No-flow underfill: Effect of chip placement speed on the void formation using numerical method

Abstract

No-flow underfill process can enhance the production lead time since the curing and reflow of solder interconnect and underfill are achieved simultaneously. Additionally, no-flow underfill can produce near void-free flow during the assembly process. This paper investigates the effect of chip placement speed towards the void formation of no-flow underfill process using numerical simulation and experimental methods. The findings show that the increase in chip placement speed effectively increased the gauge pressure and velocity of the underfill flow. The highest chip placement speed of 14 ​mm/s produces 12,300 ​Pa of gauge pressure and 0.1 ​m/s of underfill flow velocity. The flow profiles revealed that finger-like profile was formed above 5 ​mm/s speed during the compression process of no-flow underfill that will lead to issue of void formation in the ball grid array (BGA) region. This study recommended the usage of below 5 ​mm/s of chip placement speed to minimize the issue of finger-like formation and subsequently void formation.