XM-L2 dissection

Ever wondered what's inside?

The copper is the underside of the silver anode/cathode planes on the top of the package, tin plated (or something) I believe. I've scratched them on the top and saw copper under the silver stuff.

The actual substrate material is ceramic, or ceramic-like. I had to use a diamond file to get through it, and it took a while. It's definitely not fiberglass like the XM-L.

Very interesting

Correction: just tried the same with a XML, it's not fiberglass, but it's not the same stuff as the XML2. It got hairline cracks all over and fell into a million pieces...

Image # 2 reminds me of high density diskettes of the 90s. :davie: Anyway, I realize it was ceramic not some other “sophisticated” material.

The XM-L2 has a silicon carbide substrate, might explain the need for a diamond file. The XML I think was ceramic, not 100% sure.

The die is silicon carbide, not the substrate. At least on the XML2. I think that material change ('SC³ Technology Platform') is the main upgrade from XML.

Cool photos! TY.

Nice Comfychair, thanks for the step by step photos.

This is great info, thanks for doing this!

So it seems whole anode-cathode layer was covered with the non-conductive substrate… and the current is brought up through the two tiny pinhole wires.

It does bring a question though, how well does the substrate transfer heat? :slight_smile:

i hated those things, the would get bad sectors if you looked at them the wrong way, i would use two to transport a single set of data, or 3 if i needed to make sure it got through

nice photo's comfy, thanks for the sacrifice (and now the same, but starting from the other side, and one starting from the side, please :-) )

Ceramic substrate is usually sintered alumina (Al2O3 powder).

I can find no other place with information that backs this up. Looking at the pic, it does look like the die material is the same as the substrate material. Is the substrate not the same material (silicon carbide) under the die?

It's strange stuff. Though it's dark grey in all the pics, the dust that comes off while filing/sanding is white like baby powder. The stuff the die is made of is like (or is) metal, or silicon wafer stuff. The base of the die is soldered to the top surface of the plated copper cathode plane. I know it's soldered because I've had a reflow screwup where it got too hot, and the die lifted away from the base (with the bond wires still attached - I held the die down with a toothpick and re-soldered it back in place, and the LED still worked afterwards... somehow!).

Mainly what I wanted to find out was what's between the die and the thermal pad on the bottom, I think there were some folks who were assuming there was a copper or metallic pillar connecting them through the substrate.

Thanks for dissecting the led comfychair, very interesting stuff. :bigsmile:

Can you imagine if the die WERE on a copper pin? :O I'm sure whatever the substrate material is it's pretty good or else they would have used something else, but the requirement that the thermal pad be electrically neutral means quite a bit of performance has to be sacrificed.

I agree. I imagine thermal transfer quite a hit due to the substrate. Really wonder the performance leap that can be gained by adding straight thermal path.

General consumer designs rely on the thermal pad being electrically insulative though. It is probably too dangerous to let loose a design that base ground = thermal transfer to the general public.

Imagine poorly soldered positive wire dangling near a metal base (which incidentally becomes negative terminal now), and mass produced to millions of people who knew next-to-nothing about electricity. Ouch.

Take a tiny tiny diamond bit, grind away the substrate making sure you stay below the area covered by the cathode plane. Grind until you hit copper... :p

Hey comfy… here’s an idea, whaddya think. Shave off 2/3 of the emitter bottom (thermal + ground) and replace with straight copper shim, which later gets reflowed straight to Noctigon or Sinkpad. Bypass the substrate.

You think this is possible?

You mean just thinning the substrate, or grinding it away completely? The anode/cathode panes on the top surface aren't joined together well if at all, there's a line of insulative stuff between them but it's not strong enough to hold things together without the substrate.

I was thinking of cutting away just a round patch under the die, then mounting it on copper with a tiny raised mound or pillar to contact the bottom of the cathode plane right below the die.