Infrared image correlation for thermal stress analysis of power devices

Thermal stress analysis is indispensable to improve the reliability of power devices. We propose a technique to observe a temperature distribution and a thermal strain simultaneously for thermal stress analysis of power devices. A temperature distribution is measured by an infrared (IR) camera and a thermal strain is measured by a digital image correlation (DIC) with IR images under a power cycling test. To apply DIC to IR images, we propose techniques to make a random pattern on the surface which can be recognized by IR camera even if a surface temperature is changed. This technique realises an observation with completely same field of view even in a localized area on power devices. This method provides an experimental means to verify simulation results of thermal stress analysis

Improved DICM with an IR camera for Imaging of Strain and Temperature in Cross Section of TO packages

Digital image correlation method (DICM) is effective for failure mechanism investigation of power semiconductor packages by obtaining the mechanical strain in the package. In DICM, the displacement and strain are calculated by the images of a random pattern on the surface of the object captured by a camera. We have developed a new DICM system to obtain the mechanical strain and the temperature distributions simultaneously using an infrared camera (IR-DICM). In previous IR-DICMs, the strain observation was limited to high temperatures under constant condition, so that stress location and phase in the power cycle cannot be identified for failure mechanism investigation. In this paper, We successfully demonstrated the IR-DICM on TO-3P package power cycling test and obtained strain and temperature distributions throughout the power cycle using new sample preparation and special image processing algorithm.33rd International Symposium on Power Semiconductor Devices and ICs (ISPSD 2021), 30th of May and 3rd of June, 2021, Full Virtual Conferenc

Non-linear analyses of strain in flip chip packages improved by the measurement using the digital image correlation method

Numerical methods like the finite element (FE) method are often used to evaluate the reliability of electronic packages. However, the accuracy of non-linear numerical analyses should be confirmed by experimental measurements. In this study, we evaluated the strain distribution in flip chip (FC) packages with multi-layered printed circuit boards (PCBs) by combining the digital image correlation method (DICM) and the non-linear FE method, considering the viscoelasticity of resins and the elastoplasticity and creep of solder alloy. Four types of FC package consisting of two types of buildup (BU) resin and two types of underfill (UF) resin were evaluated. The distributions of strain on the cutting sections of FC packages were measured using the DICM with microphotographs obtained by a confocal laser scanning microscope (CLSM). The strain measurements showed that the UF resin with the low coefficient of thermal expansion (CTE) reduced thermal strain around a solder bump, and the BU resin with the low CTE reduced the strain concentration along the interface between a Si chip and a solder bump. We performed the non-linear FE analyses while taking into account the viscoelastic Poisson’s ratio of the UF resin and the constant instantaneous Poisson’s ratio. The result of the FE analyses with the constant instantaneous Poisson’s ratio did not correspond with the strain measurements using the DICM. The normal strain in a solder bump was less than that obtained by the measurement, and the direction of a shear strain band in a solder bump was different from that measured using the DICM. On the other hand, the FE analyses considering the viscoelastic Poisson’s ratio showed good agreement with the strain measurements using the DICM. The strain measurement using the DICM improved the accuracy of the non-linear FE analysis of microelectronic packages effectively