In Case You Missed It
Lead-Free Solder
“Measurement of Mixing Enthalpies for Sn-Bi-Sb Lead-Free Solder System”
Authors: Vikrant Singh, et al.
Abstract: Predictions of the thermodynamic behavior of higher-order multicomponent alloys from thermodynamic data of binary and ternary systems have been proven very crucial, as it is extremely challenging to investigate thermodynamic properties of higher-order systems. Therefore, it is necessary to assess thermodynamic data of various binary and ternary systems that are important to lead-free solder applications. The literature lacks thermodynamic information for some lead-free systems. Tin-bismuth-antimony (SnBiSb) is a good option as a solder ternary system free of lead. The integral and partial mixing enthalpies of a SnBiSb system were determined using a drop-solution calorimeter. At 923K, 973K, and 1023K, calorimetric measurements of the Sn-Bi-Sb system were made along five of the cross-sections. Pieces of pure tin were dropped into molten Sb0.25Bi0.75, Sb0.50Bi0.50, Sb0.75Bi0.25 alloys, bismuth into Sb0.50Sn0.50, and antimony into Bi0.50Sn0.50. Using the calorimetric data, partial and integral thermodynamic properties were determined. The integral mixing enthalpy was used to plot iso-enthalpy curves. It was found that the mixing enthalpies were temperature independent. The substitutional solution Redlich-Kister-Muggianu model was used to derive the interaction parameter based on ternary enthalpy values and, to obtain these parameters, a least square fitting model was used. When the estimated and measured values were compared, it was found that there was good agreement among them. (Journal of Electronic Materials, July 2023, https://doi.org/10.1007/s11664-023-10579-4)
Solder Joint Reliability
“Mechanical Characterization of SAC305 and SnPb36Ag2 BGA Assemblies Under Static Flexural Loading”
Authors: Jean Baptiste Libot, Olivier Dalverny, Joël Alexis and Jeremy Bosq
Abstract: Static bending-induced solder joints damage is a main reliability concern for aerospace and military industries whose printed circuit board assemblies (PCBAs) are required to remain functional under flexural loading. To dissipate heat in an equipment, it is common to install thermal gap pads on electronic packages. When compressing thermal gap pads during the fixture process, the PCBA can bend and solder joints can therefore crack if the deflection is too significant. This paper reports the durability of 96.5Sn-3.0Ag-0.5Cu (SAC 305) and 62Sn-36Pb-2Ag (SnPb36Ag2) ball grid array (BGA) assemblies under static flexural loading at -55°, 20° and 125°C. As electronics equipment can be stored at high-temperature for prolonged durations, some SAC 305 test vehicles were also aged at 125°C for 192 hr. For each test configuration, the bending tests were conducted at a ramp-rate of 2mm/min and the central displacement-to-failure was measured. Finite element modeling (FEM) analysis was conducted considering a global-local approach and the transfer function between the central displacement-to-failure and the local PCB strain near the critical solder joints were determined for each test configuration. The results give the necessary data for designers to assess whether a specific PCBA design subjected to static bending is at risk. (Journal of Surface Mount Technology, vol. 36, no. 1, 2023, https://doi.org/10.37665/smt.v36i1.34)
Sustainability
“Recyclable Paper‐Based Electronics”
Authors: Gerhard Domann, et al.
Abstract: Millions of tons of electronic waste are produced in the EU every year. With a novel approach, the new EU project “CircEl-Paper” could sustainably improve the recycling process for electronics in the future. Globally, 53 million tons were produced, only about 17% of waste was verifiably collected and properly disposed of, according to the Global E-Waste Monitor 2020 – a large amount of valuable materials produced at great expense is thus regularly lost. The CircEl-Paper project team will demonstrate the diverse areas in which paper-based PCB technology can be applied with three use cases from the fields of medicine, logistics and consumer electronics: A medical sensor for measuring glucose levels on the skin, packaging with an integrated time-temperature indicator (TTI) or greeting cards that play music exemplify the technology’s performance and adaptability. (Project CircEl-Paper, https://circelpaper.eu)
“Sustainability Considerations for Organic Electronic Products”
Authors: Iain McCulloch, et al.
Abstract: The development of organic electronic applications has reached a critical point. While markets, including the Internet of Things, transparent solar and flexible displays, gain momentum, organic light-emitting diode displays lead the way, with a current market size of over $25 billion, helping to create the infrastructure and ecosystem for other applications to follow. It is imperative to design built-in sustainability into the materials selection, processing and device architectures of all these emerging applications, and to close the loop for a circular approach. In this perspective, the authors evaluate the status of embedded carbon in organic electronics, as well as options for more sustainable materials and manufacturing, including engineered recycling solutions that can be applied within the product architecture and at the end of life. This emerging industry has a responsibility to ensure a “cradle-to-cradle” approach. The authors highlight that ease of dismantling and recycling needs to closely relate to the product lifetime, and that regeneration should be facilitated in product design. Materials choices should consider the environmental effects of synthesis, processing and end-product recycling as well as performance. (Nature Materials, June 2023, https://doi.org/10.1038/s41563-023-01579-0) 
