Droplet-on-demand and direct deposition of bumps based on pulsated orifice ejection method

The stability of micro-droplet ejection and size on-demand are important prerequisites for the direct preparation of bumps in chip packaging. The ejection experiment of SAC305 commercial lead-free solder is carried out by pulsated orifice ejection method （POEM）. The effects of the interaction of parameters such as the pulse waveform， the distance between the transmission rod and the orifice and the orifice， diameter on the ejection stability and particle size during the droplet ejection process are investigated. The surface morphology and microstructure， composition， and phase composition of the solder ball are analyzed. The results show that the stable ejection of droplets and the control of size-on-demand can be realized by coordinating the key process parameters. The deviation between the target particle size and the actual size is within 4%， which can meet the needs for the stable on-demand preparation of bumps. The results of temperature change during droplet solidification show that the cooling rate in the argon atmosphere is much lower than that in the helium atmosphere， so the microstructure is coarser. Combined with the above results， the bumps are directly deposited on the copper plate to form a metallurgical layer， which shows the feasibility of the technology and provides a new way for the direct preparation of bumps.