Who Says Solder Paste Stencils Have To Be CNC Cut?

Imagine having a surface mount kit that you’d like to stencil with solder paste and reflow solder, but which doesn’t come with a solder stencil. That was what faced [Honghong Lu], and she rose to the challenge by taking a piece of PET sheet cut from discarded packaging and hand-cutting her own stencil. It’s not a huge kit, the Technologia Incognita 2020 kit, but her home-made stencil still does an effective job.

So how does one create a solder stencil from household waste? In the video we’ve put below the break, she starts with her packaging, and cuts from it a square of PET sheet. It’s 0.24mm thick, which is ideal for the purpose. She then lays it over the PCB and marks all the pads with a marker pen, before cutting or drilling the holes for the pads. The underside is then sanded to remove protruding swarf, and the stencil can then be used in the normal way. She proves it by stenciling the solder paste, hand placing the parts, and reflowing the solder on a hotplate.

It’s clear that this is best suited to smaller numbers of larger components, and we’ll never use it to replace a laser-cut stencil for a thousand tiny 0201 discretes. But that’s not the point here, it’s an interesting technique for those less complex boards, and it’s something that can be tried by anyone who is curious to give stenciling and reflowing a go and who doesn’t have a project with a ready-cut stencil. And for that we like it.

Making your own stencils doesn’t have to include this rather basic method. They can be etched, or even 3D printed.

Continue reading “Who Says Solder Paste Stencils Have To Be CNC Cut?”

Can Solder Paste Stencils Be 3D Printed? They Can!

3D printed solder paste stencil, closeup.

[Jan Mrázek]’s  success with 3D printing a solder paste stencil is awfully interesting, though he makes it clear that it is only a proof of concept. There are a lot of parts to this hack, so let’s step through them one at a time.

First of all, it turns out that converting a PCB solder paste layer into a 3D model is a bit of a challenge. A tool [Jan] found online didn’t work out, so he turned to OpenSCAD and wrote a script (available on GitHub) which takes two DXF files as input: one for the board outline, and one for the hole pattern. If you’re using KiCad, he has a Python script (also on GitHub) which will export the necessary data.

The result is a 3D model that is like a solder paste mask combined with a raised border to match the board outline, so that the whole thing self-aligns by fitting on top of the PCB. A handy feature, for sure. [Jan] says the model pictured here printed in less than 10 minutes. Workflow-wise, that certainly compares favorably to waiting for a stencil to arrive in the mail. But how do the actual solder-pasting results compare?

3D printed solder stencil on PCB, after applying solder paste.

[Jan] says that the printed stencil had a few defects but it otherwise worked fine for 0.5 mm pitch ICs and 0402 resistors, and the fact that the 3D printed stencil self-registered onto the board was a welcome feature. That being said, it took a lot of work to get such results. [Jan]’s SLA printer is an Elegoo Mars, and he wasn’t able to have it create holes for 0.2 mm x 0.5 mm pads without first modifying his printer for better X/Y accuracy.

In the end, he admits that while a functional DIY solder stencil can be 3D printed in about 10 minutes, it’s not as though professionally-made stencils that give better results are particularly expensive or hard to get. Still, it’s a neat trick that could come in handy. Also, a quick reminder that we stepped through how to make a part in OpenSCAD in the past, which should help folks new to OpenSCAD make sense of [Jan]’s script.

DIY Dispenser Places Solder Paste Without The Mess

When doing surface-mount assembly you can certainly use a soldering iron in the traditional way, but it’s far more convenient to cover the pads with solder paste, place the components, and bake the board in a reflow oven. If you’re lucky enough to have a precut stencil this can be done in one go, otherwise a tiny blob of paste must be laboriously placed on each pad by hand. [Kevarek] has made this a bit easier by designing a low-cost handheld solder paste dispenser.

The unit takes the form of a handheld 3D printed wand containing a geared motor and a threaded shaft, that engages with a syringe full of paste clamped onto its end. There’s a control box powered by an STM32 microcontroller that not only allows adjustment of flow rate, but provides advanced features such as performing a slight retraction at the end of dispensing to avoid excess paste. There’s a push-button on the wand for control, as well as a set on the control box to adjust its parameters.

If you’ve ever handled solder paste, you’ll know it can be a uniquely annoying and finicky substance. Either it’s too stiff and clumps together, or too runny and spreads out. No doubt some readers are lucky enough to always have fresh paste of the highest quality to hand, but too often a hackerspace will have a tub of grey goop with uncertain provenance. We like this tool, and while it won’t make up for poor quality or badly stored paste, at least it’ll make applying paste a breeze.

