Characteristics of Reactive Ni 3 Sn 4 Formation and Growth in Ni-Sn Interlayer Systems
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years, the electronics industry has strived to replace lead-based high-temperature solders in packaging due to legal restrictions on these types of alloys. Simultaneously, the requirements for interconnections have increased as 3D assembly and chip technology are now based on SiC instead of Si, which has led to significantly smaller dimensions and miniaturization.[1] In these cases, low-volume interconnections are of high interest where the thickness of the solder layer cannot exceed several microns. A promising joining technique to overcome the above-mentioned issues is the so-called transient liquid phase bonding (TLPB) technique, which makes use of a (thin) interlayer arrangement consisting of a low melting point material sandwiched between two layers with higher melting points. Isothermal solidification is accompanied by the formation of intermetallic compounds (IMC) at the interfaces during processing and is completed after the liquid material is fully consumed.[2] Interlayers with a X-Sn-X (X = Ni, Cu, Ag, Au) stacking sequence are technically very promising. ADRIAN LIS, Postdoctoral Student, CHRISTOPH KENEL, PhD Student, and CHRISTIAN LEINENBACH, Group Head, are with the Advanced Materials Processing Laboratory, Empa, Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstrasse 129, 8600 Du¨bendorf, Switzerland. Contact e-mail: christian.leinenbach@ empa.ch Manuscript submitted October 13, 2015. Article published online March 22, 2016 2596—VOLUME 47A, JUNE 2016
Previous scientific studies have focused on different aspects of the kinetics and morphology of IMC formation within various layer systems to develop reliable and optimized processes for TLPB. Cu-Sn and Ni-Sn systems are especially attractive because of their low material costs. While Cu-Sn systems have been extensively studied by many researchers with regard to TLPB, few studies have examined Ni-Sn systems. According to the binary Ni-Sn phase diagram[3] shown in Figure 1, the first intermetallic target phase within the Ni-Sn system (Ni3Sn4) offers the highest re-melting temperature among the above-mentioned systems, that is, 1067.5 K (794.5 °C). Combining this aspect with the excellent corrosion resistance of Ni makes this system an interesting candidate for high-temperature applications in various industrial fields. In previous studies, different approaches have been developed to assess and analyze the solid–liquid interface reactions in X-Sn systems. Many systems have been developed to study reactions during standard soldering. They are based on the concept that partially considers the reactive features during TLPB when a (near-)eutectic composition of (Ag,Cu,Ni,Pb,Bi)-Sn is deposited on Ni substrates. It has been shown that additional alloying elements in the solder as well as the configuration of the metallization layer can significantly influence the growth kinetics and morphology of IMC formations.[4–9] A study on Ni-Sn IMC formations using Sn3.5Ag0.5Cu solder and electroless NiP layers at 523 K (250 °C) revealed how the addition of P
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