Research On Reliability Of Board Level Package-on-package In Drop Impact

As a a symbol of high technology and fashion, in resent years, the portable electronicproducts, such as mobile phones, digital cameras, personal digital assistants and so on, havebeen widely sought after in the market. However, due to the light, small, thin and portablefeatures, these electronic products are often subjected to mechanical impact and thus causeproduct damage during transportation and usage, which causes great losses to consumers.Therefore, it is very necessary to study the reliability of these portable electronic productsduring drop impact, in order to guide the design and improvement of these products.In this paper, the reliability of solder joints of POP packages, which are currently themost advanced in portable electronic products, was fistly investigated by means ofexperimental tests and numerical simulation under drop impact.Fist, based on JESD22-B111standard, a series of experimental tests were carried out forPCB assembly with five POP packages. The number of the initial failure for the assembly wasobtained in free drop test, and also the failure probability of the different drop mumbers wasanalyzed. In addition, the dynamic strain responses at some key positions of PCB board arerecorded by strain gages to study the board level response under impact and supply datavalidation for the finite element simulation analysis.Second, a three-dimensional finite element modal was established for PCB assemblywith five POP packages. The Input-G model was solved by the implicit dynamic algorithm.The validity of the model was verified by test date from free drop test, and the dynamicresponse of PCB assembly was obtained. Through simulation, it found that, for POP package,the maximum peeling stress of the solder joint at the outermost corner of the bottom packagewas larger than that of the top package; For U8A package, the solder joints at the fouroutermost corner of the bottom package were most prone to failure; For U2A package, thethird corner solder joint of the bottom package was the weakest and also the most dangeroussolder joint of the whole PCB assembly; For the corner solder joint, the side of solder jointconnecting to PCB board was the most likely to fracture.Third, the influence of the PCB damping, the shape of solder joint, the material of solderjoint and the diameter of solder joint to the drop impact performance was reseached in Input-G model. And the influence of the thickness of the cushioning, the elastic modulus ofthe cushioning, and the height of the free drop to the peak and duration of the impact impusewas also studied in free drop model.Fourth, the free drop model of PCB assembly with five POP packages was established.ABAQUS/Explicit was adopted to carry out the simulation, and then compared thecalculation results of the free drop model and Input-G model. The results showed that themaximum peeling stress of critical solder joints for the free drop model was larger than that ofInput-G model.