| In the electronic packaging industry,solder joints in electronic components are a key condition to ensure the normal use and operation of electronic products.With the vigorous promotion of lead-free packaging,the application of lead-free solder has become more widespread.The two most important parts of the package solder joints are solder and substrate.The choice of substrate material also affects the type of interface structure of the solder joints.Copper is considered the best choice as a parent material in the electronics packaging industry.However,with the diversified development of electronic products,more and more new substrate materials have attracted attention.In this paper,Sn3.0Ag0.5Cu(SAC305)lead-free solder was selected and two kinds of high-quality Cu-50Co(50 wt.%Co)and Cu-50Fe(50 wt.%Fe)dual-phase alloy substrates were prepared,and the micro-structure and the evolution of intermetallic compounds(IMC)of the interface between the solder and the different substrates were investigated.During the soldering process at 290℃ for different times,the compounds Cu3Sn and Cu6Sn5 formed at the SAC305/Cu interface,(Co,Cu)Sn3 and(Cu,Co)6Sn5 compounds appeared at the SAC305/Cu-50Co interface,and the composition of the IMC of SAC305/Cu-50Fe are(Cu,Fe)6Sn5 and FeSn2.It was worth noting that the interfacial IMC of SAC305/Cu-50Co and Cu-50Fe exhibited a strange jagged morphology,while the morphology of the IMC of SAC305/Cu was smooth and continuous.Comparing the grain morphology of three interfacial IMC of solder joints,there were many spherical Cu6Sn5 grains at the SAC305/Cu interface,which gradually matured and grew with the increase of soldering time;The grains of(Cu,Co)6Sn5 and(Co,Cu)Sn3 at the SAC305/Cu-50Co interface showed fine needle-like and stick-shaped,and(Co,Cu)Sn3 exhibited a prismatic stacking morphology during the later period of soldering.The(Cu,Fe)6Sn5 grains at the SAC305/Cu-50Fe interface showed a prismatic morphology,while FeSn2 were fine particles.The growth rates of total IMC of SAC305/Cu,SAC305/Cu-50Fe,and SAC305/Cu-50Co solder joints were 0.2823 μm/min,0.1316 μm/min and 2.2971μm/min,respectively.The SAC305/Cu,SAC305/Cu-50Co and SAC305/Cu-50Fe solder joints were designed to perform aging experiments at 150℃ for different durations.The results showed that the composition of the joint interface compounds in the solid-state aging process was the same as that in the liquid soldering process,and the thickness of IMC of the three kinds of solder joint increased with the aging time.The morphology of compound at the SAC305/Cu interface was continuous and dense,while compound at the SAC305/Cu-50Co and Cu-50Fe interface were uneven and jagged.In the later period of solid-state aging,a large number of voids appeared at the SAC305/Cu-50Fe interface,which caused defects at the IMC interface.The values of growth rate constant k of SAC305/Cu,Cu-50Co and Cu-50Fe during solid-state aging were 1.9×10-17m2/s,6.87×10-17m2/s and 4.51×10-17m2/s,respectively.The results of ultrasonic-assisted soldering showed that the ultrasonic action did not change the composition of compounds,but the average thickness of IMC decreased,which was attributed to the conduction of energy from the ultrasonic vibration to the interface reaction of solder joint.When the liquid-solid metallurgical reaction occurred,the cavitation and acoustic flow effects were caused,and the grains of the structure were refined.With the increase of ultrasonic time,the thickness of the IMC at the SAC305/Cu interface decreased,and many broken Cu6Sn5 grains were freed around it;the morphology of the(Co,Cu)Sn3 at the SAC305/Cu-50Co interface was stable,and the distribution of the(Cu,Co)6Sn5 was chaotic.The distribution range of the compound(Cu,Fe)6Sn5 at the SAC305/Cu-50Fe interface was wider,and its thickness is significantly different from that of FeSn2.During ultrasonic-assisted soldering,the large granular Cu6Sn5 grains for SAC305/Cu were transformed into fine spherical particles and prismatic grains;as for SAC305/Cu-50Co,(Co,Cu)Sn3 was obvious block-like stacking,and(Cu,Co)6Sn5 particles were clustered in fine needles;FeSn2 did not change significantly at the SAC305/Cu-50Fe interface,while(Cu,Fe)6Sn5 was slender and stick-shaped,and its grain length increased. |
