Laser assisted bonding (LAB) mechanism study on the effect of flux dipping, stage block vacuum force and chip attach misalignment

In the semiconductor industry, three major bonding technologies are commonly used: mass reflow (MR, thermocompression bonding (TCB) and laser assisted bonding (LAB). MR, which is a conventional interconnection method, has been used as a standard for interconnection technology for a long time. However, the limitations of mass reflow from the bump and pad pitch perspective have been predicted for a long time. With MR it is not easy to make interconnections with very thin die and a coreless substrate and these are major trends in recent packaging structures. MR has a high warpage, bump tearing due to highest thermal stress. To overcome the mass reflow technical limitation, TCB has appeared to minimize the thermal stress. The TCB process has many advantages such as the lowest thermal stress and the lowest warpage but the weak point of TCB process is very low productivity. With the limitation these two bonding processes, the semiconductor packaging industry focused on the next generation of interconnection technology --- laser assisted bonding. The advantages of the LAB process is a localized heating area that results in lower thermal stress and lower warpage than mass reflow. Also, LAB has very high productivity due to the shortest bonding time. The bonding time of mass reflow is about 5 to 10 minutes but the LAB process is less than 1 second. The comparison of interconnection bonding technologies is summarized in Table 1.Among them, LAB technology has been used for production since 2018 in the industry with technical advantages such as lower thermal budget with localized short heating and lower substrate warpage by stage block vacuum suction, etc. Recently, advanced flip chip packaging requires advanced bonding technology. With the industry’s interest in LAB, it will be even more popular. However, at this moment, a better understanding is required of the fundamental bonding mechanism.This paper provides the results of studying the LAB bump interconnection mechanism based on the effect of flux dipping, stage block vacuum force and chip attach misalignment with actual evaluation data including LAB infrared (IR) profiles, X-ray images and bump cross section, etc. These results will help researchers have a better understanding in the failure analysis of LAB-processed products and enhance LAB capability in the industry.