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.