Weekend Project: Wireless Microscope Light Ring

I have an Bausch & Lomb optical Stereo-Zoom (SZ4) microscope which is a great instrument and not a luxury when you do a lot of SMD prototyping and repairs. The light solution for this was a simple piece of white LED strip powered from a 12V adapter, worked well for over 6 years and I thought an upgrade to this will make a nice weekend project.

To really make this nice and portable it had to be very compact, wireless power from a rechargeable Lithium-Polymer battery. But how can this be powered from 3-4V when the LED strips require 12V?

Watch the details in the video below, along with a demo of laser-cut SMD stencils and complete hand assembly and test of the new light ring.

The before and after shots:


The design files are over at Github. Are you planning to make one or add more features? Did you learn something new from this video? Have a question or other suggestions? Let me know in the comments!

Laser Etching SMT Stencils Tutorial

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If you make PCBs and have any SMT components you likely need an SMT stencil to apply solder paste and then bake everything in an oven to reflow the paste. I’ve previously written an extensive tutorial on how to etch metal stencils from soda can material, still very popular, dirt cheap to make and pretty quick once you get a feel for it – it produces very high and extremely durable metal stencils. I’ve been literally using chemically etched soda can stencils thousands of times making Moteinos before I moved to stainless steel commercial stencils.

In this blog post I want to show you my new method that I’ve been using since I’ve purchased a laser cutter from china. It’s using the laser to etch stencils out of transparency plastic (mylar). Chances are that you already have membership or access to a local workshop or hackerspace where a laser cutter is available, so you can give this a try. The trick is to balance the power vs speed of the laser at that sweet spot where it won’t burn the plastic or over/under etch the pads. And for those really wondering why in the world I don’t order from OSHStencils (not affiliated with OSHPark) or similar affordable online services – some of it is explained in the video but mainly because instead of waiting a few days I can do it in 5 minutes, and the flat mylar allows making letter sized stencils. Don’t get me wrong, I support and use the OSHPark PCB service but I prefer to etch my own stencils on the fly on my laser, it’s really convenient and allows for errors and retries without another few days of waiting. Plus, I can do in mylar what they can’t in thin curvy kapton.

If laser etching is not an option for you, read below for another alternative method that yields great stencils from plastic transparency mylar. Continue reading

Getting more serious about SMD production

I’ve been doing all manual SMD assembly ever since I started Low Power Lab, and still do at this moment. I find it too hard to outsource assembly and too prone to some issues.

Anyway, in the beginning there were tweezers, a microscope, and a toaster over for reflowing. I very quickly realized that the tweezer method was insane to put it mildly, the only worst thing that I can think of is actually soldering everything with a soldering iron instead of using paste. Nonetheless the first ever Moteino batch was tweezer-microscope+reflow assembled. Then I figured out how to make metal stencils out of soda cans. That works beautifully, costs next to nothing, and the more you make the faster and better it gets, and those stencils never wear out, unlike mylar or other plastic stencils. It’s the closest you will get to real stainless steel stencils. But I could only spread paste on 1 piece and it gets tedious, watch this video of how I actually do it. Panelizing PCBs sounded a bit scary.

So finally I made the jump and panelized a batch of Moteinos recently. The panel has 2.5mm tooling holes that are spaced on a NxN cm grid (which would fit the Stencil8 tooling block), but quite frankly they could be spaced any way. The tooling holes match holes in the stencil such that the stencil alings perfectly with the PCB. The panels and stencils are made at Hackvana. I don’t have a tooling block because quite frankly I don’t think it’s needed (UPDATE: I actually had a MDF block milled – see this post for details). I drilled holes in some MDF using a 2.5mm drill bit (the thin sheets that come with the stencil are right size and perfect for the job), using the PCB to pilot the holes. Then 2.5mm steel tooling pins align the stencil with the PCB.

The time savings is significant, especially if multiple panels are assembled at once. I was reluctant at first and I was worried about the spacing between the PCBs and other things like that. But glad I did it and this is a first step towards more serious in house assembly. The v-scoring means the PCBs are snapped apart after reflowing, and the edges will be a bit rougher than the nicely routed PCBs I was used to. I do however snap the panels in 3 rows for easier SMD assembly with my pick and place vacuum tool. After reflow they are snapped into individual pieces. The panelization is done at the PCB fab for an extra fee.
The McMasterCarr parts for the pins and the drill bit are: here for the pins and here for the drill bit.

Next up: pick and place machine maybe? Haha.

