Possible LED attachment improvements

Agro · 2018-10-05T10:14:38.000Z

Another thing which I suspect won’t work but I’ll throw it anyway. I wonder if improvements to radiation either directly from the LED package or from the MCPCB could bring measurable performance increase?

kikkoman · 2018-10-05T14:16:39.000Z

BlueSwordM:

Soft-PGS is better in this regard than pure PGS, since while it features much higher thermal resistance(20W-28W/k vs 300-1800W/k), PC users have tested that thermal performance is much better with soft PGS because of much lower contact thermal resistance as specified above.

It’s also because soft PGS has much better thermal transfer in the Z-Axis compared to the X/Y-Axis, meaning thermal transfer of high power density products is much better than regular PGS.

I think you’re mixing up two different products.

-The one with 28 W/m·K is the EYGS series which comes in 0.2mm thickness and is electrically conductive.

-The one with high thermal conductivity in the z-axis (vs. x/y) is the EYGT series. This is graphite in a silicone matrix , it looks like this is NOT conductive (4*10^5 Ω·cm), but comes only in >0.5mm thick sheets and has a conductivity of 5 to 10 W/m·K (strangely, it goes up with thickness?). Has some sort of separator but the datasheet is not clear what its properties are or whether it needs to be removed before use.

industrial.panasonic.com

AYA0000COL24.pdf

2.18 MB

The_Driver1 · 2018-10-05T16:03:12.000Z

Agro:

Another thing which I suspect won’t work but I’ll throw it anyway. I wonder if improvements to radiation either directly from the LED package or from the MCPCB could bring measurable performance increase?

This doesn’t make much sense to me. The LED and pcb radiate into the air inside the flashligth head. Air is a very bad conductor of heat. After this the heat would still need to go through the metal of the head or through the glass lens (glass is somewhat good at conducting heat). You would need to replace the air inside the head with something else that doesn’t transmit light any worse, but has a noticeably better thermal conductivity.

Agro · 2018-10-05T16:17:45.000Z

The_Driver:

Agro:

Another thing which I suspect won’t work but I’ll throw it anyway. I wonder if improvements to radiation either directly from the LED package or from the MCPCB could bring measurable performance increase?

This doesn’t make much sense to me. The LED and pcb radiate into the air inside the flashligth head. Air is a very bad conductor of heat. After this the heat would still need to go through the metal of the head or through the glass lens (glass is somewhat good at conducting heat). You would need to replace the air inside the head with something else that doesn’t transmit light any worse, but has a noticeably better thermal conductivity.

Would air absorb significant part of the radiation? I assumed no, but maybe incorrectly.
Otherwise goes towards the optics or towards the head sides or both, depending on what radiates it and what’s the optic.
Head can absorb it, conduct it towards the edges and remove.

The_Driver1 · 2018-10-05T17:00:33.000Z

No, not in such a short distance.

Maybe a solid glass TIR lens which touches the PCB with as large of an area as possible might improve the heat transfer a bit.

Niko · 2018-10-10T20:18:16.000Z

Opinion for this wire?

Agro · 2018-10-10T11:44:58.000Z

Thermal conductivity of 65.73 K/W. Better than SnPb or SAC305, worse than Indium. Melting temp of 227C, slightly higher than SAC305.

Barkuti · 2018-10-10T12:05:41.000Z

Soldering with Sn99.3Pb0.7 is like sailing with a headwind, and it also increases stress in the soldering iron's tips. Check here: Why do tips easily oxidize when they are used with lead-free solder? @ hakko.com

I recommend standard eutectic Sn63Pb37 or Sn60Pb40 classic solder alloys, namely if newbie.

Cheers ^:)

P.S.: editing Niko's above post to reduce image size would be nice, somehow messes up with the page view on mobile or small screen devices.

Niko · 2018-10-10T12:21:14.000Z

How is S-Bi57sn43 ?
I also have this.

…sorry for extra big photo

Agro · 2018-10-10T12:31:57.000Z

I remember it’s worse than SnPb.

Barkuti · 2018-10-10T20:44:14.000Z

Niko:

How is S-Bi57sn43 ?

I also have this.

..sorry for extra big photo

Niko, you can fix the extra big photo by inserting a {width:100%} format tag in your photo link code. Example:

Before:

!https://www.nikohostwebsite.org/nikopicture.jpg!

