It’s no secret that we’re bizarrely drawn to macro videos showing solder paste during the reflow process. This electric skillet reflow guide provides the fix we’ve been jonesin’ for while including some helpful tips for first-timers and veterans alike. Not sure what we’re talking about? Look at the grey paste at the top of this image. As it heats up it’s drawn under each component as seen in the lower half of the image.
This particular guide is aimed at one-off assembly so a solder paste stencil is not used (we learned a lot about those earlier in the month). It instead uses the painstaking toothpick application technique. It takes time but the upside is that once you get the hang of it you’ll apply the perfect amount of solder each time. After placing all of the components [Count Spicy] carefully transfers the board to an electric skillet, covers it with the glass lid (so he can see what’s going on), and sets the temperature just above the solder’s specified melting point.
Since the skillet is cheap and easy to find you really just have to order the solder paste to get into this type of assembly. Our only gripe is that you can’t really follow a temperature profile with this rig. For that you need to move up to some PID controlled hardware.
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This is exactly what it looks like. [Oleg] calls it soldering in inert atmosphere, but it’s just a toaster oven reflow hack dropped into a container full of carbon dioxide.
Why go to this trouble? It’s all about solder wetting. This is the ability of the molten solder paste to flow into all of the tinned areas of a board. [Oleg] talks about the shelf life of hot air leveled PCB tinning, which is about six months. After this the tin has oxidized. It will certainly not be as bad as bare copper would have, but it can lead to bad solder joints if your PCBs are more than about six months off the production line. This is one of the reasons to use solder flux. The acid eats away at the oxidized layer, exposing tin that will have better wetting.
But there is another way. Soldering in the absence of oxygen will also help the wetting process. CO2 is heavier than air, so placing the reflow oven in a plastic container will allow you to purge air from the space. CO2 canisters are cheap and easy to acquire. If you keg your own homebrew beer you already own one!
If you’ve got everything but the reflow oven just look around for a few examples of how to build your own.
Here’s a collection of tricks to get over some surface mount prototyping issues the next time you find yourself in a bind. But first we have to address the soldering atrocity seen on most of the components above. [Rxdtxd] admits he’s using a firestick for soldering his SMD parts. The non-brand 40W iron is just about the worst thing he could be using (well, we guess a candle would be worse). Try to overlook those joints and enjoy his solutions to a couple of other problems.
First up is what to do when you lift a fine-pitch trace like would be found on a TQFP footprint. The fix for this is to grab a junked transformer and use a bit of the enameled wire from the wrappings as a jumper. The wire is quite fine, and the insulation will burn off when soldered which means you don’t need to strip it first.
The second and third tricks both deal with resistors. As you can see above he placed two 1K resistors on a single resistor footprint to make his 2k resistor. The 0603 packages were both soldered standing on end, then connected with a lead from a through-hole component. The other resistor hack piles five components on top of each other to build resistance in parallel. This is not a great idea as it will fail over the long-term, but it will get you though the prototyping stage as long it doesn’t require precise tolerance.
Here’s a demonstration which proves you don’t really need special tools to populate a surface mount PCB. We’ve seen this board before, it’s the glass PCB server which [Cnlohr] developed and demonstrated by connecting the real world to Minecraft. It’s a tiny board and we were happy to have the chance to see his method for populating the parts before reflow soldering.
In the video after the break [Cnlohr] starts by dispensing a glob of solder pasted from its storage container. He mentions that as long as you store the stuff in the refrigerator it’s rather easy to work with. Because most of his projects are single boards it’s not worth it to have a solder stencil produced. Instead he picks up a bit of the solder glob on the end of a toothpick and applies it to each pad.
This isn’t really as bad as it sounds. The fine pitch TQFP footprints can just be dragged with a bit of the paste. After this application — which took around seven minutes — he grabs some tweezers (not the vacuum type) and begins placing each component. If he missed some paste he’ll discover it in this step and add where necessary. The last step is a trip through his toaster oven.
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In an effort to ease the process of soldering Ball Grid Array (BGA) chips at home [Roger] rigged up a hands-free solution for his hot air equipment.
The main component in the build is an Aoyue hot air rework station that he already had in his workshop. He wanted an adjustable mount that would hold it steady when reflowing parts so he hit Amazon and bought a $14 articulated lamp. After ditching the funnel-shaped shade he bolted a cable clamp to the socket housing. This can be tightened on the hot air wand, with the spring tension of the lamp making it easy and quick to reposition the nozzle. [Roger] sent this project directly to our tips line and we’ve embedded the rest of the project images after the break.
If you’re looking for a more DIY rework solution you should checkout this hot air pencil hack. It uses a desoldering iron, a fish pump, and some metal mesh as a heat sink to put out a stream of very hot air.
Continue reading “Hands free hot air station”
[Zach Hoeken] has the answer to assembling multiple surface mount PCBs in the home workshop. It’s certainly not for everyone. But if you’ve ever thought of marketing your own small runs he has the equipment and methodology you need.
He had tried using hacked together equipment, but after encountering a range of issues he finds the investment in a few key items saves time and money in the long run. The first is a precision tooling fixture block; that metal plate with a grid of holes that makes up the background of the image above. It comes with machined pegs which fit the holes perfectly, and as you can see, his panel of 16 boards include tooling holes that line up with the fixture. Once in place, a steel solder stencil is aligned with the board using its own tooling holes. The alignment of the stencil and its uniformed thickness ensure that the perfect amount of solder paste is easy to apply with a squeegee. [Zach] hand places his components but he did invest in a proper reflow oven to make the soldering a set and forget process.
It’s not uncommon in cheaper devices to find a ribbon cable soldered directly to the circuit board like the one pictured above. Using a connector would have been a much more resilient approach, but adding parts adds cost. If you take a close look you’ll see things aren’t looking so great anymore. [Chaotic and Random] pulled this board out of his VW Camper Van. Rather than buy an expensive replacement part, he shows us how to repair a soldered ribbon wire connection.
This repair is rather invasive and he suggests trying some hot-air rework (possibly using a heat gun) to fix up any misbehaving connections. But if that has failed it’s time for the knife. The first step is to cut the ribbon so that the LCD can be removed from the board. From there he peels the remaining scrap off ribbon of the pads. This makes us cringe as it could lift traces from the PCB, but he was gentle enough to avoid it. Now comes the time to start reassembling. After thoroughly cleaning the pads the ribbon is cut straight and resoldered. The trick is to flow the solder without melting the ribbon. He uses tin foil to cover the tip and cools it on a moist sponge just before reflowing solder.
It sounds like more art than science. But when the only alternative is to spend hundreds on a new part it may be worth a try.