As an example of what might be achievable, consider the MicroZed™ module and a few of the associated prototype carriers. The MicroZed SOM is a Zynq-based SOM. It has 10 layers, which include two extra ground layers, ensuring an ideal reference for better signal integrity. In contrast, the three prototype carriers have six, four, and two layers for the FMC, I/O expansion, and breakout carriers. Rather than requiring a combined PCB where everything must have 10 or more layers, the complex, multi-layer circuitry is on the SOM, allowing the carriers to have potentially fewer (and analog isolated) layers.
Getting to Market
The last point to consider as a SOM advantage may be the most important of all: the ability to get to market faster with a higher-quality product. Two common-sense advantages are obvious. First, a large chunk of circuitry does not have to be designed. This circuitry alone represents a design, debug, and manufacturing investment from the SOM developer that likely translates into many man-months of engineering effort — possibly a year or more. This investment likewise speeds a new engineering project that does not have to go through the same design effort for the same circuits.
Second, since engineers are not focused on the central processing unit and core circuitry, they have more time to invest in the technology that will differentiate their product. A company’s core competency becomes the true design focus, rather than figuring out all the complex and very important details around the processing unit. This allows engineers to focus their skills rather than attempting to become a power, communications, and memory interface expert at the same time.
To add up all these savings is a challenge, but a conservative estimate is likely 12 extra man-months of engineering time, and at least one PCB revision. Each company must evaluate what this is worth. Using an industry estimate of $125 per hour engineering figure1 and $25,000 PCB revision puts the value of using the SOM at about $285,000. Adjust this figure based on your own locale, and then use it to determine the cross-over point at which you might want to consider a chipdown design.
For example, if a module costs $175 in volume, but an engineer could build a chipdown equivalent for $125, the SOM premium is $50. Taking the savings amount ($285,000) and dividing by the SOM premium ($50), engineers will find the crossover point is 5,700 modules. In this analysis, if a project required fewer than 5,700 units, then using a SOM provides a real cost advantage in addition to all the other advantages, including time to market. At more than 5,700 units, it may still be worth considering a SOM for the other advantages, but the chip-down design’s raw cost is less. A complete analysis would need to include the additional sales revenue potential that the time-to-market advantage provides.
While a full custom electronic design will never be as modular as a PC, integrating a SOM offers significant advantages over designing a complex circuit that is possibly outside your specialty. The next time you upgrade your PC memory or plug in nearly any piece of electronics, take a close look at the DIMM or the AC/DC brick power supply and consider the convenience achieved by someone else expending the effort to provide a complex, tested, and certified module. By integrating a SOM into your next design, you will find similar pre-packaged convenience and enjoy the great advantages of modular design.
This article was written by Bryan Fletcher, Technical Marketing Director at Avnet Electronics Marketing, Phoenix, AZ. For more information, Click Here.
1 IEEE-USA Consultants Fee Survey Report, IEEE-USA E-Books, 2011