Low temp solder paste and 3D printed PCB...

I have seen a lot of PCB from 3d printer projects online. But I'm looking for a better solution then solderless pens and glue for trace routes and attaching parts.

I can print really small boards with really small trace routes.

I was thinking about using low temp solder paste in the trace routes and on though hole parts... Put all of my parts on the board, then flipping it and filling in the holes and traces with the solder paste...

The 3d material melts at 180c. That's about 30c less then the paste I have seen.

I have never worked with solder paste... So is this do able? The videos I have seen of solder paste in action show it pooling into one spot. Is that possible to avoid?

Thanks any ideas or suggestions!

Dan

The Lead solder paste I use, Kester EP256, (vs unleaded) has a reflow profile:
ramp up to 125C to 150C, hold for 60-90 seconds.
ramp to 183C to 200C, hold for 60-90 seconds (at a minimum rate, like 6C/minute)
Cool down.
The ramp up rates require a 4-element toaster oven. I have an old Sears/Kenmore toaster oven that we use, with a multimeter & JK thermocouple probe to monitor the temp.

Doesn’t sound like solder paste & plastic go that well together. I’d also be concerned about stuff coming out of the hot plastic and contaminating the solder, or the effect of the flux in the solder on the plastic.
The PCBs I have made are fiberglass with 1oz copper traces and solder mask to prevent the paste from ending up as solder bridges between pins.
Surface tension on the melted solder helps pull/hold parts into proper positions. I would think that same surface tension would cause traces of solder to pull apart.

Perhaps you can add milling capability to your printer and mill away copper from plated boards to make PCBs.
Member GrumpyMike here in the forum has webpage on his PCB miller.

Kester_EP256_Data_Sheet.pdf (54.9 KB)

I'd also be concerned about stuff coming out of the hot plastic and contaminating the solder, or the effect of the flux in the solder on the plastic.

Or poisoning any nearby mammals.

There are some speciality solders based on indium which can have melting points down to 120 deg c.

Its possible to do filigree work with that but I use silicone moulds

He's talking about using the 138 degree C solder (Tin Bismuth eutectic).

That still doesn't leave you much margin, temp wise, though. (Oh, and if you used non-ROHS parts on it, they'll form a tin/lead/bismuth eutectic with melting point of 98C, which is why they don't use bismuth solder much).

As you mentioned, solder paste is supposed to form a ball if you melt a little bit of it. This is governed by surface tension, and is in fact critical to the functioning of solder paste. If it didn't have that behavior, the solder wouldn't shrink away from the solder mask, and you'd solder on an IC and all the pins would be shorted together by a big blob of mess. Old solder paste will behave that way, due to oxide on the metal particles. In your case, though, that surface tension becomes a problem, because it will make the solder try to ball up instead of staying in the grooves where you want it. And what will the flux do to the plastic?

With indium, you can make alloys that melt at a low enough temperature to take a cast of your fingerprint without burning yourself.... But this doesn't solve your problem!

The most interesting "circuit printing" thing I saw would print conductive plastic, as well as normal plastic, and was meant for making the case/frame (so your case would be your wiring harness). Not sure what the conductivity of that plastic was though - most conductive plastic sucks; I stopped looking at the kickstarter page when i saw the price, which was before I found the conductivity.

Surface tension makes this a non-starter, solders will not wet anything but metals
(excluding aluminium). Actually gallium and indium alloys may wet glass too, but
not plastics. Surface tension in metals is strong.

You need a printable conductive ink or extrude from molten under forced air cooling
perhaps. Or buried channels and micro-casting under pressure(!)

Does anyone know of a conductive liquid glue? Part of the problem I have with using the solder pens is that I was hoping to also use the solder to hold the parts in place.....

I have a .2mm print head and print parts out with very fine detail. I could upgrade my printer to run two heads and inlay the conductive filament in the part at the sometime... But then I would need to come up with a way to attach the parts securely.

If that could work it would be amazing on the time!

Right now I print place holder PCBs to put into other parts. Right now I print a 30mm x 15mm x 2mm bored with holes for parts to sit in... In less then 8 mins...

If there is some kind of fast drying conductive glue, Etching could kiss my butt!!!

dannyboyfl: If there is some kind of fast drying conductive glue, Etching could kiss my butt!!!

Well yes there are conductive paints that can do this but they are silver based possibly nickel. Expensive and the solvent may attack your plastic

Maybe find out what this kickstarter project is using?

Could you imagine the possibilities of being able to print a PCB in any shape with in minutes... And I don't mean just a flat PCB... The PLA parts at the same size of my custom PCBs are just as strong if not stronger.

Now I must find that glue! This could change my life!!!