Low Melting Temperature Solder Materials for Use in Flexible Microelectronic Packaging Applications

Abstract

The increasing application of heat-sensitive microelectronic components such as a multitude of transistors, polymer-based microchips, and so on, and flexible polymer substrates including polyethylene terephthalate (PET) and polyimide (PI), among others, for use in wearable devices has led to the development of more advanced, low melting temperature solders (<150°C) for interconnecting components in various applications. However, the current low melting temperature solders face several key challenges, which include more intermetallic compound formation (thus become more brittle), cost issues according to the addition of supplementary elements to decrease the melting point temperature, an increase in the possibility of thermal or popcorn cracking (reliability problems), and so on. Furthermore, the low melting temperature solders are still required to possess rapid electronic/electrical transport ability (high electrical conductivity and current density) and accompany strong mechanical strength sustaining the heavy-uploaded microelectronic devices on the plastic substrates, which are at least those of the conventional melting temperature solders (180-230°C). Thus, the pursuit of more advanced low melting temperature solders for interconnections is timely. This review is devoted to the research on three methods to improve the current properties (i.e., electrical and thermomechanical properties) of low melting temperature solders: (i) doping with a small amount of certain additives, (ii) alloying with a large amount of certain additives, and (iii) reinforcing with metal, carbon, or ceramic materials. In this review, we also summarize the overall recent progress in low melting temperature solders and present a critical overview of the basis of microscopic analysis with regard to grain size and solid solutions, electrical conductivity by supplementation with conductive additives, thermal behavior (melting point and melting range) according to surface oxidation and intermetallic compound formation, and various mechanical properties.

The role of printed electronics and related technologies in the development of smart connected products

“…Generally, the use of solder (tin-lead) for flexible electronics is restricted since it demands high temperatures (>250 • C) [63,64]. As a result, some solder alternatives that present lower reflow temperatures (<175 • C) based on indium, bismuth, and silver have emerged [65]. Low melting temperature solders (<150 • C) have also been developed and are usually based on tin-indium (Sn-In), tin-bismuth (Sn-Bi), and Bi-Sn-In ternary alloys [66][67][68][69].…”

Study of mechanical properties of indium-based solder alloys for cryogenic applications

“…This is the drive to study these aspects of indium solder alloys. In this work, indium-based solder alloys were developed, which were based on their melting points, as low melting point (below 150°C) and high melting point (above 150°C) (Gouda, 2014; Kim and Yang, 2017). High melting point can be easily achieved by combining indium to elements such as Sn, Zn, Au, Cu and Ag in a binary alloy (Vianco et al , 2004; Msolli et al , 2015; Ervina Efzan and Nur Faziera, 2016; Efzan et al , 2016; Wang et al , 2009), and low melting point can be achieved mostly in eutectic alloy composition of elements such as Bi, Sn, Zn and Ga via binary or ternary alloy development (Chen et al , 2016; Liu et al , 2020; Liu and Tu, 2020).…”

Intermetallic Compound Layer Growth at the Interface between Sn-Ag and ENImAg Surface Finish

“…Low temperatures of solders are needed for electronic supportability in terms of electrical conductivity [1]. It offers a variety of technical benefits such as wettability [2] spreading capabilities, ductility, fatigue resistance [3], [4] mechanical strength as well as reduces the risk of thermal shock [5].…”