Fatigue Life Prediction Methods And Experimental Research Based On Fracture Mechanics

The reliability of BGA solder joint directly affects the service life of electronic products,so it is particularly important to the study on the reliability and service life prediction. So far,there are many kinds of creep failure modes applied to the service life prediction of solder joint,but the scope of application and life prediction results are larger difference.First of all, this paper raises four common solder joint fatigue life prediction models and BGA solder joint crack propagation model based on the research results of NASA(National Aeronautics and Space Administration),which provides the theory support for designing and manufacturing the stardard specimen 、 designing and developing the fatigue testing machine.Secondly, the mian research content of this paper is how to make the stardard specimens,including the design rules of PCB board,the design of double-layer PCB board and the production process of PCB board. The top-layer of double-layer PCB board is bridge detection circuit,which can be characterized resistance change on crack extension.the bottom-layer is four symmetrical pads.According to the diameter of pad and the stencil thickness,we can roughly estimated the aperture of the plastic stencil. According to the solder paste printing process, the docking process pad and reflow process, we can calculate the percentage of solder and solder paste.Finally,in order to test the total life of the standard specimens,we designed and developed the fatigue testing machine.we do three experiments: the elastic element calibration test,the static tensile test and cycle tensile test.According to the fracture mechanics theory,depicting the stress-life curve of the solder joint.In addition,this paper introduces two sizes of pads,we can get the fatigue life of different pads and the same pad.According to the different production processes of PCB board, such as the stencil thickness and reflow temperature curve setting differences,we can get the fatigue life of the same pad under the different process conditions and the fatigue life of the different pad under the same process condition etc…...