Fatigue Life Analysis of Hybrid Bonding in Micro-LED Interconnection

Micro-LED displays have garnered widespread attention due to their high resolution, high brightness, and long lifespan. However, the heterogeneous integration and the reliability of Micro-LEDs pose significant challenges for their commercialization. As Micro-LED products develop towards larger sizes and narrower pitches, the Au/In bonding process has become a prevalent strategy for achieving high-resolution interconnections. To address the issue of the life span being affected by the plastic deformation of indium bumps, which ultimately fail in the form of yielding, an Au/In-resin hybrid bonding technique to improve the reliability of high-resolution Micro-LEDs was proposed in this paper. The reliability of the flip-chip bonding structure of a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$4\times 4$</tex> Micro-LED array was analyzed using ANSYS simulation software and finite element methods. The Anand unified viscoplastic constitutive model was employed for both indium bumps and the encapsulating resin. The model was subjected to temperature cycling loads ranging from <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$-55^{\circ}\mathrm{C}$</tex> to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$125^{\circ}\mathrm{C}$</tex> in accordance with the JEDEC temperature cycling standard. The Coffin-Manson fatigue life prediction model, which accounts for plastic strain in materials, was introduced to estimate the thermal cycling fatigue life of the Micro-LED interconnection structures. The equivalent plastic strain range of hybrid bonding device was <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$6.708\times 10^{-3}$</tex>, surpassing the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$7.59\times 10^{-3}$</tex> observed in device with conventional bump bonding. The hybrid bonding device exhibited a thermal cycling life of 12747 cycles, which was about 36% longer than that of the bump bonding device. It suggests that resin helps to extend the thermal cycling life of the device and enhance its reliability.