ST produces world's first wafer employing fully contactless testing

GENEVA, SWITZERLAND: STMicroelectronics announced the successful production of the world's first semiconductor wafer whose dice were fully tested without contact probes. ST's innovative advance in testing technology enables a wafer containing chips such as RFID (Radio Frequency Identification) ICs to be tested using electromagnetic waves as the sole link to the array of circuits on the wafer.

Higher yields, shorter testing times and lower product cost are among the potential benefits of this approach. In addition, contactless testing allows RF circuits to be tested under conditions that are close to the real application conditions.

The new EMWS technology results from an R&D project called UTAMCIC (UHF TAG Antenna Magnetically Coupled to Integrated Circuit), led by Alberto Pagani, Giovanni Girlando and Alessandro Finocchiaro from STMicroelectronics, and Professor Giuseppe Palmisano from the University of Catania, which won a prestigious 'Sesames Award' in the 'Production & Test' category at Cartes and IDentification 2010 in Paris in December 2010.

ElectroMagnetic Wafer Sort (EMWS) is an evolution of Electrical Wafer Sort (EWS), the last stage of wafer fabrication before assembly and test of the final packaged products. At this stage in the manufacturing cycle, the processed wafer contains an array of identical circuits called die. A probe card connected to Automatic Test Equipment (ATE) is moved over each of the die and, in turn, the microscopic probes make contact with test pads on the die. The ATE then performs its tests to confirm that the die is fully functional, allowing any non-functional die to be discarded before the die are assembled and packaged.

EMWS is a recent development in which the individual dice contain a tiny antenna and the ATE supplies power and communicates with the dice via electromagnetic waves. This approach reduces the number of test pads on the die, significantly shrinking the die size. Probes are still required to supply power to test high-power products but ST's novel technique (1) now enables fully contactless testing of low-power circuits.

"This breakthrough in testing technology demonstrates ST's commitment to our zero-failure policy and especially benefits customers using our low-power RF circuits," said Alberto Pagani, Test R&D and Competitive Intelligence, a developer of the new technology. "Contactless testing improves test coverage and, because the RF circuits, anticollision protocol and embedded antenna are tested under the same conditions they will operate under in the customer's application, it will significantly enhance quality and reliability."

Contactless testing drastically reduces the test cycle time because it enables high testing parallelism to be achieved in contactless mode. Moreover, it increases yield by eliminating the pad damage that occasionally occurs during standard contact testing.