The Study Of Shear Mechanical Properties Of SAC-Re Lead-free BGA Solder Joints Under Board-level Structure

With the continuous development of electronic packaging,BGA packaging technology has been widely used because of its high I/O interface number,mounting yield and good formability.BGA solder joints will inevitably be subjected to temperature load due to resistance energization during service.Under this condition,the shear stress of the solder joints will be produced due to the different thermal expansion coefficients of each component and the external random load,which will lead to the failure of the solder joints in the form of shear fracture.Previous studies have shown that the shear properties of BGA solder joints in veneer structure and board-level structure are different.The study of BGA solder joints in veneer structures tends to evaluate the properties of solder filler metals themselves.The environment of BGA solder joints in board-level structure is more similar to the actual service environment of solder joints,and the study of BGA solder joints in board-level structure mainly evaluates the overall reliability of solder joints.Therefore,it is great practical significance to study the shear mechanical properties of the BGA solder joints.This paper mainly studies the shear mechanical properties of lead-free BGA solder joints under board-level structure.Sn0.3Ag0.7Cu-0.07La-0.05 Ce lead-free solder is chosen as the main research object,Sn3.0Ag0.5Cu and Sn0.3Ag0.7Cu lead-free solder were used as control group.The effects of reflow temperature(260 ℃,270 ℃,280 ℃,290 ℃,300 ℃),reflow cycles(1,3,5),pad size(700 μm,800 μm,900 μm)and different position of solder joints on shear mechanical properties of SAC-Re BGA solder joints under board-level structure were studied.The shear strength and fracture displacement of the Cu/Sn0.3Ag0.7Cu-0.07La-0.05Ce/Cu are the highest.The fracture mode of low silver solder joints under board-level structure are always ductile fracture with the increase of reflow temperature.The shear strength of BGA solder joints under board-level structure and low-silver BGA under veneer structure are increase first and then decreased with the increase of reflow temperature.The fracture displacement of BGA solder joints is decreas with the increase of reflow temperature.The fracture mode of high silver solder joints under board-level structure are changed from ductile fracture to brittle fracture with the increase of reflow temperature.When the number of reflow cycles.The shear strength and fracture displacement of BGA solder joints under board-level structure and low-silver BGA under veneer structure are decreas.The fracture mode are always ductile fracture.Under different pad sizes,the comprehensive shear mechanical properties of Cu/Sn0.3Ag0.7Cu-0.07La-0.05Ce/Cu is the highesr.The shear strength and fracture displacement of Cu/Sn0.3Ag0.7Cu-0.07La-0.05Ce/Cu are the highesr,the fracture mode is ductile fracture.The shear strength and fracture displacement of BGA solder joints under board-level structure are increase first and then decreased with the increase of pad size.The fracture mode of BGA solder joints under board-level is ductile fracture.The shear mechanical properties of lead-free solder joints in different positions in BGA board-level structure are different.The shear strength and fracture displacement of the longitudinal position solder joints are higher than that of the transverse position solder joints and triangular position solder joints.The shear mechanical properties of the transverse position solder joints are the lowest.The shear strength and breaking displacement of low silver solder joints with rare earth elements is the largest.The fracture mode of longitudinal poition solder joints are ductile fracture and the extended direction of dimple is unchange.At the transverse position,the fracture mode of high silver solder joints and low silver solder joints are mixed-mode of ductile and brittle fracture.The fracture mode of low silver solder joints with rare earth are ductile fracture and the size of dimple is silghtly decrease and the extended direction of dimple is change.