Technical Abstracts
In Case You Missed It
Material Procurement
“Selecting Alternate Grade Parts: The Trials and Tribulations”

Authors: Dave Greinke and Christine Metz

Abstract: Selecting a new or replacement alternate-grade part, such as an automotive-grade connector for a military or aerospace system, can be tricky. The best approach uses an already qualified, approved, and preferred part with known reliability and longevity characteristics. However, with lengthening lifecycles for military systems, rapid technology development, material shortages, and other factors, replacements may be needed for parts that are no longer in production or otherwise available. Given this situation, employing established parts management and diminishing manufacturing sources and material shortages (DMSMS) management procedures can assist in finding and selecting alternate-grade parts to fit a system’s need. (Defense Acquisition Magazine, March-April 2021, www.dau.edu/library/defense-atl/blog/Selecting-Alternate-Grade-Parts-The-Trials-and-Tribulations)

Solder Joint Reliability
“Lifetime Prediction of a SiC Power Module by Micron/Submicron Ag Sinter Joining Based on Fatigue, Creep and Thermal Properties from Room Temperature to High Temperature”

Author: Chuantong Chen, et al.

Abstract: Ag sinter joining technology has gained increasing attention for its excellent thermal and mechanical properties, especially for high-temperature applications. This study focuses on the lifetime prediction of a SiC power module by Ag sinter joining based on mechanical properties, including tensile, fatigue, and creep properties from room temperature to 200°C, as well as thermal properties including thermal conduction and the coefficient of thermal expansion. These mechanical properties and thermal properties of sintered Ag paste were evaluated, and the results show mechanical properties of sintered Ag largely depend on the test temperature. The sintered Ag paste tends to soften at high temperature, and the fracture changed from nearly brittle to totally ductile with the testing temperature increase. From the S-N curve, the fatigue is close to the Morrow equation, but not the Coffin-Manson law at room temperature. The finite element simulation of the lifetime based on Morrow’s equation for the sintered Ag layer shows there was a crack occurrence with one fourth the side length after 10,000 cycles from -40° to 200°C, but the crack extension area is less than one-tenth of the sintered Ag layer. (Journal of Electronic Materials, August 2020, https://link.springer.com/article/10.1007/s11664-020-08410-5)

“Mechanical Reliability of Self-Aligned Chip Assembly after Reflow Soldering Process”

Authors: Mohd Najib Ali Mokhtar, M.Z. Abdullah, Abdullah Aziz Saad and Fakhrozi Cheanis

Abstract: This paper focuses on the reliability of the solder joint after the self-alignment phenomenon during reflow soldering. The aim of this study is to analyze joint quality of the self-alignment assemblies of SnAg alloy solder joints with varying silver content. The results from the mechanical reliability study indicate decreasing trends in the shear strength value as misalignment offset increased. For shift mode configuration in the range of 0-300µm, the resulting chip assembly inspection after the reflow process was in line with IPC-A-610G. Statistical analysis shows the solder type variation was insignificant to the shear strength of the chip resistor. The study concludes the fracture occurred partially in the termination metallization at the lower part of the chip resistor. The copper content of the joint on that area shows the crack occurred in the solder joint, and high silver content on the selected zone indicated the fracture happened partially in the termination structure, as the termination structure of the lead-free chip resistor consists of an inner layer of silver and an outer layer of tin. (Soldering & Surface Mount Technology, April 2021, emerald.com/insight/content/doi/10.1108/SSMT-12-2019-0042/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.