Possible LED attachment improvements

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Niko
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Opinion for this wire?

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

Barkuti
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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 Party 

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
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How is S-Bi57sn43 ?
I also have this.

..sorry for extra big photo

Agro
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I remember it’s worse than SnPb.

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Niko wrote:
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 Smile 

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

Niko
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!{width:100%} work, thx Smile

Agro
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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/m...

The_Driver
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Agro wrote:
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/m...

Yes, Luminus makes great LEDs. Smile

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The_Driver wrote:

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:
https://www.nanomaterials-intl.com/aluminum-diamond.html
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-compo...
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Agro wrote:
The_Driver wrote:

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: https://www.nanomaterials-intl.com/aluminum-diamond.html 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-compo...

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

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

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Niko wrote:
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

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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

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

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Can someone explain how to wet aluminium with Sn99.3Cu0.7? Tried to do it over heatsink material in the past, to no avail. I can understand it has to do with the particular aluminium alloy of the heatsink, maybe some 6061 crap, and insufficient surface sanding down. Hello?

 

Cheers Party 

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



Nanofoil
Asked for sample but heldback because the solder still limited to Sn based

https://www.indium.com/assets/videos/nanofoil/nanofoil-reaction.mp4

- Clemence

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Barkuti wrote:

Can someone explain how to wet aluminium with Sn99.3Cu0.7? Tried to do it over heatsink material in the past, to no avail. I can understand it has to do with the particular aluminium alloy of the heatsink, maybe some 6061 crap, and insufficient surface sanding down. Hello?


 


Cheers Party 

I’ll post a pic and video for you guys. But, I have to modify my hot plate (cloth iron) to 260ºC first. It’s only maxed at 210ºC. Rarely use lead free solder these days.

- Clemence

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Tried to wet large area with SC07 and 60/40 at 260ºC max. and the result was not successful. I could only wet no larger than 3mm diameter blob. With 60/40 the blob was larger and easier but 5mm was the largest I could get. I had successful result but that was using my stove hot plate at 320ºC which I no longer have. Already converted the stove hot plate to a clamping fixture on my mini milling machine. Silly



FYI, soldering aluminum with Sn based solder is not reliable, unless there’s a continuous voltage in the junction to feed the galvanic difference. Adding Zn in the solder will last longer. I don’t recommend soldering aluminum directly in everything elsa but mechanical or structural projects. Most aluminum fluxes requires high temperature to properly activated (300ish ºC). The most successful way to solder aluminum in electronics is to first plate the aluminum with nickel – gold or copper.

- Clemence

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Another thought….would vapor chamber work as a PCB base?

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Plating aluminium with copper but what kind of aluminium we're speaking of here? The aluminium used to craft heatsinks or flashlights can be some sort of suckass aluminium alloy which won't plate easily, so I hear you better first zinc plate it then copper plate or something like that. 

 

Cheers Smile 

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A quick followup on the pure Indium:

I’ve really come to like the stuff, it makes reflows much less stressful especially with larger MCPCBs. You’re nowhere near the point where the emitters start to degrade and PCBs delaminate so you can take your time.
It also helps a lot with soldering wires where a large thermal mass sucks heat away quickly, which sometimes is unavoidable.

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kikkoman wrote:
A quick followup on the pure Indium:

I’ve really come to like the stuff, it makes reflows much less stressful especially with larger MCPCBs. You’re nowhere near the point where the emitters start to degrade and PCBs delaminate so you can take your time.
It also helps a lot with soldering wires where a large thermal mass sucks heat away quickly, which sometimes is unavoidable.

Yup, really like this stuff too, except for it’s steep price

- Clemence

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That’s a bit OT but I really like soldering leads with SbBi.

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Agro wrote:
That’s a bit OT but I really like soldering leads with SbBi.

