Comparative Analysis of Package Warpage Using Confocal Method and Digital Image Correlation

Optical measurement techniques are commonly used in order to inspect the thermal warpage behavior and the deformation of packages during reflow. JEDEC standard has offered four types of methods to measure the warpage: Confocal, Digital Image Correlation (DIC), Shadow Moire, and Digital fringe projection. In this paper, the recently emerged new confocal imaging system is introduced and compared with DIC method in different aspects. The objection of the comparison is not to decide which tool is better yet to provide a general guide for both advantages and disadvantages of two kinds of methods under different situations of applications. First, the same component is measured by confocal as well as DIC method in order to verify the accuracy of the new confocal inspection system. For this measurement, surface treatment is needed for DIC method yet the confocal method does not have such a requirement. Another application for confocal method is that except for the substrate warpage, it can also measure the bump top behavior like coplanarity during cycling, which DIC is not able to measure. However, the DIC is capable of inspecting the in-plane and out-of-plane deformation so that it has the CTE measurement function that confocal method does not possess.