Research On Joint Shear Properties And Interface Structure Of BGA Solder

BGA (Ball Grid Array) package is a new type of technology to adapt to thecurrent electronic packaging technology toward the short and the light multi-direction, it is the advantage that the chip has high-density I/O terminal whichprovides the possibility. Especially in recent years, the continuous miniaturization ofmicroelectronic products make electronic package spacing and the size of thepackage interconnect pads constantly smaller. Although the solder joint sizedecreases, they are carrying increasingly the more weight in the mechanical,electrical and thermodynamic load, it has become an important reason for failure ofthe electronic device circuitry under shear stresses of soldering. Therefore, the goodmicro solder joint shear properties guarantee high reliability of the device, Becauseof the small size of the solder joint failure fracture modes study less, it is necessary toanalysis the shear strength of the different size of micro solder depth, the differencesin fracture morphology and interfacial structure.Sn-3.0Ag-0.5Cu solder object of studying, the ball diameter was200μm,300μm,400μm,500μm, making two micro solder joints on the Cu pad and plating NiRespectively. Shear strength of the solder joints are studied after reflowing160℃,aging100h and200h, fracture morphology and interface structure variation.Sn-3.0Ag-0.5Cu/Cu and Sn-3.0Ag-0.5Cu/Ni shear strength decrease with theincreasing of the ball diameter. That has a significant size effect.Two types of micro-solder joints under shear fracture morphology show thatsolder joints are both broken in the interior of the soldering material, the fracture istoughness and dimple shape is parabolic. With the increasing of the solder joint size,the fracture shows an increasing trend in the number of dimples, but the width anddepth of the dimples become smaller and lighter. Solder joints after aging test, stillfracture within the solder, parabolic dimples are elongated, reducing the number ofdimples, dimples shallow depth of flattened plastic material toughness decreases, but the mode continues to show a ductile fracture.With the aging time, interface IMC thickness of the same diameter solder jointis tended to increasing. The same ball size, thickness of IMC layer on the Nisubstrate is thinner than on the Cu substrate, showing that Ni element blocks themutual diffusion between Cu and Sn atom, inhibiting the growth of the intermetalliccompound.Sn-3.0Ag-0.5Cu/Cu solder interface metal intermetallic compound layer isCu6Sn5, after aging test, there is Cu3Sn to generate. Sn-3.0Ag-0.5Cu/Ni solderinterface metal intermetallic compound layer is (Cu,Ni)6Sn5,there are thin Ni3Sn andNi3Sn4to generate after aging test, and in the ternary compound of solderinginterface, the Ni element proportion is much larger than the Cu element.