The pcb drills might just be the ticket here. You won’t get through all 1600 holes with a single tool but they are dirt cheap so maybe it doesn’t matter if you break a few.
I used the standard aluminum fusion recipe for 0.7mm drill. Did a 5x5 grid and went 3mm deep. Came out beautifully.
Tried the same with a 0.3 and it snapped on the first hole. In hindsight, 3mm depth was kind of dumb to test with but you live and you learn.
Anyway, grab a bunch of the pcb drills and give 'em a shot. That’s my recommendation anyway.
(The B in the photo taught me to keep islands in mind 
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