Flip Chip Connections Using Bumps,Wells,and Imprinting
A conceptual framework for a new type of flip chip attachment is proposed. Gold stud bumps are provided on the chips,and
wells filled with solder paste are provided on a flexible substrate serving as the system board. Pushing the stud bumps into
the wells provides a bump/well connection,and heat is applied to melt the solder and make a permanent connection. An area
array of bump/well connections can have a pitch of 100µ or less. The connections are projected to be mechanically robust,to
support operating frequencies of 10GHz and above,and to support replacement of defective chips as many times as
necessary. Imprinting provides a fabrication method having sufficient precision to shrink the trace and dielectric feature sizes
by a factor of around 20 compared with conventional FR-4 boards,while still maintaining 50O traces. The same precision is
used to eliminate redistribution layers that are normally required between the fine pad pitch of IC chips and the coarser pad
pitch of a conventional board. By also using imprinting to fabricate the wells,a low assembly cost is achievable,potentially
below 0.06 cents per lead. This compares with an industry cost as high as 2.5 cents per lead for performance flip chip
PBGA1. The most advanced materials can be used including copper conductors and Cytop2 as the dielectric. At 10 GHz,
Cytop has a dielectric constant of 2.1 and a dissipation factor of 0.0007. The proposed manufacturing methods and assembly
techniques can be applied to a broad range of microelectronic systems including high performance circuit boards,high
density cables with controlled impedance,integrated passives,and stacked die packages.