Simulation Study Of Solidification Process Of BGA Tin-Lead Solder Ball Based On Cellular Automaton

Ball grid array(BGA)packaging technology is a kind of advanced packaging technology for integrated circuit chip.Integrated circuit chips packaged with this technology owns higher transmission efficiency during data transmission and lower power consumption.In BGA technology,the metal solder ball serves as a bridge which connected the chip and the circuit board and determines the final performance of the chip.Due to its particularly advanced performance,the solder ball manufactured by uniform droplet spray(UDS)technology has attracted many attentions.With the development of computer technology,numerical simulation with cellular automaton method is commonly used to study the process of metal solidification.However,based on cellular automaton method,the research on simulation of microstructure for tin-lead solder balls used in BGA package is just in its infancy.Considering the particularity and complexity of the solidification process of BGA solder balls,there are still many problems in the modeling process that need to be studied and solved.In the present work,based on cellular automaton method,a simulation method has been proposed for solidification of tin-lead solder ball used in BGA package during UDS process.This simulation method takes into account circular boundary morphology,conservation for solute as well as the influences of both the heat loss rate for the surface of droplet and the release of latent heat of fusion in droplet on the average temperature for tin-lead solder ball.Simulation study has been carried out for dendrite solidification process of tin-lead solder ball used in BGA package,under the conditions that the temperature field is assumed to be uniform and invariable in droplet as well as that the tin-lead droplets is solidified during UDS process,respectively.The simulation results are also discussed.Under the ideal condition,the influence of undercoolings and interfacialenergy anisotropy on the dendrite growth is discussed.A larger undercooling accelerates migration of the dendritic solid-liquid interface,makes the morphology of dendrite more stout and the branching process will be more complicated.Low interface energy anisotropy strength maintains the morphology stability during the equiaxed crystal growth.Increasing interface energy anisotropy strength makes the morphology of the equiaxed crystals more irregular and complicated.Under the UDS condition,the influences of the heat loss rate and gas temperature on dendrite solidification process of tin-lead solder ball are also discussed.If the cooling rate is higher,the growth velocity of a primary dendrite is higher and the undercooling is larger.Because of the larger temperature difference between the gas temperature and the tin-lead droplet,raising the gas temperature leads to a lower solidification speed of the BGA tin-lead ball.