Investigation On Microstructure Evolution And Thermal Damage Of 3D Packaging Solder Joints Using Particle Reinforced Sn Based Composite Solder

In this paper,the particle composite brazing materials were prepared by mixing micro and nano Sn,Zn,Cu particles and a certain proportion of rosin flux,and Cu/Sn-xZn/Cu and Cu/Sn-9Zn-xCu/Cu solder joints were prepared by transient liquid phase（TLP）joining technique.The effects of Zn particle content,Cu particle content,bonding temperature and bonding time on the evolution of microstructure,mechanical properties and fracture mode and location of particle-reinforced Sn-based composite brazing joints were investigated.On this basis,the effects of the number of thermal cycles on the thermal damage properties of the solder joints were investigated,and the time growth index n and the interfacial IMC growth rate k were calculated for the interfacial IMC of the Sn-based particle composite braze joints.The evolution of microstructure,shear properties and fracture morphology of Cu/Sn-xZn/Cu（x=0,2,5,9,30,70 wt.%）solder joints were investigated.The results showed that:the Cu/Sn-xZn/Cu solder joint consisted of two parts,the interfacial reaction zone and the in situ reaction zone;without the addition of Zn particles,When Zn particles are not added,the reaction zone at the solder joint interface consists of Cu₆Sn₅ phase and Cu₃Sn phase.When5 wt.%Zn particles are added,Cu₆Sn₅ phase transforms into Cu₆（Sn,Zn）₅ phase,and when the Zn particle content reaches 30 wt.%,it transforms into Cu₅Zn₈ phase.The thickness of the interfacial reaction zone of the solder joint shows a trend of decreasing and then increasing with the increase of the Zn particle content,and the minimum thickness of the interfacial IMC is 5.05μm,when 9 wt.%Zn particles are added;Without the addition of Zn particles,the in-situ reaction zone of the solder joint is composed of Sn phases,,and after the addition of Zn particles,the in situ reaction zone of the joints consisted of Sn-rich phase and Zn-rich phase;with the increase of Zn particle content,the shear strength of Cu/Sn-xZn/Cu joints showed a trend of first increasing and then decreasing,and when the Zn particle content was 9 wt.%,the highest shear strength of the joints was 14.18 MPa;As the content of Zn particles increases,the fracture position of the solder joint shifts from the side near the in-situ reaction zone between the in-situ reaction zone and the interface reaction zone to the Cu substrate.When the content of Zn particles is 70 wt.%,the fracture position is located at the interface IMC and Cu substrate;the fracture mechanism of the solder joints were all brittle fracture.The evolution of microstructure,shear properties and fracture morphology of Cu/Sn-9Zn-xCu/Cu（x=20,30,40,50 wt.%）solder joints were investigated.The results showed that:when the Cu particle content was 20 wt.%,the interfacial reaction zone of the solder joint consisted of scalloped Cu₆（Sn,Zn）₅ phase and laminated Cu₃Sn phase,which transformed into laminated Cu₃Sn phase as the Cu particle content increased;The thickness of the reaction zone at the solder joint interface shows a trend of first increasing and then decreasing with the increase of Cu particle content.When the Cu particle content is 20 wt.%,the IMC thickness at the interface is higher than that of Sn-9Zn,which is 5.92μm;when the Cu particle content is 20 wt.%,the in situ reaction zone of Cu/Sn-9Zn-xCu/Cu solder joints consists of Cu₆（Sn,Zn）₅ phase,Cu₃Sn phase and Zn-rich phase,when the Cu particle content is 30 wt.%,The in-situ reaction zone of the solder joint consists of Cu₆（Sn,Zn）₅ phase,（Cu,Zn）₆Sn₅ phase,Cu3Sn phase,Cu particles,and rich Zn phase.With the increase of Cu particle content,the microstructure of the in-situ reaction zone of the solder joint gradually coarsens,the content of rich Zn phase gradually decreases,and the content of Cu particles increases.When the content of Cu particles reaches 40 wt.%,the rich Zn phase disappears;The shear strength of solder joints showed a trend of increasing and then decreasing with the increase of Cu particle content,and the highest shear strength of 17.24 MPa was achieved when the Cu particle content was 30 wt.