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|Reduced Temperature Metal Based Bonding Processes for Wafer Level Packaging and 3D Integration|
|Keywords: Wafer Bonding, Metal based bonding, TLP|
|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 SLID (Solid Liquid Inter Diffusion) bonding decouples the bonding temperature from the post bond maximum working temperature which allows the selection of alloys that reduce the bonding temperature while maintaining a high post bond maximum working temperature. For example a Cu-Sn TLP process can be performed at 280�C that will survive post bond temperature of up to 415�C. The fundamentals of TLP bonding will be reviewed and data will be presented for Cu-Sn TLP bonding|
|Eric F. Pabo, Business Development Manager MEMS