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Process Development of Copper- Copper Thermocompression Bonding for Power Delivery and Heat Extraction system for the Silicon-Interconnect Fabric


The Silicon-Interconnect Fabric (Si-IF) is a platform for heterogeneous integration that seeks to advance packaging scaling by integrating dies with short interconnection pitches (≤ 10 �m) with an inter-die spacing of ≤ 100 �m. For a large, high-performance system, the power requirement is estimated to be >50 kW. This short spacing of chips on the Silicon Interconnect Fabric will pose significant power delivery and cooling challenges. To address these issues, a polymer-metallic composite structure called PowerTherm is bonded to the Silicon Interconnect Fabric using Cu-Cu thermocompression bonding. The process conditions for bonding i.e. time, temperature, and pressure must be optimized to prevent any damage to the assembled Si-IF and the PowerTherm structure while ensuring high bond strength and low electrical resistance. Cu-Cu thermocompression bonding was performed in the atmosphere and vacuum at 150-350 �C at low pressure (≤ 3 MPa) for 2 hours. The bonding was performed between an electroplated Cu- sample and Cu rod/block configuration, and between two electroplated Cu-samples. Shear strength of 25 � 1 MPa and specific electrical resistance of 2944 Ω.�m2 was achieved. The current bonding system lacks a high bonding force as well as the ability to bond non-wafer samples. To address these issues, a custom bonder was constructed and the details of its design and progress are also reported. The bonder can apply 10X more force as well as bond non-wafer samples.

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