Reverse Laser Assisted Bonding (R-LAB) Technology for Chiplet Module Bonding on Substrate

Abstract

There are several chip-to-substrate interconnection technologies in the packaging tool kit such as mass reflow (MR), thermocompression bonding (TCB) and laser assisted bonding (LAB). MR is a mature process but has known limitations on fine pitch devices and large/thin substrate packages. TCB has the advantage to minimize bump stress for low-K dielectric devices but its productivity is very low. However, LAB can provide a solution for advanced devices with its localized heating and short bonding time. Recently, demand for fine-pitch, Flip Chip bumps and large/thin substrate packages has increased, resulting in industry interest in LAB due to its good quality and high productivity. Amkor Technology invented LAB technology in 2014 and passed qualification for multiple devices from customers through many years of development and has been in high volume production for major customers since 2018. However, as the industry continues to require high bonding performance with various new devices, existing LAB technology may not support all these applications. These devices have led to the development of a new bonding concept, which is reverse laser assisted bonding (R-LAB) technology. R-LAB emits the laser to the bottom side of the substrate through a vacuum stage block, which is opposite laser emission direction to existing LAB. It was developed in 2021 by Amkor Technology and showed promising results for the packages where top LAB does not work. There are several devices that require R-LAB. One is back side metallization (BSM) die. BSM dies are necessary for metal thermal interface material (TIM) applications for high thermal performance packages. Promising results for BSM die were published in recent 72 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> ECTC [1]. Other devices that require R-LAB include chiplet module bonding on substrate and DRAM packaging in an epoxy molding compound (EMC). A chiplet module is necessary for high-performance applications such as servers, networking, artificial intelligence (AI), graphics and more. In this study, R-LAB technology is introduced, and its performance is compared with existing top LAB packaging using a chiplet module package. Infrared (IR) temperature monitoring, X-ray inspection and cross-sectional analysis were performed to verify bump interconnection quality. Good bump interconnection quality was achieved with R-LAB and it passed all reliability tests. This allows it to be another solution for future next-generation devices.