To achieve an optimal interconnect and packaging design, it is important to utilize flexible printed circuit board only when flexible printed circuit board best satisfies application and other needs.

Flexible printed circuit board is a good choice when the primary need is for flexible, conformal, thin, lightweight, etc. Flex is also a good choice for applications requiring comparatively high I/O density, low cost, or performance advantages that cannot be achieved in PCB constructions.  Flexible printed circuit board can be utilized in many applications other than the aforementioned “good choices”; however, the user is strongly encouraged to consider cables, PCB, and other suitable interconnect technologies or else risk unnecessary design complexity, reliability risk, system connector challenges, higher cost, etc. As in conventional electrical design, interconnect must be partitioned according to product specifications including performance, reliability, cost, et al.

Interconnect partitioning, intentional or otherwise, can be found in the hierarchy of interconnects that is in almost any electronic system. For example, although personal computers include state-of-the-art semiconductors and their corresponding nanometer feature sizes, the power for those semiconductors is supplied through cables that are constructed using 18-gauge or larger conductors. Likewise, packaging designers need to partition the interconnect chain to satisfy system specifications, requirements, etc., using “just enough technology.”

The Flexible printed circuit board that interconnects the detector panel and signal processing electronics is a 2ML, 150-micron pitch design. One end of the Flexible printed circuit board is bonded to the panel; the other end is bonded, using ACF, to a multilayer PCB. Multiple ASICs (in bare die form) are attached, in a linear array, on the PCB; the ASICs are wirebonded to the PCB. The ASICs amplify and convert the analog signals produced by the detector panel and route those signals through a connector to a second flexible printed circuit board that connects to the system electronics. The second flexible printed circuit board, because of multiplexing of the digitized signals, requires fewer signal conductors; thus, it is a low-density 2ML flexible printed circuit board (signal plus shield layer).

The next logical step in packaging optimization for this type of electronic system would be the integration of the ASICs and ancillary electronics into the flexible printed circuit board. This integration step, if done properly, would replace the PCB with flexible printed circuit board, reduce the number of interconnects, and reduce detector panel manufacturing steps, without increasing the cost of the flex-PCB-flex system, as above.

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