1. Field of the Disclosure
The present disclosure relates generally to testing die on wafer and, more particularly, to testing of die on wafer using a reduced pin count JTAG interface. The reduced JTAG interface enables a larger number of die on wafer to be contacted by low cost testers and tested, which results in lowering the cost of manufacturing integrated circuits.
2. Description of Related Art
Today more and more wafer testing is being performed by low cost wafer testers. Low cost wafer testers are achieved primarily in two ways. (1) Decreasing the number of test contacts, and therefore expensive tester interfacing circuitry and probing mechanisms, between the tester and die on wafer, and (2) including more design for test circuitry (i.e. built in self test circuitry, scan design circuitry, test data compression/decompression circuitry) in the die to reduce the amount of test circuitry required in the tester. Furthermore wafer test cost can be reduced by using standardized design for test interfaces and circuitry in the die, such as the IEEE 1149.1 (JTAG) interface. The IEEE 1149.1 serial interface allows die on wafer to be tested via a standard 5 wire interface consisting of a test data input (TDI), a test data output (TDO), a test clock (TCK), a test mode select (TMS), and a test reset (TRST) signal. Using this interface, the tester only needs to contact each die using these 5 test signals to input and output test data and instructions. While the IEEE 1149.1 interface can be used for wafer testing, it still requires 5 contacts per die on wafer. For example, if 500 die on wafer are to be tested in parallel, the tester would have to have 2500 contacts to the wafer (500 die×5 signals each). Additionally, the IEEE 1149.1 serial interface bandwidth is relatively low since the TCK signal that times the interface typically operates at a frequency of only 20 to 50 MHz.