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280 MEMS and Microstructures in Aerospace Applications

FIGURE 12.6 C4 (controlled collapse chip connection) flip-chip.

placed around the periphery of the die. The ability to closely pack a number of distinct
chips on a single package makes flip-chip technology especially attractive to the
MEMS industry. 11 An added feature of flip-chip is the ability to rework. Several
techniques exist that allow for removal and replacement of the chip without scrapping
the chip or the substrate. In fact, rework can be performed several times without de-
grading quality or reliability. For improved reliability, chip underfill may be injected
between the joined chip and the package substrate. Care should be taken that the
underfill covers the entire underside without air pockets or voids, and forms complete
edge fillets around all four sides of the chip to avoid high-stress concentrations.

12.5.3 SYSTEM ON A CHIP
System on a chip (SOAC) may not necessarily be classified as a packaging
technology. It is derived from the wafer fabrication process where numerous

© 2006 by Taylor & Francis Group, LLC