Laser-Assisted Bonding (LAB) Process and its Bonding Materials as Technologies enabling the Low-Carbon Era

The reflow process and its flux materials have been used for decades in surface mount technology including flip chip bonding. However, this technology has an adverse effect on the environment by generating fume and flux residues during the process. These by-products are not good for the reliability of components and systems, so additional, power-consuming series of processes such as flux residue cleaning, high-temperature aging of substrates, plasma treatment, and underfill dispensing and curing processes are required. In addition, for equipment to perform these processes, a production space with large power consumption is additionally required to maintain constant temperature and humidity. Such a high-power consumption surface mount process is not considered to be suitable in these days when we have to prepare for the low-carbon era. In particular, it can be said that the development of alternative technologies is essential these days when the market demand for developing the climate change suppression technology is strong.Laser-Assisted Bonding (LAB) technology can be considered as one of candidate technologies to replace the reflow technology. This has the advantages such as very short process time, area-selective process and small equipment space. In this study, we developed bonding materials suitable for the LAB process. All components that make up these materials are based on polymers. A material that acts as a flux, that is, reduces the oxide layer of solder, is also present as a reactor in the polymer chain. During the LAB process, this polymer-reducing agent is activated to deoxidize the oxide layer of the solder. The polymer-reducing reactor that does not participate in the reduction reaction is cured by reacting with the curing agent during post-curing after the LAB process, thereby securing chemical stability. Due to this, these materials also act as an underfill. That is, there is no need for sequential underfill dispensing and curing processes. This eliminates power-consuming processes such as flux residue cleaning, equipment cleaning from fume contamination, plasma treatment, and high-temperature substrate aging. This, also, saves power consumption for the production space. These materials can be applied in various forms such as paste or film with or without solder powder, and have been verified for passive devices mounting, flip chip bonding, and micro-LED transfer processes.