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Design007-Dec2021

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98 DESIGN007 MAGAZINE I DECEMBER 2021 Challenges in Simulating a Wirebonded CoB on a Rigid-Flex PCB ere are many good reasons to use a chip- on-board (CoB) implementation. When this is combined with wirebonding and the use of a rigid-flex PCB, challenges mount. An applica- tion that demands all three—CoB, wirebond- ing, and rigid-flex PCB—is a camera module that goes into a mobile application, the sample design used to illustrate the design and analysis challenges in this article. If you are not aware of and prepared for the potential pitfalls, it is highly likely that your project could fall short or even fail. If the camera module goes into a mobile application, cost, performance, footprint (in all three axes), and time to market become requirements that must be met. Cost and foot- print justify the use of CoB implementation due to the elimination of a package; perfor- mance and cost justify the wirebonding of the image sensor die directly on to a rigid-flex PCB, since the short wires with the eliminated pack- age improve performance and reduce cost; the restricted footprint within a mobile device calls for the use of a rigid-flex PCB. Figure 1 shows a rigid-flex PCB with an image sensor imple- mented using CoB and the MIPI signals driven to the connector on the other end of the rigid- flex PCB. e impedance of the MIPI signals traversing from the wirebonded chip to the connector must be a consistent 100-Ohm path. All Systems Go! by Brad Griffin, CADENCE DESIGN SYSTEMS, INC. Figure 1: Rigid-flex PCB with CoB and connector.

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