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60 DESIGN007 MAGAZINE I FEBRUARY 2023 ere are, however, ways to reduce the I/O requirement at the board level; by using a flexible circuit to make interconnections to terminations on the upper surfaces of the chip packages, high-speed signals can be lied out of the PCB into the space above the board. I described this approach at my previous start up, Silicon Pipe, in the early 2000s, calling it "OTT" technology, meaning off (or over) the top. OTT technology was invented to circumvent the problem of dealing with noise and cross- talk in the PCB. As the march into the third dimension of electronic interconnection using heterogeneous interconnection solutions con- tinues, the OTT solution was among the first proposed 3D interconnection solutions. Fig- ure 1 offers a graphical representation of that radical approach. e basic concept of OTT is now being conceptually exploited as "bridge" technol- ogy and employs through-silicon via (TSV) technology that allows chips to be intercon- nected—not just vertically (stacked) but also laterally between chips. is is illustrated in Figure 2. e advantages are obvious: is lay- out ensures the shortest path routing of critical signals and clocking between chips. In summary, the OTT concept proposed by Silicon Pipe some 20 years ago is finally finding practical application in today's het- erogeneous integration tool chest, offering an alternative means to getting higher perfor- mance while staying within the boundaries marked by the limits of physical science and package assembly technology. Some ideas are just born too early and need the future to catch up to them. DESIGN007 Joe Fjelstad is founder and CEO of Verdant Electronics and an international authority and innovator in the field of elec- tronic interconnection and packaging technologies with more than 185 patents issued or pending. To read past columns or contact Fjelstad, click here. Download your copy of Fjelstad's book Flexible Circuit Technology, 4 th Edition, and watch his in-depth work- shop series "Flexible Circuit Technology." Figure 2: In contrast to the earlier approach to OTT design, the current generation can be used to intercon- nect ICs having TSV technology from the backside, further improving performance and allowing for the interconnection of two or more chips within a package or between packages.