SFC Redistribution

On some die, the I/O are not located where you need to have the bumps. This is especially true when you take an existing die that is wire bonded and would like to convert it to flip chip. The SFC-Redistribution Line (or RDL) process adds "redistribution metallization" (often called "runners' or "traces") that let you re-route the signal path from the die peripheral I/O to the new desired bump locations. This process is usually seen as a transitional solution between a die that is designed for wire bonding and a die that is designed for flip chip.

Redistribution is designed to produce bumps of less than 135µm in height, although the typical bump height is 100µm. Pitch capabilities in this process are 70µm or greater. Standard Redistribution line widths are 38µm with 38µm space between lines. For fine pitch designs, FlipChip will go down to 25µm lines and 12µm space between lines. Since the process is not limited to the bi-metal restraints of an electroplating bath, tri-metal alloys (such as Sn/Ag/Cu) require nothing more than the selection of the proper tube of pre-mixed solder paste. As with all die processed with small bumps, these die will require the use of underfill during packaging.

The SFC-Redistribution process requires more process steps than the SFC-Bump on I/O or the SFC-Repassivation flows. View an outline of the SFC-Redistribution process flow (none of the drawings are to scale).