> surface mount PCB assembly for $30 for 20 boards
Often uneconomical to set up pick and place for just 20 boards. Quite often the wizardry is a little middle-aged Chinese lady who wields a vacuum tweezer like a chopstick, from 9am to 9pm six days a week.
But it's skilled work, so it'll be paying skilled wages. And you need an inspection step - especially if you're working with BGAs and other difficult components. Presumably for $30 they're shipping out boards without doing a power-on test - which makes visual/x-ray inspection even more important.
And even when the assembly is manual, you've still got to get the right parts to the right assembly station at the right time. Can't be putting in a 5% 10k 0805 resistor if the design calls for 1%.
Even with manual assembly, if they're making a profit at the prices they're charging they must be running a very efficient operation indeed.
Thats where the custom software comes in - you can program a robot to move in a pattern through setting it or through sending coordinates to it (I have done that as part of a job).
You could have software that converts the instructions for the PCB into instructions for the robot to do pick and place.
Often uneconomical to set up pick and place for just 20 boards. Quite often the wizardry is a little middle-aged Chinese lady who wields a vacuum tweezer like a chopstick, from 9am to 9pm six days a week.