Making PCBs can be "essentially free" because the manufacturer can group multiple orders on the same panel so they reduce manual workload and increase throughpu

Making PCBs can be "essentially free" because the manufacturer can group multiple orders on the same panel so they reduce manual workload and increase throughput. The PCB manufacturers typically also offer assembly services, but individual assembly orders require individual sets of components. So you either need parts feeders with a huge variety of components (read: expensive) or you need to intelligently group the orders that use the same set of parts. And for minimum cost, you'd need to group the orders that used similar parts onto the same panel so they could all go through the P&P at the same time. I suspect that it's feasible, but there's not enough cost pressure on assembling PCBs for the manufacturers to bother going down that road.