Effect Of Rare Earth On Oxidation Performance Of Cu Alloys For Lead-frame

Cu alloys have taken large quotient in Lead-frame material for integrated circuit (IC)packages due to their good electrical conductivity,excellent thermal conduction and high strength.Recently,much more attention has been paid to the oxidation performance of Cu alloys Lead-frame,because oxidation film has been deemed to one of the main matter,which leads crack or delamination occur in assembly process. This issue has studied the effects of different heat-treatment on hardness and conductivity of Cu-Cr and Cu-Cr-RE alloys,and emphasize particularly on the oxidation performance of those alloys in low and medium temperature circumstances.The specimen is Cu-0.8Cr,Cu-0.8Cr-0.05Y and Cu-0.8Cr-0.05Nd,which prepared by vacuum median frequency smelting.Two kind of processing crafts to those casting alloys(process A;casting+cold-rolling+aging,process B;casting+ cold-rolling+solution treating+aging).High-temperature metallographical microscope,SEM,XRD,microhardness instrument,eddy conductivity apparatus et al have been applied to research the rule of microhardness and conductivity with aging time change,the oxidation behaviour of those alloys at 300℃and 600℃,the morphology and structure of oxidation film,discuss the oxidation mechanism and the effects of Rare-earth on oxidation behaviour of alloys.The results are as following;(1)The oxidation weight gain of Cu-0.8Cr alloy processed via technics B greater than Cu-0.8Cr-0.05Y and Cu-0.8Cr-0.05Nd alloys,with the same technics and the same cold deformation; Y and Nd have the equivalent effects on oxidation resistance; cold deformation has scarcely any influences on oxidation performance.(2)The oxidation film of Cu-0.8Cr-0.05Y alloy has plainlier surface,tighter structure,and stranger adherence with matrix,compare with Cu-Cr alloy,processed by the same technics,that indicate Y can reduce oxidation film growth rate.Research show that Y facilitate Cr precipitated in grain boundary,which avails Cr₂O₃ growing, the steadier Cr₂O₃ has the funciton to impede oxygen diffuse into inner of the alloy.(3)Cu-0.8Cr and Cu-0.8Cr-0.05Y alloys oxidation kinetic curves approximately parabolically with increasing of time;alloys oxidation rate fairly quick at the initial stage of oxidizing,with time increase,the oxidation rate will change slowness gradually.(4)From the equation of the rate constant K_p=A exp(-E/RT),calculating shows;K_p of Cu-0.8Cr-0.05Y processed by technics B＜K_p,of Cu-0.8Cr-0.05Y processed by technics A＜K_p of Cu-0.8Cr processed by technics B＜K_p of Cu-0.8Cr processed by technics A.The reason of Y promoting alloys oxidation resistance is that Y increase E—alloys activation energy of oxidation diffusion.(5)With proper deformation and aging treatment,Cu-0.8Cr-0.05Y alloys have the semblable conductivity,which reachs to 90%IACS,whatever processed by technics A or B.Differing from conductivity,hardness of Cu-0.8Cr-0.05Y alloy processed by technics A can get to more than 145Hv,which greater than that processed by technics B.Moreover,oxidation film of alloys,processed by technics B, has more excellent in planish,compactability,adhesiveness than that processed by technics A...