SMTA International Conference Proceedings

Reliability of the Solder Joints: Is a Shear Force a Good Indicator?

Authors: Anna Lifton, Westin Bent, Irina Lazovskaya, Paul Salerno and Frank Andres
Company: Alpha Assembly Solutions
Date Published: 9/22/2019   Conference: SMTA International

Abstract: Residual Shear testing is a commonly adopted reliability test used to predict product lifetime of an assembly during accelerated failure testing such as thermal cycling and thermal shock. This evaluation technique was adapted based on the assumption that the main failure mechanism of the electronic assembly is due to reduction of mechanical strength of the solder joint from continual thermo-mechanical stress leading to increased circuit resistance and an eventual open circuit condition. In recent years, there have been several studies addressing the effect of solder paste volume, thermal cycling regimes, assembly process factors, and alloy composition on solder joint reliability. The work undertaken in this study seeks to highlight how the combination of the parameters listed above can affect shear strength reduction in application.

The test vehicle used includes commonly used component sizes: 0603, 0805, and 1206 imperial chip components. Test vehicles were assembled using different reflow profiles with varying time above liquidus (TAL) and peak temperatures. Paste volumes were varied through stencil thickness and aperture reduction as an additional factor to this study. Solder joint strength was measured using XYZ Tech shear tester. The thermal cycle profile chosen was -40 ºC and +125 ºC with 10 and 20 minute dwell times. The thermal shock profile chosen was -40 ºC and +125 ºC with 3-minute dwell time. Solder joint strength was measured at selected intervals and microstructural characterization and intermetallic growth were monitored. The solder joint reliability data was correlated to thermal cycling type, dwell time, alloy composition and printed solder paste volume. This work seeks to provide basic guidelines and recommendations for specifying assembly and test parameters to ensure consistency across multiple data sets.

Key Words: 

solder joint reliability, solder paste volume, shear strength, and solder joint inspection

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