%;As the content of Cu particles increases,the fracture position of the solder joint shifts from the interface reaction zone to the in-situ reaction zone;the fracture mechanism of solder joints is brittle fracture.The effect of bonding parameters on the microstructure,shear properties and fracture morphology of Cu/Sn-9Zn-30Cu/Cu solder joints was investigated.The results show that:When the bonding temperature is 260℃,the microstructure of the in-situ reaction zone of Cu/Sn-9Zn-30Cu/Cu solder joints consists of island shaped Cu₆（Sn,Zn）₅,Cu₃Sn,Cu particles,and Zn-rich phases.As the bonding temperature increases,the microstructure of the in-situ reaction zone of the solder joint gradually refines.When the bonding temperature is 280℃,the in-situ reaction zone of the solder joint consists of Cu₆（Sn,Zn）₅,（Cu,Zn）₆Sn₅,Cu₃Sn,Cu particles,and Zn-rich phases.When the bonding temperature is 300℃,the in-situ reaction zone of the solder joint is composed of Cu₆（Sn,Zn）₅,（Cu,Zn）₆Sn₅ is composed of a small amount of Zn-rich phase,and the bonding temperature continues to increase.The microstructure begins to coarsen,the rich Zn phase disappears,and pores are formed at the interface;When the bonding time is 15 minutes,the microstructure of the reaction zone at the Cu/Sn-9Zn-30Cu/Cu solder joint interface is composed of scallop-shaped Cu₆（Sn,Zn）₅and layered Cu₃Sn phases.When the bonding time is 60 minutes,the IMC at the solder joint interface transforms into layered Cu₃Sn phase,and with the increase of bonding time,the IMC thickness at the solder joint interface gradually increases;When the bonding time is 15minutes,the in-situ reaction zone of Cu/Sn-9Zn-30Cu/Cu solder joint consists of island shaped Cu₆（Sn,Zn）₅,Cu₃Sn,Cu particles,and Zn-rich phase.When the bonding time is 60minutes,the solder joint consists of Cu₃Sn,（Cu,Zn）₆Sn₅,Cu₆（Sn,Zn）₅,Cu particles,and Zn-rich phase.When the bonding time is 90 minutes,the rich Zn phase disappears in the in-situ reaction zone of the solder joint;As the bonding time increases,the tissue gradually coarsens and Kirkendall pores appear at the interface;The shear strength of solder joints increased first and then decreased with the increase of bonding temperature and bonding time.When the bonding temperature was 280℃,the bonding time was 60 min,and the bonding pressure was 1 MPa,the shear strength of solder joints reached the highest,17.24MPa;The fracture mode of Cu/Sn-9Zn-30Cu/Cu solder joints is brittle fracture,and the fracture position is located between the interface reaction zone and the in-situ reaction zone;The optimal bonding process parameters are:bonding temperature 280℃,bonding time 60minutes,and bonding pressure 1 MPa.The effect of the number of thermal cycles on the microstructure,shear properties and fracture morphology of Cu/Sn-9Zn/Cu and Cu/Sn-9Zn-30Cu/Cu solder joints was investigated.The results show that:as the number of thermal cycles increases,the microstructure of the solder joints all gradually coarsens,the thickness of the interfacial IMC increases,and the shear strength of the solder joints decreases;under the same number of thermal cycles,the Cu/Sn-9Zn-30Cu/Cu solder joints have finer tissue,the interfacial IMC thickness is thinner,and the shear strength is all higher than that of the Cu/Sn-9Zn/Cu solder joints,and as the number of thermal cycles increases,the shear strength of the Cu/Sn-9Zn-30Cu/Cu solder joints decreases more slowly.The shear strength of Cu/Sn-9Zn-30Cu/Cu solder joints decreases slowly as the number of thermal cycles increases;the growth curve of the IMC thickness at the interface of Cu/Sn-9Zn/Cu solder joints and the number of thermal cycles shows an approximate parabolic growth pattern,and the growth curve of the IMC thickness at the interface of Cu/Sn-9Zn-30Cu/Cu solder joints and the number of thermal cycles shows a linear growth pattern;the growth curve of the IMC thickness at the interface of Cu/Sn-9Zn/Cu solder joints at-25～125℃thermal cycling conditions,the interfacial IMC growth was mainly controlled by diffusion,with a time growth index n of0.48 and a growth rate k of 4.24×10^-5μm/s.The interfacial IMC of Cu/Sn-9Zn-30Cu/Cu solder joints was mainly controlled by reaction,with a time growth index n of 1.28 and a growth rate k of 4.7×10^-6μm/s;The shear strength of Cu/Sn-9Zn/Cu solder joints was reduced from 14.18 MPa without thermal cycling to 5.89 MPa for 1000 times,a reduction of 58.47%;The shear strength of Cu/Sn-9Zn-30Cu/Cu solder joints was reduced from 17.24MPa without thermal cycling to 9.47 MPa for 1000 times,a reduction of 45.07%;The fracture position of Cu/Sn-9Zn/Cu solder joints transitions from the interface reaction zone to the in-situ reaction zone,and the fracture positions of Cu/Sn-9Zn-30Cu/Cu solder joints are all located in the in-situ reaction zone;Cu/Sn-9Zn-30Cu/Cu joints were all located at the in situ reaction zone;the fracture mechanisms of the joints were all brittle fractures.