A Low Cost Bumping Method for Flip Chip Assembly and MEMS Integration

Abstract

In this paper, we present the development of a low cost chip/wafer bumping technique for flip chip assembly and microelectromechanical systems integration using a bump transfer approach. In this method, high melting temperature bumps such as copper, nickel, and gold bumps are fabricated on a low cost, flexible carrier and then transferred onto the target chip/wafer/board for flip chip assembly. The aluminum pads on test chips were remetallized with electroless nickel and gold layers to facilitate the bonding of bumps to the chips using thermocompression bonding. Parallel bonding and transfer of bumps has been achieved. Thermal cycling and bump shear test showed that reliable bonding was obtained between the bumps and the pads. Surface study using laser ionization mass analysis found no traces of of the polymer carrier on the surface of the bumps on the test chip after the completion of the bump transfer process.Index Terms-Bumping, flexible carrier, flip chip, microelectromechanical systems (MEMS).

Alternative approach in 3D MEMS-IC integration using fluidic self-assembly techniques

“…Using flip-chip techniques, several possible choices can be considered for suitable metals, such as In-Au, In-Sn, solder-Au and Al-Ge [10,11]. Bonding temperatures for these different metal systems range from 140 • C to 575 • C. Recently, the flip-chip technology has found increasing applications in assembly and packaging of 3D microchips, sensors and MEMS structures and devices [12]. A key step in flipchip packaging is to produce bumps on a chip/wafer for interconnections between a chip and a board.…”