Sink-pad seems popular here. I see it in many of the mod photos.
This chart is from the Bergquist company,
I have a quantity of aluminum xm-l star discs from bergquist and a handful of copper ones from sink-pad.
At almost 3X poorer thermal conductivity under what circumstances is aluminum chosen over copper? Is it purely a question of end product costs in high volume?
For the sake of diy’ing, where extremely low volume has little bearing on parts cost differences of a dollar or two, why would aluminum ever be chosen?
I’m brand new to this but confident enough in my tinkering and soldering and basic electronic skills.
With an smd led all three pads are solder flowed to the heatsink, correct?
If a copper based star is used, can/should it be soldered directly to a larger copper heatsink?
At almost 3X poorer thermal conductivity under what circumstances is aluminum chosen over copper? Isit purely a question of end product costs in high volume?
For me personally, I would say the 2 main reasons to use aluminum over copper are: 1. I have tons of aluminum stars lying around so I just want to get rid of them and 2. They are cheaper, in builds where the led is not being overdriven by a huge amount a copper star is not necessary. However, if you don't care about the price, there really is no reason to use a aluminum star (except for when a copper star does not fit due to height).
For the sake of diy’ing, where extremely low volume has little bearing on parts cost differences of a dollar or two, why would aluminum ever be chosen?
See Above.
I’m brand new to this but confident enough in my tinkering and soldering and basic electronic skills. With an smd led all three pads are solder flowed to the heatsink, correct?
Yes correct, the best way to do this is to heat up the star in some way (lighter, blow torch, stove top, etc.), tin the LED pads with a small amount of solder and then place the LED on the star with a pair of tweezers.
If the sink-pad star is used, can/should it be soldered directly to a larger copper heatsink?
Yes, it can be soldered to a large copper heatsink for better conductivity, but unless you are truly pushing the limits of the LED that is not going to be needed.
Even at the size of a star, Copper is much more expensive to produce. It is just not cost effective. Look at the going price on copper stars, from International Outdoors, versus Aluminum. There is a big gap in price and for anyone who is on a limited budget, Copper is out of the picture.
It's just not necessary at all, unless you are planning to, as an example; put 9 amps into a 3 amp max led. In that case, you should use the best heat transfer you can get, which would be a copper star soldered to a copper heat sink, or solder the led direct to a large copper heat sink. (That is my opinion only, others will disagree).
For me, Copper is just too expensive to do much with it. It has gone up in price and now I hardly use it at all any more. With the millions of flashlights out there in the world and with the tens of millions or leds out there in other lighting, (all using Aluminum), it says something for the fact that all that Copper isn't really necessary except in extreme situations, or more often, because it makes the user feel like they did something special by using it. I used to try to use it all the time, now I realize that for what I do, it's just not necessary.
I think the biggest difference is not the material of the star, but whether or not the LED is directly soldered to the star (Sinkpad, Noctigon etc) or has an insulating dialectric layer in between. Even at manufacturer specified max drive current (3A), the difference with an XM-L is about 10%, which is getting into the noticeable range (or, lets you have the same amount of light for slightly less drive current and longer runtime). I don’t know what the relative gain is of the aluminium direct mount stars, but going by Sinkpad’s figures it should be somewhere between the two.
However, the material that the star is attached to is less important IMO. What matters in keeping the LED cool is getting the heat away from the LED and into the air, so good (and few) thermal interfaces and large heatsink surface area is more important than what the heatsink is made out of.
Like mattthemuppet said, it's about creating a better thermal path by bypassing the dielectric layer. Copper stars by Sinkpad, Noctigon and some by Illumination Supply offer that. Not all copper stars bypass the dielectric layer though, and those aren't worth much more than their aluminum variants.
You can, but that creates a longer path through solder. Solder conducts heat nearly 10 times worse than copper. And as you said, you might have difficulty soldering. It seems Sinkpad has aluminum stars, and I believe those also bypass the dielectric layers to create a better thermal path, but I don't know how they address soldering issues.
An LED mounted on a massive chunk of copper would not run significantly cooler than one mounted on solder. Look there: https://budgetlightforum.com/t/-/16455#comment-340163
Its just copper, aluminium and brass, but you get the idea..
Soldering aluminium is easy - with the right equipment. Pre-soldered aluminium stars would work great.
Thermal conductivity of brass is half or less that of aluminum and up to four times lower than copper, but is still twice as high as solder. Is that enough to change the results? I don't know, but Sinkpads and Noctigons are priced low enough that I'd rather buy them than cut the dielectric layer out of under an LED.
I don't even know who sells aluminum Sinkpads without searching for it. Doesn't anyone else make direct to aluminum mcpcb's? Unless I was trying to save weight, or selling in massive quantities (bean counting), I wouldn't bother with it.
As you said, copper has 4 times the conductivity of brass and they still perform similar. Also, did you notice that aluminium was better than copper at 5A, although it has only half the thermal conductivity? Strange, isn't it? ;)
Sometimes you have to cut out the center, thinking of generic boards.
aluminium as far as I can tell. The one I used looked like it might have some sort of solder already on it, but I added some solder paste anyway. I don’t have any scientific way of testing whether or not there was a proper joint formed when I reflowed the Nichia 219 onto it, but some solder squidged out and it’s still working perfectly fine after a lot of use. It’s not driven highly though, just 1.4A and rarely at that level.
