Influence of Low Temperature Swings and Short Heating Times on the Power Cycling Capability of IGBTs in Discrete Housings

Inhalt:
This paper investigates the lifetime of IGBTs in the TO-247 package using the power cycling test with and without switching losses to achieve the same temperature rise with different load currents. It has been found that the lifetime of the devices increases with shorter switch-on times (ton). An increase of 5 % in the forward voltage VCE,cold has been determined as the cause of failure. This is confirmed in the failure analysis with cracks between bond wire and metallization as well as with heel cracks determined by a pull test. An important factor when carrying out these tests is the method of chip-temperature ex-traction via a temperature sensitive electrical parameter (TSEP). Depending on the TSEP, different sensing regions of the chip are utilized, e.g. the pn-junction (backside location of the IGBT chip) or e.g. the RG,int (front-side location of the chip) [1, 2]. For instance, it was found that in tests with short ton the solder layer and the metallization (contact to bond wires) undergo different temperature swings. The difference in these temperature swings depend on the average temperature between these two layers and a difference of 10 K was determined at a temperature swing of 30 K and a ton of 30 ms. These temperature differences are significant and must therefore be taken into account during temperature extraction and when creating lifetime models and evaluating the test results, especially in the short ton region.