It’s time to visit the topic of yield. This is a boring subject for many engineers, but for entrepreneurs, success or failure will be determined in part by achieving a reasonable yield. Unlike software, every copy of a physical good will have slight imperfections. Sometimes the imperfections will cancel out; and sometimes the imperfections gang up and degrade performance. As production volume ramps, these corner cases start adding up and a certain fraction of product ends up non-salable. In a robust design, the failing fraction may be so small that functional tests can be simplified, leading to further cost reductions. In contrast, designs sensitive to component tolerances will require extensive testing, and will suffer heavy yield losses. Reworking the defective units incurs extra labor and parts charges, ultimately leading to profit erosion.
Thus, a major challenge of moving from the engineering bench to mass production is re-designing to improve robustness in the face of normal manufacturing tolerances. This is called “design for manufacturing”, or DFM.