Key Takeaways: Fiber alignment is the main bottleneck to optical engine testing, which would be alleviated significantly by multi-site probe cards. Optical connectors must be optimized for the best optical properties yet be mechanically robust to withstand assembly and use. Simultaneous loopback on both optical and electrical sides could simplify testing. Experts At The Table : The industry is forging a path from single-site to multi-site testing while system architectures and connector types continue to evolve. Semiconductor Engineering sat down with Matt Griffin, senior product manager for optoelectronics test at Teradyne ; Ira Leventhal, vice president of research and venture at Advantest America ; Dave Armstrong, fellow at ISE Labs, a subsidiary of ASE Group ; and Kazuo Yamaguchi, silicon photonics researcher and engineer at Keysight Technologies . What follows are excerpts of that conversation. To view part one, click here . Fig. 1: (L-R): Teradyne’s Griffin; Keysight’s Yamaguchi; ISE Labs’ Armstrong; Advantest’s Leventhal. SE: Is it true that you can only test one die at a time today? Armstrong: I would hope some insertions will go away over time, but right now there are more things being added than being subtracted. It’s a hard one. In terms of testing one die, that depends on the die. If an 8 kW GPU is your main ASIC, and you have multiple connectors around multiple sides of the part from a tester resource standpoint, and the amount of power a tester can deliver and take out of the part, it’s pretty challenging to get beyond one die. But if you look down the NPO-versus-CPO path, NPO is typically a single connector device. You’re going to have to be able to go to multi-site to scale that to high volume. Insertions two and three are the fertile ground for multi-site. Those are longer more complex test insertions. PIC wafer testing tends to be single-site today. From my experience, there is some hope on the horizon to bring it up a little bit higher with some capabilities in the probe card area, notably from Technoprobe. Griffin: I agree with Dave. Most production solutions today are single-site, and when you talk about the optical engine, the main bottleneck is fiber alignment. Many companies are working on multi-site solutions, and I hope they succeed and take off because that only helps the whole industry ramp faster. But we’ve got a little bit longer to go there. SE: For these alignment ports, can you repeatedly test at that site? Griffin: Ideally, you’re able to repeatedly test almost infinitely because you should never be contacting the device with the optical probe or the fiber array unit (FAU). When you’re bringing up a new test solution, you do sometimes crash FAUs on first systems. In reality, the bigger concern is contamination on the FAU, so cleaning is needed. On the connector side, at the module level or for optical engines with receptacles attached, the optical connector lifecycle is where we need more effort, because the device-side connector is designed to be attached once and, hopefully, never disconnected. And every new connector generation changes both the connector recipe and the automation recipe. Leventhal: In a sense, this is nothing new. For instance, with BGAs, if you socket at the device too many times, then you start worrying about damaging the balls on the BGA. It’s a similar problem and the industry will gravitate toward connector designs that are more robust. Matt made a really important point about how your test side connector needs to be some sort of a hardened connector that doesn’t wear out easily after 20 to 50 insertions. It needs to last for tens of thousands or 100,000 insertions. So you’ve got to go to a hardened metal, and then you’ve got a hardened metal going against the receptacle on the device, which is not going to be that hardened metal. If you’re not careful, you could damage that connector sooner than the spec lifetime. So as the industry evolves to the winning connector de