Inductive Heating Based on VHF-ISM Radio Band Frequencies as Technology Platform for Efficient Heating of Metallic Micro-Scaled Bonding Layers in MEMS Packaging

Abstract

This paper presents a technique for selective and energy-efficient induction heating of aluminum (Al) frames to support and enhance the thermocompression bonding (TCB) for electronics packaging in the field of heterogeneous integration. The technological challenges include the use of an adapted induction coil for homogeneous heat distribution, the implementation of ISM (industrial, scientific, medical) radio band frequencies in the high frequency (HF) and very high frequency (VHF) range up to <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> = 40.68 MHz, and the assembly of a heating system based on an RF generator and automatic matching unit for impedance modulation. Finite element analysis (FEA) was used to calculate the electromagnetic (EM) fields based on the coil design used. The inductive heating was successfully carried out using a generator power of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> = 100 W with coil currents in the range of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> = 10.1 to 11.3 A (amplitudes). With this setup, a peak temperature of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>f_max</i></sub> = 633 °C in the Al frames could be achieved after <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t_h</i> = 10 s. This corresponds to an average heating rate of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dT/dt</i> = 63.3 K/s.