Sausage Factory Project Update – SMD Reflow (or, 10 steps to a nice prototyping experience)

Well, many of my friends in the Upverter and CircuitMaker world have requested more details about my first project start to finish done in Upverter.

So here’s a quick update. Since I finally got a corner of our office and was given the blessing to use it for making stuff, and since I’ve finally got all the parts, I can show the next phase of the project.

But talk about a wait!! The slider pots took 12 weeks to arrive! I should have checked the supply chain for them in Octopart before designing them into my pedal!

I’m still not ready for final testing yet – stay tuned, but at least here’s an update on my progress with hand assembly of the prototype.

Now, you may not have access to a desktop reflow oven, but if you can afford to get one of the cheaper units, or build one using a toaster oven, then I highly recommend the investment. Believe me, you’re worth the time it saves when building stuff with SMT devices. Even hand pick and place is not too painful once you’re organized – as my video demonstrates here.

But this process, though you may spend a few hours on it, is so much better and faster than it used to be. For a good flow, like what I did in the video, here’s what I recommend to anyone building prototype quantities:

      1. Find a decent workspace with enough bench area to spread out your project. Mine is about 15 ft2 but you don’t need that much, 7-10 ft2 should do the job.
      2. Get a compact desktop reflow oven, or build one, or use the hot plate method if you’re doing SMT parts just on one side of the PCB.
      3. Get some anti-static component trays, with enough 2 in2 compartments to hold your “popcorn components”.
      4. From your Bill of Materials, print out the manufacturer and reference designator columns, and cut them out as labels for each component bin or compartment.
      5. When ordering parts from DigiKey, Mouser, Arrow, or whomever, make sure that you add your reference designators to each component line item so when they ship to you, each bag, tube or tray holding the parts is labeled with the reference designator.
      6. One by one sort the components into their labeled compartments in the quantity needed for your production run.
      7. Print out the top (and bottom) assembly drawings on large (A3 or 11×17) format paper and stick them to the wall in front of your assembly area. I find it helpful to also print out the schematics in case I need to verify a part against the engineered design.
      8. Order the solder paste stencil with your boards, or get them from a good stencil shop such as OSH Stencils. If you have access to a CNC or laser cutter and you know how, you can make them yourself from polyimide or acrylic film. Usually they should be very thin! No more than 1-2 Mils. Make a jig with other scrap PCB material for aligning the stencil over your project PCB. Don’t try to use the stencil without this scrap board jig! If you do, you’ll bend it and the holes will not align correctly with your board.
      9. Pick and place the parts with tweezers or if you have one, a vacuum nozzle. Pay careful attention to the orientation of polarized capacitors, diodes, transistors and ICs. The magic blue smoke can’t be put back in if you insert them wrong!
      10. Carefully put the board into your reflow oven, or on the hotplate. If you can control the temperature you need to – this is the difficulty with using the hotplate approach, you have to watch it closely and remove the heat once you see the solder fillets fully formed. Excessive heat will damage devices and your board may be DOA if you’re not careful. If you have an oven, select a solder heating profile that is suitable for the paste you’re using. Lead free pastes need a higher temperature than tin-lead pastes.

     

Finish up by hand-soldering any through-hole parts you may have, then your board is ready for testing!

 

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