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Thermosonic Gold to Gold Intermettalic Advantages for CSP Packaging
Keywords: Flip Chip Assembly, Gold to Gold Interconnect, CSP Packagaing
Flip chip thermosonic back end assembly method is a low cost interconnection method. The advancement of flip chip thermosonic process for CSP packaging of HBLED and CMOS image sensors is occurring due to the intermetallic interconnection properties and reduction in final package geometry. This paper will investigate thermosonic metal to metal interconnection process for these high growth assembly markets. Thermosonic bonding uses a micro weld interconnection die attach method at much lower bonding temperature than C4 lead free solder method. The thermosonic metal to metal interconnection method is lead free and the process does not use flux or solder alloys. Thermosonic flip chip die attach process uses a robust individual die “scrubbing” process which reduces assembly steps and eliminates the mass reflow oven used commonly in C4 solder process. The metal to metal interconnection method provides excellent thermal performance for HBLEDs which require the Tj peak temperature to be controlled to maximize device MTBF and overall color temperature performance. The uses of metal to metal interconnection method provide superior thermal performance when compared to solder alloys. The metal to metal interconnection method provides high precision with low particle generation for high performance bonding of CMOS image die. In the case of peripheral layout of bumps on the chips the typical line and space is about 50 m / 50 m. For high density requirements bump array layout is used. A high accuracy thermosonic flip chip bonder is bonder is required to achieve this die attach precision. The allowable die bonder mounting tolerance for 50 m would be 16 m which is one third of the space and the die bonder mounting accuracy to be 7 m. Flip chip thermosonic bonding is a clean process where flux contamination is avoided along with particles from the mass reflow oven. Thermosonic bonding has fast process bonding times of < 300 msec which is important productivity factor in cost sensitive camera and solid state lighting applications.
Philip Couts, Sales
TDK Corporation of America
Mount Prospect, IL

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