Flip chip interconnects based on carbon nanofibers-solder composites

In this paper, we pro­pose the intro­duc­tion of ver­tic­ally aligned car­bon nan­ofibers (CNF) dir­ectly grown on the bond­ing pad by chem­ic­al vapor depos­ition at CMOS com­pat­ible tem­per­at­ures as a solu­tion to rein­force and con­fine the solder joint between two chips bon­ded by solder. This concept poten­tially enables the reduc­tion of pitches and size of the solder inter­con­nects. The solder joints are real­ized by thermal com­pres­sion bond­ing tech­nique and the assem­blies are char­ac­ter­ized by means of elec­tric­al meas­ure­ments of daisy chains and kelvin struc­tures formed by the con­nec­tion of the two chips. Flip chip inter­con­nects based on two solder com­pos­ite solu­tions (CNFs/​SnAg and CNFs/​SAC305) are ana­lyzed in terms of elec­tric­al res­ist­ance, and dif­fer­ent growth con­di­tions for the CNFs and a post-growth treat­ment have been tested. The addi­tion of the car­bon nan­ofibers to the solder led to an addi­tion­al res­ist­ance lower than 10 % of the total res­ist­ance, while pos­sibly improv­ing the reli­ab­il­ity of the joint.