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Gold Stud Bump for Device High Density Flip Chip Interconnect
Keywords: GGI, Flip Chip, HDI
Solder has been the material of choice for flip chip die attach. Lead free solder interconnect process normally uses a fluxing process and peak reflow temperature of over 240◦C. Package designers are looking at gold bumps as an alternative back-end process for fist level interconnect (Gold to Gold interconnect (GGI)) that provides fine pitch die attach, reduced package form factor, excellent electrical performance, and environmentally safe. Device packaging has been a gating factor in future high performance device applications. Future device packaging will used stacked die, shorter interconnects, and fine ball pitches. Future high productivity device packaging must also consider die and substrate metallization along with wafer bumping cost. The interconnect process should minimize stresses to the die. This paper will analyze two micro weld GGI die bonding techniques that provides a lead free process and fine pitch interconnect using the least manufacturing steps. Flip chip GGI thermocompression die bonding process provides an intermetallic bond using pressure and heat. GGI thermocompression bonding process is suitable for die with a large number of I/O(<500 bumps). Die size up to 30mm are being used in production. In Thermocompression the layer thickness and diffusion barrier are important to achieve a reliable bond. High precision thermocompression bonding can be a die attach process for fine bump pitches of 40m. Thermocompression bonding uses either gold plated bumps or gold stud bumps and suitable for use in system in packaging applications. Flip chip GGI ultrasonic process is used for small die attach. GGI ultrasonic bonding process is suitable for die with up to 100 I/O. Die sizes of 5 mm is a typical die size for ultrasonic die bonding applications. GGI ultrasonic bonding uses ultrasonic energy as the primary energy for the die attach process. Lower heating temperatures and loads can be used in this reliable die attach process. Gold stud bump solutions provide several advantages to package designers. There are a number of different low cost bumping processes. The gold stud bump geometry and interconnect method should be optimized to meet the manufactures long term device reliability requirements.
Philip Couts, Engineer
TDK Corp.
Mount Prospect, IL
USA


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