Thermodynamics-Aided Alloy Design and Evaluation of Pb-free Solders for High-Temperature Applications

Abstract

High temperature solders that will not be affected in the subsequent thermal treatment are required in the step soldering process of multi-chip module (MCM) packaging. High-Pb solder alloys such as 95Pb-5Sn (numbers are all in mass% unless specified otherwise) are currently being used for this purpose. However, the development of the Pb-free solder alloy for high temperature applications is needed due to environmental issues. The solder alloys of Bi-Ag, Sn-Sb and Au-Sb-Sn systems are considered as candidates in this study. Aided by thermodynamic calculations, several specific compositions have been chosen and they were investigated in terms of melting behavior, electrical resistivity, wetting angle and hardness. The Bi-Ag alloy exhibited poor electro-conductivity while the Sn-Sb system had low melting temperatures. The ternary Au-Sn-Sb solder alloy shows prospects for high temperature applications in spite of poor wetting properties.

Interfacial Properties of Zn–Sn Alloys as High Temperature Lead-Free Solder on Cu Substrate

“…[1][2][3][4][5] Au-and Bi-based alloys as representative high temperature lead-free alloys also have been faced with several serious problems during using electronic industries until now. [1][2][3][4][5][6][7] The high cost and the formation of massive intermetallic compound (IMC) or the brittle nature of Bi prevents widespread adoption of Au-and Bi-based alloys. High lead-bearing solders need to be replaced by lead-free alloys as soon as possible, because the use of high lead solder influences the recycling possibilities of electronic circuit boards.…”

“…Conventional high temperature solders have been high lead-bearing alloys, typically 85-97 mass%Pb-Sn, and Au-or Bi-based alloys. [1][2][3][4][5] Over the last 10 years, scientists have made much effort in respect to developing substantially lead-free solders to replace leadbearing solders, eutectic Sn-37 mass%Pb. Successful developments have almost led to the point where lead-free electronics assembly is accomplished.…”

Wetting of Cu Pads by Bi-2.6Ag-xCu Alloys and Phase Equilibria in the Ag-Bi-Cu System

“…It was 6 revealed that the addition of Sn to Bi-Ag eutectic improves its wetting on copper. The data on wetting of Cu by Bi-rich Bi-Ag alloys are limited [6][7][8][9] and differ with respect to reported values of the wetting angle. One important factor affecting quality of the joint, in particular its mechanical properties, is the structure of connection at the interface.…”

Shear Strength and Dsc Analysis of High-Temperature Solders

“…The type Pb-5Sn and Pb-10Sn solders are typical representatives of this group of solders with a high Pb content. Following the publications of Suganuma et al [1] and Kim et al [2] the solders based on Bi-Ag, Au-Sn, Sn-Sb, and Zn-Al alloys were selected as the basic ones for high-temperature lead-free solders.…”