Growth And Evolution Behavior Of Interfacial IMC In Cross-scale Sn-Ag-Cu/Cu Micro Solder Joints And Their Mechanical Properties

With the rapid development of three-dimensional(3D)integrated circuit(IC)integration and package technologies,the packaging density of electronic products and systems is getting higher and higher.In electronic packages,solder joints have the function of electrical interconnection and mechanical interconnection,and their sizes change in a wide range,usually from just more than ten microns for micro-bumps to several hundred microns for BGA solder joints.The size change of solder joints can seriously affect the formation and growth of intermetallic compound(IMC)at the interface of joints during the interfacial reaction process,while growth and morphology evolution of the interfacial IMC will have significant influence on the performance and reliability of solder joints.In this thesis study,solder joints with different sizes(diameter in the range of 20 to 600 ?m)were successfully prepared by using the method of planting solder balls on substrates(Cu pads).The effects of solder size(volume),type of Cu pads(substrates)and soldering process on growth and morphology evolution of the interfacial IMC during the interfacial reaction of reflowing Sn0.3Ag0.7Cu and Sn3.0Ag0.5Cu solder balls on Cu pads,and the shear behavior of Sn3.0Ag0.5Cu/Cu joints were systematically investigated.The main contents and obtained results from this thesis study are as follows:The growth and morphology evolution of the interfacial IMC in BGA structure Sn3.0Ag 0.5 Cu/Cu joints with different sizes(60,100,200,400 and 600 ?m in diameter)and the shear behavior of the joints were studied.Results show that the average size of the interfacial IMC grains increases with the decrease of solder ball diameter when reflow time is 10 s.When the reflow time is increased to 60 s and 300 s,with decreasing the solder ball diameter the average size of the interfacial IMC grains increases firstly and then decreases.The interfacial IMC grain size reaches the maximum value when the solder ball diameter is 200 ?m.At a shear loading rate of 100 ?m/s,the shear strength of solder joints increases with the decrease of solder joint size,showing an obvious size effect,but a further extension of reflow time hardly brings about obvious change in the shear strength of solder joints.In shear tests,the fracture location of solder joints is related to the size of solder joints and reflow time.When the size of solder joints is smaller than 200 ?m,the fracture occurred in the solder matrix of the joints,while for solder joints with sizes of 400 ?m and 600 ?m,with prolonging reflow time the fracture location of solder joints gradually shifted from the solder matrix to the position near the interface between the IMC layer and the solder matrix.The growth and morphological evolution of interfacial IMC grains during the interfacial reaction between the Sn0.3Ag0.7Cu solder ball with diameters of 20 to 60 ?m and the polycrystalline Cu substrate were studied.Results manifest that with increasing reflow time,the ripening mode of interfacial IMC grains changes from Oswald ripening to grain boundary ripening,and the morphology of interfacial IMC grains gradually changes from scallop-like with smooth boundary to jigsaw-puzzle-like with rugged boundaries and finally to scallop-like.As the size of micro-bump joints decreases,the proportion of surface diffusion in the interfacial reaction increases gradually,which makes the size of interfacial IMC grains decrease firstly and then increase.The growth and morphology evolution of the interfacial IMC grains in the interfacial reaction of Sn-Ag-Cu solder balls on(001)Cu substrate were also studied.Results show that when the Sn-Ag-Cu/(001)Cu assemblies were reflowed at 250 ?,the morphology of the interfacial IMC grains of solder joints was scallop-like as long as the size of solder joints was not greater than 60 ?m in diameter,regardless of the composition of solder balls(Sn3.0Ag0.5Cu or Sn0.3Ag0.7Cu).For Sn-Ag-Cu/(001)Cu joints reflowed at 300 ?,the interfacial IMC grains exhibited mainly scallop-like in the solder joints with diameter less than 60 ?m and showed prism-like in the solder joints with large diameter(600 ?m).For solder joints with 600 ?m diameter,the interfacial IMC grains grew along two perpendicular directions on(100)single crystal Cu pad.