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After the final passivation layers are applied, the entire wafer goes through backside prep, which thins the wafer to allow better heat dissipation and removes stress fractures which could cause breakage. Each finished wafer may contain several hundred actual devices or die. Automated methods are used to test each device on the wafer before it is broken into "chips." |
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A probe tester uses needle-like "probes" to contact the bonding pads (the circuit connection points) on each device and check its operation. Devices that fail the test are marked with colored dye so they won't be carried further into the production process. | |
After probe test, the wafer is scored and broken into individual die. The marked (non-functional) die are discarded and the functional die passed on into the wire bonding process. The efficiency of a given fab is determined by it's yield: the ratio of functional die to total die. |