Laminator dimmer hack for PCB or stencil toner transfer

This post will walk you through a dimmer enhanced laminator mod that allows an alternative method to transfer toner to PCBs or metal stencils.

The clothing iron transfer method works pretty well to make metal stencils. But for larger stencils it might not be so feasible, and a lot of people reported that they could not get a consistent transfer with their irons, maybe because not all behave the same. I have to say there can be lots of potential points of failure in this process. It’s a lot of trial and error, and my stencil tutorial was meant to help with eliminating some of those failures that I’ve gone through. I decided to try the laminator mod to see how that works compared to the iron. Continue reading

Illustrated guide to making a simple solder paste application jig

DSC_0962_wFor a few months I used to tape scrap PCBs on my work desk and apply solder paste there. It was the quick no-brainer solution, but the more designs I had to assemble the more issues I started having with this method:

  • I could not accomodate more than 3-4 stencils at one time
  • it was pretty annoying to keep exchanging the stencils and rearrange the outer PCBs
  • it was taking a lot of space on my work desk even for only a few small stencils
  • Since everything was taped down, I would always have to be careful not to work in that area and bend/damage the stencils

So it was time to step up a little. I had some left over MDF material from making the workbench top plate, perfect for what I had in mind. I like quick solutions that return a lot on the little investment I make. Continue reading

DIY manual SMD pick and place machine for $20

I’ve shot this video over several days a few weeks ago and finally had some time to put it together. Kind of rough cut but I think it proves the point that you can build a very effective pick and place aid tool without spending a fortune. This has already saved me tons of time assembling Moteinos and other SMD projects. I highly recommend something like this as opposed to a tweezers plus microscope/magnifier, it’s very quick and easy to get used to. This tool combined with my home-made SMD metal stencils are a huge improvement over manual solder paste dispensing and hand placing SMD components with tweezers. I also tape the SMD component strips to a piece of cardboard with double sided sticky tape, to avoid having to dump components on the table and then spend time turning and aligning all those that are upside down and in all directions. That also really helps with polarized components.

And a timelapse:

DIY SMD metal stencils – the definitive tutorial

In previous posts (here and here) I described my efforts and research to develop a DIY method to make good quality SMD metal stencils at home. I have since experimented some more and I believe I found the best method (so far) to do this with very cheap materials, yielding very good results.

Since transferring the toner to the soda can aluminum alloy was the most challenging part, I kept experimenting with different transfer mediums and other ways of possibly facilitating and perfecting the transfer.

Finally the solution is here: consistent, repeatable, “perfect” toner transfer, every time.

Continue reading

DIY metal stencils – video update

UPDATE: See the “definitive tutorial” post on how to make these.

I posted this video of the latest SMD stencil I made for my Moteino project. I ended up shrinking the pads by 8mil on this one, the reason being that the previous stencils I made I shrunk by 5mil and the stencil would dump too much solder paste, causing some solder bridging. See the stencil step through post for details how to make this.

I also discovered another very good method to transfer toner: silicone coated paper. I wiped a very thin layer of clear silicone on a blank sheet of paper (on half of it). After it dried I printed the mask directly to it. The iron method will give very good results, the toner will either transfer 100% or not at all. The spots where it doesn’t transfer are fixable with a thin Sharpie pen. The tool you use to spread the silicone has to be very flat and even, any unevenness will result in less perfect toner transfer.

DIY metal stencils – a step-by-step guide

smd_stencil_done_wThis is a step through to make your own metal stencils for PCB solder paste application. In the last post I described my trial and error details of picking the materials. I am using beverage can aluminum for the stencil material and transparency film for toner transfer. In the meantime I discovered that many other materials can be used, especially for the toner transfer medium, with various degrees of success. Read the notes at the end for details. This etching method will not produce the highest quality you can get. Laser cut stencils are higher quality but a lot more $$$. For my purposes such a home-made stencil serves me very well, and saves me a TON of time (I can now apply all the solder paste in one wipe instead of using a syringe to hand apply it on all the pads). Solder paste is very forgiving and even the most imperfect stencils I produced this way give good results after reflow. The whole point is to try to apply an approximately even amount of solder paste to the pads, such that during reflow, all your pins will look the same and won’t form bridges. Overall I think the cost vs outcome/quality ratio is very good. Once you get the hang of this and develop your own routine and choice of materials, in less than 30 minutes, you can produce a high quality home-made metal stencil (almost comparable to a stainless steel laser cut). Continue reading