A consumer device display screen is the sole interface between the user and the device, meaning the out-of-the-box customer experience relies entirely on absolute optical and tactile perfection. Even minor surface imperfections like microscopic scratches, pits, or dents can refract light, disrupt touch sensitivity. Because modern cover glass is incredibly hard but inherently brittle, a microscopic gouge acts as a hidden stress concentrator. What begins as a nearly invisible defect might propagate into a larger defect or screen failure. Quality control teams can inspect screens early in the manufacturing process, preventing defective glass from being laminated to expensive OLED panels. This reduced material waste, lowers production costs, and ensures that only flawless devices reach the market. Used phones with damaged screens can also be inspected to locate and measure the defects, repair the glass, and return to the customer or resell as a refurbished unit.
A fast, automated inspection solution
Inspecting highly reflective, multi-layered electronic displays pushes traditional 2D cameras and manual microscopes past their limits. While 2D vision struggles with glare, often mistaking harmless surface dust for critical scratches, human inspection remains slow, subjective, and prone to costly fatigue. A coaxial line confocal sensor, paired with the right analysis software, eliminates these compromises. By capturing perfectly aligned 2D intensity data and 3D topography simultaneously, the sensor effortlessly handles specular surfaces and isolates defects across complex transparent layers. When combined with defect detection algorithms, the system replaces subjective human judgment with 100% objective, metrology-grade precision—capturing the absolute truth about microscopic scratches and gouges without sacrificing inspection speed.
To harness the full capability of these sensors, Peak Metrology integrates these measurement devices into a fully automated, turnkey inspection system. Pairing the sensor with ultra-precision Aerotech motion stages ensures the flawless, vibration-free movement required for sub-micron scanning—because a high-resolution sensor is only as reliable as the motion system positioning it. This complete Peak Metrology solution automates the entire inspection workflow. Operators simply load the display and press start, allowing the system to seamlessly execute complex scan paths, collect and stitch the perfectly aligned 3D and intensity data, and run the analysis. The result is a highly repeatable, push-button metrology station that transforms raw sensor data into immediate, actionable quality control insights without requiring complex manual programming or R&D intervention.
Beyond the high speed at which these sensors are capable of, they also have good spatial resolution. The sensors provide sub-micrometer height resolution, and down to 1 micrometer spatial resolution between data points. This means that defects as small as 20 micrometers in size and a few micrometers in depth are picked up well.
Showing how fast the equipment scans the surface.
Where other inspection solutions fall short
Below is an example of using a traditional microscope for visual inspection. Using coaxial lighting (left) results in a glare in the center of the image. The details of the scratches are also lost using this lighting method. Using ring lighting (right) instead gives more detail of the scratch and is more representative of what the screen actually looks like, however as there is no height data to analyze it is dependent on a human operator to visually inspect the image and decide if the defect is significant or not.
Showing images at 30x magnification. Coaxial lighting (left), ring lighting (right).
The other issue with this method is that it usually involves an operator manually manipulating the sample under the microscope to find where the defects are located. This could result in missed nonconformities and unacceptable product being shipped. Using a confocal line sensor with intensity and 3D height data eliminates both of these problems.
Showing the solution in action
The image below shows a large area scan of the phone display glass. Multiple passes with the sensor are used to create the larger field of view image quickly. The seams in between the individual passes are <1um in height. This high resolution stitching is possible when using stages that have excellent flatness and geometric tolerances during the scanning process. The defects are then located and outlined in blue using the analysis software.
Surface Blob tool identifying defects using intensity data
Zoomed in view of a single defect.
Parameters can be adjusted to change the detection method of the defects and filter based on qualities like area, shape, and intensity value. Results such as defect size, XY location, dimensions, and total defect count with judgement conditions can be output as a data file for record keeping.
This image below shows an isometric view of the 3D sensor data. Having this data unlocks further capabilities of measuring the depth of gouges and characterizing the surface.
Isometric 3D view of the defect
Depth measurement and height map of the defect
conclusion
Relying on outdated 2D vision and subjective human inspection leaves your production lines vulnerable to costly scrap and downstream failures. By combining unique 3D sensor technology with precision motion automation, you can eliminate the guesswork and optimize your yields. Contact Peak Metrology today to discuss your automated part inspection needs and ensure every display you ship meets the highest standard of perfection.
To learn more about the equipment we build please visit our sensor scanning product page.
For more guidance and consultation please reach out to us. We offer full engineering and laboratory testing services to help guide our customers towards the right solution to their measurement challenge.