Study on the growth behavior of Ni3Sn4 layer in Cu pillar/Ni/Sn microbump under high-temperature stress

Based on the numerical analysis of Ni atomic thermal diffusion flux, a kinetic model for the growth of the Ni₃Sn₄ intermetallic compound at the Cu pillar/Ni/Sn microbump interface under high-temperature stress is established. Through in-situ microscopic comparative analysis of test samples at 100 °C, 125 °C and 150 °C over varying time intervals, it is observed that at 150 °C Ni₃Sn₄ exhibits pronounced outward protrusion due to volumetric expansion. The maximum deviation between the model-predicted and experimentally measured Ni₃Sn₄ thickness is only 0.244 μm (14.8 %). Further analysis of the Ni₃Sn₄ growth behavior based on the model reveals that its growth rate decreases progressively with increasing thickness. As the Ni₃Sn₄ thickness increases from 600 nm to 1600 nm, its growth rates at 100 °C, 125 °C, and 150 °C decrease from 0.10 nm/h, 1.22 nm/h, and 7.79 nm/h to 0.04 nm/h, 0.45 nm/h, and 2.93 nm/h, respectively, resulting in a parabolic growth trend of Ni₃Sn₄ thickness over time. The growth rate of Ni₃Sn₄ exhibits an exponential increase as a function of temperature. The temperatures corresponding to growth rates below 0.01 nm/h and above 1 nm/h are defined as the inflection point temperatures of “slow-growth” and “explosive-growth” modes, respectively. Since the growth rate of Ni₃Sn₄ gradually decreases with increasing thickness, the two inflection point temperatures also vary with the Ni₃Sn₄ thickness.