磁控溅射Cu-Cr合金薄膜与Sn-Ag-Cu焊料在时效处理时的界面反应

Interfacial reaction of Sn-Ag-Cu solder with magnetron sputtered Cu-Cr alloy film during aging treatment

采用磁控溅射的方式沉积不同Cr含量的Cu-Cr合金薄膜,通过与Sn-Ag-Cu(SAC)焊料在240℃下回焊形成焊点结构,然后将试样置于180℃下进行真空时效处理。研究Cu-Cr合金作为凸点下金属化(UBM)层时与SAC形成焊点的焊接可靠性。使用配备能量色散X射线光谱仪的场发射扫描电镜和多功能推力测试仪等分析界面金属间化合物(IMC)的形貌及焊点的剪切强度。结果表明,SAC/Cu-Cr焊点结构在回焊后形成了不同于传统的SAC/Cu焊点扇贝状IMC的针状IMC。在时效处理后,Cr在晶界处的偏析形成了富铬层,其作为扩散阻挡层阻碍Cu扩散到IMC中,使得Cu_(3) Sn和柯肯达尔空洞的生长受到抑制。剪切强度测试结果表明,回焊后SAC/Cu-Cr试样比SAC/Cu试样具有更高的剪切强度。Cr靶电流为1.5 A的Cu-Cr合金UBM层形成的焊点结构具有较小的IMC厚度,且拥有最高的焊点剪切强度。证实了Cu-Cr合金UBM层有利于提高焊接可靠性。

Cu-Cr alloy films with different content of Cr was deposited by magnetron sputtering.The solder joint structure was formed by reflow soldering with Sn-Ag-Cu(SAC)solder at 240℃,and then the specimens were vacuum aged at 180℃.The soldering reliability of the Cu-Cr alloy as under bump metallization layer(UBM layer)forming solder joint with SAC was studied.The morphology of interfacial intermetallic compound(IMC)and the shear strength of solder joint were analyzed by field emission scanning electron microscope equipped with energy dispersive X-ray spectrometer and multifunctional thrust tester.The results show that needle-like IMC,which is different from the traditional SAC/Cu interface scallop-like IMC,is formed in the SAC/Cu-Cr solder joint after reflow soldering.After aging,the segregation of Cr at the grain boundary forms a chromium rich layer,which acts as a diffusion barrier to prevent the diffusion of Cu into IMC,so that the growth of Cu_(3) Sn and Kirkendal void is inhibited.The shear strength test results show that the SAC/Cu-Cr specimen after reflow soldering has higher shear strength than that of the SAC/Cu specimen.The solder joint structure formed by the Cu-Cr alloy UBM layer with a Cr target current of 1.5 A has smaller IMC thickness and the highest solder joint shear strength.It is confirmed that the Cu-Cr alloy UBM layer is beneficial to improve soldering reliability.