Low Cost Non-Solder Flip Chip Assembly
Original Publication Date: 2003-Jun-25
Included in the Prior Art Database: 2003-Jun-25
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In a typical ACP (Anisotropic Conductive Paste) process, the paste is dispensed on the substrate in a pre-determined pattern and volume. This is followed by flip chip attach with the application of heat and pressure to cure the ACP. It is important that the correct pattern and volume is dispensed to ensure minimal voids between the die and substrate and at the same time ensuring sufficient fillet is created along the four edges of the die (figure 1). It is suggested to limit the dispensing of ACP to areas of interconnect only. In a second step a non-conductive paste (NCP) is dispensed on the necessary volume required to fill the gap between the die and substrate and to create a balanced and sufficient fillet along the die edges. By reducing the usage of high cost ACP in flip chip attachment process without affecting the quality of the resultant flip chip joints formed a low cost non-solder flip chip assembly is achieved (figure 2). Flip chip die for ACP application is typically not greater than 10x10mm and the bump layout is periph-eral. Based on a die size of 5x5mm with 72 peripheral bumps, the volume of ACP required at the in-terconnect region is only about 2% of the entire ACP volume typically dispensed. The key difference between ACP and NCP is the presence of conductive particles in ACP. These par-ticles are very costly, hence the price of ACP is at least two times higher than NCP. So drastically reducing the ACP usage causes significant cost savings in the material usage.