ENIG镀层焊盘上BGA焊点开裂原因及应对措施

Causes and Measures for Crack of BGA Solder Joints on ENIG Pad

使用金相切片、扫描电子显微镜(SEM)、X射线能谱仪(EDS)等分析方法,研究了ENIG(Electroless Nickel and Immersion Gold, ENIG)工艺处理的PCB焊盘焊点开裂样品,该样品是BGA封装的器件,焊球成分是Sn3.0Ag0.5Cu,焊膏成分是Sn63Pb37,属于有铅无铅混装工艺。研究发现,该样品中ENIG工艺处理的PCB焊盘上BGA焊点开裂原因是回流焊接工艺参数控制不当,导致磷在反应界面过度富集,形成了富磷层,以及铜元素穿过镍层扩散到反应界面,参与了界面IMC(Intermetallic Compound,IMC)层的形成,双重因素作用下使焊点界面强度严重弱化,在外界应力作用下发生开裂。

In this paper,metallographic sectioning,scanning electron microscope(SEM),X-ray energy spectrometer(EDS)and other analytical methods are used to study PCB solder joint cracking samples processed by ENIG(Electroless Nickel and Immersion Gold,ENIG)process.The research results show that the reason for the cracking of the solder joints on the PCB pads treated by the ENIG process in this sample is improper control of the reflow soldering process parameters,which leads to excessive phosphorus enrichment at the reaction interface,forming a phosphorus-enriched layer,and copper diffusion through nickel from the layer to the reaction interface,be a part of IMC(Intermetallic Compound,IMC),the strength of the solder joint interface is seriously weakened under the action of dual factors,and cracks occur under the action of external stress.