The Research Of Thermal Reliability Of Insulated Gate Bipolar Transistor (IGBT)

IGBT which was born in1982, has become the representative device that has the characteristics of high frequency and high power in power semiconductor devices. IGBT has quickly applied to the country’s economy and public life since it’s unique, irreplaceable function and showed strong vitality and development potential.IGBT often works under the condition of high voltage and large current. When IGBT dissipates power, the temperature will rise rapidly and the distribution will become non-uniform in chip. The semiconductor devices are very sensitive to temperature. High temperature may lead to abnormal and unstable of the working devices and even the whole system may be destroyed. Most failures caused by over-high temperature. At present, enhancing the reliability and researching failure mechanism of devices have already become the research hotspot. First, this article started from the thermal reliability of semiconductor devices, test methods of IGBT’s thermal resistance and the method for quality detection of the package using structure function curve obtained in the process of thermal resistance test were researched. Next, based on the finite element software of ANSYS, the failure modes under the thermal reliability assessment tests such as power cycling (PC) test and temperature cycling (TC) test were researched. Last, for the common failure modes, the improved method was studied in the area of package design of IGBT module. The research for improving the quality of devices has both theoretical significance and application value.Thermal resistance is a very important thermal parameter. For assessing the reliability of the device, it’s very important to test thermal resistance accurately. Traditional thermal resistance test method considers that temperature distribution on chip and case is uniform. It’s inevitably resulted in a large deviation in the value of thermal resistance. In order to avoid such errors introduce in the process of case temperature test, a transient dual interface method is proposed. This method doesn’t need to test case temperature. ANSYS software was used to verify the accuracy of these two test methods. By comparing the results of simulation by ANSYS software and the other two methods, the transient dual interface method was confirmed. Using the structure function of devices obtained in the process of thermal resistance test, the changes about heat capacity and thermal resistance during the heat propagation path can be described. By comparing the structure function of normal and failure devices, we can not only identify the location where the device failure but also be quantitatively described the failure degree.Three steps were used to study the failure mechanism of IGBT modules. Firstly, the common failure modes under TC and PC were studied by using ANSYS software. They include delamination and crack of solder layer, the fracture of chip and ceramic and aluminum bonding wire warping and melting. Secondly, solder layer and bonding wire were focused on where failure often occurred. In the process of studying the solder layer, we started from the problem which is most prone to lead failure-the solder voids. The impacts of size and distribution of the voids on the performance of devices were studied. The impacts of thickness and materials of solder layer on the thermal and stress performance of the devices were also studied. The research of bonding wires was started from the key issues such as warpage, cross-sectional area and arrangement. The results pointed out the development direction for manufacturing process of bonding wires. Finally, overall heat transfer performance of IGBT modules was designed for improvement. The design was focused on the choice of material, thickness of the baseplate and ceramic and features of solder and bonding wire, and then the best cooling solution was determined.