Relationship Between Mechanical Properties of Lead-Free Solders and Their Heat Treatment Parameters

Abstract

The research was undertaken to establish mechanical properties of as-cast and heat-treated Sn-Zn-based alloys of binary and ternary systems as candidates for lead (Pb)-free solder materials for high-temperature applications. The heat treatment of as-cast alloys was made under different combinations of processing parameters (168 h/50°C, 42 h/80°C, and 24 h/110°C). The systematic study of structure-property relationships in Sn-Zn, Sn-Zn-Ag, and Sn-Zn-Cu alloys containing the same amount of Zn (4.5, 9, 13.5 wt.%) and 1 wt.% of either Ag or Cu was conducted to identify the effects of chemical composition and heat treatment processing parameters on the alloy microstructure and mechanical behavior. Structural characterization was made using optical microscopy and scanning electron microscopy techniques coupled with EDS analysis. Mechanical properties (initial YoungÕs modulus E, ultimate tensile strength UTS, elastic limit R 0.05 , yield point R 0.2 , elongation A 5 , and necking Z) were determined by means of static tensile tests. All the examined Sn-Zn-based alloys have attractive combination of mechanical characteristics, especially tensile strength, having values higher than that of common leaded solders and their substitutes of Pb-free SAC family. The results obtained demonstrate that the Sn-Zn-based alloys present competitive Pb-free solder candidates for high-temperature applications.

Microstructural Aspects of Fatigue Parameters of Lead-Free Sn-Zn Solders with Various Zn Content

“…The alloys were cast in the Foundry Research Institute in Cracow as ready-for-use tensile test pieces [3].…”

“…In the field of mechanical testing they included only static tensile test [3], and also according to this test, the best properties were obtained in the eutectic alloy. Studies have shown that for the same three alloys, higher values of the mechanical parameters were obtained in the static tensile test than in the fatigue test.…”

“…Based on that research, the chemical compositions of binary, ternary and quaternary alloys were developed. The selected useful properties of those alloys were also examined and the results were disclosed in subsequent publications [e.g [3][4][5]. It should also be emphasized that progress in the studies of lead-free solders has resulted in the creation of a database of materials comprising lead-free solders and combinations thereof ( [6]).…”

Wetting and the reaction of multiwalled carbon nanotube-reinforced composite solder with a copper substrate

“…4. From the microstructural examination, the reaction between the solder and copper substrate resulted in the formation of a (Cu,C) 6 Sn 5 IMC at the interface. During thermal aging, the IMC layer thickness increased with increasing time and temperature.…”

“…With the development and the basic functions of solders having changed, not only do solders have to function in their traditional role as reliable electrical interconnects, lead-free solders must also meet mechanical requirements as well as be reliable [3][4][5][6][7].…”