Solder Two Boards At Once With This Dual Reflow Plate

Homebrew reflow projects generally follow a pretty simple formula: find a thrift shop toaster oven or hot plate, add a microcontroller and a means to turn the heating element on and off, and close the loop with a thermistor. Add a little code and you’re melting solder paste. Sometimes, though, a ground-up design works better, like this scalable reflow plate with all the bells and whistles.

Now, we don’t mean to hate on the many great reflow projects we’ve seen, of course. But [Michael Benn]’s build is pretty slick. The business end uses 400-watt positive temperature coefficient (PTC) heating elements from Amazon controlled by solid-state relays, although we have to note that we couldn’t find the equivalent parts on the Amazon US site, so that might be a problem. [Michael] also included mechanical temperature cutoffs for each plate, an essential safety feature in case of thermal runaway. The plates are mounted at the top of a 3D-printed case, which also has an angled enclosure for a two-color OLED display and a rotary encoder.

The software runs on an ESP32 and supports multiple temperature profiles for different solder pastes. The software also supports different profiles on the two plates, and even allows for physical expansion to a maximum of four heating plates, or even just a single plate if that’s what you need. The video below shows it going through its paces along with the final results. There’s also a video showing the internals if that’s more your style

We appreciate the fit and finish here, as well as the attention to safety. Can’t find those heating elements for your build? You might have to lose your appetite for waffles.

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Making A Solder Paste Stencil From What You Have On Hand

Sometimes there are moments when an engineer has to use whatever materials they have to hand in order to complete the job on time. Such a situation arose at the RevSpace hacker space in Den Haag, Netherlands, as they were the assembly venue for a conference badge.

Their problem was that the badge PCB had no solder paste stencil, and the solution was to laser cut one out of an unexpected material. The backing paper for self-adhesive vinyl sheet has properties not unlike those desired of a stencil, so they tried laser-cutting one from that material. The result was a robust stencil that outperformed the Mylar they had previously used, enabled the manufacture of 350 boards.

They think that the polymer layer on top of the paper may be silicone, and found that the laser didn’t unduly melt the edges of the cut. We’re not sure we’d feed random unknown plastics into our cutter, we’re guessing they have good quality ventilation. It’s mounted into a plywood jig in much the same way as a conventional stencil might be.

The badges were destined for WICCON, a Dutch conference from an organisation for women in cybersecurity. Sadly we’ve not seen a completed one so we’re not sure what it does, however we’re pleased to hear they were completed before the event. That’s a hurdle all badge designers will know well.

Long term readers may remember, that RevSpace have something of a history when it comes to assembling badges.

Solder stencil vacuu assist jig

Stencil Vacuum-Assist Helps Avoid The Heartbreak Of Smeared Solder Paste

While using a stencil should make solder paste application onto PCBs a simple affair, there are a number of “gotchas” that make it more art than science. Luckily, there are tools you can build, like this 3D-printed vacuum-assist stencil jig, that take a little of the finesse out of the process.

For those who haven’t had the pleasure, solder paste stencils are often used to make the job of applying just the right amount of solder paste onto the pads of a PCB, and only on the pads. The problem is that once the solder paste has been squeegeed through the holes in the stencil, it’s not easy to remove the stencil without smearing. [Marius Heier]’s stencil box is essentially a chamber that attaches to a shop vac, along with a two-piece perforated work surface. The center part of the top platform is fixed, while the outer section moves up and down on 3D-printed springs.

In use, the PCB is placed on the center fixed platform, while the stencil sits atop it. Suction pulls the stencil firmly down onto the PCB and holds it there while the solder paste is applied. Releasing the suction causes the outer section of the platform to spring up vertically, resulting in nice, neat solder-covered pads. [Marius] demonstrates the box in the video below, and shows a number of adapters that would make it work with different sized PCBs.

If you think you’ve seen a manual vacuum stencil box around here recently, you’re right — we featured one by [UnexpectedMaker] not too long ago.

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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.

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Exhaust Fan-Equipped Reflow Oven Cools PCBs Quickly

With reflow soldering, sometimes close is good enough. At the end of the day, the home gamer really just needs a hot plate or an old toaster oven and a calibrated Mark I eyeball to get decent results. This exhaust fan-equipped reflow oven is an attempt to take control of what’s perhaps the more challenging part of the reflow thermal cycle — the cool down.

No fan of the seat-of-the-pants school of reflow soldering, [Nabil Tewolde] started with a cast-off toaster oven for what was hoped to be a more precise reflow oven. The requisite temperature sensors and solid-state relays were added, along with a Raspberry Pi Zero W and a small LCD display. Adding the cooling assist started by cutting a gaping hole cut in the rear wall of the oven, which was then filled with a short stretch of HVAC duct and a stepper-controlled damper. The far end of the duct was fitted with a PC cooling fan; while it seems sketchy to use a plastic fan to eject hot air from the oven, [Nabil] says the exhaust isn’t really that hot by the time it gets to the fan. At the end of the reflow phase of the thermal profile, the damper opens and the fan kicks on, rapidly cooling the oven’s interior.

Unfortunately, [Nabil] still needs to crack open the oven door to get decent airflow; seems like another damper to admit fresh air would help with that. That would complicate things a bit, but it still wouldn’t be as over-the-top as some reflow builds we’ve seen. Then again, that calibrated eyeball thing can work pretty well too, even without a toaster oven.

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Adjustable Jig Eases PCB Stencil Alignment Process

PCB stencils make application of solder paste a snap, but there’s a long, fussy way to go before the paste goes on. You’ve got to come up with some way to accurately align the stencil over the board, which more often than not involves a jury-rigged setup using tape and old PCBs, along with a fair amount of finesse and a dollop of luck.

Luckily, [Valera Perinski] has come up with a better way to deal with stencils. The Stencil Printer is a flexible, adjustable alignment jig that reduces the amount of tedious adjustment needed to get things just so. The jig is built mostly from aluminum extrusions and 3D-printed parts, along with a bunch of off-the-shelf hardware. The mechanism has a hinged frame that holds the stencil in a fixed position above a platen, upon which rests the target PCB. The board is held in place by clamps that ride on threaded rods; with the stencil flipped down over the board, the user can finely adjust the relative positions of the board and the stencil, resulting in perfect alignment. The video below is mainly a construction montage, but if you skip to about the 29:00 mark, you’ll see the jig put through its paces.

Granted, such a tool is a lot more work than tape and spare PCBs, but if you do a lot of SMD work, it may be worth the effort. It’s certainly less effort than a solder-paste dispensing robot.

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Printed Jig Is A Welding Rig

[NixieGuy] was scheming to build robots with cable-driven joints when the pandemic hit. Now that component sourcing is scarce, he’s had to get creative when it comes to continuous cables. These cables need to be as seamless as possible to avoid getting caught on the pulleys, so [Nixie] came up with a way to weld together something he already has on hand — lengths of .45mm steel cable.

The 3D printed jig is designed to be used under a digital microscope, and even clamps to the pillar with screws. Another set of screws holds the two wires in place while they are butt welded between two pieces of copper.

[Nixie] adds a spot of solder paste for good measure, and then joins the wires by attaching his bench power supply set to 20V @ 3.5A to the copper electrodes. We love that [Nixie] took the time to streamline the jig design, because it looks great.

This just goes to show you that great things can happen with limited resources and a little bit of imagination. [Nixie] not only solved his own supply chain problem, he perfected a skill at the same time. If you don’t have a bench supply, you might be able to get away with a battery-powered spot welder, depending on your application.