how to purchase simple custom devices with low quantities? [closed]

Question

We have need for a few simple devices, mostly as adapters and connectors between other devices.

One example is:

• 6-pin Molex connector with 20-30V between two pins
• 24V to 12V DC-DC voltage converter
• 24V to 5V DC-DC voltage converter
• 2 x USB port (5V voltage output)
• 1 x simple DC power plug (12V voltage output)

I found suitable voltage converters as components: 24V to 5V, 24V to 12V

Now, my question is: how can I purchase this as an assembled device with a case? Is this prohibitively expensive for low volumes? I would need around 10 of these for testing, perhaps hunders or a couple thousand later, but nothing certain can be said about that. Should I attempt to find a simple sweat shop locally for the first 10, or can I buy them from China through some service? What are my options in general?

Answer 1

I think the other answers are missing the mark. If I understand the question correctly, you're not interested in doing the engineering and prototyping/manufacturing yourself; you're looking for someone to do the design and prototyping for you and then help you transfer the design to a contract manufacturer if/when it goes into production.

That's what an engineering consultant is for (and that's what I do for a living). This person (or firm) will take your functional specification, which you've outlined very nicely, help you refine it, then find the right electrical and mechanical components to implement it, build and test the prototypes, and in the end, provide you with all of the documentation (schematics, bills of materials, assembly instructions, user manual, etc.) required to produce it in quantity.

There are some contract manufacturers who provide this sort of design-build service in-house, which means that they'll do both the engineering and the volume production for you, and you don't need to deal with two separate entities. The types of assemblies you're talking about would actually be a good fit for this model, since it doesn't sound like you need a lot of very specialized engineering knowledge for your adapters.

So, look for "contract manufacturers" in your area, and see which ones have in-house design services. There are frequent trade shows for these services all across the country, too, and this is a good way to see what's out there. "Design-2-Part" is one series of them I'm familiar with.

Answer 2

Prototyping falls under research and development. That in it self is expensive and yields 0 profit but you can get a patent or two out of it, if not - then generate revenue to sustain your business.

What you want to do will be expensive - compared to mass production.

What you need to take into account (some free advice to get you started)

• Using SMD in protoyping is really expensive because you have to get somebody to assemble it. So try to avoid it and use traditional components, because you can assemble them your self easily- and get them cheap of eBay.
• If your prootypte uses a SoC or similar that only comes in a fine pitches package like QFN40- you might as well use SMD's because you will need somebody skilled to put the QFN onto the PCB properly!And you will have to find a local company that will do it cheap for you. I have a guy in UK who does them £15 per PCB without stencils; all hand placed.
• Producing PCB's is extremley cheap. I use Seeed bazaar (look at services link) but they also have a propagate menu option that might be interest to you.

Once you are happy with your prototypes and 6 months pass testing and assembling them. You go and find a contract manufacturer and they will make you 10 thousand units fully assembled and tested for a fraction of the unit price. Rule of thumb. The smaller the SMD the more expensive the manufacturing will be. Try not to go smaller than 0805 package.

Good Luck.

Answer 3

There are a number of funny stages you hit during this process. One is where you have SMDs that you're just trying to learn how to use, you're not sure exactly how they fit into your circuit, and you're not ready to mount them on a prototype PCB even in a run as small as 10.

Your savior here is www.proto-advantage.com. They will sell you a breakout board. They will also purchase your part from digikey, and mount it on the breakout board. They do this at a reasonable price, with fairly low delivery times.

It's the next step that's a bit harder -- having a prototype PCB that you need populated. Big assembly houses will often do this, in my experience, when they think it will lead to a real job, but you pay fairly dearly for this. It also slows things down to a crawl. It can take a house like that a week just to generate a quote for this type of job. If it's complicated or fine-pitch, they will want to cut a stencil, and they will use their own mechanism to generate a stainless steel stencil to their in-house spec, which will really add to big NRE on a small job. There will be discussions on whether your boards will be kitted, or full turnkey (that is, who's supplying the parts on the BOM).

There are smaller shops that you might be able to find that provide these kinds of services fairly routinely, but again, you'll often find the quote process can be a bit slower than somebody in a prototype frenzy wants to accommodate.

Frankly, this sort of stuff was going on around here often enough, adding a few weeks and a few thousand dollars here and there, that I tooled up with a jury-rigged reflow station -- a toaster oven refit with a Global ramp-soak controller, beefed up with some extra insulation to get some more oomph out of the heating elements, and a 10x-200x usb microscope to help deal with small parts. Hard to say if this is right for your situation, but I'm very happy that it got done. Took about three weeks of dorking around, putting in the temp controller (which many would call optional!) working out a good ramp-soak profile, learning how best to deal w/ the solder paste, ...

Total cost in parts, ~$250-$300, about $120 for the temp controller, about $20 for thermocouples (which I sort of spring-load near the biggest components on the boards), about $50 for a convection toaster oven, and about $100 for the microscope. Instructions literally all over the web.

It makes the system of using the proto-advantage boards pretty fast.

Some PCB houses even supply a free stencil along with a board. Depending on size, the types of boards I deal with usually run about $120-$150 shipped in quants of about 10, two sided, masked, with a one side silkscreen and a really nice surface finish, free stencil, with an 8-10 day turnaround.

You'll want to build a small jig to help you deal with stabilizing a stencil, if you go this route.

For maximum efficacy, a hot-air rework station would be a valuable tool. I fake that right now with a butane iron with a blower head for the two or three times I needed it, but I'll buy a cheap rework station soon.

Works great, really speeds up prototyping, and I've had no problems with components down to 0603 (and I don't have a young man's eyes!)

A problem you'll encounter if you go out-of-house is that the places that deal with assembling PCBs want nothing to do with boxing them in a case-- at least in my experience. To get this done, now you're talking about harness makers and contract assemblers. It's great to think of this stuff at the stage when you're designing your board-- it will make your Design for Manufacturability pass go much smoother. Many connector issues these days are handled right at the circuit board. I've always done this sort of prototype assembly in house. Take a look, though, at frontpanelexpress.com, particularly their enclosure service. This will be expensive (at least from my angle, maybe its a service very much worth it to you).