Microstructure, isothermal and thermomechanical fatigue behaviour of leaded and lead-free solder joints

Mohammad Ghaleeh*, Ahmad Baroutaji, Mansour Al Qubeissi

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


The reliability of solder joints is a critical issue in the microelectronics industry. The requirement of permanent electrical and thermal connections between solder alloys and the various components of a surface mount device is dependent upon the mechanical integrity of the solder and its interfaces. Accordingly, in this paper, the reliability of lead-free, Sn-3.8Ag-0.7Cu, and leaded, Sn-37Pb, solder alloys was investigated under both thermal-mechanical fatigue (TMF) and isothermal mechanical fatigue (IF) conditions. The investigation included material characterisation and fatigue testing on 4-ball grid array (BGA) specimens. The IF tests were carried out under load control at three different temperatures including Room Temperature (RT), 35 °C and 75 °C. Also, a set of ‘not-in-phase’ (nIP), ‘in-phase’ (IP) and ‘out-of-phase’ (OoP) combined thermal and mechanical cycling tests were carried out to investigate the TMF behaviour of the solders. The stress-life curves for each test condition were generated and then compared taking into account the observations on microstructure. It was found that the IF and TMF performance of Sn-3.8Ag-0.7Cu alloy was better than Sn-37Pb alloy when expressed as stress-life curves. Additionally, the Sn-3.8Ag-0.7Cu was less susceptible to the changes in temperature. This study provides a comprehensive insight into the reliability of solder alloys under a wide range of loading conditions.

Original languageEnglish
Article number104846
JournalEngineering Failure Analysis
Early online date11 Aug 2020
Publication statusPublished - Nov 2020


  • Ball grid array
  • Isothermal fatigue
  • Lead-free
  • Shear stress
  • Solder joints
  • Thermo-mechanical fatigue


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