yield

Yield is the fraction of chips coming off a manufacturing line that actually work — the single number that most determines whether a chip makes money. If you pattern 1,000 dies on a wafer and 850 pass test, your yield is 85%. Because a microchip is millions or billions of features that must every one be correct, even rare random defects — a stray dust particle, a single broken via — kill whole dies, and their effect compounds with chip area.

That last point is the heart of advanced packaging's appeal. The chance of a die being defect-free falls steeply as it gets bigger, so one huge monolithic chip can yield terribly, while splitting the same function into several small chiplets — each individually likely to be good — and recombining them in a package can yield far better and cost much less. Yield ramps over a product's life as engineers hunt down and fix defect sources; a node that yields 50% at launch may reach 90%+ at maturity, which is exactly when it becomes cheap.