Recently, I have had quite good experience on PCB assembly from PCBWay. Everyone uses them for board manufacturing, but it was quite impossible to find actual testimonials for their assembly service - so I just took the bullet and tried them, and have been very happy.
The first board was actually rather complex - I tried to get a quotation from a local, more expensive assembly house and it was a nightmarish discussion since they didn't even seem to understand the design files at all. No issue whatsoever with the Chinese! Everything was manufactured correctly, and out of 30 boards, about 400 components each, some 0.5mm LGAs, many 0.5mm QFNs, and 54-pin 0.5mm TSSOPs, and tightly packed 0402 passives, and some power components, 29 boards tested electrically perfect; one board had one solder bridge and one pad lacking a bit of solder.
When sourcing the components, they add a bit more than you'd expect on the top of the actual component prices (around +30-+50%), so this offsets the insanely cheap setup cost (typically in range of about $500 even for a complex design). (Some extra is to be expected, since they need to order some extra components - also, this increase is to pay for the sourcing job. It's still a little bit more than I had expected.)
Recently I sent them some components as well. No problem there. They are very responsive as well, and ask for confirmations (clearly written, with pictures) whenever I have forgotten to specify something, such as a LED polarity.
This reply is not sponsored or paid by them. Just a happy customer. I'm sure there are even better assembly houses, but the low cost, good customer service, and the easiness of the process has been nice.
Things to remember with any assembly service:
- Make sure the components are built correctly so the centroid file works OK: i.e., the origin must be in the middle of the component, pin1 or cathode to the left, and so on.
- In addition to P&P (centroid) file, you need to supply a basic excel BOM with quantity, designator list, and the order code
- You also need to deliver an assembly drawing, unless your silkscreen is really complete. With today's integration levels, silkscreen typically cannot fit all the info in a clear manner: so this is basically a pdf file where each component outline is drawn, and the designator is inside this outline, and the pin1 / cathode / whatever extra information for orientation is clearly marked. This file is a must because, unfortunately, the standardization for the P&P files is a rather new thing, and kind of broken, so they can't trust the automated information of the pin orientation, and need to manually check each component. For example, some datasheets draw diodes cathode to the left, some cathode to the right, some draw them vertically. How do you translate this datasheet to the PCB library component?