Optimal design configuration for aluminum pillar fabrication towards fine pitch ultrasonic bonding applications

Higher input/output (I/O) density and fine pitch bumping are becoming crucial due to higher performance requirements and a decrease in structure size in electronics such as integrated circuits (ICs) [1-3]. Currently, the focus has been put on fine pitch copper (Cu) pillar bumps due to superior conductivity, and mature technology with Cu solder bumps [4, 5]. However, Cu requires under bump metallization (UBM), and bonding substrate choice is limited to material hardness (343-369 MPa) [6, 7]. A completely new approach would be Aluminum (Al) pillar fabrication, which enables fewer fabrication steps and bonding at room temperature. It is CMOS compatible and material wise cheaper than Cu or gold (Au). Such structures on a chip can later be integrated using ultrasonic bonding, which is fast and less energy-intensive compared to Thermo-Compression Bonding (TCB) [8].