STMicroelectronics developed a new RF testing method that uses electromagnetic waves instead of contact probes to remotely evaluate wafers equipped with RFID ICs.
According to ST, this “contactless” approach results in higher yields, shorter testing times and lower product cost. In addition, contactless testing allows RF circuits to be tested under conditions that are close to the real application conditions.
The technology behind the test, dubbed ElectroMagnetic Wafer Sort (EMWS), comes from an R&D project led by Alberto Pagani, Giovanni Girlando and Alessandro Finocchiaro from STMicroelectronics, and Professor Giuseppe Palmisano from the University of Catania
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. According to ST, 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 technique now enables fully contactless testing of low-power circuits.