The Reliability Of BGA Packaging Under Board-Level Based On Shear Mechanical Behavior

Solder joints as the medium of connecting the chip and the substrate plays a crucial role in the electronic packaging.On the one hand,the solder joints provide mechanical support,transmission signal and heat transfer,on the other hand,it is subjected to high temperature and load for a long time in the high temperature operation of electronic products.Due to the coefficient of thermal expansion of each material in the solder joint does not match,easy to produce structural defects in the bulk solder/IMC interface and fatigue crack initiation and propagation induced heating,resulting in solder joint shear fracture to form failure.Therefore,it is urgent to study the shear behavior of the solder joints.Shear loading was applied to the Sn-3.0Ag-0.5Cu,Sn-0.3Ag-0.7Cu,Sn-0.3Ag-0.7Cu-0.07 La and Sn-0.3Ag-0.7Cu-0.07La-0.05 Ce solder joints using the test method.To study the loading rate(0.01 mm/s,0.05 mm/s,0.5 mm/s,1 mm/s and2 mm/s),the solder joints size(500 ?m,700 ?m and 900 ?m),the pad components(Cu/SAC/Cu and Ni/SAC/Ni board-level structure)and the assembly sequence of reflow soldering(Cu/SAC/Ni and Ni/SAC/Cu board-level structure)and isothermal aging(160 ? for 0 days,10 days,20 days,aged 30 days,40 days)of BGA board-level solder joints structure mechanical properties.The results show that:Four kinds of the shear strength and fracture displacement of solder joints under veneer structure are larger than the solder joints under board-level structure,the shear mechanical properties of low silver solder joints with rare earth element has been greatly improved in the board-level structure,which the shear strength is equivalent to the high silver solder joints,In particular,the shear strength of Cu/SAC0307-0.07La-0.05Ce/Cu solder joints is more prominent.The solder joints is broken on the bulk solder in the veneer structure,but the fracture of the solder joint is broken on the interface of the IMC and bulk solder in the board-level structure,which the shear fracture is more close to the actual working condition,and the fracture morphology fully reflects its fracture mechanism.The shear strength of the high silver solder joints in the Cu/SAC/Cu board-level structure increases first and then decreases with the increase of loading rate,but the shear strength of the other three kinds of solder joints increased continuously.The fracture displacement decreases with the increase of loading rate,but the high silver solder joint is larger.When the loading rate changed from low speed to high speed,the fracture position of high silver solder joints is changed from bulk solder/IMC to IMC,the fracture position of the low silver solder joints is changed from the bulk solder to the bulk solder/IMC.The fracture position of low silver solder joint with rare earth element is only a certain transfer to the IMC direction in the bulk solder.With the decrease of solder joints size,the shear strength of the solder joints increases gradually,the fracture displacement decreases gradually,the shear strain showed a trend of first increasing and then decreasing,and the fracture position of the solder joints is transferred to the bulk solder.The shear strength and fracture displacement of solder joints in Ni/SAC/Ni are larger than the Cu/SAC/Cu of board-level structure.The solder joints of Cu/SAC/Cu were broken at the interface of the bulk solder and IMC,but the fracture position of the Ni/SAC/Ni of board-level structure occurred in the bulk solder.The shear strength and break displacement of solder joints of Cu/SAC/Ni lower than that Ni/SAC/Cu of board-level structure.The solder joints are broken at the Cu/SAC side for the Cu/SAC/Ni board-level structure,but the solder joints are basically broken at the Ni/SAC side for the Ni/SAC/Cu board-level structure.The shear strength and fracture displacement of solder joints under Cu/SAC/Cu and Ni/SAC/Ni board-level structure to decrease with the increase of aging time,but the decline rate of solder joints under Cu/SAC/Cu is greater than that of solder joints under Ni/SAC/Ni.The shear strength of the solder joints in the two kinds of structures has been greatly reduced in the initial period of aging.In addition,the anti aging ability of low silver solder joint with rare earth element is better than that of high silver solder joints in two kinds of structure,which the solder joints show good mechanical properties.In particular,the shear strength of solder joints of Ni/SAC0307-0.07La-0.05Ce/Ni is more obvious.