The Study of Packaging Substrate Effect in FCBGA by Laser Assisted Bonding

• Main Authors: Huang, Yu Lung, Huang, Joe, Huang, C. M., Yu, Kuo Haw, Luo, Tank, Hong, Wilson, Ren, Taishin
• Format: Conference Proceeding
• Language: English
• Subjects: FCBGA; IMC; Integrated circuits; Laser assisted bonding; Laser beams; Lasers; Rough surfaces; Silicon; solder wicking; substrate effect; Surface roughness; Surface waves; thermal budget
• ISSN: 2377-5726
• DOI: 10.1109/ECTC32696.2021.00110

In order to support the high growth of Artificial Intelligence, Internet of Things, Industrial IOT, Cloud Service and 5G, the IC (Server/Router/Switch) needs higher/faster performance to collect, store, commute and transmit a mass of data. Therefore, the I/O (input/output) density of IC will increase with the silicon nodes < 5 nm, fine pitch \mu\text{bump} , and fine line width/space substrate. However, the solder reflow of IC faces two problems of the chip damages (silicon nodes: current leakage, highly electromigration; ELK (extremely low-k): current leakage, crack) and solder high stress (solder: wicking, IMC (intermetallic compound)) due to highly thermal budget of MR (mass reflow). In this paper, LAB (laser assisted bonding) will replace MR (mass reflow) to solve these problems. In this study, a test vehicle with the size of 55^{\ast}55\ \text{mm}2 FCBGA (flip chip ball grid array) was built. Two types (A and B) of substrate were applied to the FCBGA, with the differences between the solder mask (thickness, surface brightness/roughness) and substrate mass. LAB uses a semiconductor laser with wavelength of 980 nm, and the area of laser beam is 91.5% of the substrate area. The study is divided into three parts. For the first part, the surface temperature of die without substrate is higher than that of die with substrate at the same parameters about 187.2 °C. The result shows that the substrate has the function of heat storage. In addition, for the surface temperature of die with substrate, the result shows that all solders melt at 2.82 sec, and the surface temperature of the center of die is 22.8 °C lower than the four corners of it. Then the delta temperature between the surface temperature of the center of die and bump is 48.3 °C. The result shows that the overall temperature of die with substrate is not uniform. Next, for substrate effect, the surface temperature of die and B substrate is lower than that of die and A substrate based on the following reasons: for the solder mask, (a) the surface brightness of B substrate is 11% higher than that of A substrate result in an increase of the reflected light; (b) the roughness of B substrate is 26% lower than that of A substrate result in an increase of the reflected light; (c) the thickness of B substrate is 23% lower than that of A Substrate result in a reduction of Absorbed light; for substrate mass (d) the weight of B substrate is 10% higher than that of A substrate. Finally, the assembled FCBGA packag