Results show that while solid solution-strengthening by additions of Sb is effective, it is not sufficient, and other strengthening options through the introduction of additional precipitates and solid solution strengthening using Bi is most desirable. Alloys are being designed to improve toughness of interfacial intermetallic layers and provide solid solution strengthening to compensate for the loss of strength once the Ag3Sn particles coarsen. In applications such as the engine compartment of motor vehicles where extreme thermal cycles and long dwell are common, it has been necessary to look for strengthening mechanisms that better survive extremes of temperature and strain. New third generation lead free alloys are being targeted for use in harsh environments requiring resistance to both thermal and mechanical loading. Hence, newly developed solder alloys with Sn/Ag/Cu/Bi/Ni elements and Cu-OSP substrate surface finishes will be reviewed in the second section of the article. Typical solder alloys on Ni/Au surface finish were not designed for automotive application to fulfill the requirement of board level reliability. However, with market demands on automotive electronics get strong in recent years, solder joint reliability is being reviewed and discussed, especially in temperature cycling performance. SAC405 and LF35 are developed for specific requirements such as SAC405 owns better temperature cycling performance, whereas LF35 gives excellent drop performance compared to SAC305 or SAC302. With respect to second-level interconnects, SAC305 and SAC302 solder alloys give a balance performance between temperature cycling testing and drop testing, which are widely used in many field applications, such as mobile, consumer and computer. In the first section of the article, the influence of a variety of factors were reviewed, which includes reliability performance and interfacial reaction that determines the performance of Au-coated Ag to reach for developing high reliability of bonded devices. However, a new bonding wire material, Au-coated Ag, is recently developed to be an alternative solution which gives comparable performance, but lower cost compared to Au wire. Evolutions of bonding wires from gold (Au) to silver (Ag) or copper (Cu) have been reported and studied in previous literatures for low-cost solution, but Au wire still gives highest rating in terms of the performance of temperature humidity test, high temperature storage, and bond-ability, etc. The main motivation of this review is to study the evolution of first and second level of interconnect materials used in memory device semiconductor packaging.
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