1 Copyright © 2018 by ASME Proceedings of the ASME 2018 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems InterPACK2018 August 28-30, 2018, San Francisco, California, USA InterPACK2018-8396 INVESTIGATION OF THE EFFECTS OF HIGH TEMPERATURE AGING ON THE MECHANICAL BEHAVIOR OF LEAD FREE SOLDERS Mohammad S. Alam, KM Rafidh Hassan, Jeffrey C. Suhling, Pradeep Lall Center for Advanced Vehicle and Extreme Environment Electronics (CAVE 3 ) Auburn University Auburn, AL 36849 Phone: +1-334-844-3332 FAX: +1-334-844-3124 E-Mail: jsuhling@auburn.edu ABSTRACT Lead free solders are renowned as interconnects in electronic packaging due to their relatively high melting point, attractive mechanical properties, thermal cycling reliability, and environment friendly chemical properties. The mechanical behavior of lead free solders is highly dependent on the operating temperature. Previous investigations on mechanical characterization of lead free solders have mainly emphasized stress-strain and creep testing at temperatures up to 125 °C. However, electronic devices, sometimes, experience harsh environment applications including well drilling, geothermal energy, automotive power electronics, and aerospace engines where solders are exposed to very high temperatures from 125- 200 °C. Mechanical properties of lead free solders at elevated temperatures are limited. In this work, we have investigated the mechanical behavior of several SAC and SAC+X lead free solder alloys including SAC305 (96.5Sn-3.0Ag-0.5Cu) and SAC_Q at extreme high temperatures up to 200 °C. Stress-strain tests were performed on as reflowed alloys at four elevated temperatures (T = 125, 150, 175, and 200 °C). In addition, changes of the mechanical behavior of these alloys due to long-term aging have been studied. Extreme care has been taken during specimen preparation so that the fabricated solder uniaxial test specimens accurately reflect the solder material microstructures present in actual lead free solder joints High temperature tensile properties of the solders including initial modulus, yield stress, and ultimate tensile strength have been compared. As expected, our results show substantial degradations of the mechanical properties of lead-free solders at higher temperatures and with aging. The degradations are even more significant when the samples are stored in a high temperature environment for a particular span of time. Furthermore, Comparison of the results for different solders has shown that the addition of dopants (e.g. Bi, Ni, and Sb) in the traditional SAC alloys improve their high temperature properties significantly. KEYWORDS Lead-Free Solder, SAC alloy, Aging, Stress-Strain Curve, Modulus, Yield Stress, Ultimate Tensile Strength INTRODUCTION In oil and gas exploration, avionics, automotive, and defense applications, electronics typically experience very harsh environments compared to consumer electronics [1-2]. Reliability of such electronic products is a big concern now-a- days. Electronic systems in under-the-hood automotive applications are operated at temperatures over 150 °C [3-4]. The electronic modules used in oil and gas exploration applications experience ambient temperatures above 150 °C, and often up to 200 °C [5]. In Wireline logging, the logging tool is lowered into the wellbore, and the electronics experience extremely low or high temperatures depending on the location and type of the oil well. Besides, this process usually lasts 2 to 6 hours. In addition, electronic systems used in commercial and defense aircraft, ground military vehicles, high-speed civil transport, and supersonic aircraft can be exposed, most often, to temperatures up to 200 °C [2]. Electric propulsion systems in battle tanks and other ground defense applications also experience ambient temperatures above 200 °C [6]. Thus, electronic products experience very harsh environments, e.g., temperatures up to 200 °C, very close to the melting points of the various Sn-Ag-Cu (SAC) solders used by industry. Moreover, longer exposures at such high temperatures can result in extreme aging-induced changes to