a) doing some reading on design for manufacturing
b) getting some quotes for PCB assembly services and
c) considering factory-programmed microcontrollers
At quantity 200, you could have simple boards like these assembled for about a buck a piece. Microchip will program 200 PIC or Atmel microcontrollers from the factory for about 20 cents each with a $29 setup fee. Unless you're willing to work for a very low hourly rate, you should probably take advantage of someone else's economies of scale.
The real issue was that I had ended up cutting a lot of corners to try and get things done in time, particularly with regards to testing. Definitely a major lesson learned.
The MCUs didn't take long to program with a ZIF socket, but once they were baked onto boards and I was finding bugs that needed to be fixed, that's where it really turned into a pain doing it over SPI.
After all of that, I still ended up having to bodge 2 connections on all of the final boards after all was said and done (which was the 5th or 6th board revision after I did small test runs to play with things and fix issues)
They have some competition but CircuitHub is my go to. Others to check out are...
Haste makes waste, measure twice and cut once. It's one of the hardest lessons to properly internalise - bodges and firmware changes can be hugely time-consuming, so it nearly always makes sense to absolutely nail your prototype before moving to production.
Congrats on a cool project.
One/one-hundred-off prototypes are expensive but nothing beats the information gained from soldering a board, plugging in connectors, and programming chips directly. You'll do these steps at the end of a waterfall process anyways, and I'd say they're more expensive to alter then. When a problem is found, deciding to bodge wire two pads is the high-cost, low-risk solution to problems found late in the game. Discovering the problem early, fixing it in the schematic, and testing during your next prototype cycle is cheaper during production and risk is mitigated because you're still going to be testing before you ship.
Of course, this is all very much propaganda, and not all shops would follow this idealistic scenario, but I don't think hardware is any more waterfall than anything else.
1. In-person reviews with an expert. Offline reviews can be useful for getting a design out, but to understand the problem space, you need a back-and-forth conversation. Sample conversation that's easy in person but very hard over email: "Why not do it this way?" "Well, that would work, and it's a good solution a lot of the time, but you have this thing over here which makes this other approach a lot better...."
2. The hard way: sometimes there's just no substitute for experience.
At quantity 200, I think contract assemblers make a lot of sense (but do shop around: the economics of this particular supply chain can get weird), but factory-programmed parts really don't. Maybe if your firmware is final final I'd advise a client of mine to do it, but in any case where you're going to want a later firmware update, the best ROI is going to come from getting the debug port hardware perfect. That means the right connector (standard pinout, standard part, from a good quality manufacturer), level shifters where appropriate, pull-up and pull-down resistors, and all the rest. (Making sure this stuff was all explicitly spelled out on our review checklist was one of the first things I did when arriving at my current employer, and it's saved us and our clients a lot of money!)
Seeed Studio guide to DFM.
First, this is the DFM guide specifically for Seeed. Every factory will have a different set of specs depending on equipment (assembly, test, and inspection, and familiarity of operating personnel), throughout requirements, yield requirements and price points, rework allowance, and so on.
Second, these typically assume for wide tolerances. Operating environment or design may necessitate relaxing some parameters in order to allow others to tighten (aka the tolerance stack up).
Dealing with both cases effectively in volume production is what requires experience beyond the manufacturer provided DFM guide.
Someone who learns this guide inside and out will be able to DFM with Seeed but not necessarily anyone else.
More generally, the DFM guidelines for ceramic RF materials would be wildly different than for Kapton flex connectors or for standard FR4 material.
Even if some things are different across CM's, the guide at least provides an awareness of the main issues for the target audience (amateurs or people getting their feet wet) for which these things are "unknown unknowns." If someone were to follow Seeed's guidelines, they would be in a good position to adapt their stuff for a different CM as long as they're receptive to feedback and the CM is willing to review it.
Right now it is a tool for myself and my work, which puts a priority on being comprehensive; but the licensing is liberal and I’m open to input.
Also some bottom rung assemblers you don't want to trust with your production firmware!
For me, 200 boards:
1. JLCPCB board + parts + assembly service.
2. Final assembly (non placeable parts) yourself.
3. Load firmware in and test via own test/programming jig.
4. Pack and send.
It's still not quite trivial, but it's not exactly hard now for small designers to go circuit -> Amazon without ever having to do any assembly at all.
I don't think PCB assembly would be that cheap, especially for a board with lots of SMT components. What I understand is that SMT manufacturing has a high startup cost, you need to supply the factory with full tapes of parts, and the factory needs to program the assembly line, often a factory is reluctant to take any offer below tens thousand boards because its high overhead. Even for service providers specialized in prototyping then, I don't see many provide QFN and BGA packages as options.
What have I missed here?
I just requested some quotes for assembly of 200 boards with a single-side load of 25 SMT parts, of which one is a BGA. The cheapest quote was ALLPCB at $1.09 per board, followed by PCBWay at $1.33 per board. That price includes setup and testing.
No transaction involving Chinese outsourcing is without risk and you need to do your homework, but it is no longer the case that DIY assembly is your only option.