A surface imperfection not visible to the naked eye can become a glaring defect when magnified in the end product. A particle of glass, a fingerprint, or a water spot may go unnoticed until enhanced by the application of optical films. As technologies continue to advance, as devices become smaller, more powerful, brighter, and clearer, it is essential that your glass requirements are understood and met.
To help define your needs, the following is an overview of general cosmetic specifications, inspection methods, and Coresix capabilities. Coresix can work to know cosmetic specifications or help the customer to determine the appropriate specifications for a given application.
Defect Size Scratch and Dig - (MIL Spec XX)
Definition: The first number represents the maximum allowable scratch width in microns (20/10 = no scratches greater than 20um wide allowed). The second number represents the maximum allowable dig in 10's of microns as measured LxW/2 (20/10 = no digs greater than 100um allowed).
Typical Scratch and Dig Specifications:
120/80 Defects are clearly visible in normal room lighting. This is generally a commercial specification for glass that will be exposed to further wear.
80/50 Defects are discrete but visible in normal room lighting. This specification is typical for commercial and noncritical optical applications.
60/40 Defects are visible under fluorescent lighting (1.5K Lux). This specification is common for non-magnified optical applications.
40/20 Defects are difficult to detect under fluorescent light and may require a low-intensity halogen lamp (5K Lux). Typical optical applications.
20/10 Defects require Hi-Intensity halogen lighting to identify (10K Lux). A common specification for critical optical applications.
10/5 Defects require Hi-Intensity halogen lighting to identify (15K Lux or greater). A common specification for the most critical optical applications.
A scratch and dig spec can be written and an inspection standard developed around any known requirements. The sample specifications listed above are intended to provide a general guideline and encompass the most commonly used values.
Light Condition Intensity:
Coresix uses a standard "K Lux" to describe the required light intensity for a given inspection criterion. Any existing or known light intensity such as foot-candle, wattage, etc. can generally be converted to a K Lux standard. Once the standard is defined, the specification states "no defects visible with the unaided eye" under the specified light intensity, in the specified position, and within the specified inspection time.
Typical Light Intensity Specification 1.5K Lux Typically used to identify scratches beyond 60um wide and digs greater than 400um for low-end optical or high-end industrial applications. 5K Lux is typically used to identify scratches beyond 40um wide and digs greater than 200um for common optical applications. 10K Lux is typically used to identify scratches beyond 20um wide and digs greater than 100um for high-end optical applications. 15K - 50K Lux Various collimated lighting is used to identify defects to 1um for critical optical applications.
The angle, distance, and/or orientation of the glass being inspected to the light source. Angle: The angle at which the part is held to the light source can influence the visibility of a defect. The specified angle may be driven by the final application(coatings to be applied, angle to be viewed, etc.) or to achieve maximum effectiveness. Unless otherwise specified, the angle will be defined by the standard of orientation.
The orientation of the part to the light source can influence the visibility of a defect. The specified orientation may be driven by the final application or to achieve maximum effectiveness. Unless otherwise specified, the standard orientation of inspection will be transmissive. Distance: The distance of the glass from the light source is generally defined by the specified light intensity. However, under certain conditions, it may be necessary to specify the distance in conjunction with light intensity. If no specification is provided, distance from the light source will be defined by the specified light intensity.
The longer an inspector looks at a glass component under any condition, the more likely he or she is to identify defects. For production, and efficiency the specification is designed to identify the necessary cosmetic quality level in a minimal inspection time. Our standard inspection time averages 5-10 seconds per part.