336-Channel electro-optical interconnect: Underfill process improvement, fiber bundle and reliability results

The icPhotonics™ optical module assembly development was presented in [1]. The module allows for aggregate full duplex data rate of better than 1.30 Tb/s with Bit Error Rate (BER) <; 1E-12 into and out of a single ASIC die for distances up to 300m. The module assembly uses standard semiconductor processing equipment and materials. The icPhotonics™ components - an organic interposer (substrate), ASIC (standard TSMC 65nm node technology), two 168-channel 1000nm optical dies (VCSELs and photodiodes) and two Micro Lens Arrays (MLA´s) dies of 168 pixels each - are all assembled using flip-chip technology, allowing for a very high density data rate transfer. The 1.344 Tb/s data transfer rate is enabled from the 168 VCSELs and 168 PD´s through two sets of 168 multi-mode fiber bundles. The fiber-bundle´s design and special production sequence enable high efficiency and low-loss optical data transfer to a standard MT-Ferrule connector. Several icPhotonics™ modules can thus be connected and allow applications which require a very high BW data transferred between different ASIC dies, with bandwidth density of 64Gb/s/mm². A major production challenge in the icPhotonics™ production was associated with the unusual underfill application for an optical module with 2 optical dies in the center of the ASIC die and a hole in the center of the organic substrate. The overall yield of the Optical Interconnect (OI) was enhanced using MW-plasma treatment before applying underfill. In this paper the general failure modes associated with the underfill process are examined and a comparison of the yield with and without the plasma activation is presented. Various reliability tests were performed on the icPhotonics™ module, its components and the accompanied fiber-bundle assembly. The entire assembly was exposed to thermal cycles and rapid aging procedures, testing the soldering performance. The optical components, especially the VCSELs- were also exposed to prolonged rapid aging procedures while testing their optical performances. Reliability tests and results are presented, as well as additional thermal cycles performed on the large format fiber-bundle, testing BER results changes after exposure to environmental conditions.