The effects of flux materials on the moisture sensitivity and reliability of flip-chip-on-board assemblies

This paper discusses the nonproprietary aspects of the work-in-progress regarding developments in flux materials to improve the moisture-induced stress sensitivity of flip chip plastic ball grid array devices. Studies addressing the moisture characterization and preconditioning, using JEDEC Level 3, of assemblies built with four proprietary fluxes and two alternative underfill materials will be presented. This report includes the evaluation of the weight loss during a simulated die attach reflow profile for each flux type using thermogravimetric analysis. Also, the underfill adhesion strength to the die surface after assembly, after moisture preconditioning and after 48 h of autoclave stressing will be discussed. The integrity of the solder joint corresponding to each flux type and measured using die pull techniques will also be presented. The effects of the experimental variables on underfill to die/substrate adhesion will also be reviewed using C-SAM imaging methods. Proprietary aspects of Motorola's FC-PBGA materials and assembly technology will not be disclosed.