Below are images for the several different trial runs that we performed on three different Cyclone III FPGAs. Each of these three chips had a pocket milled out on the top of varying depth. More information can be found in the Acid Etching Documentation.
- Trial 1 was performed on the test chip with a 3/10mm pocket milled out in a 10x10mm square on the top of the chip. This trial shows what happens when the RFNA (Red Fuming Nitric Acid) is left on the chip for far too long.
- Trial 2 was performed on the test chip with a 1/4mm pocket milled out in a 10x10mm square on the top of the chip. This trial had significantly better results than Trial 1. The entire die can be seen (ie. not eaten away by RFNA), and there looks to be a minimal amount of damage to both the bond wires and the die itself. There was a residual amount of packaging left on the die.
After 1 Minute of Die Exposed to RFNA
After 2 Minutes of Die Exposed to RFNA
After 3 Minutes of Die Exposed to RFNA
- Trial 3 was performed on two separate Cyclone IV FPGAs. They were both milled with a smaller, 4x4mm pocket on the top, with the first chip having a pocket depth of 0.2mm, and the second chip having a pocket depth of 0.125mm.