Adhesives Properties Impact on Optical Alignment and Packaging

Artificial intelligence (AI) is growing and to meet the demand for AI scale-up and scale-out, high speed networking infrastructure is needed to keep pace. Integrating silicon photonics with advanced packaging for faster data communication and power efficiency is a rising trend. 

Although electronic packaging has seen remarkable progress, photonic packaging still faces major hurdles in achieving consistent performance and reliability. Major challenges include the need for highly accurate and efficient active alignment for optical coupling, ensuring durability and reliability during reflow and environmental testing which are common standards in semiconductor packaging. 

Adhesives have been playing a vital role in advanced packaging in the area of die attach, capillary underfill and molding. These “classical” packaging adhesives have been well studied and characterized.  Optical adhesives play a vital role in photonic packaging process, however their properties and their performance such as bonding strength, optical transmission, and resistance to environmental impact are not well understood. 

This paper explored the optical and mechanical characteristics of adhesives, as well as their ability to retain stable performance under varying operating conditions. Recent advancements in adhesive technology are also highlighted, demonstrating how they improve efficiency and reliability in photonic devices, supported by experimental results. A study on various adhesive properties and how these changes in adhesive properties impact optical performance is performed.  Actual evaluation of the adhesives through fiber array unit (FAU) coupling to silicon photonic IC (PIC) and FAU to FAU coupling is done. Optical alignment and hence coupling efficiency and insertion loss contributed by these adhesives are measured and compared after being subjected to various reliability testing such as long storage at 85oC / 85% relative humidity and harsh conditions such as multiple reflow.  Through this evaluation, preferred adhesive properties for optical alignment can be recommended for photonic packaging.