Working with Contract Manufacturers

Working with Contract Manufacturers


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As an independent engineer and sole proprietor, I don’t have a team I can delegate tasks to. Everything from product design to taking out the trash rests on the shoulders of the guy at the top. That means producing more than 10 units at a time is outside the scope of what I alone can handle. Prototypes can be hand soldered, hit with the hot air pencil, or–if you’re really fancy–run through the reflow oven. Note: the “reflow oven” may or may not have been a toaster oven in a previous life…

Production runs are starkly different from prototyping and require automation. A good process will churn out exceptionally complicated designs from a well specified set of plans. Match that with the experience of board assembly troubleshooting and the likelihood of success goes up. The automation and expertise lies in the hands of people that do these tasks every day: the Contract Manufacturer (CM).

Contract Manufacturer Export Files

The first thing you’ll discover as you start talking with different CMs is that each wants a different subset of your design documents. Some are happy to accept EDA files (say a .brd file instead of gerber files). Some want all the gerber layers and a BOM. Some might want that BOM in CSV format, but it will vary between those that want it in tab delimited vs Excel native format. If they’re feeling really froggy, they’ll ask for a placement file (with the same formatting requests). The trick to this, is having a single source that generates all your design output. Look deep into your EDA tool of choice, and work out a way for you to store every last bit of component information in there that you can. It’s already the central repository for the design and layout information, make it the centralized source for all your parts requirements too.

Contract Manufacturer Example Files

Why is centralized management important for parts? Because Contract Manufacturers will impose changes on you based on their in house inventory and their pick-n-place (PnP) capabilities. As an independent designer, the in house inventory at the CM becomes important, because they are buying at far greater volume than I ever can. Chances are, they have my 0.1uF bypass caps already loaded onto a PnP reel. If it’s already loaded onto the reel, they might cut me a deal on the setup costs, and I’m certainly going to get a cost savings because of their purchase power on those common parts.

What if that part is a different footprint size? I standardize on 0805–because I know I can solder those on my prototypes–but many CMs stock 0603 sizes. When you make that change to your PCB, it would be great if that change was automatically made throughout all your design files, including the BOM. That’s why you want to keep everything inside the EDA. When you export, you have the latest and greatest values for everything from technical spec to footprint.

Keeping Everything Organized

When you finally do get to the point of pushing the “Make My Widget” button, you might have to start dealing with higher quantity parts sourcing. Many CMs will offer to do this for you, but there are costs associated with it. In some cases, they will ask you to source and supply the parts instead. Smaller CMs do not have the manpower to do all of the sourcing for you.

If you’ll be sourcing the components, ask your CM if you can have the distributor dropship the components to them. In that case you’ll need to work out very carefully what sort of information you want on the component packaging: value, footprint, reference designator and an internal part number are most likely the minimum they’ll require. If they won’t accept a drop shipment, you’ll need to track everything as it comes in from your vendors. The box from Digi-Key. The box from Avnet. That other box with small components from a past build. Your BOM is 45 parts long and everything starts looking the same. Get well acquainted with a label maker and don’t let a single thing out of the box until you’ve got a solid documentation and tracking strategy in place. I use 2″ x 4″ shipping labels printed with the project name, project number, CM quote number (or whatever reference they supply), schematic reference, description, type, value and footprint size. One of those for every item on the BOM, and as soon as I take the bag out of the box, the label goes on. For parts in tubes, wrap a piece of paper tightly around it and use two stickers back to back on the long edge. Making it easy to get the assembly equipment set up will help ensure a friendly relationship with your CM.

Contract Manufacturer Kitting Label

Essentially, as an independent, working with a CM demands that you be flexible, but detailed. You might not be inclined to do so after having lived with your design for so long. However, mistakes can make a huge impact to your product schedule and the end product quality. The Contract Manufacturer is your business partner, and while it is their job to deliver your product on spec at the quoted price, you need to be prepared for the variety of demands and the changes imposed by that partnership.

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