Real Time Wafer Mapper

The main purpose of Real Time Wafer Mapping System is to control and to monitor the wafer test procedure. Controlling the test procedure is accomplished by driving an automatic probing machine(prober) and obtaining test results from test equipment (tester). The Real Time Wafer Mapping System loads sequentially all the wafers to be tested from prober loading cassette, positions each chip below the probecard needles, moves the stage, that the wafer is laid on, so that the probecard needles contact the bond pads of the chip, and then informs the test equipment that it is ready to start testing this chip. After obtaining a test result for the chip from the tester, the process is repeated for the chip, next to the one just tested. After testing all the chips on a wafer, the RTWM unloads the wafer and continues with the next one, if any.

In fact, the Real Time Wafer Mapping System does not receive the measurement results themselves, but an integer value, called bincode, that sum up those results. When obtaining the bincodes, RTWM displays them on the screen in a wafer map, representing each bincode by a small colored rectangle. The position of the rectangle in the wafer map corresponds to the physical position of the chip on the wafer. As all the chips on the wafer are tested, before unloading the wafer RTWM stores the wafer map in a database.

Supported Hardware

Three different automatic probing machines are supported by the Real Time Wafer Mapping System:

• TSK 6000 A
• TSK PM-90A
• EG 20001

Interfaces

The Real Time Wafer Mapping System uses different communication protocols to talk to the devices it controls.

General Purpose Interface Bus (GPIB), a popular standard interface for communication is used to communicate with the automatic probing machine.

Either TCP/IP or RS232 protocols can be used to communicate with the test equipment.

Data Bases

The Real Time Wafer Mapping System uses ODBC drivers to access the database, where wafer test results are stored. This allows various databases to be accessed. So far the program is tested with Oracle and PostgreSQL databases.