On 24 June 2016 at 14:23, Attila Kinali <[email protected]> wrote: > Unlike what most people seem to think, small batches of PCBs have always > been a business for some assembly companies.
For my sins, I am one of those... (Cambridge, UK). Yes - semi-manual assembly is the way it goes, especially for the active parts. It's just not worth teaching the machines and loading the parts for small runs. Typically, passives with more than 20 instances I'll load onto the machines, then do the rest by hand on a manual placer. Stencils - not any more. I use a dispensing robot, which is fine down to 0.4mm pin pitch as long as the ambient temperature is right (35oC, quite deeply unpleasant to share a room with). No more cleaning stencils, throwing away paste, or wishing that the customer-supplied stencil wasn't unhelpful in one of a thousand ways. It also means that I can go from CAD data to built boards in less than a day, if I ply my local PCB house with enough cash... I definitely concur with the 'make it SMT as much as possible' plan - pin-mount stuff is a pain. Also, QFN is far preferable to QFP, as catalogue suppliers don't always manage to ship fine-pitch stuff without bending legs in one direction or another. Reworking a duff QFP (or fine-pitch SOP) can take as long as assembling a whole board. With small volumes, there's no real statistical process control, you just do what you think will work, fix any defects, and update the big logbook of results. Hacked reflow ovens have a place, but there are some parts that simply won't solder with IR - the heat load to get the balls to melt is more than it takes to kill the part. LTC's modules are especially bad, but any BGA runs a risk. I'm a recent and thorough convert to vapour phase (which can also be done in a homebrew manner). Also - Pleeeeease overbuy components! those extra few 0402 resistors cost you a penny. Finding the one that pinged off or the machine threw on the spitback pile - impossible. Sorry about the offtopic. (I'm also a moderate frequency nut and EMC chamber owner, so am starting to get nutty about RF amplitudes, which is a whole new game...) Steve _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
