Localized Induction Heating of Cu-Sn Layers for Rapid Solid-Liquid Interdiffusion Bonding Based on Miniaturized Coils

Abstract

Considering the demand for low temperature bonding in 3D integration and packaging of microelectronic or micromechanical components, this paper presents the development and application of an innovative inductive heating system using micro coils for rapid Cu-Sn solid-liquid interdiffusion (SLID) bonding at chip-level. The design and optimization of the micro coil as well as the analysis of the heating process were carried out by means of finite element method (FEM). The micro coil is a composite material of an aluminum nitride (AlN) carrier substrate and embedded metallic coil conductors. The conductive coil geometry is generated by electroplating of 500 µm thick copper into the AlN carrier. By using the aforementioned micro coil for inductive Cu-Sn SLID bonding, a complete transformation into the thermodynamic stable ε-phase Cu3Sn with an average shear strength of 45.1 N/mm2 could be achieved in 130 s by applying a bond pressure of 3 MPa. In comparison to conventional bonding methods using conduction-based global heating, the presented inductive bonding approach is characterized by combining very high heating rates of about 180 K/s as well as localized heating and efficient cooling of the bond structures. In future, the technology will open new opportunities in the field of wafer-level bonding.

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

“…In addition to the typical physical challenges of absorption and reflection in induction heating, the EM spectrum in the HF and VHF range introduces the effect of standing waves caused by the electrical length G of the coil (7). This length, measured in wavelengths (8), is the distance travelled by an EM wave in one cycle at a specific frequency and can be calculated by 𝐺 = 𝐿/𝜆 (7)…”

“…Thus, micro-scale Al frames with great potential for MEMS packaging were investigated using FE simulation and induction heating experiments. Previous work by the authors has been concerned with HF-based induction heating up to f0 = 2 MHz for MEMS and power packaging [7], [8].…”

Inductive Sintering of Silver Micro Particles for Bonding of Microelectronic Components

“…In the article, the authors emphasize once again the very high heating rates of induction technology as well as the possibility to locally limit the heat input. Hofmann et al successfully realized a MEMS packaging method based on selective induction heating of Cu-Sn layers for energy-efficient bonding at chip and wafer level using miniaturized coils with optimized geometry designs [20], [21]. Even less literature is available for induction based silver sintering.…”

Inductive Sintering of Silver Micro Particles for Bonding of Microelectronic Components

“…In their article, the authors emphasized the very high heating rates of induction technology as well as the possibility of locally limiting the heat input. Hofmann et al successfully realized a MEMS packaging method based on the selective induction heating of Cu-Sn layers for energy-efficient bonding at the chip and wafer level using miniaturized coils with optimized geometry designs [24,25]. Even fewer studies in the literature are available for induction-based silver sintering.…”