one machine for PCB assembly

The LumenPnP can now do it all: deposit paste, then immediately place parts! Blank board goes in, working board comes out!

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[jaredharvey]

The most accurate and reliable way to dispense is to use air pressure pulse. Move tip to something like 0.005in from PCB. Then provide a brief puff of air pressure. Once a very accurate dab is dispensed, the air will stop moving the paste. This is how we do thousands of caps each day for the last 30 years. You should experiment with that approach.

[eshkrab]

I think lumen wants a hot plate attachment. Just cook the solder paste in place.

Shirt on point 👌

[RestartVandelay]

There is a paper called "Photo curable resin for 3D printed conductive structures" in the Additive Manufacturing journal. "In this study, researchers used acrylic as the photocurable resin, AgCu flakes, and Ag NP for the metal fillers. They prepared the mixed resin solution/paste by adding 15 wt% of ethylene glycol, 7.428 g of AgCu flakes, 5 wt% single-walled CNTs, and 8 mg of photo-initiator Irgacure-819 into 80 wt% of commercial acrylic resin followed by ultrasonication and magnetic stirring for an hour."

Not sure if these are feasible on your time scale but what you are trying is definitely possible.

[JaenEngineering]

When it comes to precision dispensing using syringes the trick is using air pressure (pneumatics) on the back of the plunger.

[TheCebulon]

I am so happy to have the energy and happiness of the videos in the beginning back again.
Love this development and engineering content back.

[stratos]

Doing this with solder paste instead of ink would make PCB assembly so much faster, and less manual. Then include a hot plate as well and boom, soldered PCBs without lifting a finger. Prototyping dream

[dfgaJK]

I'm so excited to see it going with solder paste... you could have a reflow plate on the Lumen bed so it automatically reflows after... then maybe even a flying test probe to test the board once soldered, all in the one fixture!!!

[epremeaux]

assuming you have (or are willing to get) a shop compressor, I STRONGLY recommend getting a 983a digital auto paste dispenser. It attaches to the syringe with an airtight cap via tubing. So, far less mechanical load on the lumen. Basically NO mechanical stuff to add, other than the syringe holder.
The controller gives you .. control .. over the dispense air pressure, dwell time and back-off pressure. So you can set how much pressure is needed to push the paste (solder paste needs much more than ink or glue for example). Then the wait time for dispensing (controls how much actually comes out), and finally it sucks the piston back a bit to control drool.
for interfacing, it has a foot peddle switch input (common 3.5 mm headphone style plug). As a digital input, it reduces the code on the lumen as well (no step driving.. just trigger the logic pin and wait whatever you set the paste time for.
Its really helpful for manual pasting to prevent cramping or just hand exhaustion from pressing the plunger over and over.

[Icuosnas]

Coming from the polymer world here, maybe if you tune the extrusion rate and filler percentage to optimize the conduction, a "film" is all you'd need if you let the UV resin cure for long enough. Alternatively, you could experiment with a reflective filler instead of graphite that conducts but honestly at that point solder paste with a re-flow is the mechanically better option.

[Roobotics]

One thing that would be super clever is if you had a way to dock the nozzle into an airtight sheathing so it's capped back closed as soon as the operation it's needed for is done, prevent drying out and keep it performing as best it can, since it wants to actively evaporate, so basically treat it like isopropyl.

Also I don't think the UV resin is going to pan out easily TBH, you sort of need a conductive grain suspended in a liquid that will remove itself from the equation and promote bonding between the grains to form conductive chains/blobs, because most conductive liquids are actually pretty bad at it! Resin hardly looses any mass when it cures, it won't promote those bonds, just freeze the grains in place(and if it was able to reasonably flow, that means they are spaced apart, so they are now frozen in that spaced apart state since next to no resin was lost), and as you found out, also get inhibited curing by the grains etc. You'll also have to deal with settling over time if the suspension isn't stable.

Nitpick: 'dead reckoning' is used in relation to finding an *unknown future position* by using previous known positions, headings, and speeds. You know the intended future positions already, so there is nothing to 'reckon' here. This would be referred to as running an 'open loop' placement method, instead of the 'closed loop' of the vision system and active refinements it makes. Though technically speaking your steppers themselves are also 'open loop' without encoder feedback from skipping.

Pedantic things aside, I think it's amazing you got this going already, I just knew it was coming after the prior video. For your extruder system you might need to make sure the plunger never starts spinning, else that will cause unmetered results. I'd at least put marker dots on the edges of internal things it so you can visibly observe to see if that ever does occur or the friction keeps it running straight.

[siberx]

If you could interleave the paste application and component placement (ie: paste the pads for a single component _immediately before_ placing the component, even after the part is picked up potentially) then you don't need to worry as much about having longer curing times for the paste. It only needs to stay workable on the board for a few seconds, although you do want to ensure it won't dry out too badly on the dispensing tip at least.

[ross]

Your excitement is contagious, thank you.❤

[cbmretro]

Like we have learned with the high-end 3D printers, using a gear reduction for the extruder would give you substantially more torque (given your low power stepper motor, where you mention it periodically missed steps) and also give you very finite control of the pressure. 3:1 to 8:1 ratios should be tested. This will allow complete control necessary for reversing the dispenser flow. This is the only thing missing from your design - well done!

[UnexpectedMaker]

Huzzah! That's an awesome result, well done! Yeah, forget conductive ink and get the solder paste application going. That's the golden ticket here :)

[ericlotze]

Now I’m intrigued what the “weird stuff” is!

(Granted it’s been a while since I’ve checked the discord :3 )

[TheCmdCousteau]

Congrats on this iteration ! Very inspiring. Maybe you can try putting more ink and some retraction to suck back some of the ink back in the syringe. I think the pad should then fully covered without having too much of ink. Also could add a sort of retractable cover that moves out when the ink head goes down and comes back under the syringe to prevent any unwanted drop on the table. Keep up the good work !

[tec]

The UV resin might also not work because it doesn't dry, it cures. So ther's no non conductive solvent that can evaporate from in between the conductive particles, it just stays there and polymerizes. So the resin would stay in the high resistance state like the wet glue you used.
Also, i think there's electron beam hardening glue, but that kind of defeats the purpose of being accessible

[CAB]

There's a manufacturing technique called wave soldering where a board is basically dragged across a pool of liquid solder. This works well with through hole components that are all on the same side. However this process can easily be adapted to SMD components by adding a drop of adhesive between the pads of an SMD component. Often it's two tiny drops along the nonconductive edges of the SMD component. Many power boards are made this way where all the through hole components are on one side and all the solder joints and SMD components are on the other side. Anyway, this syringe setup is perfect for this process; it could add the adhesive, then place the components in the adhesive, and then the board would be ready to solder.

[antadefector]

This is also good for dispersing glue, for glued SMD components. I remember time all SMD components where glued and wave soldered together with THT components. (Ugly memory of SABA TV chasis going trough head). Thanks for nice videos, and for hard work. Best Regards.

[EndlessRaidApp]

Try switching to indium tin oxide powder, It is both transparent and conductive, so potentially will allow more UV light to pass though, a bit expensive for the powder though.