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SFC RepassivationThe SFC-Repassivation process is similar to the SFC-Bump on I/O process, but it is designed for die that do not meet all of the I/O final metal pad and passivation opening requirements of SFC-Bump on I/O. In this process, a layer of Benzocyclobutene (or BCB) repassivation is deposited on the die before bumping. The BCB passivation corrects for the issue of the I/O passivation opening being too large for a standard flip chip bump. It also corrects for the issue of the I/O final metal pad being too small for a standard flip chip bump. The BCB layer planarizes the device surface and gives the bump structure additional strength and robustness. As with SFC-Bump on I/O, SFC-Repassivation is designed for small bumps (less than 135µm) placed directly on the die I/O. Pitch capabilities in this process are 150µm or greater for a full array I/O design and 140µm or greater for a peripheral I/O design. The number of bumps per die typically ranges from 4 to 600. The SFC-Repassivation process uses premixed solder paste for the solder bumps. This provides for outstanding control of the alloy composition across the entire wafer. 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, die bumped with the SFC-Repassivation process will require the use of underfill during packaging. If your device contains bumps that will not be placed directly on the I/O, take a look at the SFC-Redistribution flow. If you are looking for bump heights greater than 140µm, take a look at the UltraCSP flow – the industry standard Wafer Level Package (WLP) process flow. The SFC-Repassivation process requires relatively few process steps to complete the flow. View an outline of the process flow (none of the drawings are to scale) |
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