Only for leads, never use for this Sn42Bi58 for attaching LED. It has very bad thermal conductivity, approaching that of stainless steel. Somewhere around 16 W/MK. I usually mix some with Sn60/Pb40 to make melting point slightly higher. 138°C is too low

- Clemence

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I stumbled upon another Al/Diamond composite maker:
http://www.mmmt.com/resources/thermadite.html

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Agro wrote:
I stumbled upon another Al/Diamond composite maker:
http://www.mmmt.com/resources/thermadite.html

540W/MK is outstanding! So does the price I guess. Its so hard that only EDM machinable which is very slow. I machine a 2mm, 45mm deep oil passage in a hardened race bike’s crankshaft few years ago. Precise control and diameter tolerance was an issue.

- Clemence

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And another…:
http://www.rhp-technology.com

This one does only Cu/Diamond:
http://www.sumitomoelectricusa.com/products/heatsinks/copper-diamond

clemence wrote:
Agro wrote:
I stumbled upon another Al/Diamond composite maker:
http://www.mmmt.com/resources/thermadite.html

540W/MK is outstanding! So does the price I guess. Its so hard that only EDM machinable which is very slow. I machine a 2mm, 45mm deep oil passage in a hardened race bike’s crankshaft few years ago. Precise control and diameter tolerance was an issue.

- Clemence


The first one that I found would do 400 PCBs (that’s their MoQ) for mere $14K.
Maybe others are cheaper…anyway it shouldn’t hurt our record-chasers to ask for samples. Wink
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The Copper Diamond is the most interesting because it can be metalized while still electrically non conductive. With 650W/MK thermal conductivity the thermal bottleneck could the solder itself (assuming non gold plated contact used). In my opinion thermal resistance is more relevant since in the end this is what matters.
If an attachment system thermal resistance can be optimized to slightly below the thermal resistance in the LED (which we can do nothing about) then the rest of the system can use that number as the minimum resistance. In my opinion, as long as the cooling still creates negative delta temp copper or aluminum heatsink still doing OK. The higher the thermal conductivity of a material the less delta temp needed to flow the heat. We can make a superior cooling system using available budget friendly material widely available with good design and process. Manufacturers have to compromise the outcome to balance the design for a reasonable total cost.
For example:
- Use the best solder available (Indium is in the top of my list). And don’t forget to make the joint as thin as possible.
- Use the thinnest most rigid substrate possible. Metalized Aluminum Nitride can be made reliably down to 0,2mm without sacrificing rigidity. Although the thermal conductivity is only up to 180 W/MK in most cases, the thin substrate will make up the difference. This is demonstrated clearly in my MCPCB using “low” aluminum oxide dielectric with only 7,5W/MK thermal conductivity. Thermal resistance is what matters.
- Conventional wide and thick copper traces still works to further spread the heat over the entire board substrate as long as the radial thermal resistance still lower than through plane resistance.
- As flat as possible finish in the substrate and heatsink mating surface makes a big difference. Don’t compensate with thermal paste. Get the best possible mating surface first, use the least amount of thermal paste.
- Bare metal with no paint or anodization at the heat sink joint.

- Clemence

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The last manufacturer until I find some new search terms:
http://www.awindiamond.com/eng/04_application/Laser_HeatSpreaders_CDHS.html

Clemence, I don’t think that it makes sense for manufacturers to go beyond the standard SAC305. And definitely not now when even enthusiast haven’t demonstrated any improvements, only calculated some tiny ones. I’m not sure what budget materials do you mean but as far as I see budget light makers already do quite well when it comes to LED thermals. There may be tiny improvements here and there, but better materials don’t seem to be a budget choice.
Well, I imagine one possible improvement. That’s likely not a good idea anyway, otherwise saabluster would do it years ago. Eliminate MCPCB. Machine the shelf to leave a protruding thermal pad, add insulation on the rest of the shelf and make anode/cathode connections.
Or make the MCPCB several mm thick and press-fit into the head. Just like Nightwatch press-fits copper heat sinks.

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