3535 to 5050 and 5050 to 7070 DTP adapters

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thefreeman
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3535 to 5050 and 5050 to 7070 DTP adapters

It’s a thin (0.15~0.2mm) flex board DTP adapter for soldering 3535 LEDs onto a 5050 board, sometimes using another MCPCB is not possible, or in the case of Zebralight for example there is no MCPCB to swap at all.

3535 to 5050 : https://oshpark.com/shared_projects/9tmUe8Wo

5050 to 7070 : https://oshpark.com/shared_projects/PcP8ePhm (not tested)

Edited by: thefreeman on 01/24/2023 - 08:32
Gunga
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That is so awesome. I could have used a few 3535 to 5050.

KnotSoMuch
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What a great idea! Have you tested how heat transfer will be affected?

Also, do you suggest reflowing both the adapter and emitter onto the MCPCB at the same time, or in 2 steps? 

"it's of utmost importance to be strong...otherwise weakness will be exploited by your adversaries and they'll drive a truck right through it!" (paraphrased) 

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thefreeman
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I didn’t compare performance, with the adapter the only difference is a 0.15~0.2mm solder layer between the copper base and the thermal pad of the LED, while solder has lower conductivity (50W/m.K) than copper (400W/m.K) it probably doens’t affect much heat transfer over such a thin layer.

I reflowed in one step, for the thermal pad I think it’s preferable to add solder to it before reflowing instead of paste though, since it need a certain amount to fill the gap, with a lot of paste it might make a mess.

KnotSoMuch
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thefreeman wrote:
I didn’t compare performance, with the adapter the only difference is a 0.15~0.2mm solder layer between the copper base and the thermal pad of the LED, while solder has lower conductivity (50W/m.K) than copper (400W/m.K) it probably doens’t affect much heat transfer over such a thin layer. I reflowed in one step, for the thermal pad I think it’s preferable to add solder to it before reflowing instead of paste though, since it need a certain amount to fill the gap, with a lot of paste it might make a mess.

Thanks for the feedback. 

Tinning the thermal pad should be easier, which I'll trial on one sample. But applying paste with a fine tip applicator with a stencil should offer more consistent results. I'll report back if I try these out. 

"it's of utmost importance to be strong...otherwise weakness will be exploited by your adversaries and they'll drive a truck right through it!" (paraphrased) 

-former U.S. Secretary of State, Mike Pompeo

Parametrek
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Looking at Oshpark’s flexpcb data it says it is using Panasonic R-F775 substrate. That is a polyimide film with a poor thermal conductivity of 0.16 W/m.K. Oshpark’s is 0.1mm thick.

So in all this is adding 1 extra layer of solder (0.15mm = 3.3e5 W/K each) and 2 extra layers of copper (35um = 1.1e7 W/K each) and the plastic film (0.1mm = 1600 W/K). Those combine together for a thermal resistance of 1590 W/K. Which is about 90x worse than the thermal resistance of a 1.5mm copper mcpcb with a layer of solder.

I would be very careful running this at high power!

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thefreeman
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There’s a cutout for the thermal pad :

Oshpark PCB viewer doesn’t display cutouts well, the black lines indicate the edge cut and cutouts, even if it’s filled with purple color.

Edited the title and description to add “DTP”.

Parametrek
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Ah okay. Carry on Big Smile

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joebob4501
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Wow this is exactly what I’ve been looking for to use in my Zebralight sc600 mk2, I have a dedomed xm-l2 currently but looks like it’ll be getting a 519a!!

thefreeman
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uselessuser
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Interesting idea! Though with a dremel I’ve so far always been able to swap out the MCPCB.

What’s more challenging is to find boards for 3030 or 4040. Here an adapter would be awesome.