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A Direct Fanning-Out Packaging Technology using Cu Base Plate for Embedded Fine-Pad-Pitch LSI
Keywords: embedded LSI, fine-pitch LSI pad, Cu direct connection
We have successfully developed a direct fanning-out packaging technology for embedded fine-pad-pitch system LSI. 50-um-thick chips are embedded into a build-up resin layer on a 0.5-mm-thick Cu base plate, and multi-layer fanning-out wiring is fabricated, followed by dicing for the separation of each package including the Cu plate. Our package has three features; 1) high heat dissipation and high reliability characteristics, due to the rigid Cu plate, 2) small package thickness, due to thinned LSI chip and thin dielectric layers, 3) low cost process, compared to conventional FCBGA, because of Cu direct connection to fine-pitch LSI pads using laser via-hole process. LSI chips with 4-row, 80-um-pitch and 1200-pads are mounted face-up on the Cu plate. The important points for fine-pitch interconnection and high-reliability are the resin fluidity and thickness control for the resin on the chip. A low-viscosity epoxy resin is selected, and the thickness is controlled to be 20 um. The UV-YAG laser is adopted to make small via-holes of 30 um in diameter for 80-um-pitch connection. Direct via-hole openings to the LSI pads by UV-YAG laser cause no damage to the transistor devices fabricated by 90-nm CMOS technology. A 31-mm-square embedded package with five-layered wiring of 15-um in width is successfully fabricated, and its total thickness is only 0.79 mm including Cu plate, much thinner than the conventional FCBGA package with heat spreader. This package shows a very low thermal resistance of 8.2 degrees C per watt. Since Pb-free BGA balls are used, our novel package is completely Pb-free. The package-level reliability is evaluated for our novel LSI package. The temperature cycling test condition is -55/+125 degrees C for 10 minutes each. The prototypes show no crack and no electrical failures after 1000 cycles. Therefore, this technology is one of the most attractive solutions for thin and highly reliable LSI package for substituting FCBGA packages.
Hideya Murai, Principal Researcher
NEC Corporation
Sagamihara, Kanagawa 229-1198,
Japan


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