Scaling co-packaged optics (CPO) testing beyond a single die is not simply a matter of adding more probe stations. In a Semiconductor Engineering roundtable, test vendors and researchers agreed that most production optical-engine testing is still single-site, and that fiber alignment is the main bottleneck. Multi-site probe cards are seen as the key enabler, particularly for NPO-style single-connector devices where high-volume production will require testing several dies at once. Armstrong noted that PIC wafer testing remains single-site today, though new probe-card capabilities from Technoprobe offer some hope.
Connector reliability is the second major constraint. Griffin said device-side connectors are designed to be attached once and ideally never disconnected, while test-side connectors must survive tens of thousands of insertions. Leventhal compared this to BGA socketing: a hardened metal test connector can damage a softer device receptacle if the design is not carefully matched. The panel agreed that connector generations change both the connector recipe and the automation recipe, so robustness on the device side is as important as optical performance.
On simultaneous electrical and optical connection, the experts differ in emphasis. Armstrong called it 'a question of time,' and Leventhal agreed, adding that warpage and multi-axis alignment make it significantly harder. Yamaguchi, however, framed it as an RF probing problem: modulator and photodetector validation requires S-parameters at frequencies beyond 200 GHz, while probe cards have limited RF line counts and bandwidth. The takeaway is that CPO testing at scale will require coordinated advances in probe cards, connector materials, and RF test hardware.