Packaging challenges for small die

During the last few years, wafer technology has been shrinking aggressively from the 50nm node down to a much smaller technology node. This creates a disparity between die and packaging in which the die is miniaturizing, yet the packaging's physical footprint remains unchanged. Among the various packaging types, the one that is most impacted is board-on-chip (BOC) packaging, which is the current mainstream packaging for DDR2/DDR3 devices. The construction of the BOC package is a one-layer interposer with a window cut-out along the center; the die's active circuit faces down with respect to the package footprint. The interconnect between the die and package is wire, via the window cut-out. As the die shrinks, and the package footprint remains unchanged, one of the design bottlenecks is the trace fan-out issue from the bond finger to the innermost column of the ball, as well as the tighter bond finger pitch due to the die-pad pitch reduction. This paper will describe the design features that need be addressed for small-die packages — for example, the drive toward fine line trace, wire bond top pad width, and narrower bond slots. A test vehicle is tooled up as a simulation of possible manufacturing/process issues for the small-die package solution. The design and analysis of the experiment are described in full in this paper.