A Projection Moiré System for Measuring Warpage with Case Studies

Microelectronic science and technology is shrinking the world. Advanced packaging and systems make bulk electronic devices miniaturized and multi-functioned. In fact, mobile, wireless, and hand-held products are becoming the mainstream of personal, as well as business practice. This new trend makes warpage, one of the main assembly issues in electronic packaging, more critical to product yield and reliability. Warpage could affect flip chip solder joint attachment in first level interconnections, as well as misregistration between the packages and the printed wiring boards. The shadow moiré technique has been widely used to measure warpage. However, inherent configurations limit its use on certain scenarios. In comparison to the shadow moiré approach, the projection moiré method provides several advantages. It is more suited for measuring flatness of surfaces with components. The grating sizes can be easily adjusted, thus making it versatile for measuring various board and chip sizes and details. Without the grating glass, which is a substantial heat inertia, the sample can be heated more evenly during the thermal process. Also, using a laser as the light source makes the system less sensitive to ambient light. In this paper, a novel system based on the projection moiré technique is presented. The system setup is described and analyzed to reveal its advantages, resolution, and accuracy. A set of experimental results of a variety of sample sizes will be shown. It is concluded that this projection moiré system, which is integrated with an oven system, is a powerful tool to study warpage of printed wiring boards and integrated circuit packages.