After:
!{width:100%}https://www.nikohostwebsite.org/nikopicture.jpg!

Bi₅₇Sn₄₃/Bi₅₈Sn₄₂ should make your life a lot easier when soldering. Versus standard Sn₆₃Pb₃₇ or Sn₆₀Pb₄₀ you can do with around 50°C less in your iron.

Cheers :-)

Originally posted on Wed, 10/10/2018 - 19:06. Edited for a tiny explanatory addition.

Niko · 2018-10-10T20:18:53.000Z

! work, thx

Agro · 2018-10-16T13:49:20.000Z

I found an article which largely rehashes what we’ve already found, but may be interesting for some. I only skimmed over it, so there may be some gems that I missed.
https://www.ledsmagazine.com/articles/print/volume-14/issue-8/features/manufacturing/understand-thermal-characterization-of-high-power-leds-for-reliable-ssl.html

The_Driver1 · 2018-10-16T14:59:32.000Z

Agro:

I found an article which largely rehashes what we’ve already found, but may be interesting for some. I only skimmed over it, so there may be some gems that I missed.
Understand thermal characterization of high-power LEDs for reliable SSL (MAGAZINE) | LEDs Magazine

Yes, Luminus makes great LEDs.

Agro · 2018-11-13T17:11:16.000Z

The_Driver:

I just remembered an additional material upgrade. Normal dtp pcbs are made out of copper or aluminium. There is another possible material onto which the LED can be directly soldered which transfers heat even better than copper: silver. Basti in the German TLF forum made such a pcb a few years ago. He made it just for the looks though.

The thermal conductivity of silver is 7 higher than that of the best possible (most pure) copper. Most common copper alloys are not 99.99 pure though, making the difference for pronounced.

I asked him if he would make one for me for my big thrower when I was planning the build, but he is not an active flashahlic anymore.

There is even better material than silver:

NANO MATERIALS INTERNATIONAL CORPORATION

Aluminum Diamond Thermal Management Material

Overview of Nano Materials International Corporation Aluminum Diamond metal matrix composite (MMC)

It’s even readily available for purchase. The price is a little high ($14K minimal order, good for 400 PCBs), but maybe one could get some samples?
BTW, silver-diamond works even better but copper-diamond doesn’t: https://www.electronics-cooling.com/2008/11/advanced-metal-diamond-composites-love-and-heat-relationship/

The_Driver1 · 2018-11-29T13:33:41.000Z

Agro:

The_Driver:

I just remembered an additional material upgrade. Normal dtp pcbs are made out of copper or aluminium. There is another possible material onto which the LED can be directly soldered which transfers heat even better than copper: silver. Basti in the German TLF forum made such a pcb a few years ago. He made it just for the looks though.

The thermal conductivity of silver is 7 higher than that of the best possible (most pure) copper. Most common copper alloys are not 99.99 pure though, making the difference for pronounced.

I asked him if he would make one for me for my big thrower when I was planning the build, but he is not an active flashahlic anymore.

There is even better material than silver:
Aluminum Diamond Thermal Management Material - NANO MATERIALS INTERNATIONAL CORPORATION
It’s even readily available for purchase. The price is a little high ($14K minimal order, good for 400 PCBs), but maybe one could get some samples?
BTW, silver-diamond works even better but copper-diamond doesn’t: https://www.electronics-cooling.com/2008/11/advanced-metal-diamond-composites-love-and-heat-relationship/

Can you solder it?
The benefit of Silver is that you can solder the LED onto it just like with copper pcbs.

Agro · 2018-11-13T21:41:23.000Z

It’s gold plated, so you probably can solder to it.

clemence · 2018-11-28T19:12:59.000Z

Niko:

Opinion for this wire?

Known as SC07. Good for soldering aluminum. High melting point, but very strong joint. I have 250gr 0,7mm spool lying unused. Bought for it’s “slightly” better thermal conductivity but the higher melting point made it my last choice.

- Clemence

clemence · 2018-11-28T17:53:29.000Z

If you don’t plan to remove the LED later, then we can easily braze the chip directly to almost any metal. The brazing material can be anything with melting temp lower than 1500°C. Copper or Silver is a good candidate.

- Clemence

Agro · 2018-11-29T10:38:14.000Z

But such temp will destroy the phosphor. Maybe a die as well.