Session: 10-01 Interactive Presentations

Paper Number: 99219

99219 - Materials Characterization for Thermally Aged Snagcu Solder Alloys and Drop & Shock Simulation Using Input-G Method 

Harsh environment applications include farming, automotive, oil and gas drilling, avionics, and defense. Many applications, particularly in colder climates, have seen extremely low working temperatures in conjunction with significant strain loads. Furthermore, prior to their service life, electronic assemblies may be subjected to extended periods of non-climate-controlled exposure. Under varying thermal loads, lead-free solder materials continue to evolve, which can result in deterioration of mechanical parameters such as Ultimate Tensile Strength and elastic modulus. Temperatures in extreme environments can range from -65 to +200 °C [Eddy 1998, Hattori 1999, Johnson 2004 & Watson 2012] when combined with drop, shock, and vibration loads.

For extreme temperature applications, lead-free SAC solders and doped SAC solders are common alternatives. Under such loads, solder interconnects may experience significant non-linear deformation. We need a better understanding of solder alloy to develop and improve the efficiency of electrical devices. Many doped solder alloys, such as SAC-Q (CYCLOMAX), SAC-R, Innolot, and others, have recently been launched in the electronic fields. These alloys were created by combining Ni, Co, Au, P, Ga, Cu, and Sb with SAC solder alloy to improve mechanical characteristics, thermal properties, wettability, melting temperature, shock and drop performance, and solder alloy microstructure [Cai 2010, Matahir 2011]. According to microstructure research, adding Bismuth (Bi) to SAC alloy can help make it resistant to aging-induced degradations [Ahmed 2017]. There is very little published data on SAC solder alloys after prolonged storage at high strain rates and low operating temperatures.

Material properties for non-linear modeling and reliability prediction are required for risk mitigation when using alloys in high-reliability applications. Finite element modeling is commonly used in electronic packaging for solder connection design as well as drop and shock simulation. Many researchers have documented solder alloy deformities using various material models, including basic elastic, elastic, and viscoplastic. The Anand constitutive model is one of the most widely used models for capturing non-linear solder behavior in thermo-mechanical stresses. Previously, Anand constitutive models [Anand 1982, 1989, Bai 2009, Mysore 2009, Lall 2016-2021, Johnson 2012] were used to characterize the material behavior of SAC solder alloys and SnPb solder alloys.Furthermore, there is a scarcity of constitutive models in the published literature that represent mechanical deformation under transient dynamic loads at low- and high-test temperatures for aging environments.

The current study closes this gap in the literature by measuring mechanical properties of undoped SAC105 and doped SAC-Q solder alloys at low operating temperatures (-65°C to 0°C) at high strain rate after varying thermal aging periods of up to one year. The reliability of the Anand model was determined by comparing experimentally measured data with predicted data using determined model constants for both solder alloys. Anand parameters were used in a FE-framework to simulate drop events for a ball-grid array package on a printed circuit board assembly to compute the plastic work and hysteresis loop.The plastic work per shock event is a measurement used to track the progression of damage in solder interconnects. The evolution of the hysteresis loop and PWD has been studied using thermal aging. 

Presenting Author: Vikas Yadav Auburn University