aging conditions presents scallop-like shape.

Mathematical modelling of the liquid/liquid mass transfer behaviour in gas stirred ladles

“…The same conclusion was obtained by Kim et al [3] through a water/oil/thymol system. However, in the physical modelling work of Li et al [5], the mass transfer rate decreased with increasing bubble diameter at three different gas flow rates. In his work, the water-mercury system was employed, and the bubble diameter was varied in the range of 1–6 mm.…”

“…Last but not least, the effect of bubble diameter on liquid-liquid mass transfer remains controversial. Opposite conclusions were obtained from different works [3,5,18,23,24].…”

“…Ladle refining is carried out at a high temperature, which is challenging to observe and measure directly, so physical and mathematical modelling are widely used as two essential research methods [2]. Physical modelling was used extensively in the early studies [3][4][5][6][7][8][9][10][11][12]. Thymol has a partition ratio higher than 350 in water/oil systems, which is very similar to the partition ratio of sulphur among steel-slag; thus, thymol is considered an ideal substitute for sulphur [3].…”

Design Optimization of Pillar Bump Structure for Minimizing the Stress in Brittle Low K Dielectric Material Layer

“…As the IMC thickness is small compared with the pillar bump height, and its mechanical properties including the CTE, modulus and Poisson rate are similar with that of Cu, and the loading condition is only one cycle of flip chip reflow, the existence of IMC on the stress distribution on low K material can be neglected. Although in this study IMC has less effect on the stress of low K material during flip chip mount reflow, its harmful effect on the reliability must be considered during service, because the interface of IMC with Cu and Sn is the weak point for fracture generation under fatigue loading in application [3,27].…”

“…The flip chip technology can shrink the packaging size, increase the packaging density, shorten the interconnect length and lower the cost, so this packaging is increasing replace the traditional wire bonding technology. Initially the solder bump was the main selection for interconnect between the chip and substrate, and there are many researches on the performance and reliability of solder bump with different under bump metalization (UBM) structure and solder composition [1][2][3]. In the recent decade, the Cu pillar bump is gaining more market share in the high end packaging [4,5].…”