Comparison of the break-up behaviors of newton and shear thinning non-newton fluid in jet dispensing for LED packaging

Dispensing is one of the key technologies in LED packaging, as the dispensed underfill can protect the interconnection from short-circled, release the residual stress and adjust color. However, in order to meet different requirements in packaging, various of underfill are used, typically from newton fluid to shear thinning non-newton fluid. The different fluid properties will greatly affect the break-up behaviors in jet dispensing, furthermore, result in different dispensing volume consistence and dispensing qualities, which strongly affects the LED packaging performance. To reveal the different break-up behaviors of newton fluid and shear thinning non-newton fluid during the jet dispensing process, two mathematical models are developed. The whole break-up process are obtained and compared with the experiments, and the roles of surface tension and viscous fore played in the break-up process are compared and discussed. The effects of relaxation time and shear thinning index on the thread break-up were studied and compared. It is found that the non-newton fluid thread is easier to break-up and dispensed. However, shear thinning is not the main driven factor for thread break-up. Surface tension has larger effects on thread break-up position and time. Specific additive can be added for adjusting surface tension under different dispensing conditions. This study will provide valuable insights for dispenser designs of modern microelectronic packaging.