The 2022 SWTest Conference is in the books, but the accolades are coming in!

David Raschko won the People’s Choice Award for his presentation – Advances in Vertical Probing for High-Speed Digital Test at Wafer Sort.

Digital communication speeds are rapidly increasing through PCIe standards, Ethernet standards, and OIF/CEI standards. This increase in data rate leads to significantly higher system or module losses and these losses must be accounted for in the TX and RX channels of a die. To account for channel loss, equalization is used where the digital signal is altered in a manner that removes the effects of the channel loss. As this equalization becomes more prevalent throughout the semiconductor industry, wafer test methods will need to be created that will enable the testing and application of the channel equalization inherent to the device under test. This will require probe cards to emulate the loss profile of the expected channel for which the device under test is designed for in order to properly exercise the channel equalization of the die.

This paper will go over the inherent challenges of replicating system loss in a probe card, methods of matching expected system loss, and the implementation of novel probe card design features that enable proper exercising of a die’s channel equalization during wafer sort.

 

Daniel Bock, PhD, tied for Best Data Presentation for his presentation – High Speed Digital: How to Optimize a Probe Card for PAM4 Signaling to a Non-50 Ω Device.

The release of the 5G standard and the expansion of broadband internet is steadily increasing the load on the data communication infrastructure.  The data communication infrastructure operates over fiber, and is using PAM4 modulation, moving from 28 Gbps to 56 Gbps (and beyond).

For wafer test, this translates to test requirements at very high speeds and in some cases outside of the typical 50-ohm environment.  Transimpedance Amplifiers and the associated Laser Drivers in the fiber communication chain are typically not connected to a 50-ohm device (in this case a photodiode or a laser driver, respectively).  Due to this distinction, they typically have port impedances that require broadband matching between the device under test and the tester 50-ohm environment in order to pass a digital signal.

We’ll examine the advantages of putting a matching circuit on the probe card specifically tuned to the impedance of the photodiode (for example), which typically operate at non-50 ohm.  We will talk about the work done in optimizing the performance of a probe card in order to maximize the eye in a PAM4 signal.  This includes both component selection, as well as optimization of the traces on the Pyramid Probe.  In particular, making sure that the components are as close to the device under test is critical to maintain the best performance possible.  We will also present simulated eye diagrams that would be seen at the tester, to show the performance improvements due to the tuning of the circuits to maximize eye height and width of a PAM4 signal.

 

Both presentations can be downloaded here, or via the links above. Congratulations once again!