Effect of Aging on Dendritic Array, Ag3Sn Spacing, and Hardness of a Sn-2Ag-0.7Cu Solder Alloy

Author(s)

Silva, Bismarck Luiz ; Mendes, Pedro Henrique ; Garcia, Amauri ; Spinelli, Jose Eduardo

• Document type: Journal article
• Source: JOURNAL OF ELECTRONIC MATERIALS; v. 51, n. 8, p. 9-pg., 2022-06-07.

Abstract

In addition to the growth of intermetallics, phase dissolution, and precipitation, variation in the dendritic scale of the microstructure is an important aspect to consider during solder joint operations. Given the scarcity of studies on dendritic development under different aging conditions, the current study is devoted to this process. The purpose of this study is to explore the evolution of the dendritic array (lambda(1)-primary dendritic arm spacing), Ag3Sn spacing, and hardness of the SAC207 alloy from three separate as-cast states (i.e., three distinct solidification cooling rates) through 248 h, 480 h, and 720 h of artificial isothermal aging at 100 degrees C. While untreated samples are characterized by a -0.55 (n) lambda(1) power function with cooling rate, aged samples are defined by maximum and minimum limits with n values of -0.3 and -0.45, respectively. For longer aging periods, lambda(1) becomes less sensitive to the solidification cooling rate. The initial dendritic spacing established by the solder packaging process is a crucial factor determining dendritic array coarsening. The coarsening potential increases as the dendritic spacing decreases. Moreover, when compared to samples containing fiber-like particles, the Ag3Sn spacing connected to spheroidal-like particles is more susceptible to coarsening. A simple model is proposed that relates lambda(1) to the square root of D: diffusion coefficient x t: time, which appears to effectively describe the variance during the aging conditions studied here. (AU)

• FAPESP's process: 19/23673-7 - Evaluation of alloys for thermal interface contact and for additive manufacturing
• Grantee: José Eduardo Spinelli
• Support Opportunities: Regular Research Grants