Low-temperature Interconnection Process Of Al/Cu Joints Under Ultrasonic-assisted With The Help Of Nano-particles And Its Reliability

With the continuous development of electronic products in the direction of high integration,high density and miniaturization,there is an urgent need to save manufacturing processes and reduce manufacturing processes to reduce production costs.Therefore,it is urgent to realize nickel free and copper direct interconnection of chip aluminum electrode or aluminum pad.In this paper,nano-sized SAC0307 particles and micron sized Zn particles were used to realize the low-temperature interconnection between Cu/Cu(Al)with the ultrasonic-assisted.The effects of particles content and soldering temperature on the properties of Cu/Cu(Al)joints and the thermal reliability of joints under aging conditions were studied.Then Cu nanoparticles were used to optimize the quality of Cu/Al joints and improve their thermal reliability.The main conclusions are as follows:(1)When Cu/Cu was interconnected at 180?,Sn-Zn eutectic formed by adding SAC0307 strengthened the bonding between Zn particles in the soldering seam,and the interface IMC was Cu Zn₄and a small amount of Cu₅Zn₈.With the increased of SAC0307content,the shear strength of the joint first increased and then decreased slightly.The fracture mainly occurred between Zn particles and Sn-rich phase.When the content of SAC0307 was 15%,the shear strength of the joint reached the maximum value of30.42MPa,which was 250.06%higher than that without addition.(2)The IMC thickness of Cu/Zn+15%SAC0307/Cu joint became thicker with the increased of aging temperature and time.The IMC growth activation energy of upper/lower interface was 109.86k J/mol and 111.88k J/mol respectively;The type of IMC was transformed from Cu Zn₄to Cu₅Zn₈.Almost all Cu Zn₄IMC had been transformed into Cu₅Zn₈when aged at 125?,48h and 150?.With the increased of oxidation and IMC thickening,the shear strength of the joint at three temperatures decreased with the extension of aging time,and the fracture position transformed from solder to interface;When the aging temperature was 150?,the shear strength of the joint decreased obviously,and reached the lowest value of 15.5MPa after 48h,which decreased by 49.05%.(3)With the increased of soldering temperature,the fluidity of SAC0307 in the soldering seam was enhanced.The accumulation of Sn-rich phase on the Al side accelerated the mutual diffusion between Al substrate and Zn which promoted the formation of Al-Zn phase.The shear strength of Al/Cu joint first increased and then decrea-ed.It reached the highest value at 240?,which was 39.51MPa.With the increased of aging temperature and time,Al side interface and Cu side interface of Al/Zn+15%SAC0307/Cu joint appeared defects such as holes and cracks.The shear fracture at the Cu interface.The shear strength of the joint decreased with the increased of aging temperature and time.It reached the lowest value of 3.92MPa when aged at 150?for 48h.(4)After adding Cu nanoparticles,Cu_xZn_ycompound appeared in the soldering seam,and gray Al-Zn-Cu-Sn phase was accumulated between the white Sn-rich layer and the solder on the Al side interface;When the Cu content increased to 15%or more,there were a large number of Cu₅Zn₈and Cu Zn₄near the Cu side interface,and the delamination was not obvious.The shear strength of the joint reached the highest value of 49.11MPa,which was 24.3%higher than that of the joint without Cu particles.With the extension of isothermal aging temperature and time,IMC in the soldering seam grew more violently,defects appeared at the Al side interface,Cu₅Zn₈at the Cu side interface and Cu Zn₄at the center of soldering seam gradually increased,and the shear strength of Al/Zn+15%SAC0307+15%Cu/Cu joint decreased significantly.However,with the extension of aging time,the shear strength of the joint decreased more slowly than that of the joint without Cu particles,and the shear strength of the joint remained above 20MPa after aging at 150?for 96h.