# High power LED on aluminium core PCB

I'm working with a high power LED(40W heat dissipation) on a single layer aluminium core PCB.To calculate the required heatsink it did the following:

$P = 40W$

$Rjc = 0.6K/W$ (datasheet)

$Rcpcb = 0.77K/W$ case to PCB. This is the thermal resistance of the isolation layer(MSC TC-Lam 1.3, 100µm)

$dT = (Rjc + Rcpcb) * P = ~55K$

In summer $(Ta = 45°C)$ this would require a heatsink with $(Tjmax - dT - Ta)/P = (110 - 55 - 45) / 40 = 0,25K/W$ which is hard to achieve without forced air flow(not allowed in the environment) The only parameter I can change is Rcpcb.

Question: The manufacturer can mill through the isolation layer, but is there a way to connect(solder) the thermal pad directly to the aluminium core? Are there any other ways to get the heat away?

• Edit: VERY low volume production! Maybe only a single prototype.
– 1uk3
Sep 15 '17 at 7:40
• Copper core PCB? Sep 15 '17 at 8:47
• Can you give the LED datasheet? I'd like to see the mechanical dimensions... Sep 15 '17 at 14:25
• Datasheet: ledengin.com/files/products/LZP/LZP-00UB00.pdf (I can't use the provided star MCPCB because of shape/size) Copper core is quite expensive for low volume
– 1uk3
Sep 16 '17 at 20:11

I needed this TO220 to dissipate a lot more than a TO220 can. The limiting factor was the silpad at the back (similar to your case). So I soldered it on a flat piece of copper and mounted that on the heatsink. The much larger silpad area does wonder to heat removal!

Since this is a one-off I suggest doing the same, reflow the LED on a big chunk of copper, and bolt that on the heat sink with thermal grease.

• Thank you! Yes i think there is no way around some sort of copper "heat pipe". I will try to push a copper pin(9mm diameter thermalpad on the LED) through a hole in the aluminium pcb and then try normal reflow soldering.
– 1uk3
Sep 16 '17 at 20:08
• I was asking for the LED datasheet to check how it would all fit together... if it has pads underneath they you won't be able to solder it to solid copper directly, because that would short things out. Artful application of kapton tape (acting as soldermask) onto the copper block could solve this problem. Anyway, I hope you solve this, since it's a one-off, anything goes. Sep 16 '17 at 20:13
• You can find the datasheet in the comments of the original post ;) I still want to use some sort of pcb
– 1uk3
Sep 16 '17 at 21:23

heatsink is preferred. This is a design by Samsung

• Thank you. Of course i need a heatsink. I just try to get away with a smaller one by reducing Rcpcb.
– 1uk3
Sep 15 '17 at 8:51