Reflow soldering improved with carbon dioxide

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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.

Reflow oven courtesy of hurricane Sandy

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The Makerbar, Hoboken’s Hackerspace, was in desperate need of a reflow oven. Hurricane Sandy did a number on a whole bunch of household appliances, so when [Kush] saw a neighbor throw out a broken toaster oven, the Makerbar crew sprung into action.

The storm waters shorted the electronics board, fried the existing controls, and basically turned the oven into a metal shell with heating elements. It was the perfect platform for a toaster oven – every part that was going to be thrown out was already destroyed.

[Zach] over at the Makerbar ordered the Sparkfun reflow toaster conversion kit along with a few arcade buttons and set to work. After plugging the heating elements into the mains power to make sure they still worked, [Zach] attached these elements to the relay on board the controller. Three arcade buttons were wired up to the controller, and a whole bunch of code was written.

With the included thermocouple, [Zach], [Kush], and the rest of the Makerbar gang now have a very accurate and reliable reflow oven. There’s also settings for Sculpey clay and shrinky dinks, just in case anyone at Makerbar is feeling a bit creative.

Solar oven built to last

The problem with most solar ovens is that they’re flimsy builds that will stand up to only a handful of uses. But this one stands apart from that stereotype. It’s big, sturdy, and used a lot of math to efficiently gather the sun’s energy when cooking food.

This is the third version of the build and each has included many improvements. The obvious change here is a move from aluminum reflectors to actual mirror reflectors. These attach at a carefully calculated angle to get the most power from the rays they are redirecting. The orange mounting brackets for the mirrors also serve as a storage area for transport. The rectangular reflectors fit perfectly between them (stacked on top of the tempered glass that makes up the transparent side of the cooking chamber).

The body of the oven doesn’t track the sun and one of the future improvements mentions adding tilt functionality to the base. We’d suggest taking a look at some of the solar tracking setups used for PV arrays.

[Thanks John]

Fine-pitch SMD soldering with minimal tools

We try to stick to the 0805 parts because they’re still big enough to solder by hand. But [Scott] shows us that it doesn’t take too many special tools to reflow fine-pitch components at home. In this case he’s using 0402 resistors, a footprint that we consider functionally impossible to solder using an iron.

The two parts of the equation that he spent some money on are professionally produced PCBs and a solder stencil. The stencil is laser-cut from Kapton, which is heat-resistant so it doesn’t warp during the cutting process. An acrylic frame holds the PCB in place, and he just tapes the stencil over it and uses a chunk of acrylic as a squeegee to evenly apply the solder paste. Splurging on the PCB and stencil means you’ll achieve tolerances which lead to success.

The next issue is placing the components. [Scott] shows off some vacuum tweezers he built using an aquarium pump. Watch the video after the break to see how small those 0402 parts are when he extracts one of the resistors from the tape packaging. With the board manually populated (check everything twice!) he moves the board to a completely unaltered toaster oven for reflow. We have seen a lot of projects which add controllers to these ovens, but he really makes the case that you don’t need it. Instead, he uses a thermocoupler read by a multimeter just to let him know what’s going on with the temperature. He uses a smart phone as a timer, and switches the oven on and off to match the solder’s heat profile. Continue reading “Fine-pitch SMD soldering with minimal tools”

Preheat alarm added to a basic kitchen oven

[Justin] didn’t want to keep checking if the ‘oven heating’ indicator light had gone off before popping his unbaked edibles into the oven. Many models offer a buzzer to let you know when the chosen temp is reached, but for folks who own a basic oven model there’s just a light that tells when the heating element is getting juice. Not to worry, he plied his circuit design skills and built a buzzer to alert him when the oven’s ready.

It only took a few components to accomplish the task. [Justin] uses a pair of NPN transistors triggered by a photoresistor. One transistor is responsible for switching on the buzzer, the other transistor is driven by the photoresistor and controls the base of its companion transistor (see the schematic for a better understanding).

He designed and etched a small PCB to host all the parts. As you can see above, it mounts over the indicator light and is powered by a 9V battery. There’s an on/off switch to the right so the buzzer doesn’t keep triggering while cooking, and a potentiometer allows him to fine-tune the photoresistor sensitivity.

A very detailed reflow oven build

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If you do a lot of SMD soldering, a reflow oven is the fastest and most efficient way to get all those tiny components attached to your PCB. [Frank Zhao] saw the reflow ovens we featured here over the last few weeks and figured he might as well show off his rig as well. We’re certainly glad he did, because his very thorough writeup is a great stepping stone for anyone looking to construct a reflow oven of their own.

Like many others, he started off with a used toaster oven, modifying it to be controlled directly via the power cable rather than the oven’s dials. He built a small PCB to regulate the oven, which features an ATmega32u4 and thermocouple to keep the temperature in check. Control of the heating element is done using a solid state relay, for which he built his own heatsink.

He studied the reflow profile of the solder he would be using, programming the microcontroller to regulate the heating/cooling process without requiring any user input, aside from turning the oven on.

Check out the video below to see a brief overview of his system, and be sure to swing by his writeup to take a look at all the build details. There are a handful of additional videos along with plenty of pictures there, walking through each step of the process.

Continue reading “A very detailed reflow oven build”

Heater for bending acrylic

We like using acrylic in our projects but there are a couple of tricky techniques, particularly getting clean cuts for glued edges and bending the material into curves. [Giorgos Lazaridis] has a great solution to the latter, a dedicated acrylic heater. Instead of using an oven to warm the material for bending he’s using localized heat produced by a high-powered lamp pulled from an old laser printer. The next part of his solution is to keep the heated area of the acrylic as small as possible. This was achieved by creating heat sinks on either side of the bulb. The metal bars seen above have water running through them to help isolate the softening of the material to a narrow strip. See how well this system works in the video after the break.

Continue reading “Heater for bending acrylic”