The Reliability Effect Of Interface Reaction With Finishes And SnAgCu On The Solder Joint

With the lead-free era’s arrival, the reliability research of lead-free product seemsmore and more important. Various materials are being introduced into lead-free electronicspackage make the interfacial reactions become more complex. But the domestic andforeign relevant report at the reliability research of the combination of lead-free solder withdifferent materials system, especially on the study between the different plating layer andsolder are rarely. This article analyzes the failure mechanism and finds the effect ofinterface reaction with different PCB finishes and SnAgCu on the reliability throughexperiments. The whole work was carried out as follows:1. The reliability of SnAgCu solder interconnections between SBGA and PCB withdifferent finishes (ENIG, OSP, HASL and Im-Ag) under drop test and temperature cyclingtest was investigated, compared with the SnPb solder paste. Then observe the performanceof the reliability of different samples under different test through X - ray, dyeing andmetallographic analysis, analysis and discusses their failure mode and failure mechanism.2.The finite element software ANSYS was employed to analyze the reliability of thesample under the temperature cycling. The fatigue life of the sample’s solder joint waspredicted, the effect of IMC layer with different thickness on the reliability of solder jointwas discussed and in contrast to the experiment.The research results show that: (1) The solder paste reliability of the SBGA reflowedon the OSP was significantly better than that soldered on HASL and EING boards for droptest. The solder joints have the best strength when using the ENIG finishes andcomparatively less when using the OSP and HASL finishes for temperature cycling. Whenusing the Immersion Ag finishes, the solderability is the worst in two kinds of testcondition. (2) The initial reliability of the SnAgCu solder on ENIG finish boards is greaterthan SnPb solder shifting the failures to the PCB, and the SnPb solder on OSP, HASL andImmersion Ag is better than SnAgCu solder. The overall strength of the SnAgCu solder isgreater than SnPb solder after the temperature cycling. (3) We found the reliabilityperformance and the fracture mode of the same sample in drop and temperature cycling isdifferent. (4) We found the plastic strain is in a dominant position in the total strain ofsolder joint by temperature cycling simulation, and found too thick IMC might affect thereliability after forecast the thermal fatigue life of dangerous point with different thick ofIMC. The results have an important guiding significance on solder joint failure analysis.