Another Bright Idea

I swear I don’t just work on lights these days

I’ve been building and improving a little corner here at Formlabs for Electronics rework over the past year or so, and I’ve been pretty happy with it – except for the lights. Soldering reworks onto fine-pitched components and installing 0402-sized components takes both good dexterity and a good point of view, and having good eyesight only goes so far if you’re working in a cave. And we do – our building is over 100 years old and was not built to be an electronics lab, so lighting is far from great.

We made a hacked-together fix to this a while back: a PCB with some high-power LEDs mounted with some thermal grease and Superglue to the grate of our solder fume extractor (a big fan with a carbon filter), which worked…but it wasn’t as bright as it could be, the angle of the light was such that it went straight into your eyes… and it was always on. This happened to double as a lifetime tester for the LEDs, as they’re used in one of our products, and they’ve lasted over a year now – not bad!

I didn’t intend to make this into a big project – This began by simply making another light for a 2nd workbench I’ve been putting together. But things just weren’t working – I just couldn’t replicate the magical elixir of goop that held the first one on. I also changed the circuit to run all LEDs in series, allowing the full 700mA of our constant-current driver to flow through and just about doubling the light output. This had the obvious consequence of making the chips much, much warmer – capable of melting plastic in fact! ( in theory of course, I definitely didn’t actually do this by accident…)

I needed a better solution – so I gave up on the idea of being social on a Friday evening and got to work. I’ve been using Onshape often for small side-projects, and so immediately turned to the tool for creating a small bracket/heatsink combo for the PCB. The DXF import tool made it easy to copy in the board’s outline, and I was able to use the sheet metal tools to quickly produce some mounting flanges. One issue I ran into, which was definitely frustrating – when modifying a sheet metal part in Onshape, you can’t add material! you can only perform subtractions, and additional parts can only be flanges, tabs, and other sheetmetal parts. Thisrequired a decent amount of extra work to produce the inverse snowflake heatsink I decided to add to the center area of the bracket (is that a technical term? probably) Either way, I produced something that looked like it should do the trick, so I threw the flattened model onto a thumbdrive and headed to our shop’s Waterjet.

O-my! this is messy to the Max

This tool is 2nd favorite to Formlings after maybe a screwdriver – we use our Waterjet for tons of projects. It’s definitely the “unkempt barber” of our machine shop, and the messy abrasive used in the cutting gets all over, but to quickly crank out sheetmetal parts, there is no better option. I located some scrap aluminum, messed up a few times, then got two pieces of metal out that looked like brackets!

Shearly you didn’t cut those out by hand!

Our brake then made quick work of the two bends needed to complete the brackets. This tool is also quite nice – it has an electromagnetic stock holder, and a pretty precise angle gauge. making 90 degree bends is no longer a guessing game!

As we use LEDs in a lot of our projects here, we also have a lot of thermal pads, which I made use of to create a non-conductive bond from the PCB to the heatsink (this board has a design flaw that requires spacing to prevent short-circuits from the LEDs, as we’ve discovered a few times in the past…). The final step was to mount it to the fume extractor, turn it on and….see if it stays cool.

Well, it doesn’t really stay cool. the LEDs are rated to 150C, and I never saw it go above 135 C…which is below the limit, but awfully close. If only there was a method of blowing some air over the heatsinks…oh hold on.

My new motto: if it could be broke, af-fix a warning to it

I considered wiring something up so the fan and the lights turned on together, but this was a whole lot easier. I may make a printed heat shield at some point in the future, but this is already a much-improved setup and I think I might call it quits before I get too carried away.

I’m happy to share the CAD/Bill of Materials if anyone wants to re-create the light for their own use . I can’t share the PCB, but feel free to take the board outline and make your own!

There are a few more projects of mine in our lab that I should probably write something about – so that might happen in the near future.

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