We’ve covered paste dispensers quite a few times in the past, but you might also wish to read our in-depth guide to the subject.

Dispensing Solder Paste Automatically

Through-hole chips are slowly falling by the wayside, and if you want to build something with new parts you will be using surface mount components. This means spreading paste and throwing it in the toaster oven. Of course, if you don’t want to take the time to get a stencil for your solder paste, you can always lay it down by hand. For that, [owhite] has created a tiny, handheld, robotic solder paste dispenser. It’s a robotic pen that dispenses just the right amount of solder paste on your pads.

The design of this solder paste dispenser is basically a syringe filled with paste and a stepper motor to push the plunger down. Devices like this already exist, and the i-extruder can be had for somewhere around two hundred bucks. Why buy when you can build, so [owhite] set out to create his own.

The key to a successful solder paste pen, it seems, is driving the plunger with a small NEMA 8 stepper motor, using a very fine pitch on the threads of the gears pushing the plunger down, and surprisingly finding a small-diameter syringe. [owhite] found the last bit in the form of a gas-tight syringe with a nylon gasket. The electronics consist of just a Teensy 3.2, DRV8825 stepper driver, footswitch, and an OLED for a UI.

With just a few parts, [owhite] managed to create a solder paste pen that’s better than the commercial i-extruder, and with a bit of practice can be used to place paste on some SMD pads.

Tools Of The Trade – Solder Paste Dispensing

The general process of circuit board assembly goes like this: You order your PCBs. You also order your components. For surface mount components, you apply solder paste to the pads, put the components on top, and then heat the board up so the solder paste flows and makes a bond. Then for through hole components you put the leads through the holes, and solder them with an iron or a solder wave or dip. Then you do an inspection for defects, program any microcontrollers, and finally test the completed board to make sure everything runs.

The tricky part is in volumes. If you’re only doing a few boards, it’s usually easiest to assemble them by hand. In the thousands you usually outsource. But new tools, and cheap hacked tools, have made it easier to automate small batches, and scale up into the thousands before outsourcing assembly.

In this new series which we’re calling Tools of the Trade we’ll be covering a variety of tools used for building products, and we’re starting with circuit board assembly. Let’s investigate our tools of the trade: solder paste dispensing. Continue reading “Tools Of The Trade – Solder Paste Dispensing”

Solder Paste Dispenser Has No 3D Printed Parts!

If you’ve never used a solder paste dispenser, you’re missing out. Think about always using a crappy soldering iron, and then for the first time using a high-end one. Suddenly you’re actually not bad at soldering things! It’s kind of like that.

Most solder paste dispensers make use of compressed air, which requires an extra setup to use that you might not have. The goal of this project was to make a solder paste dispenser that doesn’t use compressed air, and doesn’t have any 3D printed parts (in case you don’t have a 3D printer) — and it looks like the inventor, [MikeM], succeeded!

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THP Semifinalst: Laser Solder Paste


A relative latecomer to The Hackaday Prize, [AltMarcxs] has nevertheless come up with a very interesting tool for fabrication, the likes of which no one has ever seen before. It’s a rotating laser soldering paste applicator, meant to be an add-on to a CNC machine. What does it do? RIght now it looks extremely cool while being an immense time sink for [AltMarcxs], but the potential is there for being much more than that, ranging from a pick and place machine that also dispenses solder paste, to the closest thing you’ll ever get to a carbon fiber printer.

[AltMarcxs]’s build consists of two 3W laser diodes focused just beyond the tip of the syringe. The syringe dispenses solder paste, and rotating the diodes around, [Alt] is able to put a melted solder blob anywhere on a piece of perfboard. He put up a reasonably well focused video demonstrating this.

With a few homebrew pick and place machines making the semifinalist cut for The Hackaday Prize, it’s easy to see the utility of something like this: Putting a board in a machine, pressing a button, and waiting a bit for a completely populated and soldered board is a dream of the electronic hobbyist rivaled only by a cheap and easy way to make PCBs at home. [AltMarxcs]’s machine could be one step on the way to this, but there are a few other ideas he’d like to explore first.

The build also has wire feeders that allow a bit of copper wire to be soldered to the newly formed metal blob. There are plans to replace this with a composite fiber, replace the paste in the syringe with a UV resin, cut the fiber and cure the resin with the laser, and build something much better than other carbon fiber 3D printers we’ve seen before.

SpaceWrencherThe project featured in this post is a semifinalist in The Hackaday Prize.