微尺寸SnAg凸点中孔洞生长机理的研究

Study on Void Growth in Micro-Size SnAg Solder Bump

采用电镀的方法在制备了尺寸小于100μm的Sn-3.0Ag凸点,研究了多次回流和时效过程下SnAg/Cu界面IMC的生长、孔洞的生长机理和分布以及影响因素。结果表明,回流过程中孔洞形成的主要原因是相变过程发生的体积缩减,而时效过程中孔洞形成的主要原因是柯肯达尔效应。时效过程中Cu3Sn(ε相)中孔洞的生长及分布受初始形成的Cu6Sn5(η相)影响。厚η相及η晶界处形成的孔洞促进ε相中孔洞的生长。平直的ε相/Cu界面以及ε相层内孔洞的连接对凸点的长期可靠性构成威胁。

The Sn-3.0Ag solder bumps with size less than 100 μm were fabricated by electroplating. The evolution and distribution of the void at the SnAg/Cu interface and its influencing factors were studied. The results show that the volume shrinkage during phase transformation was believed to be the main reason for the void formation during multi-reflow, while the Kirkendall effect was believed to be the main reason for the void formation during aging. The void growth in the Cu3Sn （ε-phase） was affected by the initial morphology of the Cu6Sn5 （η-phase）, a thick η-phase and the voids among interface and interconnected voids in the ε-phase would be its boundaries promoting the void growth in the ε-phase. The layered ε-phase/Cu threats to the long-term reliability of solder bumps.