| Due to the development requirements of miniaturization,multi-function and high integration of electronic products,POP stack packaging(package-on-package)gradually replaces two-dimensional packaging and is widely used in miniaturized electronic products.In POP packaged devices,solder balls play a key role in mechanical support and electrical connection,and the destruction of solder joints will directly lead to the destruction of the entire packaged device and even the entire electronic product.There are many factors that lead to the failure of solder balls,among which thermal load and drop impact load have the greatest impact on the reliability of solder balls.Therefore,it is urgent to study the reliability of packaged devices under the effect of thermal-mechanical coupling.In this paper,through the constant temperature compression experiment of lead-free solder Sn3.0Ag0.5Cu,its Arrhenius constitutive equation is established,On this basis,the reliability of the POP package under the coupling effect of heat generation and drop shock is systematically studied.The main contents of this article are:1.The effects of loading rate and temperature on the mechanical properties of lead-free solder Sn3.0Ag0.5Cu were studied by constant temperature compression experiments.It is found that temperature has a significant effect on lead-free solder,and the temperature effect is more obvious when the temperature is lower.At the same temperature,the flow stress increases with the increase of strain rate,and the lead free solder Sn3.0Ag0.5Cu has positive strain rate sensitivity.According to the experimental data,the Arrhenius constitutive model of the lead-free solder Sn3.0Ag0.5Cu is determined,and the theoretical results predicted by the Arrhenius constitutive model are compared with the experimental results to verify that the Arrhenius constitutive equation can more accurately describe the mechanical behavior of the lead-free solder Sn3.0Ag0.5Cu.2.According to the JEDEC plat level drop test standard,a three-dimensional finite element model was established using COMSOL finite element software,and the material properties of solder balls were described by Arrhenius constitutive model.Five kinds of stable powers,1W,1.2W,1.4W,2W,and 2.4W,are given to the packaged chip,and the three-dimensional model is numerically calculated with the chip as the heat source.The study obtained the temperature distribution of the chip under five different powers.Power has an obvious influence on the temperature distribution of packaged devices.When the power is 1W,the highest temperature in the model is 44.7℃,and when the power is 2.4W,the highest temperature in the model is 71.4℃.The solder ball arrays in the upper and lower layers of the 3D model were marked to obtain the temperature distribution of solder balls in different positions.3.Study the reliability of POP packaged devices under thermal coupling load,and analyze the influence of power(0W,1W,1.2W,1.4W,2W,2.4W)on its reliability.Using COMSOL finite element software,the thermally generated temperature load and the drop shock load were applied simultaneously,and the drop shock load was applied by the Input-G method.The research results show that the deflection curve of the test plate changes periodically with time,and the amplitude decreases gradually.Among them,when t=0.9ms,the maximum deflection occurs,which is the dangerous moment.At this point the critical solder joints in the POP packaged device can be identified,which are located at the fillet joints in the solder ball array,with the maximum value occurring on the side connected to the test board.At this point,the key solder spot in the POP package device can be determined,which is located at the Angle solder spot in the solder ball array,and the maximum value appears on the side connected to the test plate.And the position of the key solder joint does not change with the change of power;The peel stress of the key solder joint increases with the increase of power.According to the life prediction model established by the Power principle,calculate the thermal coupling life value of solder joints under different powers,that is,the life value of the POP packaged device,and analyze the influence of power on the life value of the device.Heat generation has a great impact on the life value of drop shock In the reliability prediction of packaged devices,the results obtained by considering the heat generation according to the actual working conditions are more accurate.In each segment with power less than 1.4W,the influence of power on life is particularly obvious.Therefore,when the packaged device may drop,the power used should be reduced as much as possible,and it is best to close the electronic product for transportation.The research conclusions of this paper will provide basic theoretical data and technical support for the development of the electronics industry. |
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