Screen Flatness Measurement by Fast 3D Non-Contact Profilometry

Flatness is an important geometric surface quality in the manufacture of precision parts and assemblies. Flatness of the surface plays a vital role in the end use of the product. For example, the parts that are connected in an air-tight or liquid-tight manner across a surface area require stringent surface conditions of superior flatness at the contact face. Flatness of the screen is critical to the functionality and aesthetics of electronic devices such as cellphones, pads and laptops. Any imperfection of the screen flatness can create negative user impression and experience of the product.

Mass production is the dominant form of screen manufacturing around the globe. It requires fast and precise measurement of the roughness and flatness on a large screen surface to ensure the narrowest tolerances in quality control. High resolution 3D scan can quickly detect and report any defects or imperfection of the screens created during the fabrication processes.

Designed for stable high speed flatness measurement, the NANOVEA HS2000 non-contact profilometer with its granite base and air bearing stages provides superior stability at high scanning speeds. In addition to the screens, virtually any kinds of surfaces fabricated from different materials such as metals, ceramics, plastics and glasses can be measured in a timely fashion, making it an ideal tool for surface inspection in production lines.

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As shown in Figure 1, the NANOVEA HS2000 profilometer provides automated surface inspection at high speeds. The optical line sensor generates a bright line composed of 192 light spots that scan the sample surface at the same time. This significantly increases the scan speed and enables rapid 3D scan of a large area up to 400 mm × 700 mm. Such a fast speed makes it possible to implement the NANOVEA HS2000 3D profilometer for quality control of a large quantity of samples.

Figure 2 and Figure 3 show the False Color View and 3D View of the computer screen, respectively. The 3D View provides users an ideal tool to directly observe the surface morphology from different angles in detail and to evaluate the shape, flatness and roughness of the sample for the purpose of quality control. The computer screen possesses a slightly lower center and elevated edges in the diagonal direction. The height variation across the sample surface is as high as 600 µm.

Table 1 lists the Roughness and Flatness values calculated by the analysis software based on ISO 25178 and ISO 12781, respectively. Such values can be applied as reliable thresholds to determine the pass/fail criteria of the screen surface quality during the quality control process.

Using the powerful analysis software, we can easily obtain the 2D profiles at different locations across the screen as shown in Figure 4. It allows further investigation on the shape, flatness, texture and possible defects, e.g. cracks and scratches, of the screen.

In this application, we showcase the NANOVEA HS2000 3D Non-Contact Profilometer equipped with an optical line sensor. High resolution scan for large surfaces as done in this study provides both roughness and flatness information in a few minutes. Moreover, the HS2000 can measure flatness of samples as large as 400mm × 700mm in seconds with sub-micron accuracy. The axial chromatism technique allows measuring the sample surface at very high speeds without touching, making it possible and simple to implement the NANOVEA profilometer in the production line so as to monitor the surface quality in situ.

The data shown here represents only a portion of the calculations available in the analysis software. NANOVEA Profilometers measure virtually any surface in fields including Semiconductor, Microelectronics, Solar, Fiber Optics, Automotive, Aerospace, Metallurgy, Machining, Coatings, Pharmaceutical, Biomedical, Environmental and many others.