Study On The Failureanalysis Of BGA Lead-Free Solder Joints

Based on experiment, this thesis explored the effect of the IMC(IntermetallicCompounds)layer of BGA Lead-free solder joint on solder joint cracking or spalling,combined the IMC-layer diffusion theoryand analysed the IMC-diffusion mechanism onsolder joints. In order to obtain the reason of the failure, analyze the solder joints of theflip-chip that have been cracking or spalling. Contrasting to natural samples make agingand themal shock test.Sum up the results and make contribution to improving thereliability of flip chip solder joints.The main contents of this thesis include:(1) Aiming at a number of flip-chip, though scanning electron microscope,metallurgical microscope, X-ray detector, bonding test and other equipment with a seriesof BGA solder joint analysis in order to identify the reasons for its failure.(2) The first is to conduct X-ray test, the results show that, besides some holes,that's no other defects observed, moreover the size of the holes is not enough to lead tofailure.Acrossing the crossing section analysis, we found most of the solder ball has acrack, some are already falling.(3) By scanning electron microscope to observe the morphology and compositionfrom the perspective of analysis, we found parts of solder joint fracture located on thechip side solder joint, Ni-Sn compounds and (NixCu(1-x))3Sn4 compounds, the root causeof breakage caused by chip side of the formation of brittle ternary (NixCu(1-x))3Sn4compounds, whose morphology is coarse block structure, the internal stress is verylarge,vulnerable to the formation of micro-cracks.(4) The PCB boards including chips are used to make aging, aging time is 100hours, 200hours, 300hours, 500hours.Then by observing after 200h aging, IMC thicknesshad a certain degree of growth, but not obvious, and the entire interface was relativelyflat, no larger pieces of IMC were found protruding phenomenon.As the aging time,when reach 500 hours, IMC thickness increased little, the interface becomes little rough..(5) Making use of the PCB board carry up thermal shock experiments, observationswere over 100 cycles, 200 cycles, 300 cycles,500 cycles .The thickness and morphology,microstructure analysis shows that after 100 cycles,200,300 cycles and 500 cycles IMCchange is not very obvious.