P对Au／Ni／Cu焊盘与SnAgCu焊点焊接界面可靠性的影响

Influence of Phosphorus on Reliability of Interface between Au/Ni/Cu Pad and SnAgCu Solder Joint

采用回流焊工艺在ENIG镀层印制电路板上组装289I/Os无铅Sn-3.0Ag-0.5Cu球栅阵列封装器件,对封装后的电路板进行随机振动可靠性试验,采用X-Ray、SEM和EDX等测试确定焊点在随机振动试验过程中的失效机制,探讨焊点沿界面失效与镀层内P元素的分布和含量的关系。在振动试验中失效和未失效的BGA焊点与镀层界面表现出类似的微观形貌,Ni层因被氧化腐蚀而在焊点截面形貌上出现"缺齿"痕迹,而在表面形貌图上此呈现黑色的氧化腐蚀裂纹。P在镀层表面的聚集对Ni的氧化腐蚀有促进作用,同时P的聚集也明显降低焊点结合界面的机械强度。Ni层的氧化和Ni层表面P元素的聚集是引发焊点沿焊点/镀层结合界面开裂的主要原因。

The content and distributing of P in Electroless Nickel/Immersion Gold （ENIG） surface finishes effect the reliability of interface between solder joint and surface fnishes. 289 I/Os lead-free Sn-3.0Ag-0.5Cu BGAs was assembled on the ENIG print circuit board by reflow soldering technology. The print circuit board was tested by random vibration. After random vibration test, the failure and not failure samples were studied by X-ray, SEM, and EDX et al. The failure mechanism was confirmed and the relation of failure and content and distributing of P in ENIG finishes was discussed. The failure and not failure samples after vibration test show similar microstructure at the interface of solder joint and surface finishes. The cross-sectioning of the affected area shows a ＂tooth decay＂ effect of corrosion of the nickel layer, and ＂mud cracks＂ in the topography on the surface. The enrichment of P on the surface accelerated the oxidation of Ni, and also reduced the mechanical intensity of interface. The oxidation of Ni and the enrichment of P on the surface result in the crack of solder/finish interface.