用热循环、扫描电镜观察焊点横截面和有限元模拟的方法研究了陶瓷球栅阵列（CBGA）封装结构中无铅焊点的组织和热疲劳行为。BGA结构的制备是通过Sn-3.0Ag-0.5Cu焊膏采用回流焊工艺把Sn-3.8Ag-0.7Cu焊球和镀银多层陶瓷芯片、镀铜印刷线路板(PCB)焊接在一起。回流焊后，在焊料与铜焊盘和银焊盘的界面处分别形成了Cu6Sn5和Ag3Sn金属间化合物(IMC)。在随后的热循环过程中，在铜焊盘处，Cu6Sn5层增厚，并且有新的化合物Cu3Sn出现；在陶瓷芯片一边，Ag3Sn层也增厚。焊球中靠近界面的Ag3Sn颗粒形态发生了从针状向球状过渡的变化。随着热循环周数的增加，焊点中出现疲劳裂纹。疲劳裂纹最先出现在芯片与焊球界面处焊球的边角位置上，从有限元模拟的结果得出此处具有最大的剪切应力。疲劳裂纹随后的生长导致了焊点的最终断裂。在印刷线路板处裂纹容易沿着Cu6Sn5和焊料的界面扩展，在陶瓷芯片处裂纹沿着靠近Ag3Sn界面层的焊球内部扩展。
Microstructure and thermal fatigue behavior of Pb-free solder interconnects in ceramic ball grid array (BGA) packages were examined by cross-sectional microscopy, thermal cycling experiments and finite element modeling. The BGA assemblies were made by reflow soldering Sn-Ag-Cu solder balls between Ag-metallized multilayer ceramic chip and Cu-metallized printed circuit board using the eutectic Sn-Ag-Cu solder paste. In the as-reflowed condition, Cu6Sn5 and Ag3Sn intermetallic compounds (IMCs) were formed at the solder interfaces with Cu and Ag metallizations respectively. Following thermal cycling, the Cu6Sn5 layer grew thicker and Cu3Sn IMC was found at the interface with Cu metallization. On the ceramic side, visible thickening of the Ag3Sn layer was also observed. The Ag3Sn in the solder near the interface went through a morphological change from the needle shape to spherical. As a result of repeated thermal cycling, fatigue cracks developed in the solder interconnects. The fatigue crack appeared first at the corner of the solder ball with the chip, where the maximum shear stress was found by the finite element analysis. Subsequent growth of the fatigue cracks led to final fracture of the solder interconnects. The cracks preferred to propagate along the Cu6Sn5/solder interface on the side of the print circuit board and in the solder joint near the interfacial Ag3Sn layer on the ceramic side.
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