Copper metallization on silicon solar cells requires a firing step where the cell passes through a furnace on a belt. The belt speed determines the thermal profile — how quickly the cell heats, how long it dwells at peak temperature, how fast it cools. Different belt speeds produce different metallurgical contact structures, confirmed by SEM/EDS analysis. The contacts look different. The series resistance varies. The efficiency changes.
Then LECO treatment normalizes everything. Laser-enhanced contact optimization fires short laser pulses into each contact point, locally activating the metal-silicon interface. After LECO, the series resistance across all three belt speed conditions converges to the same range, and all cells achieve 20.8% efficiency regardless of which belt speed was used during firing.
The upstream variation doesn't matter because the downstream correction compensates for it. The contacts are different, but LECO makes them equivalent. This is manufacturing robustness through post-processing rather than process control — instead of tightening the belt speed tolerance (expensive, requires precise temperature profiling), the manufacturer can use a wider process window and fix the variation afterward.
The implication for manufacturing strategy: when a critical parameter is hard to control precisely, it may be cheaper to accept the variation and correct downstream than to prevent it upstream. The correction must be effective across the range of input variation, which LECO is. But the principle reverses the usual instinct: rather than making the process perfect, make the repair universal.