Optical inspection equipment refers to devices used for inspecting and examining surfaces using optical methods. By implementing optical inspection equipment, precise and high-speed inspections of fine surface details can be performed, leading to improved productivity.
However, many people may have questions such as “Can optical inspection equipment provide accurate inspections?” or “How do I choose optical inspection equipment?”. In this article, we will address such concerns and provide an introduction to the mechanism and selection criteria for optical inspection equipment, as well as recommend some manufacturers. Please consider this as a reference.
1. What is Optical Inspection Equipment?
What exactly is optical inspection equipment? Among various inspection devices, what sets optical inspection equipment apart? Here, we will introduce what optical inspection equipment is and provide an overview. This will help you understand the basics of optical inspection equipment. Let’s take a closer look.
(1) Optical inspection equipment enables examination of fine surface conditions
Optical inspection equipment refers to devices that use optical instruments for inspection. Optical instruments utilize light reflection and wavelength to examine surface conditions that are normally difficult to perceive. Instead of relying on visual inspection and manual touch by skilled individuals, optical inspection equipment allows for precise and thorough inspections of small scratches and foreign substances in a quantitative manner.
Optical instruments illuminate the inspection area with light and capture images using cameras. Subsequently, image processing is performed to determine the product’s quality (good or defective). It is through the utilization of optical inspection equipment that inspections of circuit boards can be conducted, pinpointing defect locations and improving the reliability of board inspections while reducing lead time.
2. Applications of Optical Inspection Equipment
Here, we will introduce some applications of optical inspection equipment.
(1) Wafer defect inspection
Optical inspection equipment is used for inspecting semiconductor wafers. With the miniaturization of circuit patterns in semiconductor devices, the sizes of defects that need to be detected have become smaller as well. In wafer defect inspection, it is necessary to inspect not only foreign particles but also cracks, scratches, distortions, and misalignment during pattern transfer. Optical inspection equipment illuminates the wafer with laser light and detects the positions of foreign particles based on the reflected light, enabling analysis and evaluation of wafer defects.
(2) Surface inspection of products
Optical inspection equipment also plays a significant role in the surface inspection of products. Determining the quality (good or defective) of a product’s surface is challenging and often requires the confirmation of skilled inspectors. Training and securing skilled inspectors takes time, and many companies are facing a shortage of such personnel. Optical inspection equipment allows for high-speed inspections with inspection accuracy that can substitute for skilled inspectors. Even skilled inspectors experience fatigue over time, leading to decreased inspection accuracy and speed. By implementing optical inspection equipment, the aforementioned issues can be addressed.
3. Mechanism of Optical Inspection Equipment
Optical inspection equipment illuminates the target with light and identifies foreign substances and defects based on the information from the reflected light. The camera captures the degree of light reflection, and image processing is performed to detect the defects. The camera plays a role similar to human eyes, while image processing acts as the brain. Compared to conventional visual and microscopic inspections, optical inspection equipment achieves high-precision inspection results in a short time. There are various reflection methods such as transmission, indirect transmission, diffuse reflection, and direct reflection, and the appropriate method is chosen based on the shape of the desired defects.
4. Choosing Optical Inspection Equipment
Among the numerous optical inspection equipment available, you may be interested in selecting the most suitable one. To choose optical inspection equipment that matches your work requirements, there are several key points to consider. Here, we will introduce two points for selecting optical inspection equipment: the camera and lighting.
(1) Camera
The first point in selecting optical inspection equipment is the camera. Since the camera serves as the “eye” in the system, it is necessary to choose the appropriate camera type depending on the intended use. Camera types can be categorized based on imaging method and color as follows:
[Imaging Method]
- Area Camera: Captures two-dimensional rectangular images. Examples include digital cameras and smartphone cameras.
- Line Camera: Captures one-dimensional images. Examples include copiers.
Area cameras are suitable for capturing large or long products, while line sensors are ideal for high-speed inspection of continuous products. Therefore, line sensors are frequently used for inspecting industrial and processed products, detecting damages and pinholes. On the other hand, area cameras are used in surveillance, medical, transportation, security, and other applications where capturing the actual image is desired. For those considering introducing a camera in optical inspection equipment, a line camera is recommended.
[Color]
- Monochrome Camera: Captures black-and-white images.
- Color Camera: Captures colorful images with a large amount of data.
Monochrome cameras excel in resolution and speed compared to color cameras. If the purpose is solely to identify “scratches” or “breakages” on the product surface, a monochrome camera would be sufficient. However, if it is necessary to distinguish differences in brightness, a color camera should be used. Monochrome cameras are not as effective in discerning subtle color variations. For instance, determining the ripeness of fruits requires the use of a color camera.
(2) Lighting
The second point in selecting optical inspection equipment is lighting. Although it may be referred to as lighting, changing the lighting type can significantly impact the resulting image. Different images lead to variations in the outcome of image processing for pass/fail judgments. The three key factors to consider when choosing lighting are as follows:
- – Illumination method: Select an appropriate illumination method based on the product’s surface shape.
- – Lighting color: Determine which part of the product to emphasize and preserve in the image. The choice of making the detection area appear white or black also affects the outcome.
- – Lighting shape: Varies depending on the size of the detection area and illumination method.
Choosing the right lighting is crucial for stable detection and greatly influences inspection performance. Therefore, it is important to make a careful selection.