Development of Next Generation Flip Chip Interconnection Technology Using Homogenized Laser-Assisted Bonding

Abstract

Conventional flip chip technologies such as the mass reflow (MR) process and the thermal compression bonding (TCB) process are commonly used technologies in the micro assembly field. However, there is a continuous need for next generation interconnection technology to achieve a low form factor with increasing die and substrate complexities. Moreover, very thin 3D integrated packages and 2.5D packages with thin interposer die promise advanced interconnection technologies for mobile and wearable applications. With this point of view, the most important factor in interconnection is optimal thermal energy control for soldering. However, a conventional MR process cannot provide any selectivity and controlled thermal energy transferring with the traditional convection reflow. Its high thermal budget makes warpage an issue, aside from other side effects. To overcome the MR process problems, recent researches and industries have focused on developing a TCB process with non-conductive paste (NCP) or non-conductive film (NCF) due to TCB's unique advantages of low mechanical and thermal stress. However, the productivity of the TCB process is not comparably to the conventional process. Laser-assisted bonding (LAB) with beam homogenizer is considered to be the next generation interconnection technology due to its excellent thermal selectivity, extremely fast ramping up speed with purely controlled wavelength. This LAB process offers a very stable interconnection quality as well as robust functional and reliability result. Interestingly, it also achieves excellent results with thin coreless substrate due to its selective heating area availability. This paper will discuss the laser heating mechanism, multi-chip & component bonding availability and advantage of LAB from an assembly industrial perspective.