Reduced Temperature Metal Based Bonding Processes for Wafer Level Packaging and 3D Integration

Metal based bonding processes are commonly selected because of the need for a conductive interface along with a high degree of hermeticity. Metal based bonding process can be based on solid diffusion which is commonly called thermo-compression or can be based on liquefying part or all of the metal in the bond interface. Thermo-compression bonding has the primary challenges of being slow because it is based on solid diffusion and has very poor step coverage. The most common liquid metal bonding processes are commonly called solder or eutectic bonding. The solder or eutectic bonding process allows some step coverage and the time required for the process is driven by the maximum temperature required, the residence time at this temperature and the maximum ramp rate. The process temperature and the required process time can be reduced by selecting an alloy with a low melting point; however this reduced melting point reduces the maximum post bond working temperature. TLP (Transient Liquid Phase) also known as S...