Diagnosis of MEMS Packages Using Speckle Correlation Method: An Application in Pressure Sensor Packaging

Abstract

Abstract Cracked glass beads embedded in the plastic housing material of fuel vapor pressure sensors have been observed after a few hundreds of cycles of thermal shock test. In order to diagnose the root cause of the cracked glass bead, the speckle correlation method is used to in-situ measure the thermal deformation field on the surface of the glass bead. Measurements are taken at 130°C, 26°C and −40°C. The speckle patterns at different temperature are recorded digitally by a CCD camera with a resolution of 1024×1024 pixels. Every two sequential speckle patterns are compared to yield the displacement field of the sample. Then the strain fields are calculated by a finite deformation formulation. Results reveal that the material made of the glass bead is highly non-uniform, and there exists a highly tensile strain zone on the surface of the glass bead. This is correlated with the location of cracking in the bead. Moreover, there is a sliding zone along the boundary of the glass bead, which may result in leakage. As a replacement for glass bead, a metal bead embedded in housing material is examined. Experimental results show that strain level in the metal bead is lower than that in the glass bead, which will reduce disturbance on the sensor part. In addition to that, there are no potential cracking and leakage problems in the pressure sensor applications. Therefore, the metal bead is recommended for future pressure sensor applications.