Compensation Method for Displacement Caused by CTE Mismatch in Micro-LED Bonding Process

Micro-light emitting diode (LED) technology has significant potential in the display field. However, its bonding process is susceptible to displacement caused by coefficient of thermal expansion (CTE) mismatch. As the pixel size decreases, the demand for alignment precision increases, making the effect of CTE mismatch more pronounced. This article proposes a compensation method. Different temperatures are applied to the sapphire and silicon substrates to mitigate displacement. ANSYS simulations were performed to evaluate the impact of thermal expansion on the displacement between the Micro-LED pixels and bumps of substrate. Under the traditional bonding, as the temperature rises from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$120~^{\circ }$</tex-math> </inline-formula>C to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$270~^{\circ }$</tex-math> </inline-formula>C, the displacement between the outermost pixel and the bump increases from 4.7639 to 12.0581 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $</tex-math> </inline-formula>m. However, under the compensation method, the displacement is reduced. This demonstrates the effect of temperature on bonding precision and confirms the theoretical feasibility of the compensation method. Next, bonding experiments were conducted based on the simulations. The results show that with traditional bonding, the displacement increased from 5.4 to 9.1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $</tex-math> </inline-formula>m, matching the trend in the simulations. In contrast, under the compensation method, the displacement is reduced to 1.7 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $</tex-math> </inline-formula>m, representing a 64% decrease compared with the traditional bonding. This work establishes a theoretical foundation for optimizing the micro-LED bonding process and validates the process experimentally, offering valuable guidance for improving bonding accuracy.