300 Watts, not a problem, I like a challenge. Thermal management is almost a hobby of mine. I am running thermal experiments 24/7.
I am a contractor for the University of Florida to do LED grow lights for Horticulture Research. Lots of Red LEDs are used. Red LEDs have poor performance when it comes to temperature.
This Red LED loses almost 50% of its Radiant Flux at 80°C.
A grow light fixture with a Tj of 85°C is considered do have decent thermal management.
I do not use thermal vias in a traditional way. Just as I do not use metal core PCBs.
The path of least thermal resistance is NOT going through the PCB to the bottom side.
The thermal pad of the SMT FET (IPT015N10N5ATMA1) is soldered to the copper layer on the top side of the PCB. So why would I put the heatsink on the bottom side?
I'm going use a copper layer as thick as I need to get the heat away for the FET.
Good thermal conductivity required as much cross sectional area and as little distance for the thermal flux to travel.
The thermal pad of this FET is soldered to copper so I will bolt down a thick copper bar to the same copper layer, as close I as can get to the FET.
The PCB layout would be similar to this SOIC 8 Power Pad.
It has thermal vias just in case I need to sandwich the PCB between two copper bars. Mostly they give me a good place to place a thermal couple to measure thermal management.
Pad 50 is for a 4-40 machine screw to bolt to the copper bar. The left edge of this footprint would be on the edge of the PCB. I would put a piece of 0.0007 soft annealed copper foil, squeeze it in a brake press then torque the screw so tight the foil fills every little nook and cranny.
Where the copper bar goes depends on the environment. It could be a heat pipe connected to a radiator. If it's no holds barred, I'm going to attach it to a copper water pipe with ice water flow through it.
I'm done with the thermal management when I see condensation on the copper bar.
Here is an example of the PCB attached to a bar soldered to a water pipe.
The FET would be closer to the bar. Here the bar is not as close to not block the photons.
Got a new shipment of copper last week, these are the latest.
- is similar to the above board
- I use CoBs as heat sources
- This is similar to the above but has two boards attached to the pipe. This is testing a board with 32 3 Watt LEDs
- This looks like a candidate for the FET. But with a bar like #5.
- this is a 0.375 x 0.25 bar with one end bent with a radius of 0.3125" to mate with a 1/2" copper pipe.
- a 0.375" x 0.125" x 24" with both ends having a 0.3125" radius bend.
- a 0.625" diameter (same as a 1/2" pipe OD) 17-4 Annealed Cold Finish Stainless Steel, strong enough to withstand a sledge hammer beating a copper bar into submission.
Photo taken tonight
That strip with 32 3 Watt LEDs is at 38°C . Considering this is my garage in Florida and the water temp is 27°C that's not too bad. There is two boards too. To give a little more perspective the thermal vias under the LEDs, when first touched, do not feel hot at all. While the Formica surface of the table, 3" below the LEDs, is about 50°C from the photons. There is no heat coming off this board.
Photo taken tonight
My "Water Tower"