Local thermal cycles determination in thermosyphon-cooled traction IGBT modules reproducing mission profiles X. Perpin ˜a ` a, * , M. Piton a , M. Mermet-Guyennet a , X. Jorda ` b , J. Milla ´n b a Alstom Transport Tarbes, Rue du Docteur Guinier-BP4, 65600 Se ´me ´ac, France b Centre Nacional de Microelectro ` nica, CNM-CSIC, Campus UAB, 08193 Bellaterra (Barcelona), Spain Received 8 July 2007 Available online 27 August 2007 Abstract Temperature mapping in two IGBT modules cooled by a thermosyphon-based system is performed under realistic power mission pro- files. The power mission profiles are inferred from a traction design tool results based on feedback data extracted from the field, in which the service line, the train characteristics, and its speed profile are taken into account. Thereby, the chips which are more prone to fail due to a temperature-activated failure are detected by means of the experienced thermal cycles. Ó 2007 Elsevier Ltd. All rights reserved. 1. Introduction In railway applications, thermal studies are fundamental to increase the lifetime of the power inverters employed in traction chains. One of their main goals is verifying whether reliable operating and uniform temperatures fields are assured inside the used electrical switches. With these tests, dysfunctions on cooling systems behaviour or non reliable thermal designs of switch packages can be evidenced. The thermal concerns on the aforementioned electrical switches are extremely linked to their internal structure. They are composed by several semiconductor devices (IGBTs and diodes) interconnected in parallel inside the same package (IGBT module). Thereby, the high current ratings required in these applications are assured. The power modules are stratified in different material layers [1], such as die, die attach, chip interconnection layer or metallised substrate (CIL), CIL solder and base plate. Under the usual working conditions, the semiconductor device selfheating induces a temperature field inside the power module, which evolves depending on the train speed along a railway line (mission profile). As a result, the power module will experience several thermal cycles defined between the train acceleration and deceleration. This fact will create a certain strain in the interlayer interface (espe- cially on the CIL solder) and the thermal interface degrada- tion between the module and cooling system. In addition, a perfect contact to the cooling system is not always assured all over the module backside. All these facts lead to the apparition of a non-uniform temperature field inside large power modules that support high power ratings, as employed in railway traction applications. As a result, some components can reach at long term, temperature val- ues to force their destruction [1,2]. One way to increase the module lifetime is by using thermal testbenches, where the working conditions of the power modules are simulated. However, most of these test- benches have been focused on temperature measurement only at power module level or locally at the interface between the module and cooling system without considering the chip location. Finally, the obtained results are averaged overall the module, which is the usual approach to tackle the thermal design of power inverters. Thus, this work extends the thermal study to chip level. The main objective is deter- mining how the cooling system and the thermal interface 0026-2714/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.microrel.2007.07.072 * Corresponding author. Tel.: +33 5 62 53 48 63. E-mail address: xavier.perpinya@lab-pearl.com (X. Perpin ˜a `). www.elsevier.com/locate/microrel Microelectronics Reliability 47 (2007) 1701–1706