LIB3 is an open source hardware start-up from upstate New York. Thus far, the team has made some interesting products such as the piLED kit. However, they have big dreams for the future. LIB3 plans to become a contract assembly house specifically targeting low volume makers. To do this they have to build their own tools. LIB3’s latest project is a solder paste dispenser for surface mount components. Traditionally solder paste is applied with stencils made of stainless steel. In more recent years laser cut kapton has become a favorite for low volume production.
Both of these systems require a stencil to be made up. LIB3 took a different approach, and modified an old CNC glue dispenser for paste. The team got their hands on an 1991 vintage X/Y glue dispensing system. X/Y systems in this era were big, heavy affairs with powerful motors. LIB3 removed all the control electronics and built their own system from scratch. New features include direct computer control, and a vision system.
We’re floored by painter and engineer [Bob Partington’s] graffiti briefcase, which proves how well art and tech can complement one another. Fear not, Arduino haters, [Bob]’s case is an analog dream: no microcontrollers here.
The guts consist of 2 components: a linear drive system and a trigger assembly. The former takes advantage of a small RC motor with a chain drive which slides the can’s mounting unit along two stainless steel rods. The latter includes a custom wound solenoid plugged into a 24V cordless drill battery, which slams down 5 pounds of force onto the can’s nozzle to fire the paint.
This all fits into an otherwise inconspicuous looking briefcase to provide some urban camouflage. The final component is a stencil, which slides into a rectangular hole on the bottom of the case. The paint can sprays downward through the stencil and tags the ground at the touch of a brass button located near the handle. [Bob] has plenty of other cool inventions you should check out that are less illegal. Or, stick it to the man by automating your tagging with Time Writer.
Yes, we’ve seen our share of tutorials for making solder paste stencils, but [Felix] hit it out of the park with this one. It’s the definitive guide to making solder stencils at home, with quality as good as you would find in any professionally made stencil.
The material for the stencils comes from the same source as so many other DIY solder stencils – aluminium cans. The interior plastic coating and the exterior paint job are both removed with heat, acetone, and patience. After laying out the cream layer of his board in a PDF file, [Felix] used a fairly interesting transfer medium to get the toner onto the aluminum; cheap vinyl shelving paper attached to a piece of paper apparently makes for an ideal surface to transfer toner.
After transfer, the board is etched with HCl and peroxide. [Felix] is getting some very good results with his method, including a few very fine pitch IC footprints. It’s just as good as a professionally made, laser cut stainless stencil, and you probably already have all the necessary ingredients lying around your house. That’s a win anytime.
When looking for a way to make his own stencils he considered two options: plastic and aluminum. He produced both (more about the plastic stencil and his reflow process is discussed in this post). Plastic is a bit easier to work with since it lays flat. But it proves to be too thick. After applying paste with a squeegee there’s way too much solder on the pads. Aluminum beverage can walls are much thinner, depositing less paste.
We’ve seen soda cans used in the past, but they were produced through an etching process. [Simon] cut these holes using a CNC mill. This required a bit of futzing to figure out the right settings. For instance, he used Altium to produce CAM files from his circuit design. But the program is set up to mill the outside of traces, resulting in openings that are too large. He fixed this by setting the pasted expansion rule in the program to a negative value. The other advantage to using a mill is that he can cut precision tooling holes to ensure proper alignment. You can see them in the upper corners of this image.
It was time for some new T-shirts so [Andreas Hölldorfer] built a laser cutter. Wait, what? That’s the excuse he’s going with, and in the end this scratch built laser cutter did come in handy by cutting stencils to use when decorating his garments.
The first thing we thought when looking at the cutter is where’s the tube? [Andreas] didn’t use a CO2 laser, so this ends up being rather low-powered. The cutting head is a 1W blue laser diode which manages to slice the three-ring binder separator pages he’s using for the stencils. The two-axis machine is mounted inside a wooden box to protect his eyes while it’s cutting. He plans to add a drawer later on so that the cutting bed will slide in and out to swap out material for the next project. He already does a lot of 3D printing work and had an old RepRap driver board on hand to use for this projects. He designed and printed the red mounting brackets which make all of the junk-bin components work together. Not bad!
Even if you’ve overcome your fear diddling about with tiny SMD components, applying solder paste – especially if you’re populating more than one board at a time – is still a chore. The pros use very expensive laser cut stainless steel solder paste stencils, something still a bit out of reach to the casual hobbyist. [Felix] solved this problem by making his own solder paste stencils very cheaply using empty soda cans.
The process begins just like any other home etching tutorial by lightly sanding the un-bent aluminum can and applying the etch resist via the toner transfer method. Etching is done with off-the-shelf HCl and hydrogen peroxide, resulting in an amazingly clean stencil comparable in quality with a professional stencil.
Sure, going through a dozen-step process to make a solder paste stencil may not be as convienent as [Cnlohr]’s toothpick and tweezers method, but [Felix]’ method is just about up to par with extraordinarily expensive laser cut stainless steel stencils. Not bad for something that came from the recycling bin.
If you’re making your own boards with SMD parts, you might want to get a solder paste stencil. Usually made of laser-cut mylar or extremely thin steel, these stencils allow you to squeegee solder paste onto your board’s pads and make assembly a whole lot easier. [Rochey] needed a stencil for a board he was working on, and lacking a laser cutter he turned to what he had available – a few bits of plastic and a CNC machine.
[Rochey] began making his stencils out of laminating pouches and an xacto knife. This worked well, but it was time-consuming, and a bit fiddly when cutting 1 mm square holes. To speed up the process, [Rochey] put one of these laminating pouches on his CNC machine, exported the ‘Top Cream’ layer in Eagle to the CNC software of his choice, and had his machine attack the plastic with a 1 mm drill bit.
To [Rochey]’s surprise, everything went as planned; in five minutes, he had a stencil with perfectly accurate holes that masked off everything but the SMD pads.