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This is my blog about creating a startup LED flashlight business. I'm a designer, fabricator, and strategist and I'm passionate about making ideas real. I believe that products are about people, that they should be built to last, deliver real value, and that we need to do a better job than we have in the recent past.

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Tuesday, February 1, 2011

WIN!: driver mounting problem...solved

Yesterday was a good day in the shop! The last component I've been hesitating on is a little copper sleeve that holds the LED driver. The typical solution, and the one I have used on past prototypes, is to solder the edge of the board to the edge of the PCB (Printed Circuit Board) holder. This provides the necessary electrical contact and also holds the PCB in place. You can see this method used on the left image. Oh, and we are looking at the back of the flashlight head where the body threads in. The little spring contacts the (+) top of the battery.
Prototype solution (left) and final solution (right)
The soldering solution is "okay" but a bit unreliable from an assembly standpoint. The technical problem is that the copper conducts heat extremely well, making it hard to solder. The large copper mass rapidly pulls the heat out of the soldering iron, cooling it to a temperature too low for soldering. Another issue that you can see in the left photo is the tiny gap between the PCB and the copper rim. The solder does not want to cross gaps so you are forced to "blob" it on, using more than necessary. It also looks crude.

So, my next solution was to use a copper sleeve that has twice the wall thickness (on the right). I machined the seat so the PCB sits slightly below the rim of the copper sleeve. Then I used a cold chisel and a small hammer to peen the rim of the sleeve, folding it over the edge of the PCB. I was going to then solder this junction. However, it seems so solid that I won't have to use solder at all. Electrical contact is made in the two small peened areas, but also along the entire back rim of the board.

The main thing I'm excited about is that it looks much cleaner! You can click on the image above for a larger view. This one looks a little bit scrappy because I had to remove the PCB twice...which is actually another win. This means I can take it apart and put it back together without destroying the original components.

I'm working with the principle, "design for disassembly and repair." This means I need to be able to easily break everything down into its component parts. Many products use components that are permanently assembled, requiring component replacement as opposed to repair. I just don't believe this is good design and it's certainly not responsible design. I'm excited this is turning out to be such an excellent solution and is really the last engineering challenge I had to solve.
Posted by Jason at 10:55 AM
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2 comments:

  1. Mike RehmusMarch 5, 2012 at 4:40 PM

    I think you are going to have problems with the copper to copper connection. Copper corrodes over time (remember using a pencil eraser to clean contacts on electronics and such?)
    Might want to consider using one of the contact-improving fluids to keep the corrosion away and the power flowing. I use R5 from Caig. http://store.caig.com/s.nl/it.A/id.1610/.f?sc=2&category=188.
    The really best way would be to gold flash the contact points. Maybe from Creswell (I haven't use them myself) http://www.caswellplating.com/electroplating-anodizing/gold-plating-kits/gold-brush-plating.html

    Skip Adrian gave me your contact information.

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  2. JasonMarch 8, 2012 at 11:13 PM

    Hi Mike,

    Thanks for the note. There is actually no copper-to-copper connection in the light. The copper is pressed into the nickel plated body, and the gold plated driver is pressed into the copper.

    I haven't had any issues with oxidation yet but I see your point about "potential" oxidation. My thought was that the parts are pressed together so where they contact, there is no opportunity for air to oxidize the surfaces. However, I'm actually going to be going in two different directions on this issue so stay tuned :)

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