I'm with ZeeGlen here, on hand assembly, I use 0805 parts on a 100mil pitch, with 20mil tracks. This sort of spacing means its easier to jam in extra parts should you need them, and you can cut and scratch a 20mil track to retrofit a component.
The other tip for hand/proto assembly is to make the pads longer than needed, (i.e. hanging outside the component further) this gives you a reserve solder volume, and allows hand touchup with an iron or solder wick later. You can also put the paste on as a stripe for 0.5mm pitch parts, so that the stripe is outside the actual component leads, it will then suck up whatever it needs , the excess solder forms balls OUTSIDE the part. The longer pads mean you have somewhere to solder some wirewrap to if you need to reroute pins.
Another tip is to have some alcohol based flux is a squeeze bottle with a 28g tip, then you can apply a little drop of magic when needed. (i.e. when reworking, or with the paste striping technique).
Also ALL the signal pins (e.g. on CPU's) should be routed through a via somewhere even if it's not currently in use, much easier to do mods later (or retask the pcb) and it looks better, as the mod wiring is under the PCB .
And where two adjacent pins are connected together, join them outside the chip (direct connections tend to look like shorted pins after soldering, and if you change your mind later, you can't fix it).
I agree. We might be able to have a very basic model, as basic as it has all the slides and the vac system, and it will allow for a manual pick and place, all the way up to the full blown system where you put in the components and press a button, and you end up with a finished board.
Vision might be a good feature to make optional. I super high volume machines, the manufacturing pre-engineering will ensure that all components are in a known orientation. In mid volumes, or low-volume, high mix, as they describe it, it's more appropriate to have a vision system to ensure that everything is oriented properly.
With a small home-use device like this, vision would still be a very nice feature, but I could certainly see it being optional. The user could just take a bit of extra time to make sure that the machine knows to orientation of each component.
Having things like vision, past dispensing and reflow as options will give more options in the trade-off between time and money.
re: "I tried a bit of googling, but couldn't find any actual PnP accelerations."
I've been told that some of the newest machines run so fast that the heads are only barely subsonic. The drive electronics has to accommodate elasticity of the mechanism and place the component right as the component swings back over the proper spot on the board.
There is going to be a flash poll that will be posted here soon. Make sure to add your votes for the size. The commentary, though is equally valuable as to understanding why we want to do a certain size.
I would vote for either 15x15 (6x6) or 20x20 (8x8). I think that would cover a large percentage of hobby boards. It would be a good compromise between desk space and capabilities.
I might be a little biased because of where I work - you might also say I've got extra insight because of where I work - but I say that if we're going to make it a personal device, we should really design it around personal use. Convenience and the ability to fit it into small workshops should outweigh the rarely used need for larger boards.
If boards are large and sparsely populated, bigger components and hand placement is an easy option. If the boards are bigger and densely packed, then it's better off going through a commercial shop.
That is great advice if it will work for the board needs. A lot of my boards are very space constrained, and 0402s are the smallest I feel comfortable working with without having a lot of rework.
I have seen a manual pick and place machine over the last few days that has looked pretty interesting for doing smaller components. That seems like an interesting concept, and perhaps something that could be part of the modular approach that we are looking to use in this project.
@Aeroengineer improving the throughput for hand assembling SMT boards.
Design in the largest components that fit on the board, 1206 are a lot easier to manually handle than 0402. If ICs come in more than one package size use the widest lead pitch available. Use the widest copper etch possible for physical robustness.
On a side note, I would love to hear any other comments that you might have on improving the throughput for hand assembling SMT boards. I am sure that there are valuable lessons that can be learned while we are contemplating these next steps.
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