Yield analysis

Updated October 24, 2009

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New for November 2009! Yield is a measure of how good your manufacturing process is, and it directly affects the bottom line. Yield is a measure of how many circuits you build are born dead, so perhaps it is the opposite of reliability, which is a measure how long a part is expected to live.

Yield is often a closely guarded secret. If your competitors know your yield, they will have a pretty good idea of what your products cost to make. You might see questions after an IEEE or other presentation where a member of the audience steps up to the microphone and asks the "yield question". Trust us, the answer is worthless, because the speaker either has no insight into the real data (in which case his company considers his answer harmless) or he has been carefully coached to give a very high number to scare away the competition. That 90 nanometer optical tee-gate process that was used to create a terahertz amplifier provides 90% yield, sure, we buy that! Good one!

Yield analysis

Yield analysis is done in the design phase in order to"center" the design to the process specifications. Monte Carlo simulations are the most typical means.

Any expensive EDA tool will facilitate Monte Carlo analysis. You need to know what parameters will vary during manufacture, and what the variation might be. There are entire books on thie subject, but we'll try to post a few examples in the future. The classic example is filter design, where you need to preserve the passband, as well as the rejection, which play tug-of-war with your design. In an edge-coupled filter, the substrate height variation, the dielectric constant (if you are using a soft board), and the etch factor are the primary culprits. Say, that reminds us, we don't even have a page on etchfactor yet... until now.

More to come!