The Study On Microstructure And Property Of Al₂O₃ Joints Using Foam Ni Reinforce Sn Based Solder With The Assistance Of Ultrasound

With excellent properties of physics and chemistry,such as low thermal expansion,high corrosion resistance and superior high-temperature stability,alumina was often used to form assemblies of electrical and microelectronic applications.Sintering and active brazing methods were widely used in previous studies,however,the high processing temperature during sintering or active brazing inhibited the online fabrication of alumina joints which served in some electronic assemblies.Hence,low-temperature soldering technology is needed in air.However,alumina was commonly hard to wet with the filler in low brazing-temperature.To solve this problem,metallization on the alumina surface was a effective action.Some traditional methods,such as PVD,CVD were complex while these process were widely used.Compared with traditional metallized process,ultrasonic technology was a easy operation.Meanwhile,ultrasonic-assisted brazing alumina could also get a better joint.In this paper,aluminas were firstly dipped in liquid Sn with ultrasonic vibration.And then metallized aluminas were brazed with the assistance of ultrasonic vibration using the pure Sn,foam Ni/Sn and foam Ni/Sn-9Zn solder,respectively.The whole experiment process was divided into two parts:1)The alumina was dipped with different ultrasonic vibration times,then two coated aluminas were connected using pure Sn solder to observe the microstructure of the tin-coating and the joints.The shear strength of joints was texted to study the effect of ultrasonic vibration time on the tin-coating.2)The alumina that were dipped with a ultrasonic brazing time of 80s were brazed with the assistance of ultrasound using foam Ni/Sn and foam Ni/Sn-9Zn solder,respectively.The microstructures,composition distribution and phase composition were analyzed to study the effect of ultrasonic brazing time on the microstructure evolution,metallurgical reaction and fracture mode of the joints.In the process of ultrasonic dipping on alumina surface,with the increase of ultrasonic vibration time from 5s to 80s,the alumina particles were gradually flaked from the matrix,and then went into the Sn-coating;the alumina/tin-coating interface was uneven.After a ultrasonic brazing time of 40s,the connection strength of alumina/tin-coating was more than the intrinsic strength of Sn.In the process of ultrasonic brazing,with the increase of ultrasonic vibration time from 4s to 12s,the defects in the joints were gradually reduced and the foam Ni were evenly distributed in the joints.Meantimes,the ultrasonic vibration and thermal effect promoted the metallurgical reaction.The intermetallic compound layer gradually increased.There were different results for foam Ni reinforced Sn and foam Ni reinforced Sn-9Zn composite solder.For the foam Ni reinforced Sn composite solder,the intermetallic compound was the Ni₃Sn₄ that had a fast growth rate.The shear strength of the joints increased firstly,and then decreased with the increase of the ultrasonic vibration time.The shear strength of joints reached to 35⁴0MPa at 8s,and the joints fractured in the filler.For the foam Ni reinforced Sn-9Zn composite filler,Zn firstly reacted with Ni to form Ni₅Zn₂₁,which hindered the formation of Ni₃Sn₄ and slowed the growth of the intermetallic compound layer.With the increase of ultrasonic vibration time,the shear strength of the joints increased gradually.The shear strength of the joints reached to 51⁵7MPa at 12s,and the joints fractured on the alumina surface.