Advances in semiconductor technology will drive interconnect technology developments at all levels, from device to network. Performance improvements in systems require high-speed connections to be treated as transmission lines. At the device level, the trend toward the small, dense interconnects of the multichip module will continue. At board level, transmission-line techniques will be used for interconnection of high-speed logic cards. The backplane will survive, but connectors will be microstrip, stripline and coaxial structures that reduce noise and speed signal flow.
Surface-mounting will be the dominant component mounting technology. Transmission-line techniques will also be used at the subsystem level to respond to increased IC and system speeds. Plastic optical fiber will be popular for applications requiring increased bandwidth, and optical cable and multiplexing will play an important part in tomorrow’s smart home, which will be bus-wired, microprocessor-controlled, and have a wide variety of programmable electronic devices.
Advances in semiconductor technology will form the driving force for all of the important interconnect technology developments from the device level to the network level. For example, at the device level, there’s the multichip module with its small and dense interconnects between chips playing a major role in systems, a trend that will continue during the 1990s. Designers will perform trade-off analysis in deciding between using an ASIC and a multichip module for circuits of the same complexity. By the end of the 1990s, ASICs packaged in multichip modules to form specialized systems on a substrate will be commonplace.
At AMP Inc., we have a system called the Microinterposer under design for connecting planar substrates with a pressure surface-mounted technique. We no longer think of these links as simply rows of ohmic contacts. The performance improvements in systems dictate that all of the high-speed connections be treated as transmission lines.
At the board-to-board level, today’s backplane will continue to survive. But the multiple-pin connectors can no longer be simply pins in a plastic housing. Transmission-line techniques must be used to interconnect high-speed logic cards. Connectors will be stripline, microstrip, and coaxial structures designed to speed signal flow and reduce noise. Today’s pin fields aren’t most efficient in moving signals, power, and ground around a system.
There’s no doubt that surface mounting will become the primary technology for component mounting. For many connections, efforts are already underway to eliminate through-holes. Smaller center lines will lead to surface-mounted backplane connectors that use pressure connections rather than solder. Similar techniques will be used for other connector types. On the other hand, some connectors for some applications will stubbornly retain their strong links to the older through hole technology well into the ’90s.
At the subsystem level (for example, connecting a disk drive to its controller card or a power supply to its loads), advanced technology will play a major role. Here again, transmission-line techniques will be needed to keep pace with advances in IC and system speeds.
Plastic optical fiber for short links with system enclosures will gain in popularity for applications that require increased bandwidth. Inexpensive plastic optical cable will be a candidate to replace copper cable in a wide variety of subsystem (wire-harness) interconnect applications. Today, it’s difficult to consider optical fiber for short links in a high-speed system. One reason is that a time-delay penalty must be paid going between the optical and electrical domains. Considering propagation delay only, an all-copper wiring system can actually be faster than an optical system, even though the optical media has much greater bandwidth.
Automobiles are an application made to order for optical cable. In fact, cars may have to use optical wiring if the electronics continues to proliferate at its current pace. Eventually, a car will contain numerous internal control networks. Engine control is now fairly common, and it will be joined by a ride-control network that adjusts the suspension to road conditions, braking and traction controls systems, and a passenger convenience and comfort network that controls temperature, entertainment, and so on. Optical cable is much smaller and lighter than a conventional wiring harness and optical media is almost immune to the critical emi/rfi noise environment of the auto. Optical cable also may eventually fit in with the concept of multiplexed control where a microprocessor divides its time among various functions within a control group.
Optical cable and multiplexing will also play a role in future office equipment and “smart homes.” A smart home will be microprocessor controlled, essentially bus-wired, and contain electronics that make it possible for the owners to program a wide variety of functions.
Though copper cable is virtually universal in local-area networks, that may change in the next few years. Optical glass fiber will certainly be required for high-speed local networks, such as the upcoming fiber distributed data interface. However, plastic fiber with its relative ease of termination and continued performance improvements may appear more and more attractive during the decade as a cost effective means to interconnect small departments within large organizations.