How to etch your own solder paste stencils

We’re kind of surprised we haven’t covered this concept before since it only uses techniques that are commonly avaialable for home PCB fabrication. [Ray] made this solder paste stencil out of a sheet of copper using the same etching techniques you would for a circuit board. He designed and printed a resist pattern, with toner everywhere except the places where there should be holes in the stencil. He transferred the toner to the copper using an iron.

The difference here should be obvious; this a thin copper sheet with no substrate. Because of that, you must protect the copper surface before etching. he covered the entire thing, both sides, in packing tape. After that it’s into the Cupric Chloride bath to dissolve the exposed parts. Once the tape and toner has been removed you can scree a precise amount of solder paste onto your boards.

This isn’t for everyone, but if you’re assembling many boards it’s not a bad approach. If the stencil is no longer used it can be recycled, but we do wonder how corrosion on the copper will affect the stencil’s performance.

The idea for this technique came to [Ray] from a guide that’s been around for years.

One-man SMD assembly line shares a lot of tips about doing it right

Need to use that antiquated hardware that can only be connected via a parallel port? It might take you some time to find a computer that still has one of those, or you could try out this USB to Parallel port converter. It’s not limited to working with printers, as the driver builds a virtual parallel port that you should be able to use for any purpose. But what we’re really interested in here isn’t the converter itself, but the build process. [Henrik Haftmann] posted a three-part series of videos on the assembly process, which you can watch after the break.

The build is mostly surface mount soldering with just a handful of components that need to be hand soldered. The first of his videos shows him stenciling solder paste onto the boards. From what we can see it looks like he built a nice jig for this using scrap pieces of copper-clad which match the thickness of the PCB, and hold it and the stencil securely in place. There’s a bunch of other tips you can glean from the videos, like the image seen above. It’s a clamp that holds the PCB and USB jack together while they are soldered.

If you’re ever thinking of assembling a bunch of boards you should set aside thirty minutes to watch them all.

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Photographing stuff that’s not there by using stencils

This image was not made in post production, but captured during a long camera exposure. The method uses stencils to add components to a picture. [Alex] built a jig for his camera from a cardboard box. This jig positions a large frame in front of the camera lens where a printed stencil can be inserted. He printed two identical sheets of paper with black covering the area all around the 8-bit joggers. When properly aligned and inserted in the jig, the black parts of the stencil will act to mask the areas where he wants to capture the natural surroundings of the image. Once the camera shutter is triggered, he uses a flash to illuminated the stencil, then removes the the paper image from the jig and ambient light from the dark surrounding is captured during the remainder of the 20-30 second exposure time. The real trick is getting the light levels between the flash and the ambient light to balance and produce a result like the one seen above.

Is anyone else hearing the Punch Out cut-scene music in their heads right about now?

Laser cutting solder stencils

Do you have access to a laser cutter? If so, you can use [Riley Porter's] method to cut your own solder stencils. He starts with the Eagle files and exports the Dimension and tCream layers to a PDF. That file is then processed using Ghostwriter, Gview, and finally, Corel draw. The result is a 1200dpi file to feed to your Epilog laser. Now you’re ready to stencil on the solder paste and populate the PCB.

[Thanks Travis Goodspeed]

How to populate a surface mount PCB


Let’s face it friends, everything is moving toward surface mount components. We’ve seen quite a few features here that cover using stencils to populate boards and using ovens to reflow. [Oleg] has put together a tutorial on the process he uses to populate and reflow his own boards.

[Oleg] is the creator of the USB Isolator and therefore has a need to frequently populate the same board. He’s using an acrylic frame that fits the PCB perfectly to hold it in place so that paste and be applied right up to the edges of the board. He ordered a laser cut Kapton stencil for applying the solder. The paste is squeegeed into the stencil holes, the stencil is removed, and parts are placed with tweezers and a steady hand. For the final step, the boards go into an old toaster oven for reflow.

[Oleg] uses temperature marker on his boards to monitor the progress of the reflow. This marker is basically a crayon that begins to melt at a specific temperature. When the board has cooled, the melted mark can be scraped away or removed with alcohol.

Of course this is only really useful if you have a bunch of high-quality boards to populate. But with the relatively low cost of getting professionally made boards we think the need for this type of assembly process is on the rise.

Messing with barcodes


[nico] just received his credentials for an upcoming conference. On each badge, there’s a 2D barcode with the participant’s bio and contact info. These are meant to be scanned by vendors for future contact. [nico] isn’t so interested in that and plans on updating his personal info by generating a new barcode. To this end, he’s collected a number of links to help out barcode hackers. He used the SWIPE toolkit to identify the format and decode (it has an online component too). There are also several online encoders you can use, like this one from [Terry Burton]. If you’re wondering what sort of shenanigans you can get into faking barcodes, check out [fx]‘s presentation from 24C3.

[photo: seanbonner]