Temperature Cycle Reliability Analysis And Life Prediction Of Plastic Encapsulated Power Semiconductor Devices

Power semiconductor devices are the most important components in power electronics systems and are widely used in communications,transportation,defense,and aerospace.Discrete devices in a transistor-outline package provide the necessary power management and conversion control for the central processing unit,playing an irreplaceable role in the circuit,and are the most mainstream power semiconductor devices.Because of its large temperature difference and high frequency,especially for aerospace devices,it needs to face the intense radiation of the sun and the black cooling in the shadow area during the service period.Therefore,it is necessary to carry out stringent temperature cycle tests to make the products meet the corresponding performance standards,which puts high requirements on the packaging of such devices.This paper is based on the research project “Reliability Research of a Package Product” with a certain enterprise.A typical plastic encapsulated power semiconductor device designed and manufactured by the company is exposed in the GJB 7400-2011 standard temperature cycle test.The combination of theoretical analysis and finite element simulation is used to analyze the stress-strain behavior of the device in temperature cycle.Life prediction is carried out to study the influence of packaging structure and packaging material on its life.In addition,the solder spillage in the packaging process is analyzed and optimized.The content of this paper is mainly summarized as follows: 1.Firstly,according to the device data provided by the company,combined with the research requirements and the structural characteristics of the device,the finite element model is established.Subsequently,the storage modulus of the molding compound at different temperatures was obtained through the test of the molding compound parameters.Finally,the temperature cycle load was loaded based on the GJB 7400-2011 temperature cycle test.The simulation results show that:(1)the stress at the corner of the chip is the highest after the end of the temperature cycle,and the dangerous point of the solder layer is at the edge position,which is in good agreement with the temperature cycle test result of the device;(2)The equivalent stress of the solder layer dangerous point changes periodically with the temperature cycle,and the equivalent stress of the solder layer is higher in the low temperature stage;(3)The life of the device designed by the company is 303 cycles,which cannot reach the temperature cycle test.For acceptance requirements,the device needs to be optimized.2.The temperature cycling simulation of five plastic encapsulated devices shows that EK5600 GH has the lowest change rate of storage modulus,and the corresponding device temperature cycle life is the highest,which is 1534 cycles.Compared with the EK5600 GHR used by the company,the temperature cycle life is increased by 3.1 times.3.Temperature cycling simulations were performed on devices with different chip sizes and solder thicknesses.It is found that small chip size and large solder thickness can reduce the equivalent stress and dangerous point shear plastic strain range of the solder layer and increase the temperature cycle life of the device.With a 0.8mm×0.8mm chip,the device has a temperature cycle life of 3782 cycles,which is 10.4 times better than a device with an initial chip size of 3.25 mm by 3.99 mm.When the solder thickness is 50?m,the device has a temperature cycle life of 2716 cycles,which is 6.9 times higher than that of the device with an initial solder thickness of 10?m.4.Take the 8 sets of sample frames manufactured by the company for VMS image test,and obtain the solder overflow rule under the existing packaging process.According to the measurement results,the influence of different solder overflow conditions on the device temperature cycle life is analyzed.The results show that the solder overflow will reduce the temperature cycle life of the device;the one-side overflow is more serious than the four-sided overflow on the device reliability,the temperature cycle life of the upper side overflow and the right overflow is reduced by 85.1% and 85.7% respectively.5.The solder limiting groove structure is designed on the lead frame to reduce the influence of solder spillage on device reliability.The simulation shows that the height of solder extrusion can increase the temperature cycle life of the device.In this paper,10?m is used as the reference value of the engineering design.At this time,the temperature cycle life of the device is 3891 cycles,which is 3.3 times higher than that before making the limit slot.