Intermetallic compound (IMC), as an inevitable part between pad and solder, has a severe effect on the strength and reliability of microelectronic interconnection. Here, an investigation was carried out on IMC growth for different devices and complex components. The device-level experiments were conducted with five factors: peak temperature, time duration above solder liquidus temperature, the thickness of solder paste, surface finish types, and package types including BGA and QFP. Meanwhile, four complex components with the same reflow profile were conducted and compared for component-level experiments. A scanning electron microscopy was used to measure the thickness and determine the spatial distribution of the elements through the intermetallic compound. The multivariate analysis of the formation and growth of IMC during reflow soldering was studied based on Nernst-Shchukarev's equation and the results of the experiments. The difference in IMC thickness between BGA and QFP with different factors was discussed and compared separately. The results showed that the peak temperature and time above liquidus played a vital role in the IMC growth and the solder paste thickness and different pad metallization could not be ignored. SEM pictures of the solder and statistical results were revealed that the surface finish type has a marked impact on the formation of the IMC. For PCB with numbers of components, the IMC thickness and uniformity of solder joints at corner and center positions showed some regularity differences. Meanwhile, the bump shape (Cu1-xNix)6Sn5 IMC was observed for small size BGA with ENIG during the reflow process. The results have a significant meaning to optimize its reflow process parameters for complex components, to improve the interconnection reliability in engineering.
Recently, because of regional climate changes and human activities, the risk and intensity of droughts in the upper and middle Huaihe River Basin, China, have increased. These changes in rainfall may have, in turn, had an influence on the pathways of nitrate transport in this predominantly agricultural watershed. In this study, the characteristics of nitrate transport over consecutive dry years in this watershed were examined using records of streamflow and nitrate concentration data that spanned a period of 12 years (2007-2018) that included 3 consecutive dry years (2011)(2012)(2013). The baseflow was separated from the streamflow using a digital filter method and the nitrate loads were estimated using a regression method. The annual discharge and nitrate load in streamflow and baseflow averaged 23.5 billion m 3 and 41.9 kiloton (kt), and 7.4 billion m 3 and 14.7 kt, respectively. Baseflow contributed more to the total discharge and total nitrate load in the consecutive dry years (41.0% of the total discharge and 56.2% of the total nitrate load) than in wet, normal, and single dry years. Averaged over the whole study period, the monthly baseflow nitrate index (BFNI) was higher than 50% in the dry season and lower than 30% in the flood season. Over the study period, the annual baseflow enrichment ratio (BER) ranged from 0.94 to 1.46 and averaged 1.13, and was highest (1.46) in the consecutive dry years. The results suggest that nitrate was mainly transported to surface water via baseflow during dry conditions and that this process was particularly important during the consecutive dry years. Therefore, to protect surface water, measures should be urgently implemented to control nitrate transport in groundwater during consecutive dry years.
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