Development of Sn-Based, Low Melting Temperature Pb-Free Solder Alloys

Abstract

Low temperature, Sn-based Pb-free solders were developed by making alloy additions to the starting material, 96.5Sn-3.5Ag (mass%). The melting behavior was determined using Differential Scanning Calorimetry (DSC). The solder microstructure was evaluated by optical microscopy and electron probe microanalysis (EPMA). Shear strength measurements, hardness tests, intermetallic compound (IMC) layer growth measurements, and solderability tests were performed on selected alloys. Three promising ternary alloy compositions and respective solidus temperatures were: 91.84Sn-3.33Ag-4.83Bi, 212 C; 87.5Sn-7.5Au-5.0Bi, 200 C; and 86.4Sn-5.1Ag-8.5Au, 205 C. A quaternary alloy had the composition 86.8Sn-3.2Ag-5.0Bi-5.0Au and solidus temperature of 194 C. The shear strength of this quaternary alloy was nearly twice that of the eutectic Sn-Pb solder. The 66Sn-5.0Ag-10Bi-5.0Au-10In-4.0Cu alloy had a solidus temperature of 178 C and good solderability on Cu. The lowest solidus temperature of 159 C was realized with the alloy 62Sn-5.0Ag-10Bi-4.0Au-10In-4.0Cu-5.0Ga. The contributing factor towards the melting point depression was the composition of the solid solution, Sn-based matrix phase of each solder.

Microstructural development and mechanical properties of a near-eutectic directionally solidified Sn–Bi solder alloy

“…The advantages of Sn-Bi solders include good joint strength, excellent creep resistance, low coefficient of thermal expansion, good wettability, and low cost. However, segregation problems are recognized as a potential disadvantage [3,4]. For low-temperature applications, Bi-Sn eutectic or near-eutectic compositions with or without additions of alloying elements are considered interesting possibilities.…”

Calorimetric measurements of the ternary Ag–Au–Sn system

“…The 86.4Sn-5.1Ag-8.5Au alloy has a melting point of 205 • C, according to Vianco et al [3], which is much closer to the eutectic temperature of the 63Sn-37Pb of 183 • C than the one of the different SAC (Sn-Ag-Cu) solders.…”

Microstructure and Mechanical Properties of Sn58Bi Components Prepared by Laser Beam Powder Bed Fusion

“…The SnBi alloy and other low melting point alloys have aroused great interest among researchers for many years in view of their distinct applications, including solder alloys, melting model casting, tube bulging, rapid mold preparation and so on [1][2][3][4]. Eutectic Sn58Bi (wt%) alloy with a melting point of 139 • C is a typical low melting point alloy, and it is considered potentially promising as a lead-free solder alloy [5,6].…”