Understanding the Effect of Reflow Profile on the Metallurgical Properties of Tin–Bismuth Solders

Abstract

Sn–Bi alloys are desirable candidates for soldering components on printed circuit boards (PCBs) because of their low melting point and reduced cost. While certain tin–bismuth solders are well characterized many new alloys in this family have been developed which need proper characterization. The following study looks at the behavior of four different Sn–Bi alloys—traditional 42Sn58Bi and 42Sn57Bi1Ag and two new tin–bismuth alloys—in solder paste during the reflow soldering process. Each alloy was processed using different reflow profiles that had varying times above liquidus (TALs) and peak temperatures. The PCBs were then analyzed to see how the processing variables influenced wetting, voiding, microstructure, intermetallic layer composition, and thickness. After analysis, the PCBs were then subjected to thermal cycling experiments to see how reflow profile impacted microstructure evolution. The results demonstrated that reflow profile affects properties such as metal wetting and voiding. It does not however, greatly impact key metallurgical properties such as intermetallic layer thickness.

Mechanical Response of Cu/Sn58Bi-xNi/Cu Micro Solder Joint with High Temperatures

“…It is hoped that alloy solder with a liquidus temperature lower than 200 • C will be able to be used to complete the assembly under low-soldering-temperature conditions. Sn58Bi solder alloy has become a promising leadfree solder due to its many advantages, such as good wettability, low melting point, and low cost [2][3][4]. However, it is a matter of concern that SnBi eutectic solder has some disadvantages, like low ductility, poor drop resistance, and fatigue characteristics [5][6][7][8].…”

A Review on Phase Field Modeling for Formation of η-Cu6Sn5 Intermetallic

“…With the rapid miniaturization of electronic circuits, thermal, electrical, and mechanical loads on three-dimensional integrated circuits (3DIC) that provide the electrical connection between the substrate and the chip have increased [1][2][3][4]. During the soldering process, a layer of IMC is formed at the solder-substrate interface.…”

“…Based on the formation stages of the IMCs, there are mainly two types of IMCs which form during the interfacial reactions on the Cu/Sn/Cu sandwich structure that have been discovered and investigated, η-Cu 6 Sn 5 and ε-Cu 3 Sn. During the soldering process of Cu-Sn solder, the main reactions may happen as follows: 6Cu + 5Sn → Cu 6 Sn 5 (1) Metals 2022, 12, 2043 2 of 12 Cu 6 Sn 5 + 9Cu → 5Cu 3 Sn.…”