COMPUTATIONAL RESEARCH PROGRESS IN APPLIED SCIENCE & ENGINEERING (CRPASE) CRPASE: TRANSACTIONS OF MECHANICAL ENGINEERING Journal homepage: http://www.crpase.com CRPASE: Transactions of Mechanical Engineering, Vol. 06(04), 281-287, December 2020 ISSN 2423-4591 Research Article Comparative Study of Physics of Failure Assessments of Thermomechanical Fatigue for Solder Joints in Multichip Module Under Different Conditions Cheng-Geng Huang  School of Intelligent Systems Engineering, Sun Yat-sen University, China Keywords Abstract Thermo-mechanical reliability, Creep-fatigue failure, Qualification tests, Solder joints, Multi-chip module. A multi-chip module (MCM) which is integrated by multiple integrated circuits (IC) into a unified substrate can significantly reduce the interconnection spacing between various chips and enhance the electrical characteristics. Despite multi-chip module’s greater performance compared with traditional encapsulation, the corresponding problem is mainly induced by thermo-mechanical, and the reliability assessment has also been a critical issue in the electronic industry. The creep-fatigue failure of solder joints under cyclic temperature fluctuations, which is caused by both ambient temperature changes and internal power cycling, plays an important role in the thermo-mechanical reliability of the MCM. In order to assess the influence of cyclic temperature loading profiles on the fatigue life of the solder joints, three different kinds of temperature-related qualification tests, i.e. accelerated temperature cycles (ATC), thermal shock cycles and modified temperature cycles with 10- minutes dwell period, are utilized in the finite element analysis (FEA). Using the FEA method, we can obtain the critical solder joints located in the outer corner of the substrate in MCM and the specific failure location of the solder joint, which is validated by the optical micrograph. Furthermore, based on the energy-partitioning damage model, a comparative analysis of the fatigue life of critical solder joints under various temperature loading profiles is made. The results obtained can improve the design and manufacture in the field of microelectronics encapsulation. For a basic qualification test, these results can also provide the guidelines for the engineers and manufacturers. 1. Introduction At the present, the microelectronics encapsulation is making an effort towards lighter, thinner, better cost-performance and becomes much more reliable. As one of the state of the art encapsulation, MCM has been widely used in the field of military and aerospace to automotive, industrial equipment, medical facility, and electronic system products. MCM has a greater package density and power density, resulting in the greater thermal and stress or strain should be a major concern for thermo-mechanical reliability. The solder joints provide the electrical, thermal and mechanical interconnect between the substrate and the printed wiring board (PWB) of the MCM. The fatigue failure of solder joints caused by  Corresponding Author: Cheng-Geng Huang E-mail address: Cheng-geng.huang@hotmail.com Received: 19 September 2020; Revised: 18 October 2020; Accepted: 22 October 2020 Please cite this article as: Ch. G. Huang, Comparative Study of Physics of Failure Assessments of Thermomechanical Fatigue for Solder Joints in Multichip Module Under Different Conditions, Computational Research Progress in Applied Science & Engineering, CRPASE: Transactions of Mechanical Engineering 6 (2020) 281–287. alternating mismatches in the coefficient of thermal expansion (CTE) among the substrate and PWB of the MCM plays a dominant role in the failure modes of the MCM. Due to the time-temperature dependent creep and plastic behaviors of the Sn-Ag-Cu (SAC) in solder joints, fatigue life prediction of solder joints under thermal cyclic loadings still remains a difficult subject [1]. As microelectronics encapsulation should meet the requirements of specific quality and reliability for application, MCM must undergo a process of qualification to assess its quality and reliability [2]. Compared with the conventional life tests for MCM, accelerated life test is much more economical and practical. The temperature excursion can also influence the life of electronic package, which is