Electronic Design

With SoPs, Good Things Come In Small Packages

The system-on-a-chip (SoC), promulgated by the semiconductor industry, touts future circuit densities and chip sizes as projected by the International Technology Roadmap for Semiconductors (ITRS). Stated ITRS goals represent challenges for developers, some of which have no known solutions. But what if those goals don't materialize, or if they're prohibitively expensive? Fortunately, an alternative exists that's increasingly recognized as a practical solution: the system-on-a-package (SoP).

Until recently, most product engineers considered the electronic package to be a simple commodity for interconnecting signals and power to chips. The package was treated as a mechanical support structure that provided protection and cooling. This attitude is rapidly changing. The improved outlook on packaging is based on higher system frequencies, more I/O and wiring support, better cooling, embedded passives, and lower overall costs of packaged electronics (chips plus packages). The SoP is a summation of all these attributes.

While the definition of an SoP varies, it's important to distinguish it from a multichip module. A module adds value by simply connecting components, whereas an SoP provides interconnection, functionality, and performance for a target product through the packaging. Much like an IC, the SoP is shaped early in the design cycle.

Technical and legal impediments to widespread adoption of the SoC are well known. This includes the legal wrangling of buying and selling IP, long design and test cycles, and combining digital, analog, RF, and microwave signals on a single die. The highly integrated SoC may be obsolete at its debut due to the enormous amounts of time wasted overcoming these obstacles.

This doesn't mean that system chips won't have their place. Microprocessors and certain peripheral functions make perfect sense. Yet many mainstream applications will evolve to the SoP model because of its many overwhelming benefits:

Noise: EMI in dense applications like cell phones—integrating digital, analog, and RF—is an SoC killer. Isolating and shielding noise-creating components is greatly simplified with an SoP.

Integration: Functions such as memory are less costly when done on specialized processes, so they're much more rationally added to a system design as components.

Interconnect: High-density substrates have multiple interconnect layers for better power and clock distribution. This lowers IC costs by reducing the number of metal layers.

Versatility: Components can be changed to meet changing design parameters. Redesigning an entire SoC, however, is completely impractical.

Time-to-market: There's far less risk with an SoP. Plus, sourcing and designing with components can be accomplished in weeks versus months.

Legal: The model for buying, selling, and combining components is well established and straightforward. Design cycles can be shortened considerably when lawyers are removed from the picture.

Packaging technology is advancing at a blistering pace, adding to the many advantages that an SoP already has over the SoC model. Shrinks of multiple chips onto a single package commonly reduce size by at least 60%, and frequently a lot more. The result is smaller boards that can accommodate more functions.

Convergence and the consumerization of electronics are forcing the industry to build more powerful products at lower cost and faster than ever before. As a result, there's a growing contrarian view to the SoC model. Good things really do come in small packages, and the SoP will provide them.

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