Flip Chip Solder Bumps and Wafer-Level Underfill
These microscope photos show cross sections of a 250 micron pitch flip chip that was solder-bumped at the wafer level. These chips have been double bumped to produce a taller solder bump than is normally produced on such chips.
The double bump allows the solder to protrude from an encapsulant layer that has been applied to the chips at the wafer level. This patented encapsulant acts as a high-reliability underfill. These solder bumps are approximately 100 microns wide at their bases.
The taller bumps also increase the chip-to-board compliance, enhancing the reliability of the solder joints after assembly. For cross sections of chip assemblies, click here.