Evolution Of Microstructure And Mechanical Properties Of CuCGA Interconnect Solder Joints Under Low Temperature Aging

The CuCGA interconnect usually used in large-size packaging,aerospace and military applications.The solder joint is in the condition of temperature cycling and power cycling change in service which will inevitably degrade the microstructure of solder joint and reduce the reliability of the components.At present,there are many related studies on high temperature aging but there are relatively few studies on low temperature aging.The diffusion of elements at low aging temperature may be closer to the actual service peak temperature of solder joints,so it is necessary to explore the low temperature aging of solder joints.In this paper,the connection between 63Sn37Pb ball with diameter 2.4 mm and Cu column with diameter 0.8 mm is realized by means of friction welding.The solder joints were aged at low temperatures of 75?and 90?for 96 h,216 h,384 h,600 h and 864 h by means of vacuum drying box.The interfacial layer,solder microstructure and Cu column interconnect pull-out load were compared with the results of aged at 150?and before aging.The mechanical properties of solder joint before and after aging were measured by nano-indentation instrument.The study found that:1. Under the factors of friction heat and plastic deformation heat produced in the process of column planting,the interface layer was formed with an average thickness of 0.34?m by diffusion between Sn and Cu atoms with the increase of temperature.The Pb element outside the interface layer diffuses at a certain extent and adheres to the interface layer to form a Pb-rich layer with an average thickness of 0.81?m.The microstructure of solder is divided into?-IV zones from the distance to Cu column and the morphology in zone?-IV were different.The mean indentation hardness of Cu column before aging is 125.84 MPa,156.72 MPa,239.08 MPa and 252.14 MPa;,respectively.The average indentation hardness of zone?-IV before aging is 125.84MPa,156.72 MPa,239.08 MPa and 252.14 MPa,respectively.The average pull-out load of Cu columns interconnect is 23.5N.2. Cu₆Sn₅ was first formed at 75?aging interface,Cu₃Sn with a thickness of about 0.39?m appeared at aging for 600 h and the average interface thickness increased to 3.28?m after aging for 864 h.After aging for 864 h,the average thickness of the Pb-rich layer increased to 6.19?m.Adjacent Pb phases merged and grew during the aging.The average indentation hardness in zone?aging for96-864 h was higher than that before aging and the highest value was 176.08 MPa for 600 h.The average indentation hardness in zone?-?gradually decreased with the aging time prolonged but exceeded the hardness value of the corresponding region of before aging.The maximum pull-out load average of Cu column interconnect after aging for 600 h is 73.1 N.3. The aging interface has a significant change that slightly close to the scallop shape at 90?,the Cu₆Sn₅was first generated and Cu₃Sn with a thickness of about0.46?m appeared at aging for 384 h and the average thickness of the interface increased to 8.92?m after aging for 864h.After aging for 864 h,the average thickness of the Pb-rich layer increased to 7.71?m.The growth of Pb phase is more obvious than that of aging at 75?during aging.The average indentation hardness after aging for 96-864 h in zone?is higher than that at 75?and the highest value is180.28 MPa after aging for 600 h.The average indentation hardness in zone II-IV decreases gradually with the prolongation of aging time but the value is higher than aging at 75?.The maximum pull-out load average of Cu column interconnect after aging for 600 h is 84.1 N.4. Cu₃Sn with an average thickness of about 2.08?m appeared at the interface aging at 150?for 96 h and the total average thickness increased to 19.29?m after aging for 864 h.The interface of Cu₆Sn₅/Pb-rich layer appeared obvious voids after aging for 216 h and appeared cracks after aging for 600 h.The average thickness of Pb-rich layer gradually increased to 19.81?m.The growth of Pb phase was more obvious during aging.The average indentation hardness of each zone was significantly lower than aging at 90?.The pull-out load average of Cu column interconnect was gradually reduced to 18.6 N.5. The average elastic modulus was stable at 30-38 GPa before and after aging.Aging temperature and time,distance from Cu column and microstructure of solder have no obvious effect on elastic modulus of solder.However,aging temperature and time,indentation parameters and so on have obvious effects on indentation hardness.