To increase the speed of the optical subassemblies used in data centers, we have developed an EML with a high-mesa structure and a high-speed electrical interface technology that suppresses reflections of electrical signals. In addition, the reflection at the connection between the PCB and the FPC, which is the electrical interface part, was successfully suppressed to less than 12 dB over a bandwidth of 50 GHz. A 43Gb/s EML optical subassembly with these technologies was fabricated and evaluated, resulting in excellent optical waveforms with a mask margin of over 11%. Furthermore, a fabricated 424 Gb/s EML optical subassembly with four EMLs integrated into a single package showed good optical waveform quality with TECQ less than 2.5 dB for all lanes.

Solder electromigration (EM) is recognized as a potential reliability problem in power modules. This study investigates the fundamental EM phenomena under Alternating Current (AC) and Direct Current (DC). A Cu/Ni-P/Sn-0.7Cu/Ni-P/Cu joint was investigated at 175°C and 50 A/mm². The direction of the Direct Current (DC) was reversed every 96 or 48 hours in order to understand the effect of a reverse current on the EM. In the DC-EM, the growth of a P-rich layer in the Ni-P layer caused an open failure due to internal voids. In the AC-EM, Ni was EM transferred from/to the Ni-P layer depending on the electron flow direction and the P-rich layer thickness increased/decreased accordingly, resulting in suppression of the P-rich layer growth. This effect became significant with the shorter cycle time.