Metal-polymer composite interconnections for ultra fine-pitch wafer level packaging Article

Aggarwal, AO, Raj, PM, Tummala, RR. (2007). Metal-polymer composite interconnections for ultra fine-pitch wafer level packaging . IEEE TRANSACTIONS ON ADVANCED PACKAGING, 30(3), 384-392. 10.1109/TADVP.2007.901776

cited authors

  • Aggarwal, AO; Raj, PM; Tummala, RR

authors

abstract

  • The decrease in feature sizes of microelectronic devices has underlined the need for higher number of input-outputs (I/Os) in order to increase its functionality. This has spurred a great interest in developing electronic packages with fine and ultra fine pitches (20-100 μm). Most of the compliant interconnects that are currently being developed have inductance and resistance higher than desirable. This paper presents a novel low-temperature fabrication process that combines polymer structures with electroless copper plating to create low stress composite structures for extremely fine-pitch wafer level packages. Analytical models for these structures justify the stress reduction at the interfaces and superior reliability as integrated circuit (IC)-package interconnects. Low coefficient of thermal expansion (CTE) polyimide structures with ultra-low stress, high toughness, and strength were fabricated using plasma etching. The dry etching process was tuned to yield a wall angle above 80°. The etching process also leads to roughened sidewalls for selective electroless copper plating on the sidewalls of polymer structures. This work also describes a selective electroless plating synthesis route to develop thin IC-package bonding interfaces with lead-free solder. Lead-free alloy films were deposited from aqueous plating solutions consisting of suitable metal salts and reducing agents at 45 °C. The lead-free solder composition was controlled by altering the plating bath formulation. Solder film formed from the above approach was demonstrated to bond the metal-coated polymer interconnects with the copper pads on the substrate using a standard reflow process. Metal-coated polymer structures in conjunction with the thin solder bonding films can provide low-cost high-performance solutions for wafer-level packaging. © 2007 IEEE.

publication date

  • August 1, 2007

published in

Digital Object Identifier (DOI)

start page

  • 384

end page

  • 392

volume

  • 30

issue

  • 3