Technical Abstracts
In Case You Missed It
Connectors
“Impact of Thermal Cycling on Cu Press-Fit Connector Pin Interconnect Mechanical Stability”

Authors: Yeon-Jin Baek, et al.

Abstract: Press-fit technology provides an electrical and mechanical connection by inserting a press-fit pin into a through-hole of a printed circuit board. Recently, there has been wide interest in the long-term reliability of the press-fit pin interconnect of electric systems under various thermo-mechanical conditions due to the integration and minimization of electric devices. Compared to a ball grid array interconnection, press-fit pin connector interconnects are expected to have a different degradation mechanism. In this study, the impact factors affecting the reliability and degradation mechanism of press-fit connector pins were investigated. The bonding strength of inserted pins was measured before and after thermal cycling at room temperature and elevated temperature conditions. The bonding strength of the press-fit pins to the PCB copper wall was observed to increase after thermal cycling. The development of an intermetallic compound between the Cu pin and the Cu wall was observed. The microstructure of the press-fit connector pin and the Cu wall and localized stress and strain levels were analyzed by electron backscattered diffraction, including inverse pole figure maps, grain reference orientation deviation maps, and strain contouring maps. Along with the increase of pull strength after thermal cycling, an increase in residual stresses was observed, while strain contouring maps exhibited a decrease in localized strains at the interface between a press-fit pin and copper wall of a PCB. (Journal of Electronic Materials, Jun. 8, 2021, https://link.springer.com/article/10.1007/s11664-021-09045-w)

Failure Analysis
“First-Principles Prediction of Electronic Transport in Fabricated Semiconductor Heterostructures via Physics-Aware Machine Learning”

Authors: Artem K. Pimachev and Sanghamitra Neogi

Abstract: First-principles techniques for electronic transport property prediction have seen rapid progress in recent years. However, it remains a challenge to predict properties of heterostructures incorporating fabrication-dependent variability. Machine-learning (ML) approaches are increasingly being used to accelerate design and discovery of new materials with targeted properties and extend the applicability of first-principles techniques to larger systems. However, few studies exploited ML techniques to characterize relationships between local atomic structures and global electronic transport coefficients. In this work, the authors propose an electronic-transport-informatics (ETI) framework that trains on ab initio models of small systems and predicts thermopower of fabricated silicon/germanium heterostructures, matching measured data. They demonstrate application of ML approaches to extract important physics that determine electronic transport in semiconductor heterostructures, and bridge the gap between ab initio accessible models and fabricated systems. The authors anticipate ETI framework would have broad applicability to diverse materials classes. (npj Computational Materials, Jun. 17, 2021, www.nature.com/articles/s41524-021-00562-0)

Soldering
“Pioneering Chemistry Approach Could Lead to More Robust Soft Electronics”

Authors: Xu Han, et al.

Abstract: Solder joints with different microstructures are obtained by ultrasonic-assisted soldering. To analyze the effect of ultrasounds on Cu6Sn5 growth during the solid–liquid reaction stage, the interconnection heights of solder joints are increased from 30 to 50µm. The authors found scallop-like Cu6Sn5 nucleate and grow along the Cu6Sn5/Cu3Sn interface under the traditional soldering process. By comparison, some Cu6Sn5 are formed at Cu6Sn5/Cu3Sn interface and some Cu6Sn5 are randomly distributed in Sn when an ultrasonic-assisted soldering process is used. The reason for the formation of non-interfacial Cu6Sn5 has to do with the shockwaves and micro-jets produced by ultrasonic treatment, which leads to separation of some Cu6Sn5 from the interfacial Cu6Sn5 to form non-interfacial Cu6Sn5. The local high pressure generated by the ultrasounds promotes the heterogeneous nucleation and growth of Cu6Sn5. Also, some branch-like Cu3Sn formed at the Cu6Sn5/Cu3Sn interface; the interfacial Cu3Sn in ultrasonic-assisted solder joints present a different morphology from the wave-like or planar-like Cu3Sn in conventional soldering joints. Meanwhile, some non-interfacial Cu3Sn are present in non-interfacial Cu6Sn5 due to reaction of Cu atoms in liquid Sn with non-interfacial Cu6Sn5 to form non-interfacial Cu3Sn. Overall, full Cu3Sn solder joints are obtained at ultrasonic times of 60 sec. The obtained microstructure evolutions of ultrasonic-assisted solder joints in this paper are different from those reported in previous studies. Based on these differences, the effects of ultrasounds on the formation of non-interfacial IMCs and growth of interfacial IMCs are systematically analyzed by comparing with the traditional soldering process. (Soldering & Surface Mount Technology, Jul. 12, 2021, www.emerald.com/insight/content/doi/10.1108/SSMT-06-2020-0026/full/html)

This column provides abstracts from recent industry conferences and company white papers. Our goal is to provide an added opportunity for readers to keep abreast of technology and business trends.