I suppose this might have just been detected as a "high K bin" :tinfoil:, but my eyes saw something strange immediately.
When I looked at my XP-G2 to prepare for a lens removal, I noticed its die surface was extremely "white". I always view the dies under a microscope to check for their consistency and any die errors before considering for a build (since I don't have a light test meter/software). This one lonely Cree XP-G2 was a very strange LED to me!
Only 25% area of the die surface looks like it has the "proper yellow" color. The rest almost looks silvery white. It looks like a circle set on a square, partially overlapping the square corner, with the rest of wafer circle chopped off. There is a notable difference in material thickness at the line where this color changes when rotating under a microscope.
The LED is still putting out quite the light amount it appears it should be, when compared to a cool white XP-G, running up to an amp in testing.
I used the small phone aperture to get a picture through the microscope. This is around 300X (darker yellow substrate is surrounding the bond wire in that corner of the die only, rest is silvery/yellow/white to the eye):
The pattern is much more apparent to the eye through the microscope than through the phone camera I was holding. Die was viewed while rotating, to rule out any shadow casting effect.
[Notice the "holes" can actually be seen that are inside LED chips centers, which follow a pegboard-like pattern all over the die if you look closely. Never really saw them before this very "white" die was looked at to know what they really were.]
Also, a comparison photo of a proper XP-G2 image in case you haven't seen one closely:
So, is this a classic wafer mishap that is common, a very poor chip, or just a high-K bin likely, with this being the reason? Etc... I'm just wondering what this visible pattern means, performance wise.
When I looked at my XP-G2 to prepare for a lens removal, I noticed its die surface was extremely "white". I always view the dies under a microscope to check for their consistency and any die errors before considering for a build (since I don't have a light test meter/software). This one lonely Cree XP-G2 was a very strange LED to me!
Only 25% area of the die surface looks like it has the "proper yellow" color. The rest almost looks silvery white. It looks like a circle set on a square, partially overlapping the square corner, with the rest of wafer circle chopped off. There is a notable difference in material thickness at the line where this color changes when rotating under a microscope.
The LED is still putting out quite the light amount it appears it should be, when compared to a cool white XP-G, running up to an amp in testing.
I used the small phone aperture to get a picture through the microscope. This is around 300X (darker yellow substrate is surrounding the bond wire in that corner of the die only, rest is silvery/yellow/white to the eye):
The pattern is much more apparent to the eye through the microscope than through the phone camera I was holding. Die was viewed while rotating, to rule out any shadow casting effect.
[Notice the "holes" can actually be seen that are inside LED chips centers, which follow a pegboard-like pattern all over the die if you look closely. Never really saw them before this very "white" die was looked at to know what they really were.]
Also, a comparison photo of a proper XP-G2 image in case you haven't seen one closely:
So, is this a classic wafer mishap that is common, a very poor chip, or just a high-K bin likely, with this being the reason? Etc... I'm just wondering what this visible pattern means, performance wise.