How To Laser Cut Mylar Solder Stencils

Solder Stencil

When you think about the difficulties of working with surface mount components, the first thing that often comes to mind is trying to solder those tiny little parts. Instead of soldering those parts by hand, you can actually apply solder paste to the pads and place all of the components on at once. You can then heat up the entire board so all of the parts are soldered simultaneously. It sounds so much easier! The only problem is you then need a solder stencil. You somehow have to get a thin sheet of material that has a perfectly sized hole where all of your solder pads are. It’s not exactly trivial to cut them out by hand.

[Juan] recently learned a new trick to make cutting solder stencils a less painful process. He uses a laser cutter to cut Mylar sheets into stencils. [Juan] appears to be using EagleCAD and Express PCB. Both tools are available for free to hobbyists. The first step in the process is to export the top and bottom cream layers from your CAD software.

The next step is to shrink the size of the solder pads just a little bit. This is to compensate for the inevitable melting that will be caused by the heat from the laser. Without this step, the pads will likely end up a little bit too big. If your CAD software exports the files as gerbers, [Juan] explains how to re-size the pads using ViewMate. If they are exported as DXF files, he explains how to scale them using AutoCAD. The re-sized file is then exported as a PDF.

[Juan's] trick is to actually cut two pieces of 7mil Mylar at the same time. The laser must be calibrated to cut all the way through the top sheet, but only part way into the bottom piece. The laser ends up slightly melting the edges of the little cut out squares. These then get stuck to the bottom Mylar sheet. When you are all done cutting, you can simply pull the sheets apart and end up with one perfect solder stencil and one scrap piece. [Juan] used a Full Spectrum 120W laser cutter at Dallas Makerspace. If you happen to have this same machine, he actually included all of the laser settings on his site.

The Electrostatic Theory of Metal Whiskers

wiskersThanks to that wonderful ROHS stuff the EU passed more than a decade ago, we should be seeing a few high-profile failures of electronic components due to tin whiskers. These tiny hair-like extrusions of metal found most commonly in lead-free solder have destroyed billion dollar satellites and shut down nuclear reactors, despite no one knowing exactly how these whiskers form. Now there’s a new theory of metal whisker formation (abstract, unless you have access to APS) that actually has predictive power. Here’s the free version of the paper

[V. G. Karpov] from the University of Toledo suggest these whiskers are formed by differences in charge induced by metallurgical anomalies – contamination, differences in the grain of the solder, and oxides. Because of the difference in charge, the whiskers are extruded, for lack of a better word, out from the surface of the solder.

The theory of whisker growth is generally consistent with observed rates of whisker growth and other properties. With this theory, it should even be possible to grow tin whiskers. Why anyone would want to do that other than, ‘because it’s cool’ is anyone’s guess, but there you go.

Workbench With Built-In Solder Fume Extractor

Solder

There’s nothing quite like getting an eye full of solder fumes, but when it comes to solder fume extraction, the most common solution take up a whole lot of work area. Here’s a very clever solder fume extractor that doesn’t get in the way, and can be perfectly positioned over the acrid brimstone of a soldering station.

The build consists of a cheap bathroom vent fan built into the back of the workbench feeding into a long PVC pipe that blows the exhaust to the floor a few feet away. The fan is controlled by a simple wall switch, but the intake is where this build really shines. It’s a series of hard, flexible plastic segments that allow the intake to be precisely oriented above the work piece, or wherever it’s most convienent to suck solder fumes from.

This solder fume extractor is just a part of a really amazing electronics workbench. A lot of thought went into this workspace, from threaded inserts in the work surface to mount a panavise to an amazingly thoughtful equipment rack for computers, monitors, and other assorted heavy equipment.

via Hacked Gadgets

LIB3 plans to bring contract manufacturing to the masses

LIB3's paste system

LIB3’s paste system

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.

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Electric skillet reflow soldering guide

skillet-reflow-tutorial

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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Solder trick to make your own surface mount breakout boards

surface-mount-breakout-trick

We think you’re really going to enjoy this trick for making surface mount breakout boards. It’s common to use magnet wire to connect individual pins of a surface mount part to breadboard friendly protoboard with pin headers. What’s new here (at least to us) is that [Raul] solders one wire to both pins directly across from one another.

The image at the left shows an eight pin part with four wires soldered in place. To get to this point he first taped the wires down to a work surface being careful to space them to match the pitch on the chip’s leads. He then tapes the chip in place and solders all of the legs to the wires. This seems to kill two birds with one stone as aligning one wire to one leg is tough. From there he flips the chip over and cuts the wire spanning under it. This leaves an easy job of soldering the trailing side of the wire to a hunk of protoboard.

It’s perfect for chips with a small number of pins. Of course you may still want an etched breakout board for something with a ton of leads.

USB fume extractor takes stink out of soldering sessions

usb-powered-fume-extractor

Our homemade shop tools rarely reach this level of finished quality. We probably would have stopped with assembly of this USB powered fume extractor. But [X2jiggy] went for style points by adding a coat of paint.

There are several nice features included in his build. He wanted it to be very easy to power the device so he settled on the 5V USB standard. But a PC fan running at 5V won’t pull much air. He used a boost converter board to ramp that up to 12V. The enclosure is a wooden hobby box. He drilled mounting holes and an airflow opening in the bottom of the box for the fan. The lid of the box has a rectangular opening which accepts a carbon filter meant for aquariums. The rocker switch and LED seen above are also nice touches, but not strictly necessary if you build this for yourself.

We’re still in the habit of gently blowing the fumes away from us as we solder. So the question is, will this device save us from a gruesome disease down the road, or is it mostly to capture the odor of the solder fumes?

Looking for a more permanent setup? You should build a solder hood for your workbench.

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