Authors:

Diego Jimenez Rivera

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About Paper:

In modern microelectronics, most interconnections for devices are fabricated using high melting point Tin-Silver-Copper (SAC) or low melting temperature Tin-Bismuth (SnBi) solder alloys. These play an important role in the operation of microelectronic devices from cell phones and household appliances to satellites and rockets, where if one single connection is damaged, performance is reduced significantly, even causing failure. Solder alloys must therefore be as reliable as possible. However, a big challenge faced is thermal reliability, which contributes to microelectronic device failure when semiconductors heat up and cool down, and in harsh use environments. It is well known that aging of solder joints can lead to changes in their performance; however, there is insufficient data on why and how aging behavior occurs to improve the reliability of the solder alloys. By studying how solidification affects microstructure changes after soldering and aging, a thorough guide can be made for improving alloy selection. Test samples consist of Sn-Bi and SAC solder balls applied on printed circuit boards with OSP and ENIG surface finishes using different reflow profiles, then aged at room temperature from 0 to 7 days. Polishing is carried out to expose the microstructures of solder joints at the cross-sectional area. Optical microscope and SEM images are taken to carry out microstructure evaluation. By comparing the microstructures between different compositions, substrates, and aging conditions, identifying solidification effects on microstructure with room temperature aging can provide a better baseline for future mechanical and electrical testing in alloy composition selection based on application conditions. Keywords: Lead-Free Solder; Solidification; Thermal Reliability; Room Temperature Aging; Microstructure Development

Source:

Purdue University / 2025

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Co-authors:

Diego Jimenez Rivera