The Research About The Storage Failure Mechanism Of Assembly Solder Joint On Printed Circuit Board

With the continuous development of electronic assembly technology，thedensity of electronic components is increasing which leads to the higherrequirement of the reliability of the electronic products. As the weak links of theproducts, solder joints are often the main regions of invalidation.Manyelectronic products are In the non-working state and the storage is one of thefundamental types. During the period of storage, microstructure variation makesthe defect in solder joints，so the research about failure mechanism of solderjoints is very important.In this paper, the storage failure mechanism of THT solder joints and BGAsolder joints is systematically investigated. Through accelerated storagetest,solder joints were kept in in the different temperature conditions to obversethe microstructure variation and the generation of defects, and try to analyze themechanism.By the method of infrared multi-point temperature measurement,solder joints are testsd nondestructively.The electrical performance andmechanical performance test were used to obverse the performance degradationof solder joints. The surface profile and growth of IMCs were obversed toanalyze the growth kinetics and coarsening mechanism. Electron back-scattereddiffraction (EBSD) was employed to investigate the orientation relationship ofCu6Sn5during the period of storage.The results showed that cracks were formed in Cu6Sn5and Cu3Sn and therewere a lot of kirkendall voids.The relationship between the thickness of IMCsand time is parabolic and the morphology of IMCs transforms from scallop-typeto flat-type. By the method of infrared multi-point temperature measurement, thedefects of solder joints were testsd effectively. Electrical properties have noobvious change in the solder joints. Solder joint strength of THT is higher thanthe component pins, and solder joint strength of BGA declines during the periodof storage with defect formation and segregation of eutectic solder. Shearfracture position transformed from the interior of the solder to the interface,andthe facture mode transformed from ductile fracture to mixed fracture modewhich contains intergranular fracture. BGA joints on the Cu/Ni/Au pads havebetter shear strength and slower rate of descent.With the growth of IMCs,Cu6Sn5grain coarses and transforms from scallop-type to polyhedron-type.Cu6Sn5grain orientation moves forward in harmony and the ｛0001｝planes were parallel to the substrate to stand on the pad. Grain orientation Anglebecomes smaller, and low angle grain boundaries were in the majority.