Problem stsetch SNF 2009-11-29 13:34:11: Missing Die

Upon etching all the way through 400 um backside using Al holder: noted etch completed on outside dies first. Then, etched an additional 5 minutes to complete the dies near the center. At 2min remaining it looked like all dies had completed etching to BOX layer. At 1 minute, one of our dies was missing. It either a) shattered or b) popped out when the BOX layer of that die gave way. (we have pop tabs instead of dicing). The remainder of the wafer looks good and did not exhibit debris from the missing die.