Reserch On SiC Power Diode Packaging Reliability

Silicon carbide power diodes are resistant to high temperatures,high voltages with fast switching speeds.They are currently the fastest growing power devices among commercial power devices.However,at present,there are still some reliability problems such as broken and detached leads,cracks in the solder layer and desoldering of silicon carbide power diodes.In order to evaluate and analyze the packaging reliability of SiC JBS devices in metal packages and plastic packages,this paper analyzes the thermal resistance and electrical performance degradation of metal packaged devices before and after thermal shock,then analyzes causes of the degradation with a simulation analysis.This paper studies the variation law of power cycle test data,the degradation of electrical parameters and electrical properties of plastic packaged devices and the causes.The main research contents and methods are as follows: Research on the thermal resistance structure and thermal resistance network model of TO-254 metal encapsulated SiC power diode.The SiC power diode devices with solder paste materials of nano silver paste and Pb95.5Sn2Ag2.5 were selected,the thermal resistance integral structure function and differential structure function of each device were tested and calculated,and the thermal resistance structures of the two devices were extracted and analyzed from the structure function,then a four-layer Cauer thermal resistance network model with practical physical significance was established for each device.The thermal resistance of the nano-silver solder layer and Pb95.5Sn2Ag2.5 solder layer are analyzed and compared.The former is 0.149995 K / W,the latter is 0.136040 K / W,and the former is 10.25% larger than the latter.According to the related research of nano-silver paste sintering,some process factors will affect the sintering quality,such as sintering temperature,time,atmosphere,air pressure,etc.It is speculated that the sintering quality of the nano-silver solder layer of the device under study is relatively poor,and the soldering layer is not dense enough.Research on Thermal Shock Test of TO-254 Metal-encapsulated SiC Power Diode.The thermal shock test was performed on the SiC power diode devices with nano-silver paste and Pb95.5Sn2Ag2.5,respectively.The on-resistance of the nano-silver solder layer diode before and after thermal shock increased by 18.56%,from 43.1 mΩ to 51.1mΩ.However,the forward and reverse characteristics of the diode of the solder layer material Pb95.5Sn2Ag2.5 have almost not changed,and the capacitance-voltage characteristics of the two are almost unchanged.The failure analysis of the nano-silver solder layer device of the chip de-solder during the thermal resistance test is conducted,and it is inferred that there may be holes in the solder layer.Therefore,a finite element simulation analysis of the holes in the nano-silver solder layer was performed and it was found that there were obvious stress concentration around the hole,which may be the cause of chip desoldering.In this study,the ability of the nano-silver solder layer to resist temperature change is relatively poor.The solder layer is not dense enough,and there may be holes.Through the improvement of the sintering process,the use of different sintering atmospheres,the application of appropriate auxiliary pressure,etc.,it will improve the quality of the nano-silver solder layer.Research on the coefficient consistency of temperature sensitive parameters of power diodes.Since the same batch of power cycle equipment can only input a typical value of the coefficient of temperature-sensitive parameters,if there are diodes with different chip structures in the same batch of tests,the typical value of the coefficient of temperaturesensitive parameters may be different,and the junction temperature calculation may exist error.In order to study the difference of the coefficients of the temperature-sensitive parameters of different device structures,four device structures were tested during the research.The test results show that the coefficients of the temperature-sensitive parameters of the diodes of the same chip structure differ very little.Using one of the devices as a typical value to calculate the junction temperature,the error can be ignored TO-220 plastic encapsulated SiC power diode power cycle test research..The power cycle test was carried out on the TO-220 packaged diodes with the same chip structure.The packaged solder layer materials were all Pb95.5Sn2Ag2.5 and 22 test device samples.The total power cycle time is 1,000 hours,the number of cycles is 12,000,and the change in junction temperature is set to more than 100 degrees Celsius.The test results meet the purpose of accelerated life testing,and the experiment realized the device aging and parameter degradation.There was no failed device during the 500 h test,and the failure rate meets the detailed product specifications of the device.There are 7 failed devices in the 1000 h test,and representative samples of 3 failed devices are selected from the 7 failed devices.These three devices are unfailed,impending failure,and already failed.The failed device loses its reverse cut-off characteristic,the Schottky barrier height is reduced from 1.21 e V to 0.7e V,and the remaining devices are almost unchanged.In order to improve the test efficiency,an analysis program for analyzing power cycle test data is also written.Seven failed devices were analyzed,and almost all the failed samples were related to packaging factors such as cracks in the solder layer and cracks in the wire bonding.The power cycle test of plastic packaging devices shows that the development of domestic plastic packaging devices has achieved certain results,but there is still a certain gap compared with foreign advanced technology.Improving the material and process of the package solder layer and improving the level of wire bonding process are effective means to narrow this gap.