| Along with the rapid development of electronic technology, the increasing demand of microelectronic package on high-performance and reliability has already been an urging requirement that will make the devices lighter, thinner and multi-functional. As the core part of a micro-connection structure, every soldered dot is subjected to electric load and heat effect inside and outside the component, during the lifespan of an electronic piece. Therefore, the growth behavior and morphology evolution of intermetallic compound(IMC) formed at the interface of solder joint have become especially essential since it is the only product of such metallurgical bonding. The reliability and service life of an electronic device is directly determined by the IMC’s morphology, thickness and defects. Hence, in this paper, pure tin and Sn3Ag0.5Cu solder alloy were adopted to investigate the growth kinetics and size distribution of IMC under different cooling condition, coupled with the inner link between the IMC’s thickness and thermal conductivity. Main works of this paper and corresponding results are listed as follow:Air cooling and water cooling were performed to investigate the regular pattern of IMC size distribution and growth kinetics. The results show that for the same reaction time, samples undergone water cooling condition experience a slower growth momentum index that compared with air cooling condition. This kind of difference is also applied to the average grain size of Cu6Sn5 phase. The reasonable explanation is that, different with air cooling, the process of crystal precipitation at the frontier of Cu6Sn5 particles was absent in water cooling case. While faceted morphology of Cu6Sn5 particles were detected in water cooling samples mainly because severe temperature gradient resulted from chilling effect formed in solder-bump range from center to edge. Then, the free energy for Cu6Sn5’s growth changed. In brief, the pattern of Cu6Sn5 grain size evolution can be set: competitive growth(perpendicular to substrate direction) â†' homogeneous growth(parallel to substrate direction) â†' competitive growth(perpendicular to substrate direction) â†' homogeneous growth(parallel to substrate direction).In order to investigate the relationship of IMC’s thickness and correlative thermal conductivity, four groups of aging time and aging temperature samples were prepared. The results show that, for the same temperature, the thermal conductivity of solder dot decreased with the increase of aging time; while for the same aging time, the thermal conductivity of solder dot decreased with the increase of aging temperature. The major reason for this is that IMC at the interface thickened either with higher temperature or with longer aging time. According to XRD pattern, only Cu6Sn5 phase formed at the interface in all soldering conditions when pure Cu substrate was used. This indicates that there were no other factors could be considered during the evolution of IMC.New multiple solder alloy was fabricated by adding Mn element into SAC solder. The results show that the degree of supercooling of solder alloy decreased with Mn enrollment, this effect reached the peak when the amount of Mn is 1.0%. Mn addition partly dissolved into solder matrix and Sn2 Mn was dected by the SEM result. The thickness of IMC increased with the increased Mn amount, while 1.0% additions reached the peak. The addition of Mn improved the hardness of solder alloy, which further resulted in a transform of fracture model of solder joint: from plastic fracture to mixed fracture. During the aging treatment, the tensile strength of both SAC/Cu and SACM/Cu joints were improved. |
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