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The Electronic Interconnection Files - 4 - "Civil Engineering" of Electronic Interconnections
October 13, 2005 |Estimated reading time: 3 minutes
As has been increasingly noted by electronic industry pundits, electrical and electronics interconnections are presently the primary limiters of electronic performance. The industry is not entirely blind to this glaringly evident fact, but it has been slow to react in a coherent, thoughtful manner. This is largely the result of the simple fact that the electronics industry is no longer the monolithic industry it once was. Electronic design and manufacturing are disciplines that have drawn further apart since the process of disaggregation of the electronics industry began in the late 1980s. In earlier times, the designer was very commonly the manufacturer as well. These were the vertically integrated manufacturers. However, with the corporate outsourcing of almost everything but marketing and corporate governance, the OEMs of today are much more hollow entities and, as a result, they are often much less attentive to the consequences of the diffusion of design and manufacturing processes. An off-shoot of that situation is that there is little opportunity to learn and grow cooperatively to meet evolving challenges. <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />
While there has been much discussion about bridging the waters between the island of design and the various islands of manufacturing interconnection structures, it is proving a daunting task. As it presently stands, each element of the electronic interconnection hierarchy is conceived and developed with little anticipation as to the impact of the decisions on what is to come next. It is pretty much a case of "I solved my problem. It's your problem now" For example, the semiconductor is designed with little concern for the package and the package is designed with little concern for the PCB, and so on... An arguably better approach is to "walk the talk" of concurrent design and engineering. With that preamble, let's take a quick look how a semiconductor chip and package might be better integrated in terms of design and manufacture.
Semiconductor designs of today is a far cry from former times. In earlier years, an individual designer or design team would set about the task of designing the chip completely. This included all the gates required to meet the product need. Over time, the process has been simplified. Presently, IP blocks of transistors having different functions are designed by completely different teams. These are collected and integrated together into a chip design, with interconnection and I/O assignment the basic tasks. The job requirement under the present boutique paradigm is simple... make it work and get it done fast.
As the industry moves inevitably to ever higher speeds due largely to chip feature size reduction, there will be need for greater cooperation between silicon design and package design. In fact, the package can actually help to greatly improve silicon efficiency if the two are co-designed. This begs the question: How is this possible? The answer resides in the data channel.
When the data or signal channel is very clean and free from disruptions, it is possible for the signal to propagate at high rates because signal rise time is not fettered with lossy materials or a noisy transmission environment. One way to do this is to separate the high speed signals and treat them as having special needs rather than as just "more of the same." By doing so, the high speed signals can be lifted up and out of the congested on board signal traffic and rapidly shuttled to their destinations. It is, by way of analogy, basically the application of civil engineering practices to electronic engineering challenges. An example of what such a "civil engineering" solution might look in an application can be seen in the accompanying figure. It should be intuitively evident that this elevated super highway approach to signal routing has some unique advantages. Those benefits cannot be achieved without effort but the list of potential benefits is long and these will be discussed next time.
Civil engineering concepts applied to electronic circuits offers important benefits in high speed signal routing by lifting critical signals up and out of normal circuit traffic and all of its associated noise and delay.