Possible LED attachment improvements

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?

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.

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.

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.

Opinion for this wire?

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

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.

How is S-Bi57sn43 ?
I also have this.

…sorry for extra big photo

I remember it’s worse than SnPb.

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.

! work, thx :slight_smile:

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

Yes, Luminus makes great LEDs. :slight_smile:

There is even better material than silver:

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? :wink:
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.

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

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

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

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