Flex interposer-based CSPs

Flex interposer-based CSPs. This CSP type uses a flexible circuit having solder balls or metal bumps as an interconnect interposer between the chip and the next circuit board level. The bare chip is attached facedown and wire-bonded to the interposer. A thin elastomer, sandwiched between the chip and interposer, cushions the chip and the solder-ball interconnects, relieving stresses (see Fig. 1.13). The interposer generally consists of a metallized, flexible polyimide tape on which are formed electrical connections by photolithographic processes. As a final step, the exposed wire bonds and edges of the chip are molded with epoxy. 

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