Laser Sintering of Dip-Based All-Copper Interconnects

The solder alloys applied in state-of-the-art flip-chip electrical interconnects are one of the main limits to improving the high power handling of this technology. To overcome this issue, the replacement of solder with interconnects purely made from copper is desirable, owing to copper's superior electromigration resistance with respect to solder. Recently, dip-based all-copper interconnects were shown to be a promising approach to form all-copper flip-chip interconnects by the sintering of Cu nano -and microparticles between copper pillars and pads. In this process, the Cu particles are applied on the pillar tips by a dip-transfer method and then collapsed onto pads, forming an assembly. Then, the assembly is sintered for 30 min in a thermal oven under constant flow of formic-acid-enriched nitrogen. After the sintering, copper joints that connect the pillars and pads are formed, resulting in the so called "dip-based all-copper interconnects". Despite the large interest raised around this approach, the requirement of formic-acid application and the long sintering time limits its scalability. In our work, we report the first example of dip-based all-copper interconnects formed by laser sintering, without the application of formic acid and with a process time of only a few seconds. These results could lead to the development of a novel ultrafast and formic-acid free assembly technique of all-copper flip-chip interconnects.