Issues in junction-to-case thermal characterization of power packages with large surface area

Abstract

There are several ways to define the junction-to-case thermal resistance; however, it is rather challenging to characterize the heat-flow in a package by a single number in an accurate and reproducible way. For many power package families such as TO-type packages the thermal transient testing and the so-called dual interface method can give reliable results.The diverging point of structure functions from dual thermal transients gives a good picture of the material interfaces in such structures. However, the location and nature of the diverging point strongly depends on the shape and direction of the heat-spreading. If the package area is much larger than the dissipating chip the shape of the heat-flow changes when using different interfaces [1,2]. This causes structure functions corresponding to the two setups deviate much before reaching the case surface. In this paper the origin of this phenomenon is investigated.Measurement and simulation results are compared on different large IGBT modules with several modifications in their structure enabling a detailed analysis of the heat-flow path. A comparison is given between heating only a small fraction of a large module and heating all chips. Some samples went through thermal cycling reliability tests which resulted in cracks below the chips. The effect of the reduced die-attach area is visualized with the help of structure functions. KeywordsJunction-to-case thermal resistance, thermal transient testing, dual interface methodology, large substrate area power modules Problems to be addressed

On the Reproducibility of Thermal Measurements and of Related Thermal Metrics in Static and Transient Tests of Power Devices

“…The figure demonstrates that selecting a threshold between 0.05 J/K and 2 J/K, being of a ratio of 40, we can state that the R thJC junction to case thermal resistance is between 0.17 K/W and 0.19 K/W. In real cases with actual measured transients instead of simulated ones, this difference is less steep, as shown in Reference [23], but still gives a sharp detection of the R thJC quantity. In Figure 9, the structure functions generated from the Zth curves of Figure 7 are compared.…”

Performance of Cu-Al2O3 thin film as thermal interface material in LED package: thermal transient and optical output analysis

“…The dissimilar characteristic displayed by these samples at Point A is likely because of the influence of annealing temperature on the properties of Cu-Al 2 O 3 thin films, as the rate of diffusion of Cu atoms into the Al 2 O 3 structure are varied. Thus, in the system-level analysis, the R th of the DUT varies because of the resultant properties of Cu-Al 2 O 3 thin films (Vass-Varnai et al , 2010).…”

Investigation of die-attach degradation using power cycling tests

“…In order to define the failure criteria for the degradation of the die attach material, thermal transient testing can be a suitable approach [5]. It requires a unit power step anyway, which can be generated by the same source that is used to create the power cycles.…”