Review paper  综述文章

A review of lead-free solders for electronics applications
电子应用中无铅焊料的综述

Microwave Hybrid Heating (MHH) is a novel approach for material joining that is gaining attention due to its ability to achieve selective and uniform heating compared to conventional methods. In this experimental study, we prepared and characterized Sn-3.0Ag-0.5Cu nanoparticles. We investigated the interface morphology, phase composition, and mechanical properties of joints fabricated using the nano-Sn-3.0Ag-0.5Cu soldering paste and MHH technique with varying exposure times. Additionally, a reliability assessment was performed on these joints. This research investigated the impact of varying exposure times, ranging from 165 s to 420 s, on both the microstructure and strength of the joints. The joints were successfully produced under conditions of 900 W and 195 s using the MHH technique. Analysis was conducted to assess the joint morphology and mechanical properties of the after undergoing thermal shock tests, aiming to assess the reliability of joints manufactured through the MHH technique. The experimental findings revealed that the shear strength attained its peak value of 44.8 MPa when subjected to a microwave power of 900 W and an exposure time of 195 s. Moreover, the shear strength of MHH joints exhibited a 24.4% decrease after 1200 thermal shocks. Fracture analysis consistently indicated ductile fracture during thermal shocks, with no alteration in fracture mode observed.

Light-emitting diodes (LEDs) are considered an ideal substitute for low-efficiency traditional light sources with broad applications in all scientific disciplines. For the past recent years, several developments and innovations have been reported that strengthen the reliability and thermal efficiency of speeding up the LED packaging process. This paper reviews and summarizes various changes and improvements made to die attachment, wire bonding, phosphor coating, encapsulation processes, and thermal management. It also covers the reasons for choosing the materials at every stage of LED packaging. Moreover, the review reveals a broad scope for future research, particularly on thermal management by nanoparticles and improved light intensity by different synthesized phosphors.

Today, a growing number of third-generation semiconductor-based power devices are used in products that can continuously operate at high temperatures for extended periods of time. Hence, traditional tin-lead and lead-free solders are no longer suitable for modern electronic packaging. A common method is to apply Ag paste for bare Cu–Cu joints under an inert or reductive atmosphere. In this study, the citrate-coated nanosized Ag paste was utilized to generate robust bare Cu–Cu joints under atmospheric conditions. The average size of citrate-coated Ag particles was approximately 4.76 ​nm after being cleaned by deionized water and acetone. The effects of process parameters, such as cleaning, joining temperature, holding time, and joining pressure, on the mechanical properties of the bare Cu–Cu joints were thoroughly investigated. Increasing washing and joining temperatures resulted in a shear strength increase of up to 28.2 ​MPa ​at a joining temperature of 260 ​°C after seven washes. In addition, a holding time of 30 ​min and a joining pressure of 1 ​MPa were selected as optimal process conditions for the application of citrate-coated nanosized Ag paste onto bare Cu–Cu joints. The newly developed Cu–Cu joints showed excellent thermal stability at 150 ​°C using the citrate-coated nanosized Ag paste. After long-term aging, the joints exhibited stability at 250 ​°C for 144 ​h, indicating a good high-temperature reliability for three-dimensional integrated circuits (3D ICs) fabricated under atmospheric conditions.