Safe current for XML2 on Aluminum MCPCB

[clemence]

@Lightbringer

@WalkIntoTheLight

Okay, from that chart, it looks like the damaging factor is heat at the junction point, not the amount of current flowing. Current plays some role, but it appears if you properly heat-sink things, most of damage is mitigated.

Think of it like this… On a macro scale, a light with lousy thermal path doesn’t even get very warm to the touch, yet the LED is screaming because it’s pretty much on fire. Cold outside air, etc., keeps the body of the light cool, yet the LED still screams in searing pain.

Same thing on a micro scale. The LED can be cooled from the bottom (Al or Cu, doesn’t matter) as much as you want, but the current density inside the chip still cooks it from the inside as well.

That’s why an LED that isn’t reflowed well to its star has a lousy thermal path and can go blue and die with much less current than one that’s reflowed perfectly.

And yeah, those figures for θ_JA are made up of a whole bunch of “partial” θs. First one’s from junction to the chip’s substrate or something.

+1
This is exactly what I wanted to say earlier. It’s the thermal bottleneck “above” the Aluminum Nitride substrate. Every material with thickness has thermal impedance/resistance. With every resistance there is heat build up. Don’t forget that the current flow inside the chip also face resistance.

[